Tornado and Flash Flooding in North Dakota, June 7 to 8, 2021

Area Forecast Discussion
National Weather Service Bismarck ND
357 PM CDT Mon Jun 7 2021

.SHORT TERM...(This evening through Tuesday night)
Issued at 340 PM CDT Mon Jun 7 2021

The two highlights of the short term period will be the chance for
severe thunderstorms this evening into tonight across the south
central through the southeast, followed by another chance for severe
thunderstorms across the west and north central tomorrow afternoon
and into tomorrow night.

Current surface analysis places a low along or near the western
North Dakota/South Dakota border with a warm front stretching off to
the east. Gusty southeasterly flow can be found behind and just
ahead of the warm front, ushering in moist air with dewpoints now in
the 50s across south central ND and in the 60s from central SD
southward. 500 mb analysis depicts southwesterly flow with slowly,
but steadily, increasing heights as the upper ridge tries to become
more amplified. Storms are expected to overcome the stabilizing
effect of rising heights aloft and form near the warm front
boundary this evening (most likely after 00Z). Initial storms will
be capable of all severe hazards, including hail up to 2 inches
in diameter, damaging wind gusts up to 70 mph, and an isolated
tornado as vorticity looks to be maximized along the warm front.
Storms are expected to grow quickly upscale into clusters,
transitioning to mainly a wind threat as storms move off to the
northeast.

A wave in the upper flow could allow some showers and storms to form
across the west overnight and move into the north central. No severe
weather is expected with this activity; however, a few stronger
storms capable of small hail will be possible.

Tomorrow morning, some remnant showers and storms may be lingering
across the central and east from the overnight activity. Otherwise,
moisture will continue to increase ahead of a quickly approaching
shortwave that moves in from the Four Corners region with a
deepening trough across the western CONUS. This shortwave will be
responsible for the next round of storms that are expected to
develop across eastern Montana into western ND Tuesday afternoon.
The severe weather threat appears greater with this activity as
stronger shear (40-50 kts sfc-500 mb) and greater instability
(steep lapse rates resulting in 2000-3000 J/kg MUCAPE) looks to be
in place. Therefore, hail up to 2.5 inches in diameter, damaging
wind gusts to 70 mph, and a couple tornadoes will all be
possible, especially with any discrete storms that form early on
into the convective cycle. CAMs depict this activity eventually
growing upscale and moving off to the northeast. How far north the
line of storms make it before moving into North Dakota is still
in question, and a nocturnal line of storms moving into
northwestern ND and eventually into north central ND is not off
the table. If this were to happen, the primary threats would be
severe hail and wind.

.LONG TERM...(Wednesday through Sunday)
Issued at 340 PM CDT Mon Jun 7 2021

Severe thunderstorm potential on Thursday highlights the long term
forecast period.

Wednesday morning should see the exiting thunderstorm complex with
post-frontal convection possible as cooler air aloft fills in with
the shortwave. Guidance is fairly consistent with the placement of
the surface low over the eastern portion of the state, which may re-
develop thunderstorms in the afternoon over the James River Valley.
Shear is weaker in this period but given adequate instability, a few
stronger thunderstorms can't be ruled out.

Thursday, the upper level trough begins to cross the Northern
Rockies and becomes negatively tilted as a jet streak ejects out of
the trough base. In response a surface low will deepen and move
north into eastern Montana, where divergence aloft expected to be
maximized Thursday afternoon. Moderate CAPE is expected to develop
in the warm sector of the surface low across western North Dakota,
where surface dew points should likely exceed 60 F. Kinematics
look impressive with this convective setup, with 40 to near 50 kts
of 0- 6km shear orthogonal to the north-south oriented
convergence zone and strong backing low level flow promoting
longer and possibly more curved hodographs. This environment
should promote a severe thunderstorm threat with all hazards
possible, especially early when more discrete cells are possible.
There are several caveats to the threat ceiling however, with some
guidance keeping the surface low further west into Montana as
storms initiate, which may reduce the threat of a discrete storm
mode in our west. Upscale growth either way is likely as the
surface low and associated front is expected to push across the
state overnight, promoting the transition to a severe wind threat
in the overnight hours.

