Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 292300
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
600 PM CDT Fri Aug 29 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 354 PM CDT Fri Aug 29 2014

Main focus through tonight will be on precipitation chances. Compact
vort max/MCV will be main driver of precipitation through the period.
Tied highest PoPs with track of this feature which current radar
imagery supports as largest coverage of showers with embedded
thunderstorms is just ahead of this feature through early this evening.
Not sure how activity will evolve overnight...but do think that
activity may become more scattered with loss of bulk of daytime
instability and track of vort max to the north of CWA. Therefore...
did lower PoPs back for late tonight. Associated frontal boundary will
slowly ooze south and eastward overnight and begin to washout/stall out
somewhere over the central portion of the CWA bisecting from southwest to
northeast. Temperatures will be seasonably warm...i.e. upper 60s to low
70s and did not deviate from guidance too much.

Gosselin

.LONG TERM:  (Saturday through Next Friday)
Issued at 354 PM CDT Fri Aug 29 2014

Continuing with the short term theme of more scattered convection
associated with this system...have lowered PoPs for Saturday morning
across the entire area.  12Z model guidance from this morning backed
off precipitation chances and QPF for Saturday morning.  The upper
level trof will be flattening out and much of the vorticity will be
moving off to the northeast of the area.  Low level convergence will
be fairly weak and with only weak low level warm advection ahead of
the trof it looks like coverage will be limited.  Expect though as
the day heats up and the atmosphere becomes more unstable we`ll see
coverage increase.  Have therefore kept likely PoPs for Saturday
afternoon...generally along and east of the I-44/I-55 corridor.
Should see storms diminish during the evening with the loss of
daytime heating.

Keeping with the slightly drier trend to the forecast, have lowered
PoPs a bit on Sunday as weak shortwave ridging moves over the CWFA
in the wake of Saturday`s trof.  With no obvious focus for surface
convection showing up in the guidance, think the only real shot for
convective initiation will be orographic effects from the Ozarks.
Therefore have kept chance/slight chance PoPs along and south of the
I-70 corridor Sunday assuming there will be scattered storms down
there which will migrate northeastward.

Little change to the forecast for next week...other than to bump up
temperatures a little for Thursday and Friday.  The next shortwave
is still on track to dig into the Great Plains on Sunday
evening...moving into the Midwest by Monday morning.  While medium
range guidance is in general agreement with the timing of the wave,
the GFS shows a sharper/deeper wave while the ECMWF is less
amplified.  The surface front is still forecast to dip into central
Missouri before stalling Monday night.  The front remains over
Missouri and southern Illinois on Tuesday providing a focus for
convective development.  Have kept likely PoP Sunday night into
Monday night as the front moves in and lingering chance PoPs
continuing into midweek.  As the front moves back to the north
Thursday and Friday have lowered to slight chance and increased
temps as the upper level ridge builds back across the central U.S.

Carney

&&

.AVIATION:  (For the 00z TAFs through 00z Saturday Evening)
Issued at 526 PM CDT Fri Aug 29 2014

North to south band of showers/storms moving through UIN will
also move through STL and SUS early this evening, although much of
this activity may shift east of the taf sites shortly after 00z
this evening. There will likely be widely scattered showers/storms
for at least the remainder of the evening and overnight due to
approaching upper level disturbance, but may leave the tafs dry.
It appears that there will be enough cloud cover and strong
enough surface winds to deter fog formation, although could not
rule out light fog late tonight/early Saturday morning in SUS and
CPS where the surface wind will be a little lighter and in areas
which get significant rainfall this evening. Should be at least
scattered showers/storms in the St Louis metro area Saturday
afternoon along and ahead of weakening cold front/surface trough.

Specifics for KSTL: Band of showers and storms will move through
STL around 00z this evening, with widely scattered showers/storms
still possible for the late evening and overnight. Will include
showers/storms in the STL taf until at least 01z this evening, but
may leave taf dry for the rest of the night into Saturday morning
due to uncertainty in coverage and timing of additional
convection. Will include VCTS in the taf Saturday afternoon with
at least scattered showers/storms expected at this time due to
diurnal destabilization along and ahead of a weak surface
trough/cold front. Prevailing s-swly surface winds through the
period.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     73  87  73  87 /  60  60  30  20
Quincy          69  85  67  86 /  60  40  10  10
Columbia        68  88  68  89 /  40  40  20  10
Jefferson City  68  87  69  89 /  40  40  20  10
Salem           71  85  71  84 /  50  60  50  30
Farmington      71  85  69  85 /  50  60  50  30

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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