Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 182317
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
617 PM CDT THU AUG 18 2016

...AVIATION UPDATE...

.SHORT TERM...(This Evening through Friday)
Issued at 344 PM CDT THU AUG 18 2016

Weak disturbance seen drifting over southeast Nebraska in water
vapor imagery has kept a few isolated sprinkles/very light showers
in far northern KS this afternoon, with a little more coverage north
of the border. This should continue to drift off to the northeast
and do not expect a repeat of development tonight.

On Friday, main weather feature that has been well advertised is a
decent shortwave trough crossing the Plains during the late
afternoon into the overnight hours.  Surface reflection of this
trough and main lifting mechanism is the cold front moving into
north central KS late afternoon, then moving through eastern KS
during the evening and overnight. Given marginal shear
characteristics and decent instability, think the main threat with
these storms to be strong/damaging winds and perhaps some one inch
hail.

With moderate pressure gradient across the area overnight, a little
mixing should help keep temperatures up in the upper 60s most areas.
Highs on Friday are forecast to be in the mid to upper 80s over east
central KS in the more tropical airmass, while portions of central
KS should see highs in the lower 90s ahead of the front.

.LONG TERM...(Friday Night through Thursday)
Issued at 344 PM CDT THU AUG 18 2016

By early Friday evening, a mid-level trough will be stretched across
the Northern and Central Plains, and this trough will continue to
deepen across the Central Plains as it advances eastward through
Saturday. This eastward-moving trough axis will help to push a cold
front through the area, with models showing the boundary stretched
across north central Kansas late afternoon into early evening and
progressing just east of the area by Saturday morning. Expect modest
instability of 1000-2000 J/kg of MUCAPE to develop ahead of the
boundary as a result of daytime heating.  0-6km bulk shear values
continue to look marginal at around 25-30kts. However, these
instability and shear values may be enough to support the
development of some strong to severe thunderstorm clusters that may
become cold-pool dominant, with damaging winds being the primary
concern. The better chances for any stronger storms is looking to be
across north central Kansas, with lesser chances further east since
it is expected that storms should weaken through the evening with
the loss of diurnal heating and with the low-level jet being
noticeably weak across the area. Despite thunderstorm intensity
weakening overnight, widespread storm coverage is likely with some
modest rainfall possible as PWATs reach 1.75 to 2.0 inches. With the
front exiting the area by Saturday morning, expect the lingering
scattered showers and storms across far eastern Kansas to diminish
during the morning hours with dry conditions for the remainder of
the weekend as surface high pressure builds into the area.  These
dry conditions will be accompanied by cooler-than-normal conditions
with high temperatures Saturday in the mid/upper 70s and near 80
degrees on Sunday. Overnight low temperatures are expected to cool
off into the 50s Saturday night into Sunday morning.

For the extended period beginning Monday through Thursday of the
upcoming week, high pressure will dominate into the day Monday.
Tuesday morning have introduced slight chance POPs over counties
mainly south of I-70 and I-335 corridors as at least some guidance
is signaling return of moisture into the region with some isentropic
lift over portions of the outlook area as WAA begins in response to
southwest flow aloft and leeside trough tightening over the region.
While the mean Westerlies remain largely over the northern CONUS, a
North Pac Low will make its way into the Northern Plains on
Wednesday.  Organized forcing still remains to the north, but the
cold boundary will likely make its way into northeastern Kansas and
stalls out.  Probability of severe weather looks low at this point
with weak shear and perhaps moderate instability for Wednesday
during the late afternoon and evening.  However, there could be a
period of time late night Wednesday into Thursday morning that the
LLJ provides a focus for lift over the stalled boundary per the GFS
model.  If this occurs, perhaps some stronger storms could linger.
The ECMWF is more progressive with the boundary and the focus of
lift is shifted more over southeastern KS into north central OK into
the evening Wednesday into Thursday as a weak wave pulls out of the
Central Rockies.  Considering the overall pattern and setup, have
found it difficult to narrow POPs down in any given time frame late
Tuesday through Thursday until the various solutions can align
better with both position and strength of the next frontal system.
Meanwhile, do feel confidence is good that temperatures remain
around or slightly below average for this time of year with highs in
the mid 80s and lows in the mid 60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday)
Issued at 617 PM CDT THU AUG 18 2016

There are some indications of the subtropical airmass slowly
advecting north Friday morning bringing some concern for lower
VSBY and CIGS. Objective guidance shows the boundary layer
remaining mixing so confidence in fog or stratus is to low at this
time to include in the forecast, but will keep an eye on upstream
obs. TS are progged to remain just to the west of MHK through
00Z. The forecast will need to address the expected convection
with the next issuance.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...GDP
LONG TERM...Drake/Hennecke
AVIATION...Wolters



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