Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 130443
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1143 PM CDT Tue Mar 12 2024

.KEY MESSAGES...

- Unseasonably warm temperatures through Thursday.

- A few scattered showers and storms possible late tonight.
  Better coverage of showers and storms Wednesday night, which
  will carry a risk of hail.

- Severe potential increasing for late Thursday afternoon and
  evening. All severe weather modes at play including very large
  hail, tornadoes, and damaging winds. Most favored area for
  significant severe weather is west of I-55.

- Much cooler weather expected after a cold frontal passage late
  Saturday. Widespread sub-freezing lows Sunday night and Monday
  night.

&&

.UPDATE...
Issued at 917 PM CDT Tue Mar 12 2024

Overall the forecast looks on track except for pops/wx. Newer
model guidance suggest the precip over MO will diminish as it
moves into IL later tonight. Based on this newer guidance, have
decreased pops/wx across the CWA with highest pops in the west. Am
expecting precip to end by 12z. Have already updated the grids and
a new forecast should be coming shortly.

Auten

&&

.DISCUSSION...
Issued at 215 PM CDT Tue Mar 12 2024

Southwest winds gusting 20-25 mph and nearly full sunshine have
allowed temperatures to reach unseasonably warm levels early this
afternoon, in the upper 60s to lower 70s as of 2 pm. Gustiness
will diminish by early evening with the loss of diurnal heating,
and we`ll see an increase in high/mid level cloudiness as a
shortwave trough over the Plains approaches. Scattered showers and
an isolated thunderstorm are in the forecast overnight as the
trough crosses the region. Various short range guidance shows
paltry coverage and have limited PoPs to slight/low chance (20-30%).
Lows to be unseasonably mild (more typical of highs this time of
year) in the upper 40s to around 50F, aided by cloud cover and
light southerly flow.

Quiet/dry weather forecast for the daylight hours Wednesday
courtesy of low amplitude ridging behind the departing shortwave
trough. Low/mid level moisture will be on the increase through the
day (dewpoints rising through low/mid 50s) and result in
increased low and mid level clouds. Even so, another nice "late
spring" day on the thermometer with highs again in the lower 70s.

A warm front will approach the region from the southwest Wednesday
evening. Scattered storms are forecast to form ahead the front,
aided by the convergent nose of a 40-45 kt southwest low level
jet. Steep mid level lapse rates near 8 deg C/km will support a
hail risk where updrafts can be maintained by 25-30 kt deep layer
shear. The most likely timeframe for active thunderstorms is 9 pm
to 3 am. SPC has nudged the Day 2 marginal risk of severe into
west central IL.

Most model solutions push the warm front north to between I-74 and
I-80 on Thursday morning, before stalling as low pressure moves
into southeast IA during the afternoon. Forecast soundings
indicate a capped atmosphere south of the front, keeping the
active weather just to our north or along the northern fringes of
the CWA into Thursday afternoon. The parameter space is becoming
more favorable for severe storms late Thursday afternoon/evening,
as 12z guidance has trended slightly faster and further south
with the track of the surface low. Thermodynamic profiles show all
severe modes in play (large hail, tornado, damaging wind gusts)
given MLCAPEs >2000 J/kg, 50+ kt effective bulk shear, and long,
curved hodographs. The question remains where these parameters
overlap with the stronger forcing near and ahead of the triple
point, likely triggering supercells initially then evolving into
organized clusters or line segments during the evening. SPC Day 3
forecast highlights areas west of I-55 in a hatched area (10%
probability of significant severe within 25 miles of a point).
Keep updated with later forecasts as the risk/timing/location of
severe is refined.

After the cold frontal passage Thursday night, dry and cooler, but
still above normal temps prevail Friday and Saturday. Global
ensembles show another dry cold frontal passage late Saturday
followed by a more significant shot of cold air, likely pushing
temperatures below normal for a few days into early next week.

25

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1143 PM CDT Tue Mar 12 2024

VFR conditions will continue at all sites overnight and through
tomorrow evening. An area of convection that developed around
Kansas City continues to move east toward IL tonight. However, it
is diminishing as it moves east toward IL, away from the better
moisture and forcing and into a drier airmass. HiRes models also
show this diminishing as it moves into central IL overnight. Will
not have any precip at the western sites, but will have some AC
clouds at SPI, PIA, DEC, and BMI. Otherwise scattered to broken
cirrus will be present overnight and into tomorrow. The HiRes
models now show convection developing tomorrow evening just south
of the area, along a warm front, and then moving north over
central IL...which will likely affect all TAF sites during the
evening hours. There is some uncertainty with this, but seems
reasonable based on current conditions. For now, will have VCSH
only in SPI TAF starting at 03z. Winds will be south to southeast
through the period, with PIA and BMI seeing winds out of the east
tomorrow afternoon to evening. Speeds will be around 10-15kts
through the period.

Auten

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$


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