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