Area Forecast Discussion
Issued by NWS St. Louis, MO

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658
FXUS63 KLSX 222010
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
310 PM CDT Tue Aug 22 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 307 PM CDT Tue Aug 22 2017

A longwave TROF existed over eastern North America this afternoon
with a longwave RIDGE over western North America, resulting in NW
flow aloft for our region.  A surface cold front has nearly cleared
the forecast area, now over southern IL and southeastern MO and
continues to chug southeastward.  One last bout of low-topped
showers can be found right along this front.  Northwesterly surface
flow behind the front is beginning to usher in dewpoints in the 50s
into northern MO and has kept temps in the upper 70s to around 80.

A disturbance-free northwest flow aloft and a cool Canadian surface
high pressure building in from the north will be the prevailing
themes for the forecast thru Wednesday afternoon.  This will
maintain a dry column with few, if any, cloudiness once the last of
it exits our southern CWA early this evening.  The beginnings of
what appears to be an extended regime of below average temps will
begin tonight, with nighttime mins in the 50s and daytime maxes
around 80, or about 5 degrees seasonal norms for most areas.

Does this mean that summer is over?

TES

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 307 PM CDT Tue Aug 22 2017

Yes, it may be.  A persistent surface ridge will extend from the
Great Lakes region southwest into MO with upper level northwest flow
leading to a long period of relatively cool conditions and dry
weather Wednesday night into the weekend.  Although weak northwest
flow shortwaves will move through the region the low levels should
be too dry for any precipitation.  Will have persistent lows in the
middle 50s to around 60 degrees with highs in the upper 70s to lower
80s. This is about 5 to 10 degrees below normal for late August. The
next chance of precipitation will not occur until Sunday night
through Tuesday when an upper level trough drops southward through
the northern Plains sending a cold front southeastward into our
area.  The remnants of tropical cyclone Harvey should move into
southern Louisiana by Tuesday night, but should not have any affect
on our area through at least Tuesday night.

GKS

&&

.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.

TES

&&

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

$$

WFO LSX



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