Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/16/21
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1159 PM EDT Mon Mar 15 2021
.AVIATION...
A narrow band of light mixed precipitation will expand across the
southeast Michigan airspace through the early morning hours. Recent
trends suggest primarily VFR level restrictions within this moist
axis. Lowering cloud bases in the wake of precipitation 08z-09z,
with precipitation potential diminishing during this time. Extensive
low stratus then in place throughout the daylight period Tuesday.
Predominant low MVFR, but with the potential for a period of IFR mid-
late morning. Gradual improvement in ceiling heights during the
afternoon and evening. prevailing east-northeast winds become
northwesterly.
For DTW...Lingering window for possible light freezing rain through
07z. Otherwise, cloud bases solidly below 5000 ft within extensive
low stratus through Tuesday.
.DTW THRESHOLD PROBABILITIES...
* High for ceiling at or below 5000 ft midnight through Tuesday
morning, then moderate Tuesday afternoon and evening.
* Moderate for p-type initially freezing rain early this morning.
&&
.PREV DISCUSSION...
Issued at 854 PM EDT Mon Mar 15 2021
UPDATE...
Formidable magnitude and depth to the low level dry layer
/00z dewpoint of 3 degrees at DTW/ yielding a radar return offering
simply a generous supply of virga late this evening. Upstream
observational trends suggest steady top-down saturation will
commence on schedule from southwest to northeast between 04z-07z as
the 850-700 mb frontal slope makes steady inroads. As highlighted by
the afternoon discussion, there remains a model signal within the hi
res model solution space for the frontal circulation to strengthen
with time overhead under increasing dcva. This places a corridor
generally northeast of a Detroit-Pontiac-Owosso line more favorably
to witness a brief increase /1-3 hours/ in both coverage and
intensity of wintry precipitation during the early morning hours. No
shift in the overall reasoning in terms of expected precipitation
type, with a mix of snow/freezing rain highlighted within the
M-59/I-69 corridors and primarily snow with accums upwards of a
couple of inches Saginaw valley/northern thumb. A more lackluster
response appears likely for points southwest of this line, simply
pockets of very light precip yielding only minor qpf. Overall brevity
of this event outlooked across a low travel period continues to
preclude a headline consideration. Evening update forthcoming for
minor adjustments based on latest radar/temperature trends.
PREV DISCUSSION...
Issued at 405 PM EDT Mon Mar 15 2021
DISCUSSION...
A mostly light wintry mix of precipitation is on schedule for
tonight with interesting twists in evolution of the system. A
weakening trend in the band ongoing this afternoon leads to just
trace amounts of accumulation/icing from the Ohio border northward
through metro Detroit. Reintensification then occurs from the I-69
corridor northward after midnight producing a burst of higher rate
snowfall. This leads to a bump in accumulation into the 1 to 3 inch
range before ending Tuesday morning.
Afternoon radar/satellite imagery and surface analyses indicate a
textbook mid latitude cyclone positioned over the central Plains
with a warm front extending into the TN valley. Strong low level
moisture transport and isentropic lift has a band of heavy snow
extending from the upper Midwest transitioning to a rain/snow mix
over IL/IN and into the Ohio valley. The weakening trend of this
band projected by the latest models appears tied to it becoming
displaced from the upper wave resulting in a veering and weakening
of the low to mid level wind field. This in turn results in a
frontolytic weakening and reduced system relative isentropic lift as
the theta-e gradient shears apart overhead. The band then
reintensifies after midnight as strong short wave forcing develops
eastward along the elevated front from WI across central Lower MI.
Cross sections from the RAP indicate all of the usual elements for a
burst of high rate precipitation; a deep layer of instability, high
RH, specific humidity around 3 g/kg, and a strong ageostrophic
response. Speed of the system and short duration of intensity are
about the only limiting factors for advisory worthy accumulation.
Model soundings north of I-69 also indicate a high and shallow DGZ
and a deep layer below freezing but near zero for riming limitations
on snow ratio. That being said, model consensus of 12 hour liquid
equivalent QPF around 0.25 inch looks solid for accumulation toward
3 inches in the Tri Cities area before ending around 8 AM.
While snow is concentrated in the Tri Cities and northern Thumb,
enough warm air makes across the Ohio border to keep freezing rain
in the forecast at least up to the I-69 corridor. Model soundings
and mean RH projections also indicate enough mid level dry air for a
struggle maintaining DGZ saturation and really even above about -10C.
Lighter precipitation rate also has a lower wet bulb cooling
effectiveness which allows the warm air to influence liquid precip
type trends, although with just trace amounts of icing while
temperatures drop toward the upper 20s and become marginal around the
freezing mark in metro Detroit toward sunrise. The exception is the
usual colder surface temperature bias in higher terrain areas
west/north of Detroit and then farther north toward I-69. This is
where some slick spots could develop on area roads before the morning
commute.
The system carries precipitation out of the are Tuesday morning
while the surface pressure reflection lingers in Ohio. This allows
some temperature recovery even as clouds hang on through much of the
day. Short wave ridging aloft then brings some clearing Tuesday
night in time for lows in the upper 20s outside of metro Detroit. SE
MI remains between systems through Wednesday for dry and milder
weather.
The four corners low pressure system moves into the southern Plains
Wednesday and into the Ohio valley Thursday. There is some phasing
with the northern stream westerlies however the moisture pattern
remains dominated by the southern stream closed low and the easterly
Atlantic conveyor. The northern stream supplies strong high pressure
over northern Ontario and a strong gradient across the central Great
Lakes. The low level flow of dry air on gusty NE wind is expected to
set up a sharp northern edge in a cold rain pattern mainly south of
I-69 Thursday and Thursday night. Passage of this system eastward
then allows the Quebec high pressure to settle southward for dry
weather next weekend.
MARINE...
Moderate easterly flow continues this evening off the west end of
Lake Erie and this is where Small Craft Advisories remain in effect.
Low pressure brings a decrease in wind overnight at the expense of a
wintry mix of precipitation through Tuesday morning. High pressure
returns for the mid week period with light winds and waves until
Thursday when the next low pressure system moves into the Ohio
valley. The arrival of this system generates a gusty NE wind across
the central Great Lakes by Thursday. The wind pattern is sub gales
for now but will likely require a new round of Small Craft
Advisories Thursday and Thursday night.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....MR
UPDATE.......MR
DISCUSSION...BT
MARINE.......BT
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
631 PM CDT Mon Mar 15 2021
.AVIATION.../00Z TAFS/
Fair skies are expected for all areas through this evening. Well
mixed air mass in the low levels will begin to saturate a few hours
after midnight with both fog and low cigs possible. With onshore
winds falling below 5 knots for most of the early morning, there
should be some LIFR conditions developing along I-35, and there
could be some areas of dense advection fog developing around
daybreak. Steady improvements are expected back to IFR and MVFR in
the midday hours.
&&
.PREV DISCUSSION... /ISSUED 227 PM CDT Mon Mar 15 2021/
SHORT TERM (Tonight through Tuesday Night)...
Satellite visible and WV imagery and RAP analyses indicate weak
upper ridging over the four corners region between a closed low over
CA and the system over the central Plains that brought impressive
snow totals to the Front Range yesterday. Locally, weak surface high
pressure is keeping skies mostly clear, with a few cirrus developing
just to our west along a very subtle upper shortwave. Temperatures
at 19Z range from the low to mid 70s over much of the Hill Country
to the low to mid 80s in several spots, with highs today expected to
climb to 77-88, coolest over the southern Edwards Plateau.
Tonight, as sfc high pressure quickly moves east, light southerly
flow will develop and moisture will pour back in from the gulf. Dew
points currently in the 30s and low 40s across the region will rise
into the 60s across much of the region by this time tomorrow. Late
tonight, low stratus and areas of fog are anticipated and will
likely become locally dense. Where moisture remains slightly lower
along the Rio Grande and our northern border, fog shouldn`t be too
much of an issue. Should see the fog end by late morning, but low
clouds may hold on into the afternoon across much of the area and
may never clear at all over the Coastal Plains and I-35 corridor
Tuesday. This will keep temperatures in the upper 70s and lower 80s
for the most part east in the afternoon, while mid to upper 80s are
forecast along the Rio Grande.
The addition of the CAMS to the model suite has given us a much
better look at the environment we can expect tomorrow night. The
warm, moist airmass in place along with steepening mid-level lapse
rates above a relatively sharp inversion caused by low-mid-level
ridging overhead tomorrow will allow for the buildup up MUCAPE in
excess of 1500 J/kg and likely closer to 2000 J/kg by tomorrow night
ahead of an approaching cold front and upper trough. Effective shear
will also increase to 40-50 kts, and with ample frontal forcing and
some mid-level ascent as the trough nears, elevated showers and
storms are expected to develop in the late evening hours above the
cap over the Edwards Plateau, growing upscale and crossing the
region after midnight.
SPC has upgraded their outlook to include Austin and San Antonio in
a marginal risk of severe storms, while locations north of
Rocksprings to Leakey to Blanco to Georgetown are in a slight risk
(2 out of 5). At this lead time, I think this may be a bit bullish
as the fast-moving front may undercut storms before they can fully
organize. Nonetheless, the threat for severe weather is certainly
higher than it looked this time yesterday. The primary hazard would
be large hail in any rotating storms, with damaging winds or a QLCS
tornado not entirely out of the question as latest model soundings
indicate a small chance for the cap to erode fast enough to allow a
brief period of surface rooting before the sfc front sweeps through.
Latest HRRR is rather bullish with simulated reflectivity, despite
being slightly slower-progressing than the rest of the CAMS,
although in contrast the NAMNEST depicts development slightly
further north and somewhat weaker. Most of the remaining CAMS lie
somewhere between, but all of them are in general agreement in the
likelihood of thunderstorm activity and the possibility some of this
development becomes severe across at least the Hill Country
overnight. Still two full forecast packages to refine this forecast,
so stay tuned!
LONG TERM (Wednesday through Monday)...
The front is progged to move out of the area on Wednesday morning
with clearing behind. The much drier air from the northwest will be a
concern for fire weather conditions as we may reach critical
thresholds. Relative humidities over the area will drop to in the
teens and even single digit percentages in our far southwest
counties. This dry air combined with the gusty northwest winds with
gusts up to 27 mph at times may require fire weather products to be
issued. Conditions will continued to be monitored. The later half of
the week will be pleasant with continued northerly flow at the
surface keeping the air dry, and the daytime temperatures mild and
pleasant, and overnights cool. The next upper system approaches at
the start of next week.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 57 81 60 78 47 / 0 20 80 20 0
Austin Bergstrom Intl Airport 56 81 59 79 47 / - 20 80 20 0
New Braunfels Muni Airport 57 81 60 82 47 / - 20 70 20 0
Burnet Muni Airport 55 81 55 74 45 / 0 10 80 - 0
Del Rio Intl Airport 56 87 56 82 48 / 0 - 20 0 0
Georgetown Muni Airport 56 81 57 77 46 / 0 20 80 10 0
Hondo Muni Airport 56 81 57 81 46 / 0 - 60 - 0
San Marcos Muni Airport 55 81 60 79 46 / 0 20 70 20 0
La Grange - Fayette Regional 60 80 63 79 48 / - 30 50 40 0
San Antonio Intl Airport 59 81 60 79 49 / 0 10 70 10 0
Stinson Muni Airport 58 80 61 80 48 / - 10 60 10 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term/Aviation...Oaks
Long-Term...05
Area Forecast Discussion
National Weather Service Peachtree City GA
750 PM EDT Mon Mar 15 2021
.PREV DISCUSSION... /Issued 343 PM EDT Mon Mar 15 2021/
SHORT TERM /Tonight through Tuesday Night/...
