Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 101639
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1139 AM CDT Tue Oct 10 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 407 AM CDT Tue Oct 10 2017

A positively tilted upper trof was centered from western KS into the
TX Panhandle early this morning. At the surface a series of surface
lows stretched from southwest MO into western AR. A frontal boundary
stretched from the northern-most of these lows across central MO
south of St. Louis into the OH Valley, while a cold front trailed
south of the AR surface low.

It`s already been a bit active early this morning with a number of
thunderstorm clusters since last night. The majority of the storms
have been elevated in response to moisture convergence associated
with the southwesterly LLJ and a broader region of frontal
convergence extending from central IL west-southwest into southeast
KS.

The models are in relatively good agreement with the upper trof
taking on a negative tilt as it advances east-northeast into the Mid
MS Valley today. In response, the series of surface lows and
attendant cold front will also track east-northeast moving into far
eastern MO around 19-20z and into western IL by 00Z. I think we will
continue to see several waves of showers and thunderstorms thru the
remainder of the morning. There should be an uptick in coverage of
showers and thunderstorms this afternoon not only along and ahead of
the advancing front, but also extending northward into northeast MO
in response to strong large scale ascent/forcing with the upper trof
and frontal forcing. Deep layer shear will be relatively strong and
there should be sufficient heating and instability generally from
St. Louis south and east for a severe weather threat. At least early
on in the storm development this afternoon there could be some short-
lived supercells before storms consolidate into a line.

The main threat of storms this evening should be across IL along and
ahead of the advancing cold front. The upper trof and attendant low
however will be moving to the east at a good clip and I think most
of the precipitation will be over by midnight. The late evening and
overnight hours will be denoted by good CAA and extensive stratus
blanketing the area in the wake of the front.

Glass

.LONG TERM...  (Wednesday through Monday)
Issued at 407 AM CDT Tue Oct 10 2017

By Wednesday morning, surface low will have moved into Indiana,
with lingering low level moisture wrapping around system. So with
decent 925mb RH, mostly cloudy skies to persist through at least
Wednesday night. Near normal or slightly below normal temps
expected through this period.

On Thursday, will see clouds scatter out and surface ridge move off to
our east allowing southerly winds to return once again. So temps
to warm up for the last part of the work week and into the
weekend. Could even see near record highs by Saturday as highs
warm up into the upper 70s to upper 80s.

In the meantime, models have some timing differences with next
system so went with a blend. Upper level trof over western US will
begin to lift out towards region Friday night, lifting surface
system northeastward into eastern KS/western MO. So will have
increasing pops beginning Friday night and persist through Sunday
afternoon, tapering off by late Sunday night. As for temperatures
through the remainder of the extended, cooler air to begin
filtering in, so will have near normal temps by next Monday.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1119 AM CDT Tue Oct 10 2017

Surface low over south central MO will move northeastward through
southeastern MO and southern IL this afternoon and this evening.
Showers and thunderstorms will move through the taf sites this
afternoon. The cloud ceilings will likely remain at or below
1000 feet this afternoon, possibly rising briefly around
showers/storms. Most of the showers should shift east of the taf
sites early this evening, but mainly IFR cigs will continue
tonight into early Wednesday morning. Northwest surface winds will
continue at UIN and COU, with easterly winds backing around to a
northwest direction this afternoon in the St Louis metro area.

SPECIFICS FOR KSTL: Surface low over south central MO will move
northeastward through southeastern MO and southern IL this
afternoon and this evening. Showers and thunderstorms will move
through the STL area this afternoon. The cloud ceilings will
likely remain at or below 1000 feet this afternoon, possibly
rising briefly around showers/storms. Most of the showers should
shift east of the STL area early this evening, but mainly IFR
cigs will continue tonight into early Wednesday morning. May see
improvement to VFR conditions Wednesday afternoon. Easterly
surface wind will back around to a northwest direction this
afternoon.

GKS

&&

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

$$

WFO LSX



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