Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 162327

Area Forecast Discussion
National Weather Service Topeka KS
627 PM CDT Sat Sep 16 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday)
Issued at 350 PM CDT Sat Sep 16 2017

As of 19z Saturday afternoon, a H5 trough was positioned from the
northern Rockies into the central High Plains. At the surface, a
center of low pressure resided across the OK/TX panhandle region. A
cold front extended northeastward from the low pressure through
north central KS. Ongoing showers and thunderstorms in eastern KS
are being aided by modest isentropic upglide near 310K. A capping
inversion near H8 has precluded thunderstorm development and for
that matter a deep Cu field along the aforementioned cold front. At
this point, sfc based convection appears unlikely through the
afternoon and evening hours along the cold front. Mostly sunny skies
across the southern half of KS has yielded 3000 J/KG of sfc based
cape with little/if any . Sfc based storms have
developed across southern Coffey, southward to the OK border.
Steering flow is oriented ENE, which should keep the bulk of
activity south of the CWA for the time being. Later this evening,
elevated thunderstorms aided by a 30kt LLJ and weak perturbations
within the cyclonic flow are expected to develop between 00-03z this
evening along the front. Steep mid level lapse rates will yield
MUcape near 2000 J/KG with effective shear near 25-30kts. RAP/HRRR
and CAM guidance all suggest this development during the 00-03z
timeframe. Transitioning into the overnight, activity should push
southeastward across the CWA as the front sags into southern KS. A
secondary batch of thunderstorms are possible along the H85 boundary
across far northeast KS/northern MO overnight. Steering flow
associated with these storms would be easterly; quickly moving any
activity out of the area by daybreak.

As for Sunday, the cold front will become stalled in southeast KS.
With southwesterly mid level flow remaining in place. Scattered
showers and thunderstorms cannot be ruled out as weak embedded
perturbations move across the area. MUcape is expected to remain less
than 1000 J/KG. Therefore, the threat for severe storms on Sunday
appears low ATTM. North of the front, much cooler temperatures are
in store with highs Sunday afternoon reaching the middle 70s.

.LONG TERM...(Sunday night through Saturday)
Issued at 350 PM CDT Sat Sep 16 2017

Late weekend and early work week periods continue to look the
wettest of the long term. Warm air advection is rather deep Sunday
night with southern upper level jet streak moving into Oklahoma and
a mid-level wave moving ENE into the central Plains from Colorado
all contributing to ascent. With MUCAPE around 1000 J/kg could
see a few stronger storms though effective shear is not
impressive. The wave exits during the morning with drier air
moving in aloft. Low-levels remain moist as winds become
southerly, and if enough clearing can occur, could see MLCAPE
reach over 2000 J/kg with around 30 kts of deep-layer shear for a
severe weather setup. Forcing is subtle though models continue to
suggest fast lee cyclogenesis giving rise to minor surface
convergence, but subsidence behind the wave will need to be
overcome. Have kept a chance PoP for the Monday afternoon on into
early Tuesday morning as isentropic upglide persists and could
keep any renewed convection going.

Midday Tuesday to midday Wednesday should be dry with southerly
winds increasing Tuesday for a warm day. Lead wave moving out of the
western CONUS upper trough drags a cold front through the area
Wednesday though the WAA from previous periods looks to bring a
decent cap in place. Will keep a small PoP in the far southeast
where moisture is better. Drier and slightly cooler takes hold
Wednesday afternoon and night, thought the deepening western
trough brings breezy south winds and warmer air in for the later
periods, however models are overall slower with this trough
coming east. Precip chances generally increase Thursday night into
the weekend though a continued slower trend seems very plausible.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 625 PM CDT Sat Sep 16 2017

Scattered showers and storms will persist through tonight, though
confidence in timing and location of convection is low and thus
only mentioned VCTS at the TAF sites for the 00Z package. A cold
front currently bisecting NE Kansas will continue to slide SE,
with southerly winds switching to the north overnight. MVFR to
possibly IFR stratus will fill in behind the front late tonight
and into the day on Sunday.




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