Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 161227

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
727 AM CDT Sat Sep 16 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 355 AM CDT Sat Sep 16 2017

SHRA/TSRA are expected to develop upstream today near an approaching
cold front, although precipitation will probably not reach the LSX
CWA until later this evening or overnight. The front will make very
slow southeastward progress in part because the orientation of the
front is nearly parallel to the upper flow. High temperatures today
will likely be similar to yesterday due to the lack of air mass
exchange and the continued flow of warm/moist air into the region.
Overnight lows are expected to be a few degrees warmer due to cloud
cover and precipitation.


.LONG TERM...  (Sunday through Friday)
Issued at 355 AM CDT Sat Sep 16 2017

Focus thru the forecast period continues to be the above seasonal
average temps.

Not a lot of changes from yesterday. The forecast period begins with
upper ridge attempting to build into the region. Mdls now suggest
the ridge will erode somewhat as a s/w moves thru the region. While
the pattern remains similar to yesterday, lower heights coupled with
more convection possible suggests temps Sun may not be as warm.
However, have still trended above the warmer guidance as expect enuf
breaks in cloud cover to quickly warm temps.

Still expect a cold front to drop into the area early Sun. With sly
to swly flow thru the lower levels, do not anticipate the fnt being
pushed very far into the CWA. However, outflow boundaries/sfc trof
will likely be pushed further south providing a focus for storms.
Have kept PoPs to account for TSRA along these smaller boundaries.

Confidence remains low for PoPs beyond Mon due to a lack of
agreement among model solns. With the GEM as an outlier, will
discount much of this soln. Have kept PoPs low and continue thru
much of the forecast. However, models do generally agree with a sly
veering profile thru low levels thru the forecast period. Have
therefore continued an above seasonal average trend. Have also
trended warmer compared to yesterday with somewhat lower chances for
precip, tho not drastically so.



.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 635 AM CDT Sat Sep 16 2017

VFR conditions are expected for at least the first 0-9 hours of
the valid TAF period at all terminals. SHRA/TSRA will gradually
spread eastward today/tonight as a slow-moving cold front
approaches the region. The best time period for SHRA/TSRA appears
to be after 21z at KCOU/KUIN and after 09z at KSTL/KSUS/KCPS.





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