Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 181800

Area Forecast Discussion
National Weather Service Topeka KS
100 PM CDT Sat Aug 18 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 310 AM CDT Sat Aug 18 2018

Early this morning a positive tilt upper level trough was located
across the eastern Great Lakes, which extended southwest into the
lower MS river valley. An upper level trough was located across the
Great Basin. A down stream upper ridge was located across the High

Today through Tonight, the upper trough across the Great Basin will
dig southeast across the central Rockies into the central High
Plains late Tonight. Most numerical models show a shorter wave-
length upper trough moving through the base of the main upper trough
as it digs southeast across the central Rockies into the central
High Plains. This lead upper trough will amplify as it lifts
northeast into western KS by 6Z SUN, ahead of the main H5 trough.
During the late afternoon and evening hours a lee surface trough
will deepen across eastern CO, which will increase southeasterly low-
level winds across western KS and eastern CO, providing for deeper
moisture transport northwest across western KS into eastern CO. The
combination of upslope flow and DCVA ahead of the H5 trough will
cause numerous thunderstorms to develop during the late afternoon
and evening hours across eastern CO. A complex of thunderstorms may
form and move east across western KS through the night. The complex
of thunderstorms may begin to weaken after 6Z SUN as the complex
outruns the better instability axis across western KS. The eastern
edge of showers and thunderstorms may move into the western counties
of the CWA after 9Z, then slowly spread east through the remainder
of the early morning hours. Most numerical models show only about
200-500 J/KG of MUCAPE, thus any thunderstorms that move into the
western counties of CWA will not be severe. Showers and elevated
thunderstorms may form across the central and eastern counties of
the CWA towards sunrise as residual moisture return may provide
enough isentropic lift for scattered shower and isolated elevated

Highs Today will be in the mid 80s to around 90 degrees. Light and
variable winds will gradually become southeasterly through the late
afternoon and evening hours, as the surface ridge of high pressure
shifts east into MO. Lows Tonight will only drop back into the upper
60s with increasing cloud cover.

.LONG TERM...(Sunday through Friday)
Issued at 310 AM CDT Sat Aug 18 2018

Main focus for the long term remains on the late weekend into
Monday periods. The bulk of guidance is showing a lead wave
rotating northeast across eastern Kansas the around the parent
cyclone during the day Sunday with surface cyclogenesis resulting
in a weak surface low or inverted trough forming over this area.
With increasing deep moisture with PW values near 2 inches and
weak to moderate though deep isentropic upglide, expect a fairly
widespread precip event from Sunday morning into Sunday evening.
QPF trends continue to rise though the prolonged nature of the
event and generally dry ground conditions should keep flooding
potential low with modest instability and shear keeping severe
weather concerns low. Eastern areas should see a later onset of
precip for temps to reach the low to mid 80s with mid 70s more
likely to the west. Upper trough axis shifts east of the area
Monday morning with some scattered precip likely through the day
especially in deeper moisture in northern areas. Persistence of
cloud and precip may well keep temps from breaching the mid 70s
for much of the area, and feel a continued cooling forecast trend
may be in order as cold air advection takes hold on breezy north
to northwest winds.

Northwest flow aloft for Tuesday to around Wednesday night behind
the upper low keeps conditions mainly dry with surface ridging
building in and temps a few to several degrees below normal.
Southeast flow behind the surface ridge along the front range of the
Rockies will likely result in High Plains convection which could
reach central Kansas during mainly the late night to early morning
hours of Wednesday and Thursday. A more zonal pattern develops
toward the end of the week, with the 0Z ECMWF bringing a shortwave
across the northern and central Plains. Will keep precip chances
small with model variances increasing as temperatures increment
toward normal levels.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1258 PM CDT Sat Aug 18 2018

VFR conditions are expected through the TAF period. Scattered
showers are possible after sunrise Sunday morning. Better chances
for shower and thunderstorm activity looks to arrive near or
slightly after the end of the TAF period. Light southeasterly
winds at 5-10 kts are expected.




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