Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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FXUS63 KEAX 140023
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
723 PM CDT Fri Oct 13 2017

.Discussion...
Issued at 256 PM CDT FRI OCT 13 2017

Main concern continues to be potential for severe thunderstorms
Saturday afternoon and evening. A strong but neutral to slightly
positively tilted trough will move across the center of the
country Saturday. This will help push the quasi stationary front
through the area as a strong cold front. Strong forcing along the
front and large scale ascent associated with the upper trough should
be more than enough to get storms going. There are several
important variables that will aid or diminish the overall severe
threat. 1) How much cloud cover will erode within the warm sector
to build instability? 2) How veered will surface winds be to
detract from the amount of helicity? Higher resolution models
show clouds decreasing and the warm sector becoming moderately
unstable by the afternoon with 1000 to 2000 J/KG CAPE. This is
rather robust instability for this time of year. Surface winds
also are veered to the south-southwest. This is, thankfully,
limiting the amount of helicity in the pre-storm environment.
However, hodographs in our southeastern zones, ahead of the
convection, still show strong curvature and 0-1km helicity values
may be in the 150 to 250 m^2/s^2 range. This is still very high
and when put in context of a 30 kt west-to-east 0-3 km shear
vector, the near storm environment will need to be watched closely
tomorrow afternoon. While initial storms may be supercellular,
they`re expected to quickly become linear in nature. If updrafts
orient orthogonal to the 0-3km shear vectors it would greatly
enhance the environment for mesovortices and a few tornadoes,
given the higher helicity values. Regardless of the tornado
potential, the strong winds aloft suggest a good potential for
damaging winds at the surface. Folks who are outside tomorrow
afternoon need to be very weather aware as storm motions will be
very fast and any potential tornadoes could quickly spin up from
within the fast-moving line of storms.

Behind the front, much cooler air will settle over the region. Highs
on Sunday will struggle to reach 60 degrees. This will set us up for
a chilly night with temperatures falling into the middle to upper
30s. It`s possible these could be lower, depending on where the
surface high settles overnight. So the potential for frost will
exist and folks with sensitive vegetation may need to take
measures to protect their plants.

The rest of the forecast looks quiet and dry, with temperatures
getting back normal Monday, and then a bit above normal through
the end of next week.

&&

.Aviation...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 647 PM CDT FRI OCT 13 2017

Surface boundary in the vicinity of all the terminals making
winds a bit erratic, albeit at low speeds (around 5 to 10 kts).
KSTJ and KMCI are near the boundary so expect winds to be
fluctuating between south and northeast, with some light and
variable. KMKC and KIXD will likely keep VRB or southerly winds
for another couple hours before switching to VRB or northeasterly.
Low level wind shear becomes a concern later tonight when surface
winds out of the northeast at 5 kts become overrun by
southwesterly winds around 30 kts at 2000 to 3000 feet. By sunrise
the southerly winds should return and LLWS becomes less of a
concern. Some low stratus is also possible through the morning and
afternoon, but this is a medium confidence forecast for the low
stratus. KSTJ could see off and on showers all afternoon and
evening before the main round of thunderstorms move in around 00z,
while the other sites will likely remain dry until the main round
of showers and thunderstorms come through around 00z Sunday. Will
likely introduce more of a prevailing thunderstorm group in the
next issuance (06z).

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

Discussion...CDB
Aviation...Leighton



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