Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251212

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
712 AM CDT SUN SEP 25 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 322 AM CDT Sun Sep 25 2016

A cold front currently over the eastern Great Plains will move
slowly eastward into Missouri this afternoon and into Illinois this
evening.  Latest short term guidance and radar trends suggest that
the area should remain dry through at least sunrise and probably
much of if not all of the morning as well.  The area is still on the
western periphery of a strong mid and upper level ridge which is
providing synoptic scale subsidence for much of the area.  Models
have this ridge weakening through the day as the longwave trof over
the Plains continues moving east.  Removing the large-scale
subsidence should open the area up to convection late this morning
into the afternoon.  Although low level convergence ahead of the
front isn`t all that impressive, there should be enough lift to
initiate convection since CINH looks minimal with 1500-2200 J/Kg
SBCAPE.  Deep layer shear is pretty weak though...only showing 10-
15kts coincident with the strongest instability so the thunderstorms
should remain below severe thresholds.  Temperatures will likely
climb up into the mid and upper 80s ahead of the front again
today...except over parts of northeast Missouri where more extensive
cloud cover and potentially earlier onset of precip should suppress

The front should be near the I-44 Missouri/I-55 Illinois corridor by
early evening with rain ending behind it as cooler and drier air
pushes in from the northern Plains.  There will probably be some
lingering showers after midnight across parts of southeast Missouri
and southern Illinois, but the rest of the area should be dry by the
end of the evening.  Look for temperatures to drop to near seasonal
normals for overnight lows behind the front.


.LONG TERM...  (Monday through Saturday)
Issued at 322 AM CDT Sun Sep 25 2016

Continue to expect dry weather Monday through Saturday. Global
models are all showing a deep closed low digging southeastward
across the Great Lakes with a upper ridge building over the the
high plains Monday through Wednesday. Cold and dry air advection
behind the front should keep highs Monday through Wednesday in the
lower-mid 70s given that all of the global models are showing
850mb temperatures in the 5-10C range. Lows will be relatively
cool, with temperatures falling into the upper 40s and lower 50s
most nights. By late in the week, the GFS and Canadian lift the
upper low northeastward while the ECMWF keep the low over the Ohio
Valley. Either way, all of the models depict dry weather during
period with 850mb temperatures staying in the single digits
causing highs to stay in the 70s.



.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 654 AM CDT Sun Sep 25 2016

Cold front now moving through extreme southeast Nebraska into the
northwest tip of Missouri will continue moving southeast today.
Expect scattered showers and thunderstorms to develop along and
ahead of the front late this morning into the afternoon. Initial
coverage should be isolated...but will grow in coverage and
intensity during the mid to late afternoon. VFR flight conditions
are expected outside of thunderstorms. Threat of storms should
move south and east through the evening and expect precip to end
for southeast Missouri and southern Illinois after midnight.


Expect VFR flight conditions to prevail at Lambert at least
through the morning into early afternoon. Scattered showers and
thunderstorms are likely ahead of a cold front by mid-late
afternoon. Should see storms move southeast of the terminal by
mid to late evening. Otherwise, expect VFR flight conditions to
prevail outside of any thunderstorm.





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