023
FXUS63 KILX 110451
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1151 PM CDT Mon Jun 10 2024

.KEY MESSAGES...

- Summer-like temperatures return by Wednesday and appear likely
  to stick around over much of the next two weeks. Thursday is
  expected to be the muggiest day this week, with afternoon heat
  indices approaching 100F west of the Illinois River.

- There is a 30-50% chance of thunderstorms Thursday
  evening/night, some of which could be strong to severe north of
  I-72.

&&

.UPDATE...
Issued at 903 PM CDT Mon Jun 10 2024

Sprawling ridge of high pressure extending from Ontario
southwestward to the mid-Mississippi River Valley will dominate
the weather across central Illinois tonight...providing clear
skies, light winds, and chilly temperatures. 02z/9pm readings
have already dropped into the lower to middle 60s across much of
the KILX CWA, with even cooler upper 50s noted near the Indiana
border. Lowest dewpoints in the upper 30s/lower 40s are in place
along/northeast of a Bloomington to Mattoon line and this is where
the coolest overnight lows will be found. Based on rate of temp
fall so far this evening, think lows will range from the lower 40s
near the Indiana border to around 50 degrees across the far
southwest near Winchester.

Barnes

&&

.DISCUSSION...
Issued at 151 PM CDT Mon Jun 10 2024

The mostly cloudy skies that were present this morning continue to
slowly scatter out, but the combination of cloud cover and
northerly flow have kept temps in the mid 60s to low 70s as of
130pm/1830z. An upper trough remains in place over the eastern
CONUS, with an associated cold front having pushed all the way
south to the Gulf Coast. A 1018-mb sfc high pressure was situated
over the Upper Midwest. That broad, weak sfc high pressure will
remain in control through Tues. Light, southerly winds develop on
Tues, marking the start of a warming trend. Highs return to near
80F tomorrow, which is closer to normal, while dewpoints remain
seasonably low, in the 40s for most of the area.

Into the latter half of the work week, height rises occur as
ridging builds over the Four Corners region. Multiple
disturbances progress around the north side of this ridge, moving
through the northern Plains/upper Midwest. For the most part,
precip associated with these disturbances is expected to remain
north of the ILX CWA, but can`t rule out a glancing shower north
of I-74 Tues night or late Wed night (~10% chance). The better
chance (30-50%) for rain/storms is Thurs PM, when a cold front
sags south into the area and interacts with a moist, unstable
airmass. While the 500mb jet is progged to stay north of the area,
it should still provide sufficient shear to support a chance for
strong to severe t-storms. The Grand Ensemble depicts a 40-70%
chance of having both surface-based CAPE greater than 1000 J/kg
and deep layer shear over 30 knots north of I-72 Thurs PM. One
factor that could limit the severe potential locally is the
diurnal timing, as current guidance keeps storms north/west of the
CWA until later in the evening (after 00z/7pm). Ensemble mean
PWAT values are between 1.5-2", which is above the 90th percentile
of the ILX observed sounding climatology, so locally heavy
rainfall is also a concern Thurs PM. Aside from Thurs PM, precip
chances are generally low (below 15%) through the upcoming
weekend.

The other forecast concern is the heat, and it appears that above
normal temperatures will become a staple of the forecast beginning
mid-week and continuing well into the extended. By Wed, highs
push into the upper 80s/low 90s. Dewpoints will be climbing but
won`t be too oppressive on Wed. By Thurs, however, dewpoints will
range from near 70 west of the IL River to near 60 across far E
IL. With highs in the low to mid 90s, that will result in peak
heat indices around 100F west of the IL River on Thurs. The
experimental NWS HeatRisk product (which uses wet bulb globe
temperature) reaches "high" (level 3 of 4) for a few hours west of
I-55 during peak heating on Thursday. For context on that
specific category, "heat of this type represents a major risk to
all individuals who are exposed to the sun and active, or in a
heat-sensitive group".

Conditions aren`t expected to be quite as oppressive Fri-Sat, with
highs in the upper 80s/low 90s but with reduced humidity as
dewpoints fall to the 50s or low 60s. That "respite", if it can be
referred to as one, will be short-lived, with temperatures
forecast to return to the mid 90s Sun-Mon, while dewpoints climb
back toward 70. The CPC 6 to 10 and 8 to 14 day outlooks (valid
June 15 to June 23) suggest that above normal temperatures are
likely during that time (70-80% chance). Normal temperatures
during that period are highs in the mid 80s and lows in the low
60s.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1151 PM CDT Mon Jun 10 2024

VFR conditions will prevail through the entire 06z TAF period.
Light/variable winds will become SW at 5-10kt by mid to late
Tuesday morning. Other than FEW-SCT high/thin clouds, skies will
initially be mostly clear...followed by a gradual increase of
high clouds through the day. After that, models show an upper-
level disturbance tracking across the Northern Plains into the
western Great Lakes. The associated surface trough/front will
approach from the northwest late in the day, resulting in a band
of mid clouds pushing toward the I-55 corridor by late afternoon
into Tuesday evening.

Barnes

&&

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

$$