000
FXUS63 KTOP 281801
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1201 PM CST Sat Feb 28 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 323 AM CST SAT FEB 28 2015

A series of vorticity maxima is noted rotating through the upper
jet from the central plains to the western CONUS early this
morning. First disturbance to bring light to occasionally moderate
snow today is lifting east over southeast CO. Radar imagery at 3
AM depicts bands of light snow beginning to develop eastward into
southern and central Kansas. With low temps this AM in the lower
teens, dewpoint depressions continue to rise in the single digits.

Increasing southerly flow from the southwest indicates mid level
isentropic lift will continue to increase this morning as the upper
trough approaches. Could see some light flurries in the next few
hours south of Interstate 70, before light to moderate snow bands
increase in coverage as they track eastward through the afternoon.
Latest high resolutions models along with the 00Z and 06Z runs of
the operational guidance are continuing to trend the better Q vector
convergence/mid level frontogenesis further south and east of the
CWA based on the track of wave. Overall confidence remains high for
much of the CWA to see periods of snow today. Uncertainty lies in
when snowfall comes to an end on the back side of the wave. The 4 KM
WRF solutions in conjunction with the GFS and NAM are pushing weak
subsidence further south into north central Kansas by early Saturday
evening. This would bring a lull in snowfall while upper level lift
and saturation is maintained through the column along and south of
Interstate 70. For this reason, made slight tweaks by lowering
chances after 6 PM for portions of north central Kansas, keeping
likely pops for most of the CWA.

Models are also having difficulty on redevelopment of snowfall and
the depth of a southward moving upper trough and cold front through
the northern plains. Consensus guidance redevelops light QPF amounts
with the GFS remaining the highest solution and the NAM being the
outlier and dry. As the wave enters the region after midnight, would
expect light snowfall redeveloping across areas along and south of
Interstate 70. This area may see another half to one inch by 6 AM
Sunday morning. In summary, snowfall amounts for today through early
Sunday afternoon were lowered with totals between 2 and 4 inches,
locally up to 5 inches. Locations near and south of Interstate 70
see the highest probability of totals closer to the 3 to 5 inch
range.

In terms of temperatures and winds, main change was to lower highs
today and lows tonight by a few degrees as the incoming wave is
consistent in the warm advection staying south of the CWA. Winds are
not expected to play a factor in hazards with this system, generally
around 10 mph from the south on Saturday, becoming light overnight.

.LONG TERM...(Sunday through Friday)
Issued at 323 AM CST SAT FEB 28 2015

For Sunday morning, confidence in one last frontogenetical band of
snow has diminished given the 00Z and 06Z runs of the NAM drying
mid levels out with no real vertical motion. The new ECMWF shows
some lingering QPF across east central KS through the morning in a
similar location to the GFS. However the GFS is a strong outlier
to the other solutions with its forcing and moisture. Because of
this have continued with POPs in the 60 to 80 percent range over
east central KS but have also backed off on snow accumulations
through the morning and continue tapering POPs down rather
quickly after noon. Models have trended further south with the
warm nose, which may be an indication of the overall southward
trend to the system. Therefore as long as there is ice in the top
of the cloud, precip should be in the form of snow. There are
still signs of conditions symmetric instability Sunday morning, so
there may still be local enhancements to the expected snowfall for
a brief period of time. Trended highs for Sunday down a degree or
two into the lower and mid 30s, especially over east central KS,
thinking there will be very limited insolation, weak cold air
advection and new snow on the ground.

Sunday night and Monday are expected to be dry for the most part
with no obvious shortwave or other organized forcing affecting the
area. The one thing to monitor however is the low level moisture
return progged by the GFS and ECMWF late Monday and Monday night.
Forecast soundings become saturated in the lowest couple KM by
Monday evening implying there is the potential for drizzle to form.
The forecast has a chance for rain Monday night thinking the
vertical motion from increasing vorticity advection would favor
rain rather than drizzle. Another thing to monitor is temps. At
this point, low level warm air advection along with increasing low
level dewpoints support temps generally rising through the night
keeping precip liquid. Have held onto a small sliver of mixed
precip near the NEB state line for when temps may briefly cool to
freezing.

For Tuesday and Tuesday night, models continue to show energy from
the southwest lifting out across the plains while a cold front
moves through early in the afternoon. Because of this there is a
chance for rain. Although there are signs from the models that a
dry slot will work its way into central KS. Because of this the
higher POPs are reserved for far eastern KS. The GFS hints at the
possibility for some weak surface based instability Tuesday
morning. Because of this and for collaboration with neighboring
offices, have introduced a slight chance for thunder southeast of
the turnpike. Think highs Tuesday will be early in the day with
temps dropping back into the 40s and upper 30s through the
afternoon due to strong cold air advection with the front.

There may be some lingering light snow Wednesday behind the front,
but in general expect diminishing chances as dry air with the
surface ridge continues to build south. By Thursday, the upper
trough axis finally moves east of the forecast area with
northwesterly flow aloft redeveloping. This should set up a quiet
period of weather for Thursday and Friday. Temps will again be
cold Wednesday and Wednesday night as the latest arctic surface
ridge moves over the area. DID not go as cold as the GFS would
have it since the ECMWF is not quite as strong with the high
pressure system. By the end of the week, the forecast area could
return to southerly return flow with warm air advecting in from
the southwest. With this in mind, have temps warming back into the
lower 50s by Friday.

&&

.AVIATION...(For the 18Z TAFs through 18Z Sunday Afternoon)
Issued at 1150 AM CST SAT FEB 28 2015

MVFR conditions will likely continue this afternoon. Expect some
heavier periods of snow at least for the early part of the
afternoon with the areas of best lift and forcing. We could see
IFR conditions similar to earlier with these bands. This evening,
the first wave will have moved through with some gradual
improvement before the second wave arrives around midnight time
frame. Confidence with timing on this second round is a little on
the low end, but MVFR conditions are expected to remain in place
until after the forecast period. For longer term planning, check
back with the 00z and 06z TAF issuances for updates on second
round timing.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until Noon CST Sunday FOR KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Bowen
LONG TERM...Wolters
AVIATION...Drake