Area Forecast Discussion
Issued by NWS St. Louis, MO

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302
FXUS63 KLSX 210831
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
331 AM CDT SAT MAY 21 2016

.SHORT TERM... (Today and Tonight)
Issued at 308 AM CDT Sat May 21 2016

Large scale amplification will proceed this period and the
deepening upper trof in the eastern U.S. will keep a surface high
pressure system locked in across the MS Valley today and tonight.
With the exception of some patchy fog early this morning, weather
will be rather tranquil during this time frame. Highs today will
be warmer than yesterday owing to considerably more sunshine
although still below average. Lows tonight will be seasonably cool
with low dew points and light winds resulting in good radiational
cooling.

Glass

.LONG TERM... (Sunday through Friday)
Issued at 258 AM CDT Sat May 21 2016

The upper ridge across the Plains will shift into the MS Valley on
Sunday however the blocky nature to the downstream pattern will
keep surface features in slow motion. Thus the surface high will
be only slowly retreating and will continue to exert some
influence, especially across eastern MO into IL. Mainly this will
slow the onset of southerly low level flow, better WAA and moisture
return. Temperatures however will continue to moderate, and highs
on Sunday will finally be more typical of late May. Progression
will continue on Monday-Monday night, albiet slowly, with low
level WAA and moisture transport underway into central and eastern
MO during the day, and into IL Monday night as southerly flow
becomes better established in the wake of the retreating high. The
combination of these advections and several disturbances within
the southwest flow aloft will bring increasing chances of showers
and thunderstorms from west to east, with the highest threat in
central and northeast MO.

Southwest flow aloft will continue Tuesday-Friday keeping a
steady stream of weak disturbances traversing the area, as well as
maintaining relatively undisturbed steep mid level lapse rates.
These lapse rates will contribute to a persistent broad and
unstable warm sector. No well defined frontal penetrations are
evident at this point, with the disturbances aloft, the south-
southwesterly LLJ, and mesoscale features influencing what will
be continuous thunderstorm chances.

Glass

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1139 PM CDT Fri May 20 2016

Decreasing cloudiness is expected overnight. Patchy fog is
expected which should allow for some MVFR to develop between
09-15Z at KSUS and KCPS. Otherwise expect dry and VFR conditions
during the period with north to northeast winds at less than 10
kts.

Specifics for KSTL: Expect dry and VFR conditions through the
period with easterly winds backing to the north by mid-morning.

Britt

&&

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

$$

WFO LSX



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