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ACUS11 KWNS 041902
SWOMCD
SPC MCD 041901
IAZ000-NEZ000-SDZ000-042100-

Mesoscale Discussion 1009
NWS Storm Prediction Center Norman OK
0201 PM CDT Wed Jul 04 2018

Areas affected...North central and northeast Nebraska and adjacent
portions of the mid Missouri Valley

Concerning...Severe potential...Watch possible

Valid 041901Z - 042100Z

Probability of Watch Issuance...40 percent

SUMMARY...Intensifying thunderstorm development appears increasingly
possible through the 3-5 PM CDT time frame. This may include the
risk for an isolated supercell or two, and eventually the evolution
of an organized convective system. Trends are being monitored for a
possible severe weather watch.

DISCUSSION...A zone of enhanced low-level warm advection on the nose
of a weak to modest (25-30 kt at 850 mb) low-level jet has
maintained a corridor of thunderstorm development near and just
north of a convective outflow boundary across northern Nebraska.
This currently extends south of Sioux City IA into the Mullen NE
vicinity, where it intersects a weak southward advancing cold front.

South of these boundaries, daytime heating of a moist boundary layer
with surface dew points in the 70s appears to be contributing to
large mixed layer CAPE in excess of 3000 J/kg, beneath steep
mid-level lapse rates associated with very warm elevated mixed layer
air. Latest objective analysis suggests that inhibition may be
weakening sufficiently to allow for increasing surface-based
convection within the next couple of hours. It appears that the
boundary intersection may provide the primary focus for any such
development, and once this occurs, severe weather potential is
likely to increase.

Veering of winds with height in lower to mid-levels appears to be
contributing to at least marginally sufficient shear to support
organized convective development. This may include an isolated
supercell initially, accompanied by a risk for severe hail and
perhaps a tornado or two, before activity grows upscale. The
evolution of at least a small organized mesoscale convective system
appears possible late this afternoon into early evening, with
increasing potential for strong surface gusts as activity tends to
propagate eastward along the stalled outflow boundary.

..Kerr/Hart.. 07/04/2018

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

ATTN...WFO...FSD...OAX...LBF...UNR...

LAT...LON 43190007 43359751 43119628 42119583 41549661 41759821
41970041 43190007



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