365
FXUS63 KLOT 281758
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1158 AM CST Fri Feb 28 2025

.KEY MESSAGES...

- Mild, dry and very windy conditions today. Gusts over 45 mph
  possible at times. As a result, an increased threat for grass
  and brush fire spread exists.

- Conditions will be much cooler this weekend with highs in the
  30s expected on both Saturday and Sunday.

- Chance for rain on Monday, possibly mixed with some snow
  Monday morning.

- Increasing potential for a spring storm system to impact the
  region Tuesday through Wednesday with soaking rainfall, gusty
  winds, thunderstorms, and snow all possible.

&&

.UPDATE...
Issued at 1056 AM CST Fri Feb 28 2025

Opted to issue a Red Flag warning for this afternoon for areas
south of the Kankakee River due to the windy and very dry
conditions. While it will also be dry and windy north of this
area, it appears continues will not become as critical due to
slightly higher RH values and unfavorable ground conditions for
the recently melted snow cover.

KJB

&&

.DISCUSSION...
Issued at 355 AM CST Fri Feb 28 2025

Through Saturday:

Strong and gusty winds, unseasonably mild temperatures and an
elevated risk of grass/brush fire spread are the main forecast
concerns for today. Temperatures then fall sharply behind a cold
front late today/tonight, with much colder weather expected for
Saturday.

Early morning GOES water vapor imagery depicts a vigorous mid-
level short wave trough digging southeast from southern Manitoba
into northern Minnesota, with surface analysis showing a
corresponding 989 mb low pressure center just over the
international border in southwest Ontario. A broad area of
impressive 6 to 9+ mb 3 hourly surface pressure falls were
evident across the region east and south of the low,
representative of a rapidly tightening surface pressure gradient
across the region. This strengthening gradient will result in
very windy conditions developing across the forecast area today.
Latest model guidance is in very good agreement in depicting
southwest winds ramping up quickly this morning as a 60 kt low
level jet develops overhead across the central and eastern cwa,
with sustained speeds in the 25-30 mph range and gusts of 40-45+
mph by mid-late morning. There may be a bit of a lull midday as
winds shift west and eventually west-northwest behind a cold
front, but winds will ramp back up into the 40-45+ mph range
this afternoon with deeper mixing especially north of I-80. No
changes made to going Wind Advisory headlines, as the timing and
coverage continue to match expected trends. Winds will
gradually ease tonight, though will remain blustery.

Impressive warm advection is expected within the strong
southwest wind field ahead of the cold front today, which along
with very dry thermodynamic profiles should support temperatures
warming well into the 50s even across northern parts of the
forecast area, and likely into the low-mid 60s south of the I-80
corridor. Increasing high cloud cover may be a limiting factor
in more widespread 60s this afternoon, though have continued to
blend in some of the warmer high- res HRRR/RAP for surface temps
as well as lower surface dew points. Afternoon relative
humidity levels as low as 25 percent (especially south of I-80)
combined with the warm and very strong and gusty winds will
support an increased threat of grass and brush fire spread
today. Will be issuing a Special Weather Statement to highlight
this danger.

A sharp cold front will trail the deep surface low as it passes
across the northern Lakes later today, and this front will push
southeast across our forecast area late this afternoon and
evening. Some guidance develops a deep enough stratus/stratocu
layer to produce a few brief sprinkles or light showers behind
the front this evening, though the overall dryness of the
profile suggests these will be pretty inconsequential. Some
light lake-effect rain/snow showers can`t be ruled out in
northwest Indiana later in the evening as well, though better
chances look to be east of our cwa. The most impactful weather
tonight into Saturday will be sharply colder temperatures and
continued blustery north-northwest winds. Low temperatures
tonight are expected to be 30+ degrees colder than our afternoon
highs, with teens and low-20s expected by morning. Temps are
only expected to recover to the low-mid 30s Saturday, with wind
chills in the teens and 20s.

