Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 210257

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
957 PM CDT FRI MAY 20 2016

Issued at 953 PM CDT Fri May 20 2016

Showers will move out of the eastern counties by midnight. There
may be some patchy fog develop over the area late tonight into
early tomorrow morning under some clearing skies and light winds.
Otherwise, only made minor adjustments to overnight lows based on
temperature trends.



.SHORT TERM...  (Through Late Tonight)
Issued at 340 PM CDT Fri May 20 2016

Strong vort center over northeast MO, representing the old center
of the storm system that was over the southern Plains yesterday,
has been very slow to move and is expected to continue to be very
slow to exit as we head toward sundown.  As a result, the near
steady light rain that has occurred should continue until this
feature exits, which most short-range models have occurring around

Further to the south, a lobe of weaker vorticity extends thru much
of the forecast area, into southwest MO, but its ability to kick of
any additional shower development has been very much in check so far
this afternoon.  Its window of opportunity will begin to close as
the sun gets lower, and have already scaled back PoPs to slight

Otherwise, look for clearing later tonight for most places, with
clouds most persistent in the eastern forecast area around Vandalia
and Salem, IL.  Mostly sunny skies can be expected on Saturday as an
upper level RIDGE builds in.  There is another disturbance that
drops down and edges us Saturday afternoon, but it will be acting
upon a much drier column and should not produce any sensible wx.

Min temps tonight in the upper 40s and lower 50s.

Max temps on Saturday should recover into the mid 70s for many
areas, very close to average for this time of year.


.LONG TERM...  (Saturday through Next Friday)
Issued at 340 PM CDT Fri May 20 2016

Models have been very consistent with the forecast for Sunday and
beyond over the past 3 days.  Ridging through the depth of the
atmosphere should keep Sunday dry.  A warmer start to the day Sunday
morning combined with strong insolation under a mostly clear sky
weak warm advection should allow for warmer temperatures than we`ve
seen in a week.  Can`t argue with MOS guidance in the upper 70s and
low 80s.  The ridge will still be the primary influence on our
weather Sunday night and Monday.  A relatively light wind, few
clouds and dewpoints in the low to mid 50s should allow temperatures
to drop into the mid 50s to around 60 Monday morning...and highs
Monday afternoon look very similar to Sunday`s readings.

Guidance differs a bit for Monday afternoon with the NAM and ECMWF
being a bit faster in shifting the ridge east and allowing deep low
level moisture to return to the area.  They are therefore faster in
developing precip on Monday afternoon and evening than the GFS.  I
continue to lean toward the slower solution though because the
surface ridge axis to our south will help block this northward flow
of higher moisture.  Moisture from the gulf will eventually round
the west side of the ridge and make it back into our area.  Monday
night will begin another period of wet weather.  Periods of showers
and thunderstorms will be possible from Monday night through Friday.
South-southwest flow will prevail which will continue to replenish
moisture with each round of precipitation.  GFS looks to be overly
excited about grid-scale convective feedback without a dry period
from Monday night through Friday.  The ECMWF might be more
realistic showing a diurnal trend with relative minima in precip
late at night and during the morning with maxima in the afternoon
and evening.  That being said, convection will likely be very
dependent on boundary interaction for initiation, and the strength
of the nocturnal low level jet at night for maintenance. Confidence
on any kind of timing and duration on precip is therefore pretty low
at this time.  Temperatures through the period should continue the
upward trend with lows in the 60s and highs in the low to mid 80s.



.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 641 PM CDT Fri May 20 2016

Rain will move out of northeast Missouri and west central Illinois
early in the TAF period. Do not expect rain to affect KUIN at this
time. There may be some patchy fog develop around the area, but do
not expect it to affect the terminals at this time.

Specifics for KSTL: Dry and VFR conditions are expected through
the period with light winds.





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