Tue Feb 20 Meteorology for Chicago

[Brett Crapser]

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1109 AM CST Tue Feb 20 2024

KEY MESSAGES...

* Unseasonably mild to outright warm (by February standards)
through Wednesday evening

* 30-60% chance for rain showers, possibly a thunderstorm late
Wed night into mainly early Thursday, especially south of I-80

&&

DISCUSSION...
Issued at 202 AM CST Tue Feb 19 2024

Warming trend is expected to continue today. Guidance has shown
a rather significant cool bias the past couple of days and
anticipate that trend to continue today. Models generally have
925mb 2-3C warmer today vs Monday afternoon, so have bumped up
highs into the mid-upper 50s today. One exception is far
southeastern CWA where there is still some snow to melt off from
southern Ford to Benton County. Forecast 925mb temps are progged
to warm around another 3C on Wednesday, which should push highs
into the 60s CWA-wide. Just how far into the 60s temps climb Wed
will probably depend on coverage and thickness of mid-high level
cloudiness progged to spread into the area. If there is enough
mixed sunshine, highs could get into the mid-upper 60s Wed
afternoon, potentially even threatening record highs. For now,
given the uncertainty with cloud cover, opted to stay more
conservative with lower 60s, but mid or even upper 60s could be
in play with more sunshine.

A shortwave trough is progged to break off the upper low that`s
off the west coast and ripple eastward across the country into
the mid-Mississippi Valley by late Wednesday night into
Thursday. GFS is farther north with this wave and surface
reflection which would bring better rain and possible thunder
chances farther north into at least the southern half of our
CWA. The ECMWF is a bit farther south and would likely result in
thunder chances staying south of our CWA and best chances of
showers over far southern CWA. The NBM pops reflect precip
chances nicely, peaking around 20% along and just northwest of
the I-55 corridor, ranging up to low end likely pops far
southeast CWA.

A push of colder (by winter 2023-24 standards) air is expected
late in the week into the first half of the weekend with temps
closer to, but probably still just a bit above average. Pattern
is expected to remain progressive with rising heights and
transition to broad, low amplitude ridging setting for mild
Pacific air to flood eastward across most of the country. This
should result in a another period of unseasonably mild/warm
temps starting as early as Sunday, but particularly into early
next week. Didn`t make any changes to NBM temps, but there is
certainly potential for highs even warmer than the mid 50s to
lower 60s currently forecast Sun/Mon. Trough could approach the
area by Monday night and Tuesday bringing with it the threat of
showers and thunderstorms.

- Izzi

&&

AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1109 AM CST Tue Feb 20 2024

SSW winds will gust around 20-25 kts briefly this afternoon
before easing around sunset. Another period of breezy
SW winds is expected on Wednesday afternoon, although the strongest
winds will occur south and east of ORD/MDW. VFR conditions are
expected to prevail through the entire TAF period.

Carlaw

&&

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

&&

$$