Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 132357

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
657 PM CDT Wed Sep 13 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 300 PM CDT Wed Sep 13 2017

Remnant low from Irma to continue lifting northeast away from
region. In the meantime, clouds associated with it will be slow to
move out. Clouds on outer edges are more diurnal in nature and
should dissipate towards sunset. As for areas along and east of
Mississippi River, clouds will clear out late tonight. With light
winds, some concern about patchy fog development for areas that are
currently cloudy, so kept mention in. As for temperatures, with
lingering clouds and winds becoming light and southerly late, lows
will be a bit warmer, in the mid to upper 50s.

On Thursday, with surface ridge to our east, southerly winds to
return once again, allowing temperatures to warm up into the 80s,
about 5 to 10 degrees above normal for this time of year.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 300 PM CDT Wed Sep 13 2017

A relatively quiet weather pattern will give way to a more active
pattern this weekend. A cutoff low entering the California coast
along with a trough moving through the pacific northwest this
morning, will help drive the formation of a long wave trough over
the western two thirds of the country. This will lead to surface
cyclogensis  across southeast Colorado Friday into Saturday. It will
likely be a little breezy Friday afternoon and evening as the low to
the west deepens over the Plains. The approaching trough will result
in southwest flow and drive temperatures above climatological highs
on Friday and Saturday.

The low and associated weak cold front will approach the region on
Saturday. The front and attendant low pressure will move into the
area late Saturday night with showers and thunderstorms. The front
is expected to move just south of the region before moving north to
the  I-70 corridor as a warm front. Temperatures on Sunday and
Monday will be highly dependent on cloud and precipitation coverage.

The front will push back north Monday with scattered showers and
thunderstorms possible through Monday evening.  An upper level ridge
will build into the region Tuesday into Wednesday. This will pull up
a warm airmass from the Gulf of Mexico allowing for temperatures to
climb back above climatological normals.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 655 PM CDT Wed Sep 13 2017

Backedge of the cloudiness will be working thru the STL metro area
the next few hours with clear skies in its wake. While COU and UIN
should have mixed out sufficiently to preclude fog, that is not
the case for STL metro sites where they were cloudy most of the
day. Have added a bit of VSBY reduction to STL and lowered the
existing VSBY reductions at SUS and CPS where IFR VSBYs should be
easily attainable. Fog should burn off quickly in the morning with
clear skies the remainder of the day.





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