Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/27/22

Area Forecast Discussion

National Weather Service La Crosse WI

 959 PM CST Sat Nov 26 2022

.UPDATE...
Issued at 958 PM CST Sat Nov 26 2022

We continue to monitor the storm system for Tuesday/Tuesday night.
So far with the new models that are in this evening, we continue
to see the band setting up to our northwest, so no changes to the
current forecast for then. Before then, we do see light rain
spreading northeast overnight and affecting the far southeast
portion of the forecast area.

&&

.DISCUSSION...(This evening through Saturday)
Issued at 200 PM CST Sat Nov 26 2022

Key Messages:

 - Band of accumulating snow expected on Tuesday from south-
   central Minnesota to north-central Wisconsin, but uncertainty
   remains with regards to impacts and exact location.

 - Seasonal temperatures from Sunday into next weekend aside from
   a brief cold spell midweek.

TONIGHT - MONDAY: COOLER, RAIN SKIRTS TO THE EAST

It was a beautiful Saturday across the forecast area with highs
topping out in the low to mid 50s--a solid 10+ degrees above
average for this time of year. However, this warmth is fleeting as
a cold front dropping southeastward from central Minnesota sweeps
through the region tonight. To the south, water vapor imagery
depicts a cutoff low over the Texas Panhandle starting its
northeastward migration in response to an approaching northern
stream wave (also the culprit for our cold front). This
approaching system brings an increase in mid and high level clouds
this afternoon/evening and keeps these clouds around for much of
the day on Sunday.

Short range guidance continue to trend eastward with the track of
the lifting low/wave and its surface reflections. Given these
trends, have all but removed the mention of precipitation from the
forecast for southwest Wisconsin/northeast Iowa for Sunday. Highs
on Sunday are trending a hair warmer (upper 30s to low 40s) with
the bulk of the cold air staying to the north and the lessening
threat of precipitation.

Monday will be quiet weather-wise with mid to high clouds
streaming overhead ahead of our midweek system.

TUESDAY - WEDNESDAY: BAND OF ACCUMULATING SNOW LIKELY

The latest EPS/GEFS ensemble guidance continues to hone in on
south-central Minnesota up through north-central Wisconsin as the
corridor that has the highest likelihood of seeing accumulating
snow on Tuesday. The NBM snowfall probabilities have been steadily
increasing and shifting southeast--encroaching into the
northern/western forecast area. Along and northwest of a
Rochester, MN to Medford, WI line in the last 24 hours, NBM
probabilities for greater than 2 inches of snow have increased
from 30 to 70 percent while the probabilities for greater than 4
inches of snow have climbed from 0 to 20-30 percent.

This snow comes courtesy of a surface low ejecting from western
Kansas and reaching the Great Lakes region by Tuesday night. There
will be ample moisture return ahead of the low off the Gulf with
specific humidity and water vapor transport values around the 90th
percentile of normal. This moisture rides over a modest
frontogenesis zone within a realm of stout isentropic ascent and
modest kinematic lift.

A few caveats ride with this forecast. The first is that the GFS
deterministic profiles hint at is a possible misalignment between
the strongest Fgen forcing/moisture and the narrow DGZ. Due to
steep lapse rates through the DGZ, this mesoscale forcing will
need to line up perfectly to maximize the snow production
potential. We are still three days out from the event, plenty of
time for things to change on such a small scale.

The second potential fly in the ointment is the rain/snow line
during the day on Tuesday, which will be flirting closely with the
south flank of the strongest Fgen forcing. The thought at this
point is that the precipitation loading under the main band will
keep the p-type as snow, but with a quick transition to rain just
south of the band. This makes the placement of the band even more
crucial for snow amounts. If surface wet bulb values remain above
freezing under the band, this may reduce snowfall accumulation
amounts and impacts. However, as cold air rushes in Tuesday
evening, this should transition whatever precipitation remains to
snow.

The duration of the snow is also a source of uncertainty as an
increasing number of ensemble members linger light QPF values
through Tuesday night and into Wednesday morning closer to the
upper level trough passage and stronger kinematic lift. This is
reflected well in the latest NBM, which keeps mentionable PoPs
until midday Wednesday. Winds will be blustery on the backside of
the system with gusts of 25-30 kts likely on Wednesday, possibly
increasing the impacts of any light snow still falling.

The going snowfall forecast through Tuesday afternoon follows
slightly under the EPS/GEFS mean, with a 1-2 inch stripe of snow
along and northwest of the aforementioned line from southeast MN
to north-central WI. Amounts in the band may certainly be higher
if the issues noted above correct themselves. Given the broader
synoptic lift in place, most locales in the forecast area will see
light snow with this event by the time it exits on Wednesday,
with the highest totals confined to the Fgen band.

