Glenview, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

601
FXUS63 KLOT 082014
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
314 PM CDT Tue Apr 8 2025

.KEY MESSAGES...

- Periods of cold rain are expected on Wednesday, followed
  lingering showers Wednesday night into Thursday.

- Temperatures will warm to above normal early next week.

&&

.DISCUSSION...
Issued at 314 PM CDT Tue Apr 8 2025

Through Thursday:

Expect quiet conditions tonight with gradually increasing clouds
overnight. With surface high pressure over southwest Lower
Michigan in the early evening and the very dry air mass in place
this afternoon (single digits and teens dew points!),
temperatures will drop quickly after sunset. This will result in
lows in the upper 20s (locally mid 20s) to lower 30s (mid 30s in
Chicago) occurring by the late evening, followed by slowly
rising temps overnight from modestly increased southeast winds
and increasing clouds.

A modest surface low pressure embedded within broad surface
troughing across western Nebraska will scoot eastward into Iowa
into Wednesday morning, while steadily weakening/filling. A
low-level mass response in advance of this feature will
encourage the development of an intensifying southwesterly
925-850 mb LLJ which in turn will yield an expansion of
isentropic ascent across parts of the Upper Midwest. In
general, the trend today has again been towards a slower
evolution, with the main batch of WAA-induced precipitation
holding off until after 6 AM Wednesday. With some high-res
guidance even slower than the operational models, most of the
precip now looks to hold off until solidly after sunrise.

While there are still differences in the handling of moisture
depth, orientation of f-gen and warm advection, across the
guidance suite even at this relatively short lead time, the
overall slowing trend has reduced the chances for any meaningful
window of wet snow as the main p-type. In addition, coming out
of such a dry air mass, the top down saturation process will
lead to a more showery nature to the precip shield initially.
With wet bulb temperatures starting out as cold enough for snow,
if precip develops early enough, can`t completely rule out some
wet snow flakes mixing in for an hour or two, roughly over the
southwest half or so of the area.

Strengthening southwesterly flow aloft and strong large scale
ascent should yield a period of steady rain toward midday and
through the mid afternoon. A corridor of up to or upwards of
1/4 inch of rain could fall during this period. Precipitation
chances will continue through the late day, though trending
lighter, showery, and/or "drizzly" with time. Can`t rule out
a few lightning strikes during this period, although chances
still seem a bit too low to justify an expansion of thunder
probs. While another flip to snow or a rain/snow mix remains
possible across far northern Illinois Wednesday evening/night,
this signal has diminished considerably across the deterministic
and ensemble guidance given a weaker and generally more
progressive surface low (especially non-GFS/GEFS guidance).

A secondary surface trough will approach the region Wednesday
night, with additional sprockets of mid-level vorticity set to
meander overhead, possibly resulting in on and off lighter
showers or drizzle. With lingering 0-2 km moisture, there`s
some potential for low stratus to gradually build down into a
fog bank overnight into Thursday morning, particularly north of
I-80 where the low-level flow is forecast to be the weakest.
Still no mention in the gridded forecast with this afternoon`s
issuance given lingering placement uncertainties, but something
we may have to introduce in future updates.

There`s considerable variance in the guidance on Thursday
regarding primarily afternoon rain chances. Below normal
temperatures will persist for most of the area, especially north
of I-80 and particularly near the lake where onshore winds as
well as potential lingering low stratus (after morning fog)
keeps temps down in the 40s to around 50F. Highs along the
lakeshore will struggle to reach the lower to mid 40s.

Additional vorticity maxima traversing overhead could provide
the impetus for some afternoon showers to develop. With the
ECMWF/EPS suite most bullish in this regard and the rest of the
guidance notably drier, confined highest chance PoPs of 40-50%
to south of a Rockford to Rensselaer IN line, tapering to only
20-30% north of that line. A sliver of instability may develop
into the far southwest CWA where temps approach 60F amidst dew
points in the 40s, though the main thunderstorm chances look to
remain to our south. Later updates should be able to make
substantial refinements to the Thursday forecast as the guidance
(probably) comes into better agreement with time.

Castro/Carlaw

Thursday Night through Tuesday:

The upper level low will be slowly shifting east across the
lower Great Lakes/Ohio Valley Thursday night into Friday. The
blended guidance is dry during this time period as are many of
the models, with the exception of the ECMWF. Given the proximity
to the upper low, any weak wave rotating around it, will have
the chance to produce some showers. Confidence is too low to add
pops with this forecast, but trends will need to be monitored.

Southerly flow will return this weekend with warmer temps,
likely in the upper 50s/lower 60s on Saturday with a lake
breeze expected near Lake Michigan and cooler temps there. Highs
will likely make a run at 70 on Sunday, though south/southeast
winds may keep the IL Lake Michigan shore cooler.

A cold front is expected to move across the area on Monday,
bringing a chance of showers. The timing of this front will be
important for both any isolated thunder potential and also how
warm high temps climb on Monday. Blended guidance has highs well
into the mid 70s, maybe a few upper 70s. While possible, this
would be dependent on a late day cold front passage. Current
model trends suggest a morning fropa. Low chance pops seem
reasonable for now for showers, but thunder potential would
likely be pushed south of the area with a morning fropa and no
mention with this forecast. cms

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1234 PM CDT Tue Apr 8 2025

High pressure will make its way eastward through the region
today keeping conditions dry and stable. Light northwesterly
winds for most areas to start the afternoon off, with GYY
starting off northeasterly. A lake breeze will flip winds to the
northeast and eventually east or east-southeast for the Chicago
terminals as the afternoon goes on. Clear skies early afternoon
with perhaps a few cirrus clouds arrive late day.

The high pressure moves off to the east tonight, allowing
developing low pressure in the Central Plains to approach. Cloud
cover increases overnight as a result, with winds taking a more
southeasterly or even southernly direction. Rain showers will
move in Wednesday morning, arriving by mid-morning. -SHRA will
increase to -RA midday, with MVFR cigs and vis. Cigs and vis
may fall to IFR during heavier rain. Expecting south-
southeasterly winds gusting to 20-25KT during the morning hours,
turning more east- southeast and decreasing in the afternoon.
The precip moves off closer to 00z.

Mette

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 PM CDT this afternoon for the IN
     nearshore waters.

&&

$$

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