Mesoscale Discussion 0730
NWS Storm Prediction Center Norman OK
1156 PM CDT Wed Jun 13 2018
Areas affected...Parts of the mid Missouri Valley
Concerning...Severe potential...Watch unlikely
Valid 140456Z - 140730Z
Probability of Watch Issuance...20 percent
SUMMARY...Increasing thunderstorm development, which could be
accompanied by a risk for severe hail, appears possible by 3-4 AM
CDT. It is not anticipated that this will require a severe weather
watch, but trends will be monitored.
DISCUSSION...A fairly broad area of lower/mid tropospheric warm
advection has evolved across much of the north central Plains/mid
Missouri Valley region. This is generally focused beneath and on
the northeastern periphery of a broad plume of warm elevated mixed
layer air emanating from the Great Basin. Associated forcing for
ascent near the edge of the stronger capping appears to be
contributing to ongoing convective development near Sioux City IA.
This is likely being supported by weak CAPE associated with elevated
moisture return (perhaps near/above 700 mb), emanating from richer
low-level moisture beneath the cap, generally across the higher
plains to the west of the Missouri river.
However, latest VWP data from Hastings and North Platte indicate
that southerly low-level jet strengthening to 40-50 kt centered
around 1 km AGL has taken place during the past few hours. Peak
speeds will likely be reached within the next hour or two, with a
subsequent weakening, but gradually veering of the jet to a
southwesterly component through 07-09Z. As this takes place,
advection of low-level moisture into the vicinity of the mid-level
moisture gradient is expected to contribute to considerable
destabilization near/northeast of the Missouri River. Most
convection allowing guidance, including the NCEP HRRR indicate that
this will coincide with increasing/intensifying thunderstorm
development. In the presence of at least modest vertical shear,
supported by considerable veering of winds with height, the
development of moderately large CAPE may support a severe hail
threat in stronger storm development.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 44059777 44059597 42219416 41549473 41759584 42709670