Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 231129

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
629 AM CDT Mon Apr 23 2018

306 AM CDT

Through tonight...

Low-impact weather is expected through tonight as dry low-level
easterly flow continues while an upper-level low near the MS/OH
River confluence meanders along the KY/TN line. Overall conditions
today should be rather similar to what was observed on Sunday for
most the area, with a bit more mid to upper-level cloud cover
expected today.

The ongoing rain across southern IL will begin to dissipate as it
encounters the very dry low-levels across the north half of IL
today. Top-down saturation may allow for some isolated to scattered
showers to gradually spread into the southern CWA this afternoon and
the remainder of the CWA through the night. Guidance appears to be a
bit aggressive with the northward extent of this precip in terms of
coverage given the antecedent dry air mass. Overall expectation is
for isolated, low-QPF showers, with much of the area remaining dry
through the period.



306 AM CDT

Tuesday through Sunday...

Tuesday through Wednesday night: The approach of mid-level troughing
over the Upper MS River Valley should allow for a slightly better
chance of low-QPF showers across the CWA on Tuesday when compared to
tonight. Still, coverage should be isolated, with only a few being a
heavy enough to wet the ground. Any showers will shift east from the
CWA during the night. A dry, cool, and somewhat breezy day is
expected for Wednesday, with just diurnal cumulus and some passing
high clouds.

Thursday through Friday: Upper-troughing originating from western
Canada will shift SE across the Upper MS River Valley on Thursday
and the western Great Lakes Thursday night into Friday. An
associated band of scattered showers is expected to cross the CWA
late Thursday night through Friday afternoon.

Saturday and Sunday: Cool but dry conditions will prevail on
Saturday under NW flow behind the departing trough. An approaching
ridge will cross the region on Sunday, bringing a seasonable and
mostly sunny late April day to the area.



For the 12Z TAFs...

Low pressure will meander over western Tennessee today and
eventually reach eastern Tennessee by late tonight. Northeast to
east flow will be in place across northern Illinois and northwest
Indiana through the day today, along with VFR conditions. Expect a
bit of a diurnal uptick in winds speeds, but otherwise conditions
should remain fairly steady-state through the day.

Conditions could become a little more interesting this evening and
overnight as lower ceilings and a few scattered showers are
expected to develop. Guidance indicates that moisture will
stream from the mid Atlantic coast northwest into the Midwest
resulting in rain and the potential for IFR conditions. Several
models now honing in on IFR ceilings, but not ready to bite off on
this solution just yet. Early morning observations indicate that
IFR is mainly near the low center which will not come near the
local area and models are initializing poorly on the extent of the
low clouds currently in place. Reverse trajectories from late
this evening indicate source region of low level parcels from the
Upper Ohio Valley and the Virginias. Primarily VFR conditions are
in place across those areas, but there is some patchy MVFR and
higher surface dewpoints. Conceptually, dry northeast boundary
layer flow through the day and downsloping from the parcels
traversing the Appalachians doesn`t bode well for the development
of IFR so will hold off. That said, given the number of models
trending towards the lower conditions tonight it`ll be something
to keep an eye on through the day. Scattered light showers will
also be possible this evening and tonight, but still expect
coverage to stay low enough to preclude anything prevailing in the
TAF other than VCSH at this distance.



306 AM CDT

Ridge of high pressure will remain over the central and northern
portions of Lake Michigan over the next couple days while a moderate
to fresh northeasterly breeze will be in place across the south half
of the lake. A cold front will move down the lake Tuesday night with
north wind gusts increasing to around 30 kt. Moderate north flow
will continue much of the day Wednesday, but should very gradually
diminish as ridge of high pressure builds across the region. Winds
swing around to the south/southwest on Thursday behind the ridge
axis, but another cold front will sweep down the lake Thursday night
bringing another period of northerly winds gusting to around 30 kt.






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