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

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FXUS63 KEAX 192359

National Weather Service Kansas City/Pleasant Hill MO
659 PM CDT Wed Apr 19 2017

Issued at 330 PM CDT WED APR 19 2017

A relatively potent surface trough generally centered over the S/C
High Plains with its eastern periphery over eastern Kansas and
western Missouri is currently responsible for the strong southerly
winds across the forecast area. Good warm/moist air advection east
of this surface trough, along with good insolation has caused
instability over much of the area to increase through the day. A
warm front is currently situated along or near I-80 across E
Nebraska and W Iowa, which has put all of the forecast area deep in
a warm sector. Expect the rest of the daytime hours to remain warm
and sunny across the area (with exception of far northwest Missouri
and northeast Kansas). Off to the west of the forecast area, across
western and central Kansas and south central Missouri, a cold front
continues to creep E/SE. Expect this cold front to be the trigger
for deep convection across SE Nebraska and C/E Kansas within the
next 2-3 hours. In the mid/upper levels a shortwave trough is
gliding through the Northern Plains with its axis generally cutting
across central Nebraska and W/C Kansas. This trough with its 40-50
kt mid level W/SW flow will provide enough lift to help the cold
front initiate storms and provide enough shear to combine with the
instability for severe storms later this evening and into tonight.

Expect the storms to initiate along the cold front in the next
couple hours and push to the east/southeast with time, ultimately
moving into far northwestern Missouri around 7 pm, perhaps a touch
later. Southerly winds at the surface, along with the aforementioned
W/SW mid level flow will cause a veering-with-height wind profile
that will allow the afternoon/evening storms to have increased
organization, perhaps obtaining supercell characteristics. The
primary concern with this evening activity will be large hail and
strong winds. The tornado threat is somewhat limited, but still
existent. Forecast soundings taken in NW Missouri later this evening
indicated enough turning with height to warrant a tornado concern,
with somewhat clockwise hodographs, especially in the lower levels
yielding 0-1 km SRH values of around 150-250 m2/s2. That being said,
there are a few limiting factors for tornadic activity. 1.) The
vicinity of the storms to the cold front will keep cold air
undercutting of the storms in play. 2.) The convection`s proximity
to the cold front will also mean that the storms will likely
encounter more of a veered surface flow, than what would be optimal
for tornadoes. 3.) As the storms move eastward toward NW Missouri
they will likely interact with each other, which will tend to
disrupt the tornadic potential. This area, with the best low level
storm parameters lending to tornadoes, will be located across far
northwestern Missouri, namely Atchison (MO), Nodaway, and Holt
Counties, with diminishing tornado concerns east and southeast of
those counties as storms continue to interact with each other and
loss of daytime gradually stabilizes the atmosphere.

As the complex of storms moves east and southeast with time, the
atmosphere will gradually lose some instability and it will
transition more into a line of storms with primarily wind concerns
through the late evening and overnight hours. Given the shear
generally parallel to the cold front, storms could train for a
while, but given the progressive nature of the cold front these
there will still be enough forward movement of the storms to not
cause much flooding. Given that some area streams are still a little
swollen from recent rains it`s conceivable that there could be some
localized stream flooding and perhaps some isolated flash flooding
with this activity. Timing of the storms into the KC metro area look
to be around midnight, and lasting through 3-4 am before pushing off
into central Missouri.

Storms will move out of the forecast area by Thursday morning,
leaving the rest of the day dry. The next chance for rain comes
Friday night into Saturday as another fairly potent trough moves
through the area. This system will not cause any severe weather,
given its trajectory across the area. Severe weather concerns will
likely reside well to the south, with western and central Missouri
residing along the northern periphery of the surface cyclone. This
will limit any instability, and likely bring about more stratiform
rain. Depending on the trajectory of this system heavy rain will
affect portions of the area with a tight gradient between the haves
and the have-nots. Areas south of I-70 could see amounts through
Saturday reach the 1-2 inch range and area further south, toward the
Ozarks obtain 3+ inch amounts. Areas north of I-70 may only see
modest amounts ranging from perhaps a quarter inch along the IA/MO
border to maybe an inch closer to the I-70 corridor. Flooding and
perhaps some flash flooding will be the primary concerns with this
activity, again, more toward the HWY 50 corridor southward.

Dry pattern then takes over as dry continental air mass moves into
the plains through the rest of the weekend and into early next week.
The next chance for rain comes in mid week next week as moisture
flows back into the area and upstream troughing recommences.


.Aviation...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 659 PM CDT WED APR 19 2017

A cold front will push through the region tonight, impacting all
terminals between 04z-08z. A broken line of thunderstorms is
expected to continue along and just ahead of the front, but may
weaken with time, so have gone with fairly optimistic ceilings and
visibilities as the storms move through. Winds will veer slightly
just ahead of the frontal passage but overall speeds and gusts
should drop a bit after sunset to around 15 kts; then, winds will
veer sharply to the northwest following frontal passage. Patchy
MVFR stratus may linger into the morning, but will mix out by mid-
to late-morning.




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