Berwyn, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

133
FXUS63 KLOT 211809
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1209 PM CST Thu Nov 21 2024

.KEY MESSAGES...

- Winter Weather Advisory and Wind Advisory headlines in effect
  today for portions of the forecast area.

- Quick burst of snowfall rates of 1 inch or more per hour is
  expected to spread south and southeast through the early
  afternoon.

- Total snowfall amounts expected from 2-4" in the metro and
  northwest Indiana, to 1-3" farther west/south.

- West-northwest winds become strong/gusty later this morning
  and eventually turn north. Gusts as high as 50 mph at times
  before easing late today/this evening.

&&

.UPDATE...
Issued at 1127 AM CST Thu Nov 21 2024

Just a note on forecast expectations into this afternoon.
Recent reports indicate up to 3" of snow in Lake and Cook
Counties, with moderate to heavy snow continuing to fall,
including 1/4 mile visibility at KMDW as of this writing. Also
seeing less than 1/4 mile visibility at KGYY and KIGQ. A look
well upstream shows primarily snow hanging on up until central
Wisconsin, where the transition to light rain and drizzle has
taken place from a combination of warming temps and decreasing
cloud ice.

The overall trend is a slower rise in temps over the next
couple hours and correspondingly the ptype transition taking a
bit longer as well. Warming cloud tops punching south from
southeast Wisconsin will steadily diminish snowfall rates into
the Chicago metro, and then bring the anticipated changeover to
light rain and drizzle in the 2-3pm timeframe. While snow will
hang on a bit longer than earlier forecasts, little (up to a
couple tenths) to no additional accumulation is expected after
noon for most of the Chicago metro. Thus, not currently seeing
any reason to change the advisory end time of 1pm.

Farther south and east across far east central Illinois and
northwest Indiana, the worst conditions will occur from now
through about 1-2pm CST, with steady improvement thereafter. The
3pm advisory end time for these areas appears reasonable for
now. Finally, winds have generally under-performed thus far and
the window of near to a bit over 45 mph gusts may be very brief
later this afternoon. May need to consider changes to the wind
advisory with the full forecast package issuance this afternoon.

Castro

&&

.DISCUSSION...
Issued at 352 AM CST Thu Nov 21 2024

Through Friday:

Have elected to issue a Winter Weather Advisory for the Chicago
metro from 7 AM to 1 PM today for a quick burst of 2-4"
snowfall, and a Wind Advisory for all IL counties and
Lake/Porter counties in IN from 10 AM to 8 PM for strong winds
gusting as high as 50 mph.

Early morning GOES vapor imagery indicates a deep trough and
closed low centered over the western Great Lakes region. A
potent mid-level short wave was noted wrapping cyclonically
west-southwest around the northern periphery of the main
circulation with a 994 mb surface low over the eastern U.P. of
Michigan as of 3 AM. The strong vort and associated surface low
are progged to dig south down Lake Michigan today on the back
side of the upper level low, with attendant strong forcing
expect to produce a period of moderate to heavy snowfall rates
across northeast IL from just after sunrise through early this
afternoon. Snowfall amounts are expected to range from 3-4"
across a good portion of the Chicago metro area, to 1-3" farther
west and south. While these amounts are not exceptional, it
appears as if the bulk of the accumulation will occur over just
a 3 to 4 hour period in which accumulations on roads is likely,
given temps around 30F this morning. This rapid accumulation,
and being the first snow of the season tips the scales toward
issuing a Winter Weather Advisory. Snow is expected to decrease
in intensity this afternoon, and mix with and eventually change
over to mostly rain as surface temperatures rise into the upper
30s in the wake of the upper low/cold pool. Rain and rain
showers will then slowly diminish through this evening, except
for some lake-effect showers which will continue to affect parts
of northwest IN through Friday.

In addition to the wintry weather, very strong and gusty west-
northwest to north winds are expected due to the fairly quick
southward progression of the surface low and tightening surface
pressure gradient. Strongest winds, 25 to 35 mph with gusts as
high as 50 mph at times, are expected from mid-late morning
through early this evening beneath a 50+ kt low level jet on the
western periphery of the low. The axis of strongest winds looks
to favor the IL counties of our cwa, Lake Michigan and portions
of Lake and Porter counties near the Lake Michigan shore in
northwest IN. Wind gusts will ease to 25-30 mph tonight, but
will remain blustery into Friday. Temperatures will reach the
40s area-wide Friday, though the blustery north winds should
keep wind chills in the mid-upper 30s for much of the day.

Ratzer

Friday Night through Wednesday:

A lowering subsidence inversion and westward veering of the
low- level flow will gradually end lake effect rain showers in
northwest Indiana Friday night.

Ridging should then bring quiet conditions Saturday into
Sunday, but with plenty mid-level cloud cover. A longwave trough
over the northern Great Plains will then interact with a pocket
of Pacific moisture to produce an area of rain somewhere over
the western Great Lakes Sunday night into Monday, with ensemble
guidance still favoring the main area of precip to remain well
north of the forecast area. Another quick-moving wave within
broader WSW flow aloft will approach the mid-Mississippi River
Valley late Sunday as a cold front drifts southeastward across
the forecast area. Currently, the front is expected to clear the
CWA before the wave arrives and low-level Gulf moisture advects
northward, keeping rain chances mostly south of the area.
However, with decent spread in forecast time of the features
mentioned above, will maintain NBM chance PoPs through much of
the day Monday.

General Pacific flow with small chances of rain is then
expected Tuesday into Wednesday before the CONUS-scale pattern
amplifies with deeper troughing across the Great Lakes into the
northeast around Thanksgiving.

Kluber

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1209 PM CST Thu Nov 21 2024

- SN will change to -RADZ early-mid afternoon, with improving
  VSBY
- CIGS expected to lift to MVFR this afternoon and generally
  persist MVFR through the TAF cycle
- Gusty west winds will veer to more northwest to north-
  northwesterly later this afternoon

Snow is expected to transition to light rain or drizzle this
afternoon with a corresponding increase in VSBY up MVFR. VSBY
should increase to VFR late this afternoon or early this evening
as drizzle and/or light rain end. Expansive area of MVFR CIGS
upstream, so anticipating them to hang around through much of
the TAF cycle. There is some threat that CIGS could build back
down IFR tonight, but until confidence increases in IFR and
timing can be better pinned down, opted to hang onto MVFR CIGS
tonight.

Westerly winds have been under-performing this morning with
gusts mostly below 30kt. Still anticipate winds to pick up some
this afternoon with gusts over 30kt later this afternoon into
early this evening. Gustiness is expected to abate this evening,
but winds should become gusty again Friday morning.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory until 8 PM CST this evening for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

     Winter Weather Advisory until 1 PM CST this afternoon for
     ILZ005-ILZ006-ILZ012-ILZ013-ILZ020-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

     Winter Weather Advisory until 3 PM CST this afternoon for
     ILZ023-ILZ033.

IN...Wind Advisory until 8 PM CST this evening for INZ001-INZ002.

     Winter Weather Advisory until 3 PM CST /4 PM EST/ this
     afternoon for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning until midnight CST tonight for the IL and IN
     nearshore waters.

&&

$$

Visit us at weather.gov/chicago