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ACUS11 KWNS 281221
SWOMCD
SPC MCD 281220
IAZ000-MOZ000-NEZ000-281445-

Mesoscale Discussion 0914
NWS Storm Prediction Center Norman OK
0720 AM CDT Thu Jun 28 2018

Areas affected...CENTRAL AND EASTERN NEBRASKA...SOUTHWEST IOWA...AND
FAR NORTHWEST MISSOURI

Concerning...Severe potential...Watch possible

Valid 281220Z - 281445Z

Probability of Watch Issuance...60 percent

SUMMARY...An intense thunderstorm continues to move east through
central Nebraska capable of producing strong winds and large hail. A
favorable environment exists ahead of the storm and a watch may be
needed this morning. To accommodate this potential, a Slight Risk is
currently planned to be introduced with the 13Z outlook.

DISCUSSION...An isolated, severe thunderstorm complex has developed
across central Nebraska within a broad warm-air advection regime
occurring within a west-southwesterly low-level jet. This
thunderstorm has been moving east within a narrow 850-millibar moist
axis that is being focused by increasing convergence on the nose of
the aforementioned low-level jet. This moist axis extends
east-southeast from central Nebraska into central Missouri and
should depict the corridor of most likely movement for the central
Nebraska thunderstorm. A very unstable environment is found within
this moist plume as 850-millibar dewpoint temperatures around 18-19C
combine with mid-level lapse rates on the order of 8.5-9 C/km to
yield most-unstable CAPE values between 2500 to excess of 4000 J/kg.


The region of interest is on the southern periphery of the stronger
deep-layer shear. This, in turn, may actually help the thunderstorm
develop a strong cold pool with eventual upscale growth into a
mesoscale convective system (MCS). Given the strength and
orientation of the low-level jet, and the extreme instability
upshear of this potential MCS, repeated multi-cell development on
the southern/southwestern side of the thunderstorm complex should pr
mote a turn to the east-southeastward through the morning, aligning
it with the moist axis stretching into Missouri. As diurnal heating
strengthens during the morning, the residual nocturnal boundary
layer should mix out and low-level lapse rates should steepen
increasing the threat for strong thunderstorm outflow and potential forward-propagating MCS.

To accommodate this potential, a Slight Risk is currently planned to
be introduced with the 13Z outlook.

In the more immediate time frame, some uncertainty remains with how
things will evolve this morning, but confidence is increasing that a
watch may become necessary.

..Marsh/Guyer.. 06/28/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DMX...EAX...FSD...OAX...GID...LBF...

LAT...LON 42329944 42429632 41329446 39969489 41189849 41600008
42329944



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