Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 200516
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1116 PM CST Wed Nov 19 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Thursday)
Issued at 250 PM CST WED NOV 19 2014

High pressure ridge continues to build across the area from the
northwest as the mid level ridge progresses eastward over the
Rockies. The tail end of the cold front currently tracking through
the Midwest and Great Lakes region is situated right across eastern
KS this afternoon. This front will lift northward later tonight
causing winds to become southerly, but speeds remain fairly light
through tomorrow. Along this baroclinic zone a few areas of clouds
may linger through the overnight hours especially over the northeast
half of the forecast area. Although the latest satellite trends show
the clouds fighting dry air. Overall the skies tonight stay mostly
clear and winds relatively light, which should set the stage for
radiational cooling. Dewpoints have remained relatively low today
due to the cold front draped across the area and lack of much
advection. Therefore expect low temperatures to drop into the mid to
upper teens. A few model solutions were stronger with the inversion
in north central KS leading to the potential for fog. The NAM in
particular was suggesting this scenario overnight, but the latest
observations show the forecast dewpoints for this time are already
too high. This bias in moisture could definitely lead to much
quicker saturation. Given drier air in place than depicted have not
mentioned fog in the forecast at this time. High clouds associated
with the upper ridge overspread the region tomorrow. A majority of
the snow cover melted today with the exception of a few counties in
far northeast KS and southern Anderson county. High temperatures
tomorrow should not depend on this existing snow cover although a
gradient from the mid 40s in southern portions to mid 30s near the
KS/KS state line is likely.

.LONG TERM...(Thursday Night through Wednesday)
Issued at 250 PM CST WED NOV 19 2014

Initially...the large trough over the eastern CONUS moves
northeast and it is replaced by generally westerly flow across
the central US by 12Z Friday. A surface ridge just southwest of
the upper trough moves east allowing southeasterly flow to develop
over the central plains Thursday evening with a warm front over the
southern plains. The shortwave trough moving onshore on the
Pacific coast today is forecast to undercut the narrow upper
ridge over western North America. Although this wave appears to be
weak, it is forecast by the 12Z NAM/GFS/ECMWF to move through the
central US Thursday night and Friday and impact the sensible
weather over eastern Kansas. Low-level moisture returns north into
the central plains Thursday night ahead of the wave. Based on the
12Z GFS/NAM model soundings, the moisture profile slowly deepens
and it is supported by modest vertical motion in association with
warm advection and upper forcing with the wave. Surface temperatures
will be below freezing over the forecast area Thursday night into
Friday morning. Soundings support drizzle since there is little,
or no saturation below -10 C. Hourly temperatures should slowly
increase along with the moisture advection into the area. Based
freezing drizzle vs drizzle on hourly temperatures. This will need
to be refined as the system nears. In general, expect a low QPF
event with fairly widespread light freezing drizzle or drizzle
Friday morning.

In the longer term, the 12Z models continued to show the second,
stronger shortwave trough to enter the southern plains Saturday.
This trough is forecast to deepen rapidly into a strong,
negatively tilted upper trough over the central CONUS this
weekend. By Monday morning...the 12z ECMWF forecasts a closed 500
MB low over the upper Midwest and a deeper than 980 MB surface low
in the Great Lakes. The current deterministic models keep the
brunt of the precipitation east of our forecast area, but it is pretty
close. A western drift of the system would result in high POPs
and more precipitation. Whatever precipitation occurs will be in
the form of rain based on the thermodynamics of all the major
models. There should be another shot of cold air moving through
the plains early next week. However, it will be a glancing blow
and there is not an area of arctic or polar high pressure coming
down on the backside of the upper trough. This should keep high
temperatures in the 30s and 40s so not as cold as the recent
airmass over the area. Warm advection should return by the middle
of next week. After the weekend system moves by, the extended
looks mainly dry.

&&

.AVIATION...(For the 06Z TAFs through 06Z Thursday Night)
Issued at 1116 PM CST WED NOV 19 2014

VFR conditions dominate. Rather dry surface ridge keeps winds
quite light, though could see a more persistent but still light
east wind take hold in the latter half of the forecast.

&&

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

$$

SHORT TERM...Sanders
LONG TERM...Johnson
AVIATION...65






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