132
FXUS63 KLOT 061053
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
553 AM CDT Sun Apr 6 2025

.KEY MESSAGES...

- Isolated to scattered (mainly non-accumulating) gusty snow
  showers Monday into Monday evening.

- The next chances for precipitation return late Tuesday night
  through Wednesday night, with some snow possible at times.

&&

.DISCUSSION...
Issued at 323 AM CDT Sun Apr 6 2025

Tranquil weather conditions will prevail today as the
northeastern flanks of a sprawling area of high pressure
(centered across southern New Mexico and the Trans-Pecos) slides
into the region. This will inject some drier air across the
forecast area today, with surface dewpoints expected to
generally mix out into the low to mid 20s and possibly upper
teens. Fast southwesterly flow will continue aloft, however,
with a 700 mb confluence axis remaining nearly stationary from
near St. Louis, Missouri to Toledo, Ohio. Persistent mid-level
frontogenesis will thus remain in place across central Illinois
into parts of northern Indiana, with numerous embedded vorticity
maxima slated to push northeast out of Missouri. This setup
will maintain mid and upper-level cloud cover across the region
today, although we should see thinning with time, particularly
across our northwest. Can`t rule out a few sprinkles near our
US-24 vicinity locales today given the presence of steepening
700-500 mb lapse rates and the aforementioned persistent mid-
level f-gen.

Tonight, a vigorous shortwave (currently embedded within a
stream of cyclonic shear vorticity over northern Manitoba)
will push across the Arrowhead Region of Minnesota and into
lower Michigan. Significant height falls (in excess of 140 m/12
hours) and attendant DCVA will help send robust cold front
surging southward out of Wisconsin on Monday morning. While
model guidance is generally not producing much in the way of
QPF, forecast soundings reveal sufficient saturation occurring
through about 600 mb (around -20 C), combined with steepening
near-surface lapse rates to support the generation of a band of
snow with the front. Currently, this activity looks to press
south of the Wisconsin state line around daybreak and then
towards I-80 through mid to late morning. Pressure rises on the
order of 3-5 mb/3 hour, while not tremendous, should also
support the generation of occasional 30-35 mph gusts along and
behind the cold front. With surface temperatures generally at or
above freezing, not expecting roadway accumulations, with any
dustings relegated to grassy surfaces. Sharp visibility
reductions and gusty northerly winds, however, may lead to some
slowed travel during the morning commute.

Behind the front, deepening mixing and commensurately steepening
lapse rates should yield the development of a little
instability. This will likely net at least isolated snow showers
(rain or a rain/snow mix the farther south of I-80 you go)
through the afternoon hours. Again, outside of any visibility
issues, no road accumulations are anticipated. A few snow
showers could linger a bit into Monday evening, particularly
near the lake.

Skies look to largely clear out overnight Monday into Tuesday
morning (lake effect cloud cover will likely remain across parts
of northwest Indiana, however). Diminishing winds, clearing
skies, and dewpoints in the teens should allow temperatures to
fall readily overnight, with lows by Tuesday morning in the
20s, with some upper teens possible in the most sheltered spots.

Tuesday looks like an uneventful day as subsidence in the wake
of Monday`s shortwave develops. Thereafter, robust warm
advection will commence Tuesday night as a strengthening
southwesterly low-level jet materializes in response to the next
shortwave rolling out of Nebraska. Guidance is coming into a
little better alignment regarding the track of an associated
surface low, although some notable north-south discrepancies
persist. Regardless, intensifying isentropic ascent within the
burgeoning warm advection wing will lead to an expanding area of
precipitation late Tuesday night into Wednesday morning.
Thermal profiles during the initial period of precipitation
onset may be just cold enough to support snow.

How things trend during the day on Wednesday and into Wednesday
night, however, will depend on the track of the surface low
which--as mentioned previously--still hasn`t been entirely
nailed down. The ECMWF, which has been a bit of a southern
outlier recently, continues to favor a more southerly (and
therefore colder) track. Interestingly, there`s been a
significant jump in the number of EPS members producing
accumulating snow across our region on Wednesday. This trend
hasn`t necessarily been realized by the GEFS and GEPS at this
point, although a non-negligible number of those members also
suggest some degree of accumulating snow potential exists. At
this point, surface temperatures and dewpoints from even the
coldest guidance still suggest impactful accumulations will be
difficult to manage, but have boosted the snow mention a bit in
the gridded forecast, at least with the initial warm advection-
driven precipitation.

Broad troughing will linger overhead through the end of the
week, although the introduction of drier air largely looks to
suppress precipitation chances on Friday and Saturday.

Carlaw

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 553 AM CDT Sun Apr 6 2025

A relaxed/baggy surface pressure gradient forces lower than
average confidence on the forecast for the wind direction
throughout daylight hours. Generally speaking, the expectation
is for the wind direction to gradually become northeasterly
throughout the morning hours as a surface ridge approaches, and
then to become light and variable this evening as the ridge
slides overhead. Overnight, winds should become southwesterly
behind the ridge and ahead of an approaching cold front.

The cold front will sweep across the airspace after daybreak
Monday accompanied by a band of snow. Will introduce TEMPO
groups with reduced cigs/visbys due to snow in the end of the
30-hour TAF windows for ORD/MDW. North winds will also become
gusty at or above 25kt behind the front.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 AM Monday to 7 AM CDT Tuesday for
     the IL nearshore waters.

     Small Craft Advisory from 4 AM Monday to 10 AM CDT Tuesday for
     the IN nearshore waters.

&&

$$

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