Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/18/21
Area Forecast Discussion
National Weather Service Burlington VT
1018 PM EDT Wed Mar 17 2021
A mild night is on tap ahead of a cold front, with scattered rain
showers and mountain snow showers. Thursday will see morning showers
press southward with cloudy skies and cooler air in the wake of the
front, while an area of light rain moves over southern Vermont which
may end as a brief period of snow late in the day. Blustery
conditions overnight into Friday will be followed by a steady
warming trend with day after day of sunshine and low humidity
yielding large diurnal ranges.
.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 1012 PM EDT Wednesday...Did update pops again to place
values near 100% for southern Windsor/Rutland Counties on Thurs.
In addition, did increase pops along the International border
area into the likely range aft 06z tonight. A very light band of
precip is crntly developing on radar with a few obs showing
precip reaching the ground upstream over the Great
Lakes/Southern Canada. Llvl moisture advection will continue
with cloud deck lowering and bl rh values increasing overnight
on southerly winds. Any qpf acrs northern NY into mtns of VT
will be light and generally under 0.10. Continued with schc/chc
pops for the CPV, as moisture with southwest flow ahead of
boundary will limit potential for measurable precip. Slightly
better window as winds shift to the northwest behind boundary
with some localized upslope lift. Otherwise, latest 00z NAM and
HRRR continue to show a 3 to 4 hour window for light rain,
changing to mtn snow across Rutland/Windsor Counties on Thurs.
QPF generally 0.10 to 0.20 with an inch or two of snow possible
above 3000 feet south of Route 4. Temps hold mainly in the mid
30s to lower 40s tonight, but drop aft 18z on Thurs, with
developing llvl caa behind boundary. All covered well in fcst.
Previous discussion below:
Still looking at light amounts of precipitation to impact most
of our area tonight, and southernmost areas tomorrow afternoon.
Latest trends have backed off on snowfall chances for south
central Vermont as dry air associated with a northern stream
trough overpowers the moisture associated with a southern stream
low pressure system. The light rain and high terrain snow
during this period will be the only precipitation for the next
several days. See below for details.
It will be a mild night as moist southwest flow moves through the
North Country ahead of a cold front. Temperatures will not fall
below 40 across the warmest locales of the Saint Lawrence and
Champlain Valleys, and even elsewhere we should see temperatures
stay above freezing apart from the highest terrain above 2500 feet
and the coolest hollows in the Adirondacks and Northeast Kingdom. So
expect all rain tonight as fairly wide coverage of showers develops
tonight after 10 PM and spreads eastward initially across the far
northern tier before spreading quickly southward towards daybreak in
along a surface cold front. HREF indicates strengthening 700 and 850
millibar westerly flow tonight associated with a mid-level trough
that the initial batch of showers will be tied to. So we should see
significant shadowing effect of the terrain during the overnight
hours, with showers become briefly moderate across the western
slopes of the northern Vermont Piedmont and Green Mountains through
the overnight hours. As winds aloft weaken towards daybreak, should
see more showers across lower elevations with a couple hours of wet
weather ahead of the frontal passage.
By afternoon, with a plethora of dry air in the low-levels and
rising motions behind the front, chances of precipitation will be
just about zero for most of the area. Deeper moisture will hold on
in southern portions of Rutland and Windsor counties, where we
continue to expect light rain to fall during the afternoon. The main
change with this forecast is a faster push south and east of
precipitation tomorrow night. This means by the time temperatures
fall to near freezing at the lower elevations, precipitation will
likely be over. It also results in a small reduction of
precipitation amounts to mainly 0.1" to 0.2" in this area. The rest
of our forecast area should generally see up to 0.1" of liquid
through the next 24 hours, apart from the western slopes of the
Greens where locally higher amounts are forecast.
The cold air advection moving southward into the area tomorrow will
keep temperatures from rising much, with highs ranging through the
40s with values steadying and then falling in the afternoon hours,
especially over northern areas. While the combination of breezy
conditions and colder air will make for blustery conditions in the
overnight hours, the source air does not appear to be nearly as cold
as what we dealt with a few days ago. Wind chills will fall into the
single digits or lower by daybreak.
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 328 PM EDT Wednesday...Friday will be the coldest day for the
foreseeable future with temperatures expected to remain below
freezing at most locations following the cold front on Thursday. A
very slight chance of light snow will be possible across far
southeastern Vermont early Friday morning but dry air will bring a
plethora of sunshine to the region during the afternoon hours. Lows
Friday morning and again Friday night will be in the upper single
digits to mid teens.
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 328 PM EDT Wednesday...A 1038 mb surface high will begin
building across the region on Saturday and will remain overhead
through at least Monday before it ever so slowly begins to shift
eastward. We will see our 850 mb and 925 mb temperatures climb
through the weekend as we enter a more favorable advection regime
which will allow temperatures to climb into the 40s on Saturday and
into the 50s for Sunday. Given low temperatures a good bit below
freezing and highs well above freezing, this weekend is shaping up
to be very favorable for those who are tapping maple trees. This
trend of above normal temperatures will continue through at least
the middle of the week with long term guidance hinting at this
period of above normal temperatures continuing well into next
weekend. With high pressure firmly entrenched across the region
through much of the forecast period, sunny skies and dry conditions
will prevail. Fire concerns begin to grow next week as we are
quickly digging ourselves into a rainfall deficit with sunlight
baking our 10 and 100 hour fuels across the Champlain and St.
Lawrence Valleys. The next chance of rainfall won`t come until
Wednesday but even then we are looking at just a slight chance at
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Through 00Z Friday...VFR crntly at all our taf sites will become
mvfr cigs at slk/btv/mpv and rut aft midnight with a window of
ifr vis/cigs possible at rut/mpv and slk toward 12z on Thurs.
Scattered rain showers are possible after 06z, especially mtn
taf sites ahead of a sfc cold front with south winds 5 to 10
knots. These winds shift to the northwest btwn 14z-18z on Thurs,
as precip is mainly trrn focused at best, before dissipating
and cigs increasing by Thurs evening acrs our taf sites. Rutland
has the best potential for a period of light rain on Thurs with
low cigs and vis in the 3-5sm range.
Thursday Night: VFR. Slight chance SN.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.
Area Forecast Discussion
National Weather Service Billings MT
556 PM MDT Wed Mar 17 2021
Building high pressure aloft will bring dry/clear weather to our
region tonight. As low level winds veer to the southeast, boundary
layer moisture will increase in our far east, courtesy of snow
melt in WY/SD today. HRRR is starting to suggest fog in Fallon and
Carter counties so have updated for patchy fog from 09-15z. JKL
Tonight through Friday night...
A strong 500 MB Ridge will build over the region the next couple
of days producing a dry warming trend. Highs will warm into the
50s and 60s Thursday, with mostly 60s to near 70 degrees on Friday
as we get an additional boost from pre frontal warming. Look for
some gusty wind 25-40 mph developing in the Livingston/Nye
foothills picking up by tomorrow and increasing some late Friday
with a few gusts over 50 mph possible.
The ridge breaks down Friday night as an upper trough moves into
the Rockies and high plains. This will spread some precipitation
in from the west Friday night into Saturday. Some snow is
expected in the high country, but lower elevations will likely
remain rain showers. BT
Saturday through Wednesday...
Somewhat active period in store for the extended with highs in the
40s and 50s each day. Model clusters showed a Pacific trough
moving toward the region on Saturday. Precipitation amounts were
around a tenth of an inch /0.10/, with a quarter inch /0.25/ in
the Beartooths/Absarokas. The ECMWF EFI was rather unstable in the
western zones, which could indicate some thunder. Checked the GFS
sounding for KLVM and CAPE was low but there were decent lapse
rates. Still, not strong enough support to put in thunder at this
time, but it is something to watch. Rain was likely over the
central and W, with several inches of snow likely in the
mountains. Chances for rain and snow continue into Sat. evening.
