000
FXUS63 KLSX 221142
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
642 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 12z TAFs through 12z Wednesday Morning)
Issued at 631 AM CDT Tue Aug 22 2017

A large swath of rain showers and some embedded thunder stretched
from central IL thru east central MO into southwest MO early this
morning. Flight conditions were mainly MVFR within this band.
Precipitation should be ending within the next few hours at KCOU
and at the St. Louis area terminals around 15z or so as the band
weakens/diminishes and moves southeast. There may be a period of
MVFR CIGS in the wake of the ending precipitation and as winds
shift to the northwest with the cold front passage. All sites
should be VFR by early afternoon, with clouds clearing into
southern MO and southern IL by early evening. High pressure
settles into the region tonight with clear skies and light north-
northwest winds.

SPECIFICS FOR KSTL:

A large swath of rain showers and some embedded thunder stretched
thru the St. Louis area early this morning. Flight conditions
were mainly MVFR within this band. Precipitation should be ending
at KSTL around 15z or so as the band weakens/diminishes and moves
southeast. There may be a period of MVFR CIGS in the wake of the
ending precipitation and as winds shift to the northwest with the
cold front passage. Flight conditions should improve to VFR by
early afternoon with occasionally gusty northwest winds. High
pressure settles into the region tonight with clear skies and
light north-northwest winds.

Glass

&&

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

$$

WFO LSX