Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 240448 AAA
AFDTOP

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TOPEKA KS
1148 PM CDT Sat Aug 23 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 328 PM CDT SAT AUG 23 2014

At 3 PM, a weak trough of surface low pressure extended from far SE
Colorado into NW Kansas. A very weak surface boundary then extended
east near the Nebraska border with weak convergence along it and a
bit of moisture pooling just to the north of the boundary. A rather
sharp, but shearing-out, short wave trough axis extended from
western South Dakota into the Oklahoma panhandle and was pivoting
NNE around the main upper low in Montana. There appeared to be an
axis of enhanced lift just ahead of this wave in a band of deeper
moisture, but the moisture quality decreases quickly into south
central and eastern KS. Temperatures have climbed again into the
upper 90s to low 100s this afternoon except for very near the
Nebraska border where mid 90s have held on. Low level moisture has
effectively mixed out in the hot airmass today thought with
dewpoints in the upper 50s to low 60s, and the heat index has not
been much higher than the temperature. Short term model guidance is
suggesting scattered convective development possible by 6 PM in a
small area of north central KS where there is a bit of low level
convergence and slightly better moisture quality near the incoming
wave aloft. If storms develop, instability and wind shear are rather
weak, and outside of another localized strong downburst or two,
strong storms are unlikely.

The breeze will continue overnight and temperatures should hang on
in the lower to middle 70s while dewpoints recover into the mid 60s.
The low level jet will increase again overnight, with indications of
some ascent within the LLJ from around Salina toward northeast KS.
Models also indicate moistening in this layer which may be
sufficient to provide 500+ J/kg rooted around 750 hPa. If this
moistening occurs, could see scattered showers and a few storms
develop across the area, although much of east central KS would
likely remain dry. This activity may persist until just after
sunrise when the weak lift will shift northeast of the area.

On Sunday, expect more of the same weather, although a weak cold
front should begin to work into north central KS with cooler
temperatures filtering in by afternoon. The remainder of the area
should have very similar conditions today with heat index of 101-106
for the 5th consecutive day, and have extended the heat advisory to
include Sunday for all but the far northwestern counties of the
forecast area. By late afternoon, most indications point to the
development of scattered thunderstorms along and just ahead of this
frontal zone. Would once again expect localized downburst winds to
be the main hazard with any of the stronger thunderstorms.

.LONG TERM...(Sunday Night through Saturday)
Issued at 328 PM CDT SAT AUG 23 2014

On Sunday night the strong upper low over the northern plains
continues to lift northeast into southern Canada. This will push the
front further into the forecast area only for a brief period before
it lifts back to the northwest. This keeps pops confined to areas
along and north of interstate 70 where isolated to scattered
thunderstorms are possible. Surface based cape appears to be on the
order of 2500 j/kg, although deep layer shear only reaches 25 kts.
This will limit any severe or organized convection, but localized
small hail and gusty winds could not be ruled out. Temperatures are
forecast to rise into the mid to upper 90s yet the possible storms
and cloud cover could complicate the matter. As the front lifts
northward Monday night widespread convection develops in NE staying
north of the area. There is always the chance that this convection
could set off an outflow boundary strong enough to be the focus for
convection during the day Tuesday since the models have a weak cap
in place by the afternoon. The models also show modest instability,
and the moisture axis moves over the area as well. These are hard to
predict and how far south it could travel is unknown therefore
confidence is low. Pops are still confined to locations near the NE
border and north central KS. The models are in a little better
agreement that the upper low over the Rockies will get removed from
the main flow, and gradually drift east over the plains. As it
approaches precip chances increase and the front moves through the
region. The slow speed of the system could provide the area with a
few days of much needed widespread rain. The GFS is still
advertising a more open wave therefore quicker bringing the front
through. Temperatures also cool off behind the front beginning
Wednesday, and surface high pressure is likely to build in for next
weekend. Heat indices could again approach 100 to 103 mainly in east
central KS on Monday and Tuesday.

&&

.AVIATION...(For the 06Z TAFs through 06Z Sunday Night)
Issued at 1143 PM CDT SAT AUG 23 2014

Vfr conditions are still expected to persist through the terminal
forecast period with only a few mid and sct-bkn high clouds
expected. Confidence in any elevated convection affecting any of
the terminal sites thru 12z or beyond 21Z remains too low to
insert into TAFS. Prevailing south winds will continue at speeds generally
under 10 kts before gradually increasing again aft 14z with a few
gusts near 20 kts.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY from Noon to 8 PM CDT Sunday FOR KSZ010>012-
021>024-026-035>040-054>056-058-059.

&&

$$

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





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