Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 241132

Area Forecast Discussion
National Weather Service Topeka KS
632 AM CDT Sat Mar 24 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 319 AM CDT Sat Mar 24 2018

Cooler weather is on tap for today and tonight with little in the
way of sensible weather.

A compact upper level disturbance and attendant 90-kt H300 speed max
was quickly passing through the Central Plains. Drier air wrapping
in around the complex brought a swift end to precipitation over NE
Kansas shortly after 06Z this morning. At the surface, a 1002 mb low
situated just north of Wichita was also tracking nearly due east,
with northerly winds and increasing CAA taking place along the
Nebraska border. This cooler airmass overspreads the rest of the
area by sunrise and will set the stage for a cooler day. H850 temps
fall to -2/+2 C, and with the likelihood of low
stratus/stratocumulus lingering for much of the day (given upstream
satellite imagery and RAP/HRRR sounding progs), highs will be
confined in the 40s and 50s today. Surface ridging builds in for
this afternoon, helping to reduce the initially gusty northerly
winds as the day unfolds. For tonight, if the stratus continues to
linger, min temps may not fall quite as low as currently forecast.

.LONG TERM...(Sunday through Friday)
Issued at 319 AM CDT Sat Mar 24 2018

The primary impacts through this period center around shower and
thunderstorm potential during the Sunday through Monday evening time-
frame. For Sunday into Monday, the large-scale midlevel wave pattern
will amplify in response to a speed maximum advancing through the
western periphery of western-CONUS troughing. Downstream midlevel
ridging will amplify from the lower Mississippi Valley to the Great
Lakes region and Northeast, with a long fetch of strengthening
midlevel southwesterly flow becoming established over the central
States. The strengthening zonal component of the flow aloft over
the Rockies, coupled with the emergence of modest and broad
differential cyclonic vorticity advection downstream of the
aforementioned trough, will induce lee cyclogenesis over the
central High Plains on Sunday. The surface cyclone will
subsequently develop generally eastward along the warm side of a
baroclinic zone through Monday, perhaps devolving into a more
diffuse wave-disturbance as it tracks toward western Missouri amid
the lack of any salient midlevel perturbation.

Low-level southerlies preceding the surface cyclone will advect
partially modified Gulf moisture into parts of the forecast area,
from Sunday into Monday, with related isentropic ascent supporting
increasing chances for showers on Sunday. The continued influx of
low-level moisture, amid subtle midlevel perturbations transiting
the area embedded in the southwesterly flow aloft, will foster
additional rounds of showers and perhaps eventually isolated
thunderstorms into Sunday night and early Monday. Present
indications are that effective inflow layers for this activity will
be rooted above a stable surface layer/sloped frontal zone.

Proceeding from Sunday night into Monday, there should be a
tendency for the baroclinic zone to sharpen in proximity to the
migratory surface perturbation, with a loosely-defined warm sector
accompanying the surface cyclone/wave potentially developing
northward. The bounds of this warm sector -- and thermodynamic
profiles within the warm sector -- will be augmented by cloud- and
precipitation-reinforced theta-e deficits -- i.e., mesoscale
phenomena for which predictability is greatly limited. Moreover,
notable dispersion exists among numerical model solutions
regarding their depiction of the position of the larger-scale
baroclinic zone and track of the surface low. As a result,
confidence regarding prospects for warm-sector surface-based
effective inflow layers building into the forecast area is
presently limited.

Regardless, ample deep shear will exist across the area on Monday,
accompanying around 45-50 kt of 500-mb southwesterly flow, amid
moderately steep midlevel lapse rates where antecedent convective
processing is not robust. This will offer conditional potential for
strong to perhaps a few severe storms -- conditional upon pockets of
surface-based effective inflow becoming established by (1) surface
diabatic heating amid pockets of thinning clouds/cloud breaks,
and/or (2) near-surface northward mass fluxes encouraging surface
dewpoints rising into the lower 60s. This strong to perhaps
locally severe-thunderstorm potential -- albeit conditional --
would maximize during the afternoon within the open warm sector,
and potentially be reinforced along the sharpening cold front
trailing southwestward from the surface cyclone/wave.

Forecast hodographs exhibit multiple inflections through the storm
depth, and boundary-relative cloud-layer mean winds and deep shear
are expected to be oriented largely parallel to the cold front. If
sufficient pre-frontal boundary-layer destabilization were to occur,
these kinematic factors would foster mixed convective modes with
interacting convective cells locally growing upscale, particularly
in proximity to the cold front where more quasi-linear convective
modes would be supported. Present indications are that sustained
discrete-cell modes will be unlikely. This, combined with the
anticipated limited areal coverage of surface-based effective inflow
layers, may tend to temper the overall coverage/intensity of severe
potential -- though some conditional severe potential may exist.
Also of note, locally heavy rain may accompany convection with
repeated rounds of rainfall potentially affecting some areas on
Monday. Nevertheless, the lack of an influx of richer deep moisture
(precipitable water generally remaining below 1.5 inches) should
tend to mitigate flooding potential. Once again, any severe risk
would be contingent upon surface-based effective inflow layers
building into the forecast area -- for which uncertainty is
presently substantial.

Confidence is relatively higher that northwest to north winds behind
the departing surface cyclone/wave will advect cooler air into
the region for Monday night into Tuesday behind the sharpening
cold front. Isentropic ascent above the sloped frontal surface
may support some precipitation lingering into Tuesday morning, as
a southern vorticity maximum embedded within the amplified
midlevel trough drifts across the southern Rockies vicinity. For
Wednesday into late week, periodic chances for light showers will
affect the region. This will occur as the larger-scale trough re-
organizes over the central States -- in response to multiple
perturbations/speed maxima advancing through the broader-scale
flow -- and then progresses eastward.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 630 AM CDT Sat Mar 24 2018

MVFR to IFR stratus will linger for much of the period over NE
Kansas, possibly scattering out with peak heating today along and
SW of a line from CNK to OWI. Northerly winds of 10-15 kts with
gusts to 25 kts persist for much of the day, gradually decreasing
tonight and veering to the east.




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