Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KLSX 151149

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
549 AM 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.


.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

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



.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 534 AM CST Wed Nov 15 2017

A cold front was located across northwest MO early this morning. A
large area of predominately MVFR flight conditions prevailed ahead
of the front with a small region of IFR in northeast MO. This
front will move southeast today with showers and some isolated
thunderstorms impacting the St. Louis region this morning. MFVR
flight conditions will generally be the rule until 2-3 hours
after the cold frontal passage, at which time conditions should
improve to VFR. Gusty northwest winds will also accompany the
fropa with winds diminishing early this evening. VFR flight
conditions/clear skies and increasingly light winds are expected
as the night progresses as high pressure settles into the area.


Low-end VFR to MVFR flight conditions are expected through mid
morning with waves of showers and maybe a rumble of thunder. MVFR
flight conditions will then become more predominant after mid-
morning. A cold front will move through the terminal near midday
accompanied by gusty northwest winds. The MVFR flight conditions
will persist until around 2-3 hours after the cold frontal
passage, at which time conditions should improve to VFR. Gusty
northwest winds will diminish this evening with VFR flight
conditions/clear skies and increasingly light winds expected as
the night progresses.





WFO LSX is the U.S. government's official web portal to all federal, state and local government web resources and services.