Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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407 FXUS63 KBIS 280919 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 419 AM CDT Tue May 28 2024 .KEY MESSAGES... - Severe storms are possible Wednesday later in the afternoon and early evening mainly west of Highway 83. Hail up to the size of ping pong balls, 70 mph winds, and a tornado or two are the primary threats. - With this storm complex, there is a 90 percent chance or greater of a wetting rain (a tenth of an inch or more) for all of western through central ND, including the James River Valley. - Shower and thunderstorm chances will continue for the latter half of the week with temperatures remaining near to slightly above average. && .DISCUSSION... Issued at 419 AM CDT Tue May 28 2024 The forecast challenge is the potential for severe weather late Wednesday afternoon and into the early evening hours. Prior to that, an upper level ridge will work its way into the forecast area today through Wednesday, with the thermal ridge centering over the western Northern Plains Wednesday afternoon. As a result, expect dry conditions today with below average temperatures in the east (low 60s) to near average temperatures in the west (low 70s). For Wednesday, with the thermal ridge over western ND and breezy to windy southerly flow at the surface, the warmest temperatures of the week are expected in western ND, where highs may reach the low 80s. As would be indicated by southerly surface flow, surface high pressure will be situated to the east with low pressure to the west. Although not completely open due to more variable surface flow in the southeastern CONUS, this will help advect some Gulf moisture into western ND with dewpoints reaching the mid to upper 50s. Upper low pressure over central Alberta will slide eastward through the day Wednesday and by late Wednesday afternoon, a potent trough off this low will begin knocking down the aforementioned ridge. Somewhat elongated surface low/surface trough off a more pronounced low over Saskatchewan will develop over eastern Montana during the day. A warm frontal boundary with a close trailing cold front are likely to traverse ND later Wednesday afternoon through Wednesday night. This all is what will help trigger the severe weather threat. With previously mentioned Gulf moisture in place, expect a very buoyant atmosphere with the potential for over 2000 J/kg of MUCAPE. However, one major limiting factor is that deep layer shear looks pretty limited with only 20 to 30 kts of 0 to 6 km bulk shear progged in the latest model runs. Instability also rapidly drops off as the sun sets and there is the potential that the best forcing might arrive during the overnight hours. All in all, this indicates a narrow window of severe weather potential late Wednesday afternoon and into the early evening hours before a more generic thunderstorm line passes eastward through the remainder of the forecast area overnight. In regard to potential threats, it does seem all threats are on the table, albeit briefly and on a conditional basis for tornados and large hail. First, in regard to tornado potential, there is adequate 0 to 1 km bulk shear of around 15 to 25 kts progged. In addition, there seems to be adequate helicity progged as well with pockets of 100 m2/s2 0 to 1 km SRH and up to 300 m2/s2 0 to 3 km SRH. The location where these parameters look to line up the best is west central through southwestern ND, which also may be co-located with where the triple point slides through the state. Limiting factors to the tornado threat are elevated LCL levels and a storm mode that does not seem to be the most favorable either. 0 to 6 km bulk shear vectors appear to be parallel with the incoming frontal boundaries by the time they reach western ND, which less so seems the case in eastern Montana. As a result, it seems most likely that while a few discrete storms, if not a cluster develops in eastern Montana, they will probably begin to line out as they approach western ND. Not only will this help limit the tornado threat, but also the large hail threat as well. All in all, this means that there is a conditional threat for large hail up to the size of ping pong balls and a tornado or two in the late afternoon or early evening. However, with a rapidly developing linear mode, the main threat looks to be wind gusts up to 70 mph. As the line of storms moves eastward across the forecast area overnight, the risk of severe weather should rapidly diminish. However, showers and thunderstorms with moderate to heavy rain are expected as the line moves through all of western through central ND, including the James River Valley. At present, there is a 90 percent chance or greater of a wetting rain (a tenth of an inch or more) for pretty much the entire CWA. Beyond Wednesday night, expect periodic shower and thunderstorm chances, especially for the eastern half of the state. Temperatures throughout the period will be seasonable with a gradual warming trend from the mid to upper 60s on Thursday to the upper 70s to low 80s by early next week. Lows will be mainly in the 40s to the low 50s. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1246 AM CDT Tue May 28 2024 A few showers and thundershowers are present mainly south of I94 and east of the Missouri River. These will exit the area over the next couple to few hours. Patchy fog may develop in the west over the next few hours. Otherwise, VFR ceilings and visibility are generally expected through the period. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Telken AVIATION...Telken