Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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379 FXUS63 KBIS 060945 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 445 AM CDT Mon May 6 2024 .KEY MESSAGES... - Several rounds of showers with low to medium chances for thunderstorms across western and central North Dakota today through tonight. - There is a conditional risk of a few strong thunderstorms this afternoon and evening, mainly across southwest and south central parts of the state. - Strong southeast winds gusting to 50 mph expected across central and eastern North Dakota today. - Strong westerly winds are possible in southwest North Dakota on Tuesday. - Warmer and drier weather is favored later in the week. && .DISCUSSION... Issued at 444 AM CDT Mon May 6 2024 A strong low level jet resides over the Northern Plains early this morning, downstream of a potent shortwave/closed low over the Rockies. Poleward moisture transport over central South Dakota has recently initiated an area of showers with occasional lightning along and west of Lake Oahe. This activity will continue to spread northward into south central North Dakota through mid morning. More isolated shower activity has also been noted across the rest of the western half of the state at times during the early morning hours. The strong upstream mid level low will spin into the Northern High Plains today, with surface cyclogenesis underway early this morning across eastern Montana and eastern Wyoming. Expect several areas of showers with embedded thunderstorms to develop over and track through western and central North Dakota over the course of the day. Strong southeast winds will focus more over central and eastern parts of the state today as the surface low deepens near the Black Hills. Previously issued Wind Advisories for today remain on track. Afternoon temperatures are likely to reach the 60s. We are still monitoring the potential for a few stronger storms this afternoon and evening, with the primary hazard being a weak tornado or two. The main area of concern is expected to be along a northward advancing occluded front with a northwest-southeast orientation from southwest into far south central North Dakota. It is not certain that surface-based convection will initiate along this boundary (although mid to upper level forcing should be substantial), nor that uninhibited low level buoyancy will build directly ahead of the occluded front. Having said that, there is now greater ensemble support for a narrow ribbon of 500-1000 J/kg SBCAPE preceding the occluded front. Any storms that form along this boundary would likely experience 20-30 kts of 0-1 km shear, along with 100-200 m2/s2 of 0-500 m SRH. Given those shear parameters, coupled with very low LCLs and large, looping hodographs showing ample streamwise vorticity for ingestion by right-moving supercells, it stands to reason that a couple of brief, weak tornadoes could occur. Once again, this potential is reliant on the presence of SBCAPE on the order of 500 J/kg in the storm inflow air mass. Other severe hazards cannot be completely ruled out, but should be of lesser concern. A nearly-stacked low will continue to spin over western North Dakota tonight before it begins to broaden out on Tuesday. There is still some uncertainty on where the surface low circulation will settle on Tuesday, but we are still expecting a synoptic dry slot to significantly limit QPF across all but far western North Dakota beyond tonight. In fact, there are now only medium odds (less than 70 percent) for an event-total rainfall exceeding one inch along the Montana border. The far west could still see some periods of heavier rainfall on Tuesday though, moreso in the southwest where strong westerly winds could actually be the greater concern, with some guidance showing BL momentum transfer potential near 50 kts. Tuesday will be cooler than today, with highs mainly in the 50s, but possibly as low as the mid 40s in parts of the southwest. The stacked low pressure is forecast to devolve and shift southward on Wednesday, though the continued presence of cyclonic vorticity keeps medium chances for lighter rain in the forecast. A drying out and warming of temperatures should finally commence on Thursday, with highs forecast to return to the mid and upper 60s. Global models are projecting a clipper-like system diving down from Canada on Friday, but ensemble analysis shows very large spread on the evolution of the synoptic pattern heading into the weekend. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 207 AM CDT Mon May 6 2024 A strong low pressure system will bring aviation impacts to western and central North Dakota through the forecast period. MVFR to IFR ceilings are forecast to build in from southwest to northeast Monday morning, persisting through the rest of the day and evening. Periods of showers and isolated to scattered thunderstorms can also be expected throughout the day Monday and into Monday night. Southeast winds will remain strong through the forecast period, increasing to sustained speeds around 20-30 kts with gusts to 35-45 kts Monday afternoon, strongest over central and eastern North Dakota. Low level wind shear will impact parts of central North Dakota from KMOT to KBIS until early Monday morning. && .BIS WATCHES/WARNINGS/ADVISORIES... Wind Advisory until midnight CDT tonight for NDZ003>005- 011>013-022-023-025-037-048-051. Wind Advisory until midnight CDT /11 PM MDT/ tonight for NDZ019>021-034>036-042-045>047-050. && $$ DISCUSSION...Hollan AVIATION...Hollan