738
FXUS63 KILX 042340
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
640 PM CDT Thu Jul 4 2024

.KEY MESSAGES...

- Scattered showers (40 percent coverage) will continue north of a
  Macomb to Paris line through the remainder of the afternoon, but
  will taper off from the southwest with dry conditions likely
  (80-90 percent confidence) through most of the evening.

&&

.DISCUSSION...
Issued at 230 PM CDT Thu Jul 4 2024

This afternoon, a shortwave trough is noted lifting from central
Illinois into northeastern Illinois with scattered showers
occurring, mainly north of a Macomb to Paris line. Latest RAP
suggests very weak instability is in place, less than 200 J/kg but
forecast soundings show the instability does poke up above -10C
at times and an isolated storm could not be ruled out. As upper
wave continues to move northeast, subtle shortwave ridging will
move in behind and should keep conditions dry late this afternoon
through much of the evening.

Late this evening and overnight, deep/closed H5 low is progged to
dig across the Upper Midwest while attendant surface cold front
sweeps across central Illinois overnight into early Friday
morning. Showers and a few storms will accompany these features,
spreading back into the Illinois River Valley likely around or
just after midnight tonight, then across the remainder of central
Illinois overnight. A narrow plume of weak instability (MUCAPE
around 300 J/kg) will support a few storms, but the severe threat
appears low given the unfavorable diurnal timing and weak
instability. Precip amounts will be light overnight across central
Illinois. NBM 75th percentile generally runs less than a tenth of
an inch north of I- 70, with up to around a quarter inch south.

Behind the departing cold front, slightly drier (low to mid 60)
dew points will begin to advect across central Illinois along
with slightly cooler temps. Expect highs in the upper 70s to low
80s across the area Friday afternoon. Despite the drier air,
steep low level lapse rates and lingering low level cyclonic flow
should drive some cold-air stratocumulus development Friday
afternoon. Forecast soundings suggest instability may be several
thousand feet deep allowing a few light showers or sprinkles to
develop, especially near and north of I-74. Otherwise, dry weather
is expected to prevail Friday and continue into Saturday as high
pressure spreads from the central Great Plains Friday across the
mid Mississippi Valley Saturday.

Heat and humidity begin to work back across central Illinois
Sunday as the ridge axis shifts to our east allowing return flow
to overspread the area. Precip chances will return early next week
as a deep upper trough slowly moves east across the region.

Deubelbeiss

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 640 PM CDT Thu Jul 4 2024

VFR conditions will prevail through the entire 00z TAF period.
Winds will initially be E/SE at around 5kt early this evening,
then will veer to SW toward midnight as a cold front approaches
from the northwest. Once the front passes, winds will become W/NW
and gusty on Friday...with forecast soundings and numeric guidance
suggesting gusts in the 20-25kt range. FEW-SCT clouds between
3500 and 5000ft will persist through tonight, then will clear out
after FROPA. With a pocket of cold air aloft dropping southeastward
out of the Northern Plains, steep lapse rates will develop by
peak heating Friday. NAM Cu-rule indicates SCT-BKN diurnal clouds
at 3500-4000ft during the afternoon.

Barnes

&&

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

$$