Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232254
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
554 PM CDT Wed May 23 2018

.SHORT TERM... (Through Wednesday Night)
Issued at 304 PM CDT Wed May 23 2018

A stalled boundary stretched from the Ozarks through parts of
central and northern MO this afternoon. METARs and model wind
fields both show some surface convergence near the boundary,
therefore isolated thunderstorms will be possible through the
early evening hours across central MO and the eastern Ozarks. Any
lingering precipitation is expected to dissipate with the loss of
diurnal heating.

Overnight lows will be similar to last night and range from the
lower 60s in southwest IL to the upper 60s in central MO.

Kanofsky

.LONG TERM... (Thursday through Next Wednesday)
Issued at 304 PM CDT Wed May 23 2018

Overall, this looks like a June pattern rather than a May
pattern. Highs will be in the mid/upper 80s to around 90 and lows
will be in the 60s to around 70 each day from Thursday through
next Wednesday. Isolated to scattered thunderstorms will also be
possible at times due to diurnal instability as well as the
occasional passing PV anomaly.

An upper ridge will remain in place across the area through
Thursday night before an approaching trough axis arrives on
Friday. This feature will bring a chance of SHRA/TSRA to most of
the area on Fri/Fri night as it moves across the region.

Models then depict a Rex block (also known as a high-over-low
block) developing this weekend and early next week across the
east-central CONUS. This pattern is forecast to develop after an
area of low pressure drifts northward from the Gulf of Mexico
while an upper ridge simultaneously develops downstream of a large
closed low pressure system over NV/UT/ID. The Gulf of Mexico low
could bring isolated to scattered SHRA/TSRA to parts of
southeastern MO and southern IL on Sun/Mon depending on how far
north and west it progresses.

Although model solutions differ, the general idea is that the
large closed low over the western CONUS eventually lifts
northeastward next week. This feature could bring SHRA/TSRA to
the area during the middle/end of the week, but there is low
confidence in the timing and location due to model differences
regarding the upper ridge, the blocking low, the closed upper low,
and one or more shortwaves along the US/Canadian border.

Kanofsky

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 533 PM CDT Wed May 23 2018

Surface ridge extends from the Great Lakes and Ohio Valley
regions southwest into eastern MO. East-southeasterly surface
winds will continue at the taf sites through the forecast period.
Few-scattered diurnal cumulus clouds will dissipate this evening
due to the loss of daytime heating. Just some high level clouds
late tonight into Thursday morning, then scattered diurnal cumulus
clouds will develop again late Thursday morning and afternoon.
Could not rule out an isolated afternoon shower/storm in/near COU.

SPECIFICS FOR KSTL: Surface ridge extends from the Great Lakes and
Ohio Valley regions southwest into eastern MO. East-southeasterly
surface winds will continue at the taf sites through the forecast
period. Few-scattered diurnal cumulus clouds will dissipate this
evening due to the loss of daytime heating. Just some high level
clouds late tonight into Thursday morning, then scattered diurnal
cumulus clouds will develop again late Thursday morning and
afternoon.

GKS

&&

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

$$

WFO LSX



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