Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/25/23
Area Forecast Discussion
National Weather Service Quad Cities IA IL
908 PM CDT Fri Mar 24 2023
.UPDATE...
Issued at 906 PM CDT Fri Mar 24 2023
Quick secondary update on headlines. Chicago has added LaSalle
county, and given the forecast and layout of headlines, I`ve added
Putnam to fill a visual hole in the hazard map.
Again, for us, it looks like our highest totals will be in
Whiteside and adjacent sections of Carroll County.
UPDATE Issued at 841 PM CDT Fri Mar 24 2023
The arc of rainfall lifting northward continues to slowly lift
north. This is handled well by the short term guidance, showing
light qpf falling through 06z tonight. However, models are showing
a rapid transition to snow in that axis, especially near the Quad
Cities and northeast by 06z. While that seems aggressive, there is
notable dry low level air in north central Illinois, with a pocket
of lower to mid 20s dewpoints in the vicinity of Rockford. The
small reservoir of drier air, is already allowing for a ice
pellet mix near Aurora via MPING reports. Thus, at least a mix
should be in place from the Quad Cities northeast well before the
time of maximum lift.
Regarding the period of maximum lift, with the deformation zone in
the 09z through 14z time frame, there is an indication that a
short period of very deep dendritic growth of 3-5 kft is possible,
along with the HRRR suggestion of thunder. I do think the Kuchera
accumulations are too bullish in lacking the compression of such
wet snow on warm ground, but the dendritic growth may allow for at
least an hour of 2+ inch per hour snowfall rates in the advisory
counties. The best signal for a longer duration of these rates is
in Whiteside and southeast Carroll counties. So, it`s posssible
should these trends develop, a overnight upgrade to a warning
could occur with amounts potentially in the 5-10 range there.
No changes on headlines this evening.
ERVIN
&&
.SYNOPSIS...
Issued at 309 PM CDT Fri Mar 24 2023
18z surface data has low pressure in southeast Oklahoma with a
frontal boundary into southern Missouri while high pressure was over
the Great Lakes. Dew points were in the 20s across the Great Lakes
and into the central and northern Plains with 30s and 40s from the
Ohio Valley into the southern Plains.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 309 PM CDT Fri Mar 24 2023
The current winter weather headlines have been expanded south and
east.
Dry air from the high over the Great Lakes will keep dry conditions
until almost sunset across the area. Around sunset rain from the
storm system will slowly move into the southern areas and expand
northward through midnight.
After midnight the rain will cool the atmosphere and force the rain
over to all snow in roughly a two hour period; the most likely time
frame being 2 to 4 AM.
The snow will be a very wet type and initially will melt on contact
with the warm ground and roads. However toward sunrise snowfall
rates are expected to increase to 1-1.5 inches per hour. Once this
snowfall rate occurs snow will begin to accumulate on grassy
surfaces. A slushy accumulation on the roads is expected as roadway
temperatures cool. Bridges and overpasses will have the best chances
of becoming slick and snow covered.
The snow will end from west to east Saturday morning with dry
conditions Saturday afternoon.
As for snowfall amounts there has been a slight shift to the east
with the axis of the heaviest snow. Additionally there will be sharp
gradients on the western and eastern edges of the snow axis.
The axis of the heaviest snow currently looks to be from just east
of the Quad Cities, through Sterling, IL and a little east of
Rockford, IL.
Amounts in the advisory area look to be 3-6 inches east of the
Mississippi and generally north of I-80. South of I-80 and west of
the Mississippi amounts of 1 to 3 inches are expected.
.LONG TERM...(Saturday night through Friday)
Issued at 309 PM CDT Fri Mar 24 2023
Cooler than normal through mid-week then above normal temperatures
with a significant storm system.
Saturday night
Assessment...high confidence
Quiet, dry and chilly conditions will be seen as high pressure moves
through the Midwest.
Sunday through Monday night
Assessment...medium to high confidence
An upper level disturbance followed by a weak storm system will move
through the area. The disturbance will bring some light snow or a
rain/snow mix to the area on Sunday. The weak storm system is
forecast to bring a rain/snow mix to the area Sunday night
followed by rain Monday into Monday night.
Right now the model consensus has slight chance pops Sunday, chance
pops Sunday night into Monday and then slight chance pops Monday
night.
Snow accumulations for either event look to be a dusting. At the
very worst localized 1 inch amounts are possible.
Tuesday/Tuesday night
Assessment...high confidence
Quiet, dry but cooler than normal conditions will be seen as high
pressure quickly moves through the Midwest. Attention then turns to
the significant storm system.
Wednesday through Friday
Assessment...high confidence on a storm system. Medium confidence
on timing
The global models bring a significant storm system through the area
and suggest that it will arrive in two parts; the first Wednesday
into Wednesday night and the second Thursday into Friday.
From a big picture view the two separate systems will pull much
warmer air into the area. The precipitation type looks to be all
rain with the warm air over the area and a potential for
thunderstorms. Temperatures will be slightly below normal on
Wednesday but will climb to above normal by Friday.
Right now the model consensus has slight chance to chance pops
Wednesday, chance pops Wednesday night and Friday with likely pops
Thursday and Thursday night.
Overall rainfall looks to be light to moderate but could be locally
heavy from thunderstorms.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 616 PM CDT Fri Mar 24 2023
MVFR conditions will rapidly advance over southeast Iowa and
northwest Illinois this evening, as rain spreads northward. This
rain will likely reach CID and DBQ by mid to late evening, as it
changes to wet snow there on arrival. There will be a period of
poor flying weather for southeast Iowa through Illinois tonight
through mid morning Saturday, a wet snow and rain system brings
IFR conditions, possibly LIFR in moderate rain, and for a time,
potentially heavy wet snow in the 08z to 14z time period. Winds
will be east this evening, then trend north overnight, but are not
expected to be strong. A trend towards VFR is expected as the
system moves away from the area Saturday between 14z west and 18z
along the Mississippi River. Farther west, from CID to DBQ, this
improvement will occur early, and there is some potential that
those areas remain VFR and dry through the event.
&&
.HYDROLOGY...
Issued at 903 PM CDT Fri Mar 24 2023
Have issued a Flood Watch for Moline and Joslin on the lower Rock
River basin. Still 48+ hrs away but given western shift to
heavier qpf axis now projected over the basin owing to moderate
confidence at this range to go ahead and issue. Still, uncertainty
in how much of the qpf falls as rain versus snow with influence on
runoff. The Flood Watch also remains in effect for La Moine River
near Colmar.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory from 4 AM to 1 PM CDT Saturday for
Clinton-Jackson-Scott.
IL...Winter Weather Advisory from 4 AM to 1 PM CDT Saturday for
Bureau-Carroll-Henry IL-Jo Daviess-Mercer-Putnam-Rock
Island-Stephenson-Whiteside.
MO...NONE.
&&
$$
UPDATE...Ervin
SYNOPSIS...08
SHORT TERM...08
LONG TERM...08
AVIATION...Ervin
HYDROLOGY...McClure
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
641 PM CDT Fri Mar 24 2023
...AVIATION UPDATE...
.UPDATE...
Issued at 632 PM CDT Fri Mar 24 2023
Issued update to expand fog coverage for tonight.
&&
.DISCUSSION...(This evening through Friday)
Issued at 355 PM CDT Fri Mar 24 2023
Key Messages:
* Messy pattern with mostly near to below normal temperatures this
weekend through early next week
* Small, but potent, shortwave could bring band of organized
showers and possibly a narrow swath of wet snow Saturday
afternoon into the overnight. However, confidence on exact
location remains low.
* A similar system could affect the area once again late Sunday
into Monday, but this is also low confidence.
* Return flow sets up middle of next week ahead of next upper
trough forecast to impact region Thu into Fri.
