Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 160447

Area Forecast Discussion
National Weather Service Topeka KS
1147 PM CDT Fri Sep 15 2017


.SHORT TERM...(This evening through Saturday)
Issued at 336 PM CDT Fri Sep 15 2017

The early afternoon water vapor satellite imagery featured a deep
longwave trough positioned over the inter-mountain west with multiple
subtle perturbations rotating around its base and ejecting to the
northeast. One such wave helped prolong an area of showers and
isolated thunderstorms across central Kansas. Despite a 10 kft deep
wedge of dry air below cloud base, precip managed to reach the
ground thanks to the added kinematic lift associated with the
departing shortwave. At the surface, an elongated 1002 mb surface
low was located near the the Siouxland region with a trailing cold
front stretching southwestward and into far NW Kansas. NE Kansas was
located in the warm sector ahead of this front, but clouds from the
daytime precip resulted in a complex thermal field in the early
afternoon analysis.

Over the next 24 hours, the upper level longwave will pivot ENE into
the western Dakotas as a 90 kt jet streak wraps around the base of
the trough. This will help push the cold front southeastward during
the day tomorrow, approaching Concordia by the mid to late
afternoon. Aside from a slight chance of showers and storms with the
nocturnal LLJ early tomorrow morning, the next best chance for
storms will be along and ahead boundary tomorrow afternoon. MLCAPE
values will likely exceed 3000 J/kg due to steepening mid-level
lapse rates and ample surface heating ahead of the boundary.
However, the best jet dynamics and deep shear look to stay north of
the CWA. Thus, the best threat for stronger storms will be in the
incipient stages of any convection, with large hail and localized
damaging winds the main threats. This is in agreement with the SPC
Day 2 marginal outlook.

.LONG TERM...(Saturday night through Friday)
Issued at 336 PM CDT Fri Sep 15 2017

Front continues southeast through the area Saturday night, through
not terribly fast with upper flow nearly parallel to it. Should
still be enough forcing and moisture for decent coverage despite
some capping remaining with a few near-severe storms possible until
ML CAPE diminishes in the late evening. Not seeing any obvious signs
of a persistent training situation but some locations could see
locally heavy amounts. Expect decreasing coverage with time late in
the night into midday Sunday with chances increasing again Sunday
night into Monday as isentropic upglide develops through the column
and the southern branch jet comes into Oklahoma for added ascent in
its left-front quadrant. Not much focus in the ascent noted at this
time though still high-chance to likely PoPs are warranted and
elevated CAPE increasing to around 1000 J/kg could produce some
small hail. Will need to watch how much the warm sector moderates
Monday afternoon with the potential for a decent shear/ML CAPE
combination and suggestions of low level convergence remaining. Low-
level jet increase Monday night for another chance for elevated
storms. Western CONUS upper trough deepens into the midweek as
multiple waves rotate through it. Current operational models are
fairly consistent with another Pacific cold front passing through
Tuesday night and Wednesday though, though southwest flow in the mid
levels could bring a decent cap in. Have kept chances limited at
this point. Somewhat better precip chances come late in the
forecast with the upper trough pushing a bit farther east. As for
temperatures, Sunday still looks the coolest of the week with
highs perhaps not breaking the mid 70s in some locations. Highs
return to the 80s for the remainder of the week.


.AVIATION...(For the 06Z TAFS through 06Z Sunday)
Issued at 1147 PM CDT Fri Sep 15 2017

There is a little more uncertainty with the forecast than usual
because there does not appear to be a significant synoptic scale
feature to focus on for precip chances aside from the FROPA. The
HRRR/RAP continue to hang onto the idea for elevated storms moving
across north central KS by mid morning. It appears surface based
storms are most likely to occur along or just ahead of the front.
So have included a tempo for TS preceding the FROPA and included a
VCTS for generally the afternoon hours when there may be some
elevated storms of a more scattered nature. Will keep a mention of
LLWS at TOP and include it for FOE since surface winds have
remained backed to the southeast. Although the boundary layer
should not completely decouple given the decent pressure gradient
over the region progged to persist.




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