The trough will still be in the region on Sunday, but best chances
for precipitation will be S of the area. Next trough moves into
the Pacific NW on Monday, but the clusters were not in great
agreement with the system. NBM brings chances for rain and snow
into the SW half of the area Mon. night and Tuesday. For
Wednesday, most cluster members have a ridge building in, but
Cluster 4 is showing a Pacific NW trough. NBM keeps the area dry.
ECMWF Ensemble wind gusts showed gusts in the 20s and 30s for much
of the period. NBM did have gusty winds over portions of the area
during the period. Overall, there were no high impacts during the
Building high pressure aloft will bring widespread VFR through
Thursday. There could be localized valley fog near KBHK-K97M
between 09-15z (IFR or lower possible). SW wind gusts of 20-30
knots expected at KLVM tomorrow. JKL
.PRELIMINARY POINT TEMP/POPS...
Thu Fri Sat Sun Mon Tue Wed
BIL 029/062 037/068 040/051 034/052 030/054 033/049 030/055
00/U 00/U 47/R 31/B 11/B 23/O 10/U
LVM 029/061 037/061 036/048 029/047 025/047 028/044 026/050
00/U 01/N 47/O 31/B 12/O 33/S 11/U
HDN 024/062 030/069 037/053 032/054 028/056 032/051 029/055
00/U 00/U 27/R 32/O 11/B 23/O 11/B
MLS 021/057 030/066 037/053 033/054 029/055 031/051 029/053
00/U 00/U 04/R 21/B 01/U 11/E 00/U
4BQ 022/056 030/066 037/056 033/052 029/054 031/049 029/052
00/U 00/U 04/R 21/B 11/B 12/O 11/U
BHK 020/052 027/063 034/055 031/052 027/053 028/048 026/050
00/U 00/U 03/R 21/B 11/U 11/E 10/U
SHR 020/055 028/063 032/052 028/047 024/049 027/044 024/049
00/U 00/U 06/R 43/O 12/R 24/S 21/B
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1056 PM CDT Wed Mar 17 2021
Issued at 1004 PM CDT WED MAR 17 2021
With precipitation struggling to develop north of I-70, have
canceled the northern edge of the winter weather advisory.
Otherwise, forecast remains on track.
Update Issued at 833 PM CDT WED MAR 17 2021
Vigorous low pressure system moving towards the southwestern tip
of Missouri as of 02Z Thursday. Precipitation shield is filling
in south of I-70 with strong dynamics. Have seen a few sporadic
reports of light snow across the area, but as drier air filters in
from the north, combined with strong dynamics, expect
precipitation to switch over to snow despite surface temperatures
remaining above freezing overnight. Am concerned with the weakly
negative equivalent potential vorticity, which suggest the
potential for a scattered lightning strike or two throughout the
overnight hours. Could also see some enhanced pockets of snowfall
with the potential convective elements. Followed day shift lead,
and have been closely following short term Hi-res models for the
evening update. Have massaged snow amounts upwards slightly for
the southern metro and and areas just east along the Missouri
River. Have also expanded the winter weather advisory to include
Saline and Carroll counties. Update posted.
Issued at 227 PM CDT WED MAR 17 2021
- Accumulating snow is likely tonight. A few inches of a heavy wet
snow across eastern Kansas and western Missouri are expected.
- Quieter and warmer weather this weekend.
An intense upper-level storm system is tracking across Oklahoma
this afternoon. This system will track to our south this evening
and overnight. Models are in decent agreement with the overall
strength and track of the system. The main differences come in
just how cold temperatures might get tonight and how that would
affect potential snow amounts. When looking through items that
would support heavy snow, this system checks a lot of the boxes.
There is very strong and very deep upward vertical motions that
will move over the area tonight. There is a well defined TROWAL
with the deformation area coincident with the strong upward
vertical motions. The moisture transport into the
TROWAL/deformation area is very strong. Cross sections running
roughly west-to-east across the area show theta lines folding
over aloft over the area, indicative of an unstable environment.
This is supported by a large and deep area of slightly negative
equivalent potential vorticity (-EPV), all coincident with the
deformation area of precipitation. The jet structure is impressive
with strong diffluence aloft noted. All this indicates that there
will be intense upward vertical motion. Despite all these very
favorable features of this system, temperatures in the lowest part
of the atmosphere will likely remain above freezing with
temperatures at the surface dipping into the low to mid 30s. Given
the intensity of the upper-level support with this system, have
made some changes to our forecast T and Td grids to allow snowfall
to accumulate. Have trended toward colder solutions like the HRRR
and NAM for surface T and Td. This lowers temperatures into the
mid 30s and dewpoints into the lower 30s during the heaviest
precipitation. The intense upward vertical motions should
dynamically cool the atmosphere and allow temperatures to be
cooler within the heaviest areas of precipitation. With this
cooler trend, snow accumulations look likely from eastern Kansas
through west central Missouri. For now, it looks like anywhere
from 1-3 inches will be possible in this area, with some isolated
amounts around 4 inches. These amounts will be most likely on
grassy surfaces with lower amounts on the relatively warmer
paved/cement roads. With temperatures only dipping into the mid
30s, it will take higher snowfall rates to overcome the relatively
warmer pavement temperatures, cutting into accumulations. But
with all that said, will run with a winter weather advisory from
midnight tonight to noon tomorrow for parts of eastern Kansas and
western Missouri. There may be places outside of the advisory area
that still see snow, but those amounts currently look less than
an inch. With the same pavement caveats previously mentioned there
may be minimal impact to travel with the overall lower amounts.
Quieter weather will prevail after this system moves out of the
region. Temperatures will rebound into Saturday and especially
Sunday with highs climbing into the climbing into the upper 50s to
60s Saturday and middle 60s on Sunday. The next chance for
precipitation will come Sunday night into Monday as another upper-
level shortwave trough tracks across the middle of the country.
.Aviation...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1051 PM CDT WED MAR 17 2021
Upper low across south central Missouri as of 04Z will continue to
pinwheel east into Thursday. Precipitation in the form of rain and
snow is expected to mainly remain along and south of I-70 across
western Missouri. Have therefore trimmed back precipitation at
KSTJ, KMKC and KMCI; however, IFR ceilings along with strong gusty
north winds will remain. Expect ceilings to gradually improve
throughout the day Thursday as precipitation comes to an end as
upper low works east. Gusty winds are not expected to subside
until Thursday evening.
KS...Winter Weather Advisory until noon CDT Thursday for KSZ057-060-
MO...Winter Weather Advisory until noon CDT Thursday for MOZ029>031-
Area Forecast Discussion
National Weather Service Green Bay WI
1033 PM CDT Wed Mar 17 2021
Updated aviation portion for 06Z TAF issuance
Issued at 715 PM CDT Wed Mar 17 2021
Strong NE winds are anticipated Thursday as the forecast area
becomes situated between a building anticyclone over Ontario and
a cyclone tracking up the Ohio Valley. The tightest pressure
gradient will remain across southern Wisconsin. But east-central
Wisconsin and in particular the Green Bay area is susceptible to
strong NE flow funneling down the Bay. Mixing on model forecast
soundings suggests gusts into the low 30s (kts) at GRB. But most
of the soundings also showed considerably stronger winds (up to 46
kts on the HRRR) at 2K ft. In addition, the soundings indicate
almost no directional shear between the surface and 10K ft. That
may allow for somewhat strong winds than would normally occur
given the forecast low-level thermal profile.
Bumped sustained winds and gusts in the GRB area up, and will
expand the WI.Y into Brown county. Additional expansion into the
rest of E-C WI may be needed later, but there is still enough
uncertainty to hold off on doing that now.
