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ACUS11 KWNS 141958
SWOMCD
SPC MCD 141958
SDZ000-NEZ000-NDZ000-142100-

Mesoscale Discussion 0733
NWS Storm Prediction Center Norman OK
0258 PM CDT Thu Jun 14 2018

Areas affected...western SD...southwest ND...northwest NE

Concerning...Severe potential...Severe Thunderstorm Watch likely

Valid 141958Z - 142100Z

Probability of Watch Issuance...95 percent

SUMMARY...Thunderstorm development is forecast generally after 21Z
over far western portions of SD. Once thunderstorms develop and
intensify, large hail and severe gusts (60-70 mph) are possible with
the stronger thunderstorms. An evolution of a thunderstorm cluster
growing upscale into a severe-wind producing MCS will seemingly
occur this evening and significant severe gusts (greater than 75
mph) are possible during the mature phase of the MCS.

DISCUSSION...Visible-satellite imagery shows a high-based cumulus
field beginning to develop east of the Black Hills with a mid-level
accas shield moving into western SD from northeastern WY. Surface
observations show temperatures have warmed to around 100 degrees F
near Rapid City with dewpoints in the low-mid 50s. Farther
northeast, richer moisture characterized by upper 60s to near 70
dewpoints will likely be maintained as a strong capping inversion
aids in increasing moisture quality as deeper boundary-layer mixing
occurs.

Much of the large-scale forcing for ascent is forecast to pass to
the north near the ND/Canadian border. Yet, very deep boundary
layer circulations and convective temperatures likely being breached
will help facilitate convective initiation over western SD and
northwest NE from eastern WY. As the mid-level convection over
northeast WY moves downstream into an environment with richer
low-level moisture (located near the cumulus field),
high/surface-based thunderstorm development is expected near and
after 21Z.

The 19Z Rapid City RAOB showed a nearly dry adiabatic surface-500 mb
lapse rate and southwesterly flow gradually strengthening with
height and yielding around 35 kt effective shear. The moderate to
strong buoyancy farther east/northeast coupled with deep-layer shear
favorable for organized storms, will favor severe thunderstorm
development. Large hail and isolated severe gusts are the primary
threats over western SD before becoming predominately a wind threat
(perhaps significant) into central portions of SD and south-central
ND.

..Smith/Grams.. 06/14/2018

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

ATTN...WFO...ABR...BIS...LBF...UNR...CYS...

LAT...LON 42670293 43480351 45590352 46130334 46530235 46500124
43370088 42690140 42520223 42670293



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