Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 170856

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

323 AM CDT

Through tonight...

Today through Tuesday night...

Unseasonably warm and windy conditions expected today, with
afternoon temperatures expected to surge to near record levels in
the mid-80`s in many areas and south wind gusts approaching 40

The cold front which settled across the area on Sunday was already
becoming washed-out early this morning, with winds shifting south
and increasing in response to strong surface pressure falls
developing across the upper Midwest in association with a vigorous
mid-level short wave tracking across the region. Additionally, low
pressure centered over western Kansas is expected to lift
northeast toward the upper Mississippi Valley and deepen during
the day, as another strong jet streak emerges from the central
Rockies. South winds will become increasingly gusty across the
forecast area, spreading unseasonably warm air northward. Expect
that we will end up on the higher side of both temperature and
wind gusts as compared to guidance, with several models
initializing too much low cloud cover and even showers across the
area early this morning, which have not materialized. Based on
this, think guidance is too slow/too shallow with developing mixed
layer across the area today, especially compared to 00z soundings
from upstream locations such as SGF and TOP. Progged 925 mb temps
in the +22/23C range exceed highest recorded for both DVN/ILX
sounding climatology for October 17-18th, and would support
temperatures well into the mid-80`s and perhaps even an upper 80
reading this afternoon. Based on this have generally gone warmer
than mos and raw sfc/boundary layer temp guidance for today. Same
can be said for winds, where guidance again appears underdone.
Sustained speeds at/just above 20 mph and gusts 33-38 mph may even
be a bit low if boundary layer mixes deeper. Will issue an SPS
highlighting windy conditions today, though will hold short of an
advisory at this time with forecast short of criteria. Record
high temperatures for today are 87 at RFD and 86 at CHI both
dating from 1950, and could be within reach. Windy conditions are
expected to continue tonight, helping to keep temperatures above
65-70 degrees in most areas too. This is not only warmer than our
normal highs for this time of year, but would also potentially
break our record high-min temperatures for October 18th which are
63 and 65 for Rockford and Chicago respectively.

Surface low pressure continues to deepen while tracking northeast
across the northern Great Lakes Tuesday, trailing a cold front
slowly southeast across the forecast area during the day. Mid-
level forcing and moisture focuses precipitation potential north
of the area despite the front moving through during a diurnally
favorable time of day, though westerly flow aloft provides dry air
through the column with little support for rain indicated until
front is well southeast of the cwa later in the day/Tuesday night.
Mostly sunny, breezy and mild conditions will persist despite the
frontal passage, though daytime highs are expected to range from
the low-mid 70`s north to the lower 80`s southeast. Weak high
pressure spreads in behind the front Tuesday night, with lows
still above average in the upper 40`s and lower 50`s.



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 06Z TAFs...

Primary aviation concern today and tonight is with strong and
gusty south-southwest winds. Latest observational trends suggest
that most of the forecast guidance is far too pessimistic with
CIGs this morning. A warm front is in the process of lifting north
across Illinois, which will result in increasing south winds. With
there not being upstream CIG development and observed soundings
around the region not showing the lower level moisture to
saturate, have increasing confidence that the CIGs on most of the
guidance will not materialize. This will enable deeper mixing
quicker, and as strong low pressure passes to the northwest and
north through tonight, the result will be strong south-southwest
winds. Gusts could approach or even exceed 30 kt this afternoon
and evening, which could cause some cross wind issues as
directions look to range between 190 and 210 degrees.

Have almost removed the VCSH shower mention from the TAFs, as
radar trends suggest shower activity will remain northwest of all
terminals. Will continue to monitor CIG trends this morning.



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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