Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

406
FXUS63 KLOT 261133
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
633 AM CDT Thu Mar 26 2026

.KEY MESSAGES...

- Powerful cold front will move across the area today with
  temps in the 70s/80s ahead it, falling sharply into the
  40s/50s behind it.

- Thunderstorms are likely to develop near the front this
  afternoon, with the highest chances of thunderstorms near and
  south of I-80. There is a level 3 out of 5 severe threat in
  the region with large, possibly destructive hail and damaging
  winds the main threats.

- Much colder Friday before a warming trend over the weekend.

&&

.DISCUSSION...
Issued at 307 AM CDT Thu Mar 26 2026

Synopsis & temps today...

Somewhat complex surface pattern early this morning with a weak
1007 mb sfc low very near the Missouri border over south
central IA. A weak warm front extends east from that low across
our southern CWA. Farther north, another low pressure just east
of Lake Superior has a cold front trailing west southwest from
it across northern Lake Michigan and central Wisconsin west to a
1000 mb low over northern Nebraska. The weak sfc low over IA
and warm front over central IL will lift north this morning,
eventually washing out and being absorbed into the stronger
baroclinic zone over WI. This should allow the very warm and
modestly moist air mass across MO and downstate IL to spread
north across our area this morning.

As the sfc low east of Superior continues moving eastward, the
trailing cold front should tend to settle southward closer to
the IL/WI border later this morning. Meanwhile, farther west,
the low over Nebraska will rapidly ride eastward along the front
today as parent shortwave trough over WY quickly translates
eastward into the mid-Mississippi Valley. By 18z, this sfc low
is expected to reach northern IL by midday, then zip eastward
into Ohio by later this afternoon.

This secondary sfc low over the central Plains should
temporarily slow or stall the front close to the IL/WI border
this morning. This should allow most of our area to quickly
warm up this morning. However, as that fast moving sfc low
moves east of the area this afternoon, the front should begin to
accelerate southward across the area in its wake. The cold
marine layer over the lake should result in an even more
pronounced southward progression down and near Lake Michigan
this afternoon. Temperatures behind the front will likely
quickly fall into the 50s, except across the immediate Chicago
area closer to the lake where temps should quickly fall into the
40s due to lake enhancement of the front.

Convection through this evening...

Weak ongoing convection near/south of the Highway 24 corridor
should move out of our area well before sunrise this morning
leaving dry conditions through much of the morning hours. Strong
mid-upper level westerly flow will advect an impressive elevated
mixed layer (EML) eastward across the area this morning,
characterized by very steep mid level lapse rates and a
pronounced capping inversion near the base of the EML. As weak
shortwave trough currently over WY reaches IA by early
afternoon, increasing mid level ascent and moisture in advance
of this wave could lead to some isolated-widely scattered
showers developing from higher based ACCAS deck within the EML
across northern IL.

Meanwhile, air mass in advance of the front will continue
heating and destabilizing as temperatures climb into the 80s
ahead of the front. Heating of the modestly moist boundary layer
combined with some synoptic ascent should gradually weaken the
pronounced cap near the base of the EML. Given the shallow
nature of this surging cold front, it is possible that the stout
cap may prove to be difficult to penetrate much of the day along
the front.

While not a certainty, it is probable that the cap will erode
sufficiently for sfc based convection to become established
near the front later this afternoon. Even so, it may have a
tendency to be undercut by the southward surging cold front,
which combined with weak low level shear and high LCLs should
greatly limit, if not totally eliminate, the tornado potential
in our CWA.

However, MLCAPE of 1000-2000 J/kg ahead of the front combined
with 60kt+ of 0-6km bulk shear will lead to a rather high
likelihood of severe thunderstorms. Initially, given the long,
straight hodographs convection may tend to be supercellular
posing a significant large hail threat, with max hail sizes
today potentially 2"+ in diameter. These storms should fairly
quickly congeal into a QLCS with the primary severe threat
transitioning from primarily hail to more of a locally damaging
wind threat.

