Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 301829
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
129 PM CDT SAT APR 30 2016

.UPDATE...
Issued at 108 PM CDT Sat Apr 30 2016

Surface low was located in northwest MO at 18z with a southward
trailing cold front and a warm front extending east-southeast
just north of Columbia and into southern IL. The low is expected
to weaken and move eastward this afternoon with the cold front
advancing and warm front moving slowly northward. The warm sector
should continue to destabilize from west to east ahead of the
advancing front as steeper lapse rates/cold air aloft overspread
the warm sector where dimishing cloud cover will lead to increased
warming. SBCAPE on the order of 1000-1800 j/kg is expected to
evolve supporting development of scattered thunderstorms
along/ahead of the cold front between 19-21z between KCOU-KSTL.
CAPE and deep layer shear should be sufficient for organized
storms, some possibly severe with a primary hail threat into the
evening.

Glass

&&

.SHORT TERM...  (Through Late This Afternoon)
Issued at 331 AM CDT Sat Apr 30 2016

It will be an active day today. Current batch of showers and a few
thunderstorms to continue lifting northeast, slowly exiting from
southwest to northeast by midday. Then another piece of energy to
slide east across northern Missouri this afternoon and evening
helping to lift surface low off to the northeast. Models in pretty
good agreement, developing a line of convection just ahead of cold
front associated with surface low. If atmosphere is able to recover
from morning convection, decent CAPES between 1000-2000 J/kg, lapse
rates, and shear, could support some supercell development. SPC has
kept areas along and south of I-70 in a slight risk for severe
weather with the main threats being large hail, damaging winds and
possibly a few tornadoes.

As for high temperatures, it will be similar to yesterday with a
wide gradient from around 60 far north to the mid 70s south.

Byrd

.LONG TERM...  (Tonight through Friday)
Issued at 331 AM CDT Sat Apr 30 2016

(Tonight)

Storms to lift northeast out of forecast area by 03z Sunday, with
just some lingering showers slowly tapering off. Lows will be in the
upper 40s to upper 50s.

(Sunday through Friday)

Closed upper level low over Nebraska to open up and lift out of
region on Sunday. Will see showers and a few thunderstorms across
the area on back side of system before precipitation comes to an end
Sunday evening.

Surface ridge to build in with cooler temps for beginning of work
week. Highs on Monday will only be in the low to mid 60s, a bit
below normal for this time of year.

Weak surface ridging to remain over region through rest of forecast
period. Some models wanting to have upper level shortwaves under cut
the ridge with some low chances of precipitation towards end of work
week. For now kept this period dry with near normal temps in the mid
60s to mid 70s.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 108 PM CDT Sat Apr 30 2016

A warm front extending from just north of KCOU to just south of
the St. Louis region into southern IL will gradually advance
northward this afternoon. Flight conditions should improve as this
front moves north of the TAF sites. This front passage may not
occur at KUIN and at that terminal I still tried to be somewhat
optomistic with at least some improvement this afternoon before
IFR conditions settle in again at KUIN overnight and last into
Sunday morning. Scattered thunderstorms should also develop this
afternoon along/ahead of the cold front between 19-21z between
KCOU-KSTL. I have a tempo group in the St. Louis area TAFS to
account for this threat. Shower and thunderstorm threat will
largely remain displaced from the other TAF sites.

Specifics for KSTL:

Flight conditions should improve this afternoon as a warm front
moves north of KSTL. Scattered thunderstorms will also develop
this afternoon along/ahead of the cold front between 19-21z
between KCOU-KSTL. I have a tempo group in the TAF to account for
this threat between 22-01z. Potential for MVFR flight conditions
overnight into Sunday morning due to fog as surface winds become
light.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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