Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242336

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
636 PM CDT Mon Oct 24 2016

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 336 PM CDT Mon Oct 24 2016

Large ridge of high pressure centered over MN this afternoon will
move eastward tonight and Tuesday.  Just some increasing high level
cloudiness is expected tonight.  The low temperatures tonight will
be similar to last night and close to normal values for late
October.  Increasing cloudiness can be expected on Tuesday as low-
mid level warm air advection increases ahead of an approaching
shortwave.  South-southwesterly low level winds will also be
bringing increasing low level moisture into our area, particularly
across northeast and central MO, east of the low level jet.  The
atmosphere will be initially dry on the western periphery of the
surface ridge moving eastward through the Great Lakes and Ohio
Valley regions, but should moisten enough to generate a few showers
across northeast MO by late Tuesday afternoon.  The ECMWF model
looks a little too high on its QPF for our area Tuesday afternoon,
and prefer the lighter QPF of the NAM and GFS models.


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 336 PM CDT Mon Oct 24 2016

Tuesday night thru Wednesday night

The prd will feature a long wave ridge between two closed lows: one
off the coast of B.C. and the other over the Canadian Maritime
Provinces. A short wave will top the ridge Tue and approach the
region Tue night. Upper level ridging immediately downstream of the
approaching short wave will move into the area Tuesday evng. The
ridging will be short lived though with falling heights assoc with
the approaching short wave already by 6Z Wed. SFC low is fcst to
move from ern NEB Tue night to near the wrn end of Lake Erie by
Thu mrng. The SFC wave will slide E along a warm front. Tuesday
night...most of the isentropic lift will be focused along and
north of the warm front across IA/sthrn MN/nthrn IL/sthrn WI where
a 40-50kt LLJ will impinge upon the SFC warm front. The ern edge
of the LLJ will encroach upon cntrl and NE MO late Tue night as
the LLJ becomes orientated more SW to NE which could allow for
some WAA showers to dvlp overnight. MUCAPE looks negligible so
anything that does dvlp should be just SHRAs. There may be a bit
of a break Wed mrng between when the LLJ weakness and precip assoc
with the actual trough approaches. There should be a decent band
of precip that swings thru the CWA just ahead of the trough axis.
As the event approaches...the thunder potential is becoming less
of a threat. There is limited CAPE but guidance is also suggesting
a substantial cap. And without good insolation out ahead of the
short wave due to potential cloud cover...doubt there will be
enough of a warm up to erode the cap. The best forcing is not
collocated with the better shear either. Will continue to carry
chance of thunder...for now...but if trends continue any mention
of thunder may be able to be removed. Trough axis swings thru Wed
evng shutting the precip down. The GFS is a little faster than the
rest of the suite of guidance. All precip should be out of the CWA
by 6Z Thu.

Temps will continue to be aoa avg with highs in the mid 60s to lower
70s and lows in the mid 40s to mid 50s.

Thursday thru Friday

The pattern transitions to dry NW flow...though there is no true
cold air in sight. Brief ridging will build into the area Friday in
advance of the next short wave which will support a short lived

Temps on Thu are expected to be near avg but should warm to well
above avg by Fri. Deep sthrly flow in advance of the next short wave
will set up by Fri and transport much warmer air into the region.
850 temps are fcst to be in the mid/upper teens. According to the
GFS...mixing ranges from 925mb across sthrn IL to nearly 850mb
across cntrl MO which correspond to high temps in the low 70s across
sthrn IL to the mid 80s across cntrl MO. Not ready to jump on mid
80s yet...but certainly something to keep an eye on if the pattern
continues to suggest this set-up.

Friday night thru Monday

Another short wave dives SE in the NW flow Fri night and drags an
attendant cold front thru the region knocking temps back down closer
to seasonal avgs. This bndry is fcst to pass with more cloud cover
than yesterday`s FROPA with a minimal threat of precip. Going
fcst covers the precip threat with slight chance to low end chance
PoPs mainly Fri evng. The ECMWF has yet another vort max on
Sun with most of the precip fcst to remain NE of the FA. The GFS
does not depict this feature. The long wave ridge that is fcst to
reside across the wrn CONUS this upcoming week will transition E
by early next week. The GFS progresses this transition E faster
than the ECMWF. This will cause the placement of the SFC high on
the GFS to be farther E earlier allowing sthrly flow to commence
sooner...hence temps warm above avg on Mon vs Tue like the ECMWF



.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 621 PM CDT Mon Oct 24 2016

VFR through the period. Winds will gradually become southeasterly
after a surface high pressure center over the northern plains shifts
eastward. Expect increasing mid and high clouds towards the end of
the TAF period.





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