Regardless of whether or not sfc based convection can become
established along the front, elevated instability above weakly
sloped cold front will support considerable post front
convection this afternoon and evening. In fact, the post frontal
convection will probably intensify and increase in coverage this
afternoon prior to any potential sfc based storms along the
front. While the elevated instability will be somewhat less, the
strong shear and steep lapse rates would likely support some
potential for severe hail even well behind the cold front this
afternoon.

As the front slows this evening, a more prolonged period of much
needed, soaking rain is looking like a good bet south of the
Kankakee River. Given the ongoing drought and that this area
tends to be less prone to flash flooding, no plans to issue a
flood watch, but certainly possible that some areas could pick
up 1-2" of rain early this evening.

Winds...

Tightening pressure gradient and steep low level lapse rates in
the cold air advection regime should lead to strong and gusty
northerly winds behind the front later this afternoon into
tonight. Some gusts over 40 mph are possible, especially closer
to Lake Michigan. Not confident enough in widespread 45+ mph
gusts to issue a wind advisory, but this will be something for
later shifts to keep an eye on.

Friday and beyond...

Much colder conditions are expected in the wake of this system
Thursday night into Friday. Highs Friday should mainly top out
in the low-mid 40s, except holding in the 30s near the lake. A
shortwave trough embedded within the broader amplifying northern
stream trough is expected to dig southeastward into the western
Great Lakes Friday. Most guidance suggests air mass will be too
dry to support any precip, though the Hires FV3 and NAMnest
would support a threat of some rain or snow showers Friday
afternoon over far NE IL. These models are likely too moist and
opted to keep the forecast dry for now, thinking that the better
precip threat will remain farther north across WI and MI.

The weekend looks dry with a warming trend that should continue
into Monday when highs should get back into the 70s inland a
bit from the lake. Medium range guidance does suggest that the
pattern over North America will flip next week with more of a
western trough eastern ridge setup. This would likely result in
generally above average temperatures and an unsettled pattern
with chances for showers and thunderstorms at times.

- Izzi

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 633 AM CDT Thu Mar 26 2026

Key Aviation Messages through early Friday morning:
- Sharp wind shift from SW to gusty NNE late morning/early
  afternoon.
- Period of scattered elevated TS mid-afternoon into early
  evening.
- Strong NNE winds over 30 knots this evening.
- IFR ceilings likely this evening.

Winds: Light S winds at TAF issuance will settle SSW/SW and
begin to increase after sunrise in response to daytime mixing,
with sporadic gusts to around 20 knots possible late in the
morning (particularly at MDW/GYY). A strong cold front will
surge SSW across all sites roughly around 17-18Z and produce a
sharp NNE wind shift with gusts over 20 knots. Precise timing of
the frontal passage will not be clear until within a few hours
prior, so any delay in the front will allow the pre-frontal SW
winds to increase further. Behind the front, NNE winds will
continue to increase through the afternoon, yielding gusts of 30
to 35 knots this evening before slowly abating late tonight
into Friday morning. Cannot rule out some rogue 40 knot gusts
early to mid-evening.

Precip/TS: Isolated high-based SHRA are expected to develop
across northern Illinois early this afternoon. Fast-moving
scattered elevated TS will then form north of the cold front in
response to a low to mid-level disturbance mid to late
afternoon. Current forecast timing for ORD/MDW is in the 20-00Z
window, but especially focused 21-23Z, with lingering TS
possibly continuing south of the Chicago metro into mid-evening
(PROB30 TS maintained at MDW/GYY during this time). Otherwise,
periods of light RA/SHRA will continue this evening before
ending after midnight.

Ceilings: VFR conditions will continue with SCT/BKN upper-level
clouds leading up to the frontal passage. SCT to possibly BKN
high- end MVFR stratus will then begin to thicken and lower with
time after the frontal passage, yielding low-end MVFR ceilings
by late afternoon. If TS/SHRA coverage is more prevalent over
Lake Michigan late in the afternoon, IFR ceilings over the lake
will likely begin advecting over the terminals while TS is
ongoing. Either way, ceilings should settle into IFR levels this
evening, then slowly lift and/or break overnight into Friday
morning.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning from 1 PM this afternoon to 7 AM CDT Friday for
     the IL and IN nearshore waters.

&&

$$

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