Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 010829
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
229 AM CST Thu Dec 1 2016

.SHORT TERM...
229 AM CST

Through tonight...

Not too much to talk about in the short term. Pretty much what you
see out is what you get with temps only expected to rebound a few
degrees today for highs and only drop a few degrees tonight with
stratus deck helping lock temps in the 30s. Could be some spits of
rain or snow grains, mainly this morning, but not expecting
anything measurable or of any real significance.

Izzi

&&

.LONG TERM...
229 AM CST

Friday through Wednesday...

Upper trough over the region will slowly ease its grip heading
into the weekend, but continued cyclonic low level flow and lack
of dry air advection should be enough to keep stratus locked in
through Friday night. Given the low sun angle and high moving
overhead Saturday, strongly suspect that stratus could be a fairly
prominent player Saturday as well. MAV suggests clearing Saturday,
but MET guidance keep us mostly OVC, have trended init grids more
pessimistic, but confidence in the cloudy forecast is not as high
for Saturday.

If the sun make an appearance Saturday, it will be short lived as
next shortwave begins to approach the region Saturday night and
likely brings some light precipitation to the area Sunday. Thermal
profiles still look pretty borderline with regards to p-type and
currently expected rain or wet snow trending to light rain or
drizzle Sunday as we lose ice in the clouds.

Forecast confidence heading into next week remains a bit below
average. ECMWF/GFS/GEM have come into better agreement early in
the week in showing northern jet buckling north with upper ridging
over area. Simultaneously, shortwave energy cuts off into a closed
low mid/upper level low over northern old Mexico. Guidance kicks
that shearing upper low out early in the week and operational
models are showing a weaker and weakening system with little
phasing with the northern stream as it moves east. Depending on
the track and intensity it could bring a bout of precipitation to
our area in the Tuesday-ish time frame, which at this time looks
like it`d be all rain.

Midweek and beyond, medium range models and respective ensembles
are in good agreement on showing a substantial pattern change over
North America. Common theme is significant negative 500mb height
anomaly over Great Lakes region, which would support coldest air
mass of the season arriving late next week. The million dollar
question, which has had almost as many answers in the past several
days of model runs, is will there be cyclogenesis on the leading
edge of this arctic air mass, and if so, how strong and where.
Medium range guidance continues to offer the full spectrum of
answers to that question, so the potential for any precipitation
(wintry or otherwise) has much higher uncertainty than does the
expected significant downward trend in temps.

Izzi

&&

.AVIATION...
For the 06Z TAFs...

Occasional flurries will rotate through the terminals through this
morning. Flurries that may reduce vsby to MVFR will mainly stay
north of the terminals, but cannot rule out a MVFR flurry at RFD.
IFR cigs should also stay north of the terminals with MVFR
conditions persisting through the period. Southwest winds turn
west today but gust to arnd 20 kt through this aftn. Winds slacken
this evening.

JEE

&&

.MARINE...
312 PM CST

Westerly winds will set up over Lake Michigan this evening as
surface low pressure continues to shift northeastward over the
Upper Great Lakes. Wind speeds will be the strongest over the
southern end of the lake, where some 25 to 30 KT winds are
likely. We will continue the small craft advisory for the Indiana
shores due to waves and winds. However, we have continued to hold
off on a small craft for the Illinois shores due to the offshore
component. So, while some 25 KT winds are possibly on the
Illinois side, wave heights should remain below 4 FT. High
pressure will gradually build over the region by Saturday,
resulting in abating winds later in the week.

The weather pattern later this weekend into next week looks like
it could become active again. However, forecast confidence in
regards to the local impacts remains low this far out.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Small Craft Advisory...INDIANA NEARSHORE WATERS UNTIL 9 PM Thursday.

&&

$$

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