Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 200626
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
126 AM CDT FRI MAY 20 2016

.SHORT TERM...
239 PM CDT

THROUGH Friday...

Quiet and pleasant weather will continue through Friday, with no
significant forecast concerns. Main feature of note is a midlevel
shortwave noted on w/v imagery this afternoon over the High Plains
that will track toward the region tonight through Friday. Given
very dry air mass in place over the region per observed and
forecast soundings, primary impact on sensible weather from the
aforementioned wave will be a midlevel cloud deck spreading
overhead from southwest to northeast late tonight through mid day
Friday.

Light winds and clear skies under surface high pressure to
start tonight will enable temperatures to drop to the mid 40s to
around 50, with a few low 40s in interior far northeast Illinois.
Expecting the approaching mid clouds to prevent any more of a drop
despite the very low dewpoints this afternoon. Progged 925 mb
temps on Friday will be very similar if not a hair warmer than
today. However, the mid clouds are expected to result in high
temperatures inland a degree or two cooler than today, near/around
70. If the clouds are thick enough, it`s possible temps will be
limited to more widespread upper 60s. Surface high shifting
slightly east and a weak surface trough moving toward the Ohio
Valley will bring an earlier onset of easterly to northeast
winds, with the steady onshore flow keeping near lake locations in
the upper 50s to lower 60s.

RC

&&

.LONG TERM...
239 PM CDT

Friday night through Thursday...

Strengthening upper ridge and high pressure at the surface will
provide quiet weather and a continued warming trend across
northern Illinois and northwestern Indiana over the weekend and
into Monday. Expect afternoon highs in the mid to upper 70s
Saturday and Sunday while light onshore flow/lake breeze will keep
conditions cooler along the lake front. Upper ridge will be
centered across the high plains late Friday and gradually shift to
the upper midwest by Monday while low level flow becomes
southwesterly Monday as the surface high builds across the
Appalachians allowing warm/moist return flow into the western
great lakes region. This should allow temperatures to push the 80
mark Monday afternoon while suppression aloft should keep skies
mostly sunny.

From Tuesday on...expect to see more active weather across the
region as strong upper ridge begins to break down and an open gulf
allows moisture to continue to pool across the midwest. Guidance
suggests dewpoints into the 60s by Tuesday with a few low
amplitude waves pushing across the region between Tuesday and
Thursday providing periodic chances for showers and
thunderstorms...though confidence in specific timing at this
distance is low. Forecast soundings suggest moderately strong
instability will be in place though overall kinematic environment
appears more marginal with the jet stream strongest well off to
our southwest.

Deubelbeiss

&&

.AVIATION...
FOR THE 06Z TAFS...

Little of concern for the area airports today and tonight. The
Chicago area airports will experience east to northeast winds at
10-11 kt this afternoon and early evening thanks to assistance
from a lake component. Confidence on this is fairly high
especially between 20Z and 01Z...with a little less confidence on
the exact hourly start time of these 10 kt plus winds. Clouds
look to be mid-level VFR altostratus. While possible a few light
showers make it as far north as a Peoria to Champaign line this
afternoon...any activity is expected to be light with low cloud
tops and remain south of the TRACON area.

MTF

&&

.MARINE...
125 AM CDT

Surface high pressure will have the majority of influence over the
lake through the weekend meaning little of impact weather.
Developing weak low pressure across the Ohio River Valley late
today into tonight will slightly sharpen the pressure gradient
over the far southern part of the lake bringing north to
northeast 15-20 kt gusts into the Illinois and Indiana nearshore
areas. Also of minor note this weekend...a weak cold front will
drop down the lake Saturday night...re-enforcing a little more
northerly component into Sunday morning.

Next week the prevailing surface pressure pattern is forecast to
be low pressure across the Rockies and Plains states while high
pressure across the eastern U.S...a pattern equaling southerly
flow over the lake. Through at least Thursday there does not
appear to be any periods favoring above 25 kt winds.

MTF

&&

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

$$

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