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000
FXUS63 KTOP 212349 AAA
AFDTOP

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TOPEKA KS
649 PM CDT Mon Jul 21 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Tuesday)
Issued at 325 PM CDT MON JUL 21 2014

Today/Tonight:
It has been as hot as advertised today, but what has been a little
bit of a surprise is that dewpoints held 1-3 degrees warmer than a
lot of model guidance had suggested. Looking upstream, the source
region of our low level airmass in central OK is characterized by mid
to upper 70s dewpoints. The morning TOP sounding also indicated that
the moisture was fairly deep with the air not notably drier until
above 850 hPa. The result has been heat indices in the 103 to 112
range at mid afternoon with the expectation to hold at that level or
increase slightly yet this evening. A breeze should be maintained
through the night and temperatures will be slow to cool. Have lows
in the upper 70s, but some locales may not fall out of the 80s. This
offers little to no relief even overnight for exposed people and
animals. In terms of precipitation, there remains a very small
chance for one or two storms to move out of western KS into parts of
north central KS late today. The environment is not particularly
supportive of longer lived convection and there is a weak cap in
place with little to no forcing. So, have not mentioned
thunderstorms in the forecast. If a storm manages to develop over
north central KS, isolated damaging winds would be possible given a
very deep layer of dry adiabatic lapse rates.

Tuesday:
The day will begin warmer than Monday and will quickly warm into the
90s. Model guidance is once again aggressively mixing out the low
level moisture with some guidance taking dewpoints into the lower
60s and temperatures to near 110. This seems quite unlikely although
the moisture profile does appear a bit shallower on Tuesday. In
addition, a weak cold front will be drifting into northern KS during
the afternoon. Immediately ahead of this front, expect an area of
hotter temperatures, and immediately behind the front expect
substantial moisture pooling with dewpoints increasing to the mid
70s. All told, the heat index should be a wash whether temperatures
are warmer/cooler as the dewpoints will respond accordingly
lower/higher. Current heat index forecast is for a range of 104 to
112. This would suggest some potential for an excessive heat
warning, but will hold off at this time given just a bit of
uncertainty in how low the dewpoints will mix out.

As the cold front enters northern KS late in the afternoon, it
should be entering a very unstable airmass with 25-35 kts of deep
layer shear as well. The main question is whether the front will be
deep enough or strong enough to sufficiently force parcels through
the very deep mixed layer. Currently believe that isolated storms
will indeed develop, likely immediately behind the surface front.
Forecast soundings suggest a favorable environment for localize
damaging wind gusts with any storms that develop. Any afternoon
activity should be isolated, and perhaps more focused during the
evening.

.LONG TERM...(Tuesday Night through Monday)
Issued at 325 PM CDT MON JUL 21 2014

By Tuesday evening the front should be located somewhere along or
just north of the interstate 70 corridor according to the latest
model guidance. The cap still appears to be the limited factor
heading into the evening hours. This inhibition could be eliminated
depending on how much moisture pools behind the front and or the
lift is strong enough to overcome. Isolated damaging wind gusts
would be the primary threat associated any thunderstorms. The
chances for precip, which remains scattered, will continue to sag
south with the front through out the night. By morning the front
should push south of the area, and any lingering precip would
reside across portions of east central KS. On Wednesday temps cool
back to normal in the upper 80s and lower 90s, while drier air
advects southward. High pressure settles over northeast KS through
Thursday night. Early Friday morning precip chances vary with
regards to the models with the ECMWF keeping the area dry and the
GFS developing showers ahead of a front pushing through the
region. Not many changes were made to the extended forecast as the
front hangs around for the weekend keeping the chances for showers
and storms. Then strong upper level low still appears to drop into
the Great Lakes region bringing a secondary front and additional
cool air back southward.

&&

.AVIATION...(For the 00Z TAFs through 00Z Tuesday Evening)
Issued at 641 PM CDT MON JUL 21 2014

Vfr conditions will persist through the fcst period with only
sct high clouds expected. Any convection near front towards the
end of the fcst period should remain to the north of the
terminals. South winds overnight will slowly veer ahead of the
approaching front beyond 15z...but at speeds generally 12 kts or less.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY until 9 PM CDT this evening FOR KSZ008>012-020>024-
026-034>040-054>056.

HEAT ADVISORY from Noon to 9 PM CDT Tuesday FOR KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Sanders
AVIATION...63