Forecast Details:
First day back on the forecast desk in quite some time and first
thing that struck me was how messy of a pattern we`ll be in
through Monday. Upper flow will be generally zonal/SWrly and
progressive, but one that is riddled with small, but potent,
shortwave troughs. Each of these will give us at least scattered
chcs for mostly light precipitation, including ongoing wave of lgt
rain over the S today, another round Sat aftn/night, and
potentially yet another wave Sun into Mon.
Ongoing wave has brought quite a bit of cloud cover for most
areas, and even some light radar returns to mostly far W and S
zones. Radar returns are likely a bit overdone relative to ground
truth, with a fair amount of this activity falling as virga (at
least on the leading edges), owing to cloud bases 6-9K ft, and sfc
RH 40 to 50 percent. Anything more than sprinkles will probably
limited to our KS zones, and even these areas probably only see a
few hundredths. This activity will weaken substantially by
midnight as the wave deamplifies and shifts E. Late overnight,
the same areas that received light precip today (far W/SW) could
develop some fog. Recent HRRR runs have backed off on the overall
coverage and N extent compared to last night`s 00Z/06Z runs...but
think clearing skies amidst light winds in areas that have seen
little to no mixing today do argue for the potential. Have kept it
patchy, for now, but evening shift may need to ramp up the wording
for at least SW quarter of CWA if current model output persists.
The next system is forecast by most models to arrive during the
afternoon and evening hrs Sat. Think any measurable pcpn prior to
18Z is pretty unlikely. Some of the initial activity Sat aftn may
even have a rumble or two of thunder given non-zero MUCAPE. There
continues to be indications that *just enough* cold air could be
present to switch rain over to wet snow, at times, most notably
into Sat night. Strong late March sun angle and air temps well
into 40s will make changeover to snow prior to sunset Sat eve very
difficult. However, loss of daytime sun/heating and modest CAA
could allow for at least W zones to change over to wet snow after
sunset. Some hi-res guidance suggests a bit of convective element
to the precip Sat aftn into Sat night that could enhance snow
rates enough to get some slushy accums around 1" in relatively
narrow swath, but 2" and 4" soil temps in the low to mid 40s,
along with only 3-5 hr window for more than modest snw rates, will
make widespread accums more than this pretty difficult.
Furthermore, confidence on where this band of enhanced pcpn is not
exactly high as models range anywhere from our N (NAM/GFS), to
central (HREF/RAP/HRRR), to KS zones on Canadian/EC. Tend to
prefer a more central or southern solution at this time. Even the
most aggressive output suggests peak pcpn/snow amounts will only
be about a county wide.
Best pcpn chcs should shift E Sun AM, but with the messy pattern
in place at least slgt chc PoPs will continue into the day Sun.
Models vary widely with respect to timing of next wave, anywhere
from Sun eve start time to not until later in the day on Mon.
Regardless, the system will probably be similar to Saturday`s in
that initial rain may mix with and change to wet snow, but amounts
remaining on the light side.
Cool conditions continue through early next week, but at least dry
conditions should return for Tue and Wed. Return flow will set up
Wed into Thu ahead of potentially more organized upper trough late
next week. However, confidence on details is low attm given usual
weak/quick bias of GEFS relative to EPS. Wed looks to be the
warmest day with highs in the mid 50s to upper 60s. NBM guidance
is wildly variable on Thu, with nearly 25-30 deg spread between
just the 25th and 75th percentiles. The temp spread in guidance
argues for strong system, but QPF output is not overly impressive
as brunt of positive PWAT anomalies and shunted S/SE of the
region...unfortunately.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday)
Issued at 632 PM CDT Fri Mar 24 2023
Winds are expected to become southeasterly then switch to the
southwest around 06z. A northerly wind shift is expected around
15z with winds becoming northeasterly by the afternoon. Low
ceilings are expected beginning around 09z to 10z and continuing
until 14z to 15z. Fog is also possible during this time but
confidence is low.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
UPDATE...Schuldt
DISCUSSION...Thies
AVIATION...Schuldt
Area Forecast Discussion
National Weather Service Grand Rapids MI
1019 PM EDT Fri Mar 24 2023
LATEST UPDATE...
Update
.UPDATE...
Issued at 1019 PM EDT Fri Mar 24 2023
Recent runs of the HRRR and NAM-Nest lend enough confidence that
Osceola county is likely to see the same amounts and impacts as
the other counties already in the warning, so have expanded the
warning in that regard. Have also extended the end time of the
headlines to 8 PM Saturday to account for lingering light snow but
mostly the strong winds on the back side of the low pressure
system. Concern is that any locations (especially in the warning)
which remain cold enough to keep the sticky snow on trees during
the day may be at increased risk of power outages at the tail end
of the event.
Farther south, expectations are mostly the same for a wintry mix
including a tenth of an inch of glaze possible (especially in
southern Newaygo to Montcalm). This storm is reminiscent of Feb
27 in terms of track, strength, and precipitation (liquid water
equivalent) amounts, though temperatures at the surface are
perhaps less supportive of freezing rain this time. Northern Kent
and Ionia counties are worth a mention of freezing rain possible
early in the morning but not confident enough to include them in
the advisory.
Due to marginal temperatures both at the surface and a few
thousand feet aloft creating challenges ascertaining precipitation
types, and considerable spread in the models leading into this
event, confidence in the forecast is lower than usual.
Nonetheless, precip (water) amounts of an inch or more falling in
about 12 hours has the potential to be impactful even this late in
the season.
&&
.DISCUSSION...(This evening through next Friday)
Issued at 330 PM EDT Fri Mar 24 2023
-- Winter Weather Tonight through tomorrow --
Bottom line up front...Have upgraded the watch area to a warning
for Mason, Oceana and Lake Counties. Have issued an advisory for
Osceola, Lake, Mecosta, Isabella, Newaygo, Muskegon and Montcalm.
As the forecast has evolved for this system, there have been
major questions on timing and intensity. The biggest concern will
be heavy snow along the US 10 corridor and in Oceana county as
the low tracks northward. Upwards of 6 to 10 inches will be
possible. Snowfall rates of an inch per hour will be possible
between 12Z to 18Z tomorrow. While Osceola and Lake counties are
on the fringes, they could have higher amounts through their
northern halves. Based on latest guidance have left them out as
the biggest snowfall rates and ratios will be further north and
west.
Freezing rain is expected along a corridor that includes
Muskegon, Newaygo, Mecosta, Isabella and Montcalm counties. There
will be a region where the low level jet will bring in warmer air
aloft. Couple this with cold SFC temperatures and periods of
freezing rain will be possible with the greatest ice accumulations
of 0.10-0.20 with a glaze or more possible north of I-96. Areas
near and north of Rockford in Kent county could see ice
accumulations up to a tenth of an inch.
Along and south of the I-96 there could be a brief period of
Freezing rain but temperatures will be very marginal. Overnight
lows through this area will be above freezing so while locally
there could be spots overall it will be primarily rain.
-- Periods of Heavy rain with Gusty winds through SE--
Periods of heavy rainfall are possible south of the I 96
corridor with ponding on roadways possible but no flooding
expected.
Out ahead of the cold front will be a Low Level jet that will
bring gusty winds upwards of 30 to 40 mph. The highest wind gusts
will be southeast of Jackson with gusts of 40 to 45 mph possible.
Have left the region out of an advisory for now but expect the
gustiest winds to be Saturday afternoon.
The upper level low that will bring the above weather will exit
to the northeast Saturday night into Sunday. Expect cold
convergent flow to move into the region Sunday.
