059
FXUS63 KBIS 160602
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
102 AM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Potential for severe storms this evening through tonight,
  with greatest chances over southwest and portions of south
  central North Dakota.

- Active pattern with periodic shower and thunderstorm chances
  during the workweek into next weekend. A few severe storms are
  possible, more notably later in the week.

- Overall temperatures remain around average for this time of
  year.

&&

.UPDATE...
Issued at 1241 AM CDT Mon Jun 16 2025

Severe thunderstorms continue to push across from eastern
Montana into western North Dakota. The main threat remains
strong winds up to 70 mph and large hail up to ping-pong size.
The CAMs show storms persisting through the night moving into
the central North Dakota by the early morning hours. The threat
will decrease to 60 mph and quarter size hail as it treks
further eastward. There remains around 1000-1500 j/kg of MUCAPE
and 40-60 kts of effective shear. Storms will continue to
organize and become more linear has the hail threat will
decrease and the wind threat will remain. The southwest has the
greatest chances for strong winds around 70 mph as the system
comes more linear.

UPDATE
Issued at 1030 PM CDT Sun Jun 15 2025

The previously warned storm moving along the International
Border, having produced hail up to the size of half-dollars and
gusts up to 60 MPH, has diminished into a cluster of sub-severe
storms. Further upstream the main line of thunderstorms has
moved in the eastern Montana, and is expected to cross into
western North Dakota over the next few hours. With MUCAPE
values broadly from 1000 to 3000 J/KG and 0 to 6 KM bulk shear
values up to around 50 to 55 knots continuing to be an analyzed
over the forecast area this evening, thus our expectation is
for these storms to persist. The evolution of these storms can
be broken into two broad segments. The northern segment,
representing the leading edge of the NE-SW orientated line of
storms, is anticipated to be picked up by an incoming cold front
moving in out of the southern Canadian Prairies early
overnight. The southern segment, associated with the low
pressure center, is expected to to continue to move eastward
across the southern half of the forecast area overnight.

Regarding forecast updates, visibility in portions of the
southern James River Valley has started to drop as low stratus
and fog begins to develop. Have started the patchy fog over
this area a little earlier than anticipated in accordance with
the latest model and satellite trends.

UPDATE
Issued at 715 PM CDT Sun Jun 15 2025

Thunderstorms have begun to develop just over far northeastern
Montana and southern Saskatchewan at the time of this early
evening update. One of these storms in particular, found just
over the border in southern Saskatchewan, have developed quite
rapidly over the past hour, with MESH values approaching
1.5-1.75 inches. That being said, with CAPE values more moderate
around 1000 J/KG compared to the strong 0-6KM BULK Shear values
approaching 40-45 knots, MESH may be overestimated. The area
these storms are developing are relatively uncapped, though CIN
increases relatively quickly the further into northwestern
North Dakota that you move. That being said, this storm will
need to be monitored as it moves into northwestern North Dakota
over the next hour or so. For updates, have opted to start
patchy fog a few hours earlier that previously forecast.

&&

.DISCUSSION...
Issued at 133 PM CDT Sun Jun 15 2025

Currently, a weak pressure pattern was situated over western and
central North Dakota. A cluster of showers and thunderstorms
have exited the James River Valley. A complex of thunderstorms
over northeast Montana this morning, has dissipated as it moved
into western ND with some remaining residual mid and high level
clouds. Outflow from this complex looks to have laid a boundary
from around Beulah/Hazen southwest through Dickinson and the
westward through Miles City. Currently western and central ND
remains quite moist with dewpoints generally in the 60s across
the forecast area. Although areas forecast soundings indicate
instability aloft, a stout cap and shortwave ridging is keeping
convection from developing. A strong shortwave is currently
pushing through Idaho and into western Montana and isolated
convection in the higher terrain of central Montana is expected
to increase over the next few hours. Thunderstorms may initially
be discrete this afternoon before more clustering and
eventually upscale growth may occur with more of a wind threat
as convection eventually moves into the Dakotas. In western and
central ND, discrete supercell storms with a threat of large
hail looks to be small, but certainly non-zero. A supercell
could be possible along the edge of the strong capping over
northwest ND, where little CIN remains. Also in the far west,
where strong heating helps to erode the CIN. CAMS have hinted at
the convection in the northwest today. The 12Z HREF does show
some longer UH tracks over northwest ND this afternoon, and a
couple UH tracks from west central into southwest ND early this
evening, before a peppering of short UH tracks that race across
the forecast area from west to east from mid-evening through
the overnight hours. This peppering is indicative of more of an
upscale growth event. However if you look closely through the
peppering, there are some hints at longer UH tracks, thus within
a linear system that looks quite possible tonight, there may be
times when supercellular characteristics emerge. Thus although
wind is likely the main threat with a linear complex if it moves
through the area, hail will also remain a threat, especially
over the west. A tornado spinup along a bowing linear segment is
also possible, but overall the tornado threat is greatest
earlier on, while convection is mostly in Montana, or if we can
get a supercell to develop late afternoon/early evening. Later
tonight, whether it`s the aforementioned outflow boundary, or
an instability axis to the south along the ND/SD border, or
something else, with abundant low level moisture, steep lapse
rates, abundant bulk shear at or above 45 knots and the
approaching strong shortwave, it seems like it`s not a question
of if, but moreso a question of when and where. Right now the
SPC enhanced thunderstorm risk area that extends from central
Montana into southwest ND looks to be the area of greatest
concern with convection later on. The enhances areas does extend
down to the Black Hills area of SD, so a convective complex
moving into ND is not a given, but CAMS have been pretty
consistent in bringing a complex into the western Dakotas later
this evening. The next question is how will things evolve
through the night. Some CAMS weaken convection as it pushes into
central ND while others sustain it, as it tracks across the
forecast area. With such a strong shortwave and abundant bulk
shear, think the potential for strong to severe convection to
survive as it moves across the forecast area is certainly a
possibility.

Convection may then be lingering over central and into eastern
ND as we move into Monday morning. Convection should eventually
push off to the east however Monday morning. We could also see
convection develop again Monday afternoon as the moist and
unstable airmass remains over the forecast area.

As we make our way through the week, we continue to see daily
chances for showers and thunderstorms. Although we may see a
lull in the severe activity Tuesday and Wednesday, the CSU ML
page shows the severe potential increasing again as we head into
Thursday and Friday. Temperatures through the period look to
remain near normal.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1241 AM CDT Mon Jun 16 2025

Thunderstorms and showers are forecast to move west to east
tonight into tomorrow. Thunderstorms could have gusty erratic
winds and hail. Amendments will be made for storms that develop
or move near the terminals. Low clouds will continue across the
eastern half of the state this morning clearing out later after
thunderstorms pass. Winds will veer out of the northwest as
showers and thunderstorms pass as well. Visibility reductions
are possible from heavy rain and low clouds.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Adam/Johnson
DISCUSSION...TWH
AVIATION...Johnson