Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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FXUS63 KEAX 142333

533 PM CST Sun Dec 14 2014

Issued at 331 PM CST SUN DEC 14 2014

Mid-afternoon VIS satellite imagery showing a well-defined cyclonic
swirl across the OK/TX Panhandles as long awaited upper closed low
slowly inches eastward. Meanwhile...latest water vapor pics showing
main mid-level circulation beginning to lift northeast as additional
shortwave energy is now phasing with initial southern stream wave. A
little closer to home...regional radars showing an elongated band of
convection stretching from central OK north into central Kansas this
afternoon as weakly unstable air (MLCAPE values on the order of
500-1000 J/kg) continues to advect north into the central Plains
ahead of approaching storm system. Latest model guidance in excellent
agreement that shwrs with perhaps a few rumbles of thunder should
begin to enter western portions of the fcst area shortly after 00z
this evening...with steady eastward progress then expected through
the early overnight period. Models do show a fairly healthy dryslot
trying to wrap north into the region overnight and as a
result...rainfall converge and intensity may begin to wane a little
during the early morning hrs. Despite this...main frontal boundary
associated with this feature expected to hold off until later during
the day on Monday which should allow a fairly warm night across the
area with lows generally falling into the upper 40s to lower 50s.

On Monday...main mid-level closed low to track directly over the
fcst area which should lead to a gradual uptick in shwr activity as
lapse rates increase due to the cold pool aloft. Models show a
gradual decrease in MLCAPE but would not be surprised to see a few
lightning strikes from time to time. Additionally...synoptic-scale
setup favors the possible development of cold air funnels during the
day...but fortunately...these should serve as nothing more than a
photo opportunity to those who happen to catch them if they do indeed
develop. Temps through the late afternoon should fall steadily as
cold air finally reinvades the region following the passage of a
fairly strong frontal boundary. Behind this...expect increasing
northwest winds with gusts as high as 30 mph continuing through the
early overnight period.

Low clouds look to hang around until at least midday Tuesday before
drier air finally starts to work into the region as high pressure
begins settling south across the northern Plains and upper Miss Rvr
Vly. This will set the stage for a couple of dry but chilly days as
persistent northeast flow continues to advect cool air south across
our region.

Fcst becomes much more complicated and interesting by late Wednesday
as model signals continue to hint at a developing winter precip
scenario during the Wednesday ngt/Thursday time frame. Unfortunately
a fair amount of model uncertainty still exists with the overall
progression of what appears to be two separate weather features of
interest during the extended time frame. First...let/s talk about
the first system.

Upper-level flow to become highly amplified by midweek as another
upper trough/closed slow approaches the West Coast. Downstream...flow
expected to become more zonal across the Nation/s Heartland as area
will reside in-between deep upper troughing across the Northeast
while amplified ridging begins building into the Pacific Northwest.
Out ahead of this ridge...weak northern stream energy expected to
slowly dive southeast into the Plains and eventually mid Miss Rvr Vly
by midweek. Meanwhile well to our south...a strong thermal gradient
will exist as cold Canadian High Pressure remains nearly stationary
across the western Great Lakes/upper Miss Rvr Vly while return flow
out ahead of a southern stream wave initiates return flow across the
western Gulf Coast. Models (particularly the GEM and ECMWF) show
developing snow across our area Wed night as northern wave begins to
move over our region. The GFS does have some hint of this
scenario...however bulk of its model QPF is delayed until the
secondary wave begins moving out of the southern Plains later in the
fcst period. That said...have once again looked at the St. Louis
historical snow analogs and confidence appears to be increasing for
some measurable snowfall with this lead shortwave if in fact enough
moisture can work north and overcome the dry air from strong high
pressure to the north. Additionally...probabilities for developing
wintry wx also increasing on the experimental internal WPC days 4-7
winter fcsts. With cold air well entrenched over the area...a couple
of inches cannot be ruled out before lead wave slides east later

Following this feature...focus will quickly shift to the secondary
southern stream wave which is expected to begin wrecking havoc
anywhere from the ARKLATEX region north into the mid Miss Rvr Vly by
the upcoming weekend. The ECMWF and Canadian GEM suggest this feature
will remain far enough south not to have much impact while the GFS
takes the 850-hPa low far enough north to have what could be higher
consequences for our area. Considering there/s not much of a clear
signal on which solution to follow this far out into the
future...decided to maintain mid-range chc pops through the
conclusion of the fcst period.


.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 532 PM CST SUN DEC 14 2014

Combination of low end VFR and high end MVFR conditions are currently
prevailing at the terminals, but the line of storms to our west will
fix that over the next few hours. Have timed rain to reach the
terminals around 02Z to 03Z this evening. Should have several hours
of rain, but then went to a VCSH for early Monday morning as the line
is a bit discrete. Scattered showers will likely redevelop late
Monday morning as the upper level system moves across. Otherwise,
have inserted gusty winds for the late afternoon hours as a tight
pressure gradient moves in behind the exiting storm system.




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