The Ides of March are upon us -- as is an active pattern throughout
this week. The upper level ridge continues to move eastward away
from the forecast area and toward the Atlantic coast as the short
term period begins. Deep moisture is increasing over the area in the
southwesterly flow behind the ridge axis. At the surface, an old
frontal boundary remains stalled across central Georgia as a cold
front moves into the Mississippi River Valley. Meanwhile, as high
pressure over the Great Lakes Region continues to move east, a wedge
will build down the spine of the Appalachians and into the
northeastern portion of the forecast area. This wedge will remain
entrenched over northeast Georgia into the evening Tuesday. The
approaching weakening cold front will become more zonally oriented
before it reaches Georgia, stalling to the north and west of the
forecast area. This will provide a focus for convection and keep the
CWA within the warm sector through the majority of the period.
Widespread showers will enter northwest Georgia this evening and
slowly spread south and east during the overnight hours and
throughout the day on Tuesday. Some marginal instability is present
outside of the wedge and across central and west Georgia this
afternoon, which will lead to a slight chance of thunderstorms in
that area as precipitation moves into the area. Some enhanced low-
level shear is also present in the vicinity of the stalled boundary.
While severe thunderstorms are not expected this afternoon and
evening, a couple of storms along the boundary could become strong
and capable of producing gusty winds and locally heavy rain.
Better coverage of thunderstorms is anticipated on Tuesday. As a
result of continued advection of warm and moist air into the area,
relatively higher instability values will spread east into the
forecast area overnight and into Tuesday. A broad area of MUCAPE
values of 500-1000 J/kg will be present generally along and south of
the I-20 corridor during the afternoon and evening tomorrow. This
area of elevated instability will be co-located with 0-1 km shear
values of 20-25 kts and deep layer bulk shear values of 35-40 kts.
As a result, a few thunderstorms are anticipated to be strong to
severe and capable of producing damaging wind gusts, locally heavy
rain, and frequent lightning. A brief tornado cannot be ruled out.
Precipitation chances will diminish Tuesday night into Wednesday
morning, allowing a brief lull before the next system approaches.
Rainfall totals for this system remain fairly consistent with the
previous forecast run, with QPF values of 1 to 2 inches across much
of western Georgia and lower amounts elsewhere in our area. Heavy
rain in isolated strong storms could lead to locally heavier
amounts, which could lead to some instances of localized, nuisance
flooding. Widespread flooding concerns are not currently expected
during the short term period, but another round of heavy rain will
be coming on Wednesday as another system impacts north and central
Georgia.
King
LONG TERM /Wednesday through Monday/...
Main concern in the long term period is timing, likelihood, coverage
and intensity of severe convection Wed/Thurs. Heavy rainfall and
possibility of minor flooding also a concern.
At the start of the period, intense upper wave centered over OK
moving slowly east. Noted just a little slowing of system compared
with prev runs, but mainly still seeing GFS as the faster solution
while EC, CMC and NAM are slower. Using slower timing, much of
Wednesday and perhaps even Wednesday evening should be mostly dry
with just scattered showers ahead of the main line of convection.
Have used blend of model timing for now, but suspect GFS may slip to
slower timing. 12Z EC also a hair faster than previous run fwiw.
Finally, model blends once we get inside 48h projections will take
advantage of hires guidance like HIRESW, HRRR synoptic runs and
others. Should push out by Tuesday late afternoon unless further
slowing occurs.
Given strong, large-scale forcing and plenty of instability and
vertical wind shear, confidence/likelihood of severe storms growing
though best ingredients will be in place over AL rather than GA.
Even if system slows further and moderate instability develops over
the area Thurs, vertical wind shear not expected to be as favorable.
Model sig tor values, which combine instability, vertical wind
shear, CIN and LCL, are progged to be 3-6 over AL and 1-2 mainly
over Wrn GA Wed evening and overnight and again 1-1.5 Thursday.
Given strong deep shear (0-6km 60-70kts) and moderate low level shear
(0-1km 30-40kts), good directional shear and instability (SBCAPE 1000-
1500 J/kg), mode of convection expected to be supercells with line
segments, becoming more lines of cells or QLCS on Thurs as shear
becomes more uni-directional.
Total rainfall 1-3" likely for the event with one round Tues with
warm front/warm advection then the other Wed-Thurs. Greatest amounts
expected in NW GA Wed-Thurs and even with extended dry weather last
two weeks, may see rain rates exceed FFG there. Will hold off on any
kind of flood outlook or watch based on uncertainty on amounts and
limited runoff potential with dry soils and increasing vegetation.
Rest of long-term period appears dry and mild with seasonable temps.
Only very small chances of rain expected far north on Fri and Sat.
SNELSON
&&
.AVIATION...
00Z Update...
Precip has moved in across NW GA and is slowly moving SE. Should
begin to see SHRA at the ATL/AHN area TAF sites by 06z and they
will continue through the end of the TAF period. Precip will move
into the CSG/MCN areas by Tue afternoon. Winds are expected to
stay easterly through the period but wind speeds are expected to
diminish some. Currently wind speeds are in the 08-12kt range with
gust to 20kt. These gust should subside overnight with winds 10kt
or less after 09z. Ceilings are VFR right now but they will fall
into the MVFR range by 04z then IFR by 09z. Ceilings should stay
IFR through the rest of the period.
//ATL Confidence...00Z Update...
Confidence medium to high on all elements.
01
&&
.PRELIMINARY POINT TEMPS/POPS...
Athens 45 54 50 68 / 80 80 60 80
Atlanta 51 59 54 71 / 80 90 60 80
Blairsville 42 58 47 64 / 80 70 30 80
Cartersville 48 60 51 71 / 90 80 40 90
Columbus 61 74 60 80 / 70 80 70 80
Gainesville 43 54 50 65 / 80 80 40 80
Macon 58 72 58 79 / 50 70 70 80
Rome 50 63 52 72 / 90 70 40 90
Peachtree City 55 64 55 74 / 80 90 70 80
Vidalia 59 80 62 82 / 20 50 50 60
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...King
LONG TERM....SNELSON
AVIATION...01
Area Forecast Discussion
National Weather Service Grand Rapids MI
952 PM EDT Mon Mar 15 2021
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 247 PM EDT Mon Mar 15 2021
- Snow/Wintry Mix Tonight
- Another System Brings Chance for Snow/Rain Thursday
- Dry Weather Returns For the Weekend
&&
.UPDATE...
Issued at 952 PM EDT Mon Mar 15 2021
The very dry air below 700 mb continues to win out vs. the
incoming precip/lift aloft and only scattered trace amounts of
rain/snow/sleet have been reported so far. Sfc dew points are
actually still between zero and 5 above along the I-96 corridor
with RHs around 25 pct.
The Winter Weather Advisory issued earlier may be in trouble if
this trend continues much longer but latest HRRR guidance
continues to show 1-3" snow accumulations occurring north of I-96
overnight as the shortwave approaching from the southwest
strengthens and becomes negatively tilted (enhancing upper
divergence/lift). That would lead to slick, snow covered roads
for the morning commute for at least the northern sections of the
advisory area.
Meanwhile, very little QPF is shown for the I-96 corridor
southward overnight in the latest guidance. The concern here
though is for areas of freezing drizzle developing as ceilings
lower, and it doesn`t take much of that to cause slick spots and
travel impacts.
Will continue the Winter Weather Advisory as is for now and see
how things evolve over the next few hours.
&&
.DISCUSSION...(This evening through next Monday)
Issued at 247 PM EDT Mon Mar 15 2021
- Snow/Wintry Mix Tonight -
Light snow/Wintry Mix currently to our southwest will continue to
move into our area this evening bringing concerns for freezing
rain/wintry mix/snow. Mainly below freezing thermal profiles still
indicate that primarily snow can be expected for areas across
central and northern lower MI. Meanwhile, a small warm layer above
a cold and dry surface layer will bring the possibility for a
mixture of freezing rain and freezing drizzle for areas across
southern lower MI.
QPF is still relatively low with this system, however even a
glazing of ice across areas along and south of I-96 may cause
travel concerns. Meanwhile areas north of I-96 will be more
susceptible to up to 1 inch of snow with locally higher amounts
possible. By tomorrow mid to late morning this low will occlude
while it exits further northeast resulting in precipitation
weakening and ending.
- Another System Brings Chance for Snow/Rain Thursday -
Once our Monday/Tuesday system exits to our east, another low
emanating from the southwest will take it`s place and bring our next
chance for precipitation. Model trends still hint at a more
southern track of the low across the Ohio River Valley, which
would result in precipitation for the southern third portion of
lower Michigan. Precipitation type will once again be a question,
with a chance for rain or a rain/snow mix possible.
- Dry Weather Returns for the Weekend -
High pressure ridging will build back into the region following the
departure of the Thursday system. This will result in the return of
dry weather with sunshine and highs in the 50s for this weekend!
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 806 PM EDT Mon Mar 15 2021
Low confidence aviation forecast tonight in terms of cigs/vsbys
as well as precip potential and precip types.
The problem is that we have extremely dry air still present in
the low levels which is being reinforced by easterly winds gusting
up to 30 kts. (We still have sfc dew points in the single
digits.) Meanwhile precipitation is breaking out aloft but
struggling to reach the ground.
As we go through the night however the model guidance suggests
that further moistening of the atmosphere does occur causing cigs
to gradually lower into MVFR category. Precipitation should have
a better chance of reaching the ground by 03Z, and model fcst
soundings indicate mostly snow for a period at GRR/MKG/LAN, with
light FZRA/FZDZ being the primary risk at AZO/BTL/JXN.
That said, there`s also a chance that dry air could still win out
and very little precip occurs tonight.
&&
.MARINE...
Issued at 247 PM EDT Mon Mar 15 2021
Winds will be the primarily concern through the next couple days
as waves stay low due to the offshore direction of the wind. A
small craft advisory remains in effect through this evening due to
wind gusts up to 25 to 30 knots.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EDT Tuesday for MIZ037>040-
043>046-050>052-056>059-064>067-071>074.
LM...Small Craft Advisory until 2 AM EDT Tuesday for LMZ844>848.
&&
$$
UPDATE...Meade
SYNOPSIS...Thielke
DISCUSSION...Thielke
AVIATION...Meade
MARINE...Thielke
Area Forecast Discussion
National Weather Service Lincoln IL
756 PM CDT Mon Mar 15 2021
.SYNOPSIS...