-- Chance of Precipitation early next week --
A weaker system looks to clip the southern portion of Michigan
early next week but there is great disparity in the mid to long
range models.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 835 PM EDT Fri Mar 24 2023
Numerous challenges/hazards for aviation the next 24 hours as the
center of a strengthening low-pressure system tracks through lower
Michigan on Saturday. The forecast for winds, ceilings, vis, and
types of precipitation lean on a blend of today`s higher
resolution models (12Z HREF) with preference to the 18Z HRRR which
has proven to work reasonably well at this lead time for the last
several storm systems over the past month.
Between 06 and 12 Z, ceilings will drop quickly to IFR from south
to north as precipitation begins. For the first several hours,
precipitation may be a mix of ice pellets or freezing rain at or
just north of MKG and GRR. Mostly snow with LIFR to VLIFR vis is
expected for a large part of the daytime at and north of LDM, RQB,
and MOP. For AZO, BTL, LAN, and JXN, surface temperatures should
be barely warm enough for rain during the early hours of
precipitation though there may be an icing layer between 1000 and
2000 feet until 12Z.
As the center of low pressure approaches and passes by the vicinity
of many TAF sites between 11 and 15 Z, expect periods of 30 knot
LLWS below 2000 feet, wind shifts, and for some locations
temporarily light and variable winds at the surface (keep in mind
the LLWS). West winds strengthen with gusts 30 to 40 knots over
much of the area after 18z with a changeover to snow in the
remaining holdouts before precip diminishes around/after 23Z.
&&
.MARINE...
Issued at 330 PM EDT Fri Mar 24 2023
While the gusty easterly flow will be offshore it will be strong
enough to reach SCA criteria tonight into tomorrow. So have issued
an SCA until tomorrow.
The bigger concern will be the gusty winds upwards of 30 to 40
kts along and behind the frontal boundary that could bring Gales
to the entire lakeshore tomorrow. Based on that have gone with a
Gale watch from Saturday morning through Saturday night. The
gradient will be strong enough and all the high res models are in
fair agreement.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning from 4 AM to 8 PM EDT Saturday for
MIZ037>039-043.
Winter Weather Advisory from 4 AM to 8 PM EDT Saturday for
MIZ040.
Winter Weather Advisory from 2 AM to 8 PM EDT Saturday for
MIZ044>046-050-051.
LM...Small Craft Advisory from 2 AM to 11 AM EDT Saturday for
LMZ844>849.
Gale Warning from 11 AM to 10 PM EDT Saturday for LMZ844>849.
&&
$$
UPDATE...CAS
DISCUSSION...Ceru
AVIATION...CAS
MARINE...Ceru
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1013 PM EDT Fri Mar 24 2023
.SYNOPSIS...
A line of showers with embedded thunderstorms will cross the area
overnight into mid-day Saturday. Dry and warm weather will return
for Sunday. Rainfall chances return Monday and Tuesday as a warm
front approaches from the south.
&&
.NEAR TERM /THROUGH SATURDAY/...
As of 1000 PM EDT Friday: The forecast continues to be in good
shape. Convection can be seen organizing into more of a linear
mode as it crosses western TN and MS. This is as expected. This
activity is still progged to enter the Smokies in the 4 to 5 am
time frame, likely on a weakening trend, but may be strong. This
seems to be well-handled in the grids, so no significant changes
were needed with this update.
A shortwave trough will eject from the Southern Plains into the
Mid-MS Valley tonight as it takes on a negative tilt during this
transition. As the shortwave enters the OH Valley by daybreak
Saturday, an attendant cold front will swing into the area from the
west. CAMs continue to produce a robust line of storms as the main
frontal zone enters the western fringe of the CFWA overnight, where
the best upper forcing will be available with this event. There`s
not much SBCAPE to work with despite great vertical wind shear with
a LLJ on the order of 50-60 kts. CAMs continue to weaken this line
as it moves across the mountains, but enough MLCAPE (100-500 J/kg)
along this main line will be enough to support a straight-line
damaging wind threat. The low-level flow will remain unidirectional
and straight-line hodographs indicate that any tornado threat is
almost nonexistent. Still, effective SRH values in the 0-500m
layer could allow for a quick spin up tornado embedded within
the line of storms if a bowing segment can develop. Otherwise,
expect this line to gradually weaken as it pushes across the
area from overnight tonight in the mountains through the Piedmont
zones around daybreak Saturday into the mid-morning hours in the
far eastern zones, near the I-77 corridor. Based the timing of
PoPs along this line with the HRRR and HRW-FV3. The line will
be quick-moving, so a hydro threat will be very low-end, but
localized 1.00"+ QPF amounts can`t be ruled out in locations
that get stuck under strong thunderstorms. Generally speaking,
most locations should receive between a tenth to a half an inch,
with even lesser amounts further east (I-77 corridor) as the line
of storms will be its weakest in this area.
Dry air entrainment will quickly filter in following the fropa as
gusty winds develop late Saturday morning into Saturday afternoon,
while the synoptic cold front enters the area a few hours following
the main line of storms. With deep mixing and very gusty winds
at the top of the boundary layer (~775-725 mb), went ahead and
issued a Wind Advisory for all mountain zones that will be in
effect from midnight tonight through 00Z Sunday. Gusty winds will
also impact the Piedmont zones, but confidence wasn`t high enough
to warrant a Wind Advisory. Otherwise, Saturday afternoon should
be nice regarding the sensible weather as the clouds scatter out
and good insolation hits the surface. Expect temperatures to run
10-15 degrees above normal, despite a cold fropa. Last thing,
a Fire Danger Statement has been issued for the NC Piedmont zones
along the I-40 corridor as dewpoints should mix out very quickly
behind the main frontal zone and gusty winds will help dry up
fuel moisture levels as well. With lower QPF amounts forecasted
in this area, decided that under the consideration of the alluded
parameters and approval from NCFS, a Fire Danger Statement was
warranted for these locations.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 145 PM Friday...A break in active weather is on tap for Sun as
flat ridging aloft dominates the pattern. This will allow for a
transient sfc high to track northwest of the FA and helping to
maintain a relatively dry airmass. Surface td/s will mix out into
the 30 percent and perhaps even a little lower, which could make for
afternoon fire weather concerns mainly for NE GA. Things begin to
change Sun night as embedded h5 s/w energy traverses the flow and
instigates a sfc trof along and north of an existing stationary
bndry while lifting it north as an active warm front into mid-day.
The NAM looks a little too energized with this system and develops a
rather stout sfc low and thus higher QPF amts. This idea was
tempered down with a blend of the more conservative GFS/CMC solns.
Still, expect a decent amt of rain across the srn zones of around an
inch where convective enhancement will be possible. The precip gets
shunted south during the afternoon as a well agreed upon sfc high
and suppression works in from the northwest. High temps will be arnd
80 F Sun and a little tricky Mon depending on possible lingering
cloud cover south. But for now, anticipate maxes reaching abt 10
degrees abv normal. Mins will remain well abv normal thru the period
with lows held in u50s to arnd 60 F most locales.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 225 PM Friday...The pattern becomes a little uncertain Tue as
srn stream energy is progged to push in from the west and interact
with an existing sfc bndry to the south. The models disagree
sigfnt/ly with the amt of llvl moisture and dyno lift and therefore
the scope of areal precip coverage, esp the likelihood of measurable
precip making it north into the FA. So, have maintained the low
chance PoPs for now as models such as the 12z GFS are quite dry and
suppressive during this time. Strong high pressure shud return to the
area Wed and slowly crosses to the southeast thru Thu. Deeply dry
air will accompany this feature and no good chance of rain will be
had until late Thu into early Fri. The guidance is in decent
agreement with the synoptic pattern late week, which features strong
cyclogenesis across the MS Valley swinging a moist warm front over
the FA then warm sector convec activity during the day on Fri. Will
have time to work out the details of this possible system over the
next few days. Temps will generally remain around normal levels thru
the period with some drop off below normal possible on Wed with a cP
airmass mixing in.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: VFR conditions to start out the 00z TAFs. A
cold front will push a line of showers and thunderstorms from west
to east across the area in the roughly 09z-15z time frame. Gusty
winds, lower visibilities, and MVFR cigs will all be possible
with this line of storms and is represented with a PROB30 at all
terminals. The line will lose intensity as it crosses the mountains
and pushes into the Piedmont, but high-res guidance shows enuf
structure that TS seems warranted at all TAF sites. Gusty southwest
winds will pick up right ahead of the line and continue through
the end of the TAF period. Clouds will scatter out behind the
front by early aftn.
