Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 161748
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1148 AM CST Tue Dec 16 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 326 AM CST Tue Dec 16 2014

Surface low currently over Quad Cities and will continue to lift
northeast today away from forecast area. Some lingering light
rain/drizzle to persist in wrap around this morning, mainly along
and east of Mississippi River. Otherwise, sc deck to be very slow to
move out of region, as high RH at 925mb remains entrenched over
forecast area today. As for temperatures, colder air to filter in
with temps still dropping a little this morning before becoming
steady or rise a few degrees by the early afternoon hours.

Byrd

.LONG TERM:  (Tonight through Monday)
Issued at 326 AM CST Tue Dec 16 2014

It will remain mostly cloudy tonight with lows in the 20s. On
Wednesday we remain under surface ridge with partly cloudy skies and
highs in the mid 30s to low 40s.

Then the forecast for Wednesday night through Thursday is still
tricky to pin down. Surface ridge moves off to the east with upper
trof developing over southwestern US. Will see pieces of energy
eject out of trof and track through forecast area Wednesday night
and Thursday. We will remain in cold air so any precipitation that
does develop with these shortwaves will be in the form of light snow
for most of the area. QPF amounts will be on the light side with
highest amounts over southern sections of our forecast area. Could
see a few tenths of snowfall with highest amounts south of a
Columbia to Fredericktown line.

Beyond that, extended models still have differing solutions on
system that will remain south of forecast area Friday through
Saturday. GFS is a bit further north then ECMWF. For now will not
make major changes to pops through this period. As for pcpn type,
will cold air in place, should be all light snow.

Byrd

&&

.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1112 AM CST Tue Dec 16 2014

The primary forecast question for this set of TAFs is whether the
stratus will end during the next 24 hours. On one hand, there`s an
extensive area of stratus located upstream as well as northwest
winds which will continue advecting the clouds into MO/IL. On the
other hand, there`s also a hole in the aforementioned cloud bank,
and RAP forecasts (CPD) as well as BUFKIT soundings show
additional drying, which suggests that existing clouds should
start to dissipate and that it will be difficult for new clouds to
develop even within cyclonic flow. On the other other hand, the
cig/vis trend viewer in AVNFPS is evenly split on whether clouds
usually persist through 12z or become less likely after 04-06z,
depending on what conditions look like at 21z and 00z. In short,
there is a surprisingly high amount of uncertainty with the cig
forecast. This set of TAFs splits the difference and keeps MVFR
ceilings in place through 06-08z, but it`s equally likely that
ceilings could improve earlier than forecast or persist later than
forecast.

Specifics for KSTL: It`s equally likely that MVFR stratus could
persist beyond 12z or depart earlier around 06z. There might also
be a brief break between 23z-02z, depending on what happens with
the hole in the clouds over IA which was noted on satellite
imagery at TAF issuance. Regardless of what happens with the MVFR
stratus, increasing mid and high level clouds are expected after
12z.

Kanofsky

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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