SPC MD 1435


MD 1435 Image

Mesoscale Discussion 1435
NWS Storm Prediction Center Norman OK
0230 PM CDT Sun Aug 09 2020

Areas affected...eastern North Dakota and northwest Minnesota

Concerning...Severe Thunderstorm Watch 423...

Valid 091930Z - 092100Z

The severe weather threat for Severe Thunderstorm Watch 423

SUMMARY...Thunderstorms capable of strong thunderstorm winds, large
hail, and a tornado or two will move east through the afternoon
across eastern North Dakota. This threat will persist into northwest
Minnesota before weakening across north-central into northeast
Minnesota later this afternoon.

DISCUSSION...Thunderstorms have developed/strengthened across
northeast North Dakota along an eastward advancing cold front.
Additional thunderstorms have developed in advance of the cold front
along horizontal convective rolls and on the north side of a slowly
southward moving outflow boundary remnant of early day elevated
convection. These thunderstorms will continue through the afternoon
as strong-to-extreme instability (2000-4000 J/kg) and effective
layer shear between 35 and 50 knots remains in place. The kinematic
environment will remain supportive of embedded transient supercells
and supercell-like structures before eventually evolving into more
multi-cell/line-segment structures. However, given the degree of
instability and a low-level vorticity reservoir along the front, a
tornado or two will remain possible over the next couple of hours.
Otherwise, strong winds and large hail will be likely with the
strongest thunderstorm cores.

With time the thunderstorms across northern areas of the watch will
move into an increasingly less thermodynamically-favorable
environment as most-unstable CAPE decreases to the order of 1000
J/kg in the wake of early morning convection and widespread remnant
cloud cover.

Farther south, thunderstorm coverage and evolution remains somewhat
uncertain. Ongoing development should continue within the existing
severe thunderstorm watch, with initial storm motions to the east.
With time, however, uncertainty related to the
development/evolution/strength of cold pools yields lower confidence
with eventual storm motion/evolution. Some model guidance suggests
stronger thunderstorm cold pool development and an eventual
southward turn, taking storms into northeast South Dakota. If this
scenario becomes apparent, an additional severe thunderstorm watch
may be needed across portions of northeast South Dakota or
west-central Minnesota.

..Marsh.. 08/09/2020

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


LAT...LON   46069918 48619680 48379443 45569599 46069918 

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