A major concern with the wind is what will happen to the ice
floating around on the Bay of Green Bay. Glimpses of the bay
surface seen on afternoon VIS satellite imagery through breaks in
the clouds showed almost all the ice consists of loose chunks that
were drifting north in the light south flow. That ice will be
driven back to the SW by the strong NE winds tomorrow. It`s
extremely difficult to determine exactly when and where there will
be substantial ice shoves as there are numerous factors that come
into play. But at least the wind seems very favorable. So will
issue a LS.Y for Brown county to match the WI.Y. Ice shoves could
also occur in Oconto, Marinette, Door and Kewaunee counties as
well, but the risk isn`t as great as in Brown county so will leave
those areas out of the advisory, at least for now. The ice shoves
and erosion due to wave action could result in some damage at the
shoreline. But the potential for flooding is not as great as it
would have been last year because the water level of the bay/lake
Updated product suite will be out ASAP.
.SHORT TERM...Tonight and Thursday
Issued at 341 PM CDT Wed Mar 17 2021
A mix of snow, rain, and graupel continue across east-central
Wisconsin this afternoon as a mid level shortwave tracks through
the western Great Lakes region. The HRRR model captured this
flare up of precipitation fairly well in the last few runs,
keeping precipitation in across the area through the afternoon
then diminishing by early evening as the main shortwave shifts off
to the east. As temperatures continue to rise, the threat for
accumulating snow should be fairly minimal. However some bursts
could cause a few tenths of an inch to pile up in some locations.
Clearing skies are then expected tonight as the main shortwave
tracks east and high pressure builds in across the northern
Plains. Lows tonight are expected to fall into the middle to upper
20s across the north, with lows around 30 across east-central
The area will be in between a low passing through the Ohio Valley
and the aforementioned high building in across the northern
Plains. This will mean a very tight pressure gradient will exist
across the forecast area on Thursday, causing gusty northeast winds
of 35 to 45 mph at times. The worst conditions will be across the
lakeshore counties with unabated flow off Lake Michigan. These
areas will have the best chance of hitting headline criteria on
Thursday. Further inland the Fox Valley looks to be just below
criteria at this time; however, funneling through the bay of Green
Bay may necessitate a headline in subsequent forecasts. At this
time will issue a Wind Advisory for the lakeshore counties given
the higher certainty and hold off for the Fox Valley. The gusty
northeast winds could push ice into the southern bay and possibly
cause minor flooding. Highs on Thursday are expected to hover
around 40 along the lakeshore, with the highest values farther
inland across central Wisconsin with highs in the upper 40s.
.LONG TERM...Thursday Night Through Wednesday
Issued at 341 PM CDT Wed Mar 17 2021
Quiet early spring conditions are expected Thursday night into
most of Sunday. Then an unsettled pattern is setting up for next
week with at least three systems to impact the area. Each will
bring rain, some wind and possibly some wintry precip. Temps look
to be above or well above normal.
Thursday night...low pressure will work into the Mid-Atlantic
as high pressure builds into the Great Lakes. This will allow
winds to diminish through the evening hours. Lingering lakeshore
flooding and ice shove issues could persist (if already occurring)
through around midnight. Could be some lingering clouds in the
southeast early, then look for clear skies. Winds look to be the
lightest over the north, where temps will drop to 10-15 degrees
in the cold spots. Some single digits would be possible where some
snow remains on the ground. The rest of the area will be in the
teens to lower 20s.
Friday into the weekend...high pressure settles over the Great
Lakes on Friday bringing quiet weather conditions. Look for light
winds and plenty of sunshine. The clear/sunny skies continue into
Saturday as the high pressure slides east of the region and weak
return flow sets up. Clouds start to increase Saturday night into
Sunday as stronger WAA moves into the area, a frontal boundary
works towards the area and the dry air gets pushed eastward.
Temps will get a boost Saturday into Sunday as 925/850mb temps
slowly increase within the WAA pattern. If spots don`t make a run
at 60 on Saturday, many should on Sunday. Exception will be near
Lake Michigan where the south winds will keep temps in the 40s to
around 50. South winds will pick up slightly on Saturday, mainly
10-25 mph, then a breezy day expected on Sunday with south winds
gusting up to around 30 mph. Relative humidities will be low
Friday and Saturday afternoon, which could lead to some fire
weather concerns, especially as winds pick up.
Sunday night into next week...as the frontal boundary and upper
trough swing into the area, chances for showers returns to the
area, but overall coverage looks to be low. Chance for rain
showers continues on Monday as the frontal boundary stalls in the
area and washes out as low pressure develops over the Plains.
Temps will be a little cooler near/behind the front, but another
spring-like day is expected south of the front with 50s to low
60s expected, cooler near Lake Michigan. Closed low pressure will
move from the Plains Tuesday and into the western Great Lakes on
Wednesday. This will spread a large area of showers into the area
Monday night into Tuesday. Could see some thunder make it into the
area eventually, as lapse rates steepen and a shortwave tracks
into the Great Lakes, but this might be closer to Tuesday night
and Wednesday. Likely will get a pretty good slug of moisture
ahead of this system, with some locally heavy rain a possibility.
Depending on the track, some snow will be possible on the back
side of the mid-week system, but way too early to dive into those
.AVIATION...for 06Z TAF Issuance
Issued at 1032 PM CDT Wed Mar 17 2021
The chance of getting MVFR conditions has diminished, though there
could still be some patches of clouds flowing into the area off
Lakes Michigan or Superior at times. But the main aviation
concern will be strong/gusty NE winds Thursday which will impact
takeoffs and landings. Some LLWS is likely late tonight to mid-
morning Thursday as winds aloft increase more quickly than
Wind Advisory from 7 AM to 7 PM CDT Thursday for WIZ022-039-040-
Lakeshore Flood Advisory from 7 AM to 7 PM CDT Thursday for
Area Forecast Discussion
National Weather Service Indianapolis IN
1153 PM EDT Wed Mar 17 2021
...Updated Aviation Discussion...
Issued at 942 PM EDT Wed Mar 17 2021
Surface analysis this evening shows deep low pressure in place
across southern MO....with a warm frontal boundary stretching
northeast across IL to Northern Indiana. Light southeast flow was in
place across Central Indiana. Dew points were in the moist upper 40s
to lower 50s. GOES16 shows abundant cloud cover across the area.
Water vapor imagery shows a deep upper low over OK with tropical
moisture streaming north through the Tennessee and Ohio Valleys.
The surface low is projected to continue on its path northeast along
the warm front overnight...approaching Central Indiana. Late this
evening radar returns have diminished across Central Indiana as weak
ridging remains in place aloft. More organized precipitation looks
to be found across Western KY...ahead of the approaching low. HRRR
keeps rather minimal echos across Central Indiana the next few
hours...however rain looks to become more widespread late tonight as
the low approaches and rain along with the associated forcing arrive
late tonight. By 12Z forecast soundings and time heights reveal a
saturated column. Thus have trended pops lower for the next few
hours as measurable precip seems unlikely...but ramped pops back up
late overnight as better forcing arrives.
Given the expected rain and minimal cooling along with moist dew
points also trended overnight low warmer by 1-2 degrees.
.Short Term...Tonight through Thursday Night
Issued at 338 PM EDT Wed Mar 17 2021
A strong and stacked low-pressure center will track west-to-east
from the Ozarks tonight, and then up the Ohio Valley Thursday...
bringing the greatest rainfall since late November to much of the
region tonight-Thursday morning. Chances for rain showers will
increase from southwest to northeast late today and this evening,
with widespread definite POPs for the CWA from late this evening
through Thursday afternoon. Medium confidence exists in isolated to
scattered embedded thunderstorms, especially south of I-70. Any
strong/severe thunderstorms would likely be limited to southeast of
a Bedford-to-Rushville line...and be isolated at best, Thursday
morning-midday. The threat of severe storms Thursday will be focused
south/east of Cincinnati...whereas more stable air will have already
entered our region before daytime heating will have much chance to
destabilize the atmosphere.
