Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 171931

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
231 PM CDT Mon Oct 17 2016

228 PM CDT

Through Tuesday...

Surface low centered over the mid-Missouri Valley this afternoon
continues to result in strong southerly flow across northern
Illinois and northwest Indiana. Forecast soundings are a bit
divided between the various models on what degree we decouple
this evening, but either way breezy conditions should continue
through the overnight hours and decent chance we see gusts
of 25 to 35 mph continue through late tonight. Breezy conditions
along with unseasonably moist air mass with dewpoints in the mid
60s will help keep temperatures propped up overnight with lows in
the low to mid 60s northwest near the Rockford metro to near 70
south of I-80 for east central Illinois and northwest Indiana.
Meanwhile, a strong upper jet punching from the west coast across
the Rocky Mountains will continue to translate east with an
amplifying lead shortwave trough lifting across portions of the
upper midwest overnight. This will result in strong surface
cyclogenesis across Wisconsin and the Great Lakes tonight, with
the low lifting to near James Bay midday Tuesday. A trailing cold
front should push across the Rockford area around sunrise, and the
Chicago metro area by mid to late morning. Could see an increase
in stratus in the WAA out ahead of the front, but very poor
mid/upper level lapse rates and fropa occurring at diurnal min
will not be conducive for any precip. Also, there is not a sharp
contrast in air masses with this front, and it looks like
temperatures will continue to run well above normal behind the
front. Expect highs in the low to mid 70s north of I-80 and mid to
upper 80s south with a few spots touching 80.



323 AM CDT

Tuesday through Sunday...

Wednesday through Sunday...

A trend toward cooler weather will develop mid-week, with medium-
range guidance in very good agreement in amplifying an upper
trough across the central CONUS Wednesday and Thursday. Deepening
of this trough induces a surface low pressure wave along the
cold front to our southwest, rippling northeast along the
baroclinic zone across the Ohio Valley and eastern Midwest. The
northern periphery of the precipitation shield developing with
this system looks to spread north across the southeast half of the
cwa Wednesday afternoon/night, and eventually across parts of the
Chicago metro and southern Lake Michigan on Thursday. Cooler air
aloft within the trough axis (around +3C to +5C at H8 per ECMWF)
will likely result in lake effect rain showers across parts of
northeast IL and northwest IN, though backing of low level winds
to the northwest would likely push then east of the cwa Friday
morning. Coolest air looks to be in place Thursday night with
lows dipping to the 30`s and 40`s, and highs Friday in the 50`s.
Guidance remains in decent agreement latter in the period as well,
building a broad ridge over the western CONUS, which eventually
shifts the downstream trough axis off to the east. This would
allow some moderation in temps back to or a little above average
by the weekend.



325 AM CDT

Record/near record high minimum and maximum temperatures are
possible Today and tonight based off the current forecast. Below
are the current records that could be threatened.

October 16th
Record High Min for Rockford: 65 in 1968 (*Tied yesterday*)

October 17th
Record High Max for Chicago: 86 in 1950
Record High Max for Rockford: 87 in 1950

Record High Min for Chicago: 63 in 1998
Record High Min for Rockford: 61 in 1998



For the 18Z TAFs...

Increasing southerly winds are still expected, though persistent
cloud cover has delayed the onset of stronger gusts thus far.
Cloud cover has been slowly eroding from the south and starting
to see VFR conditions work back north to a VYS to GYY line early
this afternoon and should continue across the terminals over the
next few hours. Once skies scatter, should see wind gusts just up
into the 25 to 30 kt range with a few sporadic higher gusts.
Expect prevailing wind direction to stay between 190-210 through
the afternoon.

Winds will be a bit tricky as we head through sunset with a couple
possible scenarios. For the forecast, will continue to go with the
idea that wind gusts remain elevated through the overnight
hours; however, some models show winds dropping off at the surface
after sunset, but remain strong just off the deck with 50-60kt
winds possible at 020. If this latter scenario pans out, will have
to add LLWS conditions to the TAF.

A cold front will move across the region mid to late tomorrow
morning. Don`t anticipate any precip with the front, but could be
additional MVFR cigs ahead of the front. Drier air moving in
behind the front should allow a return to VFR conditions through
the remainder of the period.



356 AM CDT

The main concern is strong south-southwest winds today and
tonight. A warm front will continue to lift north across the lake
this morning, causing southerly winds and gusts to increase.
Strengthening low pressure over the Plains this morning will move
to the northern Great Lakes by early Tuesday morning. This puts
the lake in the favored path for a brief period of very strong
south-southwest winds tonight. The air mass over the lake will be
unseasonably warm for October, so winds will likely diminish some
over the open lake this afternoon and then ramp up again tonight
as the pressure gradient tightens. Despite the very warm air mass
over the lake stabilizing the near lake surface atmosphere,
sustained speeds will briefly be at or slightly above 30 kt, so
expecting a period of at least occasional gale force gusts this
evening through part of the overnight. Have opted to hold off from
issuing a Gale Warning due to guidance only indicating a window of
a few hours with gale speeds/gusts, though if this duration
increases, a warning may be needed.

Winds in the near shore will be driven by tight pressure gradient,
as well as mixing off the land. Did not make mention of gale force
gusts in the near shore forecast, but can not rule them out if
winds are stronger than current forecast over the land today. The
cold front trailing from the low pressure will move across the
lake Tuesday morning, putting an end to the strong winds, with
direction shifting to west and then northwest.



LM...Small Craft Advisory...NEARSHORE WATERS
     UNTIL 10 AM Tuesday.




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