Issued at 327 PM CDT Mon Mar 15 2021
Scattered showers and a few thunderstorms will move across central
Illinois tonight. In addition, areas of fog will develop overnight
into Tuesday morning as winds become nearly calm. Low temperatures
will range from the lower 30s near Galesburg and Lacon, to the
lower 40s south of I-70.
&&
.UPDATE...
Issued at 756 PM CDT Mon Mar 15 2021
Area of showers has advanced into west central and south central
Illinois early this evening, with much of the lightning strikes
occurring west of the Mississippi River. RAP showing a couple
hundred J/kg of MUCAPE from about Jacksonville to Paris southward
through the evening, diminishing over east central Illinois after
midnight. Some updates have been made to the timing of the
precipitation over the next several hours, with some increase in
chances south of I-70.
Some concern continues with fog potential overnight. NAM forecast
soundings show a rather stout inversion around 2,000 feet
persisting through the night, and while the GFS is not as
impressive, it does keep decent low level moisture in place below
that level. HRRR and LAMP show fog expanding in the areas that
don`t see precip after midnight (northern CWA and south of I-70),
but do try to close off the area in between later. Not really
looking for any clearing that could speed this along, but will
keep the mention of fog going across most of the CWA tonight into
Tuesday morning.
&&
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 327 PM CDT Mon Mar 15 2021
Vigorous upper low evident on 20z/3pm water vapor imagery near
Kansas City will track eastward across central Illinois tonight.
Scattered convection is beginning to develop beneath the low
across eastern Kansas into west-central Missouri and this activity
is expected to increase in areal coverage and shift eastward into
the KILX CWA this evening. HRRR/NAM have both been very consistent
with showers arriving across the far SW around Jacksonville/Winchester
after 00z/7pm. Based on the track of the low and where showers
are currently initializing, it appears the best chance for rain
will be along and south of the I-72 corridor. Forecast instability
is slightly weaker than previously thought, but MUCAPEs are still
progged to exceed 100J/kg across the southern half of the CWA.
Will mention slight chance thunder everywhere south of a Macomb to
Bloomington line accordingly. Once the low passes, showers will
come to an end from west to east before dawn Tuesday. In addition
to the precip, several CAMs are suggesting fog development
overnight as winds become light and the boundary layer remains
saturated. Based on latest RAP/GFSLAMP, have included areas of fog
in the forecast across much of the area north of I-70 late
tonight into Tuesday morning. Once the fog slowly dissipates,
mostly cloudy skies and dry conditions will prevail on Tuesday
with highs ranging from the lower 50s far north around
Galesburg...to the lower 60s south of I-70.
&&
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 327 PM CDT Mon Mar 15 2021
After a brief lull on Tuesday, the next storm system will come
into the picture by Wednesday as another highly amplified upper
low rolls eastward out of the southern Rockies. This system will
spread rain showers into central Illinois on Wednesday, with the
heaviest and most widespread shower activity focusing Wednesday
night into Thursday. With surface low pressure expected to track
from the panhandle of Oklahoma Wednesday morning into southern
Indiana by midday Thursday, central Illinois will remain mostly on
the cool side of the system. As a result, am expecting widespread
rain...with perhaps a few thunderstorms across the S/SE half of
the CWA. Given ample deep-layer moisture from the Gulf of Mexico,
this will be another efficient rain-maker, resulting in overall
rainfall amounts of 1 to 1.50 inches. Once the low departs, a
return to mild and dry weather is anticipated...with temperatures
climbing back into the lower 60s by Sunday/Monday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 622 PM CDT Mon Mar 15 2021
IFR ceilings expected to prevail early in the forecast period,
deteriorating to less than 500 feet late this evening. Some
concerns about dense fog becoming widespread between 06-09Z, but
there is some uncertainty at this point and will limit visibility
to only a mile for now. Ceilings will be slow to improve Tuesday
morning, but should gradually become MVFR early afternoon.
An area of showers and isolated thunderstorms is crossing the
Mississippi River north of KSTL currently, and is expected to
impact the KSPI-KCMI area between 01-05Z. Have kept a VCTS mention
in this corridor for this evening.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Geelhart
SYNOPSIS...Barnes
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Geelhart
Area Forecast Discussion
National Weather Service Jacksonville FL
916 PM EDT Mon Mar 15 2021
.UPDATE...
Backdoor front is basically stationary over southeast GA this
evening but expected to lift north of the area late tonight. Sfc
high is over the mid Atlantic but will push offshore tonight. Low
to mid level ridge is located east of the FL peninsula and upper
level flow is westerly, so quite a bit of veering in the 00z
sounding profile. Only precip on radar is at best some sprinkles
over southeast GA, and a couple of showers just to the east of the
offshore coastal waters. Partly to mostly cloudy skies over the
forecast area, and most of the cloudiness will likely be over most
of our southeast GA zones. Some indications of patchy fog possible
tonight given that dewpoints are in the lower 60s, though winds
may be a bit mixy for sustained period of fog or dense fog. Main
updates were to tweak min temp slightly and lower POPs over
southeast GA to below 15 percent. Warmer overnight lows due to the
addition of moisture/clouds to the area with lows in the upper
50s and lower 60s.
.MARINE...
Only minor changes for winds tonight due to the front in the
southeast GA waters and for tweaks to the sea heights. Otherwise,
forecast on track.
&&
.PREV DISCUSSION [747 PM EDT]...
.Near Term.../through Tuesday/...
Frontal boundary will lay across SE GA this evening, then lift north
of the area overnight. A few sprinkles or light showers will be
possible with this boundary this afternoon and evening. This front
will be just north of the forecast area through the day Tuesday.
Waves will move east along this boundary Tomorrow, which may push
the front a little further to the south. There is a chance for a
few showers and storms over SE GA during the day Tuesday as one of
these waves moves through. For NE FL, while the proximity of the
front will provide added cloud cover it will remain dry.
Above normal temperatures expected Tonight and Tuesday.
.Short Term.../Tuesday night through Friday/...
The frontal zone will remain just to the north through Tuesday
night. The front then sinks south into SE GA during the day
Wednesday. Expecting isolated to scattered showers and storms along
the boundary.
Models have trended slower with the main cold front, which is now
expected to reach western counties late morning Thursday, then be
east of area Thursday night. The later arrival of the front will
slow the onset of precipitation with Wednesday night dry, and
eastern half of area will have a dry morning. This will allow
eastern counties to heat well into the 80s ahead of the front. This
will create greater surface instability, increasing the potential
for a few strong storms, however better chances for stronger storms
to the north OF area closer to low center.
High pressure will build well to the north Friday, which will push a
secondary trough south toward area late in the day. At this point,
looks like a dry day Friday, but cloud cover will begin to increase
in the afternoon ahead of the trough.
Above normal temperatures Tuesday night through Thursday night, with
near normal for Friday.
.Long Term.../Friday night through Monday/...
Strong high pressure will build to the north Friday night, pushing
surface trough south across forecast area leading to a few showers.
The strong high will remain to the north over the weekend, with an
inverted trough expected to develop over the coastal waters. This
feature will result in the chance for showers and gusty winds,
especially near the coast.
The high will weaken and move toward the northeast Monday, with a
dry day expected, although can not completely rule out potential for
coastal showers.
Temperatures will be below normal over the weekend, with highs in
the 60s common north of Ocala.
.AVIATION...
[Through 00Z Wednesday]
VFR conditions expected to prevail this period, though with a mix
of some low clouds and broken mid to high clouds. A weak front is
located over the central parts of parts of southeast GA but will
lift back north of the area late tonight. A brief bout of some low
clouds below 1 kft and some vsby restriction possible at SSI
tonight based on LAV guidance and HRRR model, but uncertain on
this potential at this time so just showed TEMPO 6SM and scattered
clouds around 300 ft from 03z-06z. Occasional breezy northeast
and southeast flow this evening for terminals, except for GNV,
will settle down by midnight and become more variable and light
tonight. Increases in southerly and southwest winds near 8-12 kt
gusting near 20 kt expected Tuesday after about 14Z.
.Marine...
Frontal boundary over region will lift to the north Tonight. High
pressure will build to the southeast Tuesday, with surface boundary
just to the north. The high will sink further to the southeast
Wednesday, with the boundary remaining just to the north. Cold front
will move southeast across the region Thursday, and pass to the
southeast Thursday night. Strong high pressure will build to the
north Friday into Friday night, pushing a secondary trough south
across area. Strong high pressure will remain to the north over the
weekend, with an inverted trough over the coastal waters. The high
will weaken as it builds more toward the northeast early next week.
Rip Currents: SE GA: Moderate through Tuesday
NE FL: Moderate through Tuesday
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 60 81 62 81 61 / 10 20 20 30 10
SSI 62 76 62 77 63 / 10 10 10 10 10
JAX 61 84 62 83 63 / 0 0 10 10 0
SGJ 64 82 62 81 63 / 0 10 0 0 0
GNV 60 83 59 85 61 / 0 0 0 0 0
OCF 59 84 61 87 62 / 0 0 0 0 0
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1201 AM EDT Tue Mar 16 2021
.UPDATE...
Issued at 1201 AM EDT TUE MAR 16 2021
Rain showers have moved out of our area with the exception of
some isolated activity across far southeastern Kentucky. PoPs have
been lowered accordingly, based on the radar trends. The HREF had
decreasing low level cloud coverage through 0900z, especially
across the southern portion of the area. As such, did reduce sky
cover a bit through the night. Most of the model guidance has been
too aggressive with hourly temperatures warming overnight. The
HRRR 0100z run grids had the best handle on a more gradual warming
through dawn, as winds veer from southeasterly to more southerly.
Consequently, adjusted the hourly readings towards this idea.
UPDATE Issued at 828 PM EDT MON MAR 15 2021
Scattered to numerous showers will be exiting eastern Kentucky in
the next 1 to 2 hours. This activity is mainly associated with a
passing mid-level short wave trough, as well as moderate 850 mb
moisture transport. While the mid-level support will move on, the
850 mb transport will linger a bit longer across the area,
allowing for isolated shower activity to threaten through late
this evening, especially across far southeastern Kentucky, where
PWATs are higher. Have freshened up the PoPs through tonight,
incorporating more recent radar trends. Forecast lows were also
adjusted, as the surface trough/secondary warm front has been
slower to lift to the north early this evening. As such, some 30s
will linger north of the Mountain Parkway for another few hours,
before generally warming through the rest of the night. Updates
will be out shortly.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 327 PM EDT MON MAR 15 2021
An upper level low is pressing along through the Plains this
afternoon. At the surface, we see an occluded low in the Central
Plains and locally a surface trough across southern Kentucky. This
is leading to a strong temperature gradient from southern
Kentucky compared to the Bluegrass, as low 60s are the story in
southern Kentucky and mid 30s in the Bluegrass. The mid 30s are
likely a result of wet bulbing from the heavier precipitation
seen toward northern Kentucky. A spoke off the previously
mentioned upper level is elbowing its way into the Ohio Valley
helping to push a shortwave ridge east. This will aid by giving
way to some mid- level forcing bring the slug of precipitation
seen in central Kentucky eastward through the afternoon and
evening. This will be a light QPF, as we are still trying to
overcome the dry air at the surface in many cases. Therefore most
locations will see less than a quarter of an inch of rain. This
feature will push through most areas later this evening and
perhaps some lingering showers possible in the southeast through
the night. Temperatures tonight will remain above normal with lows
in the mid to upper 40s.
