Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 020424

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1124 PM CDT SUN MAY 1 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 324 PM CDT Sun May 1 2016

Clouds will continue to move southeast and will overspread the area
by mid evening as upper trough back over eastern Nebraska drops
southeast into Missouri and Illinois.  Isolated afternoon showers
and thunderstorms should diminish by early this evening with the
loss of daytime heating.  Some isolated showers may begin to develop
toward morning underneath the upper trough over central and
northeast Missouri.  Lows tonight will fall into the middle 40s to
around 50s.


.LONG TERM...  (Monday through Next Sunday)
Issued at 324 PM CDT Sun May 1 2016

(Monday through Wednesday)

GFS/ECMWF are in relatively good agreement that upper trough will
move across the area tomorrow with relatively deep layer moisture.
Will carry chance PoPs for much of the area for this reason.  Drier
air will begin to move into the area by Monday night, so will go
with mainly dry conditions.  A second trough moves across the area
on Tuesday which begins the switchover in the upper pattern to
northwesterly flow.  GFS/ECMWF are still showing a third upper
trough moving across the Great Lakes and the Midwest on Wednesday
that will bring an attendant cold front across Missouri and Illinois.
Models indicate that best low level moisture and forcing will
still limit rain chances to the eastern part of the CWA.

Monday still looks quite cool with clouds, showers, and cold air
advection. Tuesday will be slightly warmer with less clouds and
winds turning out of the west.  Wednesday will see near steady
temperatures during the afternoon behind the front.

(Thursday through Sunday)

CONUS will be in highly amplified upper flow late week into next
weekend because of an omega block that will set up over North
America. It still looks like we will be dry through at least
Saturday as we will lie under northwesterly flow aloft and a large
surface high will be moving across Missouri and Illinois.  By next
weekend, the GFS and ECMWF show the upper ridge moving over us and
the low level flow becoming southwesterly across the Midwest.  This
may allow for some return of Gulf moisture into our area by late in
the weekend.  Have added a chance of thunderstorms on Sunday as both
the GFS and ECMWF are hinting at a frontal boundary moving back into
the area.  This will also cause temperatures to climb from below
normal on Thursday with 850mb temperatures around 5C to above normal
temperatures over the weekend with southwesterly surface flow and
850mb temperatures around 15C.



.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1100 PM CDT Sun May 1 2016

Surface low over southern IN will continue moving eastward
late tonight. Surface ridging extended from the Plains into
northwestern MO. MVFR cigs over northern portions of MO and IL
which were over UIN and have just moved into COU should continue
to slowly advect south-southeastward into the St Louis metro area
around 06-07Z Monday. These cigs will drop into the IFR catagory
by early Monday morning. There will also be light fog late
tonight and early Monday morning. The cloud ceiling will gradually
rise into the MVFR catagory late Monday morning, and possibly into
the VFR catagory by late Monday afternoon or early Monday evening.
A narrow band of light showers moving into southwest MO may move
into COU and the St Louis metro area early Monday morning. An
upper level disturbance will also bring widely scattered showers
to the area on Monday, especially during the afternoon. A
northwesterly surface wind will continue through the period.

Specifics for KSTL: MVFR cigs will move southeastward into STL
around 06Z Monday. The ceiling will drop into the IFR catagory
by early morning with light fog developing. The fog will
dissipate by late morning along with the cigs rising into the MVFR
catagory. The ceiling may rise into the VFR catagory by late
Monday afternoon or early Monday evening. There may be a few
showers on Monday. Nwly surface wind will continue through the
period, becoming light Monday evening.





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