Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 281129
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
529 AM CST Mon Nov 28 2016

.SHORT TERM...
254 AM CST

Through tonight...

Plenty to talk about in the weather department today as powerful
mid latitude cyclone continues to impact the region in the short
term. Band of rain currently moving across eastern half of the CWA
will exit stage right prior to dawn, leaving the CWA largely void
of precipitation to start the day.

Well defined shortwave trough over New Mexico is forecast to
race northeastward toward the Midwest by late this afternoon.
Increasing ascent ahead of this feature will likely support
increasing coverage of rain and some thunderstorms over Missouri
this morning, with this activity likely to spread northeast
overspreading northern IL late morning/early afternoon. Forecast
soundings across our area today are largely void of any meaningful
instability, so any thunderstorms over MO would likely weaken as
they move northeast, but could still produce some healthy
downpours this afternoon and evening with strong forcing and
plentiful moisture will be present into the early evening.

Surface trough will move across the area late this evening
bringing an end to the rain. Could see a period of briefly strong
winds immediately behind the trough, but the strong winds should
ease fairly quickly. Impressive dry intrusion expected to result
in rapidly clearing skies late tonight, with all available
guidance suggesting that Tuesday should start out fairly sunny.

Izzi

&&

.LONG TERM...
254 AM CST

Tuesday through Sunday...

Tuesday continues to look like the best weather day of the week
and if medium range guidance is right it could be our warmest day
for quite some time to come. Sunshine should allow temps to warm
quite nicely, with 925mb temp climo supporting highs at least in
the upper 50s, but given the potential for plentiful sunshine we
could over perform with 60F temps certainly looking well within
reach.

The NAM continues to break our some convection over northern IL
Tuesday evening in advance of cold front and another shortwave
pivoting around the massive vertically stacked cyclone. Global
models remain dry and that`s how blended guidance averaged out,
but all models suggest a plume of very steep low-mid lapse rates
will advect over-top of modestly moist and unseasonably mild air
mass resulting in several hundred j/kg of MUCAPE. Given the lack
of enthusiasm for precip in the GFS/ECMWF, have opted to keep pops
in the slight chance range, but did introduce thunder into the
grids.

Cold front will move across the area Wednesday morning with
gradually colder air filtering into the area. Could see a slight
rebound in temps late morning, but as stratus moves in and CAA
continue will probably see afternoon temps begin to slowly fall.

Yet another shortwave pinwheeling around the low should steepen up
lapse rates again later Wednesday and likely set the stage for
some showers late Wednesday afternoon into Wednesday evening.
Questionable how likely measurable precip will be, but it does
look fairly likely that something should fall from the sky
Wednesday evening. Thermal profiles show only a very shallow warm
layer, suggesting any mixed liquid at the onset would likely
transition to light snow showers or flurries as small above
freezing layer shrinks due to wet bulbing. Accums look very
unlikely at this time given precip intensity and fairly mild sfc
temps.

Thursday through early Saturday have a fairly wintry look to them,
with overcast skies and seasonably cold temperatures expected.
Region will remain under the influence of this large upper
low/trough and subtle shortwave energy will likely rotate around
this trough as it slowly moves east and could certainly wring out
some light snow showers or flurries. Best signal from the GFS and
EC at this time is Thursday morning, so threw in a chance of
flurries then.

The big upper trough should begin to loosen its grip on the area
later in the weekend, but some pretty massive differences emerge
between the ECMWF and GFS in the large scale pattern by late next
weekend. For now made no changes to the blended model guidance due
to lack of confidence in forecast in that time range.

Izzi

&&

.AVIATION...
For the 12Z TAFs...

MVFR cigs have infiltrated the region and will persist through the
morning along with gusty south winds. Another rain shield spreads
across the terminals this afternoon. Cigs drop to IFR with the
rain and vsby lowers to MVFR. Heavier rain with IFR vsby and LIFR
cigs is expected this evening. A couple of isolated claps of
thunder may occur as well, but confidence and coverage are too
low to include thunder in the TAFs. Winds become southwest when
the cold front moves through. Guidance continues to indicate that
there may be a brief period of 30 kt gusts with the cold front.
Dry air moves in behind the front scattering out the persistent
cloud cover.

JEE

&&

.MARINE...
222 AM CST

Headlines...Extended the gale warning for the southern open waters
through 12Z/7AM CST Tues morning, and to 21Z/3PM CST Tues for the
northern open waters.  Winds are struggling to reach gales in the
NSH waters so left NSH headlines as is.

The low over South Dakota will slowly weaken and shift to Minnesota
through Tuesday. Its cold front slides over the lake late this
evening. A second low forms over the middle of the lake late tonight
and weakens over Lake Superior before merging with the main low
Tuesday night. The second low will tighten the pressure gradient
resulting in another brief period of gales over the open waters
Tuesday. Decided to extend the current gale warning instead of
issuing another one.

The weakened main low passes over the Great Lakes mid week with
winds becoming west 15-25 kt behind the low.  West to northwest
winds are forecast through the weekend. A large high builds over the
plains Thursday night and then passes south of the lake this
weekend.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Gale Warning...NEARSHORE WATERS UNTIL 3
     AM Tuesday.

     Gale Warning...LMZ777-LMZ779 UNTIL 6 AM Tuesday.

&&

$$

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