Outlook: Moisture returns Sunday into early next week. This
may result in another period of associated restrictions at area
terminals. Dry high pressure returns the middle of next week.
&&
.FIRE WEATHER...
A deeply dry airmass will work into the area Sat behind a cold
front. Mixing heights rise quite deep and tap into strong wind
energy which will translate fairly strong and gusty winds to the sfc
across the area. Surface dewpoints will also mix out and allow for
RH values into the lower 30 percent range. After coord with NC land
managers, it was decided a Fire Danger Statement will be beneficial
for the NC Piedmont zones Sat afternoon where small fuels and
brush will likely remain the driest.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Wind Advisory until 8 PM EDT Saturday for GAZ010-017.
NC...Wind Advisory until 8 PM EDT Saturday for NCZ033-048>053-058-
059-062>065-501-503-505-507-509.
Increased Fire Danger from Saturday afternoon through Saturday
evening for NCZ035>037-056-057-501>506.
SC...Wind Advisory until 8 PM EDT Saturday for SCZ101>103.
&&
$$
SYNOPSIS...SBK
NEAR TERM...ARK/CAC
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...ARK
FIRE WEATHER...SBK
Area Forecast Discussion
National Weather Service Indianapolis IN
949 PM EDT Fri Mar 24 2023
.Forecast Update...
Issued at 948 PM EDT Fri Mar 24 2023
- FLOOD WATCH remains in effect for much of southern Central Indiana
- WIND ADVISORY remains in effect late tonight through mid Saturday
Afternoon
- Rain overnight; Heaviest Rains south of I-70.
Surface analysis this evening shows low pressure in place over SE MO
and NE TN. A warm front extended east across TN from the low, while
a cold front was found along the Mississippi River Valley. Central
Indiana remained within the cool sector with moist easterly flow in
place. Aloft, water vapor showed a trough in place over the Rockies
with ridging in place over the middle Atlantic states stretching
north into Ontario. This was resulting in SW flow aloft flowing into
the Ohio Valley. Deep moisture was seen ahead of the broad trough
streaming north through the Mississippi and Ohio Valleys, ahead of
the surface low. Regional radar shows a large shield of
precipitation over southern IL, entering southern Indiana, with
stronger storms across western TN and Mississippi. 3 hour precip
observations across Central Indiana have generally been less than
one-third of an inch.
Overnight the surface low is expected to push northeast along the
Ohio River. This will keep Central Indiana within the cool sector,
but in a favorable location for some heavier rains on the north side
of the low path. HRRR pushes the heavier rains over southern IL
across Central Indiana through 06Z-08Z. Forecast soundings concur
with a saturation column overnight with pwats reaching over 1 inch.
Thus the ongoing flood watch appears on track as more heavy rains
will be possible overnight, resulting in areal flooding Will use 100
pops for most pops overnight, but pops will rapidly fall toward
daybreak as the low passes east and dry air begins to intrude into
the system. At that time a strong pressure gradient will begin to
develop across Central Indiana in the wake of the low. This will
allow for the beginning of impacts covered by the Wind Advisory.
&&
.Short Term...(This evening through Saturday)
Issued at 302 PM EDT Fri Mar 24 2023
Primary short term weather concerns are (1) flooding with the second
round of rain this evening/tonight (2) strong wind Saturday.
A deepening mid-latitude system with in dominant southern stream
will interact with a significant subtropical moisture connection to
bring another period of moderate to heavy rainfall to the region. At
midday, a stationary synoptic front was located near the Ohio River
with relatively cool/moist conditions north of the boundary,
including fog and drizzle. Once the system moves closer later today,
deep isentropic ascent will increase (maximized near the 305-K
surface), and rain will fill in north of the synoptic boundary.
See the hydrology section below for more details, but we are
accepting an HREF mean for QPF which generally confines heavier
amounts across southern Indiana. This will be where the primary
flood risk is and for this reason we will cancel the northern
portion of the Flood Watch and continue the southern sections
(generally south of I-70). Although ensemble members have a few
outliers for heavier amounts over the I-70 corridor, this seems low
probability, and often dynamic PV readjustment from intense
convection to our south will favor the southernmost QPF footprint in
our region.
Most of the warm advection-driven rain should move east of the area
during the night with models showing dry conveyor belt moving over
central Indiana thereafter. This scenario usually still yields
drizzle due to low-level saturation and convergence/ascent, but
rainfall intensity and amounts will decrease by then. There may be
just enough instability for some thunder, but most of the
deeper/intense convection will be confined to the frontal band just
south of our area. However, we`ll need to watch two aspects of the
convection potential. 1. The potential for a slight northward shift
of the more pronounced warm sector into our southern counties such
that deeper more intense convection and an attendant wind threat
reach our southernmost counties early tonight. This is a low
probability, as the most likely scenario should be for this
convection to outpace northward surging moisture/instability, and
thus weaken over our area. 2. Scattered convective cells early in
the morning behind the aforementioned band, due to steepening
midlevel lapse rates atop a still moist PBL. This scenario could
lead to a peak in conditional instability, and would at least drive
scattered convective showers. Given strong winds aloft, these may
enhance already windy conditions driven by the tightening MSLP
gradient.
In fact, we issued a Wind Advisory earlier for the pre-dawn hours
into Saturday afternoon given a consistent signal for post-cold
front MSLP gradient-driven winds, augmented by modest amount of
mixing. 45 mph gusts seem probable, and briefly higher possible.
&&
.Long Term...(Saturday night through Friday)
Issued at 302 PM EDT Fri Mar 24 2023
* Seasonable With Light Rain Chances At Times Through Wednesday
* Potential For More Significant Rainfall Again Late Next Week
Mostly quiet conditions are expected early in the period as weak
surface high pressure builds in behind the departing surface low
that is expected to bring another round of heavy rain tonight. The
weak surface high should move east on Sunday with return flow
helping to advect some moisture into the area. A weakening shortwave
moving through may produce isolated showers during the day, but
confidence is low due to marginal moisture and overall forcing.
There is a better chance for showers late Sunday into Monday morning
as a second shortwave trough with an associated weak surface low
moves through. However, the gulf will remain cutoff which will limit
moisture return ahead of this system and precipitation totals. Most
areas will only see QPF amounts around a few tenths of an inch at
most. Mundane weather returns through midweek with upper ridging and
surface high pressure building in.
A deepening trough across the western CONUS is expected to bring
more active weather to the region late next week. Increasing
moisture/warm air advection could bring precipitation into the area
by Wednesday night. The better chance for rain likely arrives later
in the week as a developing surface low over the plains approaches
the region. Guidance suggests increasing southerly flow will help
advect anomalous moisture into the area. This along with increasing
dynamics may bring another 1 to 2" rainfall event to the area.
Although a lot of uncertainty still remains in regards to exact
timing, strength, and track of the surface low which could
significantly impact rainfall amounts. Expect confidence to remain
low until models are in better agreement.
&&
.Aviation...(00Z TAF Issuance)
Issued at 652 PM EDT Fri Mar 24 2023
Impacts:
* IFR to LIFR visibility and ceilings expected overnight and into
Saturday morning.
