929
FXUS63 KBIS 121503
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1003 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Isolated severe storms are possible across all of western and
  central North Dakota late this afternoon and into tonight.
  Hail to the size of quarters and winds up to 60 mph will be
  the main hazards.

- Isolated to scattered severe storms are possible late Saturday
  afternoon and into the night. Hail to the size of golf balls
  and damaging winds up to 70 mph will be the main hazards. A
  tornado or two is possible northwest.

- Isolated to scattered severe storms will be possible once
  again on Sunday.

- Expect very warm temperatures and high humidity through the
  weekend.

&&

.UPDATE...
Issued at 1000 AM CDT Fri Jul 12 2024

Showers were heading towards the northwest in Montana, so PoPs
were added an 2 hours ago. Now they have does, so the forecast
was returned to 0% chance of rain there. The rest of the
forecast is still on track.

UPDATE
Issued at 621 AM CDT Fri Jul 12 2024

All of the shower activity has pretty much either dissipated or
moved out of the area. For this reason, we elected to go ahead
and remove precipitation chances through the rest of the
morning. Otherwise, no major changes were needed for this
update.

&&

.DISCUSSION...
Issued at 348 AM CDT Fri Jul 12 2024

Western and central North Dakota sits under the eastern slope
of a broad upper ridge draped over the western US. An embedded
shortwave continues to bring some localized height falls to
portions of the region as it passes through early this morning.
While thunderstorm activity diminished recently, there are
still a few showers floating around out there, mainly over the
central.

The ridge will pop back up today in the wake of this morning`s
shortwave, leading to plenty of sunshine and very warm
temperatures. Highs will range from the upper 80s to the upper
90s. Isolated triple digit readings are not out of the question
across the southwest. A stout cap and rising heights will keep
a lid on convection through most of the day but we could start
to see some height falls around 00z as the next ripple of a
shortwave flattens the ridge. Low to medium chances (20 to 40
percent) for showers and storms should develop across the west
by late afternoon, spreading into the central overnight.

Regarding the severe weather potential late today and tonight,
there will be plenty of instability, even well into the
overnight hours. The latest RAP runs have consistently been
advertising widespread MUCAPE values of 2500 to 3500 J/kg. That
being said, deep layer shear will be rather marginal, ranging
from 25 to 35 knots or so. A surface trough (almost a pseudo
dryline) will be the most likely boundary for initiation with a
cold front on it`s heels. The deep layer shear and anvil level
winds will be near parallel to the boundary over some locations
and more perpendicular over others. Thus, storm mode may be a
bit messy with multi-cell structures/line segments and maybe a
few transient supercells. The most likely hazards will be hail
to the size of quarters and winds up to 60 mph.

We will mainly clear out by early Saturday as modest ridging
once again builds in through the day, limiting the daytime
convection potential. A few lingering showers are not out of the
question during the first part of the day. The next subtle wave
approaches the northwest by the evening hours, bringing more low
to medium chances (20 to 40 percent) of showers and storms.
Thunderstorms are likely to be ongoing across northeast Montana
Saturday afternoon before making their way into the northwest
in the evening or night. They will be moving into an environment
characterized by plenty of instability and strong deep layer
shear in the 45 to 55 knot range. A couple of supercells and/or
bowing structures will be possible as this activity moves from
the northwest and into the central through the night. Hail to
the size of golf balls and damaging winds up to 70 mph will be
possible with this activity. A tornado or two may also be
possible across the northwest early in the event if storms can
remain discrete.

The other concern for Saturday could be some borderline Heat
Advisory criteria across our far southeast, mainly over eastern
portions of LaMoure and Dickey counties. At the moment, the
gridded forecast keeps apparent temperatures here under triple
digits Saturday afternoon, but it won`t take much to bring those
values up past 100 given dewpoints forecast in the 70s and
highs in the low to mid 90s.

Sunday may then be a similar story, with more isolated to
scattered severe storms possible late in the day given more
strong instability and shear. Specifics should start to come
into better focus as we get past some of these other waves
first.

Sunday remains very warm and humid but maybe just a touch less
than Saturday. Highs will range from the lower 80s north to the
low to mid 90s south. The new work week will then feature
diminishing thunderstorm chances and cooler temperatures as the
ridge retreats west and amplifies. Forecast highs on Monday
range from the lower 70s over the Turtle Mountains to the mid
80s southwest. Tuesday and Wednesday will see highs mainly in
the lower 70s to the lower 80s. Most guidance then has us
warming again to end the week as the ridge starts to approach
once again.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 621 AM CDT Fri Jul 12 2024

VFR conditions should prevail through most of the period at all
sites. However, isolated to scattered thunderstorms are
expected to develop across western North Dakota by mid to late
afternoon, spreading into portions of the central in the
evening. Given the hit and miss nature of these storms, we
leaned heavily on vicinity thunder wording in site specific
forecasts. At the moment, KJMS appears to be the site with the
lowest thunderstorm chances. A few storms could become strong
to severe this afternoon and evening with large hail up to the
size of a quarter and winds up to 60 mph. If a stronger storm
does move overhead, brief MVFR to IFR conditions are possible
along with gusty and erratic winds.

&&

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

&&

$$

UPDATE...Smith
DISCUSSION...ZH
AVIATION...ZH