Storm total rainfall will be 1.00-2.00" across the region. Moderate
confidence exists that the axis of maximum rainfall will be parallel
to and north of I-70, where totals of 1.50-2.00" are likely, with
local totals exceeding 2.00". Nuisance flooding is likely across the
region...especially near creeks/streams, in low-lying spots and poor
drainage areas. Renewed minor river flooding on central Indiana`s
main stem rivers will resume as early as Thursday evening.
High temperatures Thursday will range from the mid-40s to near 60F
...while overnight lows will be 45-55F tonight, and then the upper
20s to near 30F for most locations Thursday night as a ridge of
Canadian high pressure infiltrates Indiana from north to south. The
normal max/min for the short term period is 53/34.
.Long Term...(Thursday night through Tuesday)
Issued at 306 AM EDT Wed Mar 17 2021
The long term period looks to begin with the last of the
precipitation from the midweek system associated with the SW/NE
oriented deformation zone on the northwest side of the low making
its way through central Indiana Thursday evening. Expect that
precipitation will end by the overnight hours as the low continues
to depart and the column dries out rapidly from aloft.
High pressure at the surface and aloft will then provide dry weather
and warming temperatures through the weekend and into early next
week, with generally clear to mostly clear skies and pleasantly mild
conditions, especially late in the weekend and early next week as
widespread highs in the 60s return.
Another in what seems to be a train of closed lows then develops and
moves through the region late in the period, bringing another chance
for showers to the area. This system looks a bit more progressive at
this time, but may prolong or exacerbate any high water produced by
the upcoming system, depending on its precipitation output and the
eventual speed of travel.
.Aviation...(00Z TAF Issuance)
Issued at 1152 PM EDT Wed Mar 17 2021
- IFR to LIFR conditions are expected to arrive overnight.
- IFR to LIFR will continue through much of Thursday.
- Gusty easterly winds will develop predawn Thursday and continue
through through Thursday.
DISCUSSION: Radar trends shows echos over southern Illinois
approaching Central Indiana yet still diminishing slightly upon
approach. Thus have trended toward VCSH at IND and LAF for the first
few hours of the TAF period. These showers should arrive at BMG and
HUF near 06Z...thus have used a prevailing rain at those spots.
Extensive cloud cover across the area as seen on GOES16 is expected
to remain as the deepening low over southern MO continues to push
east toward Central Indiana along the warm front in place across
Central Indiana. IFR Cigs...particularly on the north side of the
low will begin to impact Central Indiana tonight and continue
through much of the day on Thursday. Time heights and forecast
soundings show saturation within the lower levels through the day on
Thursday before some dry air is expected to arrive after 00Z Friday.
As the deep low arrives along with the frontal boundary in
place...gusty winds are expected to develop late tonight and
continue through the day on Thursday. Look for NE winds on Thursday
with gusts to 30-40 knots in the morning through the afternoon.
Confidence is high in both IFR arriving late tonight along with
gusty winds. Low confidence in embedded thunderstorms.
Wind Advisory from 8 AM to 8 PM EDT Thursday for INZ021-028>031-
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1131 PM EDT Wed Mar 17 2021
Issued at 1131 PM EDT WED MAR 17 2021
Made only minor revisions to blend late evening obs into the
forecast, with no substantive changes overall.
UPDATE Issued at 1049 PM EDT WED MAR 17 2021
Have updated largely for timing of rounds of precip and thunder
potential over the first couple of periods. The 18Z GFS and most
recent HRRR were in reasonably good agreement and were verifying
well for precip this evening, and were used to refine the
.SHORT TERM...(This evening through Thursday night)
Issued at 305 PM EDT WED MAR 17 2021
18z sfc analysis shows a deepening area of low pressure to the
southwest of Kentucky with a warm front pushing a band of showers
and possible thunderstorms into downstream portions of the
Cumberland Valley. The thickening clouds, and a foggy start in
many places, have kept temperatures from making it quite to the
low 70s for most with even some upper 50s in the southwest as the
pcpn is moving overhead. Dewpoints are up from yesterday, though,
with upper 40s found north and low to mid 50s south while winds
are running southeast at 5 to 10 mph - for the most part.
The models lose some agreement tonight before actually come into
better alignment aloft on Thursday. They all depict ridging
pushing out of the area to the east later tonight in the face of
a deep closed off 5h low rolling into the western Tennessee
Valley. The GFS and Canadian initially take this meteorological
bowling ball east quicker than the ECMWF and NAM. However, they
come back in line with each other on Thursday taking the core of
the trough through southern Kentucky. As such, confidence is
rather high during this critical part of the forecast that the
blended NBM is a good starting point to the grids. Later Thursday
night the NAM starts to deviate more with its low dropping more
south than east. Will take that solution into consideration
through Friday morning during an upslope situation that the NWP
models always struggle with.
Sensible weather will feature a pretty active period of weather
from this evening into Friday morning. Showers will quickly
work northeast through the CWA this evening as the lead surge of
moisture outruns the warm front - leading to a diminishing trend
to those first showers. Another surge of moisture them reloads
along the warm front and more effectively moves into the area late
this evening and overnight with plenty of lift found over the JKL
CWA, at times. Some heavy rain and training of showers and storms
can be expected later tonight - will add mention of this to the
HWO. The core of this will shift east during Thursday morning
with the warm front - placing eastern Kentucky in warm sector for
the rest of the day. This is a particular concern as dry slotting
will make for a window of opportunity for destabilization and the
ability to tap into the high amount of directional shear aloft.
This shear is maximized as the core of the sfc low passes overhead
in the afternoon. For this reason a good portion of our area is
in a slight risk for severe weather on Thursday afternoon with the
rest in a marginal risk. Organized storms will be a strong threat
with a potential for damaging wind gusts the main concern, but
the tornado chances, while low, will not be zero. The sfc low
moves east Thursday evening with its backside and wrap around pcpn
moving into this part of the state in its wake that night. CAA on
brisk west to northwest winds into Friday morning will drop
temperatures into upper 30s by dawn for most with even a touch of
non-accumulating snow and some mid 30s occurring over the
Bluegrass region and north of I-64 by dawn. We will keep watching
this snow threat in further model runs.
Given the high moisture - did not deviate much from the NBM
values for the T grids through the forecast. For the PoPs - mainly
brought them up through most forecast periods with some dry slot
timing refined from the NAM12.
.LONG TERM...(Friday through Wednesday)
Issued at 323 PM EDT WED MAR 17 2021
A few rain showers will be exiting the area on Friday, as a large
and powerful area of low pressure moves off to our east. The rain
should be out of eastern Kentucky by late Friday morning. We will
see well below normal temperatures around eastern Kentucky on
Friday, as cooler air spills into the area behind the departed
area of low pressure. However, the air mass should modify fairly
quickly on Saturday, with mostly clear skies and ample sunshine
expected. Highs on Saturday should max out in the mid to upper
50s, which is right about normal for this time of year. After
that, as a ridge of high pressure becomes firmly established over
the region, we should several days in a row with above normal
temperatures and dry weather. A few rain showers may move back
into the area Tuesday evening and night, but this a very
uncertain scenario at this time. Highs should be in the 60s each
day from Sunday onward, with a gradual warming trend occurring
during that time. By the time Wednesday rolls around, daytime
maxes should be in the upper 60s to lower 70s around the area.
Nighttime lows will start out in the upper 20s to lower 30s over
the weekend, but should become quite mild into mid-week, with
nightly values only falling into the 30s and 40s from Sunday night
through Tuesday night. Strong and gusty winds will be possible
for Friday, as the pressure gradient on the back edge of the
departing low intensifies.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 1049 PM EDT WED MAR 17 2021
Conditions were mainly VFR to start the period, but there were
some sub-VFR conditions near the TN border in association with
precip moving northeast into the forecast area. This precip as
since made its way further northeast and diminished greatly.
