Quincy Vagell
EF4
This setup has been handled fairly well, especially at the synoptic level for several days. SPC even highlighted it with what has been a rare 2018 day 4-8 30% deliniation. The first day 1 outlook for this setup remains at 30%, but for significant hail. There is only a small 2% tornado deliniation near the Canadian border in northern North Dakota, but I will explain below where else I think a tornado threat will exist.
What's driving this setup is a shortwave/compact upper level low pivoting east across southwestern Canada. In the upper levels, relatively strong winds at 500mb, i.e. 50-60 knots, should translate east across Montana during the day, reaching the western Dakotas and southeastern Saskatchewan by 00z Friday. In the lower levels, a persistent southeasterly flow should transport at least mid-60s dew-points as far north as the Canadian border, with upper 60s to near 70F dew-points into central North Dakota. Given cool temperatures aloft and strong surface heating, lapse rates from 700-300mb should be quite steep, supporting a sizable area of large instability, on the order of 2500-4000+ J/kg across much of North Dakota. Instability may be somewhat less impressive across far southern Canada, in vicinity of a warm front. This type of instability is quite rare this early in the season and a quick scan of Bismarck sounding climatology suggests that the sort of instability progged will be near-record levels for June and would exceed such records at 00z Friday, if the higher-end model progs are correct. This sort of instability combined with steep lapse rates and deep layer shear on the order of at least 50 knots in much of the threat zone suggests a threat for very large hail, especially early in storm life cycles. Unlike most setups this year, in addition to instability and deep layer shear, low-level shear also appears favorable for tornadoes, considering that model data keeps LCLs generally under 1250m through much of northern North Dakota and far southern Canada, near the warm front.
Apparent chase targets can be broken into two areas...first, near the warm front from southeastern Saskatchewan into southwestern Manitoba. The second would be along a cold front from western into central North Dakota.
Both targets do have some potential caveats.
Along the warm front (southeastern Saskatchewan into southwestern Manitoba), instability will be lower than points south, but there should also be little to no capping. This suggests that storms may develop quickly by midday to early afternoon and storm modes could become an issue. Nonetheless, with favorable shear and LCLs generally near or below 1000m, the setup should yield at least a few tornadoes and it's concievable that there could be a cluster of several tornadoes, especially if storms remain at least semi-discrete for a few hours.
The cold front is another target. Warm temperatures in the mid-levels should result in a fairly stout cap through much of the afternoon. Beneath this cap, mid to upper 60s dew-points and strong surface heating should breach the cap by late afternoon. Explosive storm development is probable in western North Dakota, as convection taps into a reservoir of strong to perhaps locally extreme instability. Convective evolution and coverage are a bit unclear, but I see three factors that are net positives for this region. First, deep layer shear vectors should be oriented nearly perpendicular to the cold front. Second, the cap should prevent storm initiation through much of the day and when storms do develop, thirdly, upper level forcing will be somewhat modest, suggesting storms should be fairly isolated. Convection allowing models show some variability, but there appears to be a signal that storm modes may remain isolated/semi-discrete for several hours. There is a fine line here between too much of a cap preventing storm development and storms firing earlier, which could result in quicker upscale growth, as some data was suggesting 12-24 hours ago. Regarding the tornado potential, LCLs may be a bit too high at first in western North Dakota, as well as somewhat weaker low-level shear than points east and northeast. However, note that the sun will not set until close to 03z at this latitude, so there is some time to work with. If storms do grow upscale quickly, then the supercell tornado threat will not be all that great.
Keep in mind that the parameter space in western to central North Dakota is high-end, climatologically. The SPC environmental browser shows that the vast majority of tornadoes in the area formed with MLCAPE below 3000 J/kg and less than 50 knots of deep layer shear. This setup should, at the lower end of expectations, be near that level and quite possibly even more impressive with both instability and shear. High-end parameter spaces do not always produce, but given adequate forcing and at least isolated convective development, today certainly has the potential to produce.
Another potential target area, which is more of a non-tornadic setup, would be down across western South Dakota. Some high-based storms should develop by mid to late afternoon around the Black Hills and move east. Due to capping and fairly weak forcing, storm coverage from northwestern South Dakota into far southwestern North Dakota is questionable. Either way, storms in this area would probably have a near-zero tornado threat, but an isolated supercell or two remain possible.
