Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 231143
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
643 AM CDT TUE AUG 23 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 322 AM CDT TUE AUG 23 2016

Confidence in forecast details for today and tonight is not strong,
as sensible and convective weather for the day is driven by several
mesoscale and synoptic features, and will depend ultimately on their
interaction. Area remains under southwesterly flow aloft, ahead of a
quick series of shortwaves moving northeast over the area today and
tonight.  LLJ continues to stream overhead at this hour, bringing
increasing moisture and cloud cover as it does so.  Each chance for
convection today will impact chances for the next, and have tried
to capture best probabilistic forecast of this series of
features.

Several high resolution models continue to indicate showers and
thunder developing over southeastern Kansas this morning, and may
clip the counties generally along and south of I35.  Have also kept
some isolated chances for the north central counties as convection
forming in northwestern Kansas may clip that region on its way
northeast.  Both these chances could leave cloud cover in their
wake, and would impact both high temperatures for the day and
available instability for the afternoon hours when next system is
progged to move in.  Areas along and north of I70 have best chances
for inhibition to be eroded by mid afternoon and have increased
afternoon chances in the north and spread to the east, but again
this could be complicated by outflow or residual clouds from
morning convection. With CAPE values running around 2000j/kg and
0-6km bulk shear around 25kts, storms that develop would have
suffient energy to be strong to severe, with wind and hail the
primary threats. Think tornado threat would be more relegated to
an outflow boundary or along the stronger front north of the area.
Depending on how strong the system is as it passes, would not be
surprised to see subsidence bring a break to the storm chances
late in the evening, before next front is on approach from the
north with next potential round into Wednesday. End result is to
carry rain chances in the south and west early, then developing
north and to the east as the afternoon progresses and into the
evening hours.

.LONG TERM...(Wednesday through Monday)
Issued at 322 AM CDT TUE AUG 23 2016

Convective chances remain the main challenges through this portion
of the forecast. Models are in fairly good agreement in cold front
inching southeast into north central Kansas Wednesday afternoon with
mid-level lapse rates in the 7-8 C/km range and mixed-layer CAPE
values from 1000-2000 J/kg ahead of it. Upper jet streak over
central portions of the state ahead of a weakening mid-level wave
will help push 0-6km shear to around 30kts for an environment
supporting some severe storm. The front and wave should provide
ample lift for at least scattered storms, with mid and upper flow
nearly parallel to the front to keep storms from being isolated to
keep severe potential limited to mainly wind and hail. Of course
this setup is predicated on a quiet late morning and atmosphere
which is not a given based on short term challenges. Storms could
continue through much of the night with the boundary or outflow
continuing southeast. With precipitable water values rising to near
2 inches and the upper thicknesses and propagation vectors aligned,
a heavy rain concern exists. Conditions should stabilize somewhat
into midday Thursday with effective surface front likely pushing on
southeast of the area, but southerly winds off the surface increase
overnight as another wave nears the High Plains. This should support
at least decent moisture convergence with another opportunity for
training storms into Friday morning.

At least some chance for thunderstorms continues into the weekend as
the northern wave pushes east and some instability and good moisture
linger. Somewhat lower chances expected Saturday night into Sunday
as this wave passes, but another wave nears the region Sunday night
into Monday for better precip chances.

Warmest temperatures anticipated for Wednesday ahead of the front
and some lower 90s could be realized in southern and eastern
sections. Temps cool somewhat to the end week but should modify
again by Sunday in better insolation. Only small changes were made
to the previous forecast.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
Issued at 641 AM CDT TUE AUG 23 2016

Kept LLWS a few more hours until boundary layer mixes a bit
deeper. Lower cigs also still on track to move in for part of the
morning before scattering and lifting this afternoon. Not highly
confident in timing of convection, gave it a best estimate at 03z
with lower cigs and VCTS at this time. Will also need to watch for
return of LLWS with 40-50kt LLJ tomorrow night.

&&

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

$$

SHORT TERM...67
LONG TERM...65
AVIATION...67



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