Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251835
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
135 PM CDT Tue Apr 25 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 702 AM CDT Tue Apr 25 2017

A windy and warm day is in store for the region as a storm system
dvlps across the cntrl/shtrn Plains today. A stiff sthrly breeze
will pump a warm and moist air mass into the area thru the day.
There could be a narrow band of -SHRAs that sweep across cntrl/NE MO
this mrng but think best chances will be W of the FA. Bumped PoPs
up to 14s to account for this small chance. Better forcing moves in
from the W tonight as the upper trof approaches. This will cause low
pressure to move from the strhn Plains to the Midwest with precip
overspreading cntrl/NE MO prior to daybreak.

2%

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 702 AM CDT Tue Apr 25 2017

Still looks like this will be an active timeframe for weather with a
couple chances for strong to severe thunderstorms and still the
potential for widespread 2-5+ inches of rainfall.

Showers and thunderstorms will likely already be expanding eastward
across the CWA on Wednesday morning.  This will be in response to
the strong low level moisture convergence underneath the strong mid-
upper level ascent ahead of the mid level trough that will become
negatively tilted during the afternoon and evening.  While the
extent of the morning precipitation and clouds may limit the over
instability, there still should be enough cooling aloft and forcing
combined with 50+kts of deep layer shear for at least a few strong
to severe thunderstorms.  With low level vectors lining up deep
shear vectors, may see a line of storms develop later in the day
with the possibility for all hazards of severe weather.  Could also
see some training that could produce some locally heavy rainfall.
The rain will exit the area by late Wednesday night and early
Thursday as the upper trough quickly exits the area.

There will then be some brief dry time as a shortwave ridge axis
moves across Missouri and Illinois Thursday afternoon into Thursday
night. Then there will be an increase in showers and thunderstorms
as early as late Thursday night and Friday as a shortwave trough
moves across the Midwest.  The showers and thunderstorms will become
more widespread by Friday night and Saturday as the GFS/ECMWF are
showing the upper pattern becoming more amplified as the
southwestern CONUS upper low moves into the central Plains.  This
will cause the warm front to move north into Missouri and Illinois
by Friday night, with the GFS showing the warm front moving farther
north by Saturday afternoon than ECMWF.   Both models show the warm
sector moving into the CWA late Saturday into Saturday night with a
cold front moving across the CWA by early Sunday morning.  There
will the potential for heavy rainfall over the area from Friday
night into Saturday night given PWATs of 1.5+" and deep warm cloud
layer heights.  In addition, marginal instability and deep shear
parameters still suggest the potential for a few more severe storms
over the weekend.  Upper low will move east by next Monday leading
to dry weather.

Still looks like temperatures will vary through early next week
depending on what side of the front we are on, and if we have
precipitation or not.  It still looks like we will climb well into
the 70s ahead of the front tomorrow given 850mb temperatures near
15C, but then fall back into the 60s on Thursday.  Temperatures will
climb back into the 70s again on Friday and Saturday, but cool back
down on Sunday and Monday behind the next front.

Britt
&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 131 PM CDT Tue Apr 25 2017

VFR conditions to persist through this evening, then first round
of activity to approach taf sites. Coverage will be scattered and
diminish towards daybreak, so kept VFR cigs/vsbys with vcts
mention and showers. Then another round of storms to move in by
mid to late morning, but with timing and coverage hard to pin
down, so just have showers and vcts mention with MVFR cigs. As for
winds, gusty south winds to diminish this evening, then gradually
veer to the southwest towards end of forecast period.

SPECIFICS FOR KSTL:
VFR conditions to persist through this evening, then first round
of activity to approach metro area after 08z Wednesday. Coverage
will be scattered and diminish towards daybreak, so kept VFR
cigs/vsbys with vicinity showers. Then another round of storms to
move in after 16z Wednesday, but with timing and coverage hard to
pin down, so just have showers and vcts mention with MVFR cigs.
As for winds, gusty south winds to diminish this evening, then
remain southerly through end of forecast period.

Byrd
&&

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

$$
WFO LSX



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