Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 181100

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

332 AM CDT

Through tonight...

As the center of high pressure settles over the Middle Mississippi
Valley this morning, clear skies and light winds have developed
overnight.  Temperatures should drop into the middle 20s by
daybreak, with a few isolated locations possibly dipping into the
lower 20s, while the urbanized areas of the Chicago Metro remain a
bit warmer.  Latest satellite imagery indicates some patchy fog
creeping up the Illinois River Valley into swrn La Salle County.
There is some potential for some of this patchy fog to persist until
shortly after daybreak.  Clear, quiet conditions will persist
through the day today, with the main forecast concern being the
development of a lake breeze this afternoon.  With upper ridging
building across the region today, temperatures should be able to
climb in to the 50s today. However, a light pressure gradient and
strong differential heating between the cold lake and warmer land
should be sufficient to generate a lake breeze.  So, while much of
the CWA sees temps climbing into the 50s, the lakefront may only
reach the lower to middle 40s, before dropping back into the upper
30s as the lake breeze pushes inland.  Other than some increasing
high level cloudiness overnight tonight, conditions should remain
quiet, with lows in the upper 20s to middle 30s.


332 AM CDT

Monday through Saturday...

Have made little change to the longer term forecast.  The models are
relatively consistent with the track of a southern stream shortwave
across the South High Plains overnight tonight and across southern
Missouri to the Lower Ohio Valley tomorrow.  The wave is then
expected to weaken as it lifts through the Upper Ohio Valley
tomorrow night. The general consensus is that this system will
remain too far south to bring any associated pcpn into the CWA.  The
greater impact will come from persistent, brisk northeast winds
gusting to 25-30 mph on Monday and Tuesday as sfc high pressure
remains parked over central Canada while a sfc low associated with
the shortwave tracks south of the Ohio River.  The next significant
chance for precipitation for the area will not be until late in the
week and into next weekend.  The upper level pattern is expected to
transition to a high amplitude longwave pattern over the CONUS, with
ridging building over the Rockies and troughing over the ern CONUS.
This should keep generally seasonable temperatures across the
region.  By Friday, there are indications that the pattern will
break down and that a more organized system will track across the
midwest.  The longer range guidance is still struggling with the
timing and intensity of the system, but there is enough of a signal
to suggest wet weather for late in the period.


For the 12Z TAFs...

A lake breeze will develop this afternoon and provide a wind shift
to east-northeasterly at Chicago area airports. Confidence is
high in the wind shift occurring at ORD and MDW and speeds after
the wind shift being 9-12 kt. As for the forecast wind shift
timing near or shortly after 21Z, confidence is medium in that.

Winds look to diminish this evening, then re-increase from the
northeast to 10-15 kt by or shortly after daybreak Monday. Gusts
into the mid 20 kt range are expected by mid-afternoon Monday.
There likely will be some spotty lake effect clouds at first, with
more clouds favored Monday night as cooler air moves southward
over the lake.



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.






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