Flash Flooding and Hail in Illinois, February 22, 2023

Area Forecast Discussion
National Weather Service Lincoln IL
944 AM CST Wed Feb 22 2023

.SYNOPSIS...
Issued at 357 AM CST Wed Feb 22 2023

Showers and thunderstorms will be likely across central Illinois
today...with the potential for a few strong to severe storms during
the afternoon. High temperatures will vary greatly...ranging from
the lower 40s far north around Galesburg...to the lower 60s along
the I-72 corridor...to the lower 70s far southeast near Lawrenceville.

&&

.UPDATE...
Issued at 944 AM CST Wed Feb 22 2023

At 9 am a warm front stretched from 993 mb low pressure in
northeast KS, to near the I-70 corridor in southeast IL. North of
the front, steep mid level lapse rates noted on the 12z ILX
sounding will bring an isolated severe hail threat with elevated
cores over the next few hours. A better severe threat will occur
this afternoon over roughly the south half of the CWA where
dewpoints reach unseasonably high levels in the lower 60s. North-
south oriented convective line is forecast to develop along a
pre- frontal trough. The environment ahead of the line will be
characterized by favorable effective bulk shear at 60+ kt. As is
usually the case during cool season events, instability is the
major question mark that will determine the scope of the event.
Most recent CAM runs have shown a bit better instability with
MLCAPEs up to 500-600 J/kg. This should be sufficient to get at
least isolated severe convection going within the line this
afternoon, primarily east of I-55 and south of I-72/Danville, with
1-6 pm the most favored timing. Damaging wind gusts will be the
main threat with hail secondary in the stronger cores. An isolated
QLCS tornado risk will need to be watched as well due to favorable
shear vectors in the 0-3km layer. Flash flooding will also be a
concern. 0.50-0.75" rain has already fallen over parts of the CWA
overnight and early this morning. High PWAT airmass (near the top
of climatology for late Feb.) and potential for some training
storms as well with FFG values at 1-2" for much of the CWA this
afternoon. The warm front is forecast to become stationary near
the I-72 corridor this afternoon which will lead to a large
temperature gradient, highs near 40F over the northern CWA to the
lower 70s in the far south. Gusty southerly gradient winds will
occur in the warm sector with a few gusts 40-45 mph south of I-70
where a Wind Advisory is in effect until 8 pm.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 357 AM CST Wed Feb 22 2023

09z/3am surface analysis shows low pressure developing in the lee
of the Rockies across western Kansas...with a warm front extending
eastward into the lower Ohio River Valley. A band of scattered
showers and thunderstorms developed well north of the front and
has now lifted north of I-74. Based on regional radar mosaic and
latest HRRR/RAP output, it appears there will be a lull in precip
chances for the next couple of hours before showers begin to
re-develop along/north of the boundary by sunrise. Showers and a
few thunderstorms will be likely everywhere north of the I-70
corridor through midday...while locations further south only see
widely scattered showers. As has been advertised for the past
several model runs, more significant convection is expected to
develop along a dryline across eastern Kansas/Oklahoma this
morning, then track northeastward across central Illinois this
afternoon. 06z HRRR continues to show storms pushing into the far
W/SW KILX CWA by 2pm...then quickly exiting into Indiana by around
6pm. While instability will remain modest at just 200-400J/kg,
ample deep-layer shear will be sufficient for some storm
organization...particularly cells tracking near the warm front
draped just north of I-72. Think there will be a scattered damaging
wind threat this afternoon...with a very low risk of a tornado
near the warm front where low-level shear will be enhanced. Aside
from the storm threat, locally heavy rainfall of 1.50 to 2 inches
will be focused along/north of a Rushville to Bloomington
line...with amounts steadily decreasing to less than 0.50 along/south
of I-70.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 357 AM CST Wed Feb 22 2023

Cold front will sweep across central Illinois on Thursday:
however, with deep-layer moisture shunted well to the east, am not
expecting any additional precip. Instead the main weather stories
will be the windy conditions and falling temps throughout the day.
Preliminary forecast soundings and numeric guidance suggest
westerly wind gusts of 35-45mph...with perhaps a few isolated
gusts up to 50mph along/north of I-74. High temperatures will be
achieved early in the day...with readings dropping into the 30s
west of I-55 by mid to late afternoon.

After a chilly/dry day on Friday, a fast-moving disturbance will
bring a light rain/snow mix to central Illinois Friday night.
Little to no snow accumulation is expected. Dry weather is on tap
over the weekend...with above normal highs well into the 40s on
Saturday, then into the middle 50s by Sunday.

