Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161738
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1238 PM CDT Tue Oct 16 2018

.UPDATE...1050 AM CDT

Southwesterly wind gusts have picked up quickly this morning with
a few locations already tagging 35 mph gusts. Observed aircraft
soundings show mixing to 2500-2800 ft, and with winds to 35 kt at
this layer we may see a few higher gusts to around 40 mph. The
strong southwesterly flow and continued sunny skies will help
boost highs into the middle 50s for most areas. Current forecast
appears on track, so no major updates are needed at this time.

KMD

&&

.SHORT TERM...
150 AM CDT

Through Tonight...

The weather element of interest today is wind speed, with gusts
of 30-35 mph expected for a period late this morning through early
to mid afternoon.

Surface high pressure ridging that had been over the area last
evening has gradually been pushed south early this morning, with
the CWA now under the pressure gradient in-between this ridge and
a 1000mb surface low moving across Ontario. This gradient will
strengthen this morning while as the same time moving (3mb/3hr
pressure falls), and support increasing sustained southwest winds
to near 20 mph by late morning. While some mid cloud may drift
across the northern CWA, an otherwise sunny day will provide
mixing. Given a low-level jet over the area this morning, gusts
already by 10-11 am look to be approaching 30 mph and likely
nudging just above that early this afternoon, especially for
northeast Illinois and far northwest Indiana. The chance to exceed
35 mph is low, but if it were to occur it would likely be in
sporadic gusts between 10 am and 3 pm.

The system to our north is basically a clipper, and as such will
direct a downslope-origin warm sector over the area today. The
925mb temperatures are forecast to reach +6C, which for mid-late
October averages around 58 at Chicago. Have forecast highs near
that across the area. Dew points initially should see some mix out
into the 20s, such as yesterday, but then see a rise from west to
east as some Pacific moisture is entrained into the system. With
forecast minimum humidity to around 35 percent, this is not to the
level of increased fire weather concern, but still the gusty and
modestly dry conditions will just be something for land managers
and others in that arena to be aware of.

This moisture is very limited with this system, so as the cold
front moves through this evening, little is expected besides some
scattered stratocumulus at most. Lake effect clouds or possibly
some light showers look like they will remain east of Porter
County in northwest Indiana tonight.

MTF

&&

.LONG TERM...
312 AM CDT

Wednesday through Monday...

For the longer term forecast period, general weather trends are
expected to be relatively quiet and mainly dry with below normal
temperatures.  The one fly-in-the-ointment for this trend may a
couple chances for some patchy light rain for Friday and Saturday.

By Wednesday night, the broad, flat long wave trough over the Upper
Mississippi Valley through the nern CONUS will slowly progress east,
with the trough axis along the eastern seaboard while weak ridging
builds into the nrn and cntrl plains.  Sfc high pressure will also
build across the plains and Middle Mississippi Valley and will be
centered over IL/IN by Thursday morning.  Clearing skies and
diminishing winds will set up a very chilly Thursday morning, with
lows in the upper 20s to lower 30s across much of the area.  The
exception will be the Chicago area urban heat island around downtown
Chicago and the nwrn Indiana lakefront where temps will be limited
to the upper 30s. Highs Thursday should be in the lower to middle
50s.

For Friday and Saturday, the weak upper ridging will quickly pass to
the east as a series of northern stream shortwaves carve out another
longwave trough over the nrn plains and quickly progress east.  The
series of shortwaves and a cold front associated with the longwave
upper trough will bring periodic chances for some light rain for
Friday into Saturday.  Cyclonic flow aloft could keep a slight
chance for some sprinkles or snow flurries into Saturday evening,
but high pressure building in quickly behind the exiting front
should bring a quick end to any pcpn chances Saturday night.  The
remainder of the weekend should be dry with highs in the 40s on
Sunday and the middle to upper 50s on Monday.

&&

.AVIATION...
For the 18Z TAFs...

Gusty SW winds are the primary near term concerns. Forecast and
observed soundings depict low-mid 30 kt at the top of the mixed
layer which is increasing to near 3000 ft. Wind gusts will
generally hold in the upper 20s to around 30 kt, with peak gusts
jumping to as high as 35 kt through about 21-22z. Expect a
decrease through the evening. A cold front will graze the area
tonight, with a shift to northwest winds Wednesday. Expect gusts
in the lower (to maybe briefly mid) 20s in the morning/early
afternoon.

Model guidance does also hint that some of the lower clouds
across northern MN may sneak into the area late tonight/early
Weds, but hints that coverage of any cigs would be scattered or
possibly short lived.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IN nearshore waters until 10 PM
     Wednesday.

     Small Craft Advisory...IL nearshore waters until 7 PM Tuesday.

&&

$$

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