898
FXUS63 KILX 271702
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1202 PM CDT Mon May 27 2024

.KEY MESSAGES...

- Scattered thunderstorms (20-30% chance) will pose a threat of
  gusty winds this afternoon into the evening, primarily between 4
  PM and 9 PM. There is a level 1 of 5 risk of damaging winds.

- Tuesday afternoon/evening will also feature scattered storms
  capable of gusty winds (20% chance), mainly north of I-74.

- High pressure takes control for the latter half of the week,
  with dry weather Wednesday through Friday.

&&

.UPDATE...
Issued at 1013 AM CDT Mon May 27 2024

Late morning water vapor imagery showed a shortwave over southwest
MN, which was producing scattered showers and storms as far
southeast a central IA. This system will track southeast today,
with scattered storms (20-30% coverage) affecting most of our
counties north of I-70 from 2-10 pm. Deep mixing above 850 mb
should trend afternoon dewpoints down to the lower 50s or even
upper 40s. However, steep mid level lapse rates will contribute
to weak instability (near 500 J/kg SBCAPE), and given inverted-v
soundings, gusty winds under the showers/storms will be seen.
Given marginal deep layer shear around 30 kt and the weak
instability feel most gusts will be below severe levels, but a few
of the stronger updrafts could result in low end severe gusts,
and much of the area is in a Marginal (level 1 of 5) risk of
severe weather today. Aside from the storms, west-northwest winds
will gust 25-30 mph in a tight MSLP gradient on the back side of
low pressure over Lake Huron. As the low departs and ridging moves
in from the west, gusts will quickly diminish this evening. Highs
will be seasonable, in the mid/upper 70s.

25

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 237 AM CDT Mon May 27 2024

Early Monday morning, sfc low pressure was positioned over the
Great Lakes region, with an attendant cold front extending
through north- central IN into east-central IL. As of 2am/07z the
front had moved past a Danville to Taylorville line, but had not
yet reached Paris- to-Effingham. A few spotty showers have
developed near and just ahead of the front, so kept some low
chance PoPs during the first few hours of the forecast period.
These showers should be east of the area by daybreak today.

Today, central IL will be in the post-frontal airmass, which will
feature persistent northwest winds gusting 20-30 mph. A digging
shortwave will approach from the northwest by mid-afternoon,
leading to scattered showers/storms. Instability progs are rather
weak, less than 750 J/kg, but forecast soundings have consistently
shown a deep- inverted V profile beneath the cloud bases, which
are expected to be over 4000 feet. Efficient evaporative cooling
beneath these cloud bases could lead to sporadic strong downdrafts
capable of producing strong wind gusts. This assessment is
supported by high- res guidance, as the 27.00z HREF indicates a
20-40% chance of gusts over 45 mph with these storms. There is a
marginal risk (level 1 of 5) for damaging winds. Other severe
hazards (hail, tornadoes) are not expected.

Radar estimates suggest that nearly all of the CWA has received
at least a half inch of rain since Friday, and a majority of the
CWA has received over 1". That will hopefully stymie any blowing
dust concerns with these gusty thunderstorms.

Erwin

.LONG TERM...  (Tuesday through Sunday)
Issued at 237 AM CDT Mon May 27 2024

Tuesday looks fairly similar to Monday, with continued cyclonic
(northwesterly) flow and another shortwave approaching during the
afternoon which could kick off more showers/storms, mainly north
of I-74 (20% chance). Forecast soundings for Tuesday show similar
signatures to Monday, so gusty winds will once again be possible
with any storms that form.

Conditions are looking quite enjoyable Wed thru Fri as upper level
ridging set up over the central Plains, resulting in
strengthening, broad sfc high pressure over the Upper
Midwest/Ontario. These features will gradually shift east during
the latter half of the week, but will provide mostly dry weather
Wednesday-Friday while temperatures steadily warm each day. By
Fri, highs return to near normal, around 80F. Dewpoints in the
upper 40s/low 50s will make it feel quite refreshing.

Into the weekend, the upper ridge shifts east while a trough
approaches from the west, returning precip to the forecast Sat-
Sun. Early indications are that the severe weather potential with
this system is quite low, owing to limited moisture return.

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1202 AM CDT Mon May 27 2024

West-northwest winds gusting up to 25 kt will continue until early
evening before subsiding. A disturbance moving in from the
northwest around 00z will bring a 3-4 hour period of isolated
TSRA to the central IL terminals. Coverage is only expected to be
around 20%, so kept mention at VCTS. However if a storm does
impact a terminal a brief 40+ kt wind gust is possible. Gusty
winds will pick up again by late morning, with a BKN VFR level
stratocu deck expected to develop around the same time.

25

&&

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

$$