Area Forecast Discussion
Issued by NWS Bismarck, ND
Issued by NWS Bismarck, ND
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029 FXUS63 KBIS 280439 AFDBIS AREA FORECAST DISCUSSION National Weather Service Bismarck ND 1139 PM CDT Thu Jun 27 2024 .KEY MESSAGES... - The threat for severe thunderstorms has ended across western North Dakota, and has greatly diminished over central North Dakota. - Isolated severe storms remain possible across south central North Dakota through the early overnight hours. The main expected hazard is damaging winds up to 60 mph. && .UPDATE... Issued at 1139 PM CDT Thu Jun 27 2024 Quick update to cancel the Severe Thunderstorm Watch for all but McIntosh and Logan Counties. The severe threat continues to end with the passage of the main convective line, and even ahead of it in far south central ND the environment is proving to contain too much boundary layer stability for more than a marginal severe wind threat. We will likely be able to cancel the rest of the Severe Thunderstorm Watch before 06 UTC. UPDATE Issued at 1026 PM CDT Thu Jun 27 2024 Quick update for the cancellation of northern and far western portions of the Severe Thunderstorm Watch. UPDATE Issued at 941 PM CDT Thu Jun 27 2024 The threat for severe storms is quickly diminishing across western and central North Dakota. Storm structures per radar analysis have become much less organized and intense over the past hour, and convection is now moving into a more stable and weaker shear environment. The highest potential for a severe storm through 11 PM CDT is from the Standing Rock Reservation and Cannonball River into western Emmons County where 0- 3 km shear is still as high as 30 kts per SPC mesoanalysis. The Tornado Watch has been cancelled. UPDATE Issued at 718 PM CDT Thu Jun 27 2024 Numerous severe thunderstorms continue across western North Dakota. Things are progressing about as expected, with a few initial discrete supercells that had funnel cloud / brief tornado reports, as well as large hail. Behind these storms, a significant line of storms has developed and is quickly moving east, getting quite close to absorbing the initial supercells. Multiple wind gusts in the 80 mph range have been observed at mesonet stations, and as this line continues moving east, expecting damaging wind to be the primary threat with 0-3km shear in the 30-35 knot range and 900-1000 J/kg of DCAPE. The expectation is still for the severity of storms to slowly decrease as it moves east through central North Dakota through the evening. We do now have a Severe Thunderstorm Watch out for most of central and parts of northern North Dakota, enclosing the Tornado Watch, valid until 2 AM CDT. UPDATE Issued at 450 PM CDT Thu Jun 27 2024 Update for the issuance of a Tornado Watch for most of western North Dakota until 10 PM CDT. && .DISCUSSION... Issued at 207 PM CDT Thu Jun 27 2024 The biggest forecast challenge remains the enhanced risk for severe weather late this afternoon into tonight. A warm frontal boundary with a NNW to SSE orientation off east Montana surface low pressure should trigger thunderstorms late this afternoon. Initially, this will result in a near perpendicular orientation of the 0 to 6 km bulk shear and the frontal boundary. As a result, there will likely be a few supercells that develop in eastern Montana and/or western North Dakota late this afternoon. Very quickly, trailing cold frontal boundary will begin to occlude the front and bulk shear will switch out of the southwest. This should result in thunderstorms rapidly becoming clustered and then potentially linear. All threats remain on the table during the supercell phase. As the frontal boundary occludes, the triple point is progged to slide from northwest to southeast mainly across southwestern North Dakota, or rather, somewhere south and west of the Missouri River. Or, potentially across far northwestern South Dakota. The exact path of the triple point is uncertain, however, this will be the area where tornadoes are most favored to occur as highlighted by the highest sig tor parameter values. In regard to very large hail, with a ribbon of instability potentially reaching as high as 4000 J/kg co-located with 50 kts of 0 to 6 km bulk shear and strong anvil level winds, hail up to the size of baseballs is entirely possible. Of note, one major factor also favoring the southwest more so than the northwest for discrete cells this afternoon is that thick low level stratus is present over most of the area, except the far southwest. This will help erode any capping that is in place. At present, billow clouds are observable on satellite that highlight things are presently stable with high shear. One thing we will be watching for is when billow clouds begin to dissipate and vertical agitation occurs. That will suggest thunderstorms might fire within the next couple hours. As storms begin to cluster and potentially line out during the evening and move towards Highway 83, the tornado threat will decrease as will the hail threat, although the straight line wind risk may increase (up to 80 mph gusts possible). Hail up to the size of ping pong balls and strong winds up to 80 mph are possible mainly between areas along and east of Highway 83 and west of Highway 281. As storms approach Highway 281 and areas east, the threat will become mainly 70 mph winds, perhaps with hail up to the size of quarters. All that said, there are questions as to whether or not severe storms will have trouble penetrating further east tonight, especially for locations east of Highway 83, due to aforementioned thick low level stratus that may hinder higher instability. Conditions should be mostly dry Friday morning before another shortwave off southern Canadian upper low pressure brings additional showers and thunderstorms to the area on Friday. Locations most likely to see additional rainfall Friday are those in the north. Generally speaking, severe weather is not anticipated, although there is a marginal risk for Rolette County and clipping eastern Dickey and Bottineau Counties. Saturday should then be dry and cold for this time of year with highs mostly in the 60s. Slightly warmer temperatures are then expected for next week with highs mostly in the low 70s to low 80s. Showers and thunderstorms are then likely to return by late Sunday night and into early next week. A few storms may be severe. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 1139 PM CDT Thu Jun 27 2024 Thunderstorms will continue moving through far south central ND and the James River valley through about 07 to 08 UTC. Only a low chance of showers or thunderstorms exists behind the main line of activity overnight. There are also MVFR to IFR ceilings and fog impacting parts of northwest and north central ND as of late evening, which will persist until winds turn westerly late tonight. VFR conditions will prevail over southwest and south central ND overnight. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...CJS DISCUSSION...Telken AVIATION...CJS