619
FXUS63 KILX 171713
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1213 PM CDT Wed Jul 17 2024

.KEY MESSAGES...

- Seasonably cool and dry conditions are expected into the
  weekend, with temperatures 5 to 10 degrees below normal.

- Scattered precip chances return early next week (20-50% chance).
  The potential for severe thunderstorms or heavy rainfall appears
  low.

&&

.UPDATE...
Issued at 1022 AM CDT Wed Jul 17 2024

A cold front is located just south of I-70 in southeast IL as of
10 AM, moving slowly southward. Cloudy skies continue near and
southeast of the front, with mostly clear skies to the north as
high pressure begins to build into the area. The cooler air mass
behind the front should produce highs today ranging from as low as
80 north of I-74 to as warm as 85 south of I-70. Can`t rule out a
few showers and thunderstorms developing along the front south of
I-70 this afternoon with forecast CAPE around 1000 J/kg and some
potential surface convergence near the front, however the frontal
position looks to be south of the area by the time diurnal heating
allows some storms to form. Forecast is in good shape with most of
these features, and only minor modifications to wind forecast and
sky cover through this afternoon have been done.

37

&&

.DISCUSSION...
Issued at 128 AM CDT Wed Jul 17 2024

No hazardous weather is expected over the next five days, a
welcome change after a flurry of impactful thunderstorms over the
last 2-3 days. At the start of the period the synoptic pattern
was highly amplified, with an upper ridge axis extending from the
Four Corners region into western Canada and an upper trough over
Ontario/the upper Great Lakes.

Early Wed morning, a weak cold front was bisecting the ILX CWA
and shifting southeast in time, located near/just north of the
I-72 corridor as of 1:15am/0615z. Further south, thunderstorms
have blossomed along an outflow boundary draped east-west near the
Ohio River. These will stay south of the CWA, but anvil clouds
from these storms will continue streaming over areas south of I-70
in the immediate near term. Elsewhere, a 1020-mb sfc high
pressure was positioned near the North Dakota/Canada border, and
this sfc high will be the primary driver of the weather across IL
over the next several days.

As that cold front slowly shifts southeast today and eventually
pushes south of the CWA, isolated showers are possible (10-20%
chance) along the front. These will mainly be south of I-70 during
the daytime hours. A cooling trend begins as northerly flow
becomes dominant behind the front, and highs today will be in the
low/mid 80s beneath mostly clear skies (partly cloudy south of I-
70).

The aforementioned sfc high pressure will sink towards the Midwest
by Thurs, then remain in place through Sat, gradually weakening in
time. The NBM has high temps in the upper 70s to low 80s during
this stretch, which is about 5-10 degrees below normal. This is
well supported by ensemble guidance, such as the EC ens which has
a greater than 80% chance of temps at least five degrees below
normal Thurs-Sat. Low temps during this timeframe will range from
the mid 50s to low 60s. No precipitation is expected as seasonably
dry air accompanies the sfc high pressure, with ens mean PWAT
values below 1", which is below the 25th percentile of the
climatological norm for mid-July.

Into Sun, global models depict a weak but closed upper low forming
over Missouri. This slow-moving feature could lead to scattered
precip activity perhaps as early as Sunday, but more likely Mon-
Wed (20-50% chance, increasing with southward extent). Between the
dry antecedent airmass and seemingly limited gulf moisture
advection to interact with this system, severe storm chances look
quite low. GFS forecast soundings depict seasonably weak
instability, with less than 750 J/kg of CAPE each day Sun-Tues.
Looking deeper into the extended forecast, the CPC 8 to 14 day
outlooks call for near normal temperatures and leans above normal
(~35% chance) on precipitation to close out the month of
July.

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1213 PM CDT Wed Jul 17 2024

VFR conditions are expected for the upcoming 24 hours with
scattered cloud cover above 3000 feet expected this afternoon.
Winds NNW 10-14 kts with gusts 15-20 kts this afternoon, becoming
NNE 3-6 kts after 01Z.

37

&&

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

$$