What's driving this setup is a shortwave/compact upper level low pivoting east across southwestern Canada. In the upper levels, relatively strong winds at 500mb, i.e. 50-60 knots, should translate east across Montana during the day, reaching the western Dakotas and southeastern Saskatchewan by 00z Friday. In the lower levels, a persistent southeasterly flow should transport at least mid-60s dew-points as far north as the Canadian border, with upper 60s to near 70F dew-points into central North Dakota. Given cool temperatures aloft and strong surface heating, lapse rates from 700-300mb should be quite steep, supporting a sizable area of large instability, on the order of 2500-4000+ J/kg across much of North Dakota. Instability may be somewhat less impressive across far southern Canada, in vicinity of a warm front. This type of instability is quite rare this early in the season and a quick scan of Bismarck sounding climatology suggests that the sort of instability progged will be near-record levels for June and would exceed such records at 00z Friday, if the higher-end model progs are correct. This sort of instability combined with steep lapse rates and deep layer shear on the order of at least 50 knots in much of the threat zone suggests a threat for very large hail, especially early in storm life cycles. Unlike most setups this year, in addition to instability and deep layer shear, low-level shear also appears favorable for tornadoes, considering that model data keeps LCLs generally under 1250m through much of northern North Dakota and far southern Canada, near the warm front.
Apparent chase targets can be broken into two areas...first, near the warm front from southeastern Saskatchewan into southwestern Manitoba. The second would be along a cold front from western into central North Dakota.
Both targets do have some potential caveats.
Along the warm front (southeastern Saskatchewan into southwestern Manitoba), instability will be lower than points south, but there should also be little to no capping. This suggests that storms may develop quickly by midday to early afternoon and storm modes could become an issue. Nonetheless, with favorable shear and LCLs generally near or below 1000m, the setup should yield at least a few tornadoes and it's concievable that there could be a cluster of several tornadoes, especially if storms remain at least semi-discrete for a few hours.
The cold front is another target. Warm temperatures in the mid-levels should result in a fairly stout cap through much of the afternoon. Beneath this cap, mid to upper 60s dew-points and strong surface heating should breach the cap by late afternoon. Explosive storm development is probable in western North Dakota, as convection taps into a reservoir of strong to perhaps locally extreme instability. Convective evolution and coverage are a bit unclear, but I see three factors that are net positives for this region. First, deep layer shear vectors should be oriented nearly perpendicular to the cold front. Second, the cap should prevent storm initiation through much of the day and when storms do develop, thirdly, upper level forcing will be somewhat modest, suggesting storms should be fairly isolated. Convection allowing models show some variability, but there appears to be a signal that storm modes may remain isolated/semi-discrete for several hours. There is a fine line here between too much of a cap preventing storm development and storms firing earlier, which could result in quicker upscale growth, as some data was suggesting 12-24 hours ago. Regarding the tornado potential, LCLs may be a bit too high at first in western North Dakota, as well as somewhat weaker low-level shear than points east and northeast. However, note that the sun will not set until close to 03z at this latitude, so there is some time to work with. If storms do grow upscale quickly, then the supercell tornado threat will not be all that great.
Keep in mind that the parameter space in western to central North Dakota is high-end, climatologically. The SPC environmental browser shows that the vast majority of tornadoes in the area formed with MLCAPE below 3000 J/kg and less than 50 knots of deep layer shear. This setup should, at the lower end of expectations, be near that level and quite possibly even more impressive with both instability and shear. High-end parameter spaces do not always produce, but given adequate forcing and at least isolated convective development, today certainly has the potential to produce.
Another potential target area, which is more of a non-tornadic setup, would be down across western South Dakota. Some high-based storms should develop by mid to late afternoon around the Black Hills and move east. Due to capping and fairly weak forcing, storm coverage from northwestern South Dakota into far southwestern North Dakota is questionable. Either way, storms in this area would probably have a near-zero tornado threat, but an isolated supercell or two remain possible.
Last edited:
