Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 160814
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
314 AM CDT Sat Mar 16 2024

.KEY MESSAGES...

- Breezy southwest (morning) to northwesterly (afternoon) winds
  with average gusts of 30 to 40 mph are expected today.

- Relatively cooler temperatures are expected Sunday and Monday
  with periods of wind chills in the teens to twenties and
  flurries.

- Temperatures warm back into upper 40s to lower 50s Tuesday
  onward with the next chance for region-wide precipitation
  toward the end of next week.

&&

.DISCUSSION...
Issued at 314 AM CDT Sat Mar 16 2024

Through Sunday Night:

A quick-moving trough axis will dig southeast as a cold front
surges through the area late morning through the afternoon. A
potent 50-60 knot LLJ ahead of the front will exhibit gradual
diurnal weakening this morning, but the onset of daytime heating
will allow the growing PBL to rapidly mix into the base of the
jet by mid-morning. Gusts over 30 mph are likely by around 9am,
with some gusts over 40 mph and briefly 45 mph possible for a
few hours this afternoon across the south half of the CWA before
the front suppresses the strongest winds to the south by late
afternoon. Strong CAA will support NW gusts as high as 25 mph
through the night as temps fall to around to below freezing by
daybreak Sunday. Frequent NW gusts over 25 knots are then
expected through the day Sunday.

A meager moisture profile throughout the lowest 10kft ahead of
the trough will limit precip generation to virga for a couple
hours at any given location late morning through mid-afternoon.
Meanwhile, the combination of strong winds and RH values
possibly as low as 40% may support a localized elevated brush
fire risk during the afternoon. Dry conditions should persist
into Sunday morning and possibly through the day if low-level
mixing/drying is more robust than anticipated. However, several
CAMs, primarily those with slightly more moisture in the low-
levels, suggest the steep low-level lapse rates under a -20C
700 hPa cold core will support the generation of scattered snow
showers conditional upon sufficient low-level moisture. Have
added slight chance snow showers/flurries for most of the area,
but an increase in PoPs may be warranted with forecast updates.
Any diurnally-enhanced showers will end by Sunday evening, but
lingering LES showers may clip mainly northern Porter County
Sunday night, especially if more favorable low-level moisture
profiles with lake-induced EL values pushing 10kft.

Kluber


Monday through Friday:

The work week will start off unseasonably cold with wind chills
in the teens early Monday morning. Temperatures will struggle
to warm out of the 30s through the day. A few snow showers may
linger across northwest Indiana into Monday morning downwind of
the lake, namely Porter County and points east where lake
induced instability and equilibrium levels to 8000 ft would be
sufficient for lake effect snow which could result in a light
dusting.

As the upper trough axis pivots east of the area a broader
northwest to southeast oriented upper jet remains overhead
placing the region near the surface baroclinic zone into
Tuesday. At this time we favor near to slightly above normal
temperatures through this period (upper 40s to lower 50s). There
remain chances for precipitation later in the week (30-40
percent) as the closed upper low across the southwestern CONUS
ejects east late Thursday into Friday.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1240 AM CDT Sat Mar 16 2024

- Brief period of low-level wind shear (LLWS) early AM at RFD
- Increasing gustiness this morning from WSW then veering WNW

VFR conditions are forecast through the period with the only
concerns being wind related. First, a strong low-level jet
(45-50 kt at 1500 ft) is forecast to pivot into the area toward
daybreak. This will provide a brief window for low-level wind
shear (LLWS) at RFD before gusts more readily begin mixing to
the surface. Elsewhere think that the surface gusts should
begin increasing early enough to preclude a formal LLWS
mention. Expect surface wind gusts to quickly ramp up into the
30-35 kt range and continue through the day. Directions will
start out SW to WSW then veer to W and then WNW by late
afternoon. While the higher gusts ease some toward sunset,
expect gusty winds to persist through the overnight hours.

Increased cloudiness is expected after daybreak. Dry low-levels
should keep area terminals dry at the surface though there may
be some virga overhead late morning into early afternoon.

Petr

&&

.MARINE...
Issued at 314 AM CDT Sat Mar 16 2024

A period of frequent WSW gales to 35 knots and possibly briefly
40 knots is expected along the Illinois shore mid to late
morning as daytime heating allows mixing into a 50-60 knots low-
level jet. The strongest portion of the low-level jet will
shift south of Lake Michigan by early afternoon, but increasing
cold air advection will support another period of gale gusts mid
to late afternoon. Given the potential for two separate windows
for gales, have opted to convert the Gale Watch to a Gale
Warning from 7am-7pm today. Have included this warning for the
Illinois near-shore zones and from Gary to Burns Harbor where
offshore winds will persist through the day.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning from 7 AM this morning to 7 PM CDT this evening
     for Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from 7 PM this evening to 7 AM CDT Sunday
     for Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from 7 AM this morning to 7 AM CDT Sunday
     for Gary to Burns Harbor IN-Burns Harbor to Michigan City
     IN.

&&

$$

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