Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 170849
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
349 AM CDT Wed Sep 17 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 347 AM CDT Wed Sep 17 2014

No changes to the Dense Fog advisory issued earlier for our south
central IL counties.  Some patchy dense fog is occurring further to
the west into east central MO  but this appears to be primarilyl
confined to river valleys, and high clouds should be moving in
shortly to limit the dense fog threat along the Mississippi River.

Otherwise, concern for today is shower and thunderstorm threat, and
increasing WAA and moisture advection finally initiated convection
between 07-08z over east central KS. Low level theta-e progs suggest
that this area will continue to grow in coverage (and intensity)
over the next few hours, with the activity making an e-se surge
during the morning generally along and especially south of the
Interstate 70 corridor. While forcing and moisture advection with
the low level jet would suggest most of the precipitation threat
would be this morning, there is some indication in both the hi-res
and synoptic models that additional development will occur this
afternoon as the increasingly unstable air over the Plains interacts
with the rain-cooled dome from this mornings convection.  Because of
this will continue PoPs this afternoon, especially over southern
sections of the CWA.

Still working on temps, but believe much of the area may struggle to
warm up due to clouds and the potential of rain-cooled air,
especially if the convection can linger for any length of time this
afternoon.  Welcome to the cool season...

Truett

.LONG TERM:  (Tonight through Tuesday)
Issued at 347 AM CDT Wed Sep 17 2014

There will be a continued potential for convection mainly across
southeast MO tonight in an area of weak low-mid level warm air
advection north of a weak warm front, and where ample low level
moisture and instability exists.  The threat for any convection
should end by Thursday afternoon as a strong surface ridge builds
southward through the Great Lakes region and into MO and IL with
slightly drier and more stable air filtering southwestward through
our forecast area.  Warmer temperatures can be expected on Friday as
an upper level ridge shifts eastward into MO with southerly surface
winds on the western periphery of the surface ridge extending
southwest into southeastern MO.  Shortwaves will break down and
flatten the upper level ridge on Saturday, and this coupled with a
deepening upper level trough across the northern Plains and Great
Lakes region will allow a cold front to drop southeastward through
our forecast area late Saturday night and Sunday.  The ECMWF model
is now slower with the progression of this front compared to the GFS
model.  The chance for convection will return beginning Saturday
afternoon as the shortwave approaches, then continue Saturday night
and Sunday as the cold front moves through our area.  Most of the
precipitation should end by Sunday night, although the ECMWF model
does still have some precipitation continuing until Monday across
our area due to the slower progression of the surface cold front and
850 mb front and as shortwaves drop southeastward through our area
on the backside of the Great Lakes upper level trough.  Much cooler
temperatures can be expected beginning Sunday night and continuing
through Tuesday night as a fairly strong surface ridge moves slowly
eastward through the region with upper level troffing centered over
the Great Lakes region leading to upper level northwesterly flow
over our area.  The models drop the 850 mb temperatures to 4-8
degrees C across the forecast area by 12z Tuesday.

GKS

&&

.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1104 PM CDT Tue Sep 16 2014

Northwest flow aloft will keep the mid Fall like conditions in
place. Upper air wave will move through overnight to reinforce the
northwest flow. Models trying to generate precitation at the nose
of a low level (5000 ft) jet of 30 knots over the MO/KS border. So
far no sign of anything develping. COU looks to be the only
location with a shot at rain, but will keep them dry for now. Band
of 4k to 5k clouds rapidly advancing SE. That may put a stop to
any MVFR ceilings. Lower clouds over southern MO are slowly
expanding a bit to the north. Some fog at SUS and CPS will will
bring temporary MVFR conditions until the clouds arrive. Wednesday
looks to be VFR.

Specifics for KSTL: 4k to 5k deck should arrive from 08 to 09z.
Will go with that and hold off on any MVFR ceilings. Lower clouds
over south central MO may work their way north and the MAV
guiidance brings them in for a short time. Not that confident they
will arrive, so will leave out for now.

JPK

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...DENSE FOG ADVISORY until 10 AM CDT this morning FOR Bond IL-
     Clinton IL-Fayette IL-Marion IL-Washington IL.

&&

$$

WFO LSX






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