Wheaton, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

682
FXUS63 KLOT 250800
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
Issued by National Weather Service Lincoln IL
300 AM CDT Fri Apr 25 2025

.KEY MESSAGES...

- Scattered showers and storms are likely (50-70%) this
  afternoon, particularly south of I-80 this afternoon. Severe
  weather is not anticipated.

- Seasonably cool Saturday, followed by a return to much above
  average temps early next week.

- A chance for strong to potentially severe thunderstorms as a cold
  front moves across the region Monday into Tuesday next week.


&&

.DISCUSSION...
Issued at 300 AM CDT Fri Apr 25 2025

Early this morning, an area of showers and t-storms are ongoing
across central portions of IA, with a few additional widely
scattered warm air advection showers also noted across northwestern
IL. Much of this early morning activity is associated with a
few subtle eastward shifting shortwave impulses. It appears
likely that much of this storm activity will weaken as it shifts
eastward towards the Mississippi River into a less favorable
thermodynamic environment during the predawn hours this morning.
Accordingly, we are not expecting much more than some widely
scattered remnant showers across far northern IL later this
morning.

As we head into this afternoon, a weak surface low will track eastward
along a quasi-stationary frontal boundary in place across central
portions of IL. Along and south of this surface boundary ample
low-level moisture (low 60s dew points) is expected to result in
at least modest early afternoon destabilization across southern
sections of the area, especially from the Kankakee River southward.
This should thus result in scattered shower and thunderstorm
development in this region this afternoon, particularly between
12 and 4 PM this afternoon. Fortunately, rather poor mid-level
lapse rates and overall modest mid-level flow should curtail the
threat for any severe storms.

Temperatures today will be cooler than those observed on Thursday,
but with the much cooler air mass expected to lag well north of
the surface boundary today, readings are expected to top out in
the low to mid 60s far north, and near 70 in the south. The
only exception will be near the Lake Michigan shore, where an
onshore wind component will keep temperatures in the 50s.
Temperatures will drop off back into the upper 30s to lower 40s
tonight as the cooler air mass shifts into the area on
northerly surface winds in advance of a surface high building
across the Upper Midwest. This surface high will shift across
the western Great Lakes on Saturday. The associated onshore
northeasterly winds will result in a much cooler day Saturday,
albeit a sunny one. Well inland sections of northern IL look to
top out around 60, while areas along the lakeshore likely
struggle to get out of the 40s. This then sets the stage for a
rather chilly Saturday night, as light winds and mainly clear
skies under the surface high will allow temperatures to radiate
back into the mid to upper 30s, especially outside the Chicago
urban heat island. Also, cannot rule out some patchy frost in
some of the coldest spots late Saturday night.

Mid-upper level ridging will begin to shift east into the
Mississippi Valley on Sunday, with surface winds turning south-
southeasterly following the eastward departure of the Great
Lakes surface high. Accordingly, temperatures are expected to
begin a warming trend on Sunday, as inland highs top out in the
60s. The slight easterly component to the flow will likely
result in an IL shore lake breeze and temperatures several
degrees cooler.

KJB

Next Week....

An upper level low that will sit off the California Coast this
weekend will move onshore and begin to bifurcate as it
approaches the Rocky Mountains on Monday. The dominant shortwave
will become positively tilted with a strengthening upper-level
jet whose left exit region will move over Iowa into western
Wisconsin late in the day. With a deepening upper-level jet
streak over the region, deep layer shear will increase to over
50 knots Monday night into Tuesday. As the trough moves across
the Rockies, it will trigger lee cyclogenesis over eastern
Wyoming which will also move over the northern Plains with a
developing cold front extended from the central low. Low-level
southwesterly flow will draw mid 60s dew points into southern
Wisconsin on Monday with a warmer air mass being advected into
the region. High temperatures on Monday could easily reach into
the low 80s. Latest model runs have slowed the progression of
the upper level wave/surface low slightly. Model soundings are
showing steep mid-level lapse rates and MLCAPE values
approaching 1500 J/kg. Most soundings do show a fairly robust
cap through much of Monday which prompts the probability for
SBCAPE greater than 500 J/kg to lower from 70-80 percent down to
50 to 70 percent. Nevertheless, soundings show the cap
weakening as the front progresses through the area overnight.

As the front moves through into Tuesday morning, the upper-
level jet streak will slowly meander into the Great Lakes
placing the right entrance region over the eastern portion of
the CWA. Speed and timing of the front will be critical to
monitor with this system as there is a non-zero chance that the
front is east of the area by Tuesday morning, in which case the
threat of storms would be minimal. Given all these environmental
parameters, we will likely remain in the SPCs extended outlook
for severe weather chances on Monday into Tuesday based on
recent model trends. It will be important for people to stay
tuned to forecast updates, because as of right now it appears
the prime window for severe weather with this system could be at
night for much of the area north and west of I-57.

A brief ridge will pass over the area late Tuesday into
Wednesday to provide a brief window of surface high pressure and
quieter conditions with temperatures in the low to mid 60s.
However, the next upper-level wave will likely eject out of the
southern Rockies on Wednesday with a developing surface low over
the southern Plains that will take a northeasterly track toward
the Great Lakes. There is still a lot of uncertainty on the
exact track of the low. The Euro ensemble has it hugging the
Ohio River Valley, while the GEFS has a slightly more northern
track toward our forecast area. This results in the Euro keeping
us mainly dry, whereas the GEFS has showers with a murky chance
of storms. With it still over a week away, confidence remains
low but enough to keep a lazy eye on.

DK

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1207 AM CDT Fri Apr 25 2025

Persistent north/northeast flow will gradually result in
lowering ceilings Friday morning, with ensemble guidance
suggesting MVFR conditions at KRFD as early as 17-18Z. Chicago-
area terminals more likely to see this develop toward 22-23Z.
Concern remains with potential for IFR ceilings at KORD/KMDW
spreading in off the lake in the evening, with HREF guidance
projecting the probability around 50% and HRRR with the low
ceilings very close by. Will keep the forecast at low MVFR for
now and evaluate it a little further over the next few hours.

Much of the convective concerns from earlier forecasts look to
be setting up south of the TAF sites (though not too far from
KGYY), and thunder chances have been removed from the forecast.

Geelhart

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 PM this afternoon to 7 PM CDT
     Saturday for the IL and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago