National Weather Service Raw Text Product

306 
FXUS63 KBIS 201533
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1033 AM CDT Fri Jun 20 2025

.KEY MESSAGES...

- Scattered to numerous severe thunderstorms are possible late
  this afternoon and into tonight. 

- The main hazards will be very large hail up to the size of
  tennis balls, damaging wind gusts to 80 mph, and a few
  tornadoes. A strong tornado or two is possible along the I-94
  corridor from around Bismarck to Jamestown.

- The active weather pattern continues, with additional chances
  for showers and thunderstorms through the weekend and into 
  next week.

&&

.UPDATE...
Issued at 1024 AM CDT Fri Jun 20 2025

No changes to the forecast for today/tonight. We continue to
monitor latest CAM output and current conditions. BUFKIT
analysis (NAM/GFS) did show a rather decent capping inversion
for this afternoon, while the HRRR and RAP were less stout. Mid
level wave lifting into the region during peak heating though
may eliminate any inversion anyways. There remains uncertainty
with how today will unfold. One scenario supports convection in
eastern MT morphing into a bowing segment/MCS, then marching
east along I94 this evening, while other CAMs still want to 
fire off discrete cells (which would support an elevated tornado
risk south central and southeast given all the low level wind 
parameters). Will consider a special balloon sounding, along
with continuing to monitor near term trends. 

UPDATE Issued at 626 AM CDT Fri Jun 20 2025

The only update this morning was to expand shower chances a bit
more across the west and south over the next couple of hours.
Otherwise, just blended in the latest observations to the going
forecast.

&&

.DISCUSSION...
Issued at 409 AM CDT Fri Jun 20 2025

As of early this morning, a weak wave was moving through low
amplitude ridging aloft, bringing a few showers and an isolated
rumble of thunder to portions of western and south central North
Dakota. 

The ridge axis will amplify a little bit through the day as it
moves into North Dakota from eastern Montana. This ridging will
likely suppress convection through most of the day, but height
falls will start to spread into the west by late afternoon.
Initial storms may first develop over eastern Montana around 21z
to 23z before moving into western North Dakota. Whether storms
move in from Montana or develop over western North Dakota, the
environment is forecast to become volatile and highly favorable
for severe weather. RAP forecast soundings are suggesting MLCAPE
values in the 2500 to 4500 J/kg range across the southern half 
of the state in the afternoon and evening hours (instability 
increases from west to east), overlapping deep layer shear 
values in the 50 to 60 knot range. Storms will likely be focused
along and north of a warm front, with most CAMs suggesting 
activity moving quickly from west to east in between the Highway
200 and I-94 corridors. There does seem to be a bit of 
uncertainty exactly where this warm front will setup and it 
would appear that the CAMs could be a bit too far north with the
simulated complex of storms. Storm mode could also become a bit
complicated as it appears that we could see a few 
discrete/semi-discrete storms early before an organized MCS 
develops. Forecast deep layer shear vectors are not parallel to 
the warm frontal boundary but appear to form a ~30 degree angle 
with the boundary. Thus, an eventual mixed mode of bowing 
segments and semi-discrete supercells seems like a reasonable
scenario.

Either way, the environment should be very conducive to severe 
weather. Initial discrete storms could produce very large hail 
up to the size of tennis balls with damaging wind gusts 
becoming a larger concern as storms grow up scale. Ahead of the 
modeled MCS, CAM soundings are generally suggesting 0-3 km 
shear values in the 40 to 50 knot range and BRN shear values
over 100 m2/s2. These shear values coupled with the strong 
instability could lead to multiple significant wind gusts to 80 
mph. Additionally, long looping hodographs (especially in the
effective inflow layer) would suggest right moving dominant 
supercells if storms can remain discrete or semi- discrete. In 
the vicinity of the warm front, 0-1 km storm relative helicity 
is forecast to range from around 200 to 400 m2/s2 with 0-1 km 
shear up to 30 knots. Thus, the environment will also be highly 
favorable for tornadoes, a couple possibly strong, if convection
can remain discrete or semi-discrete. Even if storms mainly 
develop into broken line segments or bowing/QLCS structures, the
environment will still be highly favorable for a few tornadoes.
As of now, the best environment for tornadoes appears to be in 
the vicinity of the I-94 corridor from around Bismarck to 
Jamestown which matches up well with where the Storm Prediction 
Center has painted a 10 percent hatched area.

Most of the CAMs have this complex of storms quickly moving east
out of our area around 06z Saturday or so but another wave may
lead to additional thunderstorm activity west overnight and into
Saturday morning. A few elevated strong to severe storms could 
be possible with this activity as MUCAPE is forecast to range 
from 1000 to 2000 J/kg with deep layer shear up to 60 knots. 
These storms may continue or re-develop into the afternoon 
across the north central along the instability gradient but will
likely remain elevated in nature. Large hail would likely be 
the main threat with this activity but a few damaging wind gusts
cannot be ruled out. Instability will be much stronger further 
south, but limited forcing and capping may keep convection from 
developing here. If a storm or two could form in the warm 
sector, they would have strong to extreme instability and deep 
layer shear up to 45 knots to work with. Thus, there's a 
conditional severe threat here. At this time, it seems doubtful 
storms will be able to form in the warm sector, but if they do 
they could rapidly become severe with all hazards possible.

Showers and storms will be once again be possible Sunday
afternoon and evening. Surface based instability will be weak
across most of the west and central given much cooler
temperatures, but some models suggest some elevated instability.
Thus a stronger storm or two will also be possible later in the
day on Sunday. A progressive pattern then continues into the
next workweek, leading to near daily chances of showers and 
thunderstorms.

Regarding temperatures, expect highs today ranging from the
upper 70s northwest to the lower 90s southeast. Highs will be
similar on Saturday with some slightly cooler temperatures west.
Heat indices could approach the upper 90s across the southern
James River Valley each afternoon. Temperatures will then be 
much cooler on Sunday and to start the workweek with widespread
highs in the lower 60s to lower 70s by Monday. We then should
see a very gradual warmup through the rest of the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 625 AM CDT Fri Jun 20 2025

A chance of showers will remain possible across the west and
south this morning, but the probability is too low to add 
mention at any specific site. VFR conditions are generally 
expected through the period but a complex or two of intense 
thunderstorms is likely to develop late this afternoon and into
tonight. While exact placement and timing of these storms are 
still uncertain, we will message the potential using PROB30 
groups at all sites, generally in the 23z Friday through 06z 
Saturday time frame (earlier west and later in the east). The 
strongest storms could produce hail to the size of tennis 
balls, wind gusts to 80 mph, and possibly a few tornadoes. LIFR 
to MVFR visibilities will be possible under any heavier storms 
that move directly overhead.

&&

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

&&

$$

UPDATE...NH
DISCUSSION...ZH
AVIATION...ZH