605
FXUS63 KILX 050616
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
116 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 06z TAFs through 06z Friday Night)
Issued at 1143 PM CDT Thu Jul 4 2024

VFR conditions will prevail through the entire 06z TAF period.
Winds will initially be S/SE at around 5kt, then will veer to SW
after 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 5000 and
8000ft 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.
&&

$$