Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 190816
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
316 AM CDT Tue Mar 19 2024

.KEY MESSAGES...

- Windy today with an elevated risk for the spread of brush
  fires.

- Period of snow late Thursday night into Friday AM with a 60%
  chance for minor slushy accumulations along/north of I-88.

- Active weather pattern sets up early next week with widespread
  precipitation likely (70+% chance).

&&

.DISCUSSION...
Issued at 315 AM CDT Tue Mar 19 2024

Through Thursday:

A windy, dry and seasonably mild day is in store today. A cold
front currently across Minnesota will quickly shift southeast
across the forecast area early this morning. While a pre-frontal
50-60 knot low-level jet will exhibit diurnal weakening this
morning, an already mixed PBL will quickly tap into the base of
the jet shortly after sunrise. In fact, we are already seeing
some gusts to 25 mph as of 3am. Expectations are for WSW winds
to gust to 40 mph for a few hours mid to late morning before
abating early this afternoon. However, an increasingly favorable
isallobaric gradient within post-frontal CAA beginning late
this afternoon should support a renewed increase for WNW gusts
to 35+ mph. Gusty conditions will persist in a gradual weakening
trend through tonight.

Though rain late last week mitigated fire weather concerns for
several days, the recent breezy/windy and dry days have also
allowed fine fuels to becoming increasingly dry. Meanwhile,
robust mixing today will partially offset post-frontal low-level
moisture advection this afternoon to produce minimum RH values
as low as 30-35%, particularly south of the Kankakee River
Valley. The combination of the factors above warrants the
issuance of an SPS today for an elevated risk of the spread of
brush fires.

Continued CAA tonight will usher in a period of seasonably cold
conditions Wednesday and Thursday, with daytime highs generally
in the upper 30s and low 40s. After mostly sunny skies on
Wednesday, mid-level clouds will expand across the region in
response to a low-level f-gen circulation to the southwest.
Given a fairly dry airmass and recent guidance favoring any
potential precip to remain safely southwest of the CWA, will not
include any PoPs at this time.

Kluber


Thursday Night through Monday:

Attention turns to our next weather maker which arrives during
the Thursday night into Friday morning period. This is
associated with a shortwave expected to dive southeast across
the Northern Plains toward the region during this period. In
response to this wave, a weak surface low develops in western
NE/SD. Out ahead of the surface low, modest warm advection sets
up, aided by a 40-50kt low level jet, which results in
precipitation developing to its northeast. As the surface low
weakens and translates eastward this area of precipitation
expands across the area. There is strong lift within the
saturated layer with this system, peaking Friday morning.
Questions remain as to what the vertical temperature profiles
will look like and where the rain/snow line ultimately sets up.
While there continues to be a fair amount of variability in the
operational runs (including a signal for a narrow swath of
locally higher amounts), global ensembles have remained fairly
consistent.

There is still some time to hone in on the details given the
energy for this system is still nearly 1000 mi west of
California over the Pacific. Accordingly, plan to maintain the
potential (60%) for minor slushy accumulations for areas mainly
along and north of I-88 (highest toward the WI/IL state line).
The only notable change has been for a slower arrival, with the
highest QPF (and accordingly snow amounts) occurring Friday
morning. This could result in a slowed and slippery travel for
the Friday morning commute.

Surface high pressure settles into the region to start the
upcoming weekend bringing dry and continued cool conditions with
high temperatures struggling to get out of the 30s.

Sunday onward favors a more active weather pattern as a deep
western CONUS upper trough begins to eject east of the Rockies.
There continues to be ensemble support for a potent system (or
systems) to develop to the lee of the Rockies which, depending
on the timing of these features, would bring periods of
inclement weather to the region. Still plenty to watch for over
the coming days, though at this range it looks like we are
leaning toward the warmer side.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1245 AM CDT Tue Mar 19 2024

The only aviation weather concern remains a period of strong
southwest winds developing early this morning and continuing
through the afternoon, gradually turning west and then
northwest through they day. Did nudge up gusts for the morning
hours with this update when 30-35+ kt gusts appear likely as a
strong low-level jet moves overhead. Gusts diminish into the
upper 20kt range late morning/early afternoon but may increase
again above 30 kt by mid-late afternoon with deeper mixing.

VFR conditions are expected through the TAF period.

Petr

&&

.MARINE...
Issued at 315 AM CDT Tue Mar 19 2024

A 50-60 knot low-level jet shifting southeast across southern
Lake Michigan this morning combined with a well-mixed low-level
environment will support a period of frequent WSW gales to 35
knots through this morning. Some of these gales may briefly
reach 40+ knots mid to late morning, especially for any higher
platforms closer to the shore. While winds will diminish this
afternoon behind the passage of a cold front, sporadic WNW gale
gusts may continue into the evening.

Kluber

&&

.FIRE WEATHER...
Issued at 315 AM CDT Tue Mar 19 2024

There is an elevated fire danger today across all of northern
IL and northwest IN.

SW winds are expected to gust as high as 40 mph mid to late
morning before gradually becoming WNW with gusts of 30-35 mph
behind a cold front this afternoon. Dewpoints in the teens early
this morning will slowly increase through the day, though there
remains uncertainty for how fast dewpoints increase. Current
forecast RH values this afternoon will fall into the 30 to 35
percent range, which is above local Red Flag Warning criteria
of 25 percent. 10hr fuel moisture values slightly below 10
percent this afternoon combined with the gusty winds and RH
values noted above supports the issuance of a Special Weather
Statement for elevated fire danger conditions today. At this
time, it is not expected that Red Flag Criteria will be met.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning until 1 PM CDT this afternoon for the IL and IN
     nearshore waters.

     Small Craft Advisory from 1 PM this afternoon to 4 PM CDT
     Wednesday for Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from 1 PM this afternoon to 1 AM CDT
     Thursday for Gary to Burns Harbor IN-Burns Harbor to
     Michigan City IN.

&&

$$

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