Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 131713

1213 PM CDT Sat Sep 13 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 255 AM CDT Sat Sep 13 2014

A strong storm system was located over Titletown early this morning
and driving a large shield of rain out ahead of it into Michigan.
Extending further to the south towards our region was a lobe of
moderately strong vorticity.  While this had helped, among other
things, in giving most locations last night some light rain, too
much bone dry air thru the column has since invaded for this forcing
to be of any good any longer.  In fact, skies are rapidly clearing
from north-northwest and should result in clear skies for much, if
not all, of our region shortly after sunrise.  Another big story
here is the first likely venture of temps into the 30s of the very
young meteorological autumn season with readings at several sites
northwest of STL metro teetering around 40 degrees.  Otherwise, a
strong 1030mb Canadian airmass centered near Omaha dominated the
weather map and provided our region with a light north wind.

The upper level system and any lift associated with it will be long
gone by 12z this morning and at that point it will be just a matter
of timing the leading edge of the clearing.  Looks like most of our
region will be clear by 12z save some of the southeast MO sections
and these should clear out by mid-late morning.

Full sunshine is then expected through the day with a light
northeast wind.  Conditional climo supports diurnal rises of at
least 20 degrees and this casts a strong preference for the warmer
MAV MOS temps:  maxes in the low-mid 60s.


.LONG TERM:  (Tonight through Friday)
Issued at 330 AM CDT Sat Sep 13 2014

Canadian high pressure will continue to dominate our region thru
Sunday...moderating as it does so...but continuing the clear skies,
light winds, and below normal temps.  The expected position of the
high pressure ridge axis late tonight will be favorable for maximum
radiational cooling, especially for areas around STL metro and south
and east.  As a result, temps will make a run on record mins at UIN,
COU, and STL, with the forecasts all within a few degrees.  See
CLIMATE section below.  A nice recovery is then on tap for Sunday
with a larger diurnal swing than Saturday...somewhere on the order
of 25-30 degrees...leading to max temps again favoring the warmer
MAV MOS values around 70 to the low 70s.

The only notable chance for rain will be from late Sunday night thru
Monday night.  It will be a similar setup to what we just had last
night, with a strong upper level system mainly passing to our north
with decently deep lift trailing the system to the south.  The key
changes are a much more moist atmosphere with PWs over 1.5" and the
addition of a decent surface front.  So in comparison, we should see
higher PoPs with this system than with the last one and strongly
supports a continuation of our likely and higher PoPs for areas
north and west of STL metro.  Once again forecasting higher PoPs
than MOS.  The lifting mechanisms become out of phase heading into
Monday night, with the frontogenesis and upper jet support exiting
to the east with the surface front left alone to continue as it
pushes to the south.  Have lower PoPs Monday night than on Monday,
but not by too much, merely lowering to chance category as the pcpn
is expected to dry up.  The airmass behind the front is now
advertised as a bit stronger (cooler) than before and may even
result in falling afternoon temps with FROPA across northern MO and
central IL on Monday.

From Tuesday on, we see northwest flow dominate aloft with high
pressure at the surface in the vicinity with its resultant easterly
flow.  Some of the models have some minor intrusions of pcpn, but
little agreement seen here and the pattern overall favors dry with a
slow recovery of temps from below normal to near normal by late



.AVIATION:  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1209 PM CDT Sat Sep 13 2014

Morning fog and stratus has lifted into a very scattered cumulus
deck, with bases that should soon rise above 3000 feet. These will
mostly impact northeast MO and west central IL before becoming SKC
across the area later today. Can`t rule out some light fog late
tonight and toward sunrise, particularly across areas that fogged
up last night such as UIN and COU. For now thinking drier air
should prevent significant vsby restrictions and therefore kept
things VFR overnight.

Specifics for KSTL: A couple of cumulus clouds skirting STL into
early afternoon, otherwise clear skies and light winds for the
remainder of the day.



Issued at 236 PM CDT Fri Sep 12 2014

Record Lows This Weekend:

       STL        COU        UIN
13   43(1975)   33(1902)   33(1902)
14   46(1996)   40(1892)   38(1996)




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