943
FXUS63 KLOT 011714
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1214 PM CDT Tue Oct 1 2024

.KEY MESSAGES...

- A dry pattern will prevail through at least the weekend with
  generally seasonable to above average temperatures.

&&

.DISCUSSION...
Issued at 154 AM CDT Tue Oct 1 2024

Through Wednesday:

Our approaching surface cold front is shifting towards the
Mississippi River just west of our region as of 2 AM this
morning. Winds immediately west of the front are gusting (at
least briefly) up to 30-35 mph from the northwest. These trends
are expected to continue eastward across northern IL with the
front through the predawn hours. It will thus be a rather breeze
start to the day. There will be a very small chance (<15%) of a
sprinkle with the frontal passage early this morning, particularly
across my northwestern IN counties. However, the main story today
will be the plummeting dewpoints and cooler temperatures as the
post frontal airmass sweeps into the region on the breezy
northwest winds.

The cooler airmass moving into the area today will keep afternoon
temperatures rather steady in the mid to upper 60s. As dewpoints
plummet into the 30s afternoon relative humidity values are
expected to bottom out around, or just below 30 percent, most
notably across interior sections of northern IL. This does cause
some concern for the threat of wildfire spread across northern IL
this afternoon, especially since northwest winds will remain in
the 10-20 mph range for a few hours this afternoon. Fortunately,
with with the strongest winds expected early this morning followed
by gradually easing wind speeds through the afternoon we are not
expecting conditions to reach a critical level to warrant the
issuance of a Red Flag Warning. However, it may be a good idea to
postpone any outdoor burning.

A large surface high will build eastward over the Mid-Mississippi
Valley region tonight. The combination of light winds, mainly
clear skies and a very dry airmass will all help foster efficient
radiational cooling after sunset this evening. Temperatures are
thus expected to fall off quickly through the 50s and into the
40s this evening, before readings bottom out early Wednesday
morning in the upper 30s to around 40 outside of the Chicago
urban environment (and inland from the lake).

Quiet and pleasant weather is then on tap for Wednesday. Following
a chilly start to the day, temperatures will warm nicely into the
low 70s during the afternoon as the surface flow turns back out
of the southwest following the eastward passage of the surface
high. Skies are also expected to be mostly clear.

KJB


Wednesday Night through Monday:

Dry conditions will persist on Thursday amid mostly sunny skies
and highs near 80. A broad longwave trough crossing southern
Canada and the northern Great Plains Thursday into Friday will
induce a weak surface trough/cold front across the Upper
Mississippi River Valley. This front will cross the forecast
area late Thursday night into Friday morning. The combination of
a very dry antecedent airmass and poor moisture transport from
the southwest will favor a dry frontal passage, though a handful
of ensemble members still imply at least sparse coverage of
showers or convection as far south as northern Illinois.

Expansive high pressure will settle over the region later
Friday through Saturday. Another trough will cross far southern
Canada this weekend, with more prominent forcing remaining well
to the north Saturday night before a cold front crosses the area
early Sunday. Profiles continue to look rather dry ahead of the
front as Gulf moisture remains cutoff from potential tropical
activity. Signs point to a dry frontal passage, with only some
mid-level Pacific- based moisture brushing the area to the
north.

Sunday`s set-up is a somewhat classic watch-out scenario for an
elevated brush fire risk in our area. Forecast profiles suggest
that a well-mixed post-frontal airmass aided by gusty westerly
winds will be capable of lowering RH values near or potentially
below critical values of 25%. Nearly a third of extended
ensemble members indicate midday RH values under 30%, which is a
notable signal this far out. Will need to continue monitoring
the timing of the frontal passage as well as the latitudinal
location of the trough (and associated pressure gradient) to the
north as there could very well be a disconnect between stronger
winds to the north and lower RH to the south.

Kluber

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1215 PM CDT Tue Oct 1 2024

VFR through the period with no significant concerns.

Breezy north-northwest winds this afternoon will diminish
quickly with sunset this evening. The direction will shift to
south-southwest on Wednesday with speeds near/around 10 kt.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 1 AM CDT Wednesday for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CDT Wednesday for the IN
     nearshore waters.

&&

$$

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