Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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159 FXUS63 KBIS 240822 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 322 AM CDT Mon Jun 24 2024 .KEY MESSAGES... - A severe thunderstorm or two will continue to impact north central parts of the state early this morning, with hail up to golf ball size and damaging winds up to 70 mph possible. - Isolated severe storms are possible across northwest and central North Dakota this morning, with the threat ending from west to east through the afternoon. Expected hazards include hail up to golf ball size and damaging winds up to 70 mph, with the higher hail risk in the afternoon in the James River Valley. - Warm and humid across the eastern half of the state today, then slightly cooler and mostly dry Tuesday and Wednesday. - Medium to high chances for showers and thunderstorms Thursday afternoon through Thursday night. && .DISCUSSION... Issued at 321 AM CDT Mon Jun 24 2024 Shortwave energy riding over the top of a mid to upper level ridge axis has sparked areas of showers and thunderstorms from eastern Montana into western and central North Dakota early this morning, with forcing being aided by a low level jet with strong moisture transport. The strongest convection has been focused along the Canadian border in Burke, Renville, and Bottineau Counties. Two long- lived supercells have now weakened and transitioned to more of a compact linear mode, but another supercell upstream has entered northeast Burke County as of 3 AM CDT. Stronger storms were also previously located along the Missouri River in northeast Montana, with hail up to ping pong ball size at Wolf Point earlier in the night. That convection also weakened as it moved into northwest North Dakota, but small hail and gusty winds remain possible. Finally, scattered showers with occasional lightning have blossomed within a low level warm air advection zone across southwest North Dakota in a much weaker effective shear environment. There is medium to high forecast confidence that showers and storms will persist moving east across the state this morning into the afternoon, but low confidence on intensity. Through this morning, the strongest shear remains farther north. Convective evolution later this afternoon is far more uncertain, with CAMs already having struggled with overnight activity. The air mass downstream of an eastward advancing cold front/dryline will become very unstable this afternoon, with surface dewpoints increasing to the 70s and CAPE approaching 4000-5000 J/kg in a moderately sheared environment. Strong capping above the boundary layer and the unknown convective evolution this morning contribute to the uncertainty of convection this afternoon, and the best forcing through all atmospheric layers is not lined up spatially. On one end of the forecast spectrum, a few severe storms could develop this afternoon east of Highway 83, which could be new convective initiation or re-intensification of lingering convection from earlier in the day. This outcome has been offered in consecutive runs of the NAMnest, for example. On the other end of the forecast spectrum, morning convection could exit the forecast area by the afternoon, with no additional development for the rest of the day. The aforementioned cold front/dryline is forecast to cross the state from west to east through the day. The eastern half of the state will have a warm and muggy afternoon, with highs in the mid 80s to lower 90s and afternoon heat indices pushing the mid 90s in the southern James River Valley. It will be only slightly cooler but far less humid to the west. Later tonight, a mid level shortwave riding over a low level baroclinic zone could bring some scattered showers and thunderstorms along the South Dakota border. Any storms should remain well below severe limits due to negligible bouyancy. A transition to cyclonic northwest flow is expected on Tuesday, with surface ridging building from the southern Canadian Rockies into the northern High Plains. A few afternoon and evening showers are possible along the Canadian border, with breezy conditions. On Wednesday, northwest flow aloft transitions to anticyclonic with the broad surface high becoming more focused over the region. This should result in a very quiet weather day. Highs on Tuesday and Wednesday will generally range from the 70s north to 80s south. There continues to be strong model consensus for an upper level low landing on the Pacific Northwest Wednesday night, crossing the Northern Rockies on Thursday and reaching the Northern Plains on Friday. NBM PoPs begin to increase Wednesday night as a preceding lee trough intercepts the nocturnal low level jet. Then deterministic global models continue to indicate the potential for widespread showers and storms later Thursday through Friday, with NBM PoPs as high as 90 percent. CSU machine learning severe probabilities have increased over the past 24 hours, and a quick look at the CAPE/shear parameter space in deterministic guidance suggests all severe hazards could be in play. Heavier rainfall could also be a concern with this system, with NAEFS/ECMWF showing 90th- 95th climatological percentile values of precipitable water. Warm and/or humid conditions are possible on Thursday, but below normal temperatures are favored on Friday and Saturday following the passage of the trough, with the NBM now advertising highs as cool as the mid and upper 60s. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 102 AM CDT Mon Jun 24 2024 Showers and thunderstorms are possible across western and central North Dakota overnight into Monday morning before shifting off to the east. A few storms could be strong to severe, with the highest chance of a severe storm north of KMOT. VFR conditions are otherwise expected through the forecast period. Southeast winds overnight will turn to the northwest on Monday, increasing to 10-15 kts with a few 20-25 kt gusts during the afternoon. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hollan AVIATION...Hollan