Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 101656

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1156 AM CDT Mon May 10 2021

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 415 AM CDT Mon May 10 2021

Some patchy river fog has developed early this morning in areas that
have light winds and clear skies.  So far visibilities have been
variable and have not stayed dense for very long, so expect this
trend to continue considering mid-high clouds are moving in from
the west. Latest short term guidance continues to show that a
vort max will move across southern Missouri this afternoon in the
zonal flow aloft. The latest runs of the CAMS are showing some
weak returns over the southern CWA this afternoon associated with
this vort max, so have added isolated showers. Kept slight chance
of showers over the northern CWA this afternoon into early this
evening as a weak shortwave trough rotates around the southwest
side of a upper low over the Great Lakes. Late tonight still
looks dry, but have a slight chance of showers over parts of
central and southeast Missouri on Tuesday as another weak vort max
moves across Missouri.

Highs today and tomorrow will be 10-15 degrees below normal as
northeasterly winds will bring colder air into the region under a
mostly cloudy sky.


.LONG TERM...  (Tuesday Night through Sunday)
Issued at 415 AM CDT Mon May 10 2021

Still seeing decent agreement between a majority of the ensemble
members and operational runs that a upper trough will move
through the Midwest on Thursday and then the upper flow will
become west-northwesterly into the weekend. A large surface high
is still expected to extend from the southern Plains into the
Great Lakes on Thursday which will keep the Gulf cutoff and the
the trough passage dry. Thereafter, there will be a pair of
shortwaves in the flow behind trough at the same time a warm front
will move northeast into the area. These two forcing features
will keep a chance of showers and thunderstorms in the forecast
Friday into Sunday.

Temperatures Wednesday into Thursday still look like they be around
10F below normal as the surface winds will be easterly with the
surface high moving down and 850mb temperatures will be around 0C.
Temperatures by Friday into Sunday will begin to warm back up as the
surface flow turns out of the south and 850mb temperatures climb to
around 10C over the weekend.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1141 AM CDT Mon May 10 2021

There will be few-sct diurnal cumulus clouds this afternoon along
with high level cloudiness. Isolated showers are possible in the
UIN area late this afternoon and early this evening along a weak
cold front dropping southward into this area. Mainly just mid-
high level cloudiness tonight and Tuesday morning. Surface winds
will be light this afternoon and tonight, then northeasterly
Tuesday morning after the passage of the weak cold front.

SPECIFICS FOR KSTL: There will be few diurnal cumulus clouds this
afternoon along with high level cloudiness. Just mid-high level
cloudiness tonight, and VFR low-mid level cloudiness on Tuesday.
Surface winds will be light this afternoon and tonight, then
northeasterly Tuesday after the passage of a weak cold front.





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