845
FXUS63 KLOT 262031
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
331 PM CDT Sat Apr 26 2025

.KEY MESSAGES...

- Patchy frost likely outside of Chicago tonight with
  greater coverage possible in some areas.

- Turning very warm and breezy Monday, with highs in the lower 80s.

- There is a chance for thunderstorms Monday night, some could
  be strong to severe.

- Confidence in storm redevelopment Tuesday afternoon southeast
  of I-55 remains low - dependent on Monday night storm
  evolution.

&&

.DISCUSSION...
Issued at 330 PM CDT Sat Apr 26 2025

Through Saturday:

Surface high pressure will drift overhead tonight leading to
mostly clear skies and easing winds. This should allow for
efficient radiational cooling across the area, with temperatures
forecast to drop into the mid 30s to lower 40s (warmest in and
near Chicago and near the immediate lakeshore). This will likely
lead to at least patchy frost development outside of Chicago,
though some areas may see a bit greater coverage for a few hours
toward daybreak. Considered issuing a Frost Advisory for
portions of the area tonight, but confidence in widespread frost
development was not high enough with this update. Thin high
clouds may also drift into the area toward daybreak, though it
is unclear how much this would influence temperatures if it
does. For now, plan to issue an SPS to provide a bit more
awareness. Will let the evening shift get another look in case
confidence increases enough for a Frost Advisory for at least
portions of the area.

Winds will turn southeast on Sunday on Sunday as the center of
the surface high continues to drift east of the area. This will
allow temperatures to warm back into the 60s to near 70 for most
areas, with the exception of northeast Illinois near the
lakeshore due to onshore winds where temperatures likely remain
in the 50s.

Attention quickly turns to an approaching mid-upper trough and
associated developing surface low across the central Plains.
This will set the stage for strong to severe thunderstorm
development Monday afternoon across Iowa and Minnesota. This
activity is then expected to shift southeast toward the area
into Monday evening. Overall, not much has changed from previous
thinking, though a few elevated thunderstorms may clip
northwest portions of the area early Monday morning ahead of the
developing low pressure system. Main hazards would be lightning
and hail if they do develop (20% chance).

Strong southerly winds, with gusts in excess of 35 mph will
allow warm air to surge into the region, with highs forecast to
warm into the upper 70s to lower 80s areawide. Upstream
thunderstorms are forecast to move into the area along a cold
front late Monday evening and overnight. They may be in a
weakening phase as they move through the area though conditions
will remain favorable for linear storm cluster capable of severe
wind gusts. Brief embedded tornadoes also can`t be ruled out
with the strongest storms. The latest Day 3 outlook from the
Storm Prediction Center matches our thoughts well, with a
locally higher severe threat (level 3 out of 5) across northwest
Illinois into the Rockford area, then decreasing with
southeastward extent as instability is expected to weaken with
time overnight.

The forecast for Tuesday remains lower confidence and will
ultimately be dependent upon the coverage of overnight
thunderstorms and southeast progress of the remnant outflow/cold
front. GFS/ECMWF continue to trend toward faster progress of
storms with redevelopment occurring largely southeast of the
area. However, if there ends up being lower storm coverage with
the front stalling out briefly over the area (similar to the
NAM), sufficient recovery ahead of the boundary would support
strong to severe thunderstorm development further north into
parts of the area, particularly south of a Pontiac, IL to
Valparaiso, IN line. Stay tuned.

In the wake of the Monday-Tuesday system, seasonable
temperatures are forecast through the end of the week with highs
mainly in the 60s (locally cooler near the lake). After a break
in the rain on Wednesday another system is progged to lift
across the region during the Wednesday night through Thursday
timeframe which will bring our next chance for widespread
precipitation.

Petr

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1237 PM CDT Sat Apr 26 2025

Forecast concerns include...

Mvfr cigs early this afternoon.
Gusty northwest winds this afternoon.

Mvfr cigs will continue to scatter out across eastern IL and
northwest IN this afternoon with cigs likely persisting the
longest immediately south of Lake Michigan. Once this cloud
cover dissipates, SKC is expected tonight with increasing high
clouds Sunday morning.

Northeast winds will gust into the lower/mid 20kt range early
this afternoon and mainly for the Chicago terminals and near
Lake Michigan. Gusts will slowly diminish this afternoon with
speeds diminishing under 10kts with sunset. Winds will likely
become light and variable for most locations tonight and then
shift southeast to 10kts Sunday morning. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 PM CDT this evening for the IL
     nearshore waters.

     Small Craft Advisory until 10 PM CDT this evening for the IN
     nearshore waters.

&&

$$

Visit us at weather.gov/chicago