783
FXUS63 KILX 210201
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
901 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 00z TAFs through 00z Tuesday Evening)
Issued at 640 PM CDT Mon May 20 2024

VFR conditions will prevail at all TAF sites next 24hrs. High
cirrus could affect all sites through the overnight hours as the
CU that is over a couple of sites dissipates over the next couple
of hours. The cirrus should be around in the morning, but CU will
redevelop again tomorrow late morning into the afternoon, in the
very warm and humid airmass ahead of the next weather system. Any
precip is expected to hold off until after 00z tomorrow, do not
have any precip mentioned in this set of TAFs. Winds will be
southwesterly through the night and then become southerly
tomorrow. Wind speeds will be 10kts or less through the night, but
become gusty tomorrow with 20-25kt gusts in the morning,
increasing to over 30kts tomorrow afternoon.


Auten

&&

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

$$