* Steady rain arriving and persisting through the evening and early
overnight hours, particularly at HUF, BMG and IND.
* Moderate winds begin early Saturday.
Discussion:
Cool and moist NE flow will continue across the TAF sites this
evening as low pressure moves along the Ohio River. Radar shows a
rain shield associated with this feature over MO/Arkansas and
southern IL poised to push northeast within the flow across Central
Indiana. Based upon progression of the system, highest precip
amounts and heaviest rain should remain across southern parts of
Central Indiana. Nonetheless...IFR Cigs are expected to remain
across the TAF sites as the surface low passes to the south.
Forecast soundings and time heights are on board with this as
saturation remains within the lower levels.
As the low departs on Saturday, cigs are expected to improve to
MVFR, but a stronger pressure gradient is expected to develop,
leading to gusty winds persisting much of the day.
&&
.Hydrology...
Latest HREF probability match-mean QPF has widespread >0.75" amounts
across central Indiana with >1.5" amounts confined generally to
southern Indiana. There are a few outlier members (i.e., NAM nest)
that bring ~1.5" amounts further north toward the I-70 corridor, but
since this is a low probability scenario we will re-align the Flood
Watch to fit this latest data.
Intensity may be enough for tributary and some overland flooding
later tonight into early Saturday especially near and south of I-70,
roughly. This is where previous rainfall has saturated soil to the
point 3-hour flash flood guidance is near or below one inch.
MMEFS ensembles for main stem river levels show that widespread
minor to moderate river flooding is likely, particularly across the
White River and lower Wabash basins. OHRFC operational forecasts
confine the moderate flooding to the lower White, Mount Carmel on
the Wabash and Seymour on the East Fork White, with minor flooding
for the rest of the these basins and the upper White remaining below
flood stage. This is based on the southward trend of the heaviest
precipitation and is the most likely scenario. Should one of the
outlier members mentioned above play out, the flooding threat will
increase and moderate flooding further north would be more likely.
River flooding is expected to continue into next week, cresting
early-mid week on most main stems and perhaps not until late week on
the lower Wabash.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 4 AM to 5 PM EDT Saturday for INZ030-031-
036>042-044>049-051>057-060>065-067>072.
Flood Watch until 8 AM EDT Saturday for INZ051>057-060>065-
067>072.
&&
$$
Update...Puma
Short Term...BRB
Long Term...Melo
Aviation...Puma
Hydrology...CP/BRB
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1110 PM EDT Fri Mar 24 2023
.UPDATE...
Issued at 1110 PM EDT FRI MAR 24 2023
Eastern Kentucky is essentially shower-free as of 3z, as the
focus turns to upstream convection ahead of a pressing cold front.
The wavering boundary across Eastern Kentucky today has slowly
drifted back north, currently residing across the northern 2/3rds
of the CWA per the latest surface obs/analysis. CAMs suggest the
upstream line of showers and storms to weaken east as instability
dwindles with time. That said, RAP soundings along with other high
res guidance suggests limited 100-300 J/kg of MUCAPE across
mainly the southwestern third of the CWA into the overnight. This,
tied with an increasing (45-60 kt) LLJ and sufficient shear,
could pose an isolated risk for strong storms/bowing features-
particularly if the current Middle TN storms can sustain
themselves enough as they meander northeast. Have updated PoPs
based on the latest CAM and radar trends, along with minor tweaks
in sky grids. Lastly, have refined T/Td/Wind grids by loading and
blending in the latest obs. Updated grids have been sent to NDFD
and Webfarms.
UPDATE Issued at 850 PM EDT FRI MAR 24 2023
Showers have generally diminished across Eastern Kentucky as of
this hour, as the wavering frontal boundary builds back north as a
warm front. Have refined PoP grids, along with sky grids, to
better reflect the latest rad/sat trends. Have also blended in the
latest high resolution guidance for PoPs through the overnight
along and ahead of the approaching cold front. Additionally, have
refined hourly T grids to account for the north to south gradient.
Where denser clouds and more persistent rain occurred this
afternoon, temperatures were running cooler than forecast and much
cooler than locations nearer to the Tennessee border. Outside of
these tweaks, Td and wind obs were also loaded and blended.
Updated grids along with a fresh set of zones with the changes
have been sent.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 455 PM EDT FRI MAR 24 2023
JKL has endured round 1 of this ongoing system today, now for round
2 overnight. An upper level low and trough is located across the
Central Plains this afternoon, and should continue to push towards
the Mid-Mississippi Valley overnight. Given a strong upper level
ridge in place just off the Florida Coast, which isn`t budging, the
pressure gradients between the two systems will substantially
increase throughout the night and into the day tomorrow, once the
low makes it to the Lower Great Lakes.
At the surface, a cold front has now stalled from west to east
across the state through much of the day, mainly affecting the
northern half. A surface low pressure system is currently located
across the Southern Plains, becoming phased with the upper level
low, and continuing to push farther northeast towards the Mid-
Mississippi Valley and then the Lower Great Lakes by tomorrow morning.
This system will gain considerable strength as it makes this
transition, deepening from a 1004 mb low this afternoon, to a 986 mb
low by Saturday afternoon/evening (according to the latest ECMWF).
This strong of a pressure change is also indicative of increased
winds along this system.
During the day today, the stalled front brought rain to much of
eastern Kentucky. The original thought was that the far southeast of
the state would remain relatively dry, with most of the moisture
focused from west to east along the stalled boundary. However,
mother nature played a little game, and brought a decent line of
showers and embedded thunderstorms oriented from SW to NE across the
eastern half of the state, resulting in updates to pops throughout
the morning and early afternoon.
Now, as we head into the late afternoon hours, the moisture is
becoming more confined to the frontal boundary in the northern
portion of the CWA, while the SE is drying back out. Shower and
thunderstorm coverage is also ramping back up across western KY, as
the surface low begins to near them from the west. Heading into the
overnight, as the surface low continues to track northeast, this
stalled front will quickly lift back north as a warm front. This may
bring a period of drying conditions across eastern KY once the front
moves north out of the CWA, at least for a few hours. It won`t last
long though, as the next cold front then sweeps through the state on
the tail of the quick-moving low.
Showers and embedded thunderstorms are expected along and just ahead
of the frontal boundary, passing through eastern KY generally
between 5 and 12Z overnight. SPC has kept the better severe risk
more to our southwest, though a portion of the slight risk and 2%
tornado risk make their way into our far SW counties, west of I-75.
Ultimately, instability doesn`t look that great across this portion
of the state, especially as we head into overnight and lose even
more heating. Very little CAPE exists. The concern, however, is the
amount of wind being generated through the atmosphere with this
system, and the ability for it to gust down to the ground with any
shower or thunderstorm that develops. The 2% tornado risk is caused
likely to do more with the amount of low level wind sheer and
potential twisting in the 0-3km, vs. the actual instability present
to allow for lift and long-lived/organized storms.
Just behind the front, models are still showing strong evidence of a
llvl jet setting up across the central and eastern portion of the
state, along with a jet streak in the upper levels shortly
thereafter. There is just so much wind with this system. By the time
the front moves though, within an hour or two, we will lose the
overnight inversion in the lowest levels, and will begin mixing
stronger winds down to the ground. It`s unusual to see an inversion
break between 9 and 12Z, but all signs lead to it happening. Much
drier air entraining in behind the departing system won`t help
things either, as this allows for better mixing. Winds will start
gusting across eastern KY as soon as the front moves through - as
early as 8Z in the western CWA. They will continue to gain strength
throughout the early afternoon, with peak gusts still between 40 and
45 knots in the northern portion of the CWA, and between 35 and 40
kts elsewhere (especially on the ridgetops). It was no surprise that
Wind Advisories began getting hoisted for multiple NWS offices today
ahead of this wind threat. After collaboration, LMK (along with IND)
was in agreement in our earlier onset for the NWP, with ILN and RLX
delaying their start time a bit given their location farther north
and east. The wind advisory will begin at 8Z and continue through 0Z
Saturday. It is possible that we could lose the best pressure
gradients a few hours before 0Z, and highest gusts may begin to
subside - but would rather have it out just in case and cancel if
need be, verses having to extend it for just a couple hours.
