153
FXUS63 KBIS 032058
AFDBIS

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

.KEY MESSAGES...

- Another round of thunderstorms this afternoon through Tuesday
  morning. A few storms could be severe this afternoon and
  this evening.

- Strong northwest winds Tuesday through Thursday.

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

&&

.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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1227 PM CDT Mon Jun 3 2024

Fog has finally dissipated at KJMS and VFR conditions to begin
the 18Z TAF period at all TAF sites.

Thunderstorms will be the main forecast issue later this
afternoon and tonight as a potent upper level wave moves through
the region. Isolated thunderstorms are expected to develop this
afternoon over eastern MT/western ND and then become more
numerous as they spread east tonight and Tuesday morning. At
this time we focused mainly on the initial line of thunderstorms
that move through this evening and into the early overnight
hours, but there may be a couple rounds of convection. Any
storms would have the potential for MVFR-IFR visibilities and
MVFR ceilings in addition to strong wind gusts. In addition to
the convection, areas of fog are possible over eastern portions
of central ND, ahead of the convection. Then once convection
exits patchy fog could be possible at any TAF site. Tuesday
morning lingering showers and isolated thunder will exit from
west to east with strong west to northwest winds developing
towards the end of the TAF period.

&&

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

&&

$$

DISCUSSION...TWH
AVIATION...TWH