Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 081127
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
527 AM CST Thu Dec 8 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 316 AM CST Thu Dec 8 2016

Longwave upper trough remains in place over the Conus with
yesterday`s shortwave exiting early Wednesday evening. Surface
high pressure continues to build southeast into the Central Plains
with temps settling into the teens and enough wind to bring
apparent temps into the single digits.

Forecast into tonight remains fairly benign. Wind chill values
will likely reach a few degrees below zero in the north and west
around sunrise as northwest winds persist. Surface ridge continues
its build southeast today with gradient relaxing late in the day,
and expect some decreases in winds in the afternoon. Low mixing
heights in the cold airmass keeps highs in the low to mid 20s.
Surface ridge axis moves across the area late tonight with winds
going rather light, but high cloud entering the Pacific Northwest
early this morning should enter the area. This cloud should keep
lows from dropping beyond 5F as the airmass modifies.

.LONG TERM...(Friday through Wednesday)
Issued at 316 AM CST Thu Dec 8 2016

Surface ridge axis will be translating east of the CWA during the
day on Friday with weak southerly flow helping to stabilize and
reverse the previous days` cooling trends. Lee cyclogenesis along
the Front Range will cause the pressure gradient over the state of
Kansas to tighten on Saturday, with a 15 mb difference between
the western and eastern sides of the state. This will result in a
stiff southerly wind and modest WAA during the day. The GFS has
been consistent with generating a deeply-mixed boundary layer up
to about 850 mb with 35 kt winds at the top of the layer. Should
this come to fruition, high temperatures for Saturday would be
underdone by 2 to 4 degrees. The NAM is considerably less bullish
with the daytime mixing and have thus deferred to the blended
guidance for the time being until there is a better model
concensus.

Confidence in the middle to latter portions of the period is only
moderate at best with inconsistencies developing as the
aforementioned High Plains low ejects across the Southern Plains
late Sunday/early Monday. Broad kinematic forcing ahead of an
approaching 550 mb PV anomaly should be enough to generate light
QPF over the CWA on Sunday with a p-type of snow over the north.
The surface low will pull east into the Ohio River Valley by
midday Monday with zonal 300 mb flow helping to usher a surface
high through the CWA by mid to late Monday. Another wave of cold
arctic air will surge into the central CONUS on Monday and
Tuesday, though the GFS/EC have fallen out of agreement in the
timing and placement of the airmass. To put this discrepancy in
context, the raw GFS high temperatures for NE Kansas for Tuesday
are in the single digits to low teens, while the EC high
temperatures are between 26 F and 40 F. Thus leaned heavily on
the blended guidance until the models come into better agreement.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 527 AM CST Thu Dec 8 2016

VFR conditions will continue as cold and dry air high pressure
remains in place. Wind speeds will diminish somewhat in the latter
portions of the forecast.

&&

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

$$

SHORT TERM...65
LONG TERM...Skow
AVIATION...65


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