Otherwise, for Saturday, conditions should be quite nice - albeit
windy. High pressure will develop and settle over the state by that
evening and overnight. This high pressure will also be concurrent
with a llvl inversion, preventing any stronger winds aloft from
being able to make it down to the surface from that point forward.
Skies will clear out throughout the day Saturday, and rain chances
will come to an end. A couple of the CAMs do try to bring in a few
small showers, likely from wrap around moisture, into the state
during the day. However, there is little confidence in this. Did
include some slight chances in the far SE high-terrain given
lingering moisture and strong upslope flow, along with stronger
agreement amongst the CAMs.
With clear skies and high pressure in place, did include a bit of a
ridge/valley split for Saturday night, though not much. Winds aloft
will still be honking - the jet streak will actually be
strengthening across the Ohio Valley, advecting WSW flow into the
region. So without the CAA, and subsidence through the column, it
will be interesting to see just how much some of the deeper valleys
can drop. Temperatures should range from the upper 30s to the low
40s.
.LONG TERM...(Sunday through Friday)
Issued at 340 PM EDT FRI MAR 24 2023
A ridge of high pressure will bring dry weather to eastern to
begin the extended period on Sunday. After that, we can expect
periods of scattered rain showers to affect the area, as a series
of upper level disturbances move across the eastern third of the
CONUS. In general, temperatures will be above average, with highs
on the warmest days topping out in the upper 60s to lower 70s. THe
coolest days will be Tuesday and Wednesday, when we should see max
values in the upper 50s and lower 60s. These cooler temperatures
will be attributed to widespread cloud cover, scattered rain
showers, and cooler air that will all be associated with a passing
upper low. After a brief period of dry weather Tuesday night
through early Thursday morning, another bout of soaking rain may
occur to end the week, as another area of low pressure and its
surface cold front push through the region. Winds will pick up and
be quite gusty during the passage of the end of week weather
system. We may see some frost, especially in valleys, late Tuesday
night into early Wednesday morning, as temperatures fall into the
low to mid 30s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 850 PM EDT FRI MAR 24 2023
Showers have started diminishing across most of Eastern Kentucky
as of TAF issuance, allowing most sites to begin in the VFR
category. That said, where there is more consistent activity nearer
to the boundary, MVFR CIGs are in place and even brief visibility
reductions for SYM. As the boundary builds north as a warm front
into the night, all sites will return to VFR. As this occurs,
winds aloft will increase as a strong low level jet takes shape
across the area. LLWS of 35 to 45 kts will be possible for a few
hours (generally 4z-9z), before an approaching and passing cold
front allows for showers and storms into Saturday morning and the
better mix down of these winds. Guidance was optimistic through
the night, where low end VFR is possible, but dips to MVFR or
lower can`t be ruled out within heavier showers or storms. Post
front, VFR will prevail with CIGs increasing and cloud coverage
thinning overall through the day Saturday. As surface winds
increase along and behind the front late tonight, sustained values
of 15 to 25 kts and gusts between 30 and 40 kts should be
expected into Saturday morning through the afternoon. These will
slacken toward the end of the period and into Saturday night.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday morning for KYZ044.
Wind Advisory from 4 AM to 8 PM EDT Saturday for KYZ044-050>052-
058>060-068-069-079-080-083>088-104-106>120.
&&
$$
UPDATE...BB
SHORT TERM...JMW
LONG TERM...AR
AVIATION...BB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
923 PM CDT Fri Mar 24 2023
.UPDATE...
Issued at 923 PM CDT Fri Mar 24 2023
Couple tweaks to going forecast, mainly to expand the winter storm
warning a tier of counties south and adding a few counties into an
advisory.
Very little to add to the very well written and informative
afternoon short term AFD below. Satellite imagery this evening is
a text book example of cyclogenesis. Pronounced mid level dry
intrusion and attendant plume of steep mid and upper level lapse
rates adjacent to the blossoming TROWAL over northern Missouri
really is a classic set-up for convective snow and possible
thundersnow Saturday morning. Have introduced slight chance of
thunderstorms into the grids over northern IL 09-15z.
Trend in hires guidance has been upward this afternoon and early
evening with QPF and given PWATs (nearing 3/4") getting about as
high as they can get with snowfall, hard to dispute the higher
QPF. The HRRR modeled snow depth (which accounts for compaction
and melting) has been trending upward as well (this is different
than the 10:1 and Kuchera method snowfall forecasts) with max
accums over 10" within the band of heavy snow. This HRRR product
did pretty well with snowfall amounts last wet snow event earlier
in the month, so given its track record opted to err on side of
caution and expand headlines a bit farther south. The HRRR snow
depth is bringing 6" totals into northern/western Lee, most of
DeKalb, and northwestern Kane County.
Snowfall rates could reach 2"/hour, which would likely result in
snow eventually accumulating even on untreated main roads.
Updated WSW has been issued and derived products will be out
momentarily.
- Izzi
&&
.SHORT TERM...
Issued at 257 PM CDT Fri Mar 24 2023
Through Saturday...
Main forecast messages through Saturday:
* Widespread rain arriving this evening, quickly transitioning to a
wet snow in far northern Illinois overnight (transition to all
snow occurring later towards daybreak towards the I-88 and I-80
corridors and the heart of the Chicago metro)
* Intense snowfall rates (likely 1+"/hour at times) are likely to
produce a narrow corridor of 6+" of heavy, wet snow accumulation
in portions of interior northern Illinois and in locations
near/along the Illinois-Wisconsin state line
* Travel impacts in the form of sharply reduced visibilities and
slushy snow accumulations on roadways are likely within the
corridor of heavier snowfall. Uncertainty exists whether snow
will accumulate on main thoroughfares due to mild antecedent
conditions and near-surface air temperatures remaining near 32F,
though accumulations are more likely on secondary/untreated
roadways, as well as bridges and overpasses.
* The Winter Weather Advisory for Ogle, Winnebago, Boone, McHenry,
and Lake counties in far northern Illinois has been upgraded to a
Winter Storm Warning. This is where 6+" of snow accumulation is
presently most likely to occur. The timing of this headline was
left unchanged (from 1 AM CDT through 1 PM CDT).
* A Winter Weather Advisory remains in effect for Lee, DeKalb, and
Kane counties from 1 AM CDT through 1 PM CDT. Northern Cook
County has been added to this advisory, though only from 7 AM
CDT through 1 PM CDT given the expected later start time of snow
there. At least 3" of snow may fall in at least portions of
these counties, and the heavy snow rates may lead to hazardous
travel here as well.
* There is still room for the location of the narrow heavy snow
corridor to wobble north or south by roughly a tier of so of
counties. Thus, headline changes may still need to be made
tonight once observational trends become clearer.
[Updated at 3:40 PM CDT to provide additional details]
Surface cyclogenesis is well underway over the Ozarks and Ouachitas
of western Arkansas and eastern Oklahoma with a recent surface
analysis revealing the center of a 1002 mb surface low near Fort
Smith, AR at 19Z. Strong upper-level divergence downwind of the
base of an upper-level trough currently centered over the southern
Rockies/southern High Plains and in the right entrance region of
a 155+ kt upper-level jet core will foster the continued deepening
of this low as it lifts northeastward, with a mean sea level
pressure of about 985-990 mb likely to be attained by the time the
low center reaches our latitude around daybreak tomorrow. Excellent
synoptic forcing for ascent will cause a broad shield of
precipitation to spread into our forecast area from south to north
throughout this evening, while winds will gradually become
blustrier with time as the center of the deepening low approaches.
