000
FXUS63 KTOP 062329
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
529 PM CST Fri Dec 6 2013

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 223 PM CST FRI DEC 6 2013

The short term period is rather  quiet as surface high pressure
over north central Nebraska gradually builds southeast...becoming
centered over southeast Nebraska as a 1045 hPa surface high. The
airmass associated with this high is obviously very
cold...multiple observation sites in northern Nebraska have not
risen above 0 today...and should coincide with a relatively cloud
free period between midnight tonight and noon tomorrow.
Radiational cooling will be efficient as the thin cloud cover
clears out this evening, but the pressure gradient should be
sufficient to maintain a light northerly breeze through the night,
thus keeping temps a bit warmer than they would be with calm
winds. Regardless of any breeze, expect overnight low
temperatures to range from around -5 in north central KS to +5 in
east central KS, with potential for colder temps if winds are able
to become calm. While light, the breeze will have an impact on
wind chill values overnight with minimum values forecast to range
from -5 to -13, again with some small potential to go colder yet.
Wind chill advisory criteria is -15 to -24 so an advisory does not
appear warranted at this time, but colder temperatures or slightly
increased winds could result in some -15 to -18 readings near the
Nebraska border.

After a very cold start, Saturday will warm up into the upper teens
once again with winds turning out of the southeast and very
gradually increasing. Deep and persistent isentropic ascent will
develop across the area by late Saturday in advance of the next
storm system. This ascent will increase with time, but at least
through the daylight hours on Saturday the lift is expected to go
purely into cloud development and gradual saturation of a very dry
airmass...with no precip expected during the day.

.LONG TERM...(Saturday Night through Friday)
Issued at 223 PM CST FRI DEC 6 2013

Light snow still on track for the forecast area Saturday night
into Sunday. As upper trof and associated lift moves eastward,
snow begins in western zones before midnight and spreads across
the remainder of the area by sunrise. Qvectors, PVA and
frontogenetic forcing continue to favor areas across the north and
north central counties through the noon hour, with lighter amounts
to the south. NAM steepens the low level lapse rates into the
afternoon, and generates some instability in the low levels, while
GFS is less so. Could see some afternoon snow showers across the
east central counties as the lapse rates steepen into the -10/-12
range at the top of the mixed layer, but with limited moisture
don`t expect these to produce much accumulation. Totals now range
from about an inch over Franklin/Anderson counties to 2-3 inches
in NC counties and along the Nebraska border. Northeast counties
will be slowest to clear and may have light snow into the evening
hours. Could make for slick spots with snow falling overnight
especially to the north, but not expecting advisory amounts at
this time. Highs in the 20s expected.

Sunday night the reinforcing cold shot of air drops southeast
behind the wave that brought the snow Sunday, with lows in the
single digits to low teens for early Monday. Another day with
highs only in the teens. Lows Monday night similar to previous.

By Tuesday the surface return flow starts to undercut the colder
air aloft, aided in part by the large scale trof axis shifting
east and replaced by west northwesterly flow aloft. May get a
recovery back toward the freezing mark on Tuesday, before another
cold shot skirts the northern cwa. Highs for Wednesday trimmed a
few degrees around 30. May start to see some progress toward
warmer temperatures Thursday into Friday as an series of upper
trofs slide across the southern states and advect warmer
temperatures northward.

&&

.AVIATION...(For the 00Z TAFs through 00Z Saturday Evening)
Issued at 526 PM CST FRI DEC 6 2013

VFR conditions are expected through the period. Skies will clear
by 02Z as surface high pressure builds south into the Central
Plains. North winds near 10 mph will decrease to less than 10 Kts
and remain from the north. The winds will become east by 21Z Sat
with speeds under 10 kts.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...67
AVIATION...53