Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251640
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1140 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
highs.

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.

Carney

.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.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1112 AM CDT Sun Sep 25 2016

A cold front extending from near IRK southwest to near SZL will
move southeastward through the taf sites this afternoon and this
evening. Post frontal showers were moving northeastward through
northwestern MO late this mornng. Scattered showers and storms
will develop along and just ahead of the front this afternoon. A
post frontal band of showers or rain can also be expected to
impact the taf sites late this afternoon and tonight. The cold
front should move southeastward through the St Louis metro area
around 00Z Monday. There will be a post frontal band of low level
clouds moving through the taf sites late this afternoon and
tonight. The MOS guidance keeps these post frontal clouds VFR,
but would not be surprised to see a brief period of MVFR cigs.
West-southwest surface winds will veer around to a northwest
direction after fropa. Rain and showers will shift southeast of
the St Louis metro area by 12Z Monday. A clearing sky can be
expected late tonight in UIN and COU and in the St Louis metro
area Monday morning.

SPECIFICS FOR KSTL: A cold front extending from near IRK southwest
to near SZL will move southeastward through the STL area around
00Z Monday. Post frontal showers were moving northeastward through
northwestern MO late this mornng. Scattered showers and storms
will develop along and just ahead of the front this afternoon. A
post frontal band of showers or rain can also be expected to
impact STL tonight.  There will be a post frontal band of low
level clouds moving through STL tonight. The MOS guidance keeps
these post frontal clouds VFR, but would not be surprised to see a
brief period of MVFR cigs. Southwest surface winds will veer
around to a northwest direction after fropa. Rain and showers will
shift southeast of the STL area by 12Z Monday. A clearing sky can
be expected Monday morning.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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