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000
FXUS63 KTOP 301728
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1128 AM CST Sat Nov 30 2013

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 255 AM CST SAT NOV 30 2013

08z water vapor imagery shows a little bit of split flow with one
jet coming from the the tropical Pacific and another over the
Pacific northwest. There was one weak wave over the state that
continues to shear out while a couple other waves move from the
Pacific northwest through the upper Midwest. At the surface a trough
of low pressure extended from the southern high plains north to the
western MN/eastern Dakotas area, bisecting the state.

For today and tonight, the forecast area will remain under the
influence of the southern branch of the jet stream causing nearly
zonal flow aloft and no real dynamics for forcing. Because of this
the forecast remains dry. There does appear to be a little better
low level moisture moving up into eastern KS ahead of the surface
trough. But with no real forcing or vertical motion, do not think
this modest moisture advection will have much of an impact. Trended
temps a little higher for today and very similar to yesterday`s
highs. Models show some modest warm air advection at 925MB and no
real temp advection at the surface until late in the day as the
surface trough continues to slide southeast. So with a similar
airmass in place and full insolation anticipated, decided to lean on
persistence. The main concern for temps not being as warm as Friday
is the amount mixing today. With the trough slowly moving through
the forecast area, winds should be lighter and could limit how deep
the boundary layer mixes. Overnight we should start to see weak cold
air advection as the winds shift to the north behind the boundary.
Because of this and with some radiational cooling, min temps should
fall below freezing with the forecast showing lows from the mid 20s
to around 30.

.LONG TERM...(Sunday through Friday)
Issued at 255 AM CST SAT NOV 30 2013

Weak cool air advection behind the boundary should bring highs a few
degrees cooler on Sunday to around 50 degrees. The mid level trough
passing through the region Sunday evening should only be noted by an
increase in mid level clouds, helping to insulate Monday morning
lows slightly in the upper 20s to low 30s. All mid term guidance is
persistent on the potent long wave trough entering the Pacific
Northwest by Monday as flow aloft quickly veers to the northwest.
Ample warm air advects eastward Monday afternoon, quickly recovering
highs back into the middle and upper 50s. A mid level trough ejects
eastward from the main wave on Tuesday, developing a surface trough
across eastern Colorado. Warm, decent southerly flow ahead of the
trough keeps high temperatures Tuesday well above normal once again
in the lower to middle 50s.

Confidence is high for an arctic air mass to impact the area late
next week as the long wave trough slowly translates eastward into
the area by next weekend. Latest guidance beginning Tuesday evening
still has the GEM as an outlier with the cold front passing through
on Tuesday. Focus therefore was on the 00Z runs of the GFS and ECMWF
where there is a slight hedge towards the ECMWF with its better
run-to-run consistency. As the surface trough continues to deepen
southeastward Tuesday evening, an arctic cold front will push into
northeast Kansas in the early Wednesday morning to afternoon time
frame. Weak forcing along the surface and 850 MB fronts may produce
slight chances for rain showers during this time, however believe
with available moisture confined southeast of the area, rainfall
amounts will be meager. Temperatures Wednesday vary between guidance
and are dependent on the speed of the front. Until signs of a faster
cold front improve, sided with keeping highs in the lower 50s for east
central Kansas and lower 40s for north central. By Wednesday
evening, dry and very cold arctic air surges southeast towards the
central plains while a stout upper trough pivots the long wave axis
and lifts northeast towards the far northern plains. If there is
enough mid level lift generated from this wave across northeast
Kansas, light rain transitioning to snow would be possible Wednesday
evening. Confidence in the precipitation forecast Thursday into
Friday remains low at this time. Believe the expansive amount of dry
air in place may prohibit widespread precipitation from developing
despite the weak lift from the long wave trough centered to the north
and west. The GFS continues to be more amplified and convective
while the ECMWF shows the best forcing further south and east. As
this wave gradually pushes east Thursday through Friday, slight
chances for snow were mentioned with some question on the placement
of gulf moisture. In terms of temperatures, highs will continue to
fall from the low 30s Thursday to the 20s on Friday. Overnight lows
follow suit generally in the teens.

&&

.AVIATION...(For the 18Z TAFs through 18Z Sunday Afternoon)
Issued at 1124 AM CST SAT NOV 30 2013

Expect VFR conditions through the next 24 hours. A weak front will
shift winds from the southwest to the north by 6Z SUN. Winds will
remain light through the TAF period.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...Bowen
AVIATION...Gargan