556
FXUS63 KILX 061725
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1225 PM CDT Sat Jul 6 2024

.KEY MESSAGES...

- There is a 30% chance for thunderstorms west of the Illinois
  River Sunday evening, with more widespread showers and storms
  anticipated Monday into Tuesday. While severe weather is not
  expected, storms may produce heavy rain and gusty winds,
  especially Sunday evening.

&&

.UPDATE...
Issued at 906 AM CDT Sat Jul 6 2024

A pleasant and sunny start to the morning across central Illinois,
with temperatures ranging from the upper 60s to mid 70s as of
9am/14z. Weak, broad sfc high pressure sits over the central
Plains/Ozarks. Locally, diurnal Cu is expected to blossom by late
morning. No forecast updates were necessary at this time.

Erwin

&&

.DISCUSSION...
Issued at 201 AM CDT Sat Jul 6 2024

Tranquil weather conditions will prevail this weekend across central
Illinois under the influence of surface high pressure. While cool
advection is forecast to be weaker today with less afternoon wind
than yesterday, subsidence and (weak) convective mixing will
maintain seasonably dry (upper 50s to mid 60s dew points) low
levels, with radiational warming this afternoon bringing highs to
only the low 80s - still a little cooler than normal for this time
of year.

Tomorrow will be a bit warmer, however, as return flow overspreads
the region ahead of a trough across the Plains. The 00z HRRR
suggests some locations, mainly along and south of I-72, will warm
to 90 or better, and this seems reasonable if mixing brings
afternoon dew points into the 50s as the same model would suggest.
Toward late evening, some storms are expected to fire to our west
where a little more low level moisture leads to MUCAPE values over
2000 J/kg (as the 06.00z NAMNest and HRRR would have it). The
piece of shortwave energy lifting northeast into western
IL/eastern IA Sunday night could even spark a couple storms across
our western counties, though more widespread garden variety
convection isn`t expected until Monday afternoon.

Right now, NAM forecast soundings suggest inverted-V soundings
with steep low level lapse rates and notable mid level dry air
Sunday evening across our west where EPS mean brings PWATs to 1.7"
or higher (near the climatological 90th percentile), so
conceptually precip loading in the feistier storms should make
them capable of localized strong (40+mph) wind gusts in wet
microbursts when they collapse. Even so, lack of wind shear has us
expecting nothing sustained or organized, so the severe risk
remains low (5%). Forecast soundings for Monday look even less
concerning, with still an inverted-V and steep low level lapse
rates in place, but a much more moist column above the LCL; this
lack of mid level dry air leads us to believe downdrafts will be a
little weaker compared to Sunday, and once again the anemic shear
will preclude storm organization to result in a low (less than
5%) severe risk.

Monday night into early Tuesday, another piece of shortwave energy
lifting across the Prairie State will result in a LLJ currently
slated to be strongest across our southern counties (mainly
near/south of I-70) where a little more shear (NBM probs climb to 50-
70% for more than 30 kt 0m-500mb shear) can be expected for
sustained storms. LREF mean PWATs there approach 2 inches early
Tuesday, and with any training storms there could theoretically be
some localized heavy rain totals; however NBM probs remain sub 20%
for more than an inch by 12z (7am) Wednesday (morning), by which
time the axis of this first trough should be departing.

Throughout the rest of the work week, troughing is expected to
linger across the eastern half of the CONUS in response to an
amplifying ridge across the West. The significance of this is
threefold: (1) we can`t quite rule out precip any day, though (2)
severe potential will be low, and (3) temperatures and
humidity should remain near or slightly below normal.

Bumgardner

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1224 PM CDT Sat Jul 6 2024

High pressure is centered over NW Arkansas this afternoon and will
shift to the upper Ohio Valley Sunday morning. Across central
Illinois, northwest winds in place today will become light and
variable overnight with passage of the ridge axis, then set up out
of the S/SSW Sunday morning. Outside of low end fog potential
late tonight into Sunday morning which appears best east of the
terminals, VFR conditions are expected through the period.

Deubelbeiss

&&

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

$$