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

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000
FXUS63 KEAX 212058
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
358 PM CDT Fri Jul 21 2017

.Discussion...
Issued at 354 PM CDT FRI JUL 21 2017

Hot time, summer in the city...you know the rest. The dome of hot
air will sit over the Lower Missouri River Valley for another day,
through Saturday, but relief is in sight as we expect a change in
the broad scale pattern to usher in a slightly cooler and drier
airmass for at least a few days starting late this weekend well into
next work week.

More specifically, the large flat pattern across the Nation, that
shifted the prevailing storm track well to our north, and allowed
the oppressive heat and humidity to move north, is expected to
buckle a little over the weekend into early next week thanks to a
notable shortwave trough currently moving east through Alberta and
Saskatchewan. This will help push a frontal boundary, currently
wallowing across central Iowa, south into Missouri and Kansas;
with the front slowly moving into northern Missouri Saturday
afternoon. The arrival of the front will continue to justify a
slight chance of storms developing as early as the afternoon hours
of Saturday across far northern Missouri, and any storms that
bubble up would have a lot of instability to work with; but it
looks more likely that storm development will wait till the
evening and overnight hours as the supporting upper level trough
swings across the Northern and Central Plains that night. So,
while we will be watching for cooling rains and cloud cover to
move in with the front, expectations for the daylight hours of
Saturday are that the oppressive heat and humidity will prevail
one more day as dew points ahead of and behind the front will
still be in the mid to upper 70s, with highs topping out in the
upper 90s to around 100, resulting in heat indices in the 105 to
110 range yet again.

As for the type of storms we may see Saturday night; there will be
lots of instability for any storm to work with as even the most
conservative estimate of CAPE values will range above 4000 J/KG
by Saturday afternoon. However, as is common with storms in the
middle of summer, the organizing shear from the prevailing winds
will lag well behind the front, up across Iowa; therefore
expectations for severe weather with these storms is rather low.
That being said, with CAPE values over 4000 J/KG, and little
shear, storms will likely pulse up and down, likely leading to
the strongest storms when they first develop --whether that`s in
the afternoon or evening hours-- with the severe threat fading
quickly as cloud cover and rain modify the local environment.
Locally gusty winds and torrential rain and frequent lightning
currently look to be the primary threats from the strongest
storms.

Looking beyond Saturday, a secondary front will move south behind
the primary front Sunday, but it wont arrive until late enough in
the period that it wont help much with the heat Sunday. But, on
the up side the primary front Saturday will be enough to take a
little edge off the heat --Sunday highs in the low 90s-- as well
as lower the dew points, which will leave our heat index values
topping out near 100 degrees again that afternoon. However, the
secondary front will bring the notable cool off as temperatures
for Monday and Tuesday with highs in the upper half of the 80s.
Additionally, another trough will be moving east across the
Canadian Plains which might be able to help spark storms again
Monday night into Tuesday with the help of the nocturnal jet.

&&

.Aviation...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1229 PM CDT FRI JUL 21 2017

VFR conditions will prevail over the next 24 hours. Only issue to
watch for will be the low level wind shear overnight as the
nocturnal jet gets going.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Excessive Heat Warning until 8 PM CDT Saturday for KSZ025-057-
     060-102>105.

MO...Excessive Heat Warning until 8 PM CDT Saturday for MOZ001>008-
     011>017-020>025-028>033-037>040-043>046-053-054.

&&

$$

Discussion...Cutter
Aviation...Cutter



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