Area Forecast Discussion
Issued by NWS St. Louis, MO

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785
FXUS63 KLSX 030027
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
627 PM CST TUE FEB 2 2016

.UPDATE:
Issued at 617 PM CST Tue Feb 2 2016

A quick update to raise PoPs across portions of SW IL for the next
couple of hours. These SHRA with isod TS are expected to continue
to redevelop along the SW flank and slowly move newd out of the
area. Still expect this activity to be E of the CWA by 03z.

Another concern that will continue to be monitored is the area of
dense fog across IA, west central IL and extreme nrn MO. Still
expect the sfc fnt to lift nwd this evening, pushing the fog nwd
with it. However, if this nwd push does not occur, a headline may
be needed for the nrn tier of counties.

Tilly

&&

.SHORT TERM: (Through Wednesday)
Issued at 248 PM CST Tue Feb 2 2016

A large low pressure system over the plains will continue lifting
northeastward tonight, supporting scattered showers and isolated
thunderstorms through the late afternoon and early evening hours.
An isolated strong to severe thunderstorm is possible,
particularly over southwestern IL where H7-H5 lapse rates are
steeper and a few hundred J/kg of CAPE will be available through
late afternoon.

A cold front will also progress through the region during this
time. Colder air behind the front will support a slight chance of
lingering flurries and/or light snow across parts of northeast MO
and west central IL late tonight and tomorrow morning until the
upper vort max has lifted into the Great Lakes. The tight pressure
gradient behind the departing low combined with stronger wind
fields aloft will also create breezy conditions across the area
tonight and tomorrow. Sustained winds and wind gusts are both
expected to remain below wind advisory criteria attm.

Kanofsky

.LONG TERM:  (Wednesday Night through Next Tuesday)
Issued at 248 PM CST Tue Feb 2 2016

A couple of vorticity maxima will move through the upper trough
tomorrow and Thursday. The primary effect of these features for
this area is increased cloudiness which likely persists until the
upper trough shifts eastward on Thursday into Friday. A warming
trend begins on Thursday with daily high temperatures eventually
reaching the upper 40s to mid 50s by Sunday.

Models depict a brief period of upper ridging on Fri/Fri night
with a surface high pressure center shifting eastward across the
region. During that time, two low pressure systems will be
developing: one in the desert southwest and the other as a
northwest flow shortwave passing through the northern plains
towards the Great Lakes. The 02/12z runs of the GFS and ECMWF are
slightly farther south with the initial position of the northwest
flow shortwave leading to significant interaction between it and
the southern system, although the 12z GEM continues to keep these
features separate and does not show any interaction (similar to
the 02/00z runs of the GEM and ECMWF). Attm the limited moisture
available suggests very limited effects on the LSX CWA from the
northern stream shortwave regardless of its track, and the
combined southern system then passes well to the south of the
region and remains along the Gulf Coast.

The next low pressure system to affect the region will develop
within northwest flow on Sat night into Sun. The upper vort max
should be just offshore at 06/00z and might not be sampled by the
upper air network until 06/12z. Latest model runs show that the
upper vort skirts the US/Canada border and then dips into the
upper Midwest/western Great Lakes on Sunday. ECMWF/GFS/GEM offer
several potential solutions for this system and a generic RA/SN
mix with SChc-Chc PoPs looks appropriate attm for late this
weekend and early next week.

Kanofsky

&&

.AVIATION:  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 535 PM CST Tue Feb 2 2016

Much of region is currently under the dry slot of system. Ongoing
SHRA is expected to continue to pull newd out of the area this
evening, leaving behind a clear sky. Winds will increase overnight
and gradually veer to become nwly on Wed. Gusts are currently
expected to be as high as 30 kts at COU/UIN. Winds will need to be
closely watched as going forecast may not be high enough.

Clouds over wrn MO will slowly move into the region tonight.
Initially, cigs may be as high as 5 kft, but are expected to drop
quickly to high end MVFR. Can not rule out COU seeing some cigs
around 1500 ft on Wed morning.

Specifics for KSTL: Area of SHRA is expected to continue to move
newd out of the region leaving tonight SKC. Expect winds to
increase and veer to become nwly on Wed. MVFR cigs will move back
into the area around sunrise and lift to low VFR during the
afternoon hours.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX



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