Conditions dry out by Saturday, though some post-frontal convection
can't be ruled out on Friday, especially across the far north.
Friday is expected to be cooler and breezy to windy as strong flow
aloft and a pressure gradient contribute to increased westerly
winds. Amplified ridging will build this weekend, with better
agreement among 00Z global model clusters for amplitude and ridge
axis placement. Cluster analysis is consistent with a mostly dry
forecast for this period, lining up with the pattern exhibited on
the 12Z deterministic run.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1252 PM CDT Mon Jun 7 2021

Thunderstorm development is expected later this evening across
south central into southeast North Dakota, potentially affecting
KBIS and KJMS into the overnight hours. Thus, VCTS has been kept
in the TAFs for those terminals, with some adjustments likely
needed later on as confidence in timing and location increases.
Some of these storms could be severe with strong wind gusts and
hail. Elsewhere, VFR conditions are expected with variable winds.
Scattered showers and storms may develop across the west
overnight and move off to the northeast; however, confidence in
this development is lower and no mention of precipitation will be
included in the TAFs at this time. Tuesday morning, low clouds are
expected to develop across the south, potentially resulting in
MVFR ceilings from KDIK-KBIS-KJMS for a few hours before lifting.
Widespread breezy winds out of the east southeast are expected by
the end of the TAF period.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...Gale
LONG TERM...AE
AVIATION...Gale

Hazardous Weather Outlook
National Weather Service Bismarck ND
645 PM CDT Mon Jun 7 2021

NDZ025-036-037-046>048-050-051-082345-
Foster-Kidder-Stutsman-Emmons-Logan-La Moure-McIntosh-Dickey-
645 PM CDT Mon Jun 7 2021

This Hazardous Weather Outlook is for portions of south central
North Dakota and southeast North Dakota.

.DAY ONE...Tonight

Severe weather will be possible through this evening with
damaging wind gusts to around 70 mph, large hail around 2 inches
in diameter, and an isolated tornado. A Severe Thunderstorm Watch
is in effect until midnight CDT. See www.weather.gov/bismarck for
more details.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

There is a chance for thunderstorms Tuesday. A few storms could be
strong to severe.

There is a chance for thunderstorms with severe weather
on Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter are encouraged to contact the National Weather Service
with any severe weather reports.

NDZ020>023-034-035-042-045-082345-
Oliver-McLean-Sheridan-Wells-Morton-Burleigh-Grant-Sioux-
645 PM CDT Mon Jun 7 2021 /545 PM MDT Mon Jun 7 2021/

This Hazardous Weather Outlook is for portions of south central
North Dakota.

.DAY ONE...Tonight

There is a slight chance for thunderstorms late tonight. Some
storms could be strong to severe with quarter sized hail and
gusty winds up to 60 mph.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

There is a chance for thunderstorms on Tuesday. Some storms may be
severe. Damaging wind around 70 mph, large hail around 2 inches
in diameter, and an isolated tornado will be the potential
hazards.

There is a chance for thunderstorms with severe weather
on Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter are encouraged to contact the National Weather Service
with any severe weather reports.

NDZ001>005-009>013-017>019-031>033-040-041-043-044-082345-
Divide-Burke-Renville-Bottineau-Rolette-Williams-Mountrail-Ward-
McHenry-Pierce-McKenzie-Dunn-Mercer-Golden Valley-Billings-Stark-
Slope-Hettinger-Bowman-Adams-
645 PM CDT Mon Jun 7 2021 /545 PM MDT Mon Jun 7 2021/

This Hazardous Weather Outlook is for portions of north central
North Dakota, northwest North Dakota, south central North Dakota,
and southwest North Dakota.

.DAY ONE...Tonight

There is a slight chance for thunderstorms late tonight. Some
storms could be strong with penny size hail and gusty winds.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

There is a chance for thunderstorms on Tuesday. Some storms may be
severe. Damaging wind around 70 mph, large hail up to the size of
tennis balls, and a tornado will be the potential hazards.

There is a chance for thunderstorms with severe weather
on Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter are encouraged to contact the National Weather Service
with any severe weather reports.