200
FXUS63 KILX 100435
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1135 PM CDT Thu May 9 2024

.KEY MESSAGES...

- A threat for isolated lightning strikes will persist through
  the middle of this evening south of I-74.

- A low-end lightning threat will accompany a line of showers
  crossing central Illinois from late Friday evening into early
  Saturday morning.

- In the Monday-Tuesday time frame, there is a 20-40% chance of
  greater than a half inch of rainfall in 24 hours. Should this
  occur, one impact would be additional runoff into area rivers
  already running high.

&&

.UPDATE...
Issued at 731 PM CDT Thu May 9 2024

Latest surface map shows the frontal boundary has slipped
south past I-72. A couple batches of showers are working their way
through, one immediately behind the front, and another stretching
from near Quincy to northern Indiana. This, and a third area of
showers in southeast Iowa, is associated with an upper shortwave
currently swinging southeast across Iowa. Latest high-res guidance
suggests this Iowa batch of rain may hold together enough to
warrant keeping some low PoP`s going past midnight across the
Illinois River valley. Elsewhere, rain chances should gradually
wane. No lightning has been observed as of late, though some
heavier 40-50 dBZ showers were near Jacksonville this hour. Have
lingered a mention of isolated thunder across the I-72 corridor
for another hour or two.

Geelhart

&&

.DISCUSSION...
Issued at 313 PM CDT Thu May 9 2024

A frontal boundary which was nearly stationary this morning has
lifted northward slightly early this afternoon, with winds along
I-74 backing somewhat in response. Around 250-750 J/kg of MLCAPE
resides along a narrow axis from about Lincoln to Mattoon-
Charleston where the sky has cleared somewhat, and we have seen a
handful of showers reaching 40-50 dBZ or so with a few lightning
strikes. The threat for lightning should persist no later than
mid-evening as the frontal boundary pushes southward, MLCAPE
decreases and the atmosphere stabilizes.

A 500-mb short wave trough diving southward out of the upper
Midwest helping to drive some of this afternoon and evening`s
shower activity should pivot east into Indiana by early Friday
morning. Weather during the day should be fairly quiet, with the
next mid-level short wave and associated mid-level jet coming out
of the upper Midwest on Friday evening. An associated weakening
line of showers is forecast to move through central Illinois from
northwest to southeast from late Friday evening through early
Saturday morning, with around 100 J/kg of MUCAPE forecast by the
HRRR indicating at least some probability of lightning especially
Friday evening.

Look for breezy northwest winds gusting to 20-30 mph on Saturday
behind the departing short wave trough. Temperatures kick up a
notch on Sunday under short wave ridging as a mid-level low moves
out of the Colorado Rockies into the high Plains. This low is
responsible for a chance of fairly widespread rainfall in the
Monday-Tuesday time frame. The probability of SBCAPE > 250 J/kg
and sfc-500 mb shear is below 5%, with severe weather
probabilities low. Enough CAPE should be around to support some
thunder, however. NBM probabilities show about a 20-40% chance of
greater than a half inch of rain in a 24 hour period in the
Monday-Tuesday window.

Notable model variability exists in timing and strength of troughs
beyond Tuesday. Though mid-range precip chances are included
throughout Wednesday and Thursday, there`s a decent chance of at
least one dry period occurring in that stretch.

AAT

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1135 PM CDT Thu May 9 2024

MVFR cloud deck roughly east of a KSPI-KPNT line late evening,
with some embedded IFR conditions near KBMI/KCMI. While these
should lift a bit as lingering showers exit, some concern for
ceilings below 1,000 feet further west overnight. Currently, some
breaks in the clouds are seen across the Illinois River valley,
and latest HREF guidance favors 50-60% chances of ceilings below
1,000 feet developing between 09-12Z from KPIA-KSPI west.
Significant improvements expected to begin by 14Z, with VFR
conditions prevailing the remainder of the forecast period.

Geelhart

&&

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

$$