Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 181923

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
223 PM CDT Sun Mar 18 2018

223 PM CDT

Through Monday...

Nice Sunday afternoon in progress across the forecast area, with
surface high pressure drifting slowly east across the region.
Sunny skies and light winds were allowing temperatures to warm
into the upper 40`s to mid 50`s as of mid-afternoon, with an
onshore lake breeze beginning to make itself felt by dropping
temps into the mid 40`s near the lake.

Quiet weather will continue tonight, as the area remains under
the influence of ridging aloft. Surface low pressure developing in
the lee of the Rockies in eastern Colorado will move out across
the Plains by morning however, resulting in a gradual
strengthening of easterly low level winds across our area, and
producing some increase in high clouds overnight. Good radiational
cooling conditions, especially this evening, will allow temps to
fall off into the upper 20`s and lower 30`s in most locations.
Areas along the immediate Lake Michigan shore, especially in the
urban center of Chicago, may stay just above freezing through



223 PM CDT

Monday night through Sunday...

Cool, dry surface high pressure is progged to persist across
eastern Canada through much of the coming week, helping to keep
the primary storm track south of the WFO LOT cwa. Persistent
northeast to east low level winds will also keep things a bit
cooler than average however, especially close to the Lake Michigan
shore. No significant precipitation expected until the end of the

Low pressure passes well south of the forecast area Monday and
Monday night, with precipitation limited to downstate IL/IN. The
gradient between this low and high pressure to our north over
Ontario will provide somewhat blustery northeast winds however,
with winds gusting 25-30 mph at times. This persists into Tuesday,
as the low slowly tracks across the lower Ohio and Tennessee
Valleys. This northeast-north wind pattern will bring somewhat
cooler temps to the region, especially by Tuesday.

Temps moderate slightly during the mid-week period, closer to our
late-March averages, though that persistent high pressure center
over eastern Canada maintains a prevailing northeast wind which
will maintain lake-induced cooling through the period, especially
across the Chicago metro area.

Guidance remains in decent agreement in amplifying the upper
level pattern by the end of the week, with a jet streak emerging
from an upper trough off the west coast progged to develop another
area of low pressure across the Plains by late Friday. Medium-
range guidance does display differences in the details and timing
of this system into next weekend however. The general model
consensus at this point does indicate the potential for
precipitation Friday through Saturday, as an open mid-level wave
tracks across the region with it`s associated surface low moving
through central IL. Thermal fields would generally support rain
across south south, with a mix of rain/snow across the north,
particularly during the diurnally cooler nighttime periods. As
this is still out there at day 6/7, hard to offer much more detail
at this time.



For the 18Z TAFs...

A ridge of high pressure moving across the area will maintain VFR
conditions while keeping winds relatively light and providing a
favorable setup for development of a lake breeze this afternoon.
There are hints in nearshore observations and radar imagery that
this is starting to develop and work its way onshore, but felt
there was not enough new information to nudge the timing away from
existing trends.

The gradient remains light overnight and the easterly direction
persists into tomorrow. By tomorrow afternoon a center of low
pressure moving well south of the area will tighten the local
gradient and increase winds and gusts, with the direction
remaining east to northeasterly.



113 AM CDT

A weak cold front will settle over the northern part of the lake
this afternoon, turning winds to the north-northeast. Otherwise
high pressure will prevail across the southern part of the lake
with an afternoon lake breeze in the nearshores.

This week will be dominated by northeasterly flow, with general
high pressure to the north and low pressure to the south on
Monday-Tuesday and likely again late in the week. The first bout
of stronger northeast winds will take shape late tonight and
through Monday. Northeasterly wind gusts look to peak Monday
night, with the highest gusts of around 30 kt favored over the
south including Illinois and Indiana nearshores. This will support
high wave action and Small Craft Advisory criteria that will
continue through at least Tuesday. North-northeast winds continue
but less in speed midweek, before an increase in northeast or
east winds is favored again late in the week.



LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...7 AM Monday to 9
     AM Wednesday.

     Small Craft Advisory...LMZ743-LMZ744-LMZ745...3 PM Monday to 9
     AM Wednesday.




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