797
FXUS63 KBIS 012014
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
314 PM CDT Mon Jul 1 2024

.KEY MESSAGES...

- There is a Marginal Risk (level 1 of 5) to Slight Risk (level
  2 of 5) for severe thunderstorms through this evening for much
  of western and central North Dakota, excluding some
  northwestern portions. The main hazards are hail up to ping
  pong ball size and wind gusts up to 60 mph.

- Isolated to scattered thunderstorms possible Tuesday and
  Wednesday. An isolated severe thunderstorm is possible
  Wednesday, mainly in the southwest.

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

&&

.MESOSCALE...
Issued at 314 PM CDT Mon Jul 1 2024

At 230 PM CDT, a surface trough was analyzed from near Minot to the
Standing Rock Reservation. The wind shift was more pronounced in
south central North Dakota, where downstream southerly winds were
sustained around 15 to 20 mph. Water vapor/upper air analysis showed
a deeper trough ejecting off the Northern Rockies, with smaller
amplitude waves embedded in the downstream southwest flow. Dewpoints
are in the mid to upper 60s on both sides of the surface trough, and
this increased low level moisture underneath steep mid level lapse
rates has driven SBCAPE over 2000 J/kg. Satellite imagery continues
to imply a highly stable boundary layer over south central North
Dakota, although recent trends have shown rapid clearing between
Dickinson and Glen Ullin. Preliminary data from a special RAOB at
Bismarck does still show mid level capping, but not as strong as
some deterministic guidance had suggested. An increase in
thunderstorm coverage is expected from southwest into south central
North Dakota through 4 PM CDT, where the approaching upper level
longer-wave trough will increase effective bulk shear to at least 50
kts. This should set the stage for isolated to scattered severe
thunderstorms from late afternoon through mid evening.

There are still a few aspects of uncertainty for how this event will
play out. Aside from boundary layer stability concerns, it remains
unclear what the dominant storm mode will be. Downstream of the
surface trough, shear and deep layer wind vectors are currently more
orthogonal to the boundary, but should be turning more parallel over
time and are already oriented as such upstream in the more favorable
area for convective development. Coupled with the stronger mid to
upper level forcing, we give a slight preference to a clustered or
linear mode, which keeps our most likely maximum hail forecast at
ping pong ball size. However, any longer-lived discrete storm would
likely be capable of golf ball size hail. While a linear mode does
favor a damaging wind threat, DCAPE in south central North Dakota is
mostly less than 1000 J/kg, keeping our wind forecast at 60 mph. The
tornado risk still appears to be very low, if not zero, with
insufficient low level SRH along and west of the Missouri River.
Depending on convective evolution, there could be a localized
flooding risk this evening shifted slightly east of the highest
severe probabilities. Individual storm motion is forecast to align
closer to parallel to the surface boundary, but some CAMs show a
quicker eastward progression of the entire convective complex.

&&

.DISCUSSION...
Issued at 314 PM CDT Mon Jul 1 2024

Cold front is still expected to bring showers and thunderstorms
through this evening. Isolated to scattered severe thunderstorms
are still expected. Main threats will be hail up to ping pong
ball size and wind up to 60 MPH. These threats could be high if
storm mode takes on more discrete characteristics. For the
latest breakdown on the environment see the mesoscale
discussion. Timing wise look for these stronger storms to get
going mid to late afternoon then pushing eastward through the
evening. Some breezy southerly winds are possible through this
evening ahead of this front, although winds have generally
trended lower than previous forecast today. Most of the severe
weather will exit or dissipate tonight. A broad trough lingering
in the north could bring an isolated shower or perhaps
thunderstorm in these areas tonight, with a low threat for
severe weather. Low temperatures tonight will generally be in
the 50s.

This broad trough then looks to linger across the state on
Tuesday, and perhaps bring a secondary cold front Tuesday
afternoon through the evening. The result will be isolated to
scattered thunderstorm chances through the day, with higher
chances in the north. Instability and shear are limited for
Tuesday, thus severe weather is not expected at this time. Look
for temperatures in the 70s. Breezy northwest winds are also
possible for Tuesday. The upper level winds are not
particularly strong, and ECMWF EFI values are fairly low. Thus
advisory level winds are not expected at this time. A quiet
night with lows in the 50s are then expected for Tuesday night.
Another broad trough still looks to push across the state on
Wednesday. This could bring more scattered chances for showers
and thunderstorms. Instability still looks somewhat limited
although shear is increased on this day. Perhaps an isolated
stronger storm is possible, especially in the south. SPC
currently has a Marginal Risk in the southwest. High
temperatures on Wednesday will warm slightly in the mid 70s to
mid 80s.

The broad trough could still develop a cutoff low across the
region on Independence Day. This could still bring widespread
showers and thunderstorms. Of note that some clusters have this
low further south which would bring less rain to the are. This
southern solution equates to about a 40% chance of occurring,
with a 60% chance of the low maintaining a similar track that
has been forecasted. Either solution would bring cooler
temperatures to the area in the low to mid 70s. Clusters then
show northwest flow through the Holiday weekend, although a
building ridge in the west could attempt to push more eastward
later in the weekend. Temperatures could warm to near normal as
a result, and perhaps slightly warm if the ridge can build
further inland. Chances for showers and thunderstorms will be
found each day, with the potential for waves to traverse through
this northwest flow. CSU-MLP pops for severe weather are low
for severe weather during this time period.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 110 PM CDT Mon Jul 1 2024

Chances for showers and thunderstorms will increase this
afternoon and linger through this evening. MVFR to perhaps brief
IFR conditions will be possible with these storms. Some MVFR
ceilings may also be possible this afternoon ahead of these
storms. Strong winds and large hail will also be possible with
any stronger storm. Thunderstorms then push eastward tonight,
with VFR conditions generally returning. There could however be
some lingering MVFR ceilings through the night and into Tuesday
morning. An isolated shower or thunderstorms is also possible
tonight into Tuesday morning across the north, although
confidence is not high enough to include at this time. Breezy
northwest winds are also expected to return on Tuesday.

&&

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

&&

$$

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