Normal, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

927
FXUS63 KILX 231711
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1111 AM CST Sat Nov 23 2024

.KEY MESSAGES...

- Low clouds will remain prevalent today. There is a small (about
  30%) chance that ceilings will continue building down toward
  the surface, resulting in visibility falling below 1 mile this
  morning.

- South winds will become breezy (20-25 mph) on Sunday, helping
  boost temperatures toward 60 degrees, albeit briefly. A cold
  front will bring rain chances (40-60%) to areas east of the IL
  River Valley by Monday, with temperatures turning sharply colder
  Monday night (wind chill values in the teens).

- There is a medium probability (40-50% chance) for wintry
  weather by the middle of next week, which will be followed by
  very cold, January-like temperatures by Friday and Saturday.

&&

.UPDATE...
Issued at 1011 AM CST Sat Nov 23 2024

Visible satellite imagery late this morning shows an expansive
area of low stratus over most of the state, aside from clearing
near and east of the St. Louis metro. This is a result of low-
level moisture remaining trapped underneath a subsidence
inversion, as noted on the KILX 23.12Z sounding. The latest suite
of high resolution guidance (CONSShort, GLAMP, ADJLAV) shows slow
improvement beginning in our southwest counties by early to mid
afternoon as surface ridging works into the area and turns low-
level flow to the southwest. This will act to scour out low-level
moisture from southwest to northeast, but confidence in how far
north this will make it remains somewhat low going into this
evening. Updated sky cover to better reflect the latest trends,
but otherwise the forecast remains largely unchanged.

NMA

&&

.DISCUSSION...
Issued at 119 AM CST Sat Nov 23 2024

The main forecast concern for today will be timing the stratus
breakup, and how that might impact temperatures going into this
afternoon. Observational trends overnight have indicated a steady
build-down of stratus, and much of the recent guidance (RAP, HRRR,
and GLAMP) has trended even lower with the stratus build-down such
that surface visibility may fall below one mile in some areas.
With the residual moisture trapped beneath a strong subsidence
inversion, and with deep cyclonic flow still in place ahead of the
925-mb ridge axis, we have no reason to believe the low clouds
will make a quick exit today. It`s not until after 18z/12pm that
the ridge axis pushes across central Illinois, shifting low-level
winds southwesterly, do we see an opportunity for clouds to
gradually lift and break. If this is indeed how things evolve
today, afternoon highs may struggle to reach the 40s.

By Sunday, model guidance is in excellent agreement that a mid-
level shortwave will eject out of the Rockies and help bring deep
southwest flow across the Southern Plains and into the Mid-
Mississippi Valley. With increasing southerly winds and a strong
push of warm advection ahead of a sharpening baroclinic zone,
temperatures will surge into the low 60s across west central
Illinois Sunday afternoon. This sharp warm-up will be brief,
however, as a robust upper-level wave begins to dig toward the
Upper- Mississippi Valley on Monday, forcing a cold front into
central Illinois. Some rain is anticipated with frontal passage,
though model soundings exhibit a serious moisture discontinuity in
the mid-levels, which is taking a bite out of our QPE. Current
blended (NBM) and ensemble (LREF) guidance supports a 40-60%
chance for rain on Monday in areas east of the Illinois River
Valley, with QPE generally between a Tr-0.25".

With a colder, drier and breezy airmass filtering-in behind the
front late Monday evening, temperatures will bottom-out in the mid
20s with wind chill values in the teens. Below normal temperatures
will then keep its grip on the region through the remainder of
next week, with a reasonably strong signal for a January-like
chill by next weekend.

Of course, the thing overshadowing this forecast period is the
potential for wintry precipitation by the middle of next week,
which is accentuated by holiday travel. As we see it right now, if
the blended (NBM) and raw ensemble (LREF) guidance trends more
towards the `EPS Mean` in coming days, central Illinois will be
positioned for moderate winter weather impacts. In comparison to
the GEFS & GEPS, the EPS Mean exhibits a deeper/more- amplified
trough across the Southern Plains next Wednesday, which coincides
with a stronger, wetter and more northerly-oriented surface low
into Thursday.

That`s what we see right now. We do not favor one solution over
the other. Each solution seems equally plausible at this time. The
best thing to do is to not anchor toward any one solution, but
continue monitoring how the data trends throughout this weekend.

MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1109 AM CST Sat Nov 23 2024

High pressure is in place along the Mississippi River Valley this
afternoon with light southwest winds expected to veer to the S/SSE
by this evening as the ridge slowly shifts east. IFR stratus deck
remains draped across the region but there are some signs of
erosion from the SW already late this morning and should reach SPI
then DEC by mid afternoon. Guidance in general has been clearing
cloud cover too quickly over the past day and there remains low
confidence in how quickly the clearing will lift across the I-74
corridor late this afternoon or evening.

Deubelbeiss

&&

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

$$