561
FXUS63 KILX 210441
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1141 PM CDT Mon May 20 2024

.KEY MESSAGES...

- Multiple rounds of severe weather are expected over the next few
  days with portions of the forecast area in a slight risk
  (level 2 of 5) today, moderate risk (level 4 of 5) Tuesday, and
  slight risk (level 2 of 5) again Wednesday.

- Summer-like heat and humidity will be in place Tuesday. High
  temps will be near 90 degrees with dew points approaching 70
  degrees. NBM probs for high temps exceeding 90 degrees are
  50-70 percent north of the Illinois river and south of I-70.
  Probabilities generally run 20-40 percent in between.

&&

.UPDATE...
Issued at 901 PM CDT Mon May 20 2024

Showers and storms have struggled to develop into strong storms
this evening, especially in our CWA. Better sustained development
has been just south of I-80 south of the Chicago metro area. This
will likely continue tonight so have made some adjustments to the
pops/wx for the remainder of the night and confined them to
northern areas of the CWA closer to the boundary that is north of
the CWA. Remainder of the forecast looks fine and update has
already been sent.

Auten

&&

.DISCUSSION...
Issued at 133 PM CDT Mon May 20 2024

This afternoon, an elongated area of low pressure stretches from
the OK/TX Panhandle region into MN. Aloft, an MCV is lifting
across southern WI while a shortwave trough is lifting across the
IL/MO state line near St. Louis. Forcing in minimized across
central Illinois in between these features, and CAMs have been
inconsistent in placement and timing of any potential convection
across central Illinois. The general theme, though, has been for
isolated to widely scattered storms with the best chance late this
afternoon into the evening. HREF LPMM shows a few bullseyes of
2-4 inches of rainfall which is plausible if storms do develop
given the slow nature of the storms (storm motions to the NE
around 20 mph) and the high moisture content. Surface dew points
are well into the 60s across most of central Illinois and PWats
are progged to increase to around 1.5 inches today.

Tonight, low pressure will consolidate over KS/NE and lift into
the Upper Midwest Tuesday. A broad warm sector characterized by
temps near 90 degrees, dew points approaching 70s degrees, and
MLCAPE values in the 2000-2500 J/kg range will develop across
portions of IA/MO/IL Tuesday with the highest values along and
west of I-55. Deep layer shear will be strong across most of this
warm sector with 0-6km bulk shear values of 35-45 kt superimposed
over the strongest instability. Moderately strong capping will
also be in place keeping the local area dry much of the day
Tuesday. Capping should begin to erode Tuesday evening as the main
H5 shortwave trough and surface cold front push across the
Mississippi River Valley. A line of thunderstorms should accompany
these features as they push across central Illinois mid to late
Tuesday evening. The severe threat will be greatest as storms
enter the western counties of the forecast area near or shortly
after peak instability for the day, but the severe threat will
gradually diminish with time as we move past sunset allowing
instability to weaken and as storms move further ahead of the
strongest forcing along the cold front. The cold front will slowly
push across central Illinois late Tuesday night and will still be
over portions of east central Illinois Wednesday morning.

Severe weather appears possible once again Wednesday, especially
across portions of east central/SE Illinois along a cold front
that is slowly pushing through the region. Guidance indicates that
a narrow corridor of moderately strong instability (MLCAPE
2000-2500 J/kg) will develop ahead of the front by around midday.
Moderately strong deep layer shear continues to support stronger
or severe storms Wednesday afternoon and evening.

Frontal boundary is progged to stall along portions of the Ohio
River Valley Thursday and Friday and will support additional
showers and storms across the region, especially south of I-72
in central Illinois. A series of shortwaves riding atop the
surface boundary will keep precip chances going across central
Illinois through the weekend.

Deubelbeiss

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1141 PM CDT Mon May 20 2024

All sites will be VFR overnight and tomorrow morning. CU will
develop in the afternoon with mid clouds around 12kft. A front
will move into the area with showers and storms during the evening
hours, reaching PIA first around 01z, then SPI and BMI around 02z,
and DEC and CMI around 03z. Cigs will remain VFR as the storms
move through, but could be MVFR around 3kft for a brief period.
Will have these clouds scattered to indicate this level of clouds
will be around. WInds will be light out of the southwest overnight
but become southerly and quite breezy tomorrow, with gusts of
25-33kts during the day.

Auten

&&

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

$$