Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150914

Area Forecast Discussion
National Weather Service Saint Louis MO
314 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 06z TAFs through 06z Wednesday Night)
Issued at 1120 PM CST Tue Nov 14 2017

CIGs will continue to lower overnight as rain moves in and clouds
thicken ahead of a surface cold front. Places that are currently
MVFR (UIN, COU) should transition to IFR while places that are
currently VFR (STL Metro sites) should transition to MVFR. This
will then continue until a few hours after cold FROPA when rapid
clearing is anticipated. Cold FROPA is anticipated to be around
mid morning Wednesday for UIN and COU and midday Wednesday for the
STL metro sites. Ahead of the front, expect a moderate southerly
flow around 10kts while behind it winds will become gusty out of
the NW to 20-25kts. Winds should diminish around sunset. Best rain
chances will be until just before cold FROPA.

SPECIFICS FOR KSTL: There is some potential for CIGs at STL to
drop into IFR category briefly during the mid to late morning
hours just ahead of and at cold FROPA. For now have dropped to
OVC010 but it will be a race between diurnal influences and
typical biases of a cloud deck moving in from the NW as there is
high probability of IFR CIGs for areas north and west of STL


Saint Louis     57  34  48  37 / 100   0   0   5
Quincy          55  28  45  36 /  50   0   0   5
Columbia        58  31  50  40 /  60   0   0   5
Jefferson City  59  31  52  41 /  70   0   0   5
Salem           55  32  47  34 / 100   0   0   0
Farmington      58  33  51  36 / 100   0   0   5



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