Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251215

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
715 AM 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.


.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.



.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 703 AM CDT Tue Apr 25 2017

Today will be a windy warm day with sthrly winds gusting upwards
of 30-35 mph late this mrng and thru the aftn. Most of the fcst
should be VFR but there is a narrow band of SHRAs and an isld TSTM
WSW of KCOU that may briefly drop VSBYs down to MVFR. CIGs begin
to really lower after midnight and may approach MVFR towards the
end of the fcst prd. An upper level disturbance will approach the
region tonight with rain mvng into cntrl/NE MO towards sunrise.


VFR fcst thru this evng. CIGs will lower to MVFR by Wed mrng with
SHRAs/TSTMs dvlpng thru the day. Sthrly winds could gust 30-35 mph
this aftn.





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