Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172347

647 PM CDT Wed Sep 17 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 311 PM CDT Wed Sep 17 2014

Old peripheral upper level energy from the MCS that is now pushing
into northern AR will continue to generate isolated-scattered
showers into the early evening before it either weakens too much to
generate anything or it exits our area to the east.

Otherwise, a warm frontal boundary over southeast KS and extreme
southwest MO, which has been nearly stationary due to the MCS rain,
will try to move northeast later tonight and should generate a new
round of SHRA/TSRA over areas mainly to the south and west of STL
metro.  Thunder chances up our way look meager enough to leave out
for now.

Clouds are starting to break in southwest IL now and this trend
should continue and even quicken as the upper level energy
generating the showers there comes to an end or exits.  This will
leave the leftover low cloud mainly to the west of the MS river and
the light easterly flow will begin to erode the eastern edge of
this, albeit slowly, this evening.  By late tonight, though, a
favorable fog/stratus setup along the periphery of the surviving low
cloud in central-southeast MO may actually allow the leftovers to
grow a bit back to the east again.

Went with a more aggressive cooling on the IL side of the river
tonight due to expected clearing, while preferred the warmer MOS in
central MO.  In-between, tended to favor the cooler MOS guidance as


.LONG TERM:  (Thursday through Next Wednesday)
Issued at 311 PM CDT Wed Sep 17 2014

Surface ridge to continue building in on Thursday. Could see some
lingering light showers over far southern portions of forecast area
in the morning. Otherwise, clouds to clear out from northeast to
southwest with highs in the low 70s. Lows Thursday night will be in
the 50s.

By Friday, surface ridge moves off to the east allowing warmer
southerly flow to return to the region. However, next weather system
to move in on Saturday with showers and thunderstorms possible and
persist through Saturday night before tapering off on Sunday. Highs
on Friday will be in the mid to upper 70s, in the low to mid 80s on
Saturday, then begin to cool back down on Sunday as next ridge of
high pressure builds in.

Cooler weather to persist through the middle of next week with highs
in the 70s and lows in the 40s and 50s.



.AVIATION:  (For the 00z TAFs through 00z Thursday Evening)
Issued at 634 PM CDT Wed Sep 17 2014

A large area of stratus currently covers much of the region from
central IL through the St. Louis and Columbia areas into western
MO. Within this stratus, the cig heights are quite variable
ranging from low-end VFR in the eastern portion over IL to a mix
of MVFR and IFR in central MO. The low level flow within the
lowest 4000 ft veers significantly with east-southeast winds in
the lowest 1000 ft and westerly winds at 4000 ft. This makes the
forecast of cigs heights challenging. The St. Louis area could see
cig heights range from high-end MVFR to low-end VFR much of the
night, but late overnight the easterly flow deepens suggesting an
improving trend with some fog development. Conditions at KCOU
could vary some as well this evening from IFR to low-end MVFR,
however I think the general trend overnight will be for IFR
conditions and fog. All terminals should see improvement mid-late
Thursday morning.

Specifics for KSTL:

Cig heights may range from high-end MVFR to low-end VFR much of
the night but after 09z or so, easterly flow deepens suggesting
an improving trend with some fog development. VFR conditions should
previal by 14-15z and persist through the day on Thursday.





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