NWS Chicago Decision Support Briefing - Forecast

252
FXUS63 KLOT 192025
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
225 PM CST Thu Feb 19 2026

.KEY MESSAGES...

- Temperatures will tumble tonight into Friday. Some slushy snow
accumulations (not likely on pavement) are possible mainly
west of the Fox Valley Friday morning.

- Strong westerly winds develop late tonight south of I-80 then
spread across the entire area through Friday morning. Wind
Advisories in effect for gusts 45+ mph.

- Additional shots of snow late Saturday night into Monday,
mainly near the lake in NW Indiana with some minor
accumulations possible.

&&

.DISCUSSION...
Issued at 225 PM CST Thu Feb 19 2026

Through Friday Night:

Latest objective analysis depicts a roughly 994 mb surface low
just east of Kansas City. An attendant trough axis is steadily
pushing northwestward across the area, with dewpoints surging
into the 40s and lower 50s in its wake. The true system warm
front appears to be farther south across downstate Illinois
where temperatures are steadily warming into the mid/upper 60s.
The aforementioned trough axis will continue to sharpen in the
vicinity of the I-88 corridor this afternoon, as northeasterly
flow strengthens off the lake.

An initial arc (or arcs) of isolated to scattered showers and
thunderstorms may develop through the 4 to 6 PM timeframe as
moist upglide increases. With widespread cloud cover limiting
insolation, air temperatures are generally in the upper 50s/near
60 with dewpoints in the upper 40s and lower 50s. This will
result in limited instability (MLCAPE of just a few hundred
J/kg) given a lack of a deeper reservoir of cold air aloft.
While deep layer shear is quite impressive, the combination of
limited instability and lingering inhibition suggests the severe
weather threat in the area should remain fairly low. Can`t ever
totally rule out some "funny business" in the vicinity of the
area of enhanced low-level vorticity near the I-88 trough/front
if a stronger updraft manages to get going, but the chances for
this appear low. The more likely outcome is that any low-topped
storms have a difficult time becoming surface based, with mainly
a threat for small hail and locally stronger/gustier winds.

Later this evening (after 7-8 PM), an additional more strongly-
forced area of convection is forecast to develop across central
Illinois and pivot northeastward across our region through this
evening/early overnight. This activity will occur within a
narrow corridor of increased 0-3 KM MLCAPE, but without a
mature/intense squall line or stronger supercell, the potential
for surface based inflow appears fairly low based on the latest
forecast soundings. As before, the main threats with any more
robust activity looks to be from mainly small hail and gusty
winds. Can`t rule out a severe hailer or two in this regime, but
the severe weather potentially generally appears a bit lower
than it did yesterday.

The system dryslot will blast across the region late this
evening and overnight, bringing a swift end to any lingering
thunderstorm chances from southwest to northeast. Guidance
continues to suggest the surface low will track across northwest
Illinois. As this occurs, a brief period of low clouds,
drizzle, and fog will be possible. Any brief locally dense fog
threat should likely remain tied to the lake vicinity into far
NE Illinois, and will erode quickly through daybreak with the
arrival of the main cold front.

As the front arrives, expecting southwest to westerly winds to
increase markedly as low-level lapse rates steepen and impressive
pressure rises overspread the area (guidance suggests 12+ mb/6hr
and about 5 mb/3hr) with the surface low deepening as it tracks
overhead. Mean boundary layer flow is progged to increase to
near 35 kts, with top-of-channel momentum transfer suggesting
periodic gusts near 45 (possibly briefly over 50 mph) mph
developing, initially south of I-80 late tonight before
spreading across the rest of the area through Friday morning.
Have issued Wind Advisories for the area to cover the strong and
gusty wind threat. Winds will diminish steadily through Friday
afternoon and evening.

Through Friday morning, the column will cool markedly as the
surface low pulls northeast across the lake. A trailing mid-
level deformation axis is forecast to push eastward across the
area which will result in the redevelopment of stratiform
precipitation, particularly west of the Fox Valley. As this
develops, the atmospheric column will cool rapidly, supporting a
transition to all snow prior to daybreak near I-39 and then
closer to mid-late morning across NE Illinois. While ascent will
be on a steady downward trend through the morning with the low
pulling away, a brief burst of steadier snow is nonetheless
possible west of the Fox Valley and particularly in the vicinity
of I-39. Temperatures will likely be at or above freezing
during this period, so unless snowfall rates get out of hand
(which we`re not seeing a strong signal for), any slushy
accumulations (one half to maybe near an inch) would be
relegated to grassy/elevated surfaces. Activity should tend to
diminish in intensity with eastward extent through the morning,
with a transition to intermittent light flurries during the
afternoon.