Tuesday, we see a dry day in store, with some mid and high clouds
from time to time under locally zonal flow. Expect a warm one with
highs around 70 for most locations and perhaps warmer (closer to
the 75 percentile of the NBM) depending on the cloud cover.
Tuesday night the skies should clear some and we will see slight
mid-level ridging. This could lead to a slight ridge/valley split,
but the question that remains is do we see some fog or low stratus
develop minimizing this some. Right now leaned toward a little
split, with lows in the low to mid 40s in the valleys and mid to
upper 40s on the ridges. To derive the valley lows leaned toward
the 5 percentile of the NBM.
.LONG TERM...(Wednesday through Monday)
Issued at 315 PM EDT MON MAR 15 2021
The weather in the extended will be primarily influenced by a
large area of low pressure, that is forecast to move out of the
Great Plains and across the Ohio and Tennessee valley regions from
late Wednesday through early Friday evening. A warm front
associated with the low will move through our area Wednesday and
Wednesday night, with the parent low moving across the area
Thursday night and Friday. Widespread rain showers will accompany
this system as it moves through our part of the country. We may
even see a few thunderstorms along the warm front as it moves
through. Since the main time frame for thunderstorm activity
appears to be Wednesday night through Thursday morning, only
garden variety thunderstorms are expected at this time. This is
because our weather system will be lacking in instability and a
large complex of thunderstorms that is forecast to form and move
through the Gulf Coast states Wednesday and Thursday, will likely
rob a large amount of Gulf moisture from the storms that are able
to form over our area. The lack of both instability and an
uninterrupted feed of Gulf of Mexico moisture should greatly limit
or even eliminate the potential for severe weather for eastern
Kentucky.
Temperatures will above normal to begin the period, with highs in
the upper 60s to lower 70s on tap for Wednesday and Thursday. Once
low pressure moves overhead, and then to our easter, cooler air
will spill into the area. Once that happens, we will see more
seasonable highs in the 50s on Friday and Saturday. Things should
begin to warm up again over the weekend, as high pressure builds
back across the region. Highs on Sunday may reach the upper 50s
to lower 60s. Nightly lows should be in the 40s and 50s Wednesday
and Thursday night, and in the 30s and 40s thereafter.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
ISSUED AT 828 PM EDT MON MAR 15 2021
Scattered to numerous showers will exit areas east of I-75
through 02z, with a few showers lingering through around 06z
across far southeastern Kentucky. MVFR/low end VFR ceilings will
gradually improve to VFR from southwest to northeast through this
evening. VFR conditions will generally prevail thereafter,
although mostly cloudy skies will continue, due mainly to passing
mid and high level clouds. East southeast to east northeast
surface winds of 5 to 10 kts, will gradually veer to the southeast
and south through tonight, before becoming more southwest to west
southwest by Tuesday afternoon. Stronger southerly winds aloft
will also provide a threat of low level wind shear tonight into
early Tuesday morning.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...BATZ/GEOGERIAN
SHORT TERM...DJ
LONG TERM...AR
AVIATION...GEOGERIAN
Area Forecast Discussion
National Weather Service North Platte NE
628 PM CDT Mon Mar 15 2021
.SHORT TERM...(This evening through Tuesday night)
Issued at 323 PM CDT Mon Mar 15 2021
The midlevel disturbance operating across the Panhandle this
afternoon is showing no sign of weakening and sfc observations in
that area show visiblity falling to a mile and as low as 1/4 to 1/2
mile briefly. The disturbance will move east tonight favoring the
central Sandhills for the best accumulating snowfall, generally
around 2 inches according to the latest forecast. The disturbance
will affect ncntl Nebraska Tuesday morning.
Temperatures aloft support snow with h700mb temperatures of -8C to
-10C, but temperatures near h850mb will be close to 0C across the
Sandhills and slightly above 0C south of the Sandhills near
Interstate 80. This should set up a rain snow line along or north of
the interstate.
The lift shown in the RAP model is weak at the -12C-18C layer but
this system will be operating below this level, closer to the
ground, below h700mb where temperatures are -5C to -10C. Periods of
strong lift are shown in the model in this layer for a few hours
tonight.
The locally higher amounts shown in the model appear to be the
result of a mesoscale circulation developing in the h850-h750mb
level. The strength of this circulation can be hard to predict. The
snow forecast lines up well with the RAP and HRRR which suggest some
local amounts of 3 or 4 inches in spots. The new QPF suggested by
WPC this afternoon would seem to supports the local amounts
predicted by the HRRR and RAP.
The temperature forecast tonight uses the guidance blend plus bias
correction for lows in the upper 20s. This is a little cooler than
the deterministic blend. The cooler temperatures seem appropriate
given afternoon temperatures are in the 30s. The temperature
forecast Tuesday and Tuesday night also uses the guidance blend plus
bias correction which in on the cooler side of the forecast envelop.
.LONG TERM...(Wednesday through Monday)
Issued at 323 PM CDT Mon Mar 15 2021
A storm system operating across cntl California this afternoon
will sweep through the srn Rockies Tuesday and emerge onto the
Colorado and Kansas plains Tuesday night and Wednesday. This will
be another fairly strong system but favoring KS and sern Nebraska
for the best rain. Snow will likely fall on the northern side of
the storm. Earlier runs of the SREF suggested storm would curve
north more sharply producing a good chance of significant snow
across swrn and scntl Nebraska. The morning run of the SREF
however, tracks the storm more east and keeps the better snow
chance south and east of swrn and scntl Nebraska. This is in good
agreement with the model consensus which show the storm dropping
into far nrn Oklahoma.
Slowly moderating temperatures are expected Thursday and Friday.
This is the result of a storm system approaching the West Coast
which will cause a sharp rise in heights aloft. The system will be
deep enough to drive warmer Desert Southwest air across the
Rockies and in Nebraska. This should produce highs in the 50s to
near 60 Saturday and Sunday as temperatures at the h850mb level
rise toward 10C. The West Coast system could begin to affect the
weather across wrn and ncntl Nebraska Sunday night and Monday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 628 PM CDT Mon Mar 15 2021
Another piece of the Rocky Mountain storm system will continue to
spread into western and north central Nebraska through tomorrow.
Light snow is underway in the panhandle and will move east through
the night, affecting most terminals. Areas of fog are also
affecting north central Nebraska (KONL), which will likely stick
around until the snow arrives around sunrise. Overall, expect a
prolonged period of MVFR to IFR conditions due to cigs or visby
(or both during snow). Winds will gradually transition to to east
tonight then north tomorrow morning, with speeds generally 10 kts
or less.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM CDT /noon MDT/ Tuesday for
NEZ004-005-008>010-022>028-035>037-094.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Snively
Area Forecast Discussion
National Weather Service Louisville KY
851 PM EDT Mon Mar 15 2021
.Forecast Update...
Updated at 840 PM EDT Mon Mar 15 2021
Sharp warm front is draped across southern Kentucky, with BWG
sitting at 61F while it`s just 44 at EKX. Deep moisture feed and
associated precip have pushed off to the east, so the rain is done
for the night.
Main question marks tonight will be min temps and fog potential.
North of the front, we are probably at our lows for the night, and
looking at steady temps until the front lifts north, then a slow
rise toward morning. By daybreak Tuesday expect temps to range from
the upper 40s in southern Indiana to the mid 50s in south central
Kentucky. Some concern with fog, but with a respectable 30-40 kt LLJ
just 2000 feet off the deck, fairly warm ground temperatures, and
rising air temps, would expect most of the moisture to be lifted
into a low stratus deck. Will continue to monitor through the night,
especially in southern Indiana where the hi-res models hit the fog
potential the hardest. If the front gets hung up, there could be an
opportunity for locally dense fog the farther north you go.
Updates on the way shortly to come in line with hourly trends and
remove precip mention.
&&
.Short Term...(This evening through Tuesday)
Issued at 242 PM EDT Mon Mar 15 2021
Expect widespread rainfall across southern Indiana and central
Kentucky through Monday evening as a shortwave trough ejects from a
closed 5H low over the central US and moves through the OH Valley.
Latest surface analysis continues to place the triple point of the
occluded low in far western KY with the warm front extending ESE
across TN. Current radar shows rainfall with embedded moderate to
heavy showers moving NE through the CWA with measurable rainfall now
reaching as far east as Mercer and Boyle Counties. Latest HRRR and
NAM3K agree on decreasing rain rates and coverage by early evening
and most if not all rain exiting east of our area before midnight.
So far, heavier rainfall has reduced visibility down to less than 2
miles at BWG and HNB, though total rainfall amounts through this
evening are still expected to be between 0.25 to 0.50 inches.
Tuesday will remain dry yet mostly cloudy as weak surface ridging
builds over the region beneath deep SW flow. Cloud cover overnight
will keep temperatures mild with Tuesday morning mins in the mid to
upper 40s north of the Parkways and in the low 50s south of there.
WAA as a result of SW flow will result in above normal max temps
Tuesday with afternoon highs in the upper 60s to low 70s.
.Long Term...(Tuesday night through Monday)
Issued at 322 PM EDT Mon Mar 15 2021
=============================================
Synoptic Overview
=============================================
Upper air pattern at the beginning of the period will feature a
broad ridge over the southeastern US with an upper level wave moving
into the lee of the Rockies. The vigorous upper level wave will
deep as it cross the Plains and generate a surface cyclone over
Oklahoma which is then forecast to move into IL by Thursday morning
and then off into southern New England by Friday morning. Widespread
convection is forecast to occur ahead of this developing cyclone
with a substantial risk of severe weather across the southeastern
portions of the United States. Once the system moves east, upper
level ridging over the Plains will move eastward and build into the
Ohio Valley. Dry weather with a moderation in temperatures is
expected over the weekend and into next week.
=============================================
Model Discussion and Sensible Weather
=============================================
In general, the models are in decent agreement with the overall
pattern. By Wednesday morning we will see a surface low developing
over Oklahoma with a warm front extending eastward through the TN
Valley. Vigorous upper level wave is forecast to move through the
Plains with the surface low moving into southern IL by Thursday
morning. Attendant cold front will surge eastward and will probably
be in the process of occluding as it heads through the Ohio Valley.
Main forecast challenge will be how far north will the warm front
surge and where the triple point of the system will be. These
factors will heavily influence our chances at seeing strong/severe
convection.
Consensus of the current guidance suggests that the warm front will
make its way northward close to the southern Ohio Valley. Model
dewpoint forecasts suggest dewpoints getting into the upper 50s to
possibly the lower 60s. However, model soundings still have a bit
of CINH across the region with some elevated instability. Shear
values still look impressive with a low-level surface ESE flow
veering around to the southwest. Most likely scenario is that we`ll
see an increasing amount of shower and thunderstorm activity move
northward into the region Wednesday afternoon, though much of this
thunderstorm activity will likely be elevated.
