Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 261726
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1126 AM CST Fri Dec 26 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 342 AM CST FRI DEC 26 2014

Early this morning an upper level trough was located across UT and
AZ. The numerical models show this trough shearing apart with a lead
shortwave trough lifting northeast across NM into western KS and NE
by 12Z SAT. The lead H5 trough will also be filling as it lifts
northeast across western KS into NE.

At 300 AM, a surface cold front was pushing southeast across north
central KS and will gradually push southeastward across the CWA
through the day. Temperatures behind the front were in the lower
30s.

Most models are showing two areas of measurable precipitation
developing this afternoon. As the upper trough begins to lift
northeast across NM into southwest KS, large scale ascent will
develop across western KS and then spread northeast across north
central KS during the late afternoon hours. Forecast soundings show
the precip type across north central KS to be in the form of snow.
In fact the best dendritic growth zone will set up late this
afternoon through the early evening hours. During this period of
time expect light snow with perhaps some moderate snow bands
developing along and northwest of a Delphos to Washington line. This
area could see up to an inch of snow. The second area of measurable
precip will develop across the southeast counties of the CWA as
residual moisture is advected northeast across OK into southeast KS
and western MO. The resulting isentropic lift will may cause periods
of light rain to develop. The remainder of the CWA will probably see
occasional light drizzle develop during the afternoon hours. I
cannot rule out a band of freezing drizzle developing from Ottawa
county northeast in Marshall county. This will depend on how fast
surface temperatures fall below freezing behind the cold front. I
think most of the area will only see temperatures fall into the mid
to upper 30s through the afternoon hours. Highs Today will be
dependent on the speed of the front. A good portion of east central
KS will probably see late morning and early afternoon highs in the
lower to mid 50s. The north central KS will see temperatures
remaining nearly steady in the lower 30s.

Tonight, the upper trough will move from western KS into east
central NE. The better frontogenetical forcing will extend from
western KS, northeast into central NE. The northwest counties will
be on the southeastern fringe of the better forcing. Eventually
enough cold air will advect southeast across the CWA to change the
light rain over to a mixture of snow and rain then snow before
ending last this evening. After 6Z SAT the best ascent will lift
northeast into NE and any snow accumulations will be a dusting to
less than one half inch across the remainder of the CWA. After 6Z
isentropic down-glide develops between 850mb and the surface, thus I
do not see any freezing drizzle developing after midnight. Just
after 12Z, after the precip has ended, overnight lows will drop to
around 20 degrees across north central KS with mid to upper 20s
elsewhere across the CWA. Any moist road surfaces may refreeze
causing slick spots by early Saturday morning.

.LONG TERM...(Saturday through Thursday)
Issued at 342 AM CST FRI DEC 26 2014

Models are in good agreement in a rapid decrease/end to the
precipitation over the eastern cwa by 12z Saturday as drier air and
subsidence aloft overspread the area. A lower level cloud deck will
be slower to clear the cwa on Saturday and have delayed clearing
across the area until mainly the late morning and afternoon hours.
Despite the afternoon sunshine...highs will primarily only top out
in the low to middle 30s. Light winds...dry air and clear skies
should allow temperatures to fall off into the teens and lower 20s
Saturday night. As the primary northern stream shortwave lifts off
to the northeast and the flow aloft backs in response to upstream
troughing in the Rockies...the low level flow will also back around
to the southwest and south into Sunday. Some high clouds may try to
overspread the western portions of the cwa...although the warm air
advection and mostly sunny skies should allow for temperatures to
recover back into the middle and upper 30s.

As the upper trough over the western CONUS and central Canada slowly
deepens...a much stronger Canadian airmass will plunge southward
through the plains bringing much colder air to the region. The front
is expected to advance southward into the cwa Monday. The main
effects in Monday will be felt over the northwest half of the cwa
with highs only in the 20s with highs still making it into the
middle and upper 30s along and south of the Kansas Turnpike.
Temperatures should plunge into the single digits and teens Monday
night as the main push of the colder air arrives. North winds will
push wind chills into the zero to 10 below range most areas by
sunrise Tuesday. Highs Tuesday will then only top out in the teens
across most of the cwa as post frontal clouds and a chance for some
light snow lingers across much of the cwa...although any amounts
look very light as the higher chances will be focused further to the
west of the cwa.

As the Canadian high pressure center shifts off to the south and
east...winds will become more west and southwesterly by Wednesday
and continue into New Years day. This will result in a moderation in
temps back into the 20s on Wednesday then the 30s for New Years Day.

&&

.AVIATION...(For the 18Z TAFs through 18Z Saturday Afternoon)
Issued at 1121 AM CST FRI DEC 26 2014

IFR cigs continue a few more hours at terminals before lifting to
low end MVFR mid afternoon. Precipitation may be sporadic at best,
but do think will bring cigs back to IFR as better chances move in
this evening. Quickly clears west to east before sunrise and lifts
to VFR deck as system exits.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Gargan
LONG TERM...63
AVIATION...67






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