Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 252350
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
650 PM CDT Mon Aug 25 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Tuesday)
Issued at 335 PM CDT MON AUG 25 2014

This rather stagnant weather pattern is expected to continue into
Tuesday although some details are gradually changing. The pattern
continuity would make this forecast easier if not for the
storm-scale and mesoscale details that evolve every day to make the
details of the forecast quite difficult to predict. The main focus
of the forecast revolves around potential extension of heat
headlines, and the potential for thunderstorms at any given time...
some of which may be strong.

On Monday afternoon, there were many features of interest across the
region. A surface low was anchored over the Oklahoma panhandle with
a warm front extending from the low into central KS, becoming a
stationary front from central KS into southeast Nebraska, and then
being intersected by a cold front that stretched from far NW Kansas
into east central Nebraska. A remnant outflow boundary from morning
storms was also in place across the forecast area, extending from
near Council Grove to near Lawrence, and was nearly stationary. A
weak short wave trough was also present over the Oklahoma panhandle
and forecast to slowly move northeast tonight while a stronger short
wave over western Colorado was forecast to quickly move into south
central Nebraska overnight.

At 3 PM, an increasing cumulus field was developing near this
boundary in an area of limited CINH and 2000+ J/kg of MLCAPE. The
low level convergence in this zone may be sufficient for scattered
thunderstorms to develop through this evening, with the whole zone
of convergence probably gradually drifting north. Similar to
yesterday, this airmass is very hot with strong theta-e differences
(although not as substantial as Sunday afternoon). This will lead to
the potential for localized damaging downbursts once again, in
addition to some hail perhaps up to quarter size. Any late afternoon
activity would be expected to decrease in coverage by late evening.
However, by around 06Z, the LLJ is expected to intensify a bit with
the nose converging into central KS and veering toward northeast KS
by sunrise. This persistent convergence and moisture transport into
the area with modest instability present, in conjunction with the
pair of incoming pieces of short wave energy seem to point to a
favorable set up for a cluster of thunderstorms overnight from
central into northeast KS. Not all model guidance is pointing to
this, but some of the more recent high-res guidance along with the
observational cues seem to warrant at least 40% chances. There may
be a small chance for wind or hail with any stronger storms as
well...but it seems unlikely at this point.

Tuesday`s forecast depends quite a bit on any early morning
convection. The temperatures in particular will be sensitive to
this, and have not extended the heat advisory at this point due to
uncertainty in which areas will be impacted by dangerous heat.
Recent model trends have indicated that the storms certain to set up
over Nebraska tonight may target an area a bit farther south than
previously forecast which could reinforce slightly cooler conditions
locally. The bulk of precip chances on Tuesday will be focused
north, although uncertainty again exists based on any possible
boundaries in the area.

.LONG TERM...(Tuesday Night through Monday)
Issued at 335 PM CDT MON AUG 25 2014

By Tuesday night the upper low will be centered over the inner
mountain west with a lead shortwave lifting north over the high
plains. There are some differences on exact timing and track of the
wave but this should not change the outcome much. Ahead of the wave
the nocturnal low level jet should increase over western KS and NE,
and will be the focus for thunderstorm development. At the surface
the same boundary that has been stationary across the area will be
located somewhere near the NE/KS state line. The thunderstorm
complex should track eastward on the north side of the front
clipping our northern counties. There could also be some convergence
on the east side of the low level jet that will basically bisect the
area. A slight chance for storms will exist for most the area with
the better chances north of interstate 70. Similar to the past few
mornings this convection could send an outflow into the forecast
area during the day Wednesday, and could be the focus for additional
storm development. Also, with plenty of moisture and hot temps the
instability could support isolated strong storms with damaging winds
as the main threat. The GFS is slightly faster and stronger with the
lead shortwave therefore drags the front through starting on
Thursday. The main trough then ejects into the plains Thursday night
and Friday with the ECMWF being the slowest solution. This will
increase the large scale ascent over the region while the front
slowly progresses through the area. The ECMWF also keeps the precip
around through Saturday night since it is slower with the main
trough to track over eastern KS. Wednesday appears to be the last
warm day with temperatures in the 90s before things cool off to near
normal.

&&

.AVIATION...(For the 00Z TAFs through 00Z Tuesday Evening)
Issued at 639 PM CDT MON AUG 25 2014

Will maintain a dry/VFR forecast for all terminals through the
period as confidence on any terminal location being directly
affected by convection is low...however feel an MCS system may
not be too far to the northwest in the 05z-12z timeframe which
would place it closer to KMHK than the other sites. Therefore
decided to carry thunder vcnty at KMHK in the 05z-09z timeframe
and leave it out further east for now. With boundary in the area
of all 3 TAF sites...light easterly winds will be the
rule...although an outflow boundary from the north certainly
cannot be ruled out sometime in the 07z-12z timeframe.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY until 8 PM CDT this evening FOR KSZ010>012-021>024-
026-034>040-054>056-058-059.

&&

$$

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





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