Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250828

Area Forecast Discussion
National Weather Service Saint Louis MO
328 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 06z TAFs through 06z Sunday Night)
Issued at 1058 PM CDT Sat Sep 24 2016

Still need to watch for some radiational fog overnight at KSUS and KCPS,
however confidence is only modest so added a TEMPO group for MVFR
visibilites. Think the terminals will remain void of any precipitation
overnight into early Sunday morning as activity currently in
western MO is expected to weaken and dissipate.

A cold front will move across central and eastern Missouri from
late Sunday morning into the afternoon, passing through KSTL near
00Z. Expecting a lull in precipitation during the first part of
the day with development of scattered showers and thunderstorms
ahead of the front Sunday afternoon, expanding in coverage into
the evening as the front moves through St. Louis into southwest
IL. It also appears a swath of scattered showers may linger in
the wake of the front and this is most likely to bring any
precipitation to KUIN and KCOU on Sunday afternoon. The greatest
probability of showers and thunderstorms and terminal impacts will
be in the St. Louis region centered near 00z.


VFR flight conditions should prevail tonight and into at least
mid-morning on Sunday. Scattered showers and thunderstorms will
develop along/ahead of an advancing cold front on Sunday
afternoon expanding in coverage into the evening as the front
moves through St. Louis. The greatest probability of showers and
thunderstorms and terminal impacts will centered near the 00Z/26
time frame as the front moves through the area.





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