Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 010202
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
902 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 00z TAFs through 00z Sunday Evening)
Issued at 456 PM CDT Sat Apr 30 2016
Cold front extends from a surface low between COU and UIN
southwest through southwestern AR. Scattered thunderstorms have
developed just ahead of the surface low and trailing cold front
late this afternoon. Thunderstorms will move through UIN and the
St Louis metro area until about 02Z Sunday. Surface winds will
become wly in the St Louis metro area later tonight after passage
of the cold front, albeit quite weak. With light surface winds
patchy fog should develop late tonight, along with stratus also
possible 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: Thunderstorms can be expected in STL until
about 02Z this evening. Sly surface wind will veer around to a wly
direction later tonight, albeit quite weak. Light fog can be
expected late tonight and early Sunday morning. Scattered to
broken diurnal cumulus clouds will develop late Sunday morning
and afternoon with a w-nwly surface wind.