However, additional precip over TN and western KY should also move
through during the night and early Thursday. Along with this,
MVFR and IFR conditions are forecast to develop overnight. As the
bulk of the precip departs to the east on Thursday morning, VFR
conditions should return. However, more showers are possible after
some heating, especially in the afternoon. We could also see some
thunderstorms, with the best chance in most locations being on
Thursday afternoon. Any of the showers or thunderstorms on
Thursday could bring localized sub-VFR conditions.
Area Forecast Discussion
National Weather Service Louisville KY
1029 PM EDT Wed Mar 17 2021
Updated 1025 PM EDT Wed Mar 17 2021
We`ve had a break from the precip for most of the CWA over the past
few hours, but regional reflectivity shows another precip shield
over western KY and TN. Radar returns are already beginning to
intrude our south-central KY counties. 00z sfc analysis shows our
region split between two frontal features, with the sfc low located
over southern MO.
Tonight, we will see another round of showers as the sfc low
continues eastward and rides up the Ohio River as a stationary front
extends to the east and sits along southern IN. Believe the
reflectivity we are seeing in TN will lift NNE and into KY over the
next few hours. SPC mesoanalysis is not showing any sfc based
instability to speak of, but PWATs are around 1.2". Our severe
weather potential continues to diminish for the overnight hours, but
can`t completely rule out a possible flooding threat. Low 6-hr FFG
over our SE CWA (Clinton, Cumberland, Monroe) is where our highest
QPF for tonight if forecast. While current 6-hr QPF does not exceed
the FFG, any heavier cells or training precipitation could lead to
some flooding concerns.
By 08z, hi-res CAMS are wanting to bring more of a cellular precip
from SW to NNE through the CWA. However, CAMS initialize these cells
over NE AR by 02z, but current radar trends are not matching up too
well with this. Will need to continue to monitor the initialization
of those cells, as those could be our best chance of possibly seeing
a stronger storm. Confidence remains low in seeing convection
HRRR continues to paint a region of 500-750 J/kg of SBCAPE after 09z
tomorrow morning, but it appears the CAPE will be constantly trying
to catch up to the better moisture. With the bulk of the moisture
and better lift staying ahead/north of the instability, think we
will be limited to just some rain showers instead of any convection
for the overnight and into tomorrow morning.
.Short Term...(This evening through Thursday)
Issued at 320 PM EDT Wed Mar 17 2021
A surface low, currently near the Ozarks, will continue to slowly
move to the east under a mid-level closed low, and by tomorrow
evening, the slow moving system will only make it as far as
Kentucky. This slow movement will provide ample time for central
Kentucky and southern Indiana to receive plenty of precipitation
with the majority of that coming tonight.
Tonight, precipitable water values range from 1.2 to 1.5 inches, and
the CWA is expected to remain relatively stable. This will result in
more rain showers and less thunder. The best chance for thunder will
likely be from near sunset through around midnight. Areas in the
southern half of central Kentucky could see a line develop around 21-
22z and work it`s way east. Believe this is probably going to be the
best chance at any severe weather as strong directional and speed
wind shear exists, but again instability is weak and LCL heights are
high. Low level lapse rates are weak too. This will limit the high
wind threat. Expectations of severe weather are low, but always have
to watch high shear values. Expect mild low temperatures as they
only drop to into the upper 50s.
Tomorrow, a dry slot is expected to work it`s way through the CWA
choking any remaining precipitation. Precipitable water values drop
below an inch, so when precipitation builds back across the area by
late afternoon, expect only light rain shower. Highs are expected to
reach into the 60s.
.Long Term...(Thursday night through Wednesday)
Issued at 252 PM EDT Wed Mar 17 2021
By Thursday evening, the upper low will be over the central KY/TN
border as it eventually fills and moves east over the Appalachians.
Rain showers will be ongoing Thursday night and exit to our east by
Friday morning sunrise. A few snow flakes could potentially mix in
behind the departing system early Friday morning in the Bluegrass as
cold air filters in from the NW. Gusty NNE winds in the 20-30mph
range will also result from a tightening pressure gradient as
Canadian high pressure builds in from the north.
Expect dry conditions to follow for the weekend and into the early
part of next week as the aforementioned high pressure dominates a
large portion of the eastern US. Saturday morning will see the
coldest temperatures of the period with morning lows in the upper
20s to low 30s. But as the high pushes east, winds will slowly veer
to SE accompanied by WAA resulting in gradual warming that will push
afternoon temperatures above climatological norms from Sunday
through mid week. Highs Sunday will peak in the low to mid 60s, and
by Wednesday afternoon highs will reach into the upper 60s.
Our next rain chances will return Tuesday through Wednesday ahead of
a cold front the looks to push through Wednesday. Will go with model
blend solution with chance of rain showers through this period.
.Aviation...(00Z TAF Issuance)
Issued at 735 PM EDT Wed Mar 17 2021
Complex and low-confidence forecast in this TAF issuance. Currently
catching a break in the precip at SDF/BWG/HNB, and even breaking out
into mid-level ceilings. LEX should also break out shortly. The dry
and VFR conditions won`t last long as the next batch of showers
lifts NE out of western Tennessee. Should deteriorate into a rainy
night with prevailing MVFR cig/vis. However, conditions will
fluctuate a bit more as we could see ceilings break out to VFR at
times, while the heavier showers could result in brief IFR
conditions. Tried to handle it in TEMPO groups overnight.
Look for another break in precip during morning hours, with a period
of VFR in SDF and LEX toward midday. However, forecast confidence
really drops here as the mature cyclone makes its way across the
Ohio Valley. Dry slot will bring gusty SW winds, but we`ll still
need to mention at least VCSH. Precip coverage increases enough late
in the afternoon under the cold pool that we`ll go prevailing -SHRA
and use TEMPO to reflect potential for vis restrictions. Very low
confidence in afternoon wind direction for HNB and SDF as the sfc
low passes nearly overhead.
AREA FORECAST DISCUSSION
National Weather Service Morristown TN
912 PM EDT Wed Mar 17 2021
Currently still have showers and the occasional rumble of thunder
moving northeast through the eastern Tennesee Valley this evening.
We are still looking to our southwest focusing on the location of
the warm front as this remains the best chance for storms to begin
to tap into the lower level of the atmosphere and realize the
strong low level shear. Over the past several hours the front has
really slowed its northern progress (like many of the CAMs have
been anticipating) and still expect the progress to be slow going
over the next several hours. If we can get the front to begin to
occlude this will really diminish the severe thunderstorm
chances in our forecast area, and some of the hourly CAMs are
hinting this may be the final outcome as that front just barely
nudges into southeast Tennessee. Will obviously be keeping a laser
focused eye on storms moving out of AL/GA, but it may be several
more hours for stronger storms to really make significant progress
into SE Tennessee. The highest threat for strong to severe storms
and tornadoes will continue to be the highest across
central/northern Mississippi and Alabama this evening.
The more immediate (and likely more impactful) threat will Flash
Flooding across SE Tennessee as several rounds of showers and
some thunderstorms have moved over the same areas in the southern
valley. Radar estimated QPE and ground observations indicate
southeast tennessee has picked up widespread 1-2 inches over the
past 3-6 hours, with pockets of heavier amounts. Updated Flash
Flood Guidance indicates that across the southern row of SE
Tennessee counties only need to see about 1" of additional rain
over 3 hours to cause Flash Flooding, which is very likely to
happen tonight. Reports from law enforcement and EM`s in the areas
are already reporting some minor flooding of roads and other low
lying areas. With more storms brining even heavier downpours to
this area the rest of the night it looks like road closures and
flash flooding is likely tonight. A good time to remember that
night time flooding is one of the most dangerous weather
situations you can encounter and it`s NEVER worth driving through
a flooded road even if it looks passable. A flash flood watch
remains in effect for the southern Tennessee Valley down into
northern Alabama and Georgia for the rest of the night into
Thursday morning around sunrise.
