Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 302317
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
617 PM CDT Sat Aug 30 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 311 PM CDT SAT AUG 30 2014

19Z water vapor imagery shows one shortwave trough moving into the
great lakes region with another upper level trough moving into the
northern Rockies. A lead shortwave within the western trough was
moving across NV and into UT with a second shortwave over the
pacific northwest coast. At the surface, there was relatively high
pressure over the forecast area with an ill defined frontal boundary
to the southeast and a surface low forming over WY. This has allowed
winds to remain light and variable this afternoon.

This afternoon and tonight should remain relatively quiet as forcing
from the initial shortwave out west looks to hold off until the early
morning Sunday. By Sunday morning, the models are hinting at the
possibility for some very high based showers and thunderstorms
moving into north central KS around sunrise. The 315K isentropic
surface shows rather deep upglide from about 800MB to nearly 600MB
across north central KS, but the airmass is pretty dry below 700MB.
Lapse rates above 600MB look to be nearly moist adiabatic so there
does not appear to be much elevated instability for a parcel lifted
from 700MB or above. This isentropic lift is progged to eventually
break down late in the morning as the lead shortwave passes east.
Otherwise models show a decent elevated mixed layer advecting into
central KS from the southwest through the day as 700MB temps warm to
between 12 and 14 C. Currently models show this capping inversion to
hold through the afternoon and models wait for the actual front to
move into the area for surface based convection to affect the
forecast area. Think this is plausible since the initial shortwave
moving into UT should pass through the area in the morning and the
better PVA and large scale forcing focusing north and west of the
forecast area through the afternoon. So in general think there may
be some high based precip move across north central KS in the
morning with the afternoon remaining generally dry. If an updraft
were to become especially vigorous in the morning, there could be a
localized damaging winds threat due to an inverted V profile below
700MB. Have trended POPs down during the afternoon and confine
chance POPs across far northwestern portions of the forecast area
for the late afternoon which should be in closer proximity to the
surface trough/front.

With some weak mixing overnight, think overnight lows will be in the
middle and upper 60s. Gradually increasing high clouds after
midnight should also help keep lows rather mild. The pressure
gradient really strengthens for Sunday with south winds likely
gusting over 30 MPH. Strong mixing of the boundary layer to around
825MB and decent insolation to go along with the warm air advection
is expected to lift afternoon temps into the middle and upper 90s
across the area.

.LONG TERM...(Sunday Night through Saturday)
Issued at 311 PM CDT SAT AUG 30 2014

Severe weather potential continues through at least the mid evening
hours, but have some questions on how the event will transpire. The
upstream front is not very well defined and with moisture pooling
into eastern Nebraska on easterly winds, could see quite an array of
convection developing here and along the front to the west in the
late day. If storms can maintain some separation, increasing low
level shear on a stout low level jet would produce supercells,
though even if such storms don`t occur until near/after sunset, LCL
heights look rather high for a significant tornado concern, so still
looking like primarily a wind and hail concern for severe weather,
with little in the way of a synoptic set-up for flooding.

Front/effective front still appears possible to be draped across
southern areas Labor Day. Depending on persistence and track of
overnight convection, could see moderate CAPE again develop along
with some decent speed shear for more severe weather potential. LCLs
are likely to be lower though low level shear at this point doesn`t
look very strong given modest wind fields. Models differ on how fast
return flow will develop, but at least a few periods of thunder
potential seem in order into at least Tuesday evening.

Flow pattern for the Central Plains becomes weaker with modest
ridging for the mid week for warming temps and a likely dry period
for most locations Wednesday into Thursday with highest well into the
90s. Guidance differs with the next cold front`s approach, stemming
from speed variations of the next shortwave trough`s passage across
the U.S./Canada border, with the 12Z ECMWF faster than its 0Z run
and the 12Z GFS. Forecast changes were minor at this point,
including adding small chances in the north Thursday night.
Thunderstorm chances then continue into the weekend with again the
front possibly becoming stationary over the area.

&&

.AVIATION...(For the 00Z TAFs through 00Z Sunday Evening)
Issued at 614 PM CDT SAT AUG 30 2014

Expect VFR conditions through most of the next 24 hours.  Wind shear
may be a possible factor to consider for next TAF period due to the
LLJ influence as well as the possibility of VCTS late in the day
Sunday.  These have been left out for now due to low confidence in
timing and exact location.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Drake






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