Mon Feb 19 Meteorology for Chicago

[Brett Crapser]

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1138 AM CST Mon Feb 19 2024

KEY MESSAGES...

- Warming temperatures over the next few days with 50s in store
for the middle of the week

- A potential for some rain showers on Thursday, especially east
of I-55

&&

DISCUSSION...
Issued at 315 AM CST Mon Feb 19 2024

Clear skies early this morning are about to be interrupted by a
blanket of cirrus being advected in from the northwest on the
lee of an approaching ridge. Temperatures have been a bit
troublesome so far this morning with the area refusing to cool
off consistently. A handful of sites, mainly across our
northwest, have been down in the upper teens for a few hours
now. Most of the area sits in the mid 20s as of around 3 AM.
We`ll find ourselves in the upper teens/lower 20s on our way out
the door this morning. Luckily, a calm wind means there`s not
much of a wind chill factor to account for. It`s possible that
some patchy fog could develop across our south as we approach
daybreak, but nothing widespread or terribly dense is
anticipated. Temperatures this afternoon should be similar to
what we saw yesterday, perhaps a couple of degrees warmer, with
highs forecast to reach the middle to upper 40s. There remains a
little bit of snowpack across our far south which should keep
this part of the area a tad cooler once again today. Expect
filtered sunshine today on account of the cirrus overhead and
winds will remain rather light within a broad region of surface
high pressure in place.

Just upstream of the cirrus plume, a potent little shortwave is
digging over the northern High Plains with a region of circulation
evident on water vapor imagery. Models continue to deamplify the
wave quite considerably before it works across the Midwest tomorrow.
By the time it moves overhead, moisture and forcing look too scarce
to produce anything more than some added cloud cover. A second, more
subtle shortwave is progged to move over on Wednesday. This one is
more moisture-rich than the previous, but a lack forcing and some
low level dry air should again keep the area dry. The operational
Euro and a handful of its ensemble members have consistently wanted
to produce some pockets of light precip, but such solutions are few
and far between among guidance.

We`re still looking at Wednesday night and Thursday as being our
best potential for seeing precip this week. An organized system of
low pressure will trek across the lower Midwest. There is a
consistent signal among models that a strengthening southwesterly
LLJ atop the storm will stretch and elongate the low pressure center
introducing a region of deformation and, in turn, higher precip
probs to areas northeast. The question that remains is whether this
will begin to take place early enough to drop precip on the CWA
before the system is too far off to our east. The Euro, NAM, and
Canadian all have a pretty consistent signal that this process will
really begin to ramp up right over or just downstream of our CWA.
This solution appears to be the fan favorite among various ensembles
as well and would favor a mostly dry forecast with areas east of I-
55 seeing the best chance for precip. The GFS, among others, is
quicker to strengthen the LLJ and brings widespread showers to
the area. While there`s enough support that this solution
shouldn`t be discounted just yet, there is a notably stronger
signal in favor of the former.

An upper trough axis will move across late Thursday which will pull
temperatures back into the 40s for Friday and Saturday after
spending the previous few days in the 50s. Broad surface high
pressure should keep conditions pretty quiet through the weekend.
Pleasantly mild conditions look to return by Sunday with all signs
continuing to point toward a warm end to the month.

Doom

&&

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1134 AM CST Mon Feb 19 2024

Daytime heating is helping winds to become better established
with some variability in direction between south and southwest
being noted. Direction should become more uniform from the
south-southwest into early afternoon with speeds running in the
6-10 kt range. The direction will become more southerly to
south-southeasterly this evening. South winds are expected
Tuesday with gusts picking up to around 20 kt early Tuesday
afternoon.

MDB

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$