Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220844
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
344 AM CDT Tue Aug 22 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 341 AM CDT Tue Aug 22 2017

An elongated MCS stretched from northern IN across central IL
through northeast/west central MO into eastern KS early this
morning. The most intense deep convection was on the western flank
where there was strong convergence and lift via a 40+ kt
southwesterly LLJ. From central MO into central IL there has been
an overall weakening trend and decrease in the coverage of
thunderstorms. Radar trends as well as short range CAMS show a
gradual weakening of the showers and thunderstorms as they push
southeast this morning owing to diminishing CAPE, southward moving
outflow, and more focused forcing much further west. By mid-
morning there may be no more than a quickly shrinking area of
stratiform rain.

There is some question with regards to additional thunderstorm
development later today. The outflow will have moved through the CWA
by later this morning and the cold front will pass through St. Louis
near late morning, and thru the entire CWA by late afternoon/early
eve. There may be some chance for air mass recovery/destabilization
across southeast MO and southwest IL this afternoon ahead of the
front and thus potential for isolated-scattered thunderstorms.
Clouds will be somewhat slow to clear today. This combined with
north-northwest winds in the wake of the front and the associated
advection of cooler/drier air, will result in highs generally 10+
degrees cooler in most areas than yesterday.

Clouds will continue to clear across the southern portion of the
area this evening as the upper trof deepens. A pleasantly cool night
is on tap as a large surface high settles into the central Plains
and Mid MS Valley with lows nearly 10 degrees below average.

Glass


.LONG TERM...  (Wednesday through Monday)
Issued at 341 AM CDT Tue Aug 22 2017

Pleasant late August weather is on tap for the extended portion of
the forecast. Region will be characterized by temperatures generally
5-10 degrees below normal day and night accompanied by low humidity
values and little to no chance at any measurable rainfall.
Anomalously strong high pressure center will very slowly migrate
from the Upper Midwest to the Great Lakes, eventually into the New
England region. This will help continue to bring in dry
east/northeasterly flow through the period.


Gosselin


&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1145 PM CDT Mon Aug 21 2017

Cold front beginning to move into Missouri as of 05z. In the
meantime, MCS complex along and ahead of it is making its way east
into forecast area. It`s already affecting KUIN. Will see
activity spread east reaching KCOU by 06z and metro area by 08z.
Rain to taper off by mid to late morning as cold front exits.
KUIN and KCOU could see some MVFR cigs behind boundary for a few
hours, otherwise just low end VFR cigs. As for winds, to persist
from the south to southwest, then veer to the west with frontal
passage. By midday, winds to veer to the northwest to north, then
clouds to gradually clear out.

SPECIFICS FOR KSTL:
Cold front beginning to move into Missouri as of 05z. In the
meantime, MCS complex along and ahead of it is making its way east
into forecast area. Will see activity reach STL metro area by 08z.
Rain to taper off by 19z Tuesday as cold front exits. As for
winds, to persist from the south to southwest, then veer to the
west with frontal passage. By 23z Tuesday, winds to veer to the
northwest to north, with clouds gradually clearing out.

Byrd

&&

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

$$

WFO LSX



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