Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 231130
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
530 AM CST Thu Nov 23 2017

.SHORT TERM...
100 AM CST

Through tonight...

A few echoes on radar from the streaming in from the
northwest. Very dry sounding earlier in the evening from DVN is
consistent with little to nothing hitting the ground. There is
some shortwave energy riding the NW flow that will get out of here
in the coming hours, and with the surface reflection weak and the
frontal boundary also weakening, expect little more than some
lowering cloud bases and maybe some brief mixed precipitation.
This wave will depart at or even before daybreak. The surface low
will further weaken to our west leading to a mostly sunny
Thanksgiving Day under light to moderate southwest winds, which
will make for a milder day with highs in the lower 40s.

KMD

&&

.LONG TERM...
100 AM CST

Friday through Wednesday...

The next system to pass through the region is off the PacNW coast.
This will ride the ridge north into Canada before diving southeast
through Wisconsin late Friday. This system gives us more of a
glancing blow than the last front did on Tuesday. With another
impressive low across Canada, warm southwest winds will make for a
warm late fall day, and have continued the idea of temperatures
above the blended guidance and on the higher side of ensemble
guidance which would bring mid to upper 50s nearly area wide with
mixed cloud cover. The 12z EC was the only guidance bringing any
precipitation with this front and we may be able to push out some
very light rain/sprinkles, but most of the 0z model suite is
largely dry.

High pressure will fill in for the weekend, making for sunny and
near seasonal temps. We will still see a cool down on Saturday
and Sunday, but much more tempered this go around. A weaker wave
will pass through south central Canada Monday, another day where
southwest winds should usher in warm temperatures similar to
Friday where the model blend appears like it could be too cool.
Eventually an upper trough will organize across the west at a bit
farther south latitude, but guidance is still mixed as to the
impacts from this. The pattern looks somewhat progressive beyond
this, but at this point overall precip chances are not too high,
just the continued up and down temperature see-saw.

KMD

&&

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

530 am...Only forecast concern is the winds Friday. A slightly
tighter gradient will work its way across northern IL this morning
with southerly winds in the 10-15kt range with some higher gusts
possible. These winds will diminish under 10kts by late morning
and turn more west/southwest. Speeds will diminish further with
sunset as directions turn back southerly. The gradient will begin
to tighten early Friday morning and continue into Friday
afternoon. Southerly winds will begin to increase around sunrise
Friday morning. There remains some uncertainty regarding how
strong the winds will become on Friday...but gusts into the mid
20kt range appear likely from this distance.

The back edge of a 7-9kft mid deck will move across the terminals
in the next few hours and then a ribbon of 4-5kft clouds over
southern WI will move across the area late this morning.
Otherwise...high clouds for the rest of the period. cms

&&

.MARINE...

150 am...A large area of high pressure over the Ohio Valley will
move to the mid Atlantic by Friday morning as it slowly weakens.
Strong low pressure will move across Ontario Friday and into
Quebec Friday night. A trailing cold front from this low will move
across Lake Michigan Friday evening...shifting winds to the
northwest. Ahead of this front...the gradient will tighten with
southerly gales over the northern portion of the lake by sunrise
Friday morning and then across the rest of the lake by mid/late
Friday morning. These gales will diminish just ahead of the cold
front Friday evening. Wind speeds behind the front are expected to
remain in the 30kt range...though some higher gusts are possible.
Another large high will move from the Plains Saturday to the
southeast U.S. Sunday and Sunday night. Another tight southerly
gradient is expected next Monday with a chance of low end gales.
cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Watch...LMZ777-LMZ779...6 AM Friday to 9 PM Friday.

     Gale Watch...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...9 AM
     Friday to 6 PM Friday.

&&

$$

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