Area Forecast Discussion
Issued by NWS Chicago, IL

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355
FXUS63 KLOT 222307
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
607 PM CDT Sat Apr 22 2017

.SHORT TERM...
237 PM CDT

Through Sunday...

Quiet and dry conditions will persist through the period with
surface ridge really settling in tonight into Sunday. Thicker
cirrus finally shifted south of the CWA today, with clear/sunny
skies expected. Will see cool temps tonight with these clear skies
and lighter winds, with lows falling to the upper 30s. In this
setup, patchy frost will be possible tonight and have included it
in the forecast. This will be primarily for areas in northern
Illinois, but could see some additional frost development over
portions of northwest Indiana. Sunday is setting up to be a
pleasant day with sunny skies, light winds, and temps around 70.
Did increase temps Sunday over the entire CWA, including near the
lake. Although lake cooling still anticipated, think it will
mainly be confined for areas right near the lake for much of the
day.

Rodriguez

&&

.LONG TERM...
247 PM CDT

Sunday night through Saturday...

Warm and primarily dry conditions will be in place to start the
upcoming week as low pressure lifts from the Dakotas into the
Upper Midwest. Southerly flow and warm air advection will be in
place Monday and Tuesday and will help the area warm back into the
upper 60s and 70s. While the gradient picks up in the western CWA
Monday, the gradient over the Chicago Metro area remains a bit
baggy and should allow a lake breeze to develop, especially across
northern Cook into Lake County, IL. Confidence in a lake breeze
Tuesday is lower as the stronger gradient overspreads the
remainder of the CWA. Precipitation with this first low is
expected to stay well to our north, but Tuesday night into
Wednesday another low will lift from the Central Plains across far
eastern Iowa and/or northwest Illinois. Confidence in
precipitation Tuesday night isn`t the greatest with model track
differences affecting where the better convergence from the low
level jet sets up and unfavorable diurnal timing within the warm
sector for widespread precipitation. Still, guidance indicates a
narrow corridor of modest instability and PWats increasing to
1.1-1.3 inches so some ingredients will be in place for some
convective activity. Temperatures and precipitation chances on
Wednesday will depend on the position of the cold front which the
GFS pushes through several hours quicker than the ECMWF. In
general, expect warmer temperatures and higher precip chances
across the eastern CWA which has the best chance to warm pre-fropa
as compared to western counties. High pressure will bring another
dry day Thursday with moderated temperatures behind the cold
front.

Multiple rounds of showers and thunderstorms remain possible
Thursday night through the weekend as a strong upper level wave
carves out a deep trough over the intermountain west with a series
of lows lifting from the southern/central Great Plaines into the
Midwest. There are large run-to-run inconsistencies as well as
inter-model differences that make it difficult to pin down
specifics at this point, but do anticipate active weather to close
out the week and kick off the weekend.

Deubelbeiss

&&

.AVIATION...
For the 00Z TAFs...

There are no weather concerns during the period. Expect winds to
become light and variable this evening, then light out of the
west on Sunday. A lake breeze is likely to develop during the
afternoon, and this will likely result in a return to a light
easterly wind late Sunday afternoon and evening at the Chicago
area terminals. Otherwise, VFR conditions are expected.

KJB

&&

.MARINE...
247 PM CDT

A ridge of high pressure is over central portions of Lake Michigan
this afternoon with light flow over central and northern portions
of the lake and a modest northerly breeze across the south half of
the lake. South to southwest winds will increase over northern
Lake Michigan this evening ahead of an approaching cold front,
then winds will swing around to the north Sunday as the front
makes it halfway or so down the lake before weakening. A series of
lows will lift across the Great Plains over the upcoming week.
South to southeast flow to around 30 kt will develop Monday night
into Tuesday ahead of the first low. Another low is expected to
lift across Lake Michigan midweek.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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