Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251135
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
535 AM CST Sat Feb 25 2017

.SHORT TERM...
256 AM CST

Through tonight...

Main forecast concerns are with snow showers across the entire
CWA early this morning, and then with a much colder day today.

Upper level low is lifting across the region this morning, with
stout vort lobe swinging around it. At the surface, low pressure
is well northeast of the CWA, but with trough axis on the backside
of this system continuing to push through the area. With these
features in place, have seen precip blossom overnight. Precip did
initially see a brief wintry mix despite a quickly cooling column,
as deeper moisture was lacking. Overall trends would suggest that
the bulk of any precip this morning is all snow. However, the far
southern tier of counties may still observe a brief rain snow mix
before all snow is then quickly observed. Do think this snow will
continue across the area for the next 2-3 hours, before exiting.
Minor accumulations still expected with the highest amounts likely
closer to the IL/WI border, where deformation snow has been more
persistent. However, have seen more showery type snow for
remaining areas in northern Illinois this morning, including the
southern tier of counties that could support some quick minor
accumulations as well. This is especially possible for those areas
from Pontiac east to Watseka and Fowler IN, where better low
level convergence is allowing for slightly stronger snow showers.
Given the recent warm temperatures, the bulk of any accumulation
will be on grassy surfaces. However, lesser used roads may become
snow covered.

Strong CAA still occurring this morning, with temps steadily
falling into the 20s. With temps staying in the 20s for most
locations today and with gusty northwest winds, it will feel
rather chilly today. Back edge of the stratus is expected to reach
the western CWA later this morning. However, pattern would
suggest additional stratocu development throughout the day, and so
have held onto cloud cover a little longer today. Clearing skies
then expected later this evening, but anticipate clouds to return
with the arrival of mid/upper level cloud cover associated with
approaching mid level trough.

Rodriguez

&&

.LONG TERM...
331 AM CST

Sunday through Friday...

The rest of the weekend into early next week does appear to
remain on the dry side. Mid level trough expected to push further
east through the region on Sunday, but it does appear that the
stronger forcing stays just to the south of the CWA. Some
moderating of the air mass will occur, and should see temps
rebound back into the 40s on Sunday. Continued dry conditions
likely to occur on Monday, with slightly warmer temps in place.
Westerlies usher in additional shortwave energy across the central
CONUS Monday night into Tuesday. Surface reflection expected to
lift northeast across the area during this time, with additional
warming likely. Still some model variability with the next system,
but precip chances do increase by Monday night. Precip type
should be all liquid Monday night into Tuesday and as additional
forcing and moisture increase Tuesday, could see some scattered
thunderstorm development. Guidance begins to really vary beyond
this point, Tuesday night into Wednesday. Additional precip
chances are still warranted though, but confidence is low with
trends/timing. Will need to keep an eye on this system, as it is
possible for much colder air to filter in across the area while
the stronger forcing is still in place. This would then support
more wintry type precip over much of the CWA.

Rodriguez

&&

.AVIATION...
For the 12Z TAFs...

Notable weather for this cycle of TAFs include patchy snow
showers/flurries this morning, MVFR cigs and gusty northwest winds
today, a chance of brief low-level wind shear near daybreak
Sunday, and gusty southwest winds during the day Sunday.

The strong weather system is gradually pulling away from the area
but its influence will continue to be felt today. Forcing for
snow showers will gradually wane through mid-morning, and
visibility is generally 4SM or higher under any of the lingering
shower activity. It is possible some flurries linger a little
later than the TAF indicates. Cloud bases are likely to undulate
between 2000 and 4000 ft through the morning before becoming more
consistent.

Northwest winds are gusting to over 20 kt early this morning and
expect this to continue through today. Some of the higher gusts of
24-28 kt are more probable this morning. Gusts could linger early
this evening but then an easing will be seen tonight as winds
turn southerly. Winds off the deck will be increasing overnight,
with winds at 500-1000 ft expected to be around 35 kt at 12Z
Sunday, potentially bringing true LLWS depending on how quickly
surface winds increase. A sharp ramp up in sustained southwest
surface winds is expected after sunrise Sunday. Gusts around or
possibly over 30 kt are presently forecast Sunday afternoon with
direction of 210-230 degrees.

MTF

&&

.MARINE...
143 AM CST

The pattern remains active over the Great Lakes this weekend.
Departing low pressure from the central lakes this morning will
continue cold advection and at least occasional northwest gales
are likely across the north and central, while more marginal
south. Weak ridging tonight will ease the winds only temporarily,
as a quick moving low over the northern lakes on Sunday will
result in stout southwest winds. The air mass looks inherently
cool enough going into Sunday to prevent an inversion and likely
support southwest gales during the day Sunday, especially central
and south. Some near gale force gusts are possible in the Illinois
and Indiana nearshore on Sunday.

The next chance for higher wind speeds comes Wednesday behind a
northeastward moving low pressure which passes during or near
Tuesday night/early Wednesday. Still a decent amount of spread in
our computer model guidance on this system, but this could
support some near gales, as well as more of a due north wind
direction.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Gale Warning...LMZ777-LMZ779 UNTIL 3 PM Saturday.

     Small Craft Advisory...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 9 PM
     Saturday.

     Small Craft Advisory...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 AM Sunday.

&&

$$

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