Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 291733

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1233 PM CDT MON AUG 29 2016

Issued at 1059 AM CDT Mon Aug 29 2016

Still expect scattered thunderstorms to develop this afternoon
across parts of the area. Latest SPC mesoanalysis shows MLCAPES
across central and eastern Missouri into west central Illinois
have already reached 2000 J/kg with little CIN left. This is the
same area that the latest HRRR runs show scattered convection
developing between 17-19Z. Will continue to show scattered PoPs in
this area this afternoon with just isolated PoPs in southern
Illinois. Will also have isolated PoPs going into the evening
hours before they diminish with the loss of daytime heating.

Temperatures have already climbed into the mid to upper 80s. Going
highs in the lower to mid 90s still look good for now.



.SHORT TERM...  (Through Late This Afternoon)
Issued at 330 AM CDT Mon Aug 29 2016

Zonal flow aloft with the westerlies along the international border
will lead to a repeat performance with highs in the upper 80s to mid
90s and a hodgepodge of diurnal convection. Expect the better
coverage of convection in the nthrn portion of the CWA away from the
heart of the upper lvl ridge.


.LONG TERM...  (Tonight through Sunday)
Issued at 330 AM CDT Mon Aug 29 2016

Tonight thru Tuesday

Zonal flow begins to break down as a pair of short waves moves thru
the mean flow. One approaches the Pacific NW out of the Gulf of
Alaska while the other tops the ridge across cntrl Canada and starts
to drop into ern Canada. These two systems will not have much effect
on the sensible weather...yet. Expect another warm muggy night
tonight with another day of diurnal convection on Tue. The short
wave digging into ern Canada will allow a cold front to drop into
the region drng the middle of the week so the coverage of PM
SHRAs/TSTMs should be greater on Tue...esp across the nthrn portions
of the FA with better proximity to the approaching bndry. More cloud
cover and better precip chances should lead to slightly cooler high
temps on Tue than the past several days...esp N of I-70. If SE MO
and sthrn IL are able to remain mostly clear thru at least mid-
aftn...then highs may make it well into the low 90s again.

Tuesday night thru Wednesday night

The Pacific NW short wave will continue to slide down the W Coast
while the other disturbance begins digging a trough along the E
Coast of N America. The energy approaching the Pacific NW Coast will
cause the zonal flow to buckle while the digging E Coast trough will
make the amplitude of the ridge appear to be increasing while
heights actually fall across the FA in response to the dvlpng E
Coast trough. A SFC low assoc with this ern short wave will drag a
cold front thru the region Tue night. Convection should be ongoing
at the beginning of the prd. Precip coverage and intensity may wane
overnight but should continue in one form or another thru the night
as the bndry sinks S. Going fcst may have too low of PoPs Tue night.
This front will introduce a much cooler and less humid airmass into
the region. The relief will come in two stages though. The initial
wind shift along the pressure trough/cold front will introduce
cooler temps...850 mb temps falling from upper teens to mid
teens...which should take about 5 degrees off from Tue highs. Dps
are not fcst to fall off until Wed night as SFC pressures begin to
rise as a 1028mb SFC ridge begins building into the area. Due to a
secondary bndry assoc with the Dp gradient...addtnl SHRAs/TSTMs
are expected across the region Wed. This precip will be aided by a
weak short wave that is fcst to move over the FA thru the day.
Precip should move out of the sthrn zones Wed evng as the drier
air becomes better established.

Thursday thru Friday night

The E Coast trough is expected to move into the wrn Atlantic which
allows the 500mb ridge axis to move overhead Fri night. The West
Coast energy finally comes onshore and begins to dampen the
downstream ridge. At the SFC...high pressure will be in firm
control. This should be a beautiful stretch of wx. The Canadian high
pressure will usher in Dps in the 50s. Precip should be nil and 850
temps in the low/mid teens correlates to highs in the upper 70s to
lower 80s. Lows both Thu and Fri nights should be able to drop into
the upper 50s to lower ACs a break.

Saturday thru Sunday

The Pacific NW short wave continues to move inland shunting the
ridge axis to the E of the region. This puts the FA under the
influence of SW flow aloft. The SFC ridge moves from the Grt Lks to
off the Coast of NE by the end of the prd. There are some timing
issues with the SFC ridge axis...the GFS is faster than the ECMWF
but both solutions have return flow in place by Sun mrng. The wknd
looks dry with WAA precip remaining W/NW of the CWA. Temps will
slowly rebound thru the wknd as sthrly flow kicks in with Dps
noticeably higher by Sun.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1227 PM CDT Mon Aug 29 2016

Will continue to go with VCTS in all of the terminals this
afternoon as scattered thunderstorms have already developed across
central and eastern Missouri as well as west central Illinois.
These thunderstorms are expected to last through late afternoon
before dissipating with the loss of daytime heating. There maybe
some redevelopment of fog again tonight, but did not have enough
confidence at this time to add them into the taf.

SPECIFICS FOR KSTL: Added VCTS for afternoon thunderstorms which
have already developed west of the terminal. Expect these storms
to dissipate by sunset. Then expect dry and VFR conditions the
rest of the period.





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