Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 231134

634 AM CDT Thu Apr 23 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 208 AM CDT THU APR 23 2015

Northwest flow slowly loosing its grip on the central portions of
the nation as the upper low over Ontario slowly moves off and the
Rockies ridge breaks down from influences of multiple waves along
the West Coast, most notably the stronger low off Baja. Recent water
vapor imagery showing enhancement downstream of this system into
western Arizona. Low level ridge stretched from the eastern Dakotas
into southern Missouri with 850mb dewpoints of 10C+ common from the
Texas Panhandle south and east per 0Z obs. Weak isentropic upglide
and shallow moisture leading to areas of mid cloud in northeast
Kansas, with lower/more persistent cloud into southern and western
portions of the state.

Low- to mid-level moistening and forcing for ascent increase
rather slowly through today, but rise quickly tonight as the Baja
wave progresses northeast into the Four Corners area, pushing the
700-850mb ridge east for deep south to southwest flow to develop
on 850mb winds of 30-45kts. This should leave the daytime periods
dry with amount/persistence of cloud somewhat difficult to pin
down, but expect better insolation in the north and east for
warmer temps there. Precipitation tonight expected to increase
from late evening int the overnight from southwest to northeast,
though models differ on areas of best coverage. Somewhat enhanced
low-level moisture convergence is advertised in the southeast,
especially from the NAM, though signals for better upper support
come into northwestern areas, more directly downstream of the
upper wave, but have some concern this could be an artifact of
convection along the Front Range. Mid-level lapse rates increasing
to around 8C/km with elevated CAPES around 1000 J/kg and 1-6km
bulk shear of 30-40kt bring some potential for a few severe hail

.LONG TERM...(Friday through Wednesday)
Issued at 208 AM CDT THU APR 23 2015

Friday continues to be the forecast period of concern. Nocturnal
convection ongoing at the start of this period is expected to
move across the area through the late morning hours. May actually
see a break in the late morning and early afternoon. There is
still variability in how each model handles the incoming upper
wave and the development of the surface low and attendant warm
front. NAM and EC both develop the warm front front generally
along I70 while the GFS has more of a bimodal surface low that
extends the boundary northeast across our area into Iowa. Worth
mentioning that the EC is also slower with the actual upper wave
and slightly deeper as well. Factors in agreement remain the
strong upper jet moving in, and increasing mid level winds with the
approach of the wave, and a dryline set up somewhere near or just
east of Wichita around 0z. With incoming energy lifting over both
these features, expect storm development late afternoon into
evening hours and moving eastward. Amount of available instability
will be influenced by residual morning convection, and could also
influence eventual placement of the warm front, but would
anticipate higher values generally along and south of I70. Even if
values hold in the 500-1500 j/kg range, abundant bulk shear of
50+kts is ample for supercells and associated wind and hail
threat, as well as isolated tornadoes. Could also see some locally
heavy rainfall if storms can train along the warmfront as they
move east.

Saturday morning sunrise may have some lingering showers as the
upper low exits to the northeast, but expect most of this activity
to exit the area through the morning hours. Guidance pushing high
temperatures up considerably given early day showers and clouds
followed by northerly winds, and have gone cooler with highs in
the middle 60s north to low 70s south. Western side of the cooler
surface high continues to influence temperatures on Sunday, with
highs slightly cooler in the middle 60s most areas and a dry
forecast. Warm front moves into central Kansas ahead of next
incoming upper low, and will carry some showers on Monday but note
that several runs have taken this system farther southward. Slight
chance PoPs on Tuesday are for secondary piece of energy moving
through the central Plains, but this feature is farther north and
east in the EC, so just a slight chance. Sensible weather
continues highs in the 60s and lows in the 40s.


.AVIATION...(For the 12Z TAFs through 12Z Friday Morning)
Issued at 634 AM CDT THU APR 23 2015

VFR conditions expected to continue through the bulk of this
forecast. Low-level moisture slowly builds, especially after 0Z,
with MVFR ceilings expected to develop in the 05Z-09Z period. Have
delayed greater thunderstorm chances a bit given latest trends.




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