Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 212356

556 PM CST SAT NOV 21 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 258 PM CST Sat Nov 21 2015

Surface low over northwestern OH will continue moving northeastward
as a surface ridge over the central and southern Plains builds
eastward into MO and IL. The clouds will clear out across southeast
MO and southwest IL early this evening as the surface low pulls
further northeast of the area. The surface wind will weaken as
well as the surface pressure gradient relaxes. A northwest flow
shortwave will bring some mid-high level cloudiness southeastward
into our area later tonight. These clouds will be the only
limiting factor for an unseasonably cold night as the models drop
the -10 degree 850 mb isotherm southward to near STL by 06Z
Sunday. The lows tonight should be at least 10 degrees below
normal for late November. The coldest lows will likely be over the
extreme northern portion of the forecast area where a little
leftover snow cover which does not melt this afternoon will
enhance the radiational cooling.


.LONG TERM:  (Sunday through Next Saturday)
Issued at 258 PM CST Sat Nov 21 2015

Cold and dry conditions will continue for the rest of the weekend
with a warmup for the start of the upcoming work week as upper
level heights rise as the upper level trough shifts well east of
the region, and as southerly surface/low level flow begins to
strengthen on Tuesday as the surface ridge shifts well east of
our area and surface troughing develops in the lee of the Rockies.
The models begin to generate some very light QPF over our area as
early as Tuesday night. This may be more of a reflection of
increasing low level moisture and cloudiness over the area, rather
than actual measureable precipitation. More significant
precipitation will likely hold off until Thanksgiving or Thursday
night as a deep upper level trough approaches with an associated
strong cold front. The GFS model is a little quicker with this
storm system and its associated precipitation compared to the
ECMWF model. Even if the slower solution of the ECMWF model is
more correct, most of the precipitation should shift east of our
forecast area by Friday night as colder air advects into the
region behind the cold front. With precipitation likely ending by
Friday evening it appears that the precipitation type will all be
in the form of liquid rain.



.AVIATION:  (For the 00z TAFs through 00z Sunday Evening)
Issued at 538 PM CST Sat Nov 21 2015

VFR flight conditions are expected to prevail through Sunday.
Northwest flow will diminish this evening and turn to the west,
then south-southwest by Sunday morning as a ridge of high pressure
moves through the area. An upper level disturbance will swing
through and bring another round of clouds into the area. Heights
are uncertain at this time...but between 6,000-10,000 FT looks
most likely. Lower ceilings are possible across parts of northeast
Missouri and west central Illinois, but it looks like the clouds
should say above 3,000 ft regardless.

Specifics for KSTL:

Expect VFR flight conditions and diminishing northwest wind
tonight. Wind will turn to the south-southwest by late Sunday
morning or early afternoon as a ridge of high pressure slides
south of Missouri.  An upper level disturbance will swing
through and bring another round of clouds into the area. Heights
are uncertain at this time...but between 6,000-10,000 FT looks
most likely. Clouds should begin to break up during the late
afternoon/early evening.





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