Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240428

1128 PM CDT Sat May 23 2015

Issued at 857 PM CDT Sat May 23 2015

Forecast for the most part on track and have only made small
adjustments based on latest radar trends and incorporating high
temporal res model output. Small notch of rain is expected to edge
the western edge of the CWA thru midnight with pcpn in its wake to
the S-SW expected to fill in, especially as line of storms pushes
east thru OK and contributes to an expansion of the area of
enhanced stratiform rain to the north. This should result in high
PoPs for an area roughly west of a line from UIN-COU for late
evening and overnight with minimal PoPs or dry elsewhere.

One exception which has some support amongst many of the short-
term models is the idea of isolated-scattered SHRA developing over
far SE MO around daybreak and moving north towards STL metro
Sunday morning. At this point, the models still agree on a general
expansion of SHRA/TSRA coverage as we head into the afternoon



Issued at 145 PM CDT Sat May 23 2015

The middle to upper levels of the atmosphere feature a deep trof
of low pressure centered over the Four-Corners Region with
resulting southwest flow downstream across the southern Plains.
Embedded shortwave in this flow continues to produce heavy showers
and thunderstorms across KS and OK. Further east, weak warm
advection and moisture convergence along and north of the 850mb
warm front was responsible for isolated to widely scattered
showers across mainly southwest Missouri.



.SHORT TERM: (Through Tuesday)
Issued at 145 PM CDT Sat May 23 2015

Main thrust of precipitation should remain just to the west of the
CWA through tomorrow morning with the highest PoPs and QPF
concentrated across our central and northeast MO counties. That
doesn`t mean it will be completlely dry though, as isolated to
scattered showers cannot be ruled out as far east as the Mississippi
River as the 850mb warm front lifts north.

Appears that the first round of precipitation should pull northeast
of central and northeast MO during the morning hours with a threat
of renewed thunderstorm development during the afternoon and evening
areawide. Have maintained general trend of chance/sct PoP increasing
to likely during the afternoon, especially west of I-55. Believe
there will be enough dry time for temperatures to warm into the
upper 70s/lower 80s.

Sunday Night...
Not sure exactly how Sunday night will play out, as it will depend
on convective trends during the afternoon and evening. Model
guidance depicts a decent shortwave moving northeast across the area
which would make one think there should be some pretty good coverage
of precipitation. I have kept a blanket of categorical PoPs based on
pattern recognition more than anything.

Memorial Day...
At this point it looks like the vast majority of the area will be
dry on Memorial Day as the shortwave lifts northeast of the area and
we are located in area of subsidence for the daylight hours. I
suppose I can`t rule out an isolated thunderstorm developing since
we are still in southwest flow aloft and will be quite unstable, but
chances are pretty low since there is no obvious trigger.
Temperatures should be quite warm for the unofficial start of summer
with highs in the lower to middle 80s.

Monday night and Tuesday...
Next shortwave in the southwest flow parade will bring a renewed
threat of showers and thunderstorms to the CWA Monday night into
Tuesday. Temperatures may struggle some on Tuesday with cloud cover
and expected rain coverage, so knocked anticipated highs down a few
degrees across the southeastern half of the CWA.

.LONG TERM: (Tuesday Night through Next Saturday)
Issued at 145 PM CDT Sat May 23 2015

The pattern looks to remain quite active with southwest flow
expected through the period. Each shortwave will bring with it a
chance of thunderstorms and temperatures should remain warm, with
afternoon highs in the lower to middle 80s.



.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1102 PM CDT Sat May 23 2015

Mid-high level clouds will continue across the area late tonight
with at least light showers moving through COU late tonight and
possibly into UIN towards morning. Could not rule out sprinkles in
the St Louis metro area late tonight, but the better chance of
showers/storms should hold off until Sunday afternoon and night as
a sly low level jet moves through the area. Prevailing cloud
ceilings will also lower on Sunday, likely into the MVFR catagory
in UIN and COU and down to MVFR or at least low end VFR in the St
Louis metro area by afternoon. Sely surface wind will continue
late tonight, becoming relatively strong and gusty from a s-sely
direction on Sunday.

Specifics for KSTL: Prevailing VFR mid level cloudiness late
tonight, then the ceiling will lower into the MVFR or low end VFR
catagory by Sunday afternoon. May be some sprinkles late tonight
from mid level clouds, but the better threat of showers/storms
should occur Sunday afternoon and night. Sely surface wind
late tonight will strengthen and become gusty by late Sunday
morning or afternoon from a s-sely direction.





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