Area Forecast Discussion
Issued by NWS St. Louis, MO

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387
FXUS63 KLSX 241018 CCA
AFDLSX

Area Forecast Discussion...CORRECTED
National Weather Service Saint Louis MO
418 AM CST Fri Nov 24 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 404 AM CST Fri Nov 24 2017

The upper air pattern will be progressive but will undergo a good
deal of amplification over the next 30 hours. The short wave trof
currently exiting the Northern Rockies will amplify as it moves east
and into the MS Valley be early this evening. Accompanying this
short wave will be a cold front which should extend from eastern IA
through NW MO into SE KS at 00Z tonight. Mild temperatures and
breezy conditions will be the story for today. A batch of high
clouds will slide southeast across the area this morning, while the
surface pressure gradient and low level height gradient tighten.
This will result in increasing and gusty south-southwest winds from
mid-late morning into the afternoon and prominent low level WAA.
Highs today will be quite mild ranging from 15-20 degrees above
normal.

The short wave trof will continue to move east tonight and into the
OH/TN Valleys sending the cold front through the area. There is some
weak large scale forcing accompanying the upper trof and cold
front, as well a band of mid level moisture. Interestingly, a few
of the CAMS also have a little light precipitation. We previously
had some sprinkles in the forecast and the new forecast expands
the coverage in a swath that migrates southeast tonight coincident
with the weak forcing and moisture. Even though we will see a
cold fropa tonight, the air is not particularly cold, and mins
will be above normal.

Glass

.LONG TERM...  (Saturday through Thursday)
Issued at 404 AM CST Fri Nov 24 2017

Corrected Long Term Discussion.

The first part of the long-term forecast will continue to be
tranquil as a longwave trof remains in place over the eastern U.S.
This will keep the Mid Mississippi Valley in northwest flow through
much of the troposphere and lock a relatively mild ridge of high
pressure at the surface over the area through at least Sunday night
into Monday.  Temperatures for Saturday and Sunday will continue to
be above normal in the mid and upper 50s with plenty of sunshine.
Guidance is in good agreement in beginning a pattern shift on Monday
in building an upper ridge east into the Mississippi Valley.  The
surface high will be shunted further east as this happens resulting
in low level southwest flow.  Guidance members are in generally good
agreement on this shift, though the ECMWF is a bit slower than the
GFS and Canadian.  Am siding a little bit with the warmer and
breezier solution in this case since highs on Sunday will already be
running as much as 10 degrees above normal and Monday should be even
warmer than that.

The upper pattern becomes quasi-zonal on Tuesday with a shortwave
moving across the U.S. Canadian border and another wave moving off
the Rockies by around 00Z Wednesday.  The northern wave will push a
cold front into the Midwest Tuesday night and Wednesday morning.
While the atmosphere looks pretty dry, there may be enough moisture
convergence ahead of the front to squeeze out some light rain before
sunrise Tuesday over western/northern portions of the forecast area,
though QPF looks pretty meager.  Guidance is in decent synoptic
agreement with the second wave moving from the Rockies into the
Plains Tuesday night and Wednesday.  The ECMWF is about 6 hrs behind
the GFS and Canadian models, and it`s also around 100-150 miles
further north with base of the shortwave and the associated surface
low.  Backed PoPs off a bit on Wednesday to give a nod to the
ECMWF`s slightly slower and more northerly solution, though it does
look like the much of the area should see a chance of precip at some
point on Wednesday into Wednesday night.  The system should be
through the area on Thursday with high pressure building across the
Plains into the Midwest.  The ECMWF keeps some light precip over
eastern portions of the area Thursday, but with drier air pouring
into the region the chance for precip should be minimal.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1145 PM CST Thu Nov 23 2017

VFR conditions to prevail through the period. High clouds over
northwest MO will continue to stream southeast overnight and into
the day on Friday. Southwesterly winds will increase late Friday
morning into Friday afternoon, with gusts of 20-25 knots likely
ahead of a cold front. This cold front will push through all sites
Friday evening, bringing a wind shift to the northwest along with
some enhanced mid/high cloudiness.

SPECIFICS FOR KSTL:
Main TAF concern will be crosswind potential on the parallel
runways Friday afternoon. Southwest winds will increase by late
Friday morning, with gusts of 20-25 knots possible Friday
afternoon. Otherwise, a cold front will bring a wind shift to the
WNW Friday evening with some increase in mid/high cloudiness.

KD

&&

.CLIMATE...
Issued at 404 AM CST Fri Nov 24 2017

Record High Temperatures for Nov 24

STL...74 1966
COU...70 1966
UIN...69 1931

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     71  46  57  36 /   0  10   0   0
Quincy          68  40  55  33 /   5  10   0   0
Columbia        70  41  58  34 /   5  10   0   0
Jefferson City  72  42  59  34 /   0  10   0   0
Salem           61  43  56  34 /   0  10   0   0
Farmington      66  44  59  34 /   0  10   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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