FXUS63 KEAX 202101

National Weather Service Kansas City/Pleasant Hill MO
401 PM CDT Fri Oct 20 2017

Issued at 401 PM CDT FRI OCT 20 2017

Forecast for the next 36 hours has not changed much, though
confidence in timing and type of storms that are expected with
Saturday's frontal passage is growing. But, first things first.

Satellite imagery this afternoon shows a shortwave trough pivoting
form the Southern into Central Plains ahead of a larger trough
digging into the Great Basin. Lee side frontogenesis is noted across
the western high Plains ahead of the large trough, and with the help
of the leading shortwave trough, has tightened up the pressure
gradient across the Central and Southern Plains resulting in gusty
south winds today. This has helped bring abundant moisture north,
and this trend will continue overnight with breezy winds continuing
to pump moisture in our direction. Thus, by Saturday we expect
dewpoints in the 60s ahead of the front, which will help fuel the
storms later in the day. Isentropic lift ahead of the front will
help generate extensive cloud cover, especially given the cap
expected around 5000ft, but will also still be able to produce
light scattered showers. Areas of extreme northeast Kansas into
far northwest Missouri may have ongoing showers and isolated
thunderstorms ahead of the front starting as early as the late
morning to early afternoon hours due to the up-glide; but the
main show continues to look like it will wait for the front to
arrive. Speaking of the front, the timing has not changed much
with this series of model runs, thus expect arrival of the front
and strong associated storms in Northwest Missouri is between 5
and 7PM, with the arrival in the KC area between 7 and 9PM. The
front will continue to push south and east through the overnight
hours, remaining rather progressive, thus indicating that any
lingering storms should exit central and northeast Missouri before
noon Sunday.

As for the type of storms, shear ahead of and along the front
continues to be rather strong thanks to 40+ knot 850mb jet that will
prevail ahead of and along the front as it moves in. This will
result in 0-6KM shear values in excess of 25 knots for the
afternoon, with values increasing to 40+ knots near the front.
However, the shear vectors will be orientated almost parallel with
the front as it moves through in the evening hours. Instability
ahead and along the front will be sufficient for strong to possibly
severe strength storms as surface CAPE values will reach above 1500
J/KG with MUCAPE values still expected to peak above 2000 J/KG. With
precipitable water values in the 1.5 inch range, expect all of this
to lead to linear convection, with a large defined squall line being
the best way to characterized the storms Saturday evening. This will
result in strong damaging winds being the primary threat with the
storms. However, that said, low level 0-1KM helicity is still in the
200+ m2/s2 range, so small circulations ahead of and along the front
can not be ruled out completely, which may result in a marginal
chance of severe hail or a very weak isolated tornado. Additionally,
the 1.5 inches of precipitable water indicates that many of the
storms Saturday will bring torrential rain, with widespread
rainfall totals likely around 1 inch as the front moves through,
with locally higher amounts in the 2 to 3 inch range. The
progressive nature of the storms should mitigate any threat of
flash flooding, but lingering rain over running the front may
result in some flooding along area river, creeks and streams.

Cooler, drier, weather will settle into the region Sunday and
persist into the beginning of the work week.


.Aviation...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1226 PM CDT FRI OCT 20 2017

VFR conditions will dominate the next 24 hours. Issues to watch
will be focused on the wind as gusty south winds will persist
into the overnight hours, though not be as gusty. Additionally,
there will be a strong low level jet --45 to 50 knots-- which
might induce some wind shear overnight. Gusty winds will return
Saturday morning. Otherwise, current timing of storms Saturday
have them effecting the terminals closer to 00Z/22.




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