Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 212336

Area Forecast Discussion
National Weather Service Topeka KS
636 PM CDT Sat Jul 21 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday)
Issued at 345 PM CDT Sat Jul 21 2018

The region will remain beneath northwesterly midlevel flow --
between a ridge protruding north-northeastward from a strong
anticyclone over the southern Rockies vicinity and reinforced deep
cyclonic flow over the eastern states. A north-south-oriented
surface ridge will remain nearly stationary over eastern parts of
the central Plains, with light surface winds expected. Until high-
level clouds spread southeastward downstream of the aforementioned
ridge later tonight, efficient radiational cooling and lingering
ground moisture may support patchy fog -- particularly across
northeast and east-central KS. Overnight lows are expected to be in
the middle and upper 60s. Sufficient insolation across the region on
Sunday amid partly cloudy to mostly sunny skies will support
afternoon high temperatures in the upper 80s to lower 90s.

.LONG TERM...(Sunday night through Saturday)
Issued at 345 PM CDT Sat Jul 21 2018

A midlevel shortwave trough crossing the southern Canadian Prairies
and adjacent north-central states will be associated with a trailing
surface boundary that should cross the forecast area Sunday night
into Monday. This boundary will become increasingly diffuse as it
approaches the region. Also, the small wavelength between the
shortwave trough and the downstream eastern-states deep cyclone
suggests additional pre-frontal moisture return will be greatly
lacking. As a result, only low chances for showers and
thunderstorms are expected across the region for Sunday night into
Monday and strong/severe storms are not expected. The influx of a
continental air mass behind this boundary should result in dry
conditions into the mid-week time frame, with seasonable
temperatures expected.

For late week into next weekend, the latest multi-model consensus
suggests a deep cyclone may track from the southern Canadian
Prairies toward eastern Canada, with an accompanying shortwave
trough transiting the northern states. The southward/westward-
trailing segment of a surface front accompanying the midlevel
cyclone/trough should spread across the region late in the week.
Thereafter, present indications are that the broader frontal zone
will stall across the central Great Plains. More appreciable
moisture transport between the southwestern rim of weak post-frontal
surface ridging and southern High Plains lee troughing could support
repeated clusters of convection spreading southeastward in the
vicinity of the frontal zone amid enhanced midlevel
northwesterly/west-northwesterly flow. Convective outflow from this
activity will augment the exact position of the surface effective
boundary separating higher theta-e air to the south from
convectively processed air to the north.

Robust convective potential including strong-severe thunderstorms
and flash flooding with repeated convective rounds could potentially
exist across portions of the region late in the week into next
weekend. However, subtle differences among model solutions regarding
the amplitude of the larger-scale wave pattern cast uncertainty
regarding the initial location of the synoptic baroclinic zone and
related initial convective activity. Moreover, the location of the
effective boundary will become increasingly influenced by mesoscale
processes related to convection -- for which forecast uncertainty
grows substantially at these time ranges. As a result, the Hazardous
Weather Outlook and other messaging do not presently include mention
of severe-thunderstorm and flash-flooding potential, though some
potential for inclusion of these conditions may be necessitated in
subsequent forecasts.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 634 PM CDT Sat Jul 21 2018

For the 00z TAFs, VFR conditions are expected through the period
with north-northeasterly winds remaining less than 10kts.




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