More surface based thunderstorm development looks to remain south
across AR/TN/MS/AL/GA where stronger instability will reside. As
cold front heads eastward, we`ll have to be on close guard to see
how much surface based instability develops northward into the
region. CIPS analog guidance still has much of the severe threat
contained to our south. However, by Wednesday night, we do have
some steepening of lapse rates aloft and weak instability that could
promote a severe hail threat across southern KY. As mentioned in
this morning`s discussion, wet bulb values remain pretty low and the
CIPS analogs had a few events that were hail storms across TN.
Although the model soundings still show quite a bit of mid-level
saturation that may limit the overall hail threat. Current SPC risk
profile of a slight risk is justified across SW KY and I suspect that
slight risk will be adjusted a little eastward in subsequent
outlooks, though I don`t think it would come north of the BG/WK
Parkways.
Widespread showers along with scattered thunderstorms are expected
across the region late Wednesday night and early Thursday as the
occluded front works eastward through the region. With the upper
trough swinging through during the day on Thursday, additional
showers are expected to continue.
We should start to dry out by Friday as moisture gets shunted to the
east and southeast fairly quickly with a large amount of upper level
ridging building into the region for the weekend and into early next
week. A moderation in temperatures is expected through this time
frame.
As for temperatures, we`ll be quite mild on Wednesday with highs in
the mid-upper 60s with lows in the 50s. Highs in the 60s are likely
for Thursday as well, but we`ll see a cool down Thursday night and
Friday behind the departing system. Highs Friday will likely only
top out in the upper 40s to the lower 50s. Highs on Saturday
should warm into the upper 50s with upper 50s and lower 60s expected
on Sunday. We expect slightly warmer readings by Monday, probably in
the 65-70 degree range.
=============================================
Societal Impacts
=============================================
A period of strong to possibly severe thunderstorms exists for
Wednesday afternoon and Wednesday night. The highest risk of severe
weather looks to be across the southern half of Kentucky.
=============================================
Forecast Confidence
=============================================
Overall storm evolution for Wed/Thu : Moderate
Risk of strong/severe storms for S IN/N KY : Low
Risk of strong/severe storms for S IN : Low-Moderate
Drier and warming trend for weekend : Moderate
&&
.Aviation...(00Z TAF Issuance)
Issued at 705 PM EDT Mon Mar 15 2021
Tricky forecast overnight with stratus and LLWS concerns associated
with a warm front lifting north across the region. Last few showers
will be moving out and/or dissipating early this evening, and then
easterly winds will veer to nearly due south after midnight. There`s
a narrow window of opportunity just before that for some low-level
wind shear, as sfc winds will be light out of the SE while the LLJ
cranks up to 35-40 kt from the SW. Will include it briefly starting
at 05Z at SDF (and HNB and LEX) but it should abate by 08-10Z as the
warm front kicks northward.
MVFR stratus will run below 2000 feet at least through this evening,
with SDF and HNB potentially on the edge of some LIFR with the warm
front. As the night goes on, the cutoff between the lowest stratus
and possibly even VFR conditions will sharpen, so there`s some bust
potential. Will include TEMPO for IFR conditions.
Warm advection on Tue morning should mix out the low levels pretty
quickly, improving cigs to VFR.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...RAS
Short Term...CG
Long Term...MJ
Aviation...RAS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
909 PM CDT Mon Mar 15 2021
.UPDATE...
909 PM CDT
The main band of precipitation has shifted north of the area. The
focus is now on two areas of precip, the lingering drizzle across
northeast IL and another band of rain showers across central IL.
Continued low level lift in the lowering cloud deck will support
some lingering drizzle through the evening and early overnight
hours. Temperatures hover between 31 and 33 and they will likely
hold here (or maybe inch up due to increasing dewpoints).
Therefore while we may have some freezing drizzle obs, the impacts
should be fairly limited given the marginal temperatures. Still,
localized slick spots may still be possible. With the continued
moist conditions, patchy fog will continue, with no obvious sign
that things will drop significantly given some continued winds,
cloud cover, and no large surge in moisture.
The compact shortwave across Missouri will drive an area of
showers across central IL tonight. The main instability axis will
just graze the area to the south, thus these should overall be
fairly light.
KMD
&&
.SHORT TERM...
330 PM CDT
Through Tuesday night...
A true spring snow system with a hodgepodge of precipitation
types, gusty winds, embedded bursts of snow, and isolated
lightning! Snow is tapering from south to north through the rest
of the afternoon. The primary concern going forward after dark
will be the potential for freezing drizzle.
The strongly forced zone of precipitation associated with the
left exit region of a 120+ kt jet is lifting northward through
far northern Illinois and Wisconsin. Regular 1/4SM visibility
within heavy snow was seen within this, along with a handful of
CG lightning strikes in north central Illinois. The system dry
slot nose on the aforementioned jet basically is moving northward
on the back side of this, with a zone of steepened lapse rates
above 800 mb helping to force isolated showers (with sleet or
snow). Impacts into the evening commute will primarily be residual
from what has fallen, apart from the far northern Chicago metro
which will likely still see some snow activity.
Beneath the dry slot, low-level moistening is occurring with some
lowering cloud bases, although as of 3 PM these are still almost
entirely above 1,500 ft (not ideal for drizzle). This appears to
improve this evening on forecast guidance, and observational
trends support that upstream with lower clouds, as well as some
drizzle already east of Peoria northward toward LaSalle-Peru.
There was even a social media report to WFO ILX of ice
accumulation from freezing drizzle in Eureka, IL near 3 PM. This
is the concern for this evening, as today`s precipitation and deep
cloud cover lowered temperatures and will keep them down through
sunset. The 280K isentropic surface on both the RAP and NAM show a
fair amount of upglide through the evening, and model profiles
show low-level omega and veering profiles in the lowest part of
the column. At least patchy drizzle would seem probable in this
setup, but whether or not it`s heavy enough and pavement actually
becomes icy where temperatures are 32 or lower is challenging to
say. This is especially true considering much of the pavement is
wet and/or treated. Will be something we will need to watch
though. Also some fog is possible tonight as the boundary layer
moistens and with the already moist and cooler ground from today.
Otherwise the strong short wave near the Kansas City metro area
will move east-northeastward across central Illinois late tonight.
On the northern periphery of this, some convection may clip the
far southern CWA, but expecting a gradual weakening trend in this
wave overnight which will limit any amplification and northward
push to this, so not expecting this to be a big deal.
Clouds are likely to stick around under an inversion through
Tuesday. Mid-level heights only gradually rise through the day
with limited cloud bearing flow. Did tweak down highs some and may
have to a little further.
MTF
&&
.LONG TERM...
325 AM CDT
Tuesday through Sunday...
While the primary focus this morning is on our near-term
impactful weather, another strong storm system is expected to
affect the forecast area from Wednesday through Thursday
night/early Friday. Locally heavy rainfall amounts and another
round of strong gusty northeast winds are the main expected
impacts, with some thunderstorm potential across the southern
parts of the cwa as well during Wednesday night/Thursday period.
Surface low pressure and mid-level short wave trough associated
with our near-term inclement weather will exiting the are to the
east on Tuesday morning. Some patchy drizzle or light freezing
drizzle may linger past daybreak, though ascent atop the shallow
moist layer should diminish quickly with the departure of the mid-
level wave. Mid-level short wave ridging is slower to develop
eastward across the region during the day, though subsidence does
strengthen in the afternoon which may help to erode some of the
lingering low cloud cover later in the day as the associated
inversion lowers. Surface high pressure develops just to our north
and northeast Tuesday night as the mid-level ridge moves
overhead, with dry weather and lighter winds into early Wednesday.
Lingering low clouds and likely some lingering snow cover will
tend to keep temps down a bit over far north and northwest parts
of the cwa Tuesday, while modest northeast onshore winds cool
lakeshore areas in the Chicagoland area. Daytime temps Tuesday
should be closer to mid-March averages across the southern parts
of the forecast area.
By Wednesday, a sense of deja vu takes hold as attention turns to
yet another compact closed upper low tracking east-northeast
across the central and southern Plains. Guidance has come into
better agreement with the track of the mid-level vort center into
southern Missouri Wednesday night, and across southern Illinois
during the day Thursday, with the slight negative tilt to the mid-
level axis takes the surface low just a bit farther north than
some previous forecasts. Initial effects from this system will
again be increasing east-northeast winds across the forecast area
Wednesday, with precipitation developing Wednesday afternoon into
Wednesday evening as the southerly warm/moist conveyor stream
ascends north of the surface warm frontal zone within the eastern
periphery of the wave. Current model guidance depicts a warmer
thermal column than with our early-week system, resulting in
primarily rain expected. Northeast low level flow will maintain a
feed of cooler/drier air across the far northern parts of the
forecast area however, where some rain/snow mix may be possible
later Wednesday night and early Thursday as the column saturates.
This system will have a more wide-open Gulf and stronger
circulation as it transits the region, pulling warmer and higher
moisture content air into the storm. P-wats of around an inch are
progged into the southern parts of the cwa Wednesday night into
early Thursday, which combined with relatively steep mid-level
lapse rates and some elevated thunderstorm potential across our
southern cwa will have the potential for producing some locally
heavy rainfall amounts in the 1-1.50" range. With the slightly
farther north track of the low, guidance focuses some of these
higher rainfall amounts as far north as the I-80 to I-88 corridor,
with late Wednesday night into early Thursday looking like the
main period of the heavier rain. This coincides with the best
juxtaposition of deep forcing - strong moisture
advection/isentropic upglide north of the warm front and at least
weak elevated instability along with indications of coupled upper
jet exit/entrance regions over the western Lakes region. Forcing
weakens during the day Thursday as the system occludes and passes
off to our southeast.
As alluded to above, with the surface low passing south of the
area strong east-northeast winds are expected especially during
the late Wednesday night through Thursday night period. Various
model soundings and time-height sections indicate 35-40 kt winds
1000-1500 feet off the surface, supporting the potential for 30-40
mph surface wind gusts. The prolonged period of northeast winds
will likely result in high waves on southern Lake Michigan, which
could lead to minor lakeshore flooding issues along the Illinois
and Indiana shores.
Models diverge with what happens to the departing upper low
across the southeastern U.S. late in the period, though are
generally in agreement in developing upper ridging from the Plains
into the western Great Lakes northwest Friday into Saturday. This
results in sprawling surface high pressure across the Great Lakes
region Friday into Friday night, with some milder return flow
developing across the area Saturday as the ridge drifts off to the
east. So the end of the week looks quiet, with the potential for
warmer temps heading into the weekend.
Ratzer
&&
.AVIATION...
For the 00Z TAFs...
Primary Forecast Concerns
* Lingering drizzle and freezing drizzle through the evening and
early overnight hours
* Expanding IFR cigs and vis and potential LIFR early Tuesday AM
The primary band of heavy wintry precipitation has since lifted
northeast of the area with lingering light precipitation falling
mainly as light snow/drizzle/freezing drizzle. Surface
temperatures in the low 30s heading into the evening hours
suggests that at least some freezing drizzle will persist in areas
that surface temperatures remain at or below freezing. Anything
that does fall will be light, however.
