Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 310909
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
409 AM CDT WED AUG 31 2016

.SHORT TERM... (Through Tonight)
Issued at 220 AM CDT Wed Aug 31 2016

Despite the initially warm/humid start this morning, a cold front
is on track to move through the region today and ultimately bring
an eagerly anticipated cooler/drier air mass into the region
tonight.

Scattered SHRA/TSRA are expected to develop near and ahead of the
front today, especially during the afternoon when an upper trough
will be moving across the area. PW values remain relatively high
for this time of year, and some locations could experience heavy
downpours.

Pcpn will end with fropa, and a much cooler and drier air mass
then spreads into the region tonight. Overnight lows will be
around 10 degrees cooler than last night.

Kanofsky

.LONG TERM... (Thursday through Tuesday)
Issued at 220 AM CDT Wed Aug 31 2016

Expect cooler and drier post-frontal conditions for Thu, Fri,
and probably most of Sat. Friday in particular still looks like a
spectacular day. Temperatures will easily cool off at night given
the lower dew points, and overnight lows in the 50s are expected
across most of the area on Thursday night and Friday night.

A surface high pressure center located over the Great Lakes by
12z Fri will be the key factor in determining how quickly
temperatures start to warm up again and how quickly the chance of
rain returns to the area over the weekend after the upper pattn
transitions to southwest flow aloft. Initially, the sfc high will
ensure dry northeasterly to easterly flow across the area on Thu
night and Fri. Once the sfc high has progressed farther eastward
this weekend, return flow will begin over our area ahead of a
developing sfc low over the plains, bringing warmer temperatures
and increased rain chances to parts of MO/IL. Model runs 24hr ago
were in good agreement that return flow would begin on Sunday,
however the latest runs are slower with the eastward movement of
the sfc high. As the previous shift noted, this slower trend may
be due to a potential tropical system in the Atlantic which slows
the eastward progress of the sfc high and delays the return of
warm/moist wx conditions. The CR model blend depicts slightly
lower pcpn chcs for Sunday through Monday night, which seems
reasonable given the slower progress of the sfc high, and few
changes were required.

Kanofsky

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1118 PM CDT Tue Aug 30 2016

Although there was scattered convection across western MO much of
this may dissipate before getting into COU late tonight.  Could
not rule out some additional development of showers/storms
impacting the taf sites for the remainder of the night with the
actual cold front still north of the area. Fog will continue to
develop fog late tonight/early Wednesday morning due to a light
surface wind, high surface dew points, and recent rainfall.
Visibilities may drop down as low as one quarter to one half mile
at times in UIN, SUS and CPS. There may also be some patchy
stratus clouds as well. There will be scattered convection mainly
during the afternoon on Wednesday as the cold front drops
southward through the region which could impact COU and the St.
Louis metro area. North-northwesterly surface winds will
strengthen on Wednesday.

SPECIFICS FOR KSTL: Could not rule out a few showers/storms impacting
STL for the remainder of the night with the actual cold front
still north of the area. Fog can be expected to develop fog late
tonight/early Wednesday morning due to a light surface wind, high
surface dew points, and recent rainfall. Visibilities may drop
down as low as one mile at times in STL. There may also be some
patchy stratus clouds as well. There will be scattered convection
mainly during the afternoon on Wednesday as the cold front drops
southward through the region which could impact STL. North-
northwesterly surface winds will strengthen on Wednesday.

GKS

&&

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

$$

WFO LSX



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