Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 010428
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1128 PM CDT SAT APR 30 2016
Issued at 901 PM CDT Sat Apr 30 2016
Watch has been expanded into south central Illinois ahead of the
current line. There is some threat for severe weather over the
next hour across south central Illinois into southeast Missouri.
Because of this, the watch has also been extended until 10 pm.
Overall threat for severe weather is expected to gradually
diminish however in the next hour or two as instability will be
diminishing with the loss of daytime heating.
.SHORT TERM... (Through Late Tonight)
Issued at 314 PM CDT Sat Apr 30 2016
There remains the potential for a few severe thunderstorms to
develop late this afternoon and early this evening along and south
of a warm front that lies from west northwest to east southeast
across the area. Clearing over western Missouri has allowed SBCAPEs
to climb into the 1000-2000+ J/kg range. The RAP still suggests
this instability will move eastward into east central and southeast
MO as well as southern IL by late this afternoon and this evening.
Deep layer shear still support organized severe thunderstorms
capable of producing some severe sized hail and locally damaging
winds. The experimental HRRR reflectivity suggests that these
storms will move out of the CWA by mid evening. MOS guidance also
suggest there may be some patchy fog developing after midnight
across the area.
.LONG TERM... (Sunday through Next Saturday)
Issued at 314 PM CDT Sat Apr 30 2016
(Sunday through Tuesday)
Upper low will move across Iowa on Sunday bringing a weak shortwave
trough across the area. Will keep chance of showers and isolated
thunderstorms going along and north of I-70 as it passes through.
Sunday night still looks mainly dry before both the GFS/ECMWF brings
another shortwave trough through the area on Monday. Will go with
just a slight chance of showers across much of the area with this
trough. Northwesterly upper flow will set up over the area by
Tuesday with westerly surface winds, so will keep with a dry
Temperatures will be slightly cooler on Sunday, and then even cooler
on Monday as cold air advects into the area under cloudy skies.
Temperatures should begin to moderate on Tuesday ahead of a cold
front as winds turn out of the west.
(Wednesday through Saturday)
Highly amplified upper flow will continue during the middle and end
of the next week as an omega block sets up over North America. We
will stay under northwesterly flow aloft during most of this period
with the upper ridge of the omega block approaching from the west by
Saturday. GFS and ECMWF are in decent agreement that a cold front
will move through the area on Wednesday with just a slight chance of
showers. Temperatures behind the front will be near normal with
850mb temperatures in the 5-10C range until they begin to warm up
by next Saturday.
.AVIATION... (For the 06z TAFs through 06z Sunday Night)
Issued at 1101 PM CDT Sat Apr 30 2016
A cold front extends from a surface low near PPQ south-southwest
through southwestern AR. Scattered showers and thunderstorms
should move out of the St Louis metro area by 06Z Sunday. With
light surface winds and recent rainfall, patchy fog should develop
late tonight in the St Louis metro area and also possibly in COU
as well. Stratus clouds below 1000 feet along with visibilities
below 1SM in fog will likely continue late tonight and early
Sunday morning in UIN. Fog will gradually dissipate by late Sunday
morning with ceilings rising into the MVFR catagory by afternoon
at UIN. Scattered-broken diurnal cumulus clouds should develop
late Sunday morning and afternoon with widely scattered showers
possible in UIN during the afternoon ahead of an upper level
disturbance. Surface winds should be mainly w-nwly on Sunday with
a surface ridge building into the area from the Plains.
Specifics for KSTL: Showers and thunderstorms will likely move out
of the STL area by 06Z Sunday. Light fog can be expected late
tonight and early Sunday morning as the wind becomes light.
Scattered to broken diurnal cumulus clouds will develop late
Sunday morning and afternoon with a w-nwly surface wind. The cloud
ceiling may lower into the MVFR catagory late Sunday night.