Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250306
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1006 PM CDT Thu Sep 24 2020

.SHORT TERM...  (Through Late Friday Night)
Issued at 200 PM CDT Thu Sep 24 2020

Stratus and fog that was persistent across the region this morning
continues to dissipate this afternoon. Latest surface analysis is
showing a weak surface ridge across central Missouri into southern
Illinois with stationary front across the Upper Midwest. HREF is
showing this weak surface flow remaining over the region through
tomorrow morning. This combined with a moist boundary layer seen
in the RAP/NAM forecast soundings will set up another night for
fog or low stratus over parts of central and southeast Missouri
into southwest Illinois. Have kept mention of patchy/areas of fog
from late this evening into Friday morning.

Water vapor imagery is showing a weak shortwave trough moving over
the Upper Midwest that will pass to our north this afternoon with
little impacts.  A ridge currently over the Northern Plains will
flatten out as it moves into the Midwest tomorrow.  Still expect dry
weather through Friday night as there will be little ascent with a
deep, dry atmosphere.

Lows tonight will be similar to last night with lows in the 50s
given the light winds and relatively clear skies starting out this
evening. Highs on Friday will be warmer as 850mb temperature climb
into the upper teens Celsius and there will be more sunshine.

Britt

.LONG TERM...  (Saturday through Next Thursday)
Issued at 200 PM CDT Thu Sep 24 2020

Not much change in thinking in the extended part of the forecast
as the upper pattern will transition from quasi-zonal over the
weekend to a highly amplified one by the middle of next week with
a upper high over the western CONUS and a low over the Great
Lakes. The EPS and GEFS means are still in relatively good
agreement that a low amplitude trough with an attendant cold front
will move across the Midwest late in the weekend. This will bring
a chance of showers along and ahead of the front Sunday and
Sunday night along with a slight cool down behind it. A stronger
trough will dig down through the Northern Plains and Midwest on
Monday and Tuesday which still looks like it will bring an
attendant cold front through Missouri and Illinois on Monday
night. This trough may bring a chance of scattered light showers
next week.

Temperature plumes favor highs climbing well into the 80s on
Saturday as 850mb temperatures climb to around 20C.  Temperatures
will climb into the 70s and 80s again on Sunday ahead of the front
before dropping back below normal next week, particularly by
Wednesday and Thursday when ensembles are only showing highs in the
60s and upper 50`s behind the second front.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 956 PM CDT Thu Sep 24 2020

A weak surface ridge extends westward into southeastern MO. A
light southeast wind can be expected late tonight with a
southerly wind on Friday. Fog will develop impacting COU and the
St Louis metro area late tonight and early Friday morning with
patchy stratus clouds also possible in the St Louis metro area
early Friday morning. The lowest visibility will likely occur in
SUS. The fog and stratus clouds will dissipate by late Friday
morning.

SPECIFICS FOR KSTL: A weak surface ridge extends westward into
southeastern MO. A light southeast wind can be expected late
tonight with a southerly wind on Friday. Fog will develop
in the St Louis metro area late tonight and early Friday morning
with patchy stratus clouds also possible early Friday morning.
The fog and stratus clouds will dissipate by late Friday morning.

GKS

&&

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

$$

WFO LSX


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