Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 180546
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1146 PM CST Wed Dec 17 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Tonight)
Issued at 329 PM CST WED DEC 17 2014

The forecast for tonight continues to be on track with little change
in expected snowfall amounts. Precipitation continued to develop
ahead of the lead shortwave moving across the Texas Panhandle across
much of Oklahoma into southern Kansas. Stronger second wave was
pivoting northeast and was located over eastern New Mexico. Moisture
will continue to spread northward this evening. High resolution
short term models spread the precipitation northeast into the
forecast area this evening. Forecast soundings show moistening of
the low levels this evening due to evaporative cooling with the
onset of precipitation. Soundings still show a brief window of sleet
with the onset of precipitation and have already had some isolated
ice pellets or light snow fall this afternoon. Cross sections show
deep layer frontogenesis along with some convective instability as
well as some CSI (convective symmetric instability) so it is still
likely that we will see some southwest to northeast oriented bands
develop with locally higher amounts. There also may be some isolated
thunder as well as a few lightning strikes. In general have tweaked
the snow amounts slightly upward from the prior forecast, but by
only a few tenths of an inch. Timing is just a little slower for the
onset of the precipitation, mainly for areas along the Nebraska
border and have delayed onset by a couple of hours. Strongest upward
vertical motion is expected across the forecast area from mid-late
evening into the early morning hours on Thursday as the shortwave
trough rotates northeast. Expect the best snowfall rates during this
period, before tapering off. Also with there may be some freezing
drizzle mixing with the snow after 4 AM Thursday as soundings
briefly show some drying the in the dendritic ice crystal growth
region. Will see little diurnal temperature change tonight with lows
in the mid to upper 20s. No change to the winter weather advisory
for tonight across the area.

.LONG TERM...(Thursday through Wednesday)
Issued at 329 PM CST WED DEC 17 2014

In the wake of the exiting shortwave trough early Thursday...drying
will take place above 700mb with time...but remain fairly saturated
below. Therefore...although there may be some lingering very light
snow/flurries...the lack of cloud ice aloft and weak forcing in the
low levels will still favor some patchy freezing drizzle as
temperatures remain at or below freezing for much of the day. The
lift is weak and any additional accumulations of light snow or
freezing drizzle beyond 9 am should be very light. This scenario may
linger into Thursday night as well as the northern stream and the next
southern stream shortwaves approach and begin to phase...but any
precipitation should remain very light and patchy if at all. The
phasing of the two upper trough will focus precip to the south and
east of the county warning area into Friday so will keep Friday and
Friday night dry. Lowered highs through the 30s on Thursday and
Friday with the expected snowcover and overcast conditions.

May see some breaks in the clouds by Saturday...but expect to still
be dealing with some residual snow on the ground in some places...so
have limited highs to the upper 30s to lower 40s. Warm advection
will increase across the area into Sunday ahead of the next
deepening trough over the northern plains. Will therefore warm highs
through the mid and upper 40s Sunday into Monday before the next
cold front Monday night lowers highs back into the upper 30s and
lower 40s. Will keep a chance for rain across mainly the eastern
portions of the cwa Sunday night into Monday in the warm
sector...then a chance for rain or snow Monday night and  Tuesday
with the colder air in the wake of the front.

Will go dry in the wake of the departing trough on Wednesday but
keep highs in the upper 30s and lower 40s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Thursday Night)
Issued at 1140 PM CST WED DEC 17 2014

Expect heavier snows at TAF sites to occur mainly between now and
09z before backing off in intensity through the morning hours.
Cigs will still be low however and IFR conditions continue. Think
cigs will start to lift at or above 1000ft agl around the noon
hour.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...53
LONG TERM...63
AVIATION...67





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