Sunday, June 24, 2012

6/24 - 10:35am MDT - The Chase Begins!

This morning we're heading toward Cheyenne, Wyoming from Denver as we continue to look at weather data coming in. Today's setup still looks marginal by most accounts, but there are a few small features that could cause a few isolated storms to go severe. For one, surface winds out of the east in Wyoming, Northeast Colorado, and Nebraska will generate upslope flow, which is the lift mechanism we need to get storms going.

These winds will also create some shear because they will be interacting with southwesterly winds at 500 mb (18,000 feet). The issue with this is that the faster winds at this level will be further north toward Rapid City, South Dakota instead of where the more favorable surface winds will be just to the south. In any case, the wind direction at 500 mb will be good enough to usher in the wind shear and maybe some drying of the air at that level to increase instability.

When you put the expected helicity (caused by wind shear) and the instability together for today, you get the Energy Helicity Index (EHI). According to the 14z RAP model, the EHI may try to ramp up a little bit in Northeast Colorado and it even breaks out a little bit of precipitation just west of there too. Surface heating is going to be massive since temperatures will be in the 90's and 100's in some places, so we're hoping this also helps overcome some of the warm temperatures aloft (the cap) so that isolated storms can develop. We're grasping for small features today since there isn't any one thing jumping out to get our attention, but so far it looks like a storm or two could fire on the elevation near Cheyenne. We'll also be watching an area closer to Rapid City, SD to see how things develop up that way.

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