Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160518

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1118 PM CST Fri Dec 15 2017

Issued at 945 PM CST Fri Dec 15 2017

Forecast on track with only subtle adjustments made. A nice setup
for a BIG warmup on Saturday with SW surface winds of 10-15mph and
full sunshine, such as it is for mid-December. MET MOS looks like
a good starting point for max temps and even edged up another
degree or two from there. Still should fall several degrees below
record values, which are in the CLIMATE section below.



.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 332 PM CST Fri Dec 15 2017

High pressure will move across the Lower Mississippi Valley into
the southeast U.S. over the next 24 hours.  West-southwest wind will
continue to back to the southwest tonight.  The southwest breeze
will bring warmer air into the region tonight and Saturday.  It`s
likely that temperatures will fall quickly this evening but steady
off around midnight and hold in the low to mid 30s through daybreak.
 Warm advection in southwest flow will continue on Saturday and
temperatures are expected to warm well above normal.  Went with
highs on the warm side of consensus MOS guidance in the mid 50s to
low 60s.


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 332 PM CST Fri Dec 15 2017

The high amplitude pattern we`ve been stuck over the past several
days is beginning to break down.  The cut off low over the southern
Gulf of California will open up and move northeast across Texas and
Oklahoma Saturday night resulting in low level cyclogenesis over the
Great Plains.  Southwest flow still looks likely to bring sufficient
moisture up into the Mid Mississippi Valley to develop precip on
Sunday morning as the wave moves up and across Missouri and
Illinois.  All guidance is pointing to warm temperatures in the
boundary layer and aloft so all of this precipitation will be
liquid...however clouds and rain will keep temperatures about 10
degrees cooler on Sunday.

Quasi-zonal flow with weak ridging to our east should keep mild air
over the region for much of the week.  Medium range guidance is
having trouble resolving the details of the forecast as is typical
in zonal flow.  There may be some light precipitation...most likely
rain Tuesday or Wednesday as another shortwave moves across the
region.  The ECMWF shows a slower and more vigorous wave than the
GFS does, and it is quite a lot wetter than the GFS Wednesday into
Wednesday night.  Both models re-amplify the upper pattern on Friday,
digging a strong longwave trof across the Desert Southwest.  The
details that far out get pretty murky but this looks like it will be
the start of another cold snap for the region with temperatures
falling back to near or even a few degrees below seasonal normals.



.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1118 PM CST Fri Dec 15 2017

VFR conditions, dry weather, and S-SW surface winds will prevail
at the TAF sites thru the valid period. A marginal LLWS event is
either ongoing for UIN and COU or still anticipated to begin
shortly for the STL metro sites and to continue until diurnal
mixing occurs around 15z as the low level jet translates into
gusty winds at the surface of up to 20kts. Winds will then
diminish around sunset (23z) and continue into Saturday evening.



Issued at 334 AM CST Fri Dec 15 2017

Record high temperatures for Saturday December 16, 2017

St. Louis  70 in 1889
Columbia   70 in 1889
Quincy     65 in 2006




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