END OF THE WEEK: DRIER, BRIEFLY COOLER

In the wake of our midweek storm system, Canadian air rushes
southward and keeps highs solidly in the 20s/low 30s for Wednesday
into Thursday per the tightly-clustered NBM guidance. The vast
majority of the ensembles shunt the surface ridge axis east of the
forecast area by Thursday afternoon in a continued progressive/
amplified regime. A moderating southerly flow on the backside of
the ridge should bring temperatures back to around average for the
end of the week. Confidence in the overall temperature and
precipitation forecast decreases quickly into the weekend as the
next shortwave ejects eastward along the International border, but
given the active pattern, some place in the north-central CONUS
will probably see snow over the weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 550 PM CST Sat Nov 26 2022

VFR conditions through the evening, however MVFR conditions should
expand from MN southward Sunday morning.

High clouds have been on the increase well to the north of the
storm system over northern Texas/Oklahoma. This storm system will
continue to spread mid clouds northward tonight, however, an
advancing trough from the north will drag a cold front through
this evening. North to northeast flow will deepen with stratus
developing behind the cold front. The latest RAP has the stratus
arriving around 09Z-12Z at KRST and around 12Z-15Z at KLSE,
however observations of stratus are limited over Ontario, thus
will need to monitor the timing on this. The stratus continues
Sunday morning, but tries to break up some in the afternoon. Wind
shift to the northwest 5 to 15kts with stronger gusts 20 to 25kts
Sunday.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

UPDATE...Zapotocny
DISCUSSION...Skow
AVIATION...Zapotocny



Area Forecast Discussion

National Weather Service Lincoln IL

 719 PM CST Sat Nov 26 2022

.SYNOPSIS...
Issued at 313 PM CST Sat Nov 26 2022

Ahead of a low pressure system approaching from the south, rain
will overspread central Illinois this evening to bring widespread
precipitation totals of 0.75" to 1.5" by noon Sunday. On the back
side of the low, the area will be much cooler Sunday and Monday
with afternoon highs in the 40s across the board. Another system
will bring warmer weather but also another chance for rain by
Tuesday.

&&

.UPDATE...
Issued at 716 PM CST Sat Nov 26 2022

As of 7 pm this evening, low pressure is centered over the far NW
corner of Arkansas while aloft, a negatively tilted shortwave
trough is noted over northern Arkansas and is producing showers
across portions of Missouri and southern Illinois. Rain associated
with these features is on track to spread north across the
forecast area through the evening, but have slowed down the timing
a few hours. 00Z KILX sounding continues to show a deep layer of
dry area up to around 500 mb that will take some time to saturate.
Latest runs of the HRRR/RAP show the axis of heaviest precip from
roughly Jacksonville through Bloomington where rainfall amounts
in excess of 1.0 to possibly 1.5 inches is expected through midday
Sunday. This is a slight jog north from earlier expectations.
Otherwise, forecast largely remains on track.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 313 PM CST Sat Nov 26 2022

Mostly clear skies have allowed temperatures to warm into the mid
50s - around 5 to 8 degrees above normal for this time of year -
amidst strong southerly flow ahead of an approaching low pressure
system. Warm air advection will continue through this evening, but
with sunset at 4:34 PM CST the loss of surface heating will
prevent temperatures from rising much (if any) more at this point.
Simulated reflectivities from the CAMs suggest rain will
overspread the CWA at some point between roughly 7 and 10 PM, with
the heaviest burst of rain during the 11 PM to 4 AM timeframe.
The NAMNest and HRRR are each suggesting pockets of 50+dBZ will be
embedded within the main precipitation band, mainly east of I-55.

40% percent of members in the GE have 1" or more of 24 hour QPF
at KBMI for the period ending at 6 PM tomorrow. Our forecast is
closer to the NBM 90th percentile, which looks similar to the
ensemble mean from HREF, and has a large swath of 1" or greater
amounts falling mainly between 06z and 12z Sunday (i.e., midnight
and 6 AM). The maximum QPF from HREF has pockets of upwards of
1.75" of 6-hour QPF across our area, which suggests that locally
even heftier amounts than forecast are possible with embedded
convection within the warm-frontal rain band tonight. With 3 hour
Flash Flood Guidance (FFG) around 1.8-2.0" across our CWA, we will
need to keep a close eye on the rainfall rates tonight and
monitor for flash flooding, which could be an issue if most of
that 6-hour QPF falls within a shorter time period.

