Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 111812

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1212 PM CST Mon Dec 11 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 334 AM CST Mon Dec 11 2017

A fair amount of weather going on thru tonight, with the main focus
being temps and winds.

Clipper evident in satellite data currently over Northern Plains
will swing southeastward today, but remain north and east of the
CWA. As has been discussed the past few days, this system has two
distinct shortwaves and associated cdfnts to impact the area today.

The first cdfnt shud arrive in the CWA by mid morning with little
more than some mid to high clouds and much higher westerly winds.
While temps will be cooler behind this fnt than ahead of it, with
temps ahead of the fnt reaching the lower 60s, the much colder air
will not arrive until tonight behind a secondary cdfnt. Have
therefore trended aoa the warmer guidance for the srn half to two-
thirds of the CWA today, and trended twd the cooler guidance for
much of the CWA tonight. Did not go too cold tonight despite a
clouds clearing out of the area as mixing shud persist thru the

Have issued a Red Flag Warning thru this afternoon given the very
warm temps and low dewpoints resulting in low RH and high winds. Am
a little concerned that going forecast wind speeds are not high enuf
far enuf east and therefore, the RFW wud need to be expanded. Given
the timing of the cdfnt into central MO, do not expect changes over
that area. However, going dewpoint forecast may be too high just
behind the fnt.

Will need to monitor wind gusts this afternoon across nrn portions
of the CWA. Momentum transfer technique suggests gusts into the
35 kts range, just below wind advisory criteria. Some sites
upstream are currently seeing gusts to around 40 kts. However,
these sites are also closer to the sfc low compared to where the
low is anticipated this afternoon.

Lower clouds are expected to accompany the secondary fnt this
evening. Have held off mentioning sprinkles tonight as setup is not
great with strong gusts expected thru much of the night. Will need
to continue to monitor, but if it occurs, wud expect sprinkles and
shud occur before temps drop below freezing.


.LONG TERM...  (Tuesday through Sunday)
Issued at 334 AM CST Mon Dec 11 2017

Colder temperatures can be expected on Tuesday due to strong
northwesterly upper level flow behind the Great Lakes upper level
trough, and as a strong surface ridge builds into our region from
the Plains.  A northwest flow shortwave will drop southeastward
through our area Wednesday afternoon and evening.  Could not rule
out a few sprinkles or flurries ahead of this feature Wednesday and
Wednesday evening, but it appears that measurable precipitation
will be east-northeast of our forecast area along and left of the
track of a surface low where more favorable moisture will exist. Low-
mid level warm air advection and surface winds backing around to a
southwest direction will lead to warmer high temperatures on
Wednesday.  Colder conditions can be expected again on Thursday and
Thursday night after the passage of a cold front, and as a
positively tilted upper level trough moves southeastward through the
region. A warming trend will begin Friday afternoon with above
normal temperatures this weekend as upper level heights rise, and
the surface wind becomes southwesterly.  The model solutions diverge
some this weekend with timing differences on the next upper level
trough and associated cold front.  The ECMWF model drops a cold
front southeastward through our forecast area Saturday night, while
the GFS was a little slower with the progression of the front. The
GFS model keeps any precipitation southeast of our forecast area,
while the ECMWF model has most of its QPF north-northeast of our
forecast area.  Will keep the forecast dry for now as this will
likely be another dry frontal passage for our area.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1206 PM CST Mon Dec 11 2017

VFR ceilings and conditions will persist through 0z over the area.
An area of MVFR ceilings will move into north central and central
Missouri around 3z and push southeast through the region
overnight into early Tuesday morning. Winds will turn to the
northwest behind the trough and remain gusty through 11z before
slowly weakening Tuesday afternoon.


VFR ceilings and conditions will persist through 0z for the
terminal. MVFR ceilings will move over the terminal around 3z and
persist through early Tuesday morning. Winds will turn to the
northwest by 0z behind the trough and remain gusty before slowly
weakening Tuesday afternoon.



Saint Louis     57  24  37  27 /   5  10   0   5
Quincy          51  21  33  25 /  10  10   0   5
Columbia        55  23  38  27 /   5   5   0   0
Jefferson City  57  24  39  27 /   5   5   0   0
Salem           56  24  34  22 /   5  10   0   0
Farmington      62  25  38  25 /   5   5   0   0


MO...Red Flag Warning until 6 PM CST this evening for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Dent 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...Red Flag Warning until 6 PM CST this evening for Monroe IL-
     Randolph IL-Saint Clair IL.



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