Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 202316
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
616 PM CDT Sat Sep 20 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 343 PM CDT SAT SEP 20 2014

Main focus for the short term is on the development of thunderstorms
as a cold front progresses southward through the forecast area.
Water vapor imagery showed a broad trough across the northern U.S.
with an embedded shortwave trough skimming across northeast Kansas.
This passing wave has been helping to push the cold front southward
into the area, with the boundary stretching from roughly Minneapolis
to Randolph and Hiawatha. Scattered thunderstorms had developed
along this boundary across northeast Kansas by early afternoon,
however the very pulse-y nature of these storms suggests that the
best forcing is limited to just near the boundary. While there are
still plenty of variances amongst the short-range models with the
progression of this system, in general they seem to trend toward
more scattered thunderstorms developing along and north of I-70
(i.e., along the cold front) between 20z-00z as little to no
inhibition is in place. With 2000-3000J/kg of surface-based CAPE and
generally 30-40kts of 0-6km bulk shear, some of these storms could
be strong to severe mid-afternoon through early this evening,
especially across far northeast and east central Kansas, with small
hail, gusty winds, and locally heavy rainfall being the primary
threats.  Some limiting factors though to this severe potential are
that the steep low-level lapse rates only extend up to around 800mb
and there also is a fairly narrow zone of convergence with limited
frontogenetical forcing near this boundary. Model soundings show the cap
building back into the region around or shortly after sunset, so any
storms across east central Kansas early this evening will likely
become elevated and gradually weaken and diminish in coverage
through the evening hours. While these storms should mostly be south
of the forecast area by late evening, cannot rule out a few
lingering storms into the overnight hours before clearing out.

With winds veering to the north behind the front, cooler air will
start advecting into the region with overnight low temperatures
ranging from the mid/upper 50s north to the low/mid 60s over east
central Kansas. This CAA will persist through the day with highs
only reaching into the mid/upper 70s, despite mostly sunny skies.
Dry conditions are expected through the day on Sunday as surface
high pressure comes spilling southward into the region behind the
exiting system.

.LONG TERM...(Sunday Night through Saturday)
Issued at 343 PM CDT SAT SEP 20 2014

Will maintain mostly clear/mostly sunny skies Sunday night into Monday
beneath and eastward expanding upper level ridging ahead of the
approaching intermountain west trough. With light winds and good
radiational cooling...a pleasantly cool early Fall night in the
upper 40s to lower 50s still looks on track. With the cool start to
the day...light southeast winds and a very slow increase in clouds
late in the day...will keep highs in the middle 70s..although
stronger mixing and more veered llvl winds could lead to a little
warmer temps.

As the western trough moves eastward into the plains...then lifts
northeastward in response to amplifying eastern ridge...moisture
advection and forcing will overspread the county warning area from
west to east from late Monday night on into Tuesday night.
Precipitation chances will then be highest across the western 2/3 of
the county warning area Tuesday night into Wednesday before
decreasing as the upper trough begins to shear and weaken. Will then
go with a dry fcst for Friday on into next Saturday as upper ridge
becomes dominant across the central plains. The thicker clouds and
higher precip chances still appear will limit highs Tuesday and
Wednesday across the northern cwa to the low to middle 70s...with
highs then moderating to around 80 by Friday then continuing on into
Saturday. Lows will commonly be in the upper 50s to lower 60s
Wednesday into the weekend.

&&

.AVIATION...(For the 00Z TAFs through 00Z Sunday Evening)
Issued at 615 PM CDT SAT SEP 20 2014

Thunderstorm activity should remain south of TAF sites for the
rest of the evening although there is still a very small chance
for a TS through around 02Z. The cold front should pass through
TAF sites by around 02Z, with a wind shift out of the northwest.

&&

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

$$

SHORT TERM...Hennecke
LONG TERM...63
AVIATION...Barjenbruch






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