IFR cigs and vis are expanding in coverage this evening as the
system pulls away from the area. With the fresh snow/sleet
pack felt more confident to introduce a period of LIFR cigs early
Tuesday morning. There remains some uncertainty with how quickly
the LIFR/IFR cigs stick around into the morning hours. For now
have things improving around 15Z.
Winds will remain a bit gusty here this evening into the 20kt
range but will gradually ease overnight. Winds then become light
out of the N/NE into early Tuesday with a reinforcing lake breeze
possible Tuesday afternoon.
Petr
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IL nearshore waters until 4 AM Tuesday.
Small Craft Advisory...IN nearshore waters until 10 PM Monday.
&&
$$
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Area Forecast Discussion...UPDATED
National Weather Service Memphis TN
947 PM CDT Mon Mar 15 2021
.UPDATE...
9 PM / 02Z surface analysis showed a stationary front across
central MS, curving northeast to near Monroe county. Dewpoints in
the Aberdeen and Columbus areas prevailed in the lower 60s, while
further north, lower 30s dewpoints were common across the border
in west TN.
Isolated severe thunderstorms that formed over central MS along
the front earlier this evening have weakened and moved into AL.
Short range convection-allowing models (CAMs) - earlier HRRR runs
excepted - kept thunderstorms out of northeast MS overnight.
Latest HRRR have fallen in line, keeping storms over east central
MS and AL, where a stronger low level jet will set up. Low PoPs
remain in order for northeast MS overnight, given the proximity
of the stationary front. Areas of fog will be possible over north
MS and portions of west TN near the TN River toward morning, as
the stationary front begins to lift north as a warm front.
Early look at 00Z guidance for Wednesday shows instability, steep
lapse rates and directional shear are likely to be in bountiful
supply. All severe weather modes, including tornadoes, appear to
be possible.
PWB
&&
.PREV DISCUSSION... /issued 622 PM CDT Mon Mar 15 2021/
UPDATE...
Updated for the 00Z Aviation Discussion
PREV DISCUSSION... /issued 338 PM CDT Mon Mar 15 2021/
DISCUSSION...
The primary focus in today`s forecast is the midweek severe
weather potential. Guidance continues to highlight a multi-
hazard threat Tuesday night through Wednesday evening affecting
much of the Mid-South. At this time, the main question is how far
north the warm front will lift, representing the northern extent
of the primary threat area. The current Enhanced Risk is the first
for the Memphis County Warning Area (CWA) since May 3, 2020.
The occluded low over the central CONUS will meander over the
Plains into the midweek period as the shortwave currently over
CA carves out a deeper trough across the Southern Plains Tuesday
into Wednesday. In the meantime, the front that moved through
the CWA today will stall just south of the area. Warm advection
over the top of this boundary may result in scattered showers and
thunderstorms tonight, mainly south of Tupelo. Any instability
will be elevated, but these storms could produce small hail and
heavy downpours. Elsewhere, generally dry weather is expected
across the Mid-South overnight with fog possible (mainly along and
south of I-40). The potential for a few storms will continue on
Tuesday along the southern boundary of the CWA but otherwise warm
and dry weather is expected.
The warm front is expected to lift north Tuesday night, providing
the impetus for elevated convection during the overnight period.
Strong forcing for ascent downstream of the approaching trough
will steepen lapse rates, enhancing the instability aloft.
Hodographs show a good amount of helicity in the elevated layer
and could support a marginal supercell environment with hail being
the primary concern. The warm front will continue to lift north
during the day, putting a large chunk of the Mid-South within the
warm sector by peak heating.
Most of the messy convection is expected to lift north with the
warm front, but if the warm sector is contaminated, it could
limit instability. However, at this time we expect SBCAPE
exceeding 1000 J/kg throughout the Enhanced Risk area. Low-level
wind shear will be strong area wide with 0-6 km bulk wind
difference in the range of 50- 60 kts. This will be more than
favorable for rotating storms, especially any discrete cells that
develop within the warm sector. All modes of severe weather remain
on the table, including large hail, damaging winds, and tornadoes
(perhaps some strong). The warm front will represent the northern
extent of the severe weather risk, so this risk will expand
northward if this front lifts more aggressively.
The cold front will swing across the area late in the day through
the evening hours. Storms are likely to line up along the front as
it moves across the Mid-South with a shear vector oriented
roughly orthogonal to the boundary. Given low-level hodographs
and strong line-normal shear, a QLCS with tornado and damaging
wind potential will be possible. This convection will move easter
into the Wednesday night period but should be east of the area
before sunrise.
The parent upper-level cyclone will move across the OH Valley on
Thursday. Most guidance keeps this low just north of the CWA,
though the ECMWF favors a slightly farther south solution. Strong
westerly, post-frontal winds are expected on the southern
periphery of this low. Ensemble guidance indicates a zonal
component of the 1000 mb wind in the 97th+ percentile, which
pushes wind speeds up near Wind Advisory criteria. There are still
plenty of moving parts, but we`ll be keeping an eye on this
potential. Cooler and drier air will settle over the region
Thursday through the weekend. However, some wrap-around light rain
is possible through Thursday, mainly in the northern half of the
CWA. Dry conditions are expected Friday through Sunday.
Temperatures will take a step back to slightly below normal Friday
and Saturday but are expected to begin a warming trend by Sunday.
Finally, we`re still not to our normal last freeze date but a lot
of vegetation is beginning to bloom. With that in mind, we`ll be
watching the potential for a light frost over the weekend within
the cool, dry air mass. That said, the surface anticyclone may be
too far removed to the north.
MJ
&&
.AVIATION...
VFR conditions will be found across much of the Mid-South for the
entire forecast period. Low clouds will move into portions of
northeast Mississippi overnight producing MVFR ceilings and maybe
some patchy areas of fog. The low clouds should exit the region by
mid-morning on Tuesday. Winds will be mainly from the south at
around 10 knots this evening before diminishing to around 5 knots
overnight. Winds will shift to the west on Tuesday.
ARS
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&
$$
Area Forecast Discussion
National Weather Service Mobile AL
1022 PM CDT Mon Mar 15 2021
.Overnight /Now Through Sunrise Tuesday/...Through sunrise
Tuesday, deep convection is expected to re-develop over portions
of interior SE MS and Inland SW Alabama sometime just after
midnight and generally along an axis from Wayne Co., MS to Choctaw
Co., AL). Individual updrafts are forecast to move northeast.
This axis seems to be shifting subtly southeastward with each
latest model run and we continue to monitor. The ongoing cluster
of deep convection over SE LA has produced outflows that are
observed to be propagating northward and this will aid in the
initiation later tonight (along with deep moisture flux
convergence that is already operating to actively pool low level
water vapor in a regional warm sector that will remain
synoptically steady-state overnight). SPC SREF forecasts mean
MLCAPE of at least ~1000 J kg-1 through 06-09 UTC, so instability
will not be an issue. The ambient pre-storm environment at the
time of initiation will be characterized by the greatest low-
level vertical wind shear below about 1.5 km, which is seen to be
contributing most of the clockwise curvature to the forecast
regional hodographs (and producing Effective SrHel values of
200-250 m2 s-2, and this is close to what already is being
observed as of this writing.) Straight-line VWS above ~1.5 km with
lots of storm-relative flow which promotes updraft longevity,
tends to favor the right-moving member of splitting updrafts (as
we have already observed with a pre-cursor updraft earlier this
evening) and also aids developing hail embryos as they move
through the hail growth zone. There is also sufficient CAPE
forecast to be in the hail growth zone at that time to support
perhaps up to 1.5" diameter hail. A brief short-lived tornado and
damaging wind gust cannot be ruled out. The SPC has maintained a
Marginal Risk through 7 AM CDT, and we concur locally. So, areas
generally west of I-65 and mainly north of Highway 84 are the
areas of concern in the wee hours of Tuesday morning). /23 JMM
.NEAR TERM /Tuesday Through Wednesday Night/...The pattern on
Tuesday is not expected to be too different from that of Monday,
with a conditional threat of severe weather associated with any
stronger thunderstorms that develop and SPC maintains the Marginal
Risk of severe storms over the northern half of our forecast area
on Tuesday. Expect to have ongoing convection during the early
morning hours on Tuesday morning, primarily over the northwestern
portions of the forecast area. Leftover convection from the pre-
dawn activity will become more widespread over the northern half
of the forecast area during the course of the day in association
with the lingering convergence zone just to the north of our area
in conjunction with some weak shortwave activity in the west-
southwest flow aloft.
With daytime heating, MLCAPE values will increase to be between
500-1000 J/kg by Tuesday afternoon, with the higher instability
values up to near 1600 J/kg over our northern counties. Also,
0-6 KM bulk shear values will be around 35-45 knots across much of
the area during this time, along with 700-500 mb lapse rates
around 6.0-6.7 C/km and 0-1km SRH generally between 100-200 m2/s2
(especially Tuesday morning). There will be some weak capping
between 700-600 MB, and similar to Monday, this could have a
limiting affect on the convection at times. But sufficient daytime
heating and deep layer moisture could aid in eroding the cap and
lead to increased chances for thunderstorms (especially over
southeast Mississippi and inland southwest and south-central
Alabama), and some of these storms could be strong to severe (as
previously mentioned. Curved low-level hodographs could also
result in some rotating cells. Thus, the main threats anticipated
are damaging winds and hail; but, a tornado or two cannot be ruled
out. By late Tuesday afternoon through Tuesday night convection
diminishes somewhat, although an isolated to scattered storm will
still be possible overnight (especially over the northern portions
of the forecast area). At this time, it does not appear that there
will be much of a severe threat with those.
High temperatures on Tuesday will range from the mid and upper 70s
over most of the forecast area, but a pocket of lower 80s will be
possible over interior south central Alabama and part of the
interior western Florida panhandle. Tuesday night low temperatures
primarily in the low to mid 60s across the entire area. A HIGH RISK
of rip currents continues along the beaches for Tuesday and
Tuesday night. /12
An active severe weather day looks to unfold on Wednesday into
Wednesday night. An upper level trough centered over the south-
central Plains states takes on a negative tilt into the night
Wednesday as it shifts east into the east-central Plains and
Midwest. Upper level ridging amplifies in response over the far
southeastern U.S. and western Atlantic during the period.
Uncertainty remains in model guidance on exact evolution of the
upper level trough, and southeastern periphery of best upper level
difluence. Despite some questions on overall magnitude of large
scale forcing for ascent over our CWA, ample wind shear and CAPE
will be available in advance of an eastward moving cold front.
During the day Wednesday, forecast models are in general agreement
on developing 1,500 to 2,000 J/kg of SBCAPE, with similar MLCAPE
values nearer 1,500 J/kg. Some hi- res guidance like the HRRR
suggests higher SBCAPE and MLCAPE values could be realized, and is
something to keep an eye on as we near Wednesday. CAPE values
taper off in the evening somewhat, remaining more than adequate
for severe storms with 1,000 J/kg MLCAPE and 1,500 J/kg of SBCAPE.
Very steep low level lapse rates look probable nearer 7C/km, with
mid-level lapse rates approaching 8C/km. Shear will undoubtedly
be supportive of severe thunderstorms, including supercells.
Elongated, curved hodographs with deep layer shear around 40kts
will be present during the day Wednesday, strengthening into the
evening and overnight to over 50kts as the nocturnal low level jet
begins to crank upwards of 50kts. This will in turn help to
enlarge hodographs and increase Storm Relative Helicity values
appreciably after dark in excess of 300 to 400m^2/s^2 from
afternoon values around 200 m^2/s^2. All hazards of severe weather
are possible Wednesday late afternoon into the overnight hours,
with damaging winds, tornadoes (some strong), and large hail (up
to golf ball size) possible. A potential limiter for day time
convective coverage would be the presence of a healthy EML
(Elevated Mixed Layer) located at the 700mb level. This will help
to keep the environment capped until better forcing can move in or
daytime heating can overcome the EML.
It is important to note/reiterate the uncertainty in where best
forcing will align with the aforementioned ingredients along with
timing of better forcing. This will affect overall timing of better
severe weather potential. The first round of isolated to scattered
convective potential appears to potentially develop during the early
to mid afternoon hours across much of the CWA. This would likely be
in the form of isolated to scattered discrete to semi-discrete
thunderstorms capable of all severe hazards that move and develop
from southwest to northeast across the area. A better threat for
strong to severe thunderstorms will likely evolve from west to east
during the late evening into the overnight hours along the cold
front as a line of strong to severe thunderstorms pushes eastward
across the region. Convection quickly tapers off behind the front
during the late overnight into early morning hours, with the front
exiting the CWA prior to or near daybreak Thursday.
Outside of the severe threat, high temperatures look to peak in the
upper 70`s to lower 80`s during the afternoon, with lows Wednesday
night in the middle to upper 50`s west of I-65, and lower 60`s to
the east of I-65. Best rain and thunderstorm chances appear to be
late afternoon into the late night hours, waning from west to east
following the frontal passage during the overnight hours. In
addition to the severe risk Wednesday, strong wind gusts are
possible ahead of the front over the open warm sector during the
afternoon into night time hours. Wind gusts of 30 to 35mph appear
probable amidst strong southerly low level flow, and would not be
surprised if a Wind Advisory becomes necessary for parts of the CWA
during the period. A HIGH RISK of rip currents continues through the
day Wednesday into Wednesday night. MM/25
&&
.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk through Friday morning for ALZ265-266.
FL...High Rip Current Risk through Friday morning for FLZ202-204-206.
MS...None.
GM...None.
&&
$$
This product is also available on the web at:
http://weather.gov/mob
next weekend. The upcoming forecast discussions and packages will
focus more on this storm system with additional details after the
current system exits the region.
&&
.AVIATION...as of 6:00 PM PST Monday...For the 00Z TAFs. KMUX
radar shows widely scattered to scattered showers over the
southern half of the cwa. Metar observations show VFR and gusty
west to northwest winds, ceilings briefly lowering to MVFR with
passing showers. With the loss of diurnal warming expect clearing
tonight and surface winds decreasing. VFR tonight and Tuesday.
Vicinity of KSFO...VFR, northeast wind 5 to 10 knots, wind
shifting to west 10 to 20 knots by mid evening then decreasing
overnight. West wind 10 to 15 knots Tuesday.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR, west to northwest winds 10 to 20
knots until mid to late evening the decreasing overnight. East to
southeast cold air drainage winds at 5 to 10 knots developing late
tonight and early Tuesday morning. West to northwest winds 10 to
15 knots Tuesday afternoon and early evening.
&&
.MARINE...as of 01:11 PM PDT Monday...As the cold front has passed
over the waters, scattered showers continue and are expected
through this evening, with a slight chance for an isolated
thunderstorm. The bigger impact to mariners will be the strong and
gusty, gale force northwest winds that are forecast to continue on
through tonight, generating very steep combined seas of 15 to 20
feet at roughly 10 to 12 seconds. These very steep seas and gusty
winds can capsize small vessels and bring other hazardous
conditions across the seas. Winds look to start to calm down in
the bays this afternoon, with coastal waters following around
sunset. Outer waters will remain gale force through most of the
night tonight. Seas are expected to subside late on Tuesday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Frost Advisory...CAZ506-516-528
GLW...Pt Arena to Pt Reyes 0-10 nm until 9 PM
GLW...Pt Reyes to Pigeon Pt 0-10 nm until 9 PM
GLW...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
GLW...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
SCA...Mry Bay until 3 AM
&&
$$
PUBLIC FORECAST: DRP
AVIATION: Canepa
MARINE: Dhuyvetter
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Area Forecast Discussion
National Weather Service Pocatello ID
704 PM MDT Mon Mar 15 2021
.UPDATE...Added precipitation along the Utah border and in the
Central mountains for early this evening. Little, if any,
precipitation is expected to hit the ground. Also adjusted this
coming mornings lows slightly up.
Wyatt
&&
.PREV DISCUSSION... /issued 152 PM MDT Mon Mar 15 2021/
SHORT TERM...Tonight through Wednesday night. Deep narrow trough
shifting through coastal states continuing to split. Southern
closed low tracks well south of Idaho through the rest of today
and tonight. A few very spotty showers/virga still possible this
afternoon and evening, but confidence is extremely low as models
continue to trend drier over East Idaho. Best chances COULD be
over the northwest portion of Custer county and along the Southern
Sawtooth region, then along the Wyoming border overnight and into
early Tuesday. HRRR develops a stronger downvalley gradient
overnight, mainly across the INL, but guidance keeps winds low. As
low tracks through Utah during the day Tuesday, wrap around
moisture could impact areas in the southeast corner. This carries
a higher confidence with greater model consensus. Otherwise the
short term looks rather dry and remaining above normal for
temperatures. DMH
LONG TERM...Thursday through Monday night. Dry, mild and delightful
late-winter conditions will punctuate conditions on Thursday as
southerly flow gradually increases in advance of an incoming low
pressure trough and attendant surface cold front. Speaking of this
incoming system, the NBM continues to trend faster with the
precipitation onset by a few hours. Did not adjust this offering as
the NBM is well within the realm of possible scenarios. At this
time, ensemble cluster analysis still favors a slightly slower
solution, albeit by only a few hours. Current NBM will represent the
official forecast, and as such a quickly blossoming area of
precipitation is depicted across the central Idaho mountains during
the morning, followed by an eastward expansion during the afternoon
and early evening. As mentioned, a slightly slower onset may come to
fruition, but only by a few hours. Ensemble and deterministic models
continue to support the development of an organized NE-SW oriented
band of precipitation Friday evening. There are some differences
with regard to timing and placement, with possible scenarios ranging
from the band developing across the central Idaho mountains,
southern Snake Plain, eastern Magic Valley and points south towards
the NW UT/NE NV. An alternate scenario depicts the band developing
across the eastern highlands, also on Friday evening. The NBM does a
nice job of adequately representing both scenarios with a blended
approach. Valley rain and mountain snow appears increasingly likely
by late Friday afternoon/early evening beneath this band. Snow
levels are initially forecast in the 7,000-8,000 foot range, but the
combination of diabatic cooling and modest cold advection will
result in a gradual decrease in snow levels through Friday night.
The above-mentioned precipitation band is shown moving out of the
area Saturday morning on faster scenarios, limiting potential snow
accumulations to high-elevation eastern highland valleys. The slower
scenario is a bit more interesting, as thermal profiles may be cold
enough for snow in the Snake Plain Saturday morning, assuming
moisture and lift remains to support precipitation. At this point,
either scenario is possible. Either way, much welcome rain and snow
is looking like a good bet with this system. Precipitation should
become more showery in nature by Saturday afternoon with activity
becoming more focused across higher terrain areas. The most likely
scenario currently depicts a drying trend for Sunday before another
system spreads rain and snow across the area for Monday. Many detail
differences remain, but the overall trend would favor an increase in
precipitation chances during this time.
AD
AVIATION...Mid to high level clouds are forecast to continue
allowing for VFR ceilings for much of the period. Some lower cloud
decks are expected to work their way into the region overnight into
Tuesday morning with a chance for showers/virga in the vicinity,
mainly at KBYI and KDIJ. Low-level winds will increase as the
pressure gradient tightens in response to a pair of nearby low
pressure systems, the stronger of which passing through the southern
Great Basin and the weaker one meandering through central Oregon. As
a result, low-level N-NE winds will increase across the region
tonight into Tuesday morning. Forecast soundings indicate NE winds
increasing into the 25-35kt range between roughly 1kft-1.5kft around
09Z at KPIH and KIDA. Should surface winds slacken with the loss of
daytime heating (as indicated on soundings) wind shear would meet
thresholds, and as such have added a WS mention from about 09-15Z at
KPIH and KIDA. Surface winds are then shown to switch to the west
Tuesday morning (mainly after sunrise). Given KBYI`s location
relative to a nearby wind-shift line, WS may need to be added here
as well.
AD
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Reno NV
131 PM PDT Mon Mar 15 2021
.SYNOPSIS...
Snow showers and gusty northwest winds are expected this evening as
the atmosphere remains somewhat unstable. High pressure will move
into the region Tuesday leaving the forecast dry through Wednesday
and early Thursday. A warmer Pacific storm will bring mountain snow,
light valley rain showers, and gusty winds Thursday night through
Friday. The long range forecast for next week is leaning drier than
normal, although storms can`t entirely be ruled out.
&&
.DISCUSSION...
* Somewhat unstable airmass coupled with deformation aloft will
continue to yield snow showers into this evening. Latest HRRR and
HREF bring more of an organized band of showers through W Nevada,
Tahoe, and the eastern Sierra between 0z-6z evening which could
drop from a dusting up to 1". As temperatures fall this could
result in areas of icy roads later in the evening, overnight, and
Tuesday morning. We`ve actually had quite a bit of snow today from
Cedarville to Lovelock to east of Fallon - probably 2" or more
based on webcams. But most has stuck only to non-paved surfaces
with NDOT sensors indicating pavement temps well into the 40s. But
anything that falls after sundown could be more problematic.
Classic March snow.
* Next item of interest is a Pacific storm projected to impact
the area Thursday night through Friday. This one is warmer than
today`s and has more of moisture tap, but not an atmospheric
river. Latest ECMWF and GFS ensemble guidance showing most
members with a low-moderate end precip event in the Sierra, with
only 1 in 10 indicating more than 1" SWE at the crest (mainly
GFS members). NBM snowfall also indicating a low-moderate end
event along the crest - 4-9" at Donner and 1-5" for Mammoth in
the 50th-75th percentiles. For W Nevada the ensemble guidance is
pretty pronounced with the shadow so just light rain showers
expected along with breezy winds especially Friday. Not a high
wind scenario but enough for typical road and aviation travel
impacts.
* Long range ensemble guidance is leaning toward a less active and
warmer pattern for next week with high pressure ridge along the
coast becoming a dominant feature. No large storm signals in the
ensembles or AR landfall probability charts, but there are members
that bring a low-end system through Monday-Tuesday next week with
a few rain or snow showers. All in all our snowpack will get a
minor boost this Friday, otherwise it`s pretty much locked in as
is for the rest of the month.
