Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 181651
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1151 AM CDT Tue Apr 18 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 406 AM CDT Tue Apr 18 2017

Main focus for today will be temps.

The sfc ridge will build ewd today allowing sfc winds to become sly
to swly thru today. Much of the area shud see only thin high clouds,
although, the srn and sern portions of the CWA are expected to see a
bkn cloud deck thru mid morning or so. A CU field shud develop
across this same area this afternoon becoming widely sct to bkn. Mdl
soundings for this area suggest anywhere from 300 to around 1000
J/kg CAPE with little to no CAP. A few CAMs suggest a very isod SHRA
wud be possible this afternoon. Have kept this afternoon dry for
now, but may need to add mention of isod SHRA with future updates.

As for temps, shud see ample insolation today across much of the
CWA. Mdls prog 10-12C 850mb temps across the CWA by this afternoon.
Based on these temps last week, much of the area shud reach the
lower to mid 80s today. However, with some question on cloud cover
and weaker sfc flow, have kept temps in the upper 70s to near 80,
still well above MOS.

For tonight, a cdfnt will drop into IA as an upper trof treks across
the nrn Plains. Mdl solns are much further nwd with precip, keeping
any activity fairly close to the fnt. Considering the mid level CAP
in place just south of the fnt, this makes sense. Have kept low PoPs
for far nrn portions of the CWA to account for some uncertainty.

Tilly

.LONG TERM...  (Wednesday through Monday)
Issued at 406 AM CDT Tue Apr 18 2017

Models slower with next frontal system, with rain not moving in til
Wednesday night and Thursday, as atmosphere will be capped during
the day on Wednesday.

By Wednesday night, main shortwave associated with system will begin
to lift surface low over Iowa to the northeast towards Great Lakes,
dragging the cold front slowly across the forecast area. Instability
to diminish, so severe chances looking less likely now for northern
portions of forecast area Wednesday evening. As front moves through
on Thursday, will see increasing chances of storms, especially by
the afternoon hours over southeast Missouri and southern Illinois.

With front stalling out just south of Missouri/Arkansas border, will
see lingering showers over far southern portions of forecast area
Thursday night.

Precipitation chances to increase once again beginning Friday
afternoon as cutoff upper low over Central Plains begins to slide
east along I-70 corridor through the weekend, basically vertically
stacked with surface low. With position of surface low along MO/AR
border, better instability will be just to the south of the forecast
area. So majority of forecast area to see shower activity Friday
through Saturday night, tapering off on Sunday. Some storms not out
of the question late Friday night and Saturday over portions of
central and southern Missouri.

Beyond that, drier weather to move in for the first part of the work
week.

As for temperatures, Wednesday will be our warmest day with highs in
the low to mid 80s. As cold front finally exits region, much colder
air to filter in with highs a bit below normal in the mid 50s to low
60s by Saturday. Temperatures will finally moderate, warming back up
to near normal on Monday, in the mid to upper 60s.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1133 AM CDT Tue Apr 18 2017

It appears the MVFR cigs will remain south and west of the taf
sites this afternoon, but there will be VFR, low-mid level clouds.
Any diurnal, air mass convection should remain southeast of the
taf sites. A cold front will drop southward into southern IA and
northern IL tonight, but it appears that the convection associated
with this front will remain north of the taf sites. Mainly just
mid-high level cloudiness tonight and Wednesday morning. South-
southeasterly surface winds will veer around to a south-southwest
direction Wednesday morning.

SPECIFICS FOR KSTL: It appears the MVFR cigs will remain south
and west of the STL area this afternoon, but there will be VFR,
low-mid level clouds. Any diurnal, air mass convection should
remain southeast of the STL area. A cold front will drop
southward into southern IA and northern IL tonight, but any
convection associated with this front will remain well north of
the STL area. Mainly just mid-high level cloudiness tonight and
Wednesday. South-southeasterly surface winds will veer around to
a south-southwest direction Wednesday morning.

GKS

&&

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

$$

WFO LSX



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