Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 111433
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
933 AM CDT Fri Aug 11 2017

.UPDATE...
Issued at 850 AM CDT Fri Aug 11 2017
Isolated to scattered showers and thunderstorms in southeast
Missouri and southwestern Illinois will continue to push east this
morning. A look at current CAMS runs indicate this trend will
continue along and south of the interstate 70 corridor through
this afternoon due to daytime heating. The cold front is
currently just north of the St Louis metro area and will slowly
move southeast through the rest of the region today and clear the
region by early this evening. High pressure with cooler and drier
air will filter into the area by late tonight.


Kelly

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 348 AM CDT Fri Aug 11 2017

Isolated to scattered SHRA/TSRA will continue across the area today
ahead of an approaching cold front. Some expansion in SHRA/TSRA
coverage is expected across the southern half of the CWA during the
afternoon hours due to diurnal heating. By early evening, the front
and its associated precipitation should be south of the CWA. A
cooler and drier post-frontal air mass will begin spreading into the
region tonight.



.LONG TERM...  (Saturday through Thursday)
Issued at 348 AM CDT Fri Aug 11 2017

The synoptic pattern at the start of the long term period will
feature the persistent regime of a mean trough over the northeastern
CONUS and an upstream ridge across the west central CONUS. This
pattern will attempt to deamplify through the period, however it
appears yet another reinforcing northeastern trough will try to
build in by late next week.

High confidence exists regarding the forecast at the beginning of
the period, before confidence steadily declines as we head late into
this weekend and into the middle of next week. Saturday will feature
a surface ridge centered across the Upper Midwest. Guidance is in
general agreement that this surface high will be strong enough to
drive a surface cold front to the south of the region, allowing
slightly cooler and drier air to filter in.

Forecast confidence begins to decline on Sunday. The ECMWF, which
had been dry for Sunday/Sunday evening, has now trended wetter while
the GFS/GEM/NAM solutions which had been wet have now trended dry
for Sunday. Given how far south the effective front is likely to be
displaced by the seasonally strong surface ridging on Saturday,
think it will be hard for the front to lift back to the north given
the expected WNW upper-level flow. Therefore, prefer the drier
solutions at this time and have confined any slight chance pops to
mainly southeast MO for Sunday/Sunday evening.

It appears there will be one more low-amplitude shortwave to contend
with on Monday/Monday night. The GFS remains wetter and further
north with this feature, while the ECMWF is drier/further south.
GEFS mean fields are closer to the ECMWF solution, thus have
preferred a drier forecast continuing Monday/Monday night.

Heights will begin to slowly rise over the area Tuesday afternoon
into Wednesday, which should allow the boundary to lift back to the
north as an effective warm front. This will bring renewed chances of
showers/storms areawide Tuesday night through the end of the period
as a series of weak shortwave troughs traverse atop the boundary.

Temperatures through the period will continue to run below normal
(especially this weekend), however moderation to near normal
temperatures is expected by the middle/end of next week.

KD

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 607 AM CDT Fri Aug 11 2017

Isolated to scattered SHRA/TSRA will continue across the area today
ahead of a cold front. An area of ongoing SHRA/TSRA at TAF
issuance should move east of the St. Louis metropolitan area
terminals during the first few hours of the TAF period, but
additional thunderstorms are expected to re-develop after 11/18z.
Rain will end after the front has moved south of the area. Fog
will be possible at all terminals after 12/03z due to the recent
rainfall.

Kanofsky

&&

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

$$

WFO LSX



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