Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160533
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1133 PM CST Mon Jan 15 2018

.UPDATE...
Issued at 1117 PM CST Mon Jan 15 2018

Temperatures have fallen a little more than expected across the
northern CWA and therefore have lowered mins by a few degrees.
Wind chills across this region still should be in the 20 to 24
below range.

Issued at 937 PM CST Mon Jan 15 2018

Made a few changes to the remainder of tonight and into Tuesday
morning. These were namely with cloud cover. High clouds remain
persistent across the southeast third or so of the CWA, while
upstream there is a lack of extensive stratocu. Upstream
clouds/stratocu are rather patchy until you get well into IA, and
the low level RH progs from the RAP really don`t show much
increase until overnight. Thus have slowed the increase in cloud
cover from the north overnight and then spread clouds -
stratus/stratocu southeast on Tuesday morning within the cyclonic
low level flow.

Wind chill advisory is right on the mark. Forecast at this time
appears right on target and dangerous wind chill levels are now
occuring in northeast MO and west central IL. The bitter cold/
dangerous wind chills will continue to spread southeast the
remainder of the night as temps fall.

Glass

&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 332 PM CST Mon Jan 15 2018

(Tonight)

Area of light snow has moved to the southeast of the area with
decreasing clouds well behind the surface cold front. Story for
tonight continues to be the well below normal temperatures and
dangerous wind chills expected tonight. Northwest winds will lighten
up a bit tonight but still remain on the order of 10-15mph and that
combined with the low temperatures near zero will yield wind chill
values of -15 to -20F for much of the area. Wind chill advisory
still looks good so no changes made.

(Tuesday)

One more bitterly cold day as surface high pressure settles into the
mid-Missouri Valley. Steep low-level lapse rates and increasing
stratus from the north should yield at least a chance of flurries
across the area. Otherwise, very cold with high temperatures only in
the teens under a mostly cloudy sky.

Gosselin

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 332 PM CST Mon Jan 15 2018

Despite upper level trof sliding through region Tuesday night, will
only see an increase in clouds with its passage. Otherwise, surface
ridge to build in with light and variable winds. So it will be
another cold night with lows in the zero to 10 degrees above zero
range. Winds will be light enough that wind chill indicies will
not reach advisory criteria.

On Wednesday, surface ridge to begin moving southeast out of area,
allowing southwesterly flow to return to the region with the thermal
ridge building into the area. Gradual warmup expected through the
rest of the work week and into next weekend with highs in the 50s by
Saturday and Sunday.

In the meantime, the next system to lift out of the southwestern US
towards region beginning Saturday. Will see increasing low level
moisture and some decent WAA activity pop up during the day Saturday
into Saturday night. Better chances of rain will be during the day
on Sunday and into Sunday night as deepening surface low lifts
northeast through region, dragging a strong cold front through.
Models in some agreement on timing and placement with several rounds
of rain through the last half of the weekend.

As system exits region Sunday night through Monday morning, will see
colder air spill in on back side of system with rain changing to
snow before ending. Highs by Monday will be in the mid 30s to mid
40s.

Byrd

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1117 PM CST Mon Jan 15 2018

Cloud trends this evening have been rather odd. Narrow streaks of
stratocu have been appearing within the low level cyclonic flow.
Some that develop earlier have since dissipated, but there has
been an increase in them across eastern MO and extreme western IL
within the last hour. I have added some scattered stratocu to all
TAFS but KCOU overnight, with a TEMPO initially to account for
brief periods of broken CIGS. The height of the cloud bases has
been between 2000-3000 ft. I am not sure of the longevity of
these, they could come and go all night. A better increase in
stratocu should occur during the predawn hours across northern MO
into west central IL with clouds spreading/developing southward
Tuesday morning. MVFR flight conditions should occur with this
stratocu and there could be a few flurries as well. CIG heights
should improve to VFR as the afternoon progresses, and think much
of the cloudiness will diminish near/after sunset. Modest
northwest winds will continue overnight and into Tuesday.

SPECIFICS FOR KSTL:

Narrow streaks of stratocu have developed across the St. Louis
region within the last hour. I have added some scattered stratocu
to KSTL and a TEMPO to account for potentially brief periods of
broken CIGS. The height of the cloud bases has been between
2000-3000 ft. I am not sure of the longevity of these, they could
come and go all night. A better increase in stratocu is expected on
Tuesday morning as clouds spread/develop into the area from the
north. MVFR flight conditions should occur with this stratocu and
there could be a few flurries as well. CIG heights should improve
to VFR as the afternoon progresses, and I think much of the
cloudiness will diminish near/after sunset. Modest northwest winds
will continue overnight and into Tuesday.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Chill Advisory until noon CST Tuesday for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Wind Chill Advisory until noon CST Tuesday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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