Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 130012

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
612 PM CST Tue Dec 12 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 310 PM CST Tue Dec 12 2017

A very dry airmass and mixing up to 900mb has caused dewpoints to
fall into the single digits across the area this afternoon.  A
surface ridge currently over western Missouri will move east across
the area this evening and then the current westerly surface winds
will back southerly by morning.  There will be a slight chance of
rain over northeast Missouri into west central Illinois on Wednesday
morning/early afternoon as a weak shortwave moves southeast across
the Midwest.  The attendant cold front will move south across the
region by tomorrow afternoon bringing an reinforcing shot of cold
air to the region. Lows tonight will be similar to what they were
this morning. Highs tomorrow will be warmer than today as 850mb
temperatures climb to around 0C, and surface winds will turn out
of the southwest ahead of the front.


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 310 PM CST Tue Dec 12 2017

Colder temperatures will then move into the area for late week as
850mb temperatures drop to between -5 and -10C in the
northwesterly flow aloft according to the latest runs of the
GFS/ECMWF/GEM. These days are still expected to be dry, however
these models are still advertising that there will be a pattern
change by the weekend as the eastern longwave trough moves east
which allows the northwesterly upper flow to transition to
southwesterly. This will allow for warm and moist air to advect
northward into the Midwest over the weekend. At this point, will
keep above normal temperatures over the weekend with a chance of
rain over the southern half of the area on Sunday. The best chance
of rain with a chance of mixed precipitation will be on Sunday
night over the southern half of the CWA. Do have some concerns
with this forecast as the timing and placing of QPF amongst the
models differs. Dry weather is expected on Monday and Tuesday as
a surface high moves across the area.



.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 541 PM CST Tue Dec 12 2017

Dry VFR conditions for all terminals through the period. Cold
front will pass through all sites tomorrow morning. Winds begin
the period from the west and backing to southerly overnight ahead
of the frontal passage. Winds will veer to the northwest during
the afternoon tomorrow as front moves thorugh the area with gusts
25-30 kts. Low level wind shear during the late morning is
possible at all sites.


Dry and VFR for entire forecast period for STL. Winds will shift
from nortwest to southerly overnight as cold front approachs from
the nortwest. With this frontal passage tomorrow morning expect
winds to veer back to the northwest with gusts 25-30 kts. Low
level wind shear in the late morning is possible as cold front
moves through.



Issued at 310 PM CST Tue Dec 12 2017

Heightened fire danger is expected again over parts of southeast
Missouri on Wednesday. This area is experiencing severe drought with
fuel moistures at the RAWS stations in southeast Missouri dropping
below 10 percent this afternoon.  Forecast minimum relative humidity
will fall to between 25-30 percent during the afternoon and
sustained westerly winds will be between 12-15 mph.





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