Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 052043

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
243 PM CST Mon Dec 5 2016

231 PM CST

Through Tuesday...

We remain between a departing high pressure ridge and low pressure
over the plains.  As such, winds drop off tonight. There should be
ample low level moisture with the dense snow pack so expecting
widespread fog tonight. Dense fog is possible especially in outlying
areas.  Low temps will be at or just below freezing. The fog may
freeze on elevated objects, and if roadways cool enough, fog may
create slick conditions on some roads. Confidence is low in
widespread freezing fog and slick conditions.

Another low forms over the southern Mississippi valley tonight
and moves up the Ohio valley. Precip may clip the southeast
portion of the outlook area...mainly southeast of a Valparaiso, IN
to Chatsworth, IL line. Precip will be a wintry mix at the
beginning. Freezing rain is possible given forecast soundings and
forecast low temps. Ice accumulation will mostly be a light glaze
as temps will climb above freezing by mid to late morning. As
such, precip should turn over to all rain before coming to an end
late in the morning.

Fog dissipates in the late morning as the cold front moves through
and west winds pick up.  Otherwise we should see some melting
tomorrow as high temps will be in the mid to upper 30s.



231 PM CST

Tuesday night through Monday...

Well below normal temperatures will prevail throughout the latter
half of the week as a strong Canadian high builds into the Great
Plains and eventually shifts across portions of the Midwest.

Low pressure over the northern Plains today is expected to lift
across Ontario to near James Bay  Wednesday with strong cold air
advection occurring across the northern Plains and upper Midwest in
the wake of this low. Ridging from a 1050mb high over the Canadian
Rockies will stretch southeast into the central and southern Plains
helping to drive 850mb temps into the -10 to -12C range Wednesday
night into Thursday. Highs in the mid 20s north to low 30s south
Wednesday will likely only top out in the low 20s Thursday and
Friday with morning lows in the teens. While the lake effect
machine ramps up for the latter half of the week, outside of any
of this activity creeping west into Porter County, anticipate the
remainder of the CWA to remain dry through Friday.

Upper pattern becomes more zonal over the weekend into early next
week with an upper level disturbance digging into the northern
Plains by early next week. At this distance, we are still dealing
with large track and timing differences, but do anticipate
temperatures to moderate out ahead of the wave this weekend with the
baroclinic zone lifting back towards the local area. Precip chances
will return under the mid level WAA and again with a cold front as
it pushes across the region early next week.



For the 18Z TAFs...

Made significant changes to the forecast as cigs and vsby will
likely not improve until the cold front moves through tomorrow

For ORD/MDW/GYY: IFR cigs and MVFR vsby lower overnight. The
1/4SM fog will stay just west of these terminals, but vsby will
drop to around 1/2SM around midnight. Vertical vsby may fall to
LIFR as well but not overly confident in that so kept IFR cigs

For DPA & RFD: Cigs and vsby may improve slightly this aftn, but
expecting conditions to drop to LIFR and 1/4SM tonight.

The front moves through Tuesday morning and winds become west
behind it. This should help mix out some of the low level moisture
leading to improving conditions.



233 PM CST

Moderate south flow will remain in place across Lake Michigan today
behind a departing high over the Ohio Valley and ahead of a
developing low over the Plains. The low will lift across northern
Minnesota Tuesday to James Bay Wednesday with a trailing cold front
pushing across Lake Michigan Tuesday afternoon and evening turning
winds westerly. Tuesday night into Wednesday, expect westerly winds
to peak around 30 kt with a few gales possible, mainly over northern
Lake Michigan. Expect west to northwest winds to around 30 kt to
persist through the remainder of the week with another possibility
for gales behind a secondary front Thursday night into early






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