Area Forecast Discussion
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FXUS63 KLOT 231733

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1133 AM CST Thu Nov 23 2017

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.



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.



For the 18Z TAFs...

The one concern for aviation weather is wind on Friday, with
south-southwest gusts around 30 kt in the afternoon appearing more

Southwest winds today will show some fluctuation at times late
this afternoon into the evening but will be below 10 kt in that
time. As a deep weather system moves east across southern Canada
late tonight into Friday, south-southwest winds will be on the
increase. The pattern favors temperatures to warm considerably at
the surface on Friday and as such, the atmosphere will likely mix
down higher gusts than shown by models in the afternoon. Still,
there is decent uncertainty on just how high gusts will get and
especially how frequent gusts of around or even slightly higher
than 30 kt will be in the afternoon. Confidence is high though on
the peak time of winds being between 17Z-23Z, and in the direction
being between 190-220 degrees during that time.

Wind speeds around 2000 ft look to approach 50-55 kt from the
southwest, and there should be a fairly steep inversion between
1000-2000 ft. While not mentioning low-level wind shear because it
will likely be below criteria, 50 kt+ speeds are not often seen
below 2000 ft during the afternoon, so worth noting here.




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.


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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