-Chris
&&
.AVIATION...
Through mid-afternoon, occasional SHSN or pellets may bring short
periods of MVFR/IFR conditions to the main terminals. There is a
possibility of a more steady snow area developing around the Tahoe
and far western NV terminals around 22-23Z, and continuing until
02-03Z around KTRK/KTVL and 04-05Z around KRNO/KCXP/KMEV/KRTS.
Farther south at KMMH, separate snow shower bands are most likely
between 21-01Z.
While runway accumulations are less likely due to most of this
snow falling before sunset, some patchy slush could develop in
areas where snow lingers after dusk. Cloud cover and just enough
NW-N wind after the snow ends may hold temperatures above freezing
long enough to allow sufficient drying and limit ice formation on
pavement overnight, although this would depend on how much
moisture collects during the snow band.
Otherwise, the other possible effect of evening snow is whether
skies clear out overnight and allow for patchy FZFG and/or low
stratus. Current projections on the blended guidance keep enough
cloud cover in place to limit fog, although the HREF indicates
some clearing between 10-12Z which could lead to some AM fog.
Aside from tonight`s activity, we`re looking at generally VFR
conditions (except possible early Wed AM FZFG at KTRK) through
Thursday morning, then another storm will bring increased
aviation-related wind and rain/snow impacts from Thursday
afternoon through Friday. MJD
&&
.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory until 2 AM PDT Tuesday for Lake Tahoe in
NVZ002.
Lake Wind Advisory until 5 AM PDT Tuesday for Pyramid Lake in
NVZ004.
CA...Winter Weather Advisory until 5 PM PDT this afternoon CAZ071.
Winter Weather Advisory until 5 PM PDT this afternoon CAZ070.
Winter Weather Advisory until 5 PM PDT this afternoon CAZ073.
Lake Wind Advisory until 2 AM PDT Tuesday for Lake Tahoe in
CAZ072.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno
Area Forecast Discussion
National Weather Service Tallahassee FL
940 PM EDT Mon Mar 15 2021
.NEAR TERM [Through Wednesday]...
Light to moderate southerly low-level flow lies beneath fast
westerly flow aloft. In the confluent southerly low-level flow,
CAMS guidance shows shower activity blossoming overnight south of
the Walton and Bay County coastline. Showers should then move to
the north-northeast onshore around sunrise, then move inland and
across southeast Alabama, curling northeast across southwest
Georgia. It will probably take until this cluster is curving
northeast in the afternoon to start producing lightning.
Otherwise, low stratus is already moving onshore out near Destin,
so it seems reasonable to that low stratus or fog will lift north
through the Panhandle late tonight, then up across southeast
Alabama and counties near the Chattahoochee early in the morning.
For the evening update, have lowered PoPs for the rest of
tonight, most notably across SE Alabama. Raised rain chances a
little early in the morning around Bay County for the showers that
are expected to move onshore.
&&
.PREV DISCUSSION [758 PM EDT]...
.SHORT TERM [Tuesday Night Through Wednesday Night]...
The loss of daytime heating should reduce the threat for any
isolated severe storms for the overnight period Tuesday night. For
Wednesday, the forecast area will be in a warm advection pattern
within the warm sector with highs in the lower 80s and dew points
in the mid 60s. Isolated to scattered severe storms will be
possible during the afternoon. However, the main event should be
in the form of a squall line ahead of an approaching cold front.
That should begin impacting our western counties after midnight
with impact weather advancing eastward ahead of the front. Most of
the weather should be east of the area Thursday afternoon. The
primary threats will be damaging straight line winds and isolated
tornadoes.
.LONG TERM [Thursday Through Monday]...
This period should be dry and cooler, albeit not really cold.
Overnight lows will generally be in the 40s with highs in the 60s
or 70s. The coolest afternoon looks to be Saturday with highs
ranging from the upper 50s between Albany and Valdosta to the
upper 60s for the southern Big Bend counties. By Monday, everyone
will be back in the 70s.
.AVIATION...
[Through 00Z Wednesday]
Fog and low stratus will again be a concern late tonight through
a couple hours after sunrise on Tuesday morning in low-level
southerly flow. Already, beachfront locations such as Destin are
already reporting ceilings of 500 feet or less, so the marine soup
is poised to spread inland late this evening and overnight, with
VLD the most likely terminal to miss out.
Recent runs of the HRRR show a cluster of low-topped shower
activity lifting north across the coast near ECP soon after
sunrise on Tuesday, eventually affecting DHN and possibly ABY
later in the morning.
.MARINE...
Light to moderate onshore winds will increase to cautionary levels
from Wednesday afternoon through Friday night. A wind shift from
southwest to northwest will occur from Wednesday night through
Thursday night and it is during this period where winds will reach
small craft advisory criteria at times.
.FIRE WEATHER...
The best chance for a wetting rain will be Wednesday into Thursday.
Dense fog is possible tomorrow morning in the Florida Big Bend.
Elsewhere, fog will be patchy. Otherwise, there are no fire weather
concerns.
.HYDROLOGY...
The Suwannee River at Rock Bluff will gradually recede and drop
below flood stage sometime Wednesday or Wednesday night. Rainfall
with the next system is not expected to be sufficient for flooding
concerns as forecast totals have come down. Heavier rain is
expected north of the area. There may be implications down stream
in our area if rainfall in the northern part of the ACF basin is
excessive.
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur (while following all local, state, and CDC guidelines) by
calling the office or tweeting us @NWSTallahassee.
&&
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 62 78 64 80 66 / 10 20 10 20 30
Panama City 65 75 65 77 66 / 20 40 20 30 60
Dothan 63 78 64 80 65 / 20 70 20 60 70
Albany 61 78 64 81 65 / 10 60 30 50 50
Valdosta 59 80 63 83 63 / 0 20 10 20 10
Cross City 60 80 62 82 63 / 0 0 10 10 10
Apalachicola 64 73 64 74 65 / 10 20 10 20 30
&&
.TAE WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk until 10 PM EDT /9 PM CDT/ this evening
for Coastal Bay-Coastal Gulf-South Walton.
GA...None.
AL...None.
GM...None.
&&
$$
NEAR TERM...Haner
SHORT TERM...Wool
LONG TERM...Wool
AVIATION...Haner
MARINE...Wool
FIRE WEATHER...Montgomery
HYDROLOGY...Wool
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
745 PM EDT Mon Mar 15 2021
.UPDATE...
Existing forecast on track with no changes necessary. Warm temps
continue with overnight lows in the lower 60s and afternoon highs
in the lower 80s along the immediate coast thanks to the sea
breeze and mid/upper 80s elsewhere. Fog appears to be less of an
issue tonight although a few areas may see development of late
night/early morning fog.
&&
.AVIATION...
VFR expected through period. Light/variable winds overnight
increase out of the S/SE during morning, veer SW during
afternoon, decrease to light/variable during evening.
&&
.Prev Discussion... /issued 145 PM EDT Mon Mar 15 2021/
Synopsis...
17Z water vapor and H4 RAP analysis showing broad and protective
mid/upper ridging continue in place of the eastern Gulf of Mexico
and Florida peninsula. Shortwave energy ejecting through the TN
valley and the associated inclement weather is being kept well
removed from our region...and will remain so for a couple more
days. The 12Z sounding from KTBW indicated a well-defined
subsidence inversion located at around 860mb...in connection with
the aforementioned ridging aloft. PW values are not unseasonably
low at around 0.75", but it is dry enough to prevent any of the
sea-breezes today from being able to support shower development.
That time of year is just around the corner though.
At the surface...high pressure extends down the eastern seaboard
and over the peninsula. The pattern as a whole is providing us
with dry, benign and warm conditions. Temperatures early this
afternoon are into the 80s away from the coastline, and are
generally holding in the mid/upper 70s at the beaches as the
diurnal sea-breeze kicks in and transports some "cooler" air off
the shelf waters of the eastern Gulf of Mexico.
SHORT TERM (Tonight through Wednesday)...
The overall synoptic pattern will not be changing much through the
mid-week period, and hence neither will be forecast philosophy.
Mid/upper ridging holding in place will keep our forecast dry and
increasingly warm. Will likely see temperatures (especially
inland) creep up by a couple of degrees each day, and will not be
surprised to see a few spots flirt with 90 on Wednesday afternoon.
LONG TERM (Thursday through the upcoming weekend)...
Progressive shortwave energy ejecting out of the southern Plains
on Wednesday will eventually cut off as it moves over the MS/TN
valleys Thursday into Thursday night. Good agreement in the
ensemble guidance that this energy will finally be able to break
down the protective ridge. A cold front trailing from an area of
low pressure over the Ohio Valley later Thursday will reach the
northern FL peninsula Thursday evening and then slowly sink
southward into Friday morning, and then clearing into the Florida
Straits Friday afternoon/evening.
The best height falls/synoptic support to support organized
frontal convection and the potential for strong storms appears as
though it will sneak just to our north during the second half of
Thursday. However, it will be a close call for the Nature coast
zones and will need to keep a close eye on the potential for a
stronger storm to move ashore off the Gulf. The best potential for
measurable precipitation will also be to the north of the I-4
corridor, although amounts do not look impressive. Likely 1/4" or
less. The frontal support only lessens with time and southern
progress Thursday night and expect just a broken band of showers
(maybe a thunderstorm) for areas along and south of the I-4
corridor Thursday night/early Friday).
Friday and Friday night are looking cooler (not cold) and dry in
the post-frontal environment. Beyond Friday night, the forecast is
of lower confidence. The upper level pattern becomes rather
complex, with varying degrees of cut-off energy interacting with
the baroclinic zone of the Gulf Stream off the GA/NE Florida
coast. Have kept the forecast dry for the weekend as of now, in
line with the majority of the ensemble guidance.
MARINE...
High pressure keeps winds below 15 knots and seas on the low side
through the middle of the week. Look for afternoon sea-breezes to
turn winds onshore after 1-2pm each day. Stronger flow to
cautionary levels is expected from the south ahead of an
approaching cold front during Thursday, then shift to the
northwest, and remain near cautionary levels Thursday night and
Friday in the wake of the front.
FIRE WEATHER...
Dry and warm conditions continue through the middle of the week.
Despite temperatures well into the 80s away from the coast the
next several days, increasing low level moisture should help keep
relative humidity generally above critical levels. A cold front
will bring a chance for a wetting rainfall later Thursday into
Thursday night, with best potential for measurable rainfall to the
north of the I-4 corridor. Expect cooler and drier weather with a
wind shift to the north and northeast for the end of the week
behind this front.
&&
.Preliminary Point Temps/PoPs...
TPA 66 83 67 84 / 0 0 0 0
FMY 65 85 64 86 / 10 0 0 0
GIF 65 88 64 89 / 0 0 0 0
SRQ 64 82 65 83 / 0 0 0 0
BKV 59 87 59 87 / 0 0 0 0
SPG 68 80 68 81 / 0 0 0 0
&&
.TBW WATCHES/WARNINGS/ADVISORIES...
FL...None.
Gulf waters...None.
&&
$$
UPDATE/AVIATION...Hurt
UPPER AIR/DECISION SUPPORT...Sobien