Fri Feb 09 Meteorology for Chicago

[Brett Crapser]

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1107 AM CST Fri Feb 9 2024

KEY MESSAGES...

- Chance (25 to 35 percent) for showers tonight south and east
of I-55.

- Above normal temperatures through the Sunday, though slightly
cooler over the weekend

- Slight chance for snow south and east of I-57 on Monday with
another chance for precip mid week as temperatures get colder

&&

DISCUSSION...
Issued at 345 AM CST Fri Feb 9 2024

A 989 mb surface low over northeast Minnesota is occluding and
will continue to weaken as it moves northeastward through
Friday. The low`s associated cold front will continue to move
east as well ushering in clearer, drier skies with southwest
flow aloft. Temperatures are expected to be 15 to 25 degrees
above normal, in the upper 40s and 50s, with the chance of low
60s along the far southern counties in the forecast area.

However mid levels winds will gradually veer to the northwest
Friday night. With a large swath of stratus clouds covering
Wisconsin to North Dakota, the forecast was updated for the
chance of cloudier conditions to be advected southeastward over
areas north of I-80 Friday night.

Ensemble models have been depicting a short wave trough that will
move eastward from the Colorado front range Friday afternoon toward
Chicago Friday night. While recent model runs have weakened the
short wave amplitude a bit, its associated vort max aloft and a weak
f-gen circulation could provide enough forcing to generate some
precip and with steeper lapse rates aloft, even an isolated
thunderstorm is possible.

However, the main hang up in forecasting showers, let alone
storms, is with the lack of moisture present. While there will
be steep lapse rates aloft, the weak to modest lift present may
be insufficient to cool and moisten the mid-levels to allow for
(elevated) convective initiation. Still, better chances for
rain are south and east of I-55 with around a 30 to 50 percent
chance. Thunderstorms were kept out of the official forecast for
now mainly due to uncertainties in convective initiation in the
first place, but if better moisture is realized, PoPs (and
storm chances) might need to be increased in later forecast
packages. The wave is expected to exit the region to the east
Saturday morning.

Weak ridging aloft is expected to build, driving slightly
higher pressure and drier conditions over the weekend. Persistent
north to northwest winds will help bring temperatures down to
the upper 30s and low 40s for highs however, they look to
remain above normal for February, but cooler than recent days.

A positively tilted trough will gradually move eastward from the
Texas Panhandle early next week. With it still being four days
away, there is still uncertainty on the exact track, but it
brings with it the next chance for precipitation for the area.
Despite surface temperatures being above freezing, there is a
fairly strong signal for both sub-freezing 850 mb temperatures
and surface wetbulbs. Currently the best chances for snow look
to be areas south and east of I-57, being closer to the track of
the low, but will be monitored as the system starts to come
into range of higher res guidance.

As a weak ridge builds over the Plains on Tuesday and an upper level
trough deepens over New England, this will subsequently keep
northwest to southeast flow over NE IL/NW IN resulting in an
active weather pattern. Confidence remains low this far out, but
it looks like another disturbance may approach the area mid
week for another chance for rain, snow, or even a rain snow mix.

DK

&&

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1103 AM CST Fri Feb 9 2024

Gusty west winds will begin to ease this afternoon and turn
northwesterly overnight. An MVFR cloud deck (ceilings near 1500
ft) in Wisconsin may drift southeastward toward the terminals
overnight, but confidence remains too low to explictely
advertise a ceiling at this time (will maintain SCT). If the
clouds to reach the terminals, they should begin to erode
toward the end of the TAF Period.

Borchardt

&&

CLIMATE...
Unseasonably warm temperatures may approach records for both
Rockford and Chicago. The following are the record highs and
record high minimum temperatures:

Friday, February 9th:

Chicago: Record High: 56 in 1886.
Record High Min: 47 in 1966.

Rockford: Record High: 54 in 1925.
Record High Min: 43 in 1966

Petr/DK

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 5 PM CST this afternoon for the IL
nearshore waters.

&&

$$