186
FXUS63 KBIS 010704
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
204 AM CDT Mon Jul 1 2024

.KEY MESSAGES...

- Showers and thunderstorms continue to move across the state
  from west to east tonight.

- Breezy conditions are expected tonight.

- 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 ping
  pong ball 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.

&&

.UPDATE...
Issued at 202 AM CDT Mon Jul 1 2024

Just a quick update to say that the Severe Thunderstorm Watch
across the far west has been allowed to expire at 2 AM CDT.

UPDATE
Issued at 1250 AM CDT Mon Jul 1 2024

Thunderstorms across eastern Montana have begun to move into
northwestern North Dakota, mostly as a large, messy cluster.
These storms are not severe, but have had quite a bit of
lightning associated with them. Hail doesn`t appear to be a
concern with these, and likely won`t be a concern over the next
few hours as well. The low level jet intensifying could
potentially cause these storms to strengthen temporarily, but at
the moment, we aren`t seeing much in terms of strengthening.
The Severe Thunderstorm Watch continues for the time being.
Otherwise, the forecast remains on track, with minor edits to
PoPs and sky coverage to keep in line with the storms moving
through the area.

UPDATE
Issued at 920 PM CDT Sun Jun 30 2024

Thunderstorms have increased over southeast Montana over the
past hour from around Garfield and Hysham east to Miles City.
This is within an areas of strong low level and mid level lapse
rates and MUCAPE up to 2000 J/KG. Coordinating with SPC GGW and
BYZ, will be issuing a Severe thunderstorm watch that includes
Golden Valley, Billings and McKenzie counties in North Dakota.
Uncertain about the eastward extent of the convection, but with
current activity increasing and the low level jet expected to
increase think it`s warranted to include at least a portion of
ND in the watch. Will always be able to then cancel of things
don`t pan out, or expand a bit later if needed. Updated text
products will be transmitted shortly.

UPDATE
Issued at 603 PM CDT Sun Jun 30 2024

Thunderstorms continue over central ND and are also develop in
the higher elevations of Wyoming and southeast Montana. , as
well as around the Black Hills. Any convection over southeast
Montana would have a hard time making it into the state this
evening. Later this evening and overnight, aided by an
increasing low level jet, convection from Montana will have a
better probability of making it into western ND, and perhaps
strong to severe. Until then, look for breezy to windy
conditions this evening with variable cloudiness. Made some
small adjustments to sky cover with more cloud over eastern
portions of central ND early this evening and then increasing
clouds late from west to east.

&&

.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 /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 12350 AM CDT Mon Jul 1 2024

Thunderstorms are moving into northwest North Dakota, and will
continue to move east throughout the night. KXWA will see gusty,
erratic winds, as well as moderate to heavy rain for a few
hours, with all other terminals potentially seeing showers and
thunderstorms nearby later on in the night. Generally MVFR/VFR
ceilings are expected with these. Gusty southeasterly winds are
expected across all terminals overnight, with all locations
tapering off apart from KJMS, which will remain breezy until
around 00z. Some low stratus may develop behind these showers as
they move through, reducing ceilings to MVFR in some areas.
However, KJMS is expected to see some IFR ceilings around 18z,
lasting through the remainder of the TAF period. As the current
wave of showers and thunderstorms move out of the area Monday
morning, a second wave of showers and thunderstorms are expected
to develop, arriving around 22z and continuing through the end
of the TAF period. The greatest chances for precipitation will
be across the south central and southern James River Valley,
including KBIS and KJMS.

&&

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

&&

$$

UPDATE...Besson
DISCUSSION...Jones
AVIATION...Besson