Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 101946
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
246 PM CDT Tue Oct 10 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 245 PM CDT Tue Oct 10 2017

A surface low was over southeastern MO with an inverted surface
trough extending northward along or near the Mississippi River this
afternoon.  This surface low will move northeastward through
southern IL this evening and into the OH Valley region by early
Wednesday morning. Scattered showers and thunderstorms will continue
to move through our forecast area late this afternoon into the early
evening ahead of the upper level trough now centered over eastern
KS.  There may be a few strong to severe storms late this afternoon
into the early evening hours across pasts of southeast MO and
southwest IL where there has been some diurnal heating and hence
sufficient instability.  By early evening most of the precipitation
should be confined to northeast MO and west central IL and southwest
IL, and by midnight it should be east-northeast of our forecast area
as the upper level trough and associated surface low and trailing
cold front shift east of the region.  Much cooler air and less humid
air will filter into our area tonight, more typical of Fall.  Lows
tonight will be close to seasonal normals.  The low level cloud
cover will persist tonight and most of the day on Wednesday. This
cloud cover will hinder solar insolation Wednesday and lead to
slightly below normal high temperatures.

GKS

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 245 PM CDT Tue Oct 10 2017

The synoptic pattern at the start of the long term period will
feature amplifying flow aloft, as a ridge builds across the eastern
CONUS and a trough begins to build into the western CONUS.  This
regime will persist through much of this week, although the western
trough will attempt to push through the area this weekend.

After a brief cool down Wednesday (see short term section above),
temperatures will begin to warm Thursday through the end of next
week. In fact, temperatures by Saturday will approach record
values as they climb well into the 80s to near 90 degrees.

The next chance of precipitation will come Saturday into Sunday as
the approach of the western trough helps to sag a cold front into
the area. Instability will build across portions of western and
northern MO Saturday afternoon, leading to the development of strong
to severe thunderstorms. These storms will likely lose some of their
punch as they sag into central/eastern MO and IL with the loss of
daytime heating, but it does appear we will keep enough instability
(500-1000 J/kg MUCAPE) overnight to keep the threat of some strong
storms going Saturday night into the first part of Sunday.  The
front should clear the area by Sunday evening, allowing cooler
temperatures to filter back into the region.

KD

&&

.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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