Ratzer


Saturday Night through Thursday:

Mid-level ridging and its associated surface high will be
building into northern IL and northwest IN on Sunday. While the
high will generate mostly sunny skies and begin to advect in
warmer air, temperatures on Sunday still look to remain in the
mid to upper 30s for most locations. Though a few spots, mainly
near and west of I- 39, may flirt with 40 degrees. The rest of
the upcoming week is forecast to be warmer with highs back into
the 40s to around 50, but a pattern shift will also bring more
active weather.

The first period of active weather is expected to occur on
Monday as the upper low off the coast of southern California
pivots across the southwestern CONUS and into the Ohio River
Valley. As it does so, the low is forecast to broaden into a
weak shortwave trough and continue to be in a decaying state as
it passes through central IL and IN on Monday. That said,
precipitation is expected to develop within the warm advection
wing of this system and spread into our area early Monday
morning. Initially, temperatures are forecast to be around if
not just below freezing which will allow precipitation to begin
as snow. The snow will transition over to rain by midday Monday
as temperatures (both at the surface and aloft) warm above
freezing. Therefore, any snow accumulations with this system
look to be limited in our area to maybe a dusting on colder
surfaces. Precipitation with this first system is expected to
taper Monday evening, but another system will be moving in as we
head into Tuesday.

The second, and notably stronger, system is forecast to be
moving onshore along the California coast on Monday as an upper
low before it broadens into a shortwave trough over the
southwest CONUS Monday night. This shortwave is forecast to
maintain its intensity as it traverses the southern Plains on
Tuesday where it is expected to interact with a strong (120+ kt)
upper jet resulting in the development of a surface low. As
this surface low develops and progresses east into the southern
Mississippi Valley, it should push a warm front northward across
IL and IN allowing precipitation (in the form of rain) to
spread back into our area Tuesday morning. Rain is expected to
continue through most of the day on Tuesday as the surface low
continues to track through the area Tuesday night into Wednesday
deepening as it does so. With the current low track forecast to
move right overtop of northern IL, the system`s warm sector
should be positioned across the southern third to half of the
CWA which should allow dew points to peak into the 50s and
result in some modest (200-300 J/kg) of MUCAPE to materialize.
While normally instability values of this magnitude are not a
cause for concern, the strong forcing generated by the surface
low and associated shortwave should be enough to overcome the
limited instability. Therefore, some thunderstorms may develop
Tuesday afternoon and evening across portions of northeast IL
and northwest IN a few of which could even be on the strong side
given the 30-35 kts of deep layer shear forecast to be in
place.

The shortwave and surface low are forecast to begin to pivot
east of the area on Wednesday, but another shortwave is progged
to be diving across the northern Plains and into the Great Lakes
during this time. These two shortwaves are expected to phase
over northern IN and lower MI which should shove the surface low
northeastward across the eastern Lakes and into southern
Ontario by Wednesday night. While this phasing does not look to
alter the forecast for our area, the secondary shortwave is
expected to provide a shot of cold air which guidance suggests
will transition the rain over to snow/wintry mix along the
backside of the low Wednesday afternoon. However, with
temperatures during this time forecast to be near peak warmth
and in the mid to upper 30s confidence on any snow actually
accumulating is very low. Thus, have decided to maintain a rain-
snow mix for this time period which seems more reasonable given
the temperature profiles. That said, the bigger concern from
this system is the potential for soaking rainfall on top of
frozen ground that could lead to river rises and maybe localized
flooding. Obviously this threat will be highly dependent on how
deep frost depths will be during this period and how much rain
actually falls, but with ensemble guidance indicating a 70-80%
chance of at least 0.5 inches of rain and a 30-40% chance for
amounts over an inch this will be something to monitor closely.

In addition to the precipitation, the storm system also looks
to bring a threat for gusty winds northwest winds Tuesday night
into Wednesday. While exact wind magnitudes will depend on low
track and its strength, there is a decent signal for gusts to be
in excess of 30 mph during this time.

