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

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FXUS63 KEAX 181729

National Weather Service Kansas City/Pleasant Hill MO
1229 PM CDT Thu May 18 2017

Issued at 330 AM CDT THU MAY 18 2017

Main concern in the near term will be strong/severe storm chances
this evening and tonight as another shortwave trough digs through
the main longwave trough over the western CONUS, edging deepening
surface low pressure out into the High Plains and providing both
the shear and upper-level support for deep convective initiation
along the eastward-bulging dryline late this afternoon. The main
fly in the ointment and ingredient to watch this morning will be
the northward progression of stratus currently surging northward
across northeast TX and far southeastern OK, which could impact
surface-based instability this afternoon both upstream of our CWA
where convection is expected to develop, and in our area where
instability will impact the longevity and strength of convection
as it moves through eastern KS and into the forecast area. Current
thoughts are that the NAM is a bit too aggressive with the
stratus coverage and progression, and while stratus may make it
into southeast KS by midday, sufficient instability should build
both across our southern forecast area and along/ahead of the
dryline in western KS... will just need to monitor this as it
could impact severe potential for the remainder of the day if
cloud cover is more significant than anticipated.

A warm front/moisture surge currently evident on IR satellite
imagery will also push northward this morning, settling somewhere
between I-70 and Hwy 36 this afternoon, and serving as a "track"
on which storms may travel and develop this evening. Midlevel
lapse rates should sharpen and shear values will increase as the
shortwave trough approaches, making the environment favorable of
upscale growth and QLCS organization as the updrafts begin to
interact and merge later in the evening. In addition, curvature
of the 0-1 km hodograph plus the orientation of the 0-3 km bulk
shear vector normal to the likely northeastward movement of the
developing complex of storms will be maximized near and just north
of the surface warm front, making this a target area for possible
severe weather as storms arrive late this evening. Wind, hail in
stronger and rotating updrafts, and brief tornadoes are all a
possibility, but all depend on how robust storm updrafts remain
as they head our direction this evening.

Another round of storms will develop along the dryline again
Friday afternoon and will again lift northeastward, but morning
cloud cover may be a bit more extensive and could limit
instability for the afternoon and evening. The upper trough will
also be ejecting northward during the evening and overnight hours,
progressively pulling upper-level support away from the eastward-
developing convection, possibly also reducing severe potential.
However, despite these caveats deep layer shear values remain
strong and a severe threat cannot be ruled out across much of the
forecast area. Heavy rain is also possible especially if storms
become a bit more disorganized, and as both PWATs increase to
around 1.5 inches and warm cloud depth increases as warmer
temperatures aloft surge north ahead of the northward pulling
upper low. If significant rain occurs with the complex coming in
this evening and the forecast holds for Friday night, flash
flooding may become a concern.

Quieter conditions are expected behind the Friday system, with
most rain moving out by late morning or midday Saturday. A few
more lobes of energy attempt to swing southward through the main
upper trough as it passes across the central CONUS late in the
weekend or early next week, but overall precipitation chances and
definitely the strength of any convection that develops looks much
lower as the upper pattern transitions more to northwest flow.


.Aviation...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1225 PM CDT THU MAY 18 2017

VFR to MVFR cloud cover will steadily build over the terminals
through the afternoon and evening. While afternoon convection is
possible along a warm front across western Missouri, widespread
storms should hold off until just after sunset. This will come in
two rounds, with the second round persisting through the duration
of the overnight. Low level wind shear is also possible as 2kft
winds approach 35 to 40 kts overnight, though increased surface
winds should at least partially mitigate this potential. Storms
will then exit the terminals Friday morning before the next round
of activity develops by Friday afternoon.




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