SPC Jun 18, 2021 1630 UTC Day 1 Convective Outlook

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SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook NWS Storm Prediction Center Norman OK
1137 AM CDT Fri Jun 18 2021 Valid 181630Z - 191200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY INTO THE MIDWEST REGION... ...SUMMARY...
Scattered severe storms will pose a threat of damaging wind, large
hail and perhaps a couple tornadoes this afternoon and tonight over
parts of the Ohio Valley region and mid Mississippi Valley. ...Ohio Valley through Middle Mississippi Valley... Only modest adjustments have been made to previous forecast in this
area. Ongoing MCS from Lake Erie through OH should continue
weakening, and in the wake of this feature the atmosphere is in the
process of recovering as a southwesterly low-level jet transports
rich low-level moisture through the pre-frontal warm sector. A plume
of steeper (7-7.5 C/km) mid level lapse rates have overspread this
region, and areas of strong diabatic heating will further
destabilize the atmosphere with MLCAPE from 2500-3000 J/kg likely by
late afternoon. Thunderstorms are expected to redevelop ahead of a
southeast-advancing cold front, especially from OH westward through
central and southern IN and spread southeast. Vertical wind profiles
with 30-40 kt effective bulk shear will support some supercells, but
tendency will probably be for storms to grow upscale into
lines/clusters with time. Large hail and damaging wind will be the
primary threats, though a couple of tornadoes will also be possible
given sufficient 0-1 km hodograph size for low-level mesocyclones.
Potential will also exist for a few significant wind gusts,
especially if activity evolves into a more organized MCS. ...Upper MS Valley... Trailing portion of the front will stall across northern IL through
southern IA. The atmosphere in this region will become strongly
unstable (3000-3500 J/kg MUCAPE) supported by steep lapse rates
associated with an EML plume that resides above rich low-level
moisture. Potential will exist for a few storms to develop along
this boundary this afternoon, but storms should become more numerous
into the evening as a strengthening southwesterly low-level jet
augments mesoscale forcing within the frontal zone. Supercells with
large to very large hail will be the initial primary threat before
activity evolves into an MCS with an increasing threat for damaging
wind. ...Central High Plains... Isolated to widely scattered thunderstorms should develop this
afternoon and last into part of the evening, moving eastward across
the outlook area. Isolated severe wind and hail will be the main
concerns. After the frontal passage, northeasterly flow will veer gradually to
easterly, imparting a substantial near-surface upslope component
that will aid in enhancing deep shear, as well as in moist advection
and storm-relative winds in the inflow layer. Associated lift,
along with diabatic heating of elevated terrain, will promote
deepening afternoon convection beneath steep midlevel lapse rates,
with MLCAPE to near 1000 J/kg, atop a well-mixed and deep subcloud
layer suitable for strong to locally severe gusts. 35-45-kt
effective-shear vectors will support mostly multicells, but with at
least transient supercell characteristics possible. ...Gulf Coast... A tropical storm is forecast to develop from an area of low pressure
now over the west-central Gulf, its center making landfall on the
south-central to southeastern LA coastline late tonight. [See the
latest NHC advisories for specific details on forecast track and
intensity, as well as all tropical-related watches and warnings.] A
couple of tornadoes cannot be ruled out as this system moves inland
overnight. ..Dial/Bentley.. 06/18/2021

Read more Originally posted at National Weather Service Storm Prediction Center