701
FXUS63 KILX 051045
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
545 AM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Isolated (30% coverage) thunderstorms will exit eastern Illinois
  mid to late morning, with the next chance (40-50%) for scattered
  storms arriving Sunday and lingering into Tuesday.

&&

.DISCUSSION...
Issued at 113 AM CDT Fri Jul 5 2024

Two areas of thunderstorms continue approaching central Illinois at
this early hour: one lifting quickly across the Ozarks via warm
advection that noses into the Prairie State south of I-70, and
another being dragged along slowly by a seasonably sharp cold front
across central and eastern Iowa. While most locations in central
Illinois will be missed by each of these waves, we`ve maintained 20-
40% PoPs to account for an isolated shower/storm along the cold
front near and north of I-72, while PoPs are a bit higher (40-50+%)
further south where the most persistent of the Ozarks storms
could make an appearance near dawn. Meanwhile, patchy fog has
developed across our east, where dewpoint depressions are
generally less than 2 degF thanks to light winds and a lack of
appreciable cloud cover. CAMs suggest this will continue at least
the next several hours, perhaps becoming locally dense (HREF probs
for sub 1/2 mile vis briefly climb to 20-30%), though the
incoming convective clouds may help offset radiational cooling
near dawn.

Looking at the corridor of maximum dew point and theta-E spread from
the HREF, it appears the cold front will reach the I-57 corridor mid-
late morning and finally exit the CWA to the east-southeast sometime
early afternoon, by which time our PoPs come to an end everywhere
except along and north of I-74. There, low level cyclonic flow and
steep low level lapse rates amidst the drier airmass may prove
sufficient for a stray shower or two, although the better chance
will definitely be further north where NAM and GFS forecast
soundings appear more favorable. It`ll be a breezy Friday by July
standards as momentum is transferred well to the surface via
convection given the aforementioned steep low level afternoon lapse
rates, with gusts reaching the 25+ mph range if forecast soundings`
winds at the top of the mixed layer materialize.

In the wake of the upper low, surface high pressure will build into
the Ozarks, Midwest, and Ohio Valley heading into the weekend,
theoretically keeping the area dry. However, a couple mid-upper
level shortwaves lifting northeast across the Plains may graze us
with showers/storms Sunday into Monday, with the highest chances
across our west; there`s not going to be much in the way of
instability or shear which should maintain a low (<5%) severe risk,
though the feistiest cells might bring some gusty (mainly sub-
severe) winds to the surface given the dry mid level air in place
and steep low level lapse rates contributing to efficient
evaporational cooling and hence negative buoyancy of downdrafts.
Sometime Tuesday into Wednesday, the deterministic models suggest
the parent upper level trough will shift east toward New England.
However, the Midwest should generally remain beneath weak and stable
flow heading through mid-late week as a ridge of high pressure
becomes anchored across the West.

Bumgardner

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 544 AM CDT Fri Jul 5 2024

KILX radar shows isolated showers moving across central Illinois
ahead of a cold front which is nearly to the I-55 corridor at this
time. Behind this east-moving front, winds will veer sharply from
SW to WNW, with gusts over 20 kt at times during the afternoon.
Scattered to broken stratocumulus in the 4000 to 5000 ft range
today will diminish this evening with the loss of diurnal heating,
but redevelop tomorrow a bit lower - possibly (30-50% chance) in
the MVFR range for PIA, BMI, and CMI - near and after the end of
this forecast package.


Bumgardner

&&

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

$$