Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 190546
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1246 AM CDT Tue Mar 19 2024

.KEY MESSAGES...

- Windy with an elevated danger for the spread of brush fires
  Tuesday.

- Period of snow Thursday night into Friday morning with potential
  (60%+ chance) for minor slushy accumulations along/north of
  I-88.

- Below normal temperatures persist through the weekend.

- Active weather pattern likely (60+% chance) to foster more
  widespread precipitation late in the weekend into early next
  week.

&&

.DISCUSSION...
Issued at 304 PM CDT Mon Mar 18 2024

Through Tuesday:

Scattered flurries will end for west to east this afternoon with
some clearing expected late this afternoon into this evening.
Some heavier snow showers across far northwest Indiana may
reduce visibilities for a few more hours though no accumulation
expected and nothing seen so far on area webcams.

Northwest winds will diminish early this evening and turn
westerly, then will steadily increase overnight as directions
turn southwest by daybreak, when gusts into the 25-30 mph are
possible. Winds will continue to strengthen after sunrise
Tuesday morning with a gusts into the 35-40 mph range possible.
Wind directions will turn back westerly by midday and then to
the northwest in the afternoon. While the entire day will be
windy, gusts may settle back into the 30-35 mph range by early
afternoon and then are expected to quickly diminish with sunset
Tuesday evening. A secondary cold front will move across the
area late Tuesday night/early Wednesday morning, with another
period of northwest winds gusting into the mid 20 mph range and
colder air spreading back into the area. After highs in the 50s
for most locations Tuesday, lows will drop back into the mid 20s
to around 30 by Wednesday morning.

The strong winds and dry conditions will create an elevated
fire danger Tuesday. More on this potential in the fire weather
section. cms


Tuesday Night through Monday:

Cold air advection following a cold frontal passage Tuesday night
will result in a colder and blustery day on Wednesday.
Accordingly, in spite of ample sunshine through the day,
temperatures will hold in the 30s to low 40s for afternoon highs.
Similar weather is expected for Thursday in advance of our next
approaching weather maker for Thursday night into Friday.

Warm air advection is expected to kick up across the Upper
Midwest into the western Great Lakes Thursday night in advance of
a northern stream impulse tracking southeastward towards the Mid-
Missouri Valley. This is expected to result in the blossoming of
widespread precipitation to the north and northeast of a weak
surface low shifting across the Lower Missouri Valley into Friday.
Cold antecedent conditions leading into the development of this
precipitation is likely (60%+ chance) to result in it falling
primarily as wet snow, especially across approximately the
northern 1/3rd to 1/2 of the area (highest snow chances north of
I-88). Conversely, more rain then snow is favored farther
south, where the column looks to warm above freezing on Friday.
Snow accumulations continue to be plausible with this period of
wet snow, with the highest chances currently (60%+ chance of
1"+) looking to be north of I-88. There are still some
uncertainties as to where the heaviest snow may fall, so we will
continue to monitor this period for any potential travel
impacts.

The weekend may end up being largely precipitation free, but
cool, as transient surface high pressure ridge temporally builds
overhead. However, late in the weekend into early next week
there is strong ensemble support for a significant impulse to
eject eastward across the central and southern Rockies. A wave
such as this would be favorable to support Lee Cyclogenesis and
a Colorado or Texas Panhandle type surface low that would be
favored to track northward somewhere across the central part of
the county Monday or Tuesday of next week. Certainly with this
being a week away there are inherently high uncertainties with
the overall evolution of this potential system. While this is
the case, there is above average confidence that at least parts
of the area will experience a period or two of inclement weather
into early next week.

KJB

&&

.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

&&

.FIRE WEATHER...
Issued at 220 PM CDT Mon Mar 18 2024

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

Strong southwest winds are expected Tuesday morning, possibly
gusting into the 35 to 40 mph range. Winds will turn more
westerly midday with gusts perhaps diminishing slightly into the
30-35 mph range for Tuesday afternoon. Dewpoints will likely be
starting in the teens Tuesday morning but some increase in low
level moisture is expected through the day, though there remains
uncertainty for how fast dewpoints may increase through the day.
Based on the most recent data and trends, minimum relative
humidity levels are expected to reach 30 to 35 percent, which
would be above local red flag warning criteria of 25 percent.
Ten hour fuel moisture is always difficult to forecast and is
currently at 10 percent this afternoon at Midewin. It is
possible it will dip lower, into the 8-9 percent on Tuesday.
Thus, conditions will be approaching red flag warning criteria,
but at this point, we`re not expecting to reach local criteria.
Trends will need to be monitored overnight with possible SPS
needed Tuesday morning. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning from 4 AM early this morning to 1 PM CDT this
     afternoon for the IL and IN nearshore waters.

     Small Craft Advisory from 1 PM this afternoon to 7 PM CDT this
     evening for the IL and IN nearshore waters.

&&

$$

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