Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 141726
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1126 AM CST Sat Jan 14 2017

.UPDATE...
934 AM CST

Light freezing rain showers are skirting the far southern CWA
this morning, especially Gibson City to Paxton. The ILX dual-pol
radar data indicates full melting of hydrometeors to the surface
and reports via mPING and social media confirm this, with freezing
on surfaces with an air temp around 30 degrees. The 12Z ILX
sounding indicates around 60 J/KG of MUCAPE right above the
melting layer, supporting the nature of the showers. The good news
for our CWA is that the more moderate showers are just south, and
the orientation/progression is fairly quick across the southern
CWA (lasting about an hour or less in any one spot). Of course
with freezing precipitation it need not be long to cause quick
issues on roads and sidewalks. Have addressed with a Graphical
NOWcast and Special Weather Statement.

The elevated moisture transport is orienting a tad more easterly
per ILX VWP data, and it will also weaken through early
afternoon, so any regenerating light precipitation after 11 a.m.
or 12 p.m. should be to our south. The rest of the afternoon
forecast is in good shape, with still some sun expected by early-
mid afternoon north of I-88.

MTF

&&

.SHORT TERM...
222 AM CST

Through Sunday...

On the front burner this morning is potential for a period of some
light wintry precip over our far southern CWA this morning. Short
range guidance continues to show the northern flank of an swath of
mainly light precip providing a glancing blow portions of Ford,
Benton, and Iroquois counties, mainly south of US 24. Forecast
soundings would suggest more of a sleet threat than freezing rain,
which given the very light amounts could pose less of a travel
hazard. At this point, not planning any headlines, but will
continue to monitor trends this morning for any signs of a more
substantial icy threat.

Otherwise, the remainder of the weekend looks dry and uneventful
until Sunday night. In fact, it would appear as though we could
see some clearing take place over especially northern CWA later
this afternoon. That same clearing could allow temps to get colder
than previous thought tonight. Cloudiness will increase and
thicken Sunday ahead of the next round of precip slated to arrive
after dark Sunday.

Izzi

&&

.LONG TERM...
222 AM CST

Sunday night through Friday...

As the big upper low over the southwest begins to lift out into
the plains, guidance suggests a band of light precip will move
across our CWA later Sunday night into Monday morning. Forecast
soundings suggest precip could briefly start as some snow, before
transitioning over to mostly light freezing rain and/or sleet.
Amounts at this distance look to be light, though the threshold
for impact with wintry mix events (particularly freezing rain) is
quite low and would anticipate a winter wx advisory eventually
becoming necessary if current trends in model guidance holds.

It appears as though could be a break in the precip for a time
Monday morning, during which time temps will likely inch up above
freezing most locations, setting the stage for appears to be
primarily a rain event by the time the main precip shield arrives
with the system Monday afternoon and especially Monday evening.
Rain with this system should end overnight Monday or early Tuesday
morning, but a northern stream shortwave fast on its heels could
provide for at least a threat of some of isolated showers Tuesday
as lapse rates steepen.

The quick transition to zonal flow and an extended period of above
average temps still looks quite likely through the rest of the
week into next weekend. In the latest medium range models, there
are more differences in the smaller scale features later in the
week and over the weekend, which will impact how extreme the late
week warmth will be and dictate precip chances. At this distance,
the pattern evolution looks pretty complex and confidence is low
in the details, but confidence is high in above (probably much
above) average temperatures Thur through the weekend.

Izzi

&&

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

Winds are turning northwest and should maintain that direction
this afternoon and evening as a secondary surface high builds
across Iowa. The northwest flow is light through the low-levels,
thus not giving a good push to the 4,000 ft clouds. These clouds
should want to advect south of the area by late afternoon/early
evening, but cannot rule out few/scattered lower clouds this
evening. A patch of IFR clouds in Wisconsin on the back edge of
the moisture should also fade this afternoon, but may clip RFD
near 20Z/21Z. Confidence in this is low, but if the IFR occurs it
will be very short lasting.

Winds probably will be near calm at daybreak Sunday, eventually
turning light southeast later Sunday afternoon. Precipitation is
presently not expected through Sunday evening.

MTF

&&

.MARINE...
302 AM CST

A broad ridge stretches from the Upper Midwest to New England
early this morning and is resulting in fairly weak flow across
much of Lake Michigan. A weak trough over Manitoba is expected to
move east to near James Bay midday and will result in increasing
southwest to west flow developing over far northern Lake Michigan.
Wind are expected to peak around 25 kt today, then should ease
late this afternoon into the evening as the gradient relaxes. High
pressure will consolidate over the Upper Midwest behind the trough
this evening and tonight and then shift to the Atlantic coast by
early Monday. Meanwhile, low pressure is expected to begin lifting
across the southern and central Plains Monday and will arrive
across the western Great Lakes Monday night into Tuesday.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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