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

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FXUS63 KEAX 261953
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
253 PM CDT Wed Jul 26 2017

.Discussion...
Issued at 320 AM CDT WED JUL 26 2017

Large convective complex is spreading across much of Nebraska into
northern Kansas associated with a well-defined upper wave. This
activity will encounter a more stable low-level airmass over
northeast KS and northern MO later this morning which should allow
for some weakening, but could still get scattered showers and a
few weak storms tracking into areas north of the Missouri River
into the late morning and early afternoon.

The scattered precipitation and widespread cloud cover associated
with this wave throws a lot of uncertainty into the heat advisory
that is ongoing for today. If today were sunny, 850 hPa temps as
high as 23C would support highs in the middle to upper 90s which
would yield heat index values as high as 105 to 110 given
dewpoints rising into the middle to upper 70s. However, the cirrus
shield is already getting pretty thick and temperatures appear
unlikely to get this high. Will go ahead and let the heat advisory
ride for now, since even a little bit of sun coming out this
afternoon could allow temperatures to get into at least the lower
90s with heat index values around 100 to 105. If clouds don`t
thin out then at least northern parts of the advisory may need to
be dropped.

The main focus then becomes the potential for very heavy rain
across northern Missouri tonight as a strengthening low level jet
begins to feed into a cold front approaching from the northwest.
Strong moisture transport within this jet will bring precipitable
water values into the very high to extreme category, likely
exceeding 2.5 inches. Combine this with very deep warm cloud
depth, a nearly saturated troposphere and tall/thin CAPE profiles
similar to a tropical airmass and all ingredients are in place for
very efficient rainfall rates possibly exceeding 2 to 3 inches
per hour. While the ground across northern Missouri has had some
time to dry out, and 3-hour flash flood guidance is as high as 3
to 4 inches in spots, these amounts could certainly be exceeded in
some locations given the high rain rates and potential for
training storms along the boundary. Will therefore issue a flash
flood watch for areas near and north of US 36 Highway until 7 AM
Thursday. Will have to watch to see if this heavy rain axis
shifts a bit further south of the current watch area as a few
models are beginning to suggest, in which case more counties may
need to be added.

A secondary concern this evening will be the potential for strong
to severe storms ahead of the front especially if clouds can clear
out and allow the airmass to become moderately or strongly
unstable. Should this occur, marginal shear values and increasing
low-level shear in the vicinity of the low-level jet would be
supportive of a few severe storms with damaging winds, especially
from northeast KS into northwest MO and even as far south as the
KC metro area. One big difference between this event and what
occurred Saturday night will be quite a bit more mid-level
moisture. This lack of dry air aloft will cut back on the
potential for strong downward momentum and make it unlikely that
we see multiple damaging downbursts over a large area like what
occurred on Saturday. Any damaging wind gusts should be much more
scattered in nature this time.

Scattered showers and storms will likely redevelop near and south
of I-70 on Thursday as the front makes slow southward progress
into the Ozarks. Shear will be quite a bit lower so these are
unlikely to be very strong. This activity will clear out by early
evening setting the stage for a very nice end to the week with
highs in the low to mid 80s and much lower humidity. These cooler
and drier conditions will likely last into at least the middle of
next week.

&&

.Aviation...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 251 PM CDT WED JUL 26 2017

Light spotty rain showers will move into and out of the terminals
through the afternoon. After a break in the rain later this
evening another round of thunderstorms will be possible at the
terminals. Confidence in impacts at the terminals is low to medium
at this point so will continue with VCTS mention for now. After
rain departs the terminals for good expect a period of MVFR CIGs
through the early to mid morning hours on Thursday.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...Flash Flood Watch through Thursday morning for MOZ001>008-
     011>017-023>025.

&&

$$

Discussion...Hawblitzel
Aviation...Leighton



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