307
FXUS63 KILX 212342
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
642 PM CDT Tue May 21 2024

.KEY MESSAGES...

- Strong south winds will gust up to 40 mph into early this
  evening. This will create blowing dust in spots where fields
  have recently been plowed.

- There is a level 4 of 5 (moderate) risk for severe weather this
  evening west of the Illinois River, with gradually lower chances
  further east. While all severe hazards are in play, the greatest
  risks will be damaging wind gusts and brief tornadoes. A level 1
  of 5 (marginal) risk will linger south of I-70 tomorrow
  afternoon.

- An active pattern continues into this weekend with another risk
  of severe storms on Sunday.

&&

.DISCUSSION...
Issued at 211 PM CDT Tue May 21 2024

18z surface map placed 996 mb low pressure over extreme southeast
Nebraska, which is forecast to deepen as it tracks northeast into
northern WI tonight. Well within the warm sector this afternoon,
central IL is being bathed in summertime heat and humidity with
temperatures in the upper 80s and dewpoints in the mid 60s as of 1
pm. A tight MSLP gradient will promote 30-40 mph southerly winds
gusts into early this evening. Dry top layers of soil and active
farming activity will lead to blowing dust in spots through late
afternoon.

A warm layer aloft centered near 775 mb should keep convection
suppressed in the warm sector this afternoon, and our attention is
focused on the cold front trailing south of the low, which is
forecast to fill in with convection over the next few hours. With
the better kinematic fields lifting northeast along with the
surface low, mesoanalysis suggests the more significant severe
weather potential (long track tornadoes, very large hail,
widespread wind damage) affecting areas to our northwest across
IA, far northwest IL, and southern WI into this evening. We do
maintain a risk of severe storms this evening locally,
particularly west of I-55 in a 7 to 11 pm window. As the
line of storms moves into this area, strong deep layer shear and
moderate instability will favor damaging straight line wind gusts
in the more intense line segments. While instability will decrease
with time and eastward extent, a 925-850 mb jet will strengthen
overhead, which may keep the severe threat going toward midnight
or a little later than the CAMs have been trending. The tornado
risk will mainly be tied to QLCS tornadoes, based on favorable
0-3km shear vectors northwest of the IL River.

Behind the front, a more typical May airmass will filter into most
of central later tonight and Wednesday with cooler highs in the
70s and lower humidity. The exception will be south of I-70 where
the front is slower to clear, leading to another warm day and a
few afternoon storms. The severe weather risk is much reduced in
this area from previous forecasts with higher instability (CAPEs
1000+ J/kg) suppressed near and south of the Ohio River based on
the 12z HREF. Still a couple strong afternoon storms can`t be
ruled out given 30 kt deep layer shear and SPC has a Marginal risk
(level 1/5) near/south of I-70.

For Thursday through early next week an active pattern will remain
in place across the region, with shortwaves shown crossing the
Midwest every 36-48 hours. Significant uncertainty in the
forecast details exist given differences in timing and placement
of these features, however Friday and Sunday look to be the
favored periods for more widespread showers and storms and this is
where higher PoPs have been placed. For severe weather prospects,
Sunday is currently the most concerning, especially if the 21/12z
ECMWF verifies with low pressure deepening just to our northwest.
Again, widely varying solutions are noted in the ensemble
envelope, so keep updated on later forecasts as the pattern
evolves.

25

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 641 PM CDT Tue May 21 2024

South winds will gust 30-40 kt into this evening ahead of a cold
front. A broken line of TSRA is expected to cross the central IL
terminals this evening, and have a 3-hr tempo for IFR conditions
and gusty winds associated with the storms. Winds veer west behind
the frontal passage and lose gustiness. Patchy MVFR ceilings
could develop behind the front, primarily at KBMI-KDEC-KCMI and
have added a scattered cloud group there for the overnight hours.

Shimon

&&

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

$$