Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 171201
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
701 AM CDT Sun Sep 17 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 356 AM CDT Sun Sep 17 2017

SHRA/TSRA will slowly spread across the area today due to an
approaching cold front. As the last several forecast discussions
have noted, the lack of a strong surface high behind the front as
well as the largely parallel wind field aloft will make it difficult
for the front to make much southeastward progress today/tonight
before it lifts back northward as a warm front (see discussion
below). Today`s high temperatures will likely exhibit a strong
gradient, ranging from the mid/upper 70s across northern MO to the
mid/upper 80s in southeastern MO and southwestern IL. The cooler
temperatures reflect the influence of clouds and precipitation for
areas which are closest to the front, while the warmer temperatures
reflect the limited cloud cover and warmer air mass ahead of the
front. Overnight lows will be in the 60s areawide with some local
variations depending on cloud cover and the location of the front.

Kanofsky

.LONG TERM...  (Monday through Saturday)
Issued at 356 AM CDT Sun Sep 17 2017

Main concern this week is the timing and chances of rain this week.

Upper flow will become more amplified through the week.  The global
models show shortwave troughs moving across Missouri and Illinois on
Monday into early Tuesday as a warm front moves north of the area
early on Monday morning.  With the ascent from the shortwave and
decent low level moisture convergence over the area, there should be
a chance of showers and thunderstorms, particularly along the front
Monday morning.

The chance of rain will lower late Tuesday into Wednesday as a
shortwave ridge moves across the area.  The chance for showers and
thunderstorms will increase again by Wednesday afternoon and
Wednesday night over central and northeast Missouri as well as west
central Illinois as a cold front moves into Missouri from the west.
This will occur as a shortwave trough moves across the Midwest ahead
of a deepening longwave trough over the western CONUS.  This front
will get pushed back north by early Thursday.  Rain chances from
Thursday into Saturday will be lower as a longwave ridge builds
over the area in response to the trough deepening over the west.

Temperatures this week will be well above normal given the front
staying north the region and upper ridge building over the area.
850mb temperatures will generally be between 15-18C which favors
temperatures between 85-90 degrees outside of showers.

Britt

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 633 AM CDT Sun Sep 17 2017

SHRA/TSRA will accompany a slow-moving cold front as it moves
towards the terminals during the TAF period. Initially
southwesterly or westerly winds will become northwesterly to
northeasterly after fropa. The best opportunity for prevailing
MVFR ceilings appears to be after 18/03z due to rainfall and
nocturnal cooling, but temporary cig/vis restrictions during
precipitation are still possible earlier in the TAF period.

Kanofsky

&&

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

$$

WFO LSX


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