00Z TAF DISCUSSION.
Showers across the area with a few embedded rumbles of thunder in
SE TN. Coverage of storms will increase and thunderstorm chances
will increase as well, especially around 06z at KCHA as a warm
front moves northward. Expect the peak time for thunderstorms to
be between 03z to 10z, but a few isolated strikes can occur
outside these times. Flying conditions will remain poor overnight
as strong to severe storms move into the area from AL/MS/GA.
Don`t expect improvement in conditions until these storms move
out by mid morning. Another round of scattered rain could occur
during the day tomorrow, but kept mention out to limit TAF length
and focus on the first round of storms tonight.
/ISSUED 337 PM EDT Wed Mar 17 2021/
SHORT TERM...(Tonight through Thursday)
1. Scattered showers/thunderstorms will lift northward this evening
with locally heavy downpours possible.
2. A line of strong to severe thunderstorms will reach the S Plateau
near Midnight and move across the S Valley and SE TN reaching SW NC
by 10 or 11Z.
3. Wind damage, large hail, locally heavy rain, and a low chance of
isolated tornadoes are expected across the S Plateau and the S
Valley as the line moves through.
4. This line will also affect parts of the N Plateau, N and central
Valley, NE TN, and SW VA late tonight as it moves eastward, but only
pockets of wind damage and hail are the main threats in those areas.
5. The storm threat for Thursday has greatly diminished.
A band of convective showers is moving N across the Plateau and S
and central Valley as of mid afternoon. Lightning activity has
nearly all diminished, but a rumble of thunder and brief moderate
rainfall remains possible as this band continues to lift to the N
and NE toward NE TN into SW VA. This elevated convection has been
tied to WAA and isentropic ascent north of a low/mid level warm
front that is now quickly moving N, and a 30-40 kt LLJ across AL has
been advecting elevated instability northward. However, much of the
East TN Valley has been in cooler, much more stable air, which is
why the lightning has diminished. Nevertheless, kept thunder in the
forecast grids through the evening as the LLJ strengthens and
advects greater amounts of elevated instability into our region.
Latest surface analysis shows the surface warm front still well to
the S across central AL, where surface based convection, including
discrete supercells, have been exploding over the past 1 to 2 hours
in a highly sheared environment. It is this surface warm front that
will dictate how much severe weather we see across the S Plateau and
S Valley overnight (see tonight section below).
Meteorology and Hazard Overview
As the deep, closed mid/upper low currently near the OK/AR borders
lifts ENE through the mid MS Valley tonight, the surface low nearly
stacked beneath it will deepen to around 995 mb over central IL by
Thurs morning. This will pull the aforementioned surface warm front
NE into the S Plateau and S Valley after Midnight, and the latest
RAP and HREF members project this front to reach the far S Plateau
and S Valley (Marion and Hamilton Counties) in the 06-09Z timeframe.
It is common for the warm front to surge N a little faster than
guidance predicts, and the left exit region of a 110-120 kt upper
jet will force a 50+ kt LLJ helping to force the front N, so would
not be surprised to see it reach these southern areas by 04Z. Low-
level shear and SRH continue to look very high in the vicinity of
the surface warm front with 40-50 kts of 0-1 Km shear, 300-600 m2/s2
of 0-1 Km SRH, and 400-700 m2/s2 of 0-3 km SRH. However, the
location of the frontal boundary will dictate tornado potential
because it will not only locally enhance the shear, but it will mark
the surface instability/theta e gradient. The latest RAP and HREF
project a few hundred joules of surface based CAPE along and S of
this warm front, and with the highly sheared environment, this leads
to significant tornado parameter values (STP) of 1 to 1.5 across the
S Plateau into the S Valley, especially Marion, Hamilton, S Bledsoe,
and perhaps parts of Bradley counties. This area will need to be
monitored closely for a few tornadoes possible in the roughly 04 to
09Z timeframe. Farther N, the instability will be elevated, so
despite very impressive deep layer and low-level shear up there too,
convection will mainly produce large hail with pockets of damaging
In terms of how the convection will evolve, scattered multi-cell
clusters lifting out of AL this evening will give way to a QLCS
moving in from the W, and this QLCS should cross in the 04-10Z
timeframe. It will likely reach the S Plateau and S Valley W of I-75
between 04 and 07Z, then cross the rest of the region in the 07-10Z
timeframe. As stated earlier, a few tornadoes are possible in the S
Plateau and S Valley, and these will generally occur with rotation
embedded in the QLCS, but we`ll need to watch for discrete cells
ahead of the line depending on how quickly the warm front can surge
into that area.
Flooding Potential and Mountain Winds
Another hazard will be locally heavy rainfall leading to localized
flash flooding. This will generally be limited since the convection
will be moving fast (40+ kts), but the S Plateau, S Valley, into SW
NC have the greatest chance to see some flooding since that area saw
1-2 inches of rain yesterday. High Wind Warning remains in effect
for the E TN mountains and foothills this evening through 18Z Thurs
as the 50+ kt LLJ crosses the terrain. The flow will be SW and not
overly perpendicular to the terrain, but the high speeds will lead
to warning criteria winds of 70+ mph in the highest peaks.
The early morning QLCS will exit E quickly after 11 or 12Z, and as
the storm system continues to shift toward the lower OH Valley, it
will occlude with the cold front crossing our region rapidly behind
the warm front. This greatly limits the amount of recovery time that
we will have in the narrow warm sector before the cold front crosses
in the late morning to early afternoon timeframe. CAMS have caught
onto this idea with only a scattered, weak line redeveloping during
the mid morning. Deep layer shear remains strong ahead of the cold
front (60-80 kts 0-6 Km), but low-level shear and SRH will quickly
diminish, and with the limited instability/lack of recovery time, do
not expect much in the way of severe weather. Scattered
showers/thunderstorms with 40-50 mph winds, small hail, and limited
lightning are the most likely scenario quickly moving W to E from
mid morning through early afternoon with all activity gone by 17Z.
As the upper low and associated cold pocket aloft approaches during
the afternoon, WBZ heights lowering below 6000 ft and surface
warming will create low-level instability for scattered, low-topped
convective showers capable of pea sized hail, so kept chance PoPs
through the afternoon and evening. Highs in the 65-70 degree range
in the morning will fall through the 60`s during the afternoon.
LONG TERM...(Thursday Night through Wednesday)
Closed H5 low will be entering the Plateau as Thursday night begins.
Models are slightly disputing the path of its center, with the NAM
the southernmost solution passing south of Gatlinburg, while the
GFS, ECMWF, and CMC keep the center north of I 40. That NAM solution
generates some mountaintop snows by 12Z Friday, so there may be some
accumulations above 5000 feet. Otherwise, the precip ends quickly
from the west Friday, lingering longest and lightly over the
Afterwards, high pressure will dominate the area for several days,
with dry and warming weather Saturday through Tuesday. The next
uncertainty is how long the ridge of high pressure can hold.
Troughing takes hold across the western U.S., and the next weather
system to approach us will eject out of that broad western trough.
The GFS is quickest with the onset of rain, impacting us late Tues
through Wed. But the ECMWF and CMC are stronger with our ridging and
keep us dry through next Wednesday night. So I`m just tossing in low
POPs for next Tues night through Wednesday night until we and
surrounding offices can lean more firmly one way or the other.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 59 64 46 56 39 / 90 40 20 10 10
Knoxville McGhee Tyson Airport, TN 60 69 45 53 35 / 90 80 60 20 10
Oak Ridge, TN 59 66 44 54 35 / 90 80 60 10 10
Tri Cities Airport, TN 55 70 42 52 30 / 80 90 80 30 10
TN...Flash Flood Watch until 8 AM EDT /7 AM CDT/ Thursday for Bledsoe-
High Wind Warning until 2 PM EDT Thursday for Blount Smoky
Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky
Mountains-Southeast Carter-Southeast Greene-Southeast
Area Forecast Discussion
National Weather Service San Francisco Bay Area
852 PM PDT Wed Mar 17 2021
.SYNOPSIS...Light rain will return to the region late tonight into
Thursday morning as a weather system approaches. Light to
occasionally moderate rainfall will become more widespread Thursday
afternoon as a cold front slowly moves southward and inland
across the region. While lingering rain showers may be possible
into Friday, drying conditions are likely to return and continue
into the upcoming weekend.
