Area Forecast Discussion
Issued by NWS St. Louis, MO

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609
FXUS63 KLSX 290824
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
324 AM CDT THU SEP 29 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 323 AM CDT Thu Sep 29 2016

Main concern today will be clouds and a chance of showers.  Most of
the area remains clear and any scattered showers are currently
northeast of the area over eastern Illinois.  Do expect cloud that
are rotating around an upper low that is currently over Indiana to
spread westward today.  RAP is showing low level moisture moving
westward today and there will be embedded vort centers moving on the
west side of the upper low.  This will be conducive to both low
clouds overspreading the area and scattered showers developing over
south central Illinois.  The chance of showers will continue into
tonight as a little more pronounced shortwave rounds the upper low
and moves across the region.

Went a bit closer to the warmer NAM MOS temperatures, particularly
over the west have of the CWA where I expect a bit more sun into the
afternoon before it turns mostly cloudy.  Temperatures tonight will
be close to the agreeable MOS guidance which are supported by the
SREF mean surface temperatures.

Britt

.LONG TERM...  (Friday through Wednesday)
Issued at 323 AM CDT Thu Sep 29 2016

The upper level low is still expected to wobble over the Ohio Valley
on Friday and Saturday before beginning to lift out Saturday night
and Sunday.  GFS and NAM are continuing to show a well developed
moist conveyor belt on the northern side of the system.  The
moisture feed remains pretty constant through Saturday with a tongue
of 8+ g/kg spec humidity traveling on the 295K isentropic surface
westward from the Atlantic across the Great Lakes and then wrapping
around the low into the Mid Mississippi Valley.  Models continue to
spit QPF under this moisture feed...with highest amounts mainly east
of the Mississippi River.  Based on QPF, it looks like the highest
PoPs should be Friday afternoon, and this makes good synoptic sense
as the low is forecast to meander back from the eastern
Kentucky/Indiana border to the central Illinois/Indiana border. This
will increase broad scale lift over our area and diurnal heating
should do the rest.  Indeed, MOS PoPs are now up in likely and
categorical range along and east of the Mississippi for Friday.  The
low drifts east on Saturday which will likely decrease the areal
coverage of precip...but with plenty of moisture still available and
probably a bit more diurnal heating would expect at least isolated
to widely scattered showers to develop along and east of the
Mississippi.

Low should be ejecting northeast on Sunday and even though the GFS
and ECMWF are kicking out an isolated hundredth or two of precip, I
think the day will be dry since the synoptic forcing will be rapidly
moving out of the area.  Medium range for Monday through Wednesday
looks mostly dry under the influence of a strong ridge. Temperatures
should warm up to near seasonal normals...perhaps a bit above normal
Monday and Tuesday as southerly flow increases ahead of the next
trof. Timing on when that trof will move out of the Great Plains
into the Mississippi Valley is currently low confidence with the
ECMWF bringing it in Wednesday but the slower GFS holding back until
later next week.  Think the compromise forecast with PoPs increasing
to slight chance/low chance Wednesday and temperatures warming well
above normal into the upper 70s to around 80 looks good for now.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1141 PM CDT Wed Sep 28 2016

VFR conditions and NW surface winds will prevail at the TAF sites
for much of the valid period. Some MVFR CIGs expected for a period
Thursday morning and into midday over STL metro sites as diurnal
influences take place, but this should lift back into VFR by early
afternoon. Some gusts between 15-20kts anticipated during Thursday
afternoon over many sites.

SPECIFICS FOR KSTL: VFR and NW surface winds for much of the valid
period. Exceptions are a brief period of MVFR CIGs during late
Thursday morning and midday and again late Thursday night with
anticipated stratus moving in from the NE. Will begin CIGs at MVFR
level although some guidance is suggesting IFR.

TES

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     69  57  70  58 /  20  20  50  20
Quincy          72  55  67  57 /  10  10  30  30
Columbia        72  54  69  56 /   5   5  10  20
Jefferson City  73  54  69  56 /   5   5  10  20
Salem           68  55  68  54 /  40  40  60  30
Farmington      67  55  66  54 /  10  10  30  20

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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