Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 152134

Area Forecast Discussion
National Weather Service Saint Louis MO
334 PM CST Fri Dec 15 2017

.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 18z TAFs through 18z Saturday Afternoon)
Issued at 1141 AM CST Fri Dec 15 2017

VFR flight conditions are expected to prevail across the area
through Saturday. West wind will turn to the southwest this
evening. A strong southwest low level jet between 40-50kts is
expected to develop late this evening and persist into Saturday
morning. Low level wind shear conditions look likely until daytime
heating begins to mix the lower atmosphere. Some gusty winds are
possible Saturday morning as this occurs.


VFR flight conditions are expected to prevail at Lambert through
Saturday. Wind will turn to the southwest this evening and a
strong low level jet is expected to develop creating low level
wind shear. Wind shear conditions will persist until daytime
heating mixes the lower atmosphere in the mid to late morning.
There may be some wind gusts in the morning as this process takes



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


Saint Louis     34  61  39  49 /   0   0  10  80
Quincy          32  56  35  46 /   0   0   5  70
Columbia        33  62  38  49 /   0   0  20  80
Jefferson City  33  65  39  49 /   0   0  30  80
Salem           31  55  37  46 /   0   0   5  70
Farmington      30  58  38  49 /   0   0  40  70




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