Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230713

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
213 AM CDT Sun Apr 23 2017

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



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

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.



For the 06Z TAFs...

1224 am...Dry/vfr through the period. A ridge of high pressure is
centered over the area early this morning and will slowly shift
southeast tonight into Monday. Light/calm winds at most locations
through sunrise will become light westerly later this morning. A
lake breeze will develop shifting winds northeast at gyy this
morning...then easterly at ord/mdw this afternoon. Only medium
confidence on timing from this distance. Winds will remain light
easterly tonight...possibly variable at times. Skc this morning
with few/sct high clouds later today and tonight. cms



213 am...Weak low pressure near James Bay early this morning will
move into northern Quebec today. A trailing cold front will move
south across northern Lake Michigan this morning and then into
central portions of the lake this afternoon. There remains some
uncertainty as to how far south this front may push. Its possible
this front may move as far south as the IL/WI state line by late
this afternoon...on the west side of the lake. A ridge of high
pressure over the southern lakes region will slowly sag south
today and tonight.

An area of low pressure will move from the western plains tonight
to Lake Superior it dissipates. A trailing cold front
will extend from the western lakes to the a second area of low
pressure over the southern plains Tuesday. This low will lift
northeast across the western lakes region Wednesday into Wednesday
night. cms





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