Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 221748

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1248 PM 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.


.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.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1250 PM CDT Tue Aug 22 2017

One final band of showers is moving thru STL metro now but should
largely be south of the TAF sites except for CPS at the valid
time. Otherwise, look for VFR conditions and dry wx to prevail
after 19z at all TAF sites with NW surface winds thru the rest of
the valid period. Winds will be a bit stronger around 10kts than
tonight or Wednesday.





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