509
FXUS63 KBIS 152124
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
424 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Scattered severe thunderstorms are possible across western and
  central North Dakota late this afternoon through early Sunday
  morning. Expected hazards include damaging winds up to 70 mph
  and hail up to tennis ball size, with a tornado or two
  possible.

- The highest risk for damaging winds is across northwest and
  north central North Dakota this evening through early Sunday
  morning, where isolated gusts to 80 mph are possible.

- Isolated to scattered severe thunderstorms are possible across
  south central and southeast North Dakota Monday through Monday
  night.

- Warm and humid today, followed by below normal temperatures
  through the first half of next week. Windy in the northwest on
  Sunday.

&&

.MESOSCALE...
Issued at 423 PM CDT Sat Jun 15 2024

At 4 PM CDT, a diffuse surface trough was analyzed from the
southwest corner of the state to near the Turtle Mountains. Attempts
at sustained convective initiation are evident along this boundary,
with the most successful attempt as of yet occurring over
Mercer County as of this writing. Another more prolonged attempt
at sustained convection is noted in Bowman/Slope Counties where
agitated cumulus have been percolating for the last hour. The
storms developing near Beulah/Hazen would seemingly have better
odds of sustainment given its location on the nose of southerly
winds advecting in mid 60s dewpoints. But approaching high
clouds in the southwest could also be a trigger for sustained
convection there. The Mercer County development is in an
environment with higher CAPE (near 3000 J/kg SBCAPE) but lower
shear (30-35 kts effective), and this is being borne out in
radar observations with rapidly intensifying updrafts with no
tilt. Farther west, there is relatively lower CAPE (around 2000
J/kg SBCAPE) but stronger shear (40-45 kts effective).

&&

.DISCUSSION...
Issued at 238 PM CDT Sat Jun 15 2024

Upstream troughing digging into the Pacific Northwest places the
Northern Plains under southwest flow aloft this afternoon. At the
surface, a lee trough is developing just west of the ND/MT border.
The air mass downstream of the lee trough is capped, but low to mid
60s dewpoints coupled with strong diurnal heating has already
resulted in 2000 J/kg SBCAPE. A gradual lowering of mid level
heights combined with low level convergence could provide enough
forcing for convective initiation to overcome the capping in western
North Dakota late this afternoon, and there are already signs for a
sustained storm on satellite imagery along the MT/ND border near
Trotters. Bulk shear through all layers AGL is forecast to increase
this afternoon and especially this evening. Any storms that develop
along the lee trough later this afternoon are favored to remain
discrete, with long hodographs supporting very large hail up to
tennis ball size.

With a weakening of the capping inversion and an increase in the low
level jet with poleward moisture transport early this evening,
convection should become more widespread across western North
Dakota. The enhanced southerly return flow could introduce a brief
tornado threat with any discrete storm, with 0-500 m SRH increasing
to 100-200 m^2/s^2 and 0-1 km bulk shear increasing to 15-25 kts.
This may be especially true for the northwest due to a deepening
northeast Wyoming low augmenting the surface wind field to a
predominant easterly direction. Later in the evening and into the
early overnight hours, several CAMs bring severe storms that
originate in central Montana into northwest and north central North
Dakota as an intense bowing complex. Simultaneously, existing
convection could grow upscale and merge into a forward-propagating
linear complex. The kinematic environment over northwest and north
central North Dakota looks favorable for a higher-end damaging wind
threat, with 0-3 km shear exceeding 40 kts and near surface winds
directly opposing storm motion. This is where the highest potential
for significant severe winds of 75 to 80 mph exists.

Later tonight, following the convection, a deepening low over
southern Saskatchewan will drive a cold front across the state. This
will result in a cooler, drier, and windier Sunday. The strongest
winds are expected in the northwest, where afternoon gusts could
approach 45 mph. Outside of the southern James River Valley which
could approach 80 degrees, high temperatures will primarily be in
the upper 60s to mid 70s on Sunday.

Multiple rounds of showers and thunderstorms are expected over the
north central CONUS Sunday night through Monday night as a longer
wave trough translates across the Northern Rockies. For Sunday night
into Monday morning, there are medium chances (40 to 70 percent) for
showers and storms across the southern half of the state, including
a lower probability risk for elevated strong to marginally severe
storms posing a large hail threat along the South Dakota border and
east of the Missouri River. This will be conditional on the
northward advancement of elevated buoyancy into a a highly sheared
environment. For Monday afternoon through Monday night, there are
high chances (70 to 90 percent) for showers, with thunderstorm
chances ranging from low northwest to high southeast. All convection
over this time frame looks to be elevated, but MUCAPE around 1000-
2000 J/kg paired with effective bulk shear of at least 50 kts could
support a severe threat with any storm whose elevated inflow layer
contains no CIN. Buoyancy prognostics limit this threat spatially to
south central and eastern North Dakota.

Showers remain in the forecast for Tuesday as the base of the
shortwave trough swings through, though thunderstorm chances will be
much lower. A southwest flow aloft regime is favored to continue
through the week, with low confidence in the timing of shower and
storm chances. Temperatures are favored to remain below through at
least the middle of next week before warming back closer to normal
by next weekend. The coolest time period is expected to be Tuesday
through Tuesday night, with highs mainly in the 60s and lows mainly
in the 40s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1238 PM CDT Sat Jun 15 2024

Scattered showers and a few thunderstorms will remain possible
across northwest North Dakota early this afternoon, but VFR
conditions should prevail. Later this afternoon and evening,
chances for thunderstorms will increase across western North
Dakota, shifting into central North Dakota later in the evening
and overnight. Some storms could be severe with very large hail
and damaging wind gusts as high as 60 kts. The highest
probability for storms is from northwest to north central North
Dakota during the late evening and early overnight hours. A
TEMPO group has been introduced to the KXWA and KMOT TAFs for
TSRA with IFR visibility and 45 kt gusts. A brief period of
lower ceilings is also possible with any storm. A cold front
trailing the storms later tonight into Sunday morning will shift
winds to the west-northwest around 15 kts. Prior to the frontal
passage, KMOT could have enhanced low level wind shear
overnight.

&&

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

&&

$$

MESOSCALE...Hollan
DISCUSSION...Hollan
AVIATION...Hollan