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Area forecast discussion
National Weather Service Topeka Kansas
550 am CDT Sat Sep 21 2019

..update to aviation forecast discussion...

Short term...(today and tonight)
issued at 325 am CDT Sat Sep 21 2019

Early this morning the upper trough was located from Montana into
Arizona with a southwesterly upper flow present across the plains
and a ridge over the Great Lakes. Water vapor satellite shows a
stream of moisture from eastern Kansas southwest into the eastern
Pacific this morning. Precipitable water values were generally
around two inches across eastern Kansas this morning which is
roughly 200 percent of normal for this time of the month. A cold
front extended from the Dakotas to low pressure in eastern Colorado.

For today, severe weather continues to be a possibility especially
if the clouds are able to breakup in the afternoon hours allowing
for further destabilization. For areas south of the frontal boundary
around 2500 to 3500 j/kg of MLCAPE is forecast by mid to late
afternoon. RUC forecast soundings show an eml across east central
Kansas which erodes by late afternoon. Expect elevated showers
through part of the morning within an area of isentropic lift.
Profilers suggest the presence of weak pv anomalies moving northeast
within the southwest flow as well. Models are in agreement for
convective development during the late afternoon and early evening
hours along and ahead of the cold frontal boundary. Some discrete
storms are possible ahead of the front where shear of 35 to 45 kts
is forecast. Hodographs support the possibility of a tornado with
helicity values around 200 m2/s2. Strong mid level shear and
steepening lapse rates will favor large hail formation in the
afternoon and evening hours. Storms should consolidate during the
evening hours and progress southeast through the overnight hours
into Sunday.

Forcing for ascent will increase overnight with the approaching mid
level trough. Strong moisture transport is forecast ahead of the
trough into eastern Kansas. 925 mb to 850 mb moisture convergence
will increase during the evening and overnight hours with the
backing of the low level jet. Upper level divergence is forecast to
increase across northeast and east central Kansas within the area of
the entrance region of the upper jet. Training of cells will lead to
heavy rainfall in the 2 to 4 inch range with locally higher amounts
approaching 6 inches or higher through Sunday morning. Therefore
will maintain the Flash Flood Watch through early Sunday
afternoon.

Long term...(sunday through friday)
issued at 325 am CDT Sat Sep 21 2019

The frontal boundary moves southeast of the forecast area Sunday
evening with the passage of the upper trough bringing an end to the
precipitation in east central Kansas. A dry period is expected
Monday and Monday night with the return of precipitation chances
again on Tuesday as a mid level wave is forecast to move across
Nebraska and Kansas. Tuesday night into Wednesday a trough will move
across the plains and bring another frontal boundary southeast into
Kansas on Wednesday. Models differ with the timing and handling of
the ejection of the upper low over the southwest states into the
Central Plains. Therefore confidence is not high and have maintained
small chances of precipitation into next Friday. High temperatures
will be near normal through the period with highs in the upper 70s
to around 80.

&&

Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 550 am CDT Sat Sep 21 2019

MVFR cigs with stratus are expected to remain for much of the
period with some periods of VFR cigs. Isolated to scattered thunderstorms and rain
expected through 16z, then again by 00z. More widespread tsra
expected after 02z through the end of the period. Have lowered
vsbys to MVFR with storms after 03z at mhk and 05z at top and foe.
South winds around 14 kts with gusts to 23 kts decreasing to
around 10 kts around 01z.

&&

Top watches/warnings/advisories...
Flash Flood Watch from this evening through Sunday afternoon for
ksz010>012-022>024-026-035>040-054>056-058-059.

&&

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