Evanston, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

029
FXUS63 KLOT 040511
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1111 PM CST Tue Dec 3 2024

.KEY MESSAGES...

- Scattered gusty snow showers/squalls Wednesday afternoon and
  evening.

- Conditions turn sharply colder with sub-zero wind chills
  behind an arctic front Wednesday night.

&&

.DISCUSSION...
Issued at 300 PM CST Tue Dec 3 2024

Through Wednesday Night:

An area of high pressure continues to drift across the Ohio
River Valley this afternoon which has resulted in dry conditions
over northern IL and northwest IN. While there was some sun
earlier, an axis of stratus has developed over western IL and
will continue to spread eastward across the rest of the area
this evening. That said, temperatures are not expected to warm
much above their current readings but the increasing clouds and
southerly winds tonight should aid in keeping temperatures in
the mid-20s overnight. Finally, there remains a low chance
(<15%) for some freezing drizzle to develop in central IL and IN
late tonight into Wednesday morning as the warm advection
interacts with some moisture trying to surge northward. Given
that the moisture profile in forecast soundings looks to be very
shallow (<1000 ft) confidence on the drizzle developing in our
area remains low and therefore have left out a formal mention in
the forecast. Though, we will continue to monitor areas south
of a Paxton to Rensselaer line in the off chance something does
materialize.

The main forecast concern for the day on Wednesday will be a
strong arctic cold front that will sweep across the region
Wednesday afternoon and evening. While precipitation chances
along the front look minimal, guidance continues to show a
decent set up for scattered snow showers and squalls to develop
behind the front as an upper-level shortwave and associated jet
streak pivot overhead. However, moisture continues to look
modest especially within the DGZ which may limit the coverage
and/or intensity of such showers should they develop. That said,
if the steep low-level lapse rates can overcome the lacking
moisture, the snow showers/squalls will have the potential to
produce sharply reduced visibilities, snow accumulations
(generally under 0.5 inches), and slippery travel conditions for
the evening commute. Given the convective nature of these
showers confidence on the exact location of any shower is low
and therefore have maintained a broad 20-40% chance for such
across the area. Though the greatest coverage in hi-res guidance
does seem to be favoring areas along and north of a Dixon to
Rensselaer line.

Aside from the snow showers, temperatures on Wednesday are
expected to be warmer than today prior to the frontal passage
with highs in the mid to upper 30s. However, once the front
passes temperatures will quickly cool into the low teens to near
signal digits by Thursday morning. Couple these falling
temperatures with the increasing west-northwest winds and
conditions will be in place for wind chills to dip into the sub-
zero range Wednesday night. Furthermore, wind gusts Wednesday
afternoon and night may also have the potential to exceed 45-50
mph if sufficient mixing is achieved. Since confidence on the
degree of mixing is somewhat low have decided to cap wind gusts
in the 35-45 mph range for now, but if confidence grows then we
may need to consider a Wind Advisory for this period.

Yack


Thursday through Tuesday:

Bitterly cold temperatures and sub-zero wind chills are
expected at the start of the morning on Thursday. While wind
gusts will gradually ease through the day as the surface
pressure gradient begins to relax, continued cold air advection
into the region should hold highs in the 20s with wind chills
in the low-teens. Most of the area is expected to be dry under
clear skies, with the exception of northeast Porter County
where lake effect snow showers could linger through the day
and result in additional snow accumulations.

A series of weak disturbances will move within the broader
northwest flow aloft through the end of the week but any
precipitation associated with these features looks to remain
mainly outside of the area. As broad surface high pressure
shifts to the south of the area, southwest flow will return late
Friday ushering a gradual warming trend into early next week
with highs back into the mid-upper 40s by Sunday.

There remains variability in the handling of a cut-off low
forecast to stall over the desert southwest which eventually
ejects northeast sometime early next week. This will bring
increasing precipitation chances during the Sunday night through
Tuesday period as it lifts across the region. At this range the
higher probabilities for rain lie southeast of I-55 (40-60%)
with further refinement in the details expected over the coming
days. A period of cooler temperatures returns in the wake of
these systems midweek next week.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1111 PM CST Tue Dec 3 2024

Main Aviation Concerns:

- Breezy SW wind gusts in excess of 22-28kts continue overnight
  through Wednesday morning, with increase expected Wednesday
  afternoon in excess of 35-40kts from the WNW/NW.

- Areas of MVFR ceilings 1200-1500ft continue for the next few
  hours, before a break clearing of the low levels. Additional
  MVFR ceilings expected to arrive early Wednesday morning.

- Potential remains in forecast for convective snow showers
  Wednesday afternoon through evening, with possible IFR
  visby`s and minor accumulations.

Breezy S/SW winds continue overnight, with gusts in the 22-28kt
range. Wednesday morning starts breezy from the WSW, however
sustained winds and gusts increase substantially through the
afternoon from the west. Behind fropa during the mid afternoon,
winds rapidly change to the WNW/NW with gusts in excess of
35-40kts (isolated higher). Gusty winds remain through the end
of the period from the NW, as blustery air invades the region
into Thursday morning.

Ceilings are forecast to remain MVFR with a cover of secondary
stratus clouds shifting into the western terminals. With both
layers of cloud coverage, expecting MVFR to continue over the
next couple of hours before VFR returns near 08z. Additional
MVFR ceilings arrive near the 13-15z time frame from NW to SE,
and remain overhead throughout much of the period.

Still watching model depiction of snow showers Wednesday
afternoon through the evening across the region. Winds ramp up
in this time period, along with ceilings around 2kft and visby`s
reduced to 1SM, creating squall activity near the surface.
There is potential for lower visby`s (<1SM) and ceilings
(<2kft), however at this time confidence is not high enough to
include in forecast.

Baker/DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 3 PM CST Wednesday for the IL and
     IN nearshore waters.

     Gale Warning from 3 PM Wednesday to 9 AM CST Thursday for the
     IL and IN nearshore waters.

&&

$$

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