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FXUS63 KTOP 041145 AAA
AFDTOP

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TOPEKA KS
545 AM CST Wed Dec 4 2013

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 334 AM CST WED DEC 4 2013

Cold front moving through east central Kansas at 3 am with winds
gradually becoming northerly which should allow for the low
visibilities in fog to slowly increase this morning and will
likely either let dense fog advisory go until expiration or even
cancel early in drier air advects in faster. Otherwise stratus
expanded overnight with isentropic lift north of the front.
Increasing ascent within the cloud layer has aided the development
of drizzle across much of the county warning area...with freezing
drizzle occurring over the north central where temperatures have
dropped below freezing. Expect the stronger forcing/lift to shift
eastward across the CWA through mid morning with a trend of
increasing drizzle in the east and decreasing/diminishing trend to
the freezing drizzle in the north central. If the freezing drizzle
or its intensity persists longer than expected in the colder air
over the north central counties...a winter weather advisory may be
needed. Will continue to monitor trends through sunrise. Either
way...am expecting the southeast 2/3 of the CWA to remain warm
enough this morning to not produce any freezing drizzle. Otherwise
it will be a mostly cloudy and much colder day with highs only
recovering about 4 to 6 degrees above the morning lows with highs
ranging from around 30 north central to the middle 40s in the
Garnett area. Although expecting a dry afternoon...there will be
another opportunity for some very light snow/snow flurries over
the north central counties as the southern extension of a vort lobe
in the northern plains clips the area. The bid weather story for
tonight will be the continued downward trend in temps with lows
falling into the teens...although the northwest winds will push
wind chill indices as low as 5 above east central to 5 below in
the north central.

.LONG TERM...(Thursday through Tuesday)
Issued at 334 AM CST WED DEC 4 2013

Models have trended in pushing the deeper moisture and better
saturation south of the forecast area for Thursday through Friday
morning. And while there is likely to be some frontogenetical
forcing across the area, both the NAM and GFS indicate there will
be some dry air in the lowest couple of kilometers for any light
precip to overcome and the ageostrophic component of the frontal
circulation does not look to be very deep. Vertical motion in
general appears to be maximized south of the forecast area so am
not sure whether the weak CSI that briefly moves across east
central KS will play much of a role. So in general am not to
excited about precip chances Thursday through Friday morning. The
better chances will be across Coffey and Anderson counties where
accumulations around a half inch are possible. If better
saturation is able to move a little further north, than amounts
could be a little higher given snow to water ratios on the order
of 17 to 1. However a fairly deep northerly wind through 850 MB
suggests there will not be much moisture advection going on. So
have adjusted POPs generally lower for much of the forecast area
save the far southeastern corner where some chance POPs where
maintained. Strong cold air advection and 925 temps between -10
and -14C support the going forecast for highs in the lower to mid
20s. A north wind of 10 to 15 MPH will likely cause wind chill
readings to be between zero and -10F.

The moisture and forcing exit to the east by Friday afternoon and
Saturday leaving a cold dry forecast. Cold air advection persists
into Saturday with the arctic surface ridge to the north of the
forecast area. So there really isn`t much hope of a warm up even
with some sunshine.

The better chances for snow look to be late Saturday night and
into Sunday evening as the ECMWF/GEM/GFS continue to show a
slightly positively tilted shortwave tracking across the state.
There doesn`t appear to be much in the way of cyclogenesis with
the wave so forcing for precip is not overwhelming. Nevertheless
models have been persistent in some broad vertical motion with the
PVA of the wave and forecast soundings indicate saturation will
not be a problem. Because of the model consistency over the past
three days, have bumped up POPs into the 40 to 50 percent range.
The GFS BUFKIT data suggests that snow to water ratios will remain
between 15 and 20 to 1 due to the very cold airmass in place. With
this being the case, it would not be out of the question for the
forecast area to see 1 to 3 inches of accumulation through the day
Sunday.

With overcast skies likely, do not anticipate much of a warm up
for Sunday. Then the cold air advection recommences for Sunday
night into Monday. Therefore the bitter cold is expected to
continue into Tuesday. There are signs that mid level heights will
begin to rise for Tuesday as the long wave trough breaks down and
mid level flow becomes more zonal. This would favor a warming
trend in temps, but is the first run the ECMWF has shown the
pattern breaking down so have not made many changes to the temps
from the prev forecast just yet.

&&

.AVIATION...(For the 12Z TAFs through 12Z Thursday Morning)
Issued at 537 AM CST WED DEC 4 2013

Occasional drizzle will persist until the 14-16z time frame west to
east across the terminal sites. Primarily LIFR cigs and vsbys
will improve to vfr vsbys by 16z as cigs become mvfr. Ceilings
will remain mvfr until 00z/05 when they should scatter at FL025
and remain vfr remainder of fcst. North/northwest winds will increase
through 15z with gusts over 20kts remainder of fcst.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY until 8 AM CST this morning FOR KSZ054>056-
058-059.

WINTER WEATHER ADVISORY until 9 AM CST this morning FOR KSZ008-
009-020-021-034.

&&

$$

SHORT TERM...63
LONG TERM...Wolters
AVIATION...63