Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 272215

415 PM CST Sat Dec 27 2014

Issued at 413 PM CST Sat Dec 27 2014

Quick update to the forecast to boost POPs to categorical as band
of rain has formed in wake of the front. Rain is mixing with sleet
and snow where lower atmosphere has cooled into the middle 30s. No
accumulation is expected due to warm surface/ground temperatures.

No other changes made at this time.



.SHORT TERM:  (Through Late Tonight)
Issued at 341 PM CST Sat Dec 27 2014

Cold front is exiting forecast area. Still have lingering light rain
mixed with light snow on backside of system. This area of
precipitation will continue to move to the east tonight, tapering
off from west to east. Even though temperatures dropping off into
the 30s behind this front this evening, the ground is too warm for
any accumulation where the snow falls. As system moves away from
region, will see clouds begin to scatter out over central and
northeast Missouri as well as west central Illinois towards
daybreak. Lows will range from the low 20s to low 30s.


.LONG TERM: (Sunday through Next Saturday)
Issued at 341 PM CST Sat Dec 27 2014

(Sunday through Tuesday)

Expect mainly dry conditions through early next week as the GFS and
NAM show that precipitation with current system will continue move
off to the southeast tomorrow as subsidence and dry air move into
the area.  Only chance of precipitation will be associated with weak
shortwave trough that will move quickly across the area on Monday
night.  The NAM/GFS/ECMWF all show weak ascent with some moisture
moving across the area on Monday night, but only the NAM develops a
meager amount of QPF across the northeast Missouri and west central
Illinois.  Have introduced a slight chance of light snow because of
this, and feel that the strength of the vort max and the amount of
available moisture is enough for a chance of flurries over most of
the CWA on Monday night before it exits the area by Tuesday

Temperatures will fall back below normal after being warm for
several days.  Used a blend of temperature guidance the next few

(Wednesday through Saturday)

Upper low will eject out of the southwest CONUS and move eastward
sometime Friday or Saturday which will give us a chance of wintry
precipitation.  Confidence in this forecast is not high as there are
still differences in the operational models runs today.  The fairly
consistent GFS is still much faster and ahead of most of it`s own
ensemble members while the ECMWF has shown some continuity problems
but is in decent agreement with the GEM.  Even with this said, it
still looks like Wednesday and Thursday will be dry with
temperatures on Wednesday below normal with 850mb temperatures
around -10C and slight cold air advection at the surface before they
begin to moderate on New Years Day.  Even though that there are
significant differences by Friday with respect to how quickly the
upper low will moves through area, both models are showing
precipitation developing over the area.  The GFS develops
precipitation ahead of it`s faster upper low solution whereas the
ECMWF has a broad area of warm air advection/low level moisture
convergence developing across the Mid Mississippi Valley.  Will
continue the chance of rain/snow that is already in the forecast
Thursday night into Friday.  There could be some sleet or freezing
rain in the mix during this period given that warm air will likely
be advecting in over colder air at the surface, but will hold off
mentioning it at this time given the uncertainties in the forecast.
Currently have the rain/snow chances continuing into Friday night
before lowering them to slight chances over all but the
southeastern part of the CWA by Saturday.  At this point, the GFS
would move the precipitation off to the east and ECMWF`s track is
farther to the south which would act to move the wintry mix out
quicker to the south during the day.



.AVIATION:  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1150 AM CST Sat Dec 27 2014

Cold front has moved through taf sites, so winds have veered to
the northwest. MVFR cigs to persist through the afternoon hours
with some light rain/light snow. But hard to pin down where it
will fall. For now just have light snow at KCOU, dry elsewhere.
Cigs to begin lifting and scattering out late this afternoon/early
this evening. Mostly clear skies expected rest of forecast period
with light northwest winds. Could see some light fog at KUIN, so
added tempo mention between 09z-13z Sunday. Enough high clouds at
rest of taf sites to help keep any fog at bay.

Specifics for KSTL:
Cold front has moved through metro area, so winds have veered to the
northwest. MVFR cigs to persist through the afternoon hours with
some light rain/light snow. But hard to pin down where it will
fall. For now have dry taf. Cigs to begin lifting and scattering
out by 01z Sunday. Then high thin cirrus expected rest of
forecast period with light northwest winds.





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