After that, another moisture-laden storm system will move into the
region early next week. While exact details are still somewhat
uncertain, confidence is growing that an all-rain event will
unfold Sunday night into Monday...with storm total rainfall likely
over 1 inch across much of central Illinois.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 553 AM CST Wed Feb 22 2023

1130z/530am surface analysis shows warm front between I-72 and
I-70. Ceilings are beginning to lower along/north of the boundary
and will become MVFR at all terminals by 14z/15z. Based on latest
radar trends, included VCTS at all sites except KPIA for the next
couple of hours. After that, focus turns to a line of thunderstorms
expected to track across parts of central Illinois this afternoon.
Following HRRR timing, included a TEMPO group for thunder at KSPI
between 20z and 23z...and further east at KCMI between 22z and
01z. Once the convection pushes into Indiana, a few showers will
linger early this evening before precip comes to an end and
ceilings scatter before midnight. Winds will initially be E at
10kt or less, then will become S/SE at the I-72 terminals by late
morning as the warm front edges northward. It appears KPIA/KBMI
will remain north of the boundary and will maintain E/NE winds
today. Once the system departs, winds will turn to S/SW at all
sites tonight into early Thursday morning.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 8 PM CST this evening for ILZ063-067-068-
071>073.

&&

UPDATE...25
SYNOPSIS...Barnes
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Barnes

Hazardous Weather Outlook...UPDATED
National Weather Service Lincoln IL
707 AM CST Wed Feb 22 2023

ILZ027>031-036>038-040-041-231200-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-
707 AM CST Wed Feb 22 2023

This Hazardous Weather Outlook is for central Illinois.

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected through sunset. A few of them
may be on the strong side this afternoon, mainly in areas south of a
Rushville to Bloomington line, with isolated strong wind gusts and
hail. In addition, rainfall of 1 to 1.5 inches is likely through
this evening, heaviest east of the Illinois River.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

West winds will gust to around 40 mph on Thursday, causing some
difficult travel for high profile vehicles.

A fast moving disturbance will bring light snow to the area Friday
night, though accumulations currently appear to be minimal.

Another storm system early next week has the potential to produce
additional heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon, with the most likely
time frame between noon and 3 pm.

Expected storm motion is toward the east northeast around 60 mph.

ILZ042-047>052-231200-
Logan-Cass-Menard-Scott-Morgan-Sangamon-Christian-
707 AM CST Wed Feb 22 2023

This Hazardous Weather Outlook is for central Illinois and west
central Illinois.

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected through sunset. Some of these
will be strong to severe this afternoon. Damaging winds are the main
concern, though isolated large hail and a tornado or two cannot be
ruled out. In addition, rainfall around an inch is likely.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

West winds will gust from 35 to 40 mph Thursday morning, causing
some difficult travel for high profile vehicles.

Another storm system early next week has the potential to produce
additional heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon, with the most
likely time frame between 1 pm and 4 pm.

Expected storm motion is toward the east northeast around 60 mph.

ILZ043>046-053>057-061-231200-
De Witt-Piatt-Champaign-Vermilion-Macon-Moultrie-Douglas-Coles-Edgar-
Shelby-
707 AM CST Wed Feb 22 2023

This Hazardous Weather Outlook is for east central Illinois.

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected through sunset, though they
will taper off for a time during the afternoon. Some of the storms
may be strong to severe, especially west of I-57. Damaging winds are
the main concern, though isolated large hail and a tornado or two
cannot be ruled out. In addition, rainfall around an inch is likely
north of I-72 and Danville.

South winds will gust from 30 to 40 mph this afternoon, causing some
difficult travel for high profile vehicles.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

West winds will gust from 35 to 40 mph Thursday, causing some
difficult travel for high profile vehicles.

Another storm system early next week has the potential to produce
additional heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon, with the most likely
time frame between 3 pm and 5 pm.

Expected storm motion is toward the east northeast around 60 mph.

ILZ062-063-066>068-071>073-231200-
Cumberland-Clark-Effingham-Jasper-Crawford-Clay-Richland-Lawrence-
707 AM CST Wed Feb 22 2023

This Hazardous Weather Outlook is for east central Illinois and
southeast Illinois.

.DAY ONE...Today and tonight.

South winds will gust over 40 mph at times today, causing some
difficult travel for high profile vehicles.

Isolated thunderstorms are expected this morning, with a better
chance toward mid to late afternoon. The afternoon ones have the
potential to be strong to severe. Damaging winds are the main
concern, though isolated hail and a tornado or two cannot be ruled
out.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

A storm system early next week has the potential to produce heavy
rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon, with the most likely
time frame between 4 pm and 6 pm.

Expected storm motion is toward the east northeast around 60 mph.

Geelhart