Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 012259

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
559 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 00z TAFs through 00z Monday Evening)
Issued at 455 PM CDT Sun May 1 2016

Surface low over southeast IL will move eastward tonight. Any
showers/storms should be east of the taf sites this evening. MVFR
cigs in UIN should drop back down into the IFR catagory later this
evening. The low level cloud cover over northern MO will advect
south-southeastward into COU and the St Louis metro area later
this evening and overnight, leading to MVFR cigs initially, then
dropping into the IFR catagory late tonight/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. An upper level disturbance will bring
widely scattered showers to the area on Monday. W-nwly surface
wind will become more n-nwly on Monday.

Specifics for KSTL: MVFR cigs will move into STL late this
evening, then drop into the IFR catagory late tonight along with
light fog. 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, weakening early this evening.





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