Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232309

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
609 PM CDT Sun Oct 23 2016

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 352 PM CDT Sun Oct 23 2016

The cold front extends from just north of Kansas City to Kirksville
up into northwestern Illinois.  You wouldn`t know if from looking at
visible satellite since there isn`t a cloud in the sky near the
front.  Little change to the going forecast with respect to the
FROPA.  Still expecting it to be dry with the wind shifting to the
north as it passes.  Lows will be 5 to 10 degrees cooler tonight
than they were last night across most locations.  The exception will
be the Ozarks where it will actually be a little warmer than last
night since the front won`t make it down there until 09-12Z.

Northeast flow behind the front on Monday will veer to the east
through the day as high pressure builds southeast from Minnesota
into the Ohio Valley.  The cool easterly flow under the influence of
the high should suppress highs to as much as 15 to 20 degrees below
today`s readings.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 352 PM CDT Sun Oct 23 2016

Monday night thru Tuesday

Upper ridge centered across the Plains will slowly dampen as a short
wave gets ejected from the West Coast trough. At the SFC...a large
high pressure centered over wrn Hudson Bay with the ridge axis
extending S to the nthrn Gulf of Mexico slowly drifts E with an erly
component of the SFC wind. The short wave will induce lee side
cyclogenesis early in the week across the nthrn High Plains.

850 temps of 8-12C will corresponds to high temps in the mid 60s
across the nthrn and ern FA to the lower 70s in cntrl MO. Mixing to
850mb would suggest highs in the 70s areawide but guidance indicates
we will not mix that deep on Tuesday due to low level erly flow.
Mixing heights should increase from around 925mb across the nthrn
and ern portions of the CWA to closer to 900mb-875mb across cntrl
MO. When compared to climatology...these values match nicely to the
going fcst.

Tuesday night thru Wednesday night

The short wave tops the ridge and deepens some as it slides SE
towards the region Tuesday night. This feature passes the FA Wed PM.
The 12Z GFS has come into better agreement with the ECMWF and has
slowed the progression of the trough by 3-6 hrs with the new 12Z
run. Meanwhile...the SFC low is fcst to move from ern NEB Tue night
to near lower MI by Thu mrng. Tue night the best WAA forcing will
reside along and N of the warm front that will stretch across IA and
into nthrn IL and sthrn WI. This is the area that will have a decent
40kt LLJ lifting over the warm front with decent 850mb moisture
convergence across IA/MN/SW WI and NW IL. The wrn and nthrn FA will
be on the ern fringe of the LLJ Tue night so can`t rule out
isld/scttrd WAA SHRAs/TSTMs...mainly after midnight. The main
forcing with the trough moves thru drng the Day on Wed with
increasing PoPs from W to E thru the day. The trough axis moves E of
the FA drng the evng bringing an end to the precip. The upper level
ridge restrengthens the the prd as jet stream energy rounds the base
of the trough along the West Coast and enters the Pacific NW.

Temps are expected to remain at or above average thru the prd.

Thursday thru Sunday

Model guidance has been inconsistent with how they handle the trough
as it moves E of the CWA. The 00Z ECMWF had a secondary vort max
dropping down the backside of the trough as it passed on Thursday
with a reinforcing shot of cold air for the OH Vly...while the GFS
and GEM moved the trough E and built the West Coast ridge back into
the region. But...the 12Z ECMWF has come into better agreement with
the GFS and GEM...which means Fri could be warmer and windier
than the current fcst indicates. By the wknd the GFS is out of sync
with the ECMWF. The GFS has a trough mvng thru the region Fri
night/Sat night while the ECMWF is a little slower with this feature
not bringing it thru until Sat night. This discrepancy has
significant impacts on the sensible wx for the wknd. Regardless of
the would appear that we should get at least one dry
day next wknd.

Fri should be the warmest day of the next 7 days...but no cold air
is in sight thru next wknd with temps continuing to remain aoa avg.



.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 609 PM CDT Sun Oct 23 2016

VFR conditions will prevail through the valid TAF period. A couple
of wind shifts were pushing through the region this evening, one
having already passed through all sites shifting the winds more
westerly, and another coming overnight which will shift winds
more to the NNW. Each of these wind shifts will be dry with mainly
clear skies persisting. Monday will feature high pressure passing
to the northeast, which will veer the northerly winds back to more
easterly through the daytime hours.

SPECIFICS FOR KSTL: VFR conditions to prevail through the
period. Westerly winds currently will swing to the NNW tonight,
and finally to the east through the day on Monday as high pressure
moves off to the northeast. Mainly clear skies are expected
through the period with a few passing high clouds from time to





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