Severe Weather Potential Wednesday

Today has turned out to be a much more active severe weather day than anticipated, with the SPC just putting out a slight risk for the black hills and a severe weather watch which includes Wall, SD. The severe threat looks greatest to the west of Wall, but we should see some more rain tonight as the storms roll off of the hills as a nocturnal MCS. I think we will see a few hailers in the black hills and just south of the black hills today, much as has occurred over the last few weeks. I do not think we have the wind energy to support a high wind event in the area, and the tornado threat isn't high. However, good backing of the winds supports rotating storms...which could produce a tornado if everything comes together for a particular cell.

For tomorrow:

This looks like the much greater severe weather threat day for South Dakota and North Dakota. A decent 'cool' front (as the NWS calls it) will push through the Dakotas, brought about by a low pressure system moving through southern Canada near the apex of an upper level ridge. Ahead of this front will be great southerly flow (not southeasterly however) pumping in abundant moisture. In fact, dewpoint temperatures reach 65F all the way into southern Canada. The GFS and NAM are in agreement about the placement of this front, which should pass through the western Dakotas in the evening. This frontal boundary, and slight vorticity advection in North Dakota, should initiate storms as the CIN degrades later in the afternoon or early evening. A lot of the storm initiation points will depend on the nocturnal MCSs from tonight which may still be lingering over the Dakotas. If the cloud deck stays around, this severe threat could be lessened as heating wont be as intense. However, the models are saying that these clouds should clear out enough for additional afternoon/evening storms.

The map above gives you a great indication of what the frontal boundary looks like tomorrow evening. You can see the sharp dewpoint drop in North Dakota, which is just north of the 200/300 mb jet max which traverses through the ND/SD border region. Like I said earlier, PVA will be greatest in North Dakota, and a theta-e ridge should build into the area in the afternoon. CAPE of 2000 J/kg, after the loss of CIN as the frontal boundary approaches, should be sufficient (obviously) to support storms which should go severe quickly. I think the greatest threat region for hail and wind will be from the SD/ND border to Canada (and likely into Canada as well). Helicity should be in the range of 50-150 m2/s2 just ahead. of the storms. If this helicity is ingested into a storm, a quick tornado spin up could be possible. A secondary maximum of heavy rainfall, and possible severe weather, could occur along the primary theta-e ridge along the SD/NE border. I think there will be heavy rain in this region as CAPE could approach 3000 J/kg and CIN is forecast to be zero, and it will likely swipe away the greater threat of severe weather in SD itself robbing any storm that does develop in SD of its inflow moisture.

So, in conclusion, I see two areas of interest, western to central ND and the SD/NE border into NE from the west to the central region. Heavy rain will be more likely in the southern area, with severe weather more likely in the north. I expect 30% SPC threat for hail in ND, and possibly wind. 5% tornado in central ND as well, but I do not think we will see many tomorrow. No moderate risk.