Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 212058
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
358 PM CDT Thu Aug 21 2014

.SHORT TERM...(This Evening through Friday)
Issued at 356 PM CDT THU AUG 21 2014

At 3 PM, surface low pressure was situated over the Oklahoma
panhandle...connected by a weak cold front to another surface low in
southwest Minnesota. There was a second weak boundary, more of a
moisture discontinuity extending from just north of Russel, KS to
near Marysville, KS. immediately north of this moisture boundary,
low-level convergence and the presence of deeper moisture/more
instability have led to persistent showers and a few storms in
southern Nebraska and extreme northern Kansas. Aloft, a stream of
very weak disturbances were moving out of the desert southwest into
the central Plains, and will continue to do so through tomorrow.
Southwest flow aloft on the west side of an upper ridge has allowed
for continuous warm advection and a very hot regime locally.
Temperatures today have been in the upper 90s to lower 100s (with
the exception of areas very close to the NE border where there have
been more clouds) while dewpoints especially north and east have
held in the lower 70s. This has led to heat index values in the 102
to 108 range with the highest values east. Have issued a heat
advisory for northeast and east central KS where the highest T/Td
combinations should be in place through this evening.

This evening into tonight, will be watching a few features for
potential thunderstorm development. The first is the frontal zone in
north central KS. Surface based CAPE greater than 1000 J/kg is in
place in the airmass just north of the weak boundary. Wind shear is
rather weak, but between the ample afternoon heating of the boundary
and what seems to be an incoming weak short wave trough, could see
scattered thunderstorm development in north central KS. If storms
can develop through early evening, the very steep low level lapse
rates would support localized strong downbursts. However, severe
potential appears low as there may not be sufficient
lift/instability to support the precip loading needed for severe
winds. Will need to monitor regardless as the depth of the steep
lapse rates would support damaging winds with only moderate
mid-level downdrafts.  As the evening progresses, expect a low level
jet to increase a bit with some weak convergence into north central
KS and a zone of more aggressive moisture transport from south
central into northeast KS. This may further support north central KS
thunderstorms by around 03Z, and could support further development
into northeast KS by late evening and early morning. The chances are
slight for thunderstorms at any given point, and the potential for
severe weather overnight appears even lower yet given the expected
elevated nature of the storms.

Friday is a bit uncertain regarding temperatures and potential heat
headlines. This is mainly due to uncertainty in how long any
scattered precip or remnant cloud cover will be over the area. The
current forecast leans toward a mainly cloud-free late morning and
early afternoon. This, along with slightly warmer 850 temps would
suggest temperatures near or slightly warmer than Thursday with
dewpoints near or slightly lower than Thursday. IF this scenario
plays out, a heat advisory could be needed for parts of the area
again, but given at least some potential for convective debris and
lower temps, have not issued at this time. Will then look to late
afternoon for more potential for scattered storm development, mainly
in northern KS.


.LONG TERM...(Friday Night through Thursday)
Issued at 356 PM CDT THU AUG 21 2014

The mid-level pattern is expected to remain fairly unchanged Friday
night into the weekend as models show the mid-level ridge staying
anchored over much of the southeastern U.S. with the mid-level
trough in place over the western U.S.  Friday night into Saturday
this mid-level trough currently over the Pacific Northwest is
expected to deepen and dig southward along the western Rockies
before a strong embedded shortwave trough lifts northeastward toward
the Northern Plains Saturday night into Sunday. As this shortwave
trough pivots northward, it will help to slowly push the stationary
front that will remain stalled out over north central Kansas and
along the Kansas/Nebraska border eastward through the forecast area
Sunday into Monday. Ahead of this frontal passage, southwesterly
surface winds will prevail as surface low pressure remains anchored
over the High Plains. As a result, warm air advection will persist
through the weekend with unseasonably hot conditions. Highs for
Saturday are expected to reach into the mid/upper 90s with afternoon
heat indices rising into the 98F to 102F degree range. As winds
shift to the north with the frontal passage, a slight cool-down is
expected by early next week with highs in the upper 80s to low/mid
90s on Monday. As for precipitation chances through this period,
there is a chance for some isolated nocturnal showers and
thunderstorms Friday night and Saturday night with the help of the
low-level jet, primarily focused over north central Kansas and along
the Kansas/Nebraska border. Thunderstorm chances increase by Sunday
night into Monday with the frontal passage. Models continue to show
this front lifting northward over the region as a warm front by
Monday night, however there are still some model discrepancies with
regards to just how far north this warm front will lift. At this
time though, models seem to be trending toward much of the southern
half of the forecast area being in the warm sector as this boundary
will likely become stationary once again near the Kansas/Nebraska
border through Tuesday night, so expect temperatures to warm up once
again into at least the low/mid 90s and possibly into the upper 90s
for some locations. Tuesday night into Wednesday we may see a repeat
of events as models are showing the stationary boundary once again
transitioning to a cold front that will progress eastward across the
region as a stronger mid-level trough develops and deepens across
the Rockies. This stronger trough should help to finally push this
system east of the area mid-week, with increased precipitation
chances Tuesday night and Wednesday followed by slightly cooler
temperatures in the mid 80s to near 90 degrees.

&&

.AVIATION...(For the 18Z TAFs through 18Z Friday Afternoon)
Issued at 102 PM CDT THU AUG 21 2014

VFR conditions are likely through the TAF period. Will be
monitoring a weak front in north central KS as it may develop a few
thunderstorms with a small chance of impacting MHK...mainly
between 02Z and 07Z. TS seems unlikely at this point though.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY until 9 PM CDT this evening FOR KSZ011-012-022>024-
026-038>040-054>056-058-059.

&&

$$

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






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