.DISCUSSION...as of 08:51 PM PDT Wednesday...Cloud cover is
increasing into the night as the next system approaches the
region. The mostly cloudy to overcast conditions will allow for a
warmer overnight temperatures with lows in the mostly in the 40s.
The main event tonight will be the initial chances for rain moving
into the North Bay in the late night. Higher-resolution models and
the local WRF place the first few showers in Sonoma Co between 2 to
3 AM and that rain moves into the San Francisco Bay around 5 AM.
Rainfall chances look to reach the Santa Cruz Mtns around that time
as well and slowly stretch into the Monterey Bay closer to sunrise.
Most of the rainfall rates look light through much of the late
morning but could increase into more moderate rates into the day.
Thursday afternoon offers a stronger band of rain around the
Monterey Bay. Some models are showing some local rainfall rates
increasing to as much as 0.40" an hour during that time, but
confidence isn`t high that these rates will last. While these rates
are below debris flow thresholds, this will be something operations
will examine closely through the afternoon.
Thursday evening`s rainfall will more focused on the northern
portions of the Big Sur coast. The HRRR and the local WRF show the
potential for rainfall rates reaching 0.30"-0.45" per hour along
higher elevations but this doesn`t look to be widespread. Luckily
these higher rates do not appear to cross into the Monterey Co burn
scars, but again will be something the forecaster team will keep a
close eye on.
Rainfall rates look to taper off into the late night with light
showers remaining well into Friday. The last few lingering rain
chances will move east and out of the area Friday evening, leading
into another dry trend. Rainfall totals over the next few days
remain consistent with what was mentioned in the previous discussion
.PREV DISCUSSION...as of 01:46 PM PDT Wednesday...Mid/high level
clouds have held temperatures down across the region this
afternoon with most locations still in the low/mid 50s. While
additional daylight may allow for a few locations in the interior
areas of the Central Coast to reach around 60 deg F, this will
likely be the exception. Thus, have lowered afternoon temperatures
for today by a few degrees. Look for temperatures overnight to be
warmer as well given the cloud cover overhead with lows Thursday
morning only dropping into the 40s for most areas.
The forecast remains on track for light rain to develop over the
North Bay and along the coast beginning after midnight and through
sunrise as moisture advects inland ahead of an approaching frontal
boundary. The latest thinking is that the cold front will drop from
north to south across the Bay Area Thursday morning and then down
across the Central Coast during the afternoon/evening. Southerly
winds will increase over the Pacific tonight ahead of this boundary
with breezy to gusty conditions possible along the coast and in the
hills into Thursday morning. Wind gusts of 25 to 35 mph will be
possible with the higher peaks potentially exceeding 45 mph. By
Thursday afternoon, a deeper plume of moisture is forecast to advect
inland over the Central Coast as the boundary drops southward. This
will likely result in more widespread moderate rainfall over the
Santa Cruz Mountains and Santa Lucia Range during the afternoon and
evening hours. This said, still not expecting excessive rainfall
rates which would trigger debris flows over recent burn areas.
Conditions will begin to dry out from north to south throughout the
day with lingering rainfall over the Central coast into Thursday
night before the boundary finally pushes south of the region. A few
showers may linger into Friday morning as well, yet most of the
region can expect drying conditions during the day Friday with
seasonably cool temperatures.
With this forecast update, have lowered rainfall amounts over the
North Bay and greater San Francisco Bay Area and increased them from
the Santa Cruz Mountains southward. Looking for rainfall totals from
Thursday through early Friday morning to range from 0.25"-0.50" for
most urban areas of greater San Francisco Bay Area with 0.50"-1.25"
in the coastal ranges and Bay Area Hills. There is the possibility
that rain shadowed Valley locations such as San Jose may only see
0.10"-0.25". To the south, 0.25" to 0.50" will be likely for most
urban areas with upwards of 1.00" for places such as Santa Cruz and
hills of the Central Coast. The greatest rainfall looks to occur
over the Santa Cruz Mountains and Santa Lucia Range where 1.00"-
2.00" will be possible. Lastly, snow levels at the time of
precipitation look to remain greater than 5,000 feet before lowering
below 3,000 feet on Friday once precipitation has ended. Thus, snow
is unlikely to be a concern with this weather system.
Dry weather and seasonably cool temperatures are likely for the
upcoming weekend. Overnight conditions will likely drop back into
the 30s for many interior locations, yet widespread freezing
temperatures are not expected at this time. A gradual warming trend
is then forecast to occur during the middle part of next week and
potentially into late next week as high pressure builds over the
region. The ensembles are in good agreement with the development of
this pattern along with dry weather conditions for next week.
.AVIATION...as of 05:00 PM PST Wednesday...For the 00Z TAFs.
Satellite imagery shows an approaching storm system over the
eastern Pacific with thickening high clouds arriving from the west
and patchy mid level clouds bringing 2500-3500 ft MVFR BKN-OVC
cigs near Monterey Bay and similarly heighten few-sct clouds
elsewhere. Radar imagery depicts light reflectivity returns
arriving with the high clouds in the warm sector but no ground
tips have been reported, thus it is falling as virga. With this
system, expect breezy to occasionally gusty south to southwest
winds, gusts roughly 20-25mph, MVFR cigs and visbys, and wet run
ways at times. Precipitation with the upcoming system will be
segmented out with the initial rain arriving late Wednesday night
into early Thursday morning. A secondary slug of moisture ahead of
the primary cold boundary will bring potentially mod to briefly
heavy rain for the Santa Cruz mountains regions beginning midday
Thursday afternoon before transitioning to focus on the Monterey
Bay terminals by late Thursday afternoon through Thursday evening.
Vicinity of KSFO...VFR with FEW to SCT at 2500 to 3500 ft this
evening as well as lowering/thickening high clouds at 15000 feet.
Winds will gradually weaken and back towards the south overnight
then increase to become breezy with occasional gusts 20 to 25mph
as the front nears through Thursday. For tonight, expect to see
continued VFR conditions until the pre dawn hours Thursday morning
as precipitation begins at roughly 12Z. Expect to see some periods
of improving conditions through the late morning to early
afternoon before another round of precipitation arrives Thursday
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Intermittent MVFR/VFR cigs through the
night, ie SCT-BKN, becoming OVC by the predawn hours of Thursday
morning. VCSH/-SHRA will begin around 12Z, accompanied by lower
MVFR cigs with occasional vis drops. Gusty S/SE winds for KSNS
around 12Z lasting through the period. A second slug of rain
arrives later Thursday and could bring borderline IFR/MVFR
conditions with mod to briefly heavy rain into the evening.
.MARINE...as of 08:47 PM PDT Wednesday...A storm system will move
across the coastal waters between late tonight and through the day
tomorrow. Southerly winds ahead of the front will increase
overnight, becoming breezy through the night, then strengthening
further to become moderately gusty, ie 25 to 30 kts, occasionally
up to 35 kts, by the predawn hours Thursday morning as the front
nears. Data indicates peak winds along the immediate coast will
occur through the sunrise hours then gradually taper off through
the day as the front pushes inland. These winds will generate
locally steep fresh southerly swell of roughly 8 feet at 8 to 10
seconds, creating hazardous conditions for small craft vessels
near the front. Otherwise, a light northwest swell today will be
replaced by a larger northwest swell of roughly 12 to 16 feet at
15 seconds on Friday.
.Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM
PUBLIC FORECAST: RGass/Murdock
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Updated for aviation forecast discussion.
.SHORT TERM...(Tonight through Friday night)
Issued at 331 PM CDT Wed Mar 17 2021
The enhanced risk of severe storms continues unchanged for areas
generally south of a Van Buren Missouri to Hickman Kentucky line.
That said, the prospects for bonafide surface-based instability
are dwindling. The warm front is just south of KMEM and arcs
northwest into northwest Arkansas. The southerly winds and some
tangible SBCAPE will eventually work eastward into southeast
Missouri late this evening, but by then the mid and upper flow
will back to nearly due south which makes it difficult to have
any significant shear to organize convection.
The latest HRRR indicates that we may see a few hours of relative
dry weather through 00Z as the current area of rain continues
northeast out of the area by 00Z. We are still expecting our next
round of showers and some storms to sneak up into southeast
Missouri around 00Z. This area is still expected to be elevated
and instability will continue to be meager. This area of
convection will push northeast through the evening with the same
general weakening trend we have seen with the two rounds so far
today. We will keep an eye on the environment this evening, but
severe weather is not looking very likely at this time.
As for the Flash Flood Watch, we will let it ride. It captured the
heaviest rains from earlier today, and they overlap the 1"
additional QPF through tonight. Any flooding should be very
isolated over southeast Missouri and southern Illinois. Am
somewhat concerned for the southern Pennyrile, where over an inch
of rain will be possible tonight, but they did not have nearly as
much earlier today.
The upper low will move east over the region Thursday. Cannot
completely rule out a rumble of thunder with it, but will settle
for just mentioning showers.
As the surface low passes by just to our north Thursday
afternoon, strong north winds will bring much cooler air into the
region Thursday night. Any lingering showers are expected to be done
by midnight, so there is no wintry concern at this time. However,
temperatures may reach freezing by daybreak Friday over much of
southern Illinois, so if the showers linger into the overnight
hours we may need to re-evaluate the wintry potential.
Despite plenty of sunshine on Friday, it will be much cooler with
highs only in the lower 50s. Much of the region may drop to
freezing Friday night with clear skies, light northeast winds, and
dewpoints well into the 20s.
.LONG TERM...(Saturday through Wednesday)
Issued at 331 PM CDT Wed Mar 17 2021
Surface high pressure will be centered over the northeast U.S. this
weekend as an upper level ridge builds over the middle Mississippi
and lower Ohio valleys. This will keep the PAH forecast area dry
Saturday through Monday. Temperatures will be near seasonal
Saturday and Saturday night with easterly winds, then winds will
become southerly by Sunday, resulting in gradually warming
temperatures Sunday and into the early part of the work week.
By Monday night, models show a surface low over the Central Plains.
This low will move slowly northeast due to the surface high pressure
and upper level ridging over the eastern U.S. Models are generally
on the same page and take the surface low northeast into the upper
Mississippi valley by Wednesday. At this point, model blends bring
showers into far western portions of the PAH forecast area Monday
evening, with chances spreading slowly east across our entire region
by midday Tuesday. Good chances of showers will continue across our
entire area Tuesday afternoon into Tuesday night as the cold front
moves across the PAH forecast area. Some of the slower model
solutions take even longer to get the front through our area, and
the blends account for this by lingering slight chances for showers
Due to various models timing differences with the movement of the
front, confidence is too low to include any thunder at this point.
As models come to better agreement, we could see some thunderstorm
potential across at least southern portions of our region at some
Temperatures will remain above normal into mid week as winds
continue from the south.
Issued at 633 PM CDT Wed Mar 17 2021
After the afternoon convection finally moved east of the area,
more showers and storms have already moved into parts of southeast
MO as of this writing. This will be the trend as we head into the
evening hours. The activity impacts southeast MO and far west
KY early in the period, will pivot northeast and impact the rest
of the terminals later this evening and overnight. There may be a
brief lull period as a sfc low moves across the area. However,
scattered showers will gradually return to the area Thursday. Cigs
will be MVFR in the convection and likely stay that way for the
majority of the period, except for possibly in that lull period.
Winds will be southeasterly but go through several changes in
direction as the surface low passes across the area overnight
tonight and into tomorrow.
IL...Flash Flood Watch through Thursday morning for ILZ075-076-
MO...Flash Flood Watch through Thursday morning for MOZ076-086-087-
KY...Flash Flood Watch through Thursday morning for KYZ001>006.
...Update to aviation forecast discussion...
Issued at 358 PM CDT Wed Mar 17 2021
A strong and dynamic system is expected to bring more rain, wind,
and even some snow to the area, resulting in an active next 18 hours
The upper low has been progressing northeast and is currently over
OK as of 2030Z, while the sfc low has been deepening throughout the
day and is centered over OK/AR at 1000mb. This leaves eastern KS on
the northwest side of the system with CAA and cloudy, misty
conditions keeping temperatures in the upper 30s to low 40s across
the CWA - not really having a chance to warm up much today. The next
batch of rainfall is on its way from southern and central KS and
should become more scattered to widespread across northeast and east
central KS later this afternoon and especially this evening. As the
upper low continues to lift northeast, colder air aloft wraps around
the back side of the system and results in more CAA, turning rain
over to snow from west to east overnight. What makes this
particularly concerning is this snow potential exists during periods
of stronger forcing with increasing mid-level frontogenesis within
the deformation zone. Hi-res models are picking up on snow banding
more easily than the GFS, as can be expected, but given the
potential for this set-up to produce snow amounts of 1-3 inches,
felt it was worth issuing a winter weather advisory for areas along
and southeast of a line from Council Grove to Topeka. Would not rule
out some locally higher amounts as well, which can be seen from SREF
plumes showing a mean of 3-3.5" for Topeka and Emporia. Little to no
accumulation is expected for areas northwest of the advisory.
Additionally, the strong pressure gradient puts us in a position to
see near advisory-level winds, although guidance varies on this
potential to some extent as well. The HRRR would suggest seeing wind
gusts around 40-45mph, whereas the RAP is not nearly as aggressive
and other guidance gives gusts around 35mph. Still, these kinds of
winds with wet snow are enough to present a concern for reduced
visibilities, which would also cause travel impacts. It should also
be mentioned that with surface temperatures so close to the freezing
mark and the colder air aloft, just a few degrees difference in
temperature will be crucial to whether certain areas see more rain
vs snow during the overnight hours.
As we head into the early morning hours of Thursday, also can`t rule
out some freezing drizzle or drizzle on the back edge of the system
as we lose saturation in the vertical profile, and therefore lose
cloud ice. As a whole, however, temperatures should warm up enough
through the morning and the better forcing should move far enough
east after sunrise to see diminishing impacts after the morning
commute. Temperatures should reach the 50s in the afternoon for
most, except perhaps the far east central areas which may see
lingering drizzle and cloudiness further into the day.
An upper ridge moves into the area late this week, bringing a return
to warmer and drier conditions to round out the work week and enter
the weekend. We see a return of temperatures in the 60s by Saturday
and lasting into next week, with the next upper trough bringing the
next chance of rain possible on Monday. However, differences in
timing between the models keeps low chance PoPs into
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 632 PM CDT Wed Mar 17 2021
Rain showers will continue to increase over the evening hours. This
rain will likely mix with or change over to snow for a time,
especially at KTOP/KFOE, before gradually ending by early morning.
MVFR and IFR visibility reductions are likely within the
precipitation, especially in any heavier snow. Ceilings will
continue to hover around the MVFR to IFR border overnight,
gradually rising to MVFR and eventually VFR during the day
tomorrow. Winds will remain northerly, sustained at 15 to 20 kts
and gusting 25 to 35 kts.
Winter Weather Advisory from 10 PM this evening to 9 AM CDT
Thursday for KSZ026-037>040-054>056-058-059.