582
FXUS63 KBIS 302014
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
314 PM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Isolated to scattered strong to severe thunderstorms are
  possible tonight, with up to a Level 2 of 5 risk. The main
  hazards are hail up to quarter size, and wind gusts up to 60
  mph.

- Breezy to windy conditions are expected today, especially
  southwest.

- There is a Level 2 of 5 risk for severe thunderstorms Monday
  in southern North Dakota, and a Level 1 of 5 risk for much of
  the rest of the area. The main hazards are hail up to half
  dollar size and wind gusts up to 60 mph.

- The chance for showers and thunderstorms on Independence Day
  is 60 to 80 percent across all of western and central North
  Dakota.

&&

.DISCUSSION...
Issued at 314 PM CDT Sun Jun 30 2024

This afternoon, a very shallow upper ridge was moving over
eastern Montana, with an upstream trough deepening over the
Pacific Northwest. At the surface, a low pressure continued to
deepen over northern Wyoming, while a broad surface high
stretched across Minnesota, creating breezy to windy southeast
winds across western/central North Dakota in between these
surface features. These winds have been gusting up to around 40
mph, but have been staying below advisory criteria as expected.
Scattered radar returns have been persistent through the day,
although with such high cloud bases, these have been virga, with
no evidence of precipitation making it to the ground.

The main forecast concern tonight is the potential for strong to
severe thunderstorms, particularly across western North Dakota.
High-res guidance has been painting a similar picture through
the morning, with convection developing off the higher terrain
in central Montana later this afternoon ahead of the trough base
before moving east into North Dakota. A 50kt low- level jet is
also forecast to develop over eastern Montana and western North
Dakota late this evening. Moisture will be a bit lacking, with
both current and upstream dewpoints (as far south as Nebraska)
only in the 50s, and the 12Z HREF paints a narrow plume of
MUCAPE values of 1000-1500 J/kg across western North Dakota. The
main concern we see at this point is that forecast soundings
continue to advertise significant capping across the entire
forecast area. Although a Level 2 of 5 risk does extend into far
western North Dakota, at this point the potential for any severe
thunderstorms tonight is quite conditional, but recent CAMs runs
support the idea that convection will weaken as it crosses into
North Dakota. The low-level jet will sustained scattered showers
and thunderstorms, however, as the wave moves west to east
across the forecast area through the night.

As the previous shift noted, there is a low but non-zero chance
for storms to re-intensify as they get further into central
North Dakota late tonight into Monday morning, entering an
environment with slightly greater moisture. We are still
carrying the Marginal Risk (level 1 of 5) across most of our
central counties, which seems appropriate to cover this
potential.

The convection overnight and into Monday morning is a large
forecast concern in determining how the potential severe
thunderstorm threat on Monday will evolve. The deeper trough
base aloft will approach from Montana, while at the surface a
weak cold front and surface low will progress west to east
through the day. Continued southerly low-level flow and richer
moisture will boost dew points into the 60s, with a plume of
higher instability extending north-south across the central
Dakotas and overlaid with around 40 knots of 0-6km shear. CAMs
are consistent in developing scattered storms across much of the
Dakotas, although are inconsistent in storm mode and
progression through the evening. HRRR forecast soundings
advertise long hodographs, favoring a hail threat, although the
uncertainty in storm mode is still a concern when deciding the
threat ceiling. We did decide to increase the hail size in our
messaging to up to the size of ping pong balls, and kept the
damaging wind gust magnitude at 60 mph.

Storms exit the area through Monday evening, but precipitation
chances return briefly on Tuesday as a transient wave moves
through cyclonic flow aloft. The active pattern is the main
story of the work week as we stay in a broad troughing pattern,
with temperatures near to slightly below normal Monday through
Wednesday.

Unfortunately, chances for precipitation on Independence Day
continue to increase, with the latest blended POPs advertising
widespread 60 to 80 percent chances of rain through the day.
Ensemble members are honing on a deep trough base and
potentially closed low moving through the Northern Plains
Thursday into Friday, bringing showers and thunderstorms to the
area. CSU Machine learning probabilities continue to show a
low chance for severe weather on the holiday, however. With
this wave of precipitation, most locations have a 50 percent
chance of at least 0.25" of rain. Thursday also looks like the
coolest day of the extended period based on NBM temperature
percentiles, with highs in the lower to mid 70s. Behind the
upper trough, ridging is likely to begin building over parts of
the western CONUS, leading to warmer temperatures on Friday and
Saturday.

Ensemble members are then advertising a few different solutions
regarding the evolution of the synoptic pattern. Guidance is
split on where the ridge axis will be located by the end of the
weekend, with one potential solution having it over the Northern
Rockies, while another has it much further west off the coast
of British Columbia with subsequent downstream region over the
Northern Plains. There seems to have been a slight downward
trend in potential high temperature ranges from the latest NBM
runs, although precipitation chances still look relatively low
starting Saturday and continuing into the middle of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1246 PM CDT Sun Jun 30 2024

Low-level wind shear is forecast at KBIS/KDIK/KJMS for a few
hours tonight as a 50 kt low-level wind max develops as low as
1500 ft AGL. Showers and a few thunderstorms are forecast to
move out of Montana and into western ND in the 05-09 UTC time
frame, and into central ND from 08-12 UTC. Low MVFR to IFR
ceilings are expected with this activity, most likely at
KMOT/KBIS/KJMS, and potentially persisting at KJMS through
Monday morning.

&&

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

&&

$$

DISCUSSION...Jones
AVIATION...Jones