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FXUS63 KBIS 281132
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
632 AM CDT Tue May 28 2024

.KEY MESSAGES...

- Severe storms are possible Wednesday later in the afternoon
  and early evening mainly west of Highway 83. Hail up to the
  size of ping pong balls, 70 mph winds, and a tornado or two
  are the primary threats.

- With this storm complex, there is a 90 percent chance or
  greater of a wetting rain (a tenth of an inch or more) for all
  of western through central ND, including the James River
  Valley.

- Shower and thunderstorm chances will continue for the latter
  half of the week with temperatures remaining near to slightly
  above average.

&&

.UPDATE...
Issued at 632 AM CDT Tue May 28 2024

Very patchy fog has developed mainly in western North Dakota.
Based on satellite imagery where it`s barely detectable and
webcams, this appears to be very shallow radiational fog as has
occurred the past few morning. Any fog will dissipate rapidly
over the next couple hours. Otherwise, the forecast remains on
track.


&&

.DISCUSSION...
Issued at 419 AM CDT Tue May 28 2024

The forecast challenge is the potential for severe weather
late Wednesday afternoon and into the early evening hours.

Prior to that, an upper level ridge will work its way into the
forecast area today through Wednesday, with the thermal ridge
centering over the western Northern Plains Wednesday afternoon.
As a result, expect dry conditions today with below average
temperatures in the east (low 60s) to near average
temperatures in the west (low 70s). For Wednesday, with the
thermal ridge over western ND and breezy to windy southerly
flow at the surface, the warmest temperatures of the week are
expected in western ND, where highs may reach the low 80s. As
would be indicated by southerly surface flow, surface high
pressure will be situated to the east with low pressure to the
west. Although not completely open due to more variable surface
flow in the southeastern CONUS, this will help advect some Gulf
moisture into western ND with dewpoints reaching the mid to
upper 50s.

Upper low pressure over central Alberta will slide eastward
through the day Wednesday and by late Wednesday afternoon, a
potent trough off this low will begin knocking down the
aforementioned ridge. Somewhat elongated surface low/surface
trough off a more pronounced low over Saskatchewan will develop
over eastern Montana during the day. A warm frontal boundary
with a close trailing cold front are likely to traverse ND later
Wednesday afternoon through Wednesday night. This all is what
will help trigger the severe weather threat.

With previously mentioned Gulf moisture in place, expect a very
buoyant atmosphere with the potential for over 2000 J/kg of
MUCAPE. However, one major limiting factor is that deep layer
shear looks pretty limited with only 20 to 30 kts of 0 to 6 km
bulk shear progged in the latest model runs. Instability also
rapidly drops off as the sun sets and there is the potential
that the best forcing might arrive during the overnight hours.
All in all, this indicates a narrow window of severe weather
potential late Wednesday afternoon and into the early evening
hours before a more generic thunderstorm line passes eastward
through the remainder of the forecast area overnight.

In regard to potential threats, it does seem all threats are on
the table, albeit briefly and on a conditional basis for
tornados and large hail. First, in regard to tornado potential,
there is adequate 0 to 1 km bulk shear of around 15 to 25 kts
progged. In addition, there seems to be adequate helicity
progged as well with pockets of 100 m2/s2 0 to 1 km SRH and up
to 300 m2/s2 0 to 3 km SRH. The location where these parameters
look to line up the best is west central through southwestern
ND, which also may be co-located with where the triple point
slides through the state.

Limiting factors to the tornado threat are elevated LCL levels
and a storm mode that does not seem to be the most favorable
either. 0 to 6 km bulk shear vectors appear to be parallel with
the incoming frontal boundaries by the time they reach western
ND, which less so seems the case in eastern Montana. As a
result, it seems most likely that while a few discrete storms,
if not a cluster develops in eastern Montana, they will probably
begin to line out as they approach western ND. Not only will
this help limit the tornado threat, but also the large hail
threat as well. All in all, this means that there is a
conditional threat for large hail up to the size of ping pong
balls and a tornado or two in the late afternoon or early
evening. However, with a rapidly developing linear mode, the
main threat looks to be wind gusts up to 70 mph.

As the line of storms moves eastward across the forecast area
overnight, the risk of severe weather should rapidly diminish.
However, showers and thunderstorms with moderate to heavy rain
are expected as the line moves through all of western through
central ND, including the James River Valley. At present, there
is a 90 percent chance or greater of a wetting rain (a tenth of
an inch or more) for pretty much the entire CWA.

Beyond Wednesday night, expect periodic shower and thunderstorm
chances, especially for the eastern half of the state.
Temperatures throughout the period will be seasonable with a
gradual warming trend from the mid to upper 60s on Thursday to
the upper 70s to low 80s by early next week. Lows will be mainly
in the 40s to the low 50s.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 632 AM CDT Tue May 28 2024

Very patchy fog is reducing visibility mainly over western North
Dakota. However, based on satellite imagery and webcams, this
fog is similar to the past few mornings where it is very shallow
in nature hence MIFG being present in the Dickinson TAF. Any fog
should rapidly dissipate over the next couple hours. Otherwise,
VFR ceilings and visibility will prevail through the period.

&&

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

&&

$$

UPDATE...Telken
DISCUSSION...Telken
AVIATION...Telken