International Border
HRRR forecast 500mb wind, heights
Storm chasing prospects today are north, near or possibly north of the international border with Canada, as a climatologically significant setup targets the area. As upper level energy pivots east from southwestern Canada, a moist return flow near the surface will transport seasonally impressive moisture levels into North Dakota and far southern portions of adjacent Canada. While warm temperatures in the mid levels will work to keep the atmosphere capped for most of the afternoon, cool temperatures aloft will support steep 700-300mb lapse rates. With strong surface heating and more than adequate deep layer shear in place, the result should be a highly volatile setup in place as storms set to develop by late afternoon.
Based on climatology for past tornado events in North Dakota, the parameter space expected this afternoon is high end. A consensus of high resolution models brings instability levels into the 2500-4000 J/kg range with at least 50 knots of 0-6km shear. It is even a realistic scenario that the 00z Bismarck sounding could near or exceed all-time June instability levels, as SBCAPE approaches 5000 J/kg in that area. That far south, convective initiation and coverage are question marks, as capping will limit the ability of the atmosphere to overcome a capping inversion. It is farther north where the most interest is with respect to tornado potential.
HRRR forecast shear, instability
Low pressure should be situated near the North Dakota/Montana border around mid-afternoon with convective temperatures being approached from far northwestern North Dakota into southeastern Saskatchewan. Explosive thunderstorm development is likely on the nose of this low pressure and extending northeast into southwestern Mantioba in vicinity of a warm front. Given the environment in this area, it seems probable that at least a few tornadoes will form, as in additional to deep layer shear and instability, favorable LCL heights, i.e. below 1250m, should be present, along with adequate low-level shear. There is some concern about storm modes becoming messy north of the border, which would not be the most ideal for storm chasing.
If storm modes remain at least semi-discrete, it is possible that a localized tornado outbreak will occur and this could extend as far east as portions of north-central North Dakota and south-central Manitoba through early evening. The low-level jet is forecast so rapidly intensify by the 00-02z time frame to 35-50 knots, which becomes increasingly favorable for tornadoes. The environment can certainly support a significant tornado (EF-2) threat given the degree of instability and favorable low-level shear. Note that the sun will not set until about the 03-04z time frame at this latitude, so there is a fairly large window of daylight to work with as well.
HRRR forecast 850mb/500mb wind, SCP
The initial target is going to be northwestern North Dakota, but being open to chasing on either the southern or northern side of the international border. The road network in that portion of Canada is very favorable for storm chasing, so if that appears to be the favored area for intense storms, it will be preferred. With southward extent, convective coverage and intensity becomes a question. A few supercells will probably track across far northern North Dakota, but farther south along the cold front, especially down near I-94 and points south, convection should struggle to develop. There is a conditional risk for a supercell or two in south-central North Dakota as well, but convection here may struggle to intensify or have a long residence time, given weaker forcing and warmer mid-level temperatures in comparison to points north. Note that storms that can form ahead of the cold front will be in a region where deep layer shear vectors are nearly perpendicular to the cold front, suggesting discrete storm modes.
