FXUS63 KTOP 191148
Area Forecast Discussion
National Weather Service Topeka KS
648 AM CDT Sun Aug 19 2018
...Update to aviation forecast discussion...
.SHORT TERM...(Today and tonight)
Issued at 326 AM CDT Sun Aug 19 2018
Early this morning an upper trough was located across western SD and
extended south-southwest into eastern CO. A minor lead shortwave
trough was lifting east-northeast across central KS and northern OK.
Through Tonight, the upper trough across the central High Plains
will dig southeast and amplify into a closed upper low across
southern NE and northern KS by 00Z MON, then slowly drift east-
southeast across northeast KS by 12Z MON.
As the upper trough digs southeast into western NE stronger ascent
ahead of the upper trough will lead a deepening area of surface low
pressure across south central KS by 18Z SUN. A warm front will
extend east across southeast KS. Showers and thunderstorms will
continue to develop as DCVA increase as the upper trough deepens and
digs southeast towards south central NE. Deeper moisture will also
be advected northward, which will increase isentropic lift north of
the surface warm front. Expect an area of widespread showers and
elevated thunderstorms across the central portions of KS early this
morning to to shift eastward across the CWA through the mid and late
morning hours. Individual showers and elevated thunderstorms will
move to the north-northeast.
This afternoon the surface low near ICT around 18Z SUN will slowly
shift east-northeast across south central KS into extreme southern
portions of east central KS. The 00Z NAM tracks the surface low
along I-35, which will lift the surface warm front northward across
the southeast counties of the CWA late this afternoon and evening.
Most CAM models keep the sfc warm front south of the CWA through the
afternoon and early evening hours. Thunderstorms that develop north
of the warm front will be elevated, any may not be strong to severe.
However, if the warm sector does manage to reach northward into the
southeast counties of the CWA, then MLCAPES may increase to 500-1000
J/KG. Forecast hodographs along and south of the surface warm front
show good low-level curvature and the 0-1 KM SRH values are
forecasted between 200-400 J/KG. Given an environment with strong
low-level vertical windshear, there is a chance along and south of
the surface warm front for low top supercell thunderstorms which may
produce brief tornadoes and some larger hail. This will be more of a
mesoscale forecast, since the better chance for isolated tornadoes
would occur with more discrete surface based storms that develop
along and south of the surface warm front. The area with the better
chance for low top supercells will be southeast of I-35 from 21Z SUN
through 02Z SUN. However, most of the CWA will just see widespread
rainshowers with embedded thunderstorms that will be elevated. MUCAPE
values north of the warm front are only forecasted to be under 500
J/kg by many of the CAM models. If MUCAPES do increase over 500
J/KG, as forecasted by the 12Z NAM, then there will be enough
vertical windshear for some of these elevated storms to exhibit mid-
level rotation and produce penny to quarter size hail.
Highs Today across the northern and western counties of the CWA may
only reach the lower to mid 70s due to the steady rainfall and cloud
cover. The east central counties may reach the upper 70s to lower
Tonight, The surface cold front will shift southeast across east
central KS through the night but the upper trough will become more
of a closed upper low as it tracks east-southeast across
northeast KS. The stronger ascent and wraparound moisture will
keep rain chances through the night. We may see a decrease in
elevated thunderstorms through the early morning hours of Monday.
PWATs across the CWA will range from 1.75 to 2.25" thus most areas
of the CWA will receive 1 to 2 inches of rainfall through Monday.
The heavier rainfall amounts may occur across the north central and
northeast counties where 2 to 2.5" within the deformation zone on
the north side of the upper low. where stronger frontogenetical
forcing may occur for a more prolong periods of heavier rainfall.
.LONG TERM...(Monday through Saturday)
Issued at 326 AM CDT Sun Aug 19 2018
Upper low exits Monday with deep moisture remaining in place into at
least the midday hours, and some potential for a TROWAL or
deformation zone to linger into northeastern Kansas. Precipitation
chances will be higher here but amounts should be modest compared
to previous periods. In concert with cold-air advection and little
insolation, temperatures likely will not pass the 70s. Slowly
clearing skies Monday night and still some northwest wind keep
lows in the upper 50s to lower 60s.
Tuesday should be dry but periods of mid-level isentropic upglide
resulting from northwest flow aloft under southeast winds behind the
anticyclone traversing the central Plains bring some chance for
elevated precipitation to mainly western and southern locations late
Tuesday night through Thursday morning. After a slightly cooler
night Tuesday night, temps should moderate somewhat during these
Models are coming into better agreement with a shortwave quickly
passing through the Plains on zonal flow Thursday night and mid-
level warm-air advection should support thunderstorm chances
Thursday night into Friday morning. Increased south to southwest low-
level flow brings temps back to slightly above normal levels for
Friday and Saturday.
.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 642 AM CDT Sun Aug 19 2018
light rain will move into the terminals through the mid morning
hours. Early this afternoon elevated thunderstorms with some
heavier rainfall may drop visibilities down to 3 to 4sm. Ceilings
will remain VFR but may lower to MVFR at times with the heavier
rainfall. The heavier rain will shift northeast of the terminals
this evening. Winds will shift to the northwest late this evening
and MVFR stratus ceilings may move southward across the
terminals, and possibly some IFR ceilings at times.
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