Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251213

713 AM CDT Sat Apr 25 2015

.SHORT TERM: (Through this Evening)
Issued at 240 AM CDT Sat Apr 25 2015

Well advertised storm system will bring two rounds of showers and
thunderstorms to the CWA over the next 12 hours. The first round is
just now taking shape as warm advection increases ahead of the
shortwave now lifting from the southern Plains into the lower
Missouri River Valley. Surface low pressure depicted by model
guidance the past few days seems to be associated with well defined
MCV on regional radar currently spinning in far southeast Nebraska.
Showers and thunderstorms should continue to develop from northwest
Missouri to southeast Missouri and lift north through the predawn
hours. Dry slot will push through the southeastern half of the CWA
ahead of the low pressure this morning and early afternoon.  This
will cause the band of warm advection showers and thunderstorms to
steadily march northeast of the CWA. It will also set the stage for
at least some breaks in the cloud cover south of Interstate 70 and
instability to increase this afternoon.

The second round of precipitation today will take shape later this
morning and into the afternoon as the low pressure center traverses
east-southeast across the CWA.  Rain showers and isolated
thunderstorms will accompany the low pressure center (MCV) and
additional thunderstorm development is likely ahead of and to the
south of the surface low. SPC continues to highlight the likelihood
of severe thunderstorm development this afternoon, mainly southeast
of the St. Louis Metro.  Latest explicit model guidance depicts
discrete storm development between 2 PM and 4 PM just south of St.
Louis, with this activity exiting the CWA shortly after 7 PM. Large
hail and damaging wind gusts will be the primary threats with the
supercells this afternoon and early this evening. The threat of
tornadoes is more conditional and will likely hinge on how much
instability can be realized ahead of the low and if the surface
winds can remain backed across this area.


.LONG TERM:  (Tonight through Friday)
Issued at 240 AM CDT Sat Apr 25 2015

Showers will come to an end from northwest to southeast this
evening and clearing is still expected on Sunday with below normal
temperatures. Rest of the forecast remains unchanged with
temperatures gradually returning to normal by the end of the week
and precipitation chances remaining low.



.AVIATION:  (For the 12z TAFs through 12z Sunday Morning)
Issued at 642 AM CDT Sat Apr 25 2015

Aviation overview: A slow-moving low pressure system will move
east-southeast across the region today. Periods of SHRA/TSRA are
expected at all TAF sites at different times of the day depending
on each terminal`s location relative to the track of the low
pressure system. A trailing cold front will then move through the
region tonight behind the departing low pressure system.

Specifics for KCOU: Initially IFR ceilings at TAF issuance should
improve to at least MVFR for several hours before additional
SHRA/TSRA develop during the afternoon. Cigs should eventually
fall back to IFR tonight on the cold side of the cold front.
Initially southeast winds will veer and become southerly to
southwesterly today, then become northeasterly early tonight
behind the cold front.

Specifics for KUIN: Based on upstream trends, prolonged periods
of SHRA/TSRA are expected at KUIN since it will be located north
of the surface low track. One cluster of thunderstorms was located
just upstream from KUIN at TAF issuance, and it should reach the
terminal by 13z. Initial thoughts are that KUIN should be too far
north to be affected by much in the way of afternoon thunderstorm
development, although a few embedded thunderstorms may occur. If
any clearing occurs at KUIN this afternoon, then the resulting
instability will aid thunderstorm development. Initially
southeasterly winds will back and become easterly to northeasterly
today, then remain northeasterly through the end of the TAF

Specifics for KSTL, KSUS, KCPS: The southern end of a SHRA/TSRA
cluster was approaching St. Louis metro area terminals at TAF
issuance. After the morning convection tapers off, there should be
a dry period lasting several hours before the next round of
thunderstorms develops during the afternoon. After some
improvement during the late morning or early afternoon, cigs are
expected to fall back to MVFR tonight on the cold side of the
cold front. Initially southeasterly winds will veer and become
southerly to southwesterly today, then turn northeasterly early
tonight behind the cold front.





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