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000
FXUS63 KTOP 121128
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
528 AM CST Thu Dec 12 2013

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 343 AM CST THU DEC 12 2013

Surface high pressure centered over the mid MS valley as of 08Z will
continue to retreat eastward this morning. Winds have already
shifted to the south southwest and will steadily increase through
the morning. The increasing winds should promote boundary layer
mixing and prevent temperatures from falling. With the aid of the
southerly flow temps will generally increase as well. Sunny skies
today give way to high temperatures in the low 40s with the
exception of the areas with snow cover along the KS/NE state line
where highs only reach the mid 30s. The southwesterly winds stay
increased during the daytime hours with gusts up to 25 mph possible
especially along and south of interstate 70, where deeper mixing
will occur due to the lack of snow cover.

The next system to affect northeast KS will kick out of the northern
Baja and lift northeast into the SW CONUS and eventually the
southern Plains. Meanwhile, as the surface high pressure retreats
eastward return flow on the back side allows low level moisture to
surge northward into TX and OK during the day today. That moisture
in the form of low stratus and fog reaches southern KS later this
evening, and portions of east central KS by midnight, then finally
northeast KS by sunrise tomorrow. Later this evening clear skies and
decoupling winds support decent radiational cooling with all areas
falling below freezing before the moisture arrives. Latest guidance
is suggesting dense fog will be possible for a majority of the area
during the early morning hours tomorrow as the moisture works into
the cool air mass in place. Forecast soundings show that there is
low level lift maximized around 850 mb, which happens to be above
the saturated boundary layer...therefore do not expect any drizzle
across the forecast area before 12Z. Low temperatures for Friday
morning will likely depend on the speed and extent of the cloud
cover. For southern portions of the area the lows should occur in
the late evening hours before the clouds arrive. The northern areas
will have more time to cool and also be under the influence of snow
cover as well, but expect the clouds will reach those areas by
sunrise. With that said lows should range from the mid 20s in east
central KS to the upper 10s along the KS/NE state line.

.LONG TERM...(Friday through Wednesday)
Issued at 343 AM CST THU DEC 12 2013

Southwesterly 850mb winds will advect somewhat deeper moisture
northeast across eastern KS during the morning hours. Temperatures
by 12Z FRI will be in the upper 20s to lower 30s across East Central
Kansas, thus as the moisture advect north above the shallow cold
airmass the resulting isentropic lift will cause freezing drizzle
and light freezing rain to develop from south to north across the
eastern counties of the CWA. The southerly surface winds will
gradually advect slightly warmer air northward through the morning
hours. Areas along and south of I-35 will probably switch over to
rain by 9 AM and the remainder of the eastern counties of the CWA
should see an all rain pattern by Noon. There may be some slick
roadways developing as the freezing drizzle and light freezing rain
develops northward across the eastern counties of the CWA through
the mid morning hours.

As the upper trough axis shifts east across western KS and western
OK during the late afternoon hours, stronger ascent will cause the
vertical temperatures profiles to cool allowing the light rain to
begin to mix with snow and ice pellets across northeast KS. The mix
precip should spread southeast across east central KS during the
early evening hours and eventually change over to light snow. The
last two runs of the ECMWF are not as amplified with the upper level
trough as the 00Z WED run. The stronger frontogenetical forcing will
remain south of the area across eastern OK and AR, then northeast
into MO. The ECMWF and GEM models continue to show a weaker TROWAL
developing across East Central KS...thus there could be around an
inch of snowfall with some isolated 2 inch amounts along the MO
border by 12Z Saturday for areas along and southeast of the KS
turnpike. Both the NAM and GFS fill the H5 trough as it shifts east
across the southern plains. The NAM model show little ascent and the
dendritic growth zone region remains unsaturated. The NAM model
shows more of a drizzle to freezing drizzle event through the
evening hours of Friday. Given the continued uncertainty in the
numerical models, I kept a chance for snow across northeast KS with
a rain and snow mix changing over to snow across the southeast
counties during the mid and late evening hours. I also placed a
chance for freezing drizzle as well in case the NAM model verifies.
A cold front will move southward across the CWA Friday night, thus
lows will eventually drop into the mid teens across north central KS
and lower to mid 20s across east central KS.

Saturday and Saturday Night, a Cold surface ridge will build
southward across eastern KS. A secondary H5 trough will move east
across TX and will keep any precip well south of the CWA. Skies will
clear from northwest to southeast across the CWA during the morning
hours of Saturday. Highs will range from the mid 20s across the
northern counties of the CWA to lower 30s across the southern
counties. Brisk northerly winds will diminish through the afternoon
hours. Clear skies and light winds will allow overnight lows to drop
into the teens, perhaps some single digits across the extreme
northeast counties.

Sunday through Wednesday, the upper level flow will become more
zonal into the middle of next week. Expect dry conditions with a
warm up into Tuesday with Highs on Sunday warming into the upper 30s
east to mid 40s west. Tuesday`s Highs will warm into the lower to
mid 40s east and upper 40s west. An upper level trough will dig
southeast out of Canada into the northern plains Tuesday Night. This
will cause a weak front to push southeast across the CWA Wednesday
Morning, which may cause Highs on Wednesday afternoon to cool
slightly back to the lower to mid 40s.

The longer range models continue to show another Arctic front
pushing southward across the plains by Friday, December 20th. Thus
it may remain quite frigid through late December. The upper trough
will dig southeast, farther east across the plains. If this solution
were to verify, any snow storm that develops will be east of KS
across the mid MS river valley and northeast into New England. The
extended models could change, so it will be best to keep up with the
latest forecast if you are planning any Holiday travel.

&&

.AVIATION...(For the 12Z TAFs through 12Z Friday Morning)
Issued at 514 AM CST THU DEC 12 2013

Conditions are expected to be VFR until around 06Z when low level
moisture works into the area. Confidence is high that the ceilings
will be most likely be IFR, and visibilities will be restricted.
The uncertainty is how low the ceilings and visibilities actually
get before the end of the period, and the arrival times at each
site. There is the possibility of dense fog, but surface winds
may inhibit development unless they go calm. These details will need
to be adjusted and tweaked as the event gets closer.

&&

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

$$

SHORT TERM...Sanders
LONG TERM...Gargan
AVIATION...Sanders