Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262339

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
639 PM CDT THU MAY 26 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 310 PM CDT Thu May 26 2016

Convection from morning MCS has finally shifted southeast of our
forecast area this afternoon. Convection was currently developing
across northwest MO and this activity may eventually shift east
into northeast MO this evening. New development is also expected
across southwest MO along a weak warm front and also along an
outflow boundary left over from the morning convective complex.
These storms should move northeastward into central MO this
evening. Activity may congeal into an MCS later this evening and
overnight and impact much of the forecast area, eventually moving
into our IL counties late tonight. Some of the storms this evening
may be severe, especially across northeast and central MO where
the better instability and shear exists.


.LONG TERM...  (Friday through Next Thursday)
Issued at 310 PM CDT Thu May 26 2016

A better potential for widespread showers/storms is expected on
Friday and Friday night as the upper level trough now over the
southwest US approaches our area. Will go with likely to
catagorical pops. The high temperatures will be cooler on Friday
due to the cloud cover and widespread and potentially long lasting
precipitation. At least scattered showers/storms should occur on
Saturday and Saturday evening until the upper level trough shifts
northeast of our area. Quieter and drier weather is expected by
Sunday as a weak surface trough moves southeastward through the
forecast area with only slight chance pops over the southern and
eastern portion of the forecast area. Precipitation chances should
increase again by Tuesday as an upper level trough moves eastward
through the northern Plains sending a cold front southeastward
through our area. The ECMWF model is quicker than the GFS with the
progression of the upper level trough and associated cold front.
Potentially cooler and less humid conditions can be expected by
the end of the extended forecast period after the passage of the
cold front.



.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 623 PM CDT Thu May 26 2016

Cluster of thunderstorms is slowly heading northward toward KCOU
so added a TEMPO group to account for this activity. Believe KUIN
and metro terminals should continue to stay dry through the
evening with chances of showers and thunderstorms increasing
overnight tonight. Still hard to pin down best chances of activity
at these terminals so did not deviate too much from previous
forecast. Chances of showers and storms should continue through
the day on Friday as main upper-level shortwave finally ejects out
of the desert southwest. MVFR visibilities and ceilings possible
in thunderstorms with IFR visibilities possible in heavier
activity. Surface pressure gradient will also tighten across
eastern Missouri so added some wind gusts to the metro terminals.

Specifics for KSTL:

Still lots of uncertainty on how convection will evolve tonight.
Will have to watch areas to the south/southwest and see how
convection develops tonight but current expectation is for chances
to increase toward midnight tonight. Probably will be at least one period
of showers/storms with visibility impacts with chances of storms
through Friday evening. Wind speeds will also increase as pressure
gradient tightens so added some wind gusts for Friday afternoon of
around 25 knots.





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