Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151831
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1231 PM CST Wed Nov 15 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 311 AM CST Wed Nov 15 2017

The coverage of showers has exploded since midnight in response to
lift with the strengthening southwesterly LLJ, and as large scale
ascent associated with the upstream short wave spreads into the
area. This trend is expected to continue into the early morning
hours as the short wave continues to move east and large scale
ascent increases. As expected there have also been a few embedded
thunderstorms supported by elevated instability with MUCAPE from 250-
500 J/KG. The models are in rather good agreement that large scale
lift associated with the migratory short wave will be east of the
CWA by 18Z, and given the lion`s share of precipitation is
associated with this lift, there will be only minimal precip chances
remaining into early this afternoon. Those will be confined to a
small area from south central IL into extreme southeast MO, well
ahead of the advancing cold front. Present indications are the cold
front should be thru the CWA by 21Z. Temperatures today are a bit
tricky. They have decreased due to evaporative cooling with the
precipitation since midnight, and there will also be some slight WAA
component ahead of the front. The back edge of post-frontal stratus
currently lags the cold front by anywhere from 40-70 miles or so.
Thus, with the post-frontal clouds and CAA/gusty northwest winds
there will be a period of more defined cooling before the clouds
clear. This will be most impactful in southeast MO and southwest IL
as clearing won`t be until late in the afternoon, whereas northeast
and central MO will have time for a temperature rebound. Tranquil
weather, clear skies, and slightly below normal temperatures are
forecast tonight as surface high pressure settles into the MS Valley
in the wake of the cold front.

Glass

.LONG TERM...  (Thursday through Tuesday)
Issued at 311 AM CST Wed Nov 15 2017

(Thursday-Thursday Night)

Still looks to be dry and tranquil through Thursday night as surface
ridge moves off to the east. Highs on Thursday will be about 5 to 10
degrees below normal, in the mid 40s to mid 50s. Lows Thursday night
will be in the mid 30s to low 40s.

(Friday - Saturday)

By Friday, warm southerly winds kick in with low level moisture on
the increase. So still expect scattered showers to develop across
region. As for temperatures, still some uncertainty on how warm it
will get depending on development and spread of stratus. For now
have mid 50s northeast to the upper 60s over central MO. This WAA is
due to south winds ramping up to 10 to 20 mph with gusts to near 25
mph at times.

00z model runs still have some timing differences with GFS a bit
faster, especially after 12z Saturday, as stronger shortwave aloft
lifts system into Great Lakes region, dragging front out of forecast
area between 12z-14z Saturday. ECMWF doesn`t have cold front exit
forecast area til closer to 18z Saturday. So for now kept a blend of
the two models, with best chances of showers and some thunderstorms
Friday night/Saturday morning. With timing of precipitation and
little if any instability, feel that severe chances are greatly
diminished.

Still expect some wrap around showers on back side of system during
the day on Saturday, then taper off by late Saturday afternoon. With
colder air filtering and gusty northwest winds, will see steady or
slowly falling temperatures Saturday afternoon.

(Saturday Night - Tuesday)

Dry and below normal conditions expected for the last half the
weekend with lows Saturday night in the mid 20s to low 30s. Highs on
Sunday will only be in the 40s. By Monday, surface ridge moves off
to the east allowing southerly winds to return once again and temps
to moderate, warming into the upper 40s to mid 50s for Monday and
Tuesday.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1219 PM CST Wed Nov 15 2017

A cold front is moving across the area this afternoon. The front
currently stretches from near K3LF to KBLV to near KFAM. Current
indications are that the front will be through the remainder of
the forecast area by 20-21Z. MVFR flight conditions will prevail
ahead of the front across southeast Missouri and southern
Illinois, but the rest of the area behind the front will be VFR.
Wind is picking up from the northwest behind the front with gusts
to 20-25kts. Expect wind to diminish this evening, becoming light
and variable by early Thursday morning. VFR flight conditions are
expected to prevail across the area tonight and into Thursday
morning. There may be a few MVFR level clouds across northeast
Missouri and west central Illinois tonight as the cloud deck over
northern Iowa continues to sink south...though confidence is low
on how far it will get.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail after the clouds
clear out over the next hour or so. Gusty northwest flow up to
around 20-25kts this afternoon will diminish this evening and then
become light and variable overnight. Wind will turn to the east-
southeast Thursday afternoon as high pressure moves east of the
region.

Carney

&&

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

$$

WFO LSX


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