With surface temperatures in the mid 30 to low 40s (coldest north;
warmest south) at the onset of precipitation, most, if not all of
our forecast area will see rain initially. However, thermal profiles
in interior far northern Illinois look cold enough to where
precipitation may either be snow or a rain/snow mix initially at
onset, or will quickly change over to all snow within 2-3 hours of
onset after robust dynamic/evaporative cooling all but eliminates
any lingering hydrometeor melting energy within the atmospheric
column. This transition to all snow should be more gradual farther
south towards the I-88 and I-80 corridors and into the heart of
the Chicago metro, but the expectation is that thermal profiles
should become supportive of mostly or all snow at these locations
by around daybreak Saturday. Locations south of I-80, and even
more so south of the Kankakee and Illinois river valleys, may not
witness this full changeover and only see rain throughout the
duration of this event. Can`t rule out some embedded thunderstorms
occurring in the southern half or so of our CWA as well given the
dynamics in play.
As has been discussed the past couple of days, intense snowfall
rates likely exceeding 1"/hour at times are likely to be seen
wherever the main snowfall deformation axis sets up, owing to the
strong synoptic forcing for ascent that will be augmented by robust
mesoscale forcing induced by a pronounced frontogenetic circulation,
as well as the presence of steep upper-level lapse rates/convective
upright instability and deep column moisture. As is usually the
case in these late-season events, heavy snow rates will be a must
in order for any meaningful snow accumulations to occur given the
mild antecedent conditions that we`ve experienced in the lead-up
to this event, as well as the fact that near-surface air
temperatures likely won`t fall much below freezing throughout the
duration of the event, and should even remain above freezing
across a large chunk of our CWA that is expected to see snow. This
scenario is actually somewhat similar to the one we saw two weeks
on March 9-10, when strong frontogenetic forcing coincident with
steep lapse rates laid down a swath of 6+" of snow across far
northern Illinois into southern Wisconsin despite mild antecedent
conditions and marginal air temperatures. Road impacts with that
event were primarily limited to secondary, untreated, and elevated
roadways with mild pavement temperatures and road treatments
keeping most main thoroughfares in relatively good shape, and have
a hunch that something similar may be seen with this event.
Regardless of whether the snow ends up accumulating on roadways,
sharply reduced visibilities are likely within the more intense
snowfall, and that on its own could still lead to hazardous travel
for any motorists who will be traveling early Saturday morning in
northern Illinois.
The frontogenesis signal with that March 9-10 event was perhaps not
as pronounced and more ephemeral than what most forecast guidance is
suggesting will be the case for this event, which leads to the
thinking that the snow rates with this event will be more intense
and longer lasting than what we saw two weeks ago. However, one key
consideration with this setup that wasn`t present for the March
9-10 event is that there is a large wad of convection to our
south. Since models often struggle with handling convection, there
are often errors in how they handle the intensity and placement
of snowfall on the northern sides of systems like these. As a
result, there are still some lingering uncertainties regarding
exact snowfall totals and the placement of the narrow heavy snow
corridor, which based on recent guidance, could still shift
north/west or south/east by a tier or so of counties compared to
what we`re currently forecasting. For seemingly the umpteenth this
cold season, a sharp snowfall gradient is also likely to be seen
somewhere between the Illinois-Wisconsin state line and the
I-88/I-80 corridors and heart of the Chicago metro, where a
longer duration of rain and slightly milder surface temperatures
will limit how much snow will be able to accumulate.
Putting everything together, confidence was high enough in a narrow
corridor of 6+" of snow accumulation occurring across our far
northern counties to warrant an upgrade to a Winter Storm Warning
there, even though overall travel impacts may not necessarily end
up being truly Winter Storm Warning-worthy. The Winter Weather
Advisory was kept for Lee, DeKalb, and Kane counties, where heavy
snowfall may produce lesser accumulations, but still some travel
impacts. Northern Cook County was also added to this advisory with
confidence now being slightly higher in 3+" snow accumulations
and associated travel impacts occurring in at least far western
portions of this headline zone.
Precipitation should end from west to east late Saturday morning
and into the afternoon. Warming daytime temperatures and perhaps
some glimpses on sunshine may melt a large chunk of the newly
minted snowpack prior to sunset.
Ogorek
&&
.LONG TERM...
Issued at 122 PM CDT Fri Mar 24 2023
Saturday night through Friday...
Broad troughing and attendant cyclonic flow looks to persist
across the CONUS through next week. Numerous mid-level
perturbations are slated to ride along the associated fast jet
streak, and while widespread precipitation isn`t forecast each
day during the extended, several chances for precipitation (some
of the wintry variety) exist.
The follow-up disturbance to Saturday`s storm system is slated to
arrive during the day on Sunday. This looks to be a fairly compact
and lower amplitude one, and guidance remains all over the place
regarding placement, timing, and moisture depth/saturation. A
fairly steep reservoir of lapse rates are forecast to precede the
main forcing with this feature, but the compact nature, fast
forward motion, and lacking moisture suggest just carrying some
lower-end PoPs for the time being. Thermal profiles will be right
on the cusp of supporting rain/snow across our area, but based on
the currently-advertised surface temperatures, any wintry
precipitation doesn`t look to be of the overly impactful variety.
Arriving fast on the heels of this feature will be a third
perturbation late Sunday night into Monday. This again looks to be
a very short wavelength shortwave, but potentially of higher
amplitude than the previous and riding along the sharp, cyclonic
shear side of a robust 160+ kt jet streak. Still seeing plenty of
spread in the guidance at this range, but there is a general,
developing signal of a deepening surface reflection translating
across central Illinois into Indiana during this period. Ensemble
guidance continues to depict a narrow west-east oriented swath of
some snow accumulations as this feature acts to sharpen up a
well-established baroclinic zone. While not off the charts,
moisture (PWATs a bit north of a half inch) and instability may be
in somewhat better supply with this disturbance, so we`ll continue
to keep an eye on guidance trends over the next few days. The
latest multi-model consensus suggests the best chances for any
slushy snow accumulations focusing across far northern Illinois
and towards the Wisconsin state line.
We may get into a brief break in the action during the middle of
the week as an expansive 1025-1030 mb high builds across the Upper
Midwest. This will be short-lived, however, as model guidance is
in good agreement regarding the next round of lee cyclogenesis
taking place Wednesday night and Thursday across the plains. Still
way too far out for much stock in any single model run/solution,
but the overall consensus seems to favor a deepening surface low
tracking somewhere off to our north and west to close out the
week.
Carlaw
&&
.AVIATION...
For the 00Z TAFs...
638 PM...Forecast concerns include...
Snow overnight/Saturday morning with lifr/vlifr cigs/vis.
Strong/gusty northeast winds shifting northwest Saturday morning.
Light rain currently over central IL will slowly spread north and
increase in coverage this evening. The rain will change to snow
first across northwest IL after midnight and this transition to
snow will spread southeast across the rest of the terminals in the
predawn hours. While timing tweaks may be needed as trends emerge,
current tafs look in good shape. As the precipitation transitions
to snow, there could be a brief period of sleet at ORD/DPA.
Visibilities also may drop into the 1/2sm range at ORD/DPA. There
is some potential for 1/4sm, especially at RFD but confidence too
low to include with this forecast. While the heaviest snow is
expected to fall just northwest of ORD/DPA, if it were to shift
further to the southeast, then lower conditions may become
prevailing and persist longer. The snow is expected to slowly
weaken in intensity by midday and end from west to east during the
early afternoon, possibly mixing with some light rain or drizzle.
