Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 131724
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1124 AM CST Fri Jan 13 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 432 AM CST Fri Jan 13 2017

Forecast challenges remain rather large with southwest flow aloft
over the cold and dry surface airmass and reinforcing northeast
winds. Scattered freezing rain developed overnight in southern
Missouri as deeper moisture begins to move north.

Models are consistent with levels from 900-800mb saturating in east
central Kansas this morning as isentropic lift increases, but then
winds in this layer veer to weaken the lift. Could see some light
precip in freezing rain or freezing drizzle come of this depth of
saturation despite little forcing. Near-surface saturation is hard
to nail down for much of today and tonight with northeast winds
tapping into sub-zero F dewpoints into central Iowa at 10Z. Model
guidance is quite varied with dewpoint trends with the NAM on the
wet side and ECMWF on the dry, nearly 30F apart in some locations at
0Z. Moisture does deepen across all but northwest sections tonight
though again forcing for ascent is largely lacking, with even a bit
of 850mb cold air advection late. Will continue with a light
freezing precip mention for most areas but widespread and persistent
precip seems unlikely. Have tapered back onset of the Warning with
time for most locations based on the slower RH increase. Lows
tonight also rather tricky with cloudy skies dominating but
questions on the dewpoints. Lowered values toward the middle of
guidance.

.LONG TERM...(Saturday through Thursday)
Issued at 432 AM CST Fri Jan 13 2017

Models are a little slower on bringing precipitation northward on
Saturday, especially during the morning hours. As the upper trough
and low moves east during the day on Saturday into northwest Mexico,
the 850 mb winds will become more southerly and begin transporting
moisture northward into southern Kansas. As the upper low progresses
eastward Saturday night and Sunday into the western Texas Panhandle
isentropic lift will increase and transport moist air over the low
level cold air in place across the area with models producing the
highest QPF during this time period. The GFS continues to be on the
warm end of the spectrum with respect to the eroding of the low
level cold air, while the rest of the model suite continues to hold
onto the low level cold air longer. The result will be a prolonged
period of freezing rain Saturday night and Sunday. By Sunday
afternoon with the upper low lifting northeast forcing for ascent
will increase along with a diffluent upper flow over eastern Kansas
Sunday night which will lead to an additional quarter to half inch
of precipitation for the area. Ice accumulations for the event place
most of the area around a half inch with areas of east central
Kansas closer to three quarters of an inch. Will keep the ice storm
warning going. Main thing to watch will be if the warning will need
to be extended into Monday morning for north central Kansas. Thermal
profiles warm Sunday night after 06Z with soundings showing
precipitation mainly in the form of rain across almost all of the
area by 12Z Monday. Surface temperatures are expected to warm
through the night above freezing, except for parts of north central
Kansas. Additional precipitation is expected across north central
Kansas Monday night as moisture is transported around the upper low
as it progresses northeast and within the trowal. A combination of
rain, freezing rain. sleet and snow possible. The system moves out
on Tuesday with dry weather expected for the rest of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1123 AM CST Fri Jan 13 2017

MVFR ceilings have moved over TOP/FOE while MHK may stay VFR through
the period as ceilings moving in from the west are still above 4kt.
Believe that TOP/FOE will remain MVFR through the period.  There is
a small chance for FZRA late in the period, but chances are too low
to include in this TAF issuance.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Ice Storm Warning from 6 PM this evening to midnight CST Sunday
night for KSZ010>012-021>024-034>038.

Ice Storm Warning until midnight CST Sunday night for KSZ026-039-
040-054-055.

Ice Storm Warning from noon Saturday to midnight CST Sunday
night for KSZ008-009-020.

Ice Storm Warning until midnight CST Sunday night for KSZ056-058-
059.

&&

$$

SHORT TERM...65
LONG TERM...53
AVIATION...Heller



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