769
FXUS63 KBIS 040304
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1004 PM CDT Mon Jun 3 2024

.KEY MESSAGES...

- Showers and thunderstorms tonight through Tuesday morning. A
  few storms could be severe this evening.

- Strong northwest winds Tuesday through Thursday.

- Seasonable temperatures expected through the week with
  slightly warmer temperatures possible late in the week.

&&

.UPDATE...
Issued at 953 PM CDT Mon Jun 3 2024

Broad area of rain stretches from north to south through central
and parts of western North Dakota, which continues to move to
the east-northeast. Some thunderstorms continue over southern
portions of the area where modest instability remains, with a
few lightning flashes noted here and there further north.
Further west, a line of showers with a few lighting flashes
continues to move east through eastern Montana affiliated with
an approaching cold front. This should move into western North
Dakota during the next hour, though some additional showers are
starting to fill in a bit over northwest North Dakota between
the systems. All this activity will then push towards the east
overnight, with chances lingering over central North Dakota into
Tuesday morning.

UPDATE
Issued at 704 PM CDT Mon Jun 3 2024

Line of convection has developed over southwest North Dakota
right along the corridor of stronger CAPE values (~1000 J/Kg),
though storms are now starting to push to the east of the higher
values. Latest guidance tries to pull the core of elevated
instability east, but appears that the storms may continue to
push ahead of this. We did have one severe event (quarter size
hail) over Adams County with our strongest storm, but that has
since weakened, and the strongest storm in the area remains
over Perkins County, SD. Would not be surprised to see a few
more storms increase in intensity and become strong with gusts
to 50 mph and small hail, but the severe risk remains low,
though can`t be ruled out given the marginal shear in place. At
this time, the Perkins County storm is the one to keep the
closest eye on as it gradually makes its way northeast towards
our area. Current area of storms will continue to move east,
with additional showers/storms later tonight affiliated with a
cold front now pushing through central into eastern Montana make
their way east.

&&

.DISCUSSION...
Issued at 203 PM CDT Mon Jun 3 2024

A potent storm system will track from the Pacific North west
this afternoon, across the Northern Rockies and close off into
a closed upper low as it moves into the southern Canadian
Prairie Provinces by Tuesday. Strong upper level divergence is
expected to develop over western ND this afternoon, while
increasing low level convergence develops along the
Montana/North Dakota border. The latest satellite imagery shows
an increasing cumulus field over southeast Montana and into the
western Dakotas. As far as potential convection this afternoon
and evening, not much has changed from this morning. Modest
500-1000 J/Kg MUCape with 30-40 knots of bulk shear will provide
the potential for a few strong to severe storms. As for the
storm mode, starting around 21 UTC the bulk shear is pretty much
perpendicular to a thermal trough the looks to develop along
the MT state line. A more stable airmass on satellite looks to
be situated from around Beach northward, and also looks to be
lifting to the north. Cumulus is building southwest and
expected to continue building northward this afternoon. This
could set the stage for a few discrete cells developing this
afternoon. Current CIN is pretty high over southwest into south
central ND, but you can see a min in the CIN poking into
southeast MT that should lift northward late this afternoon. The
SPC HRRR does show that CIN then increases quickly early this
evening. By this time the shear backs to the southwest and
trends to more parallel to the trough, but not completely, so
you could have a mixed mode of convection with a trend towards
a mixed or linear mode later in the evening and overnight as the
forcing increases with the approaching. However, CIN also
increased and elevated convection would be favored. Therefore
the best bet for strong to severe storms looks to be late
afternoon the southwest and possibly north into the west
central, depending on how the more stable atmosphere in
northwest ND erodes. All hazards would be possible here but the
window appears small. A few NUCAPS soundings over the Mondak
regions shows around 2000 J/KG cape in near Baker MT, but a nice
bump of mid level warming providing a nice C cap. A Buffalo SD
sounding showed a much more unstable atmosphere with MUCAPE
above 3000 J/KG but also with a cap, albeit a not as strong.
Both these soundings may be a bit warm for surface temperatures
as well. A sounding north of Dickinson shows a more modest 1000
J/KG MUCape but was less capped than those soundings to the
west. Not much vertical development of any CU at this time in
southeast Montana, but possibly will develop more with heating
and as cumulus meanders a bit farther east. Low level flow over
ND is more south to southeast, ahead of the thermal trough,
potentially yielding a longer residence time of any developing
updrafts. Will certainly need to monitor. As for the threats, we
mentioned all three, the tornado threat we think would be quite
early on in the convective development with strong surface
heating and some low level shear present. Large hail look to be
a threat if we could get a rotating mesocyclone. Otherwise, CAPE
in our local are seems less favorable for large hail compared
to farther south into South Dakota. Thus quarter size seems
reasonable. The wind threat would be more favored later on if we
get some liner convection or bowing segments. But also here,
the later we get into the evening, the more likely convection
would be elevated. Thus 60 mph also seems reasonable. The strong
shortwave will keep at least a small threat of strong winds as
convection moves into the central part of the state, but
overall, we think the severe potential would be quite a bit less
later and farther east, especially after around 10 PM and east
of the Highway 83 corridor.

Overall we think the NBM probabilities of convection may be a
bit high, especially this afternoon and early evening. However,
showers and thunderstorms should become more widespread (but not
severe hopefully) as we go through the late evening and
overnight hours.

Over central ND, ahead of the convection we could see some fog
develop again from the James River Valley to the Turtle
Mountains. However uncertainty in this is pretty high so we did
not include fog at this time. Late tonight and into Tuesday we
could also see some fog post convection but again, too uncertain
for any one area.

Showers and thunderstorms will exit the area on Tuesday with a
strong westerly surface flow moving in from the west. Tuesday
looks to be breezy over western North Dakota.

Wednesday, however, looks to be the most likely day for wind
highlights as a strong northwest surface flow develops beneath
the Canadian upper level low. At this time it looks like a wind
advisory will likely be needed for at least northern and western
portions of the forecast area, and possibly all of western and
central ND. The ECMWF continues to show a pretty good signal (80
percent probability) for significant winds and gusts over much
of the forecast area, with the 90 percent probability
approaching the northwest. With a strong upper jet in the area,
a case could be made for possible HWW criteria winds given the
strength of the winds aloft. There does seem to be quite a bit
of low and mid level cloudiness around and some upward motion
limiting the wind potential. Will need to monitor this as well.

Wind potential shifts into eastern ND on Wednesday, but breezy
to windy conditions could be felt over the central portion of
the state.

Beyond Wednesday we look to dry out with temperatures possibly
showing a small warming trend as we head towards the weekend.
Mid week will be more seasonable with 60s and 70s. Late in the
weekend into next week the warming trend could continue but high
NBM ensemble high temperature spreads increase so confidence in
anything warmer is not high at this time.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 704 PM CDT Mon Jun 3 2024

Showers and thunderstorms over western North Dakota will
continue to spread east this evening, with additional
showers/storms passing through overnight. This will bring
periods of MVFR/IFR visibility. In addition, small hail and
gusty winds will be possible with the storms. The storms will
exit from west to east late tonight into Tuesday morning, but
westerly winds will be on the increase behind a cold front,
possibly gusting to around 35 kts.

&&

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

&&

$$

UPDATE...JJS
DISCUSSION...TWH
AVIATION...JJS