Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 250729

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
229 AM CDT Wed Apr 25 2018

207 AM CDT

Through tonight...

North winds have generally been gusting 20-30 mph with a few gusts
to 35 mph behind a cold front crossing the CWA early this
morning. This will continue into the daylight hours with an
enhanced pressure gradient in place as weak troughing slowly exits
central/southern Illinois. Expect these winds to ease slightly by
this afternoon, then quickly diminish tonight as a weak surface
ridge builds in from the west.

A rather dry airmass per upstream RAOBs and satellite trends will
supports sunny skies today with some passing cirrus and maybe a few
cumulus clouds through early afternoon. Guidance has continued to
show a slight cool-bias with sunny days over the past week, so have
increased max temps a couple degrees away from the moderation of
Lake Michigan. Max temps today are expected to range from the upper
40s along the immediate shore to the low 60s well inland.



228 AM CDT

Thursday through Tuesday...

The long range features an upper air pattern shift and one to
provide a stretch of warmer than normal days. It has been two
months since we have had consecutive days with well above normal
temperatures (10+ degrees), and even two months since some
locations have had one! But that looks highly likely to end early
next week. General northwest flow aloft into the weekend will
shift west-southwesterly for next week. While some small rain
shower chances late Thursday night, and possibly Friday evening,
it looks mainly dry through Tuesday.

High pressure will move over the area during the day Thursday,
with a lake breeze anticipated. Thursday looks like a day with
deep mixing and humidity could drop to 25 percent or less in some

A cold front will move through the area Thursday night. The best
forcing for showers is to the north, but it is possible overnight
some are seen in the CWA. The parent upper level feature,
indicated by a strong vorticity maximum, drops southeast over the
western Great Lakes Friday afternoon into the evening. This could
support spotty showers, mainly in far northeast Illinois into
northwest Indiana, with the better chance again to our northeast.

Sunny and low humidity but light wind conditions are expected
through the weekend. Upper ridging moves of the area later Sunday
and the low-level thermal ridge to the immediate west of this
ridge then spreads in for Monday. With gradual cyclogenesis across
the Rockies, and a strengthening surface high offshore of the
Southeast U.S., well-above normal temperatures are forecast to
advect northeast between these features. Climatology for the
850/925 mb temperatures would support local highs well into the
70s, with low 80s in some areas probable by Tuesday and even
Wednesday if no showers/storms. Have collaborated warmer than
the guidance blend during that time. These days look breezy too.
Moisture should be on the increase especially by Tuesday, so fire
weather concerns at this time look low, but may need to watch how
quickly moisture returns on Monday.

The setup favors convection across the Plains into the Upper
Mississippi Valley during the first half of next week. Too far
out to say timing for us midweek, but as the upper ridge begins
to break down (sometime within Tue night - Thu given current
forecast solutions), there will likely be thunderstorm chances.



For the 06Z TAFs...

A cold front will track southward across northern IL over the next 1-
2 hours, ushering in gusty N to NNE winds. A period of high-end MVFR
ceilings are also expected for a 2-3 hour window behind the front.
Drier air will then allow for much of the cloud cover to dissipate
by daybreak Wednesday. The gusty winds will gradually abate during
the afternoon and evening as a weak surface ridge edges into the



230 PM CDT

A cold front will move down Lake Michigan this evening and overnight
with northerly flow strengthening in its wake. Wind gusts are
expected to peak around 30 kt late this evening and overnight, then
should very gradually diminish through the day Wednesday as a ridge
of high pressure spreads across the region. A small craft advisory
remains for the Illinois and Indiana nearshore waters for this
evening through Wednesday evening. Winds flip to southwest behind
the ridge axis on Thursday and ahead of another approaching cold
front. This next front is expected to sweep across the Lake Thursday
night possibly bringing another period of north winds gusting to
around 30 kt.



LM...Small Craft Advisory...IL nearshore waters until 10 PM

     Small Craft Advisory...IN nearshore waters until 1 AM Thursday.




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