Special Weather Statement, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
108 AM CDT Sat May 22 2021

.UPDATE...
Issued at 108 AM CDT Sat May 22 2021

Limited changes needed tonight. A broad area of showers with
embedded thunderstorms has moved in across ND along a frontal
boundary. These showers should continue through the night as they
move northeastward. Lingering elevated cape, combined with some
increased shear, could make for an isolated stronger storm
tonight. Main threat will be hail and gusty winds. As rain
diminishes later tonight into Saturday morning, areas of patchy
fog may also be found. Patchy smoke also continues to be observed
in north central areas. That all said, mostly updated pops based
on current radar trends for this update.

UPDATE Issued at 937 PM CDT Fri May 21 2021

Thunderstorms are currently entering the southwest while becoming
more widespread across western South Dakota. These storms will
continue to increase in coverage as they move north and east.
Shear will be sufficient for severe weather (around 40 knots of
effective shear) but instability will be limited with MUCAPE
values in the 500 to 1000 J/kg range per latest SPC mesoanalysis.
Storms will be elevated so wind is not too much of a concern, but
some small hail will be possible. For this update just tweaked
PoPs based on the latest radar trends and CAM trends, which have
shift the path of the heaviest storm core just a slight bit east.
This seems reasonable based on current observations.

UPDATE Issued at 615 PM CDT Fri May 21 2021

No major changes needed for this update. Just tweaked some of the
sensible weather fields using some of the latest short term
guidance and also blended in the latest observations. Convection
should continue to develop in the vicinity of the Black Hills
this evening, which will expand as it moves north towards the
southwest and south central part of North Dakota, spreading from
south to north through the night. Still not anticipating much, if
any, severe weather with this activity. Although, some small hail
and frequent thunder and lightning is likely with the stronger
storms.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 300 PM CDT Fri May 21 2021

The forecast area is now between H5 waves as the one from earlier
has pushed into Manitoba and the next in the southwest H5 flow
will be moving out of Wyoming this evening. The surface boundary
across the area was resulting in a significant spread of
temperature, from 40 at Williston to 74 at Jamestown. More
pronounced was the 45 at Dickinson to the - 100 miles away - 72
at Bismarck.

Showers and isolated thunderstorms will move into southwest North
Dakota closer to sunset and then spread north and east. As far as
the risk of severe storms, it is low, with the most likely
scenario being small hail, maybe to the size of a dime, from the
stronger storms that develop. Wind gusts to 40 mph seem the best
bet on any of the stronger storms, based on weak downdraft CAPE.
The area most at risk for seeing hail and gusty winds would be the
south-central part of the area, around and south of Bismarck,
where CAPE is higher and shear is more favorable to get a rotating
storm. They are both forecast to weaken as the evening wears on
and so the question is whether or not storms will be able to fire
/ move in / by then.

The timing of the wave suggests showers and storms will hold on
longer into the daylight hours of Saturday than what they did on
Friday. Still, timing looks to be moving it out by late morning
and leads to a dry afternoon before the next batch closer to
Saturday night.

.LONG TERM...(Saturday night through Friday)
Issued at 300 PM CDT Fri May 21 2021

The series of H5 waves continues as the cutoff H5 low moves up
through central Montana. There is weak diffluence aloft and the
boundary persistant at the surface over North Dakota. With a
stronger H5 wave coming in for Sunday afternoon, and more
favorable convective parameters, the risk for severe storms will
be higher into Sunday night. Still, though, CAPE is only around
1000 J/kg and there is a bit of CIN forecast that would need to be
overcome. There is decent downdraft CAPE that could lead to a
severe wind threat, and lapse rates to support marginally severe
hail sizes. At this point, convective parameters just don't seem
to be lining up to pinpoint a most at risk area and for what
severe weather threat, though the southern part of the state seems
more favored, along with marginally severe storms. This too as
the location of the surface boundary, that will be meandering,
will be critical in combination with the orientation of shear
parameters, to determine storm type. We will have to see how these
things come together over the next 48 hours, or are forecast to
come together, but I am leaning toward fewer discrete storms and
more of a multicellular storm type. Finally, a check of the
latest CIPS analogs suggest the far southwest part of the state
is at the higher risk, but not very high at that.

Beyond that it will drying and warming as the H5 cutoff low
slowly moves away. With that said, an afternoon heating of the
day shower will certainly be possible with colder air aloft over
the area. The next cutoff low is forecast to begin influencing the
North Dakota weather by Thursday or so.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 108 AM CDT Sat May 22 2021

Widespread MVFR/IFR conditions will continue through much of the
period with a mix of low ceilings, patchy fog, and widespread
showers and thunderstorms. Precipitation and fog will begin and
end from southwest to northeast overnight and into Saturday
morning. Conditions will improve Saturday afternoon with
visibility and ceilings rebounding somewhat, although MVFR clouds
may linger into Saturday evening.

&&

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

UPDATE...Anglin
SHORT TERM...JPM
LONG TERM...JPM
AVIATION...Anglin

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Special Weather Statement
National Weather Service Bismarck ND
122 AM CDT Sat May 22 2021

NDZ045-046-220645-
Sioux ND-Emmons ND-
122 AM CDT Sat May 22 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SIOUX AND SOUTHERN
EMMONS COUNTIES UNTIL 145 AM CDT...

At 121 AM CDT, a strong thunderstorm was located 9 miles north of
Kenel, or 11 miles southeast of Fort Yates, moving northeast at 55
mph.

Penny size hail and wind gusts to 40 mph will be possible with this
storm.

Locations impacted include...
Linton, Fort Yates, Temvik, Cattail Recreation Area and Beaver Bay
Recreation Area.

Very heavy rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek shelter
inside a building or vehicle.

&&

LAT...LON 4604 10075 4647 10052 4633 9999 4594 10039
      4594 10059
TIME...MOT...LOC 0621Z 203DEG 47KT 4599 10044

ANGLIN

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