It should be noted that while guidance (both deterministic and
ensemble) are in rather good agreement on the forecast
expectations described above, there is still some uncertainty
especially in the surface low track. That said, if the low track
shifts then impacts to our local area could change drastically
and mean either colder temperatures with more snow (a more
southern low track) or warmer temperatures and higher
thunderstorm potential (more northern low track). So be sure to
check the forecast frequently for updates as we hone in on the
details over the coming days.

Lastly, precipitation from the aforementioned system is
expected to taper Wednesday night as a surface high builds into
the area. While this will offer a brief reprieve from the active
weather, the upper level pattern is forecast to remain in a
northwest flow state. This means that additional disturbances
are likely to pivot through the area and possibly bring more
chance for precipitation towards the end of next week and into
the following weekend. While details are obviously fluid at this
range, it does appear that temperatures should remain
seasonable through next week with highs in the 40s and lows in
the mid-20s.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1158 AM CST Fri Feb 28 2025

Key Messages:

- Strong westerly to northwesterly winds to continue into this
  evening.

- There is a 20-30% chance for flurries and MVFR ceilings
  overnight tonight.


The main aviation forecast item of note remains the strong
westerly to northwesterly winds occurring as a result of a deep
low pressure system tracking through the Great Lakes. Peak gusts
in the 40-45 kt range are expected to occur between the mid-
afternoon and early evening before gradually subsiding through
the night as the prevailing wind direction veers more northerly.

A BKN-OVC stratocumulus deck is expected to move in tonight
behind a cold front. Cloud bases are generally expected to
remain above 3000 ft AGL, though MVFR ceilings aren`t entirely
out of the question at this point. While the chances for rain
showers occurring along the cold front have decreased, there is
still a chance that some flurries could occur overnight tonight,
mainly between 06Z and 12Z. Didn`t have enough confidence in
that yet to add a -SN mention to the TAFs, but even if flurries
were to occur, no notable visibility reductions or snow
accumulations are expected.

Ogorek

&&

.MARINE...
Issued at 245 AM CST Fri Feb 28 2025

- Gale Warning in effect for the nearshore waters from this
  morning through this evening.

A strong area of low pressure under 990 mb will track from
northern Minnesota to Lake Ontario today. This will bring a
period of strong winds to the southern Lake Michigan.

Southwest wind gusts are expected to increase rapidly to near
40 kts this morning, before backing to the west-northwest later
this afternoon and evening. Gales may ease for a time around
midday, but are expected to increase again during the late
afternoon and into the evening.

Carlaw/KJB/Ratzer

&&

.FIRE WEATHER...
Issued at 245 AM CST Fri Feb 28 2025

- Elevated Fire Danger expected across most of the area on
  Friday.

An initial "pop" of southwesterly winds gusting near 45 mph may
occur between about 9 AM and noon, mainly for locales along and
east of about I-55 this morning. This will be followed by winds
turning out of the west-northwest and routinely gusting 40-45+
mph again during the afternoon. Afternoon relative humidity
values are currently forecast to fall into the 25-35 percent
range, with the driest conditions expected roughly south of
I-80. In these areas, it`s possible that RH values may even
trend a bit lower on a brief basis.

This combination mild, dry and windy conditions is expected to
result in an increased threat for grass and brush fire spread
across the entire region, but particularly along and south of
I-80 this afternoon.

Carlaw/KJB/Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory until 6 PM CST this evening for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ103-
     ILZ104.

     Wind Advisory until 2 PM CST this afternoon for ILZ019-ILZ020-
     ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ105-ILZ106-ILZ107-
     ILZ108.

     Red Flag Warning until 6 PM CST this evening for ILZ023-ILZ032-
     ILZ033-ILZ039.

IN...Wind Advisory until 2 PM CST /3 PM EST/ this afternoon for
     INZ001-INZ002-INZ010-INZ011-INZ019.

     Red Flag Warning until 6 PM CST /7 PM EST/ this evening for
     INZ010-INZ011-INZ019.

LM...Gale Warning until 10 PM CST this evening for the IL and IN
     nearshore waters.

&&

$$

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