Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251751

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1251 PM CDT Wed Apr 25 2018

1244 PM CDT

Have made only minor tweaks to hourly temp/wind grids for the
afternoon as the going forecast remains on track. Temps continue a
slow rise well inland of the lake and highs around 60 are on
track. Temps have leveled off in the chicago metro and areas near
the lake so forecast highs in the 40s/50s look to be in good



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 18Z TAFs...

Tight pressure gradient remains in place but is loosening as
surface ridging approaches. As a result, northeast winds remain
breezy with gusts into the low 20s which will continue through the
afternoon before easing up early this evening. High pressure will
be overhead early Thursday allowing for much lighter winds which
will favor a southwest direction away from the lake. Expect a lake
breeze to develop but it is not clear how far inland across IL it
will make it before Thursday evening. Will keep it out of ORD/MDW
for now. Winds will likely flip to the southeast Thursday evening
but speeds will be light as this occurs. Otherwise, VFR will



259 AM CDT

Stout north winds today will gradually ease this afternoon and
then rapidly this evening. High waves and hazardous conditions
for small craft in the Illinois and Indiana nearshores will
continue into this evening. After brief southwest winds on
Thursday, another cold front will drop over the lake Thursday
night with a push of north winds to 30 kt behind it. Yet another
cold front will push through Friday night, though with weaker
northerly winds behind it. Southerly winds will settle in on
Sunday and be the rule into next week. Small craft advisory
conditions are likely in the Illinois and Indiana nearshores
during the days Monday-Wednesday with strong offshore winds.



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

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




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