Carlaw


Saturday through Thursday:

While the upper-level pattern will remain active on Saturday
with numerous perturbations and broad (yet disorganized)
cyclonic flow in place, the eastern fringes of a robust 1040 mb
surface high will build into the region which looks to keep
things generally quiet. A lingering tight pressure gradient will
ensure northwesterly breezes remain in place leading to
blustery conditions as winds gust into the 20-25 mph range with
temperatures only warming into the mid to upper 30s.

A series of shortwaves embedded within the broad cyclonic flow
will drop south out of Wisconsin and Michigan on Sunday and
Sunday evening. In turn, mid and upper-level winds will turn
northwesterly and colder air will spill southward. Some increase
in boundary layer moisture, coincident with steepening lapse
rates may support the development of some snow showers,
primarily downwind of the lake into parts of northwest Indiana.
With 850 mb temperatures forecast near -15 C, lake effect
parameters don`t appear overly significant, but sufficient to
sustain accumulating snow showers with lake-induced ELs progged
near 6-7 kft. Generally NNW to NW boundary layer flow looks to
focus the bulk of this activity across parts of Porter County at
this time. That said, there are some indications pointing to
the flow veering more northerly Sunday night into Monday which
could focus additional LES a bit farther westward.

A surface high will transit the region through Monday night with
southwesterly return flow redeveloping on Tuesday. Strong/gusty
south-southwest winds will start to push a warmer airmass
overhead, although a lingering stout inversion will likely limit
the degree of mixing we see Tuesday afternoon. Still, medium
range guidance suggests we may mix deep enough to drive 30-40
mph gusts and temperatures warming into the low to maybe mid 40s
across our far southwest (cooler towards the northeast). Noting
that the ECMWF remains a bit warmer than the rest of the
guidance suite, and has RHs falling to around 20 percent Tuesday
afternoon. If this materializes, we`d have to keep an eye on
another heightened grass fire threat, although the latest multi-
model consensus suggests slightly cooler temperatures and
higher humidity.

Active split flow pattern will continue through the middle/end
of next week with the next chances for precipitation in the
Wednesday/Thursday timeframe.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1158 AM CST Thu Feb 19 2026

Main Concerns:

- Potential for TSRA at times late today through this evening.

- Reduced flight categories in DZ and BR possible early Friday.

- Strong west winds and snow showers/flurries at Chicago area
sites on Friday, with a period of accumulating wet snow
possible at RFD.

Initial relatively quiet conditions featuring east winds around
10 kt with occasional gusts and 2-4kft AGL CIGs will turn more
active later today through the rest of the period. Showers with
embedded TS should develop/lift into the area late this
afternoon, possibly followed by a break, and then another round
later in the evening. Opted to lengthen the PROB30 TSRA for now
to encompass both plausible windows. After this activity lifts
north, east-northeast winds will shift to southeast and then
gusty southwest overnight with gusts pushing 30 kt as low
pressure tracks over the area. Earlier rain and moist low
levels may be supportive of BR and a period of lower CIGs.

From the predawn hours until about mid-morning Friday, if
precip occurs at the Chicago metro sites, forecast soundings
suggest it will be in the form of drizzle (with temps solidly
above freezing). Later in the morning into the afternoon, much
colder air and additional upper level disturbances will support
flurries and the potential for more robust snow showers at times
(PROB30 mention). At RFD, a period of heavier snow Friday
morning may bring a slushy accumulation up to 1".

Aside from the snow potential on Friday, expect strong westerly
winds gusting up to 35-45 kt and MVFR CIGs which may scatter late.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory from 6 AM to 4 PM CST Friday for ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ103-
ILZ104.

Wind Advisory from 1 AM to 4 PM CST Friday for ILZ019-ILZ020-
ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ105-ILZ106-ILZ107-
ILZ108.

IN...Wind Advisory from 6 AM CST /7 AM EST/ to 4 PM CST /5 PM EST/
Friday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 1 AM to 6 AM CST Friday for Winthrop
Harbor to Northerly Is. IL.

Gale Warning from 6 AM to 4 PM CST Friday for Winthrop Harbor
to Northerly Is. IL.

Gale Warning from 2 AM to 4 PM CST Friday for Northerly Is. IL
to Michigan City IN.

&&

$$

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