533
FXUS63 KBIS 160708
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
208 AM CDT Sun Jun 16 2024

.KEY MESSAGES...

- Scattered severe thunderstorms are possible across western and
  central North Dakota tonight through early Sunday morning.
  Expected hazards include damaging winds up to 80 mph and hail
  up to golf ball size, with a tornado or two 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.

&&

.UPDATE...
Issued at 207 AM CDT Sun Jun 16 2024

Severe thunderstorm threat starting to become more isolated, and
the tornado threat is even more diminished as the cold front
continues to push from west to east. Thus let the Tornado Watch
expire at 2 AM CDT. The Severe Thunderstorm Watch in
northeastern North Dakota remains until 6 AM CDT. Wind gusts up
to 70 mph will still be the main threat through the night. Hail
up to 1 inch in diameter is also possible through tonight.

UPDATE
Issued at 1244 AM CDT Sun Jun 16 2024

A line of thunderstorms has now formed along a cold front from
the Canadian border to the South Dakota border. Winds will be
the main threat along this line, with some recent reports up to
75 MPH. As a result a down stream Severe Thunderstorm Watch has
been issued, while much of the Tornado Watch remains. Areas
behind the cold front have been dropped from the Tornado Watch.
In northwestern North Dakota, strong winds in the wake of severe
weather have been found. Thus issued a High Wind Warning to
cover this threat. Perhaps this will need to be expanded
eastward if this trend continues behind the northern line of
severe storms. Will continue to monitor.

UPDATE
Issued at 1035 PM CDT Sat Jun 15 2024

The line of storms that had been impacting northeast Montana has
arrived to northwest North Dakota and we`ve had a handful of
reports in the 55 to 65 mph range and one report just north of
Alexander of 83 mph. This line of storms should continue to
move east northeast over the next few hours and the chance for
more 70 to 80 mph wind gusts still looks reasonable given the
environment in place and radar presentation. The southern end of
the line may start to struggle with some capping as it moves
further east. No major changes were needed for this update.

UPDATE
Issued at 829 PM CDT Sat Jun 15 2024

Quick update to issue a Tornado Watch for all of western and
most of central North Dakota through 2 AM CDT / 1 AM MDT.

UPDATE Issued at 631 PM CDT Sat Jun 15 2024

Minimal updates were needed for the gridded forecast early this
evening. We did slightly adjust precipitation chances to better
reflect the latest trends and observations and blended in the
latest observations to the forecast. For more details regarding
the latest on the severe threat, please see the mesoscale
discussions below.

&&

.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 /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1244 AM CDT Sun Jun 16 2024

A line of strong to severe storms will continue to push
eastward across the state. MVFR conditions could briefly be
found along this line. In addition strong winds with gusts over
50 knots could be found along and behind this line. VFR
conditions should return for Sunday, although breezy to windy
westerly winds may be found through the day. These winds then
diminish Sunday evening.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 3 AM CDT early this morning for NDZ001-
002-009-010.

&&

$$

UPDATE...Anglin
DISCUSSION...Hollan
AVIATION...Anglin