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This is the forecast I posted to MN-Chase on May 1st, the night before the Badger, SD tornado Well I'm actually quite excited about Tuesday's possibilities. I know a lot of people are teeter-tottering on if this thing is going to happen or not, and I can see those arguments, but my gut (for what that's worth) and a little science really lead me to think this could be a great CHASE day. I capitalize CHASE because this is not going to be a big severe weather event. I think its important to differentiate between a good chase day and a good severe weather day. A good chase day is one that can be well forecasted and well chased due to storm structure, movement, terrain, timing, etc. A big low that has severe weather and heavy rain everywhere moving at 90 MPH is going to make for a terrible chase day. I think everything lines up well for nice, relatively discreet supercells along a warm front near the low initiating in South Dakota. I'd say between Brookings and Huron around 5 p.m. Storms do have the possibility of going tornadic with good low level and moderate deep layer shear, ok cloud bases, fair helicity, etc. Not big tornadoes perhaps, but maybe some photogenic ones with medium cloud base heights? Good cold mid levels and moderate instability along with low level instability and good surface vorticity all encourage my forecast. I also like to see that huge mid level dry intrusion punching in. The 2 things I'd be concerned about are a possibly narrow instability axis, giving perhaps a limited amount of time for the storms to get together, and limited surface and 850mb boundary layer moisture. Although right now models are hinting that these parameters may be 'ok'. Vertical motion is so-so. Subtle areas of subsidence may be something to watch for. This is a baby low compared to some we've had in the past few weeks, which may be good and may be bad. Its good because we shouldn't have widespread rain dampening the whole thing, but it may be bad because the amount of lift available may be limited.... although the 700mb shortwave looks pretty impressive. Given enough surface heating I think a lot of CU fields along the boundaries may give clue to where initiation may be. I think it's worth the risk to Eastern South Dakota if the morning analysis and satellite look good. Summary: I think it's worth the gamble to get between Brookings and Huron (De Smet, SD) by 4-5 p.m. and watch for a cell to pop up near the triple point, and follow the warm front into Southwest Minnesota. The cell would travel to between Clear Lake, SD to Canby, MN by 7 p.m. Potential exists for a tornado. I think the chase ability factor on targeting and chasing as well as the possibilities make this one I want to chase. Storm Motion about 23 MPH, just about due East, but building a hair to the north to give it a sense of almost ENE movement.
Andrew Revering |