It will be a mild night for temperatures, as abundant cloud cover
mitigates radiational cooling. Lows in the 40s are forecast
across the board, with the warmest locations being in our
southeast CWA. Sunday will be much cooler, as cold air advection
develops amidst gusty northwest winds in the wake of the low which
is projected to reach Lake Erie by noon. North and west of I-57,
highs are expected to be in the 40s; when combined with wind gusts
of 25 to 30 mph, this will yield wind chills in the 30s
throughout the day. The bulk of the rain should exit the CWA by 11
AM, though an isolated shower or two cannot be ruled out
throughout the remainder of the day given the weak surface based
instability driven by steep low level lapse rates behind the cold
front.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 313 PM CST Sat Nov 26 2022

Near normal temperatures will continue Monday as surface high
pressure dominates our weather in the wake of the aforementioned
low pressure system. However, by Tuesday, another system is
forecast to develop across the midsection of the country, and
ahead of this system strong warm advection will bring above normal
temperatures to central IL yet again. South of I-70, there will
be around an 80-90% probability for high temperatures in the 60s,
with those probabilities tapering to around 30% for KPIA where
highs in the mid to upper 50s are more likely.

Depending on the track of the surface low, convective activity
might be possible with its approach Tuesday night. 83% of the
Grand Ensemble (GE) has nonzero CAPE at KLWV from 9 PM Tuesday to
3 AM Wednesday, and several members have over 500 J/kg, which is
the cause for the chance of thunder in the forecast. NBM has 25+%
percent probabilities for thunder there during that time, which
seems reasonable. SPC has the 15% risk for severe weather well to
our south. We`ll continue to monitor whether there`s a severe
threat for our area, but at this time the risk appears low. It
will ultimately be a function of the track and strength of the
low, as a stronger surface cyclone could yield sufficiently high
kinematic fields to overcome the lack of instability for
convection, though that is appearing increasingly unlikely with
each iteration of model output.

Considerable uncertainty surrounds Wednesday`s temperature
forecast at this point. Ultimately, it will depend on the timing
of the low, and could be one of those situations in which
Wednesday`s high occurs before sunrise. Given the differences in
the way deterministic and ensemble models are handling the low,
NBM is struggling. Its interquartile range (IQR) for high
temperatures at KLWV spans 38 to 56 Wednesday. By definition,
this means there is a 50% probability that high temperatures will
fall within that range, and a 50% chance that high temperatures
will fall outside of it. In other words, the likelihood of high
temperatures either (1) greater than 56 or (2) less than 38 is
equal to the probability that high temperatures will be between 38
and 56, which signifies incredible uncertainty. The IQR is
narrower farther north on Wednesday, which implies the cold front
is more likely to cross those areas early and hold temperatures
down for a chilly day. NBM gives a ~60% chance that high
temperatures will be below freezing at KGBG on Wednesday, which is
not surprising given 61% of the GE has 850 temps plunging to less
than -10C there during the 3 PM to 9 PM timeframe Wednesday
afternoon. As skies clear and high pressure rebuilds over the
region Thursday morning, efficient radiational cooling will
likely bring temperatures into the teens in parts of the area. The
NBM gives a 75% probability for lows less than 20 at KPIA.

Otherwise, it will be a breezy midweek time period. The EPS` mean
6 hour max wind gust forecast is between 32mph and 38mph from
noon Tuesday through 6 PM Thursday at KAAA. Quite a few members
are suggesting we`ll gust over 40mph at some point though. On the
bright side, the number of members suggesting we`d gust over 50mph
has trended down over the past couple runs.

Uncertainty in the synoptic scale pattern becomes evident in
cluster analysis by day 7 (6 PM Thursday to 6 PM Friday). By that
time, the primary solution is for ridging to be building back
into the area while the CONUS coasts are overtaken by weak
troughing. However, one cluster (dominated by the CMCE) has a
trough developing in the country`s midsection, and another
(predominantly the EPS) is significantly more amplified. The
latter solution has 500hPa heights increasing to upwards of 560
dam. Only three of its members have 24 hour maxT less than 45F at
KAAA for Friday, while 36% of the other two clusters combined have
highs less than 45F. NBM suggests there`s around a 30% chance
we`ll return to the 50s by Friday, with probabilities for 50+
increasing further for Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 521 PM CST Sat Nov 26 2022

Low pressure will track from roughly St Louis to Danville
overnight into Sunday morning. As this occurs, ceilings will
lower to MVFR and IFR and rain will overspread the terminals.
Conditions at DEC and CMI will be the lowest closest to the low
track. Uncertainty is greatest at PIA which is expected to be very
near the back edge of the IFR clouds and for now is favored to
bottom out MVFR. S/SE winds in place now will gradually back
through the period, becoming NE early Sunday morning, then
northwest by late morning and picking up with gusts around 20 kt.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Deubelbeiss
SYNOPSIS...Bumgardner
SHORT TERM...Bumgardner
LONG TERM...Bumgardner
AVIATION...Deubelbeiss