Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191741

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1241 PM CDT FRI AUG 19 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 335 AM CDT Fri Aug 19 2016

Primary forecast concern for today and tonight is precip chances.
Seasonably warm and humid air will remain over the area today and
tonight ahead of a cold front which will drift through Iowa today.
Southerly flow ahead of the front will allow dew points to pool
across our area producing generally 1500-2000 J/Kg of CAPE. Forecast
soundings for most guidance show a weak cap, and with only weak
upper level support and no synoptic boundaries over our area I
expect only scattered convection this afternoon. If a cluster of
storms can get organized though, the coverage could be greater
than anticipated.

The front will move into northwest sections of the CWFA after
midnight tonight with what looks like a dying MCS ahead of it.  The
MUCAPE ahead of the front isn`t very impressive except on the
NAM...and I`m not sure how much trust to put in it at this time.
NSSL and NCEP 4km WRF models actually do not have very much
convection over our area tonight with most of the storms staying up
over Iowa closer to the better upper support, and down over
southwest Missouri, Oklahoma and Nebraska where the low level jet
will be stronger.  Hard to ignore MOS PoPs in the 30-80% range
across the area though.  Think the most likely areas to receive rain
will be over northwest Missouri into west central Illinois on the
edge of the weakening MCS after 06Z.  Stuck with low to mid chance
PoPs further south.


.LONG TERM...  (Saturday through Thursday)
Issued at 335 AM CDT Fri Aug 19 2016

Going forecast looks on track with the GFS and ECMWF showing a
strong upper trough moving across the Midwest late Saturday and
Saturday night.  Both models are consistent that the attendant cold
front will move through the CWA during the late morning and early
afternoon hours on Saturday morning.  There will be enough low level
moisture convergence ahead of the cold front underlying decent mid
level ascent generated by the trough to keep the going likely/
categorical PoPs for showers and thunderstorms.  Rain chances will
end by early Saturday night as the front moves well southeast of the
area and subsidence moves in.

Dry weather is expected to continue through Monday and Tuesday in
the wake of the upper trough as a large surface high moves across
the area.  The chance for showers and thunderstorms will increase
again by Wednesday and Thursday as the next upper trough moves into
the area.  Best chances for rain will be focused along a cold front
that will be moving southeast into Missouri and Illinois by

Temperatures still look like they will cool off behind the front
with temperatures staying below normal much of the week.  850mb
temperatures will be 10-15C range.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1236 PM CDT Fri Aug 19 2016

Isolated to widely scattered showers and thunderstorms look to
stay south of the terminals w/ exception of KCOU this
afternoon/early evening. Cold front will approach the region late
tonight/early on Saturday and will likely bring a round of
showers/storms along ahead of it. Behind the front...MVFR
ceilings appear possible along with a wind shift from the south to
the west is expected.


Believe most of diurnal shower/storm activity to stay south of the
terminal so took out previous mention of VCTS this afternoon. Cold
front will approach the termnial Saturday morning with a round of
showers/thunderstorms expected out ahead of it. After the frontal
passage...borderline MVFR ceilings are possible along with a wind
shift from the south to the west by Saturday afternoon.





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