Area Forecast Discussion
Issued by NWS St. Louis, MO

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345
FXUS63 KLSX 152340
AFDLSX

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

.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 00z TAFs through 00z Tuesday Evening)
Issued at 530 PM CST Mon Jan 15 2018

The cloud trends tonight are a bit unclear. The stratocu well to
the north and northwest appears to have a diurnal heating
component and this would suggest the coverage will diminish the
next few hours. With this in mind, I think the TAF sites will be
VFR tonight with mainly scattered clouds. On Tuesday morning there
should be a big increase in stratocu within the cyclonic low level
flow, resulting in MVFR to low-end VFR CIG Heights. Modest
northwest winds will continue this evening, with the highest
values and continued occasional gusts across far eastern MO into
western IL.

SPECIFICS FOR KSTL:

VFR flight conditins are expected tonight. On Tuesday morning
there should be a big increase in stratocu within the cyclonic low
level flow, resulting in high-end MVFR to low-end VFR CIG
heights. Given the uncertainty in the cig heights, I have gone
with a more optomistic approach for now. Modest northwest winds
will continue tonight with occasional gusts this evening.

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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