Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 012032
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
232 PM CST Sun Dec 1 2013
.SHORT TERM: (Through Late Tonight)
Issued at 231 PM CST Sun Dec 1 2013
Very weak cold front has settled into srn portions of MO and IL this
aftn, while surface ridge over the northern Plains was shifting ewd
into the Great Lakes region. Some of the mid-high level cloudiness
across the nrn Plains, ahead of weak shortwaves will likely advect
e-sewd into our forecast area tgt, especially the nrn half. Also
expecting the development of patchy stratus and fog late tgt, mainly
over the srn portion of the forecast area where the sfc/boundary
layer will be more moist as evident by higher sfc dew points and the
development of a little diurnal cumulus clouds this aftn. Surface
winds will also be light or calm tgt aiding in fog formation.
.LONG TERM: (Tonight through Saturday)
Issued at 335 AM CST Sun Dec 1 2013
(Tonight - Tuesday)
Have not made too many changes to going forecast during this
period. Low level moisture progs suggest that stratus will
redevelop this evening, particularly over the southern and
eastern part of the CWA. Have kept chance of light drizzle in
these areas where this moisture will be the deepest and there will
be some very light ascent. As we go into Monday, GFS/NAM/ECMWF all
show a weak shortwave trough racing into the area from the west,
though it is not as deep as was forecast 24 hours ago. Have left
chance of sprinkles in for tomorrow morning as the trough axis
will move through the area by midday.
Temperatures will begin to warm up ahead ahead of the next storm
system. Expect temperatures to climb into the 50s on Monday with
some spots reaching 60 on Tuesday.
(Wednesday - Saturday)
Main concern continues to be the potential for a wintry precipitation
and the big cool down mid to late week. There still ia a great
deal of uncertainty regarding timing, precipitation types and
amounts. While the GFS is still the fastest with the passage of
the cold front, the 00Z ECMWF now brings the cold front through
the area during the day on Wednesday instead of Wednesday Night.
The cold front will have moved to the south of the area
Wednesday. Best forcing for precipitation will hinge on mid-level
frontogenesis and shortwave troughs moving through fast west-
southwesterly flow aloft. Have likely pops on Thursday and
Thursday Night over southeastern half of the CWA with the chance
continuing into Friday. Will continue to have a simple mix of rain
and snow because of the uncertainty for now, but thermal profiles
from forecast soundings certainly suggest the potential for sleet
or freezing rain over the southern half of the CWA. 850mb
temperatures by next Friday and Saturday will be in the -10 to
-12C range supporting highs only in the 20s with lows in the
single digits and teens.
.AVIATION: (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1050 AM CST Sun Dec 1 2013
Very weak cold front has just pushed se of CPS late this mrng.
Only expect light nely sfc winds at UIN and COU this aftn, and
nwly in the St Louis metro area veering around to a nely direction
by early evng. The sfc wind will remain light tgt and continue to
veer around to an e-sely direction by late tgt as the sfc ridge
over the nrn Plains moves ewd through the Great Lakes region. The
sfc wind will strengthen some from a sely direction Monday mrng.
Mid-high level clouds will advect into the region tgt. It appears
that there will be patchy fog and stratus clouds redeveloping late
tgt. The best potential for stratus clouds may be south of the taf
sites, but there will likely be at least light fog impacting the
COU and St Louis areas and possibly also UIN as well.
Specifics for KSTL: Light nwly sfc wind this aftn will gradually
veer around to a nely direction by this evng, e-sely direction by
late tgt, then strengthen to 7-9 kts from a s-sely direction Monday
aftn. Mid-high level cloudiness will advect into STL by late tgt.
May also have some light fog late tgt/early Monday mrng as well as
patchy stratus clouds mainly Monday mrng.