Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190545
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 PM CST Sat Nov 18 2017

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 321 PM CST Sat Nov 18 2017

The synoptic pattern early this afternoon features a sharp trough
carving out across the Great Lakes and Midwest region. This will
keep cool, northwest flow in place through the period.

Surface low has rapidly deepened and moved northeast into northwest
Ohio. The surface cold front has pushed well off to the southeast,
allowing a much cooler airmass to filter in on gusty northwest
winds.  Pittsfield, IL (PPQ) recently gusted to 51 mph, thus will
continue with the Wind Advisory for the next few hours.  An
impressive frontogenetical band forced by a steeply sloped frontal
surface and frontogenesis in the 850-700mb layer was pushing
eastward across eastern MO and western IL. While most of this band
has been rain, have had a couple instances of some wet snowflakes
mixing in from time to time.  The band should quickly push east by
00Z, leaving the area dry tonight. Cold air will continue to filter
into the area allowing low temperatures to dip into the upper 20s
and low 30s.

Surface ridging will move into the central part of the country by
Sunday afternoon. This will keep northwest surface flow in place
through the day on Sunday. Despite copious sunshine, this cool flow
will keep temperatures confined to the 40s.

KD

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 321 PM CST Sat Nov 18 2017

Southwest flow on Monday ahead of the next trof is expected to warm
temperatures back up above normal.  Bumped up temps a bit to what
the consensus of MOS is indicating...mainly in the upper 50s to low
60s.  The aforementioned shortwave trof will deepen into a full
latitude longwave on Tuesday which will push another cold front
through the area.  There appears to be little if any low-mid level
moisture for this system to work with even though it will be another
strong cold front.  Medium range guidance pushes the front through
our forecast area between 12Z-20Z.  Strong cold advection should
drop temperatures back down into the 20s for lows Tuesday night and
highs will struggle into the upper 30s and low 40s on Wednesday.

Northwest flow will prevail aloft over the Midwest through the end
of the week as the upper trof sharpens over the Deep South and
Southeast U.S. Thursday and Friday.  Temperatures will likely warm up
to near normal on Thursday and then back above normal on Friday as
the upper level pattern finally shifts and the trof flattens out and
moves east.  Southwest flow returns and ensemble guidance pushes
highs into the 50s and hints at around 60 in southern zones.  The
next shortwave digs into the Midwest on Saturday.  There is decent
model consensus on the positions of the trof and surface front for
180 hrs so went with the consensus forecast which calls for cooler
Temperatures Saturday and a chance of rain as the front moves
through.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1123 PM CST Sat Nov 18 2017

Clear sky likely through the period with brisk northwest winds
slackening overnight. Surface ridge will move across the area
Sunday afternoon/evening with winds eventually becoming out of the
south/southwest. VFR conditions should continue through the
period.


SPECIFICS FOR KSTL:

Mostly clear sky with VFR conditions through the period. Northwest
winds will weaken overnight tonight. Winds will become westerly
Sunday afternoon and eventually southerly as surface ridge departs
into the Ohio Valley.


Gosselin

&&

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

$$

WFO LSX



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