Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 132343
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
543 PM CST Sat Dec 13 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 311 PM CST SAT DEC 13 2014

20Z water vapor imagery shows the upper level trough out west
continuing to progress east into the Rockies. Meanwhile the upper
ridge overhead is slowly weakening as height falls spread east. At
the surface, southerly low level flow persists between a ridge over
the southeast and troughing in the lee of the Rockies. Dewpoints in
the lower and middle 50s continue to move north into the central
plains.

Tonight there remains little large scale forcing, but the general
subsidence from the upper ridge should go away as it weakens.
Because of the lack of forcing, think chances for measurable precip
are relatively small given the moisture will be capped by the pesky
inversion and no real lift to force the moisture above the
inversion. However the continued advection of higher dewpoints north
along with some modest isentropic lift could lead to areas of
drizzle overnight. The RAP and NAM suggest isentropic lift will not
be any better organized than what is occurring this afternoon. So
thinking is the drizzle overnight will only amount to a trace. Temps
are expected to remain fairly steady with overcast skies and south
winds preventing any cooling. Min temps are forecast to be in the
lower to mid 50s

Sunday will see increasing large scale forcing in the form of
vorticity advection as the upper trough propagates east and a
negatively tilted shortwave lifts out from the southern Rockies. The
combination of the forcing with mid level cooling is expected to
create some modest convective instability (surface based CAPE around
500 J/KG). With this in mind, showers and thunderstorms should
develop over the southern high plains and spread into central KS by
the afternoon. Any strong to severe thunderstorms seem to be
dependent on the degree of surface heating and resultant
destabilization. At this point, heating is forecast to be modest due
to overcast skies. Although it is not out of the question there
could be a strong storm or two with some hail and wind. Highs Sunday
should be around 60 as southerly flow and warm air advection
persists.

.LONG TERM...(Sunday Night through Saturday)
Issued at 307 PM CST SAT DEC 13 2014

Initial band of precip with likely embedded convection should be
moving through Sunday evening. Kept PoPs above guidance but could
see a few places miss some precip in possible gaps in the band.
Minor instability still anticipated with this band, with somewhat
greater concern for severe weather arises in the evening to early
overnight hours with south low level winds persisting and wind
fields increasing as models are in good agreement with another area
of precip developing NE of the of the upper low. The NAM seems a bit
overdone with CAPE, mostly via cooling around 925mb on SW winds,
which seems unlikely. Still, with low tops the CAPE that is there is
a more impressive and minor wind and hail concerns remain. Monday
into Monday brings steady drying conditions but decreased PoPs
somewhat Monday night with NE KS well on the back side of this
system. Still have a hard time seeing much more than rain fall with
this event, with ice crystals aloft becoming hard to come by as the
lower levels cool. Falling temps on track for the daytime hours
Monday as NW winds increase.

Tuesday into at least Tuesday night still looking dry, but models
continue to struggle with upper troughing splitting NE into Canada
and SE into the southern tier states as well as how energy will
interact with an upper high pushing east across the southern
Canadian provinces. This puts much of the Northern and Central Plains
in weak flow and seasonable temperature fields, with any waves
passing near enough from the south to bring light precip
potential, with the later work week periods again looking the most
likely for this to occur. Low chance PoPs at best are in order
with somewhat cooler lower levels supporting less mixed precip
potential.

&&

.AVIATION...(For the 00Z TAFs through 00Z Sunday Evening)
Issued at 525 PM CST SAT DEC 13 2014

Challenges for the TAF period remain the CIG/VIS through the
first part and most of the last half of the period into Sunday
afternoon. Expect CIG/VIS conditions to continue to exhibit a
range within the IFR/LIFR categories. It is not out of the
question to dip into the VLIFR range overnight for periods of
time. Outside of that, late afternoon on Sunday could see the
potential for showers and mostly weak general thunderstorms to
move into the area associated with the upper level trough to the
West of the terminals. A very isolated thunderstorm with small
hail could be embedded, but any potential for that should be after
the TAF period ends.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Drake






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