Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 170156

856 PM CDT Tue Sep 16 2014

Issued at 845 PM CDT Tue Sep 16 2014

Going forecast looks on track this evening. Sky is clear/mostly
clear across the area with just a bit of cloud cover hanging in
across our SE MO counties. Short range guidance continues to show
an increasing amount of low level moisture convergence over
eastern Kansas/western Missouri this evening with convection
breaking out between 06Z-08Z. Models are pretty consistent in
keeping all but perhaps a few showers out of our area through 12Z
with the lion`s share of the precip back over southwest Missouri.
Should see scattered showers and thunderstorms spread into parts
of central and eastern Missouri later Wednesday morning. RAP and
HRRR seem to want to bring some showers into northeast Missouri by
15Z as well...and I may tweak the PoPs up before sending out the
midnight update if the new 00Z NAM and GFS agree.



.SHORT TERM:  (Through Tonight)
Issued at 230 PM CDT Tue Sep 16 2014

A weak s/w will approach the CWA late tonight bringing a chance
for storms to wrn and srn portions of the CWA late tonight.
Otherwise, expect clouds to continue to break up during the
afternoon and into the evening. Clouds are expected to build into
the region from the W tonight ahead of the s/w. Have trended twd
a compromise of guidance for wrn portions of the CWA and twd the
cooler guidance for ern portions. Latest guidance suggests FG will
develop late tonight impacting srn and ern portions of the CWA
where radiational cooling will be greatest.

.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 309 PM CDT Tue Sep 16 2014

(Wednesday through Friday)

Main concern continues to be rain chances tomorrow into tomorrow
night over mainly central and southeast Missouri.  GFS/NAM/ECMWF are
still in relatively good agreement in dropping a weak shortwave
trough across Missouri during the day tomorrow.  Each of these
models shows some weak low level moisture lingering across central
and southeast Missouri into Wednesday night, so will continue a
chance of showers and thunderstorms in this area.   This scenario is
depicted pretty well at least through 00Z by the reflectivity on the
NSSL WRF.  Thereafter will maintain a dry forecast Thursday and
Friday as a surface ridge moves across the area at the same time a
upper ridge builds in from the west.

Went on the cooler side of guidance for highs the next couple of
days given the easterly surface flow and it matches up better with
mixing down the 900mb temperatures.   Likewise followed the cooler
NAM MOS for lows.

(Saturday through next Tuesday)

While there is still some disagreement between the GFS/ECMWF
regarding the speed and depth of a trough that will pass through the
area this weekend, it still appears that the attendant cold front
will move through on Saturday night and early Sunday.  Will keep
chances of showers and thunderstorms going Saturday into Sunday.
Will keep Monday and Tuesday dry at this point as we will be on the
back side of the the upper trough, though the latest runs of the GFS
is showing a secondary through dropping down in the northwesterly
flow on Tuesday.  This is a new trend that the ECMWF is not
showing.  Still expect at or just above normal temperatures ahead of
the front on Saturday before they drop back below normal for early
next week given expected 850mb temperatures in the 6-9C



.AVIATION:  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 541 PM CDT Tue Sep 16 2014

Northwest flow aloft continues through the period with a
reinforcing short wave coming through tonight. High pressure at
the surface shifts east allowing for a weak southerly flow to
develop. Low level jet, about 5000 ft, kicks in pointing at KS/MO
border,thus most models want to develop precipitation overnight in
this area. Looks like rain will stay west of terminals with COU
having the best chance, but chances still low enough to leave out
of the forecast. VCSH may be needed for the next forecast. Models
also want to bring in some MVFR ceilings. Given the pattern is
more mid-Fall like rather than late summer, and with 60 dew points
not that far away, will go with this at COU and STL. Have a few
doubts about this at STL, so will not hit it extremely hard.

Specifics for KSTL: Looks like any rain that develops will stay to
the soutwest of the terminal. Big question is if MVFR ceilings
will arrive. Given the cool pattern, feel it is possible but have
doubts about how extensive the MVFR shield will be. Surface wind
will be weak, so it is up to the low level jet to bring in the
MVFR clouds. Will bring in MVFR ceilings for a while in the
morning, starting around 12z, then raise them about 4 hours
later. Rest of the period should be VFR





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