Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 191739
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1239 PM CDT Thu Apr 19 2018

.UPDATE...
1049 AM CDT

Morning Update...

Minor changes to going forecast, primarily to raise afternoon max
temps (!) across most areas, save far northern IL where melting
snow cover from overnight may keep temps a tad cooler, and along
the lake where winds should turn northeast this afternoon.

Morning GOES imagery depicts mid-level short wave trough exiting
stage right, with strong drying noted in water vapor channel
across the region. This is indicative of strong subsidence, and
will continue to result in sunny skies for the remainder of the
day. Temps already rising into the low-mid 40`s across the heart
of the Chicago metro and areas south of the snow cover from last
night, and have raised maxes for this afternoon with local 925 mb
climo generally supporting lower 50`s for highs. Exception will
be along Lake Michigan where north-northeast flow will keep things
in the low-mid 40`s, and over far northern IL where melting snow
cover and north winds off of deeper snow cover to the north may
keep things a few degrees cooler. All in all, a marked improvement
over yesterday.

Digital/text forecast products updated and available.

Ratzer

&&

.SHORT TERM...
222 AM CDT

Through tonight...

Area of snow moving across portions of northeast Illinois and all
of northwest Indiana will continue to shift to the southeast over
the next couple of hours. As this occurs, expect the current
diminishing trend to also continue, with much of the snow
southeast/east of the area by the 9-10z time frame. Under the
heavier snow which was in place a couple of hours ago, some light
accumulation was possible on some less traveled roads. However,
with the current diminishing trend, would anticipate any
additional light snow accumulation to mainly be on grassy
surfaces.

Rodriguez

&&

.LONG TERM...
222 AM CDT

Friday through Wednesday...

Significant weather not expected at this time.

Rodriguez

&&

.AVIATION...
For the 18Z TAFs...

Only aviation concerns are wind direction a lake breeze expected to
push through ORD/MDW later this afternoon, and the potential for
some patchy MVFR fog west of the Chicago area early Friday morning.

Surface high pressure across western Minnesota and western Iowa
will continue to spread east through the TAF period, in response
to sinking air aloft behind the departing disturbance from
Wednesday. Northerly winds were varying from about 340-020 deg per
ORD/MDW obs, and though guidance not bullish in turning winds more
fully northeast, northerly winds of 340 deg or better usually turn
northeast with cold lake conditions despite stronger NNW gradient.
Thus am expecting an eventual turn to the northeast at ORD/MDW by
late afternoon. Gusts have been slow to develop, though with
temps up to 50 degrees we`ve mixed deep enough for at least some
occasional gusts 15-20 kts.

Winds will become light/variable tonight as surface high slides
overhead. Light winds and clear skies will allow strong
radiational cooling, with the potential for some patchy fog mainly
west of Chicago by Friday morning. Some high res guidance picks up
on this mainly DPA/RFD and further northwest, and have indicated a
tempo for MVFR vis there.

Ratzer

&&

.MARINE...
222 AM CDT

I did not make any changes to the going headlines.

North winds will diminish as high pressure currently over the Plains
builds over the Upper Mississippi Valley today.  High pressure will
remain over the lake through the weekend.  A low pressure system
will move across southern Canada reaching Hudson Bay Monday evening
while a second, weaker low travels across the Gulf states Sunday-mid
next week.  A low pressure system is forecast to reach the Western
Great Lakes mid next week.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...Gary to Michigan City IN until 1 AM Friday.

     Small Craft Advisory...Winthrop Harbor to Gary IN until 7 PM
     Thursday.

&&

$$

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