South Dakota Mesoscale Discussion

Areas affected…North Dakota

Concerning…Severe Thunderstorm Watch 551…

Valid 050808Z – 050945Z

The severe weather threat for Severe Thunderstorm Watch 551

SUMMARY…Thunderstorms continue along and ahead of a slowly
southward-advancing cold front. Although the environment will
continue to support hail and gusty winds, increasing thunderstorm
coverage should limit a more widespread severe threat in the near

DISCUSSION…A midlevel vorticity maximum continues to slowly
progress southeast from Canada into North Dakota. Associated with
this vorticity maximum, a surface cold front is also making its way
slowly southward across the region. Severe thunderstorms developed
along and ahead of this front early this evening producing hail and
strong winds. With time, increasing cold pools and precipitation
shields have merged into a large, west-east oriented mesoscale
convective system (MCS).

The overall environment will continue to support severe
thunderstorms. Mixed-layer CAPE between 500-1500 J/kg, with
most-unstable CAPE closer to 3000 J/kg existing just downstream of
the MCS, should continue to provide ample buoyancy for ongoing
thunderstorms. Additionally, deep-layer shear between 35-50 knots
should support updraft/downdraft organization. Hail and gusty
thunderstorm winds will be the likely threat with the strongest

The limiting factor for a more widespread severe event will be the
combination of increasing surface-based inhibition and the expanding
cold pool. NWS 88D radar imagery from Bismarck, North Dakota,
indicates the MCS outflow has pushed well downstream of the main MCS
by 1-2 counties, limiting this portion of the MCS to ingesting
elevated parcels. Farther east, ahead of the main MCS, elevated
thunderstorms are developing, which should act to lessen buoyancy
and increase surface-based inhibition.

With all this written, given sufficient buoyancy, seasonably-strong
deep-layer shear, and convergence along the cold front, the threat
for hail and gusty winds on an episodic basis should continue for at
least another few hours.

Later this morning, near the commencement of diurnal heating, an
increase in convective intensity may occur as ongoing thunderstorms
move into a less convectively contaminated environment. If this
occurs, a new downstream watch may be needed later this morning.

..Marsh.. 08/05/2019

…Please see for graphic product…


LAT…LON 47340404 48630404 48650294 48540289 48560227 48800213
48710186 48470183 48470106 48630099 48620044 48520041
48549949 48399949 48389890 48519899 48519833 48209827
48169652 47889648 47769629 47749589 47889562 47499557
47499603 47169608 47149623 46639622 46619630 46049633
46049656 45929662 45979898 46299907 46269992 46639994
46640073 46940097 47260104 47220140 47230174 46980175
46960216 47020221 46970300 47310307 47310307 47340404

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