Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 112254
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
454 PM CST Wed Jan 11 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 326 PM CST Wed Jan 11 2017

Next system/frontal boundary extends from northeastern IL
southwestward through northeastern MO to southeastern KS. This
boundary will sink south exiting forecast area by mid morning on
Thursday. In the meantime, shortwave to slide along boundary helping
to generate scattered activity. Moisture is limited with this
system, so precipitation will be light in nature. Some concern about
brief freezing rain/drizzle after midnight tonight for portions of
northeast/central MO as well as west central IL. With pavement temps
in the mid 40s to low 50s, feel that these areas will be okay,
though will advise evening crew to keep eye out on conditions as
they develop.

Another issue later tonight will be slight chances of isolated
thunderstorms mainly to the south and east of the STL metro area
after midnight. Theta-e advection along the southwesterly low-level
jet will contribute to weak instability, thus MU CAPES between 100
and 300 J/kg possible. So added mention between 06z and 18z Thursday
for this area.

As for low temps, decent CAA behind boundary, so lows will depend on
where the cold front is. For now have lows ranging from the low 20s
far north to the upper 50s far south. Gusty winds ahead of boundary
to diminish shortly after sunset this evening.

Temperatures on Thursday will either be falling or steady most
locations as front exits area. For now highs will be from the low
30s to low 60s.

Byrd

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 454 PM CST Wed Jan 11 2017

Main forecast issue will be the approaching ice storm event.

Overall, not much change in the prev forecast with still a general
quarter to half inch of ice expected thru Sat afternoon. Will leave
the headline as-is for now.

Main changes to the prev forecast was lowering temps slightly on Fri
and Sat. Main time period for ice accum still appears to be late
Thurs night and Fri. While have continued likely PoPs Fri night, QPF
amounts are expected to be lower. That said, this may actually make
ice accretion worse during this time period with dry air advecting
into the area with fairly light sfc winds.

The same questions for Sat still exist for this forecast with
discrepancies among mdl solns. However, the 11/12z GFS/NAM solns
were slightly colder today. Adding to the dilemma, the 11/18z GFS is
now warmer on Sat, similar to yesterday. So, have trended temps on
Sat slightly cooler once again. The going forecast may still be too
warm, but did not want to make drastic changes. One element leading
to the uncertainty in temps is that the mdls which are generally
warmer are suggesting a colder soln, while mdls which are usually
colder solns, are warmer during this time.

Regardless, available guidance suggests Mon will be much warmer and
going forecast is probably too cold. This warm trend continues thru
the end of the forecast period with the bulk of the precip out of
the CWA by Tues afternoon.


Tilly

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 548 AM CST Wed Jan 11 2017

Expect mainly VFR conditions through the morning and early
afternoon hours until a cold front moves from northwest to
southeast across the area. Then MVFR ceilings can be expected
behind this front. There will be some precipitation along this
front, with scattered showers ahead of the front. Gusty south
winds will occur again today which will cause crosswinds east-west
runways.  Winds will veer northwesterly behind the front.

SPECIFICS FOR KSTL: Mainly VFR conditions are expected through 06Z
tonight. Southerly surface winds will be gusty once again today.
Then a cold front will move through the terminal after 06Z with a
chance of rain and ceilings falling into the MVFR category.

Britt

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     42  43  23  31 /  50  40  10  70
Quincy          26  31  15  27 /  30  20   0  20
Columbia        30  36  19  28 /  40  20   5  60
Jefferson City  34  38  21  30 /  40  20  10  60
Salem           53  54  25  32 /  70  60  10  70
Farmington      55  56  26  31 /  40  50  60  70

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-
     Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

IL...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Bond IL-Clinton IL-Madison IL-Marion IL-
     Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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