Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262313
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
513 PM CST Fri Dec 26 2014

.SHORT TERM: (Through Sunday Night)
Issued at 329 PM CST Fri Dec 26 2014

Low pressure will develop along the cold front currently over
northwest Missouri in response to shortwave trough ejecting out of
the base of mean trough over the western CONUS tonight.  This low
will move northeast into the Great Lakes by tomorrow at the same
time that the shortwave moves into the the Upper Midwest.  NAM and
GFS show that the cold front will enter the northwest part of the
CWA late tonight and exit the CWA by tomorrow afternoon.  While
precipitation is currently limited on radar over the central CONUS,
expect rain chances to increase rapidly this evening as low level
moisture convergence increases ahead of shortwave trough. Latest
runs of the HRRR as well as the NSSL-WRF have depicted rain
developing throughout the evening hours with it becoming more
concentrated over southeast Missouri into southern Illinois after
midnight. Have continued going forecast trend of increasing
chance PoPs through the evening hours and with likely PoPs over
the southeast half of the CWA after midnight. Then concentrated
likely PoPs tomorrow morning over the southeast half of the CWA
when the GFS depicts increasing mid level frontogenesis associated
with the shortwave trough. Kept a chance of rain or snow going
over the far southeast part of the CWA tomorrow evening before
drier air and subsidence works into the area on Saturday evening.
Sunday and Sunday evening still looks dry at this point.

Kept with falling temperatures will frontal passage tomorrow.
Otherwise MOS guidance are in decent agreement and looks
reasonable.

Britt

.LONG TERM: (Monday through Next Friday)
Issued at 329 PM CST Fri Dec 26 2014

There is relatively good agreement in the global models in that a
positively tilted mean trough will stay established through at
least the first half of next week from central Canada into the
western CONUS. This will keep a relatively fast zonal flow over
MO/IL through most of the period. A large area of surface high
pressure will move under the zonal flow with no real notable
shortwaves troughs that would offer any precipitation chances at
least through Thursday. Model discrepancies show up by Friday as
the operational GFS is faster than it`s own ensemble mean in
ejecting the main upper low out of the southwest toward the
Midwest. While this is faster than the rest of the models, even
the ECMWF is showing precipitation developing over the area in a
broad warm air advection regime ahead of it bringing the upper low
through the area on Saturday. So with this said will go ahead and
introduce snow with some rain to the forecast on Friday.

Cold front will pass through the area on Monday and temperatures
will fall below normal on Tuesday and Wednesday before returning to
near normal for the start of a new year late in the week.

Britt

&&

.AVIATION:  (For the 00z TAFs through 00z Saturday Evening)
Issued at 500 PM CST Fri Dec 26 2014
Wave development along a cold front across far western Missouri
has slowed its eastward movement, so think MVFR cigs will be
delayed for several hours, reaching KCOU around 06Z and KSTL
around 09Z. There may be a few scattered very light showers or
sprinkles before the surface cold front passes. The front will reach
KCOU around 12Z and KSTL by 16Z. MVFR ceilings will continue for
several hours after frontal passage, but MVFR ceilings will
gradually lift to VFR during the afternoon.


Specifics for KSTL: VFR cigs will continue through at least 06Z,
with MVFR cigs reaching KSTL around 09Z. There may be a few
scattered very light showers or sprinkles before the surface cold
front passes. The front will reach KSTL by 16Z. MVFR ceilings
will continue for several hours after frontal passage, but MVFR
ceilings will gradually lift to VFR during the afternoon. MVFR
cigs should last well into Saturday evening.

Browning (WFO LSX)/MAB (EAX CWSU)

&&

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

$$

WFO LSX





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