Northeast winds will slowly increase this evening with gusts into
the lower/mid 20kt range. Directions will become more northerly by
daybreak when gusts into the 30kt range will be possible, though
gusts may diminish during the heaviest snow periods. Directions
will shift to the northwest during the mid/late morning and then
become more westerly during the afternoon with speeds/gusts slowly
diminishing. Speeds are expected to diminish under 10kts Saturday
evening. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008...4 AM
Saturday to 1 PM Saturday.
Winter Weather Advisory...ILZ103...7 AM Saturday to 1 PM
Saturday.
Winter Weather Advisory...ILZ010-ILZ011-ILZ012...4 AM Saturday
to 1 PM Saturday.
IN...None.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...1 AM Saturday to 4 AM Sunday.
&&
$$
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Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1036 PM CDT Fri Mar 24 2023
.SHORT TERM... (Through Late Saturday Night)
Issued at 239 PM CDT Fri Mar 24 2023
Latest analysis shows surface low pressure near northwest AR,
approaching the southwest sections of MO. A broad area of rainfall
extends east along a quasi-stationary boundary that runs through
northern Arkansas into Tennessee. Another line extends southward
through western Arkansas along a cold front extending south of the
surface low.
Low pressure will lift northeast ahead of a negatively tilted upper
level trough this evening through Saturday morning. The surface
boundary makes a slight jaunt northward ahead of the surface low,
lining up near the MO Bootheel. All CAMs support some form of
widespread rainfall along the west-east oriented boundary ahead of
the surface low with better convective potential in closer proximity
of the boundary extending east of the surface low. Much of the
SBCAPE remains south of the MO/AR border eastward into the Tennessee
Valley with little concern for stronger storms further north.
However, heavy rainfall overrunning the boundary is likely to impact
far southern sections of the CWA (especially Reynolds, Iron, and
Madison Counties), where 2-3 inches have already fallen. Hi-res
meteograms indicate heavy rainfall may affect the same areas with a
majority of HRRR and SREF members adding 1-2 inches with roughly
half of the members at 2-3 inches as far north as KFAM by Saturday
morning. The Flood Watch will remain in place as-is.
Meanwhile, as the surface low deepens, the mid-level low closes off
as it traverses mid-MO tonight. A broad deformation zone is expected
to take shape on the back side of the system late tonight into
Saturday morning. In between the leaf of mid to upper lift and the
surface low, dry air wraps into the system, creating a void for some
locations in a southwest to northeast orientation, generally between
Jefferson City and St. Louis. So, while widespread rainfall
initially overspreads all areas this evening, those under the dry
air intrusion will likely see more of a scattered coverage later
tonight into Saturday morning. The bulk of the precipitation
associated with the deformation zone track from central MO through
northeast MO and west-central Illinois, resulting in a broad area of
0.50-1.00 inch amounts north of the heavier rainfall to the south.
Little has changed since the last update regarding the system`s
departure. As it begins to exit to the northeast Saturday morning,
cooler air wraps in behind the system, which could cause some snow
to mix in over far northeast Missouri. While sounding show sub-
freezing temperatures aloft, the lowest 2k feet trend above freezing
with mid-30s near the surface. This all occurs in a brief 2-3 hour
window between 10z and 13z before moisture evacuates the mid to
upper levels. Therefore, the chances for accumulating snowfall are
quite low.
Dry conditions will settle in behind the system Saturday with breaks
in the overcast skies Saturday afternoon. There is a weak shortwave
the tracks from the central Plains along the MO/IA border Saturday
night, providing low chances for an isolated shower. Moisture is
limited further southeast of the shortwave. While showers may
initially extend southeast through portions of central Missouri,
better support and moisture remains over northern sections of the
CWA. Anything that pans out is expected to result in just a couple
hundredths of an inch over northern sections of the CWA.
Maples
.LONG TERM... (Sunday through Next Friday)
Issued at 239 PM CDT Fri Mar 24 2023
The period begins with an expansive closed low being the
dominant feature over the Hudson Bay on Sunday. Broad cyclonic flow
over Canada gradually bleeds into predominantly zonal flow over the
central U.S., acting to channel multiple upper level shortwaves from
the Pacific Northwest through the central Plains.
Saturday night`s shortwave and weak associated surface low will
continue to move east along the MO/IA border early Sunday morning.
Its compact nature should keep most precipitation north of the CWA,
though an isolated shower is not out of the question in northeast MO
and west-central IL, focusing along a wing of weak mid-level f-gen
and narrow corridor of deeper saturation (near IA/MO/IL borders).
Much of the day Sunday remains dry elsewhere with a north-south
spread in temperatures (low 50s north/mid-60s south).
A second shortwave located just east of the Four Corners Region has
better potential to bring light rain to the area Sunday night.
Though upper level flow is being characterized as zonal, there is a
slight lean out of the southwest, which will carry the shortwave
east-northeast into the mid-Mississippi Valley. The 850mb fields
show a varying degrees of mid-level low development between
individual guidance underneath the upper ascent of the shortwave
running near the MO/IA border. Soundings depict deeper saturation
than the previous shortwave, coinciding with an area of mid-level
forcing along a west-east oriented baroclinic zone. Isentropic lift
will result in an area of light rainfall somewhere within 18z Sunday
through 12z Monday window. GEFS/EPS ensembles show approximately 50
percent of the members with measurable rainfall between 03z through
15z moving west to east. CMC ensembles are a bit more bullish with
70 percent of members favoring measurable rainfall in the same
period. When increasing the QPF threshold to 0.25 of an inch, each
of the ensembles show lower potential with 20 percent or less of the
members favoring such. All-in-all, a quick light rain event is
looking more likely.
Rain moves east Monday morning with the start of the work week
leaning in favor of dry weather and near normal temperatures. Zonal
flow brings yet another weak upper shortwave along the MO/IA border
ahead of a mid-level thermal ridge situated to our west. It
initially looked like it would remain dry as this wave lacks
moisture. However, a few members do support a brief bout of isolated
showers late Monday night into early Tuesday. Current NBM PoPs of 20-
30 percent (00z-06z Tue) may have a bit more bark than bite with
little indication that any steady rainfall will result.
Confidence begins to wane in the midweek period as spatial and
temporal details diverge and create greater spread amongst the
ensemble guidance. Despite this, general themes can be parsed out
that show surface ridging building in from the northern Plains as
mid to upper ridging amplifies over the central U.S. While the
placement of the surface high and amplitude of the mid/upper ridging
pattern varies between guidance, the patter provides some confidence
that temperatures will moderate from mid to late week.
By Thursday, an amplified upper trough extends southward over the
Intermountain West, further amplifying the ridge over the Midwest.
While a majority of GEFS/EPS/CMC ensemble members remain dry through
late Wednesday, Thursday (important day in St. Louis...wink wink)
looks less certain. The pattern will support an increasing potential
for precipitation as the trough moves east. Strengthening southerly
flow and upper ridging ahead of the trough draw moisture northward
with a milder, progressively more active pattern to end the period.
Maples
&&
.AVIATION... (For the 06z TAFs through 06z Saturday Night)
Issued at 1033 PM CDT Fri Mar 24 2023
Although the bulk of the steadier rain has moved east, another
round of rain will move into northern parts of the region
overnight. This is most likely to affect Quincy, where some snow
may mix in by morning. Rain could also approach Columbia or
Jefferson City. IFR conditions prevail at all sites, but some
periods of MVFR improvement have been observed. Occasional
deterioration to LIFR is also possible. Winds turn to the north
and then west by morning with conditions improving during the
morning to early afternoon. By afternoon, VFR is likely area wide.
Kimble
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX