This is a convoluted severe weather threat developing across the state this afternoon with several things working toward a major, high-end outbreak and several things working against.
There’s no question the atmosphere will be primed for big severe weather later today. As I’ve written about quite a bit on this blog we will have an elevated mixed layer over Connecticut this afternoon with northwesterly winds in the mid levels of the atmosphere. This is an immediate red flag for high end severe weather potential!! The elevated mixed layer is a region of very steep lapse rates (temperatures decreasing quickly with height) 2 to 3 miles up in the atmosphere. When coupled with warmth and humidity near the ground a “loaded gun” sounding develops. If you can tap into that instability – watch out!
The 12z sounding from Pittsburgh shows an elevated mixed layer firmly in place. The OKX sounding shows an EML as well with a lifted index of -4.5C. Not bad for 12z.
So we have the instability – but do we have enough wind shear? Wind shear is important in promoting storm organization and developing rotating updrafts. Without a rotating updraft you’re not getting big hail. Today it appears we have the shear.
While winds at 500mb (or about 3.5 mile up) are only modestly strong there is significant directional shear. Winds near the ground will be out of the south while winds upstairs will be out of the northwest! With enough speed this will develop long and curved hodographs as seen above off the 6z NAM. This indicates supercells are possible. The low level shear especially is quite impressive indicating the potential for tornadoes. Both deep-layer and low level shear is not to the level it was last June 1st, however.
So what’s the negative? What’s working against today’s storm potential is the lack of a solid trigger and large scale subsidence. You’d like to see some type of shortwave or disturbance in the atmosphere with falling 500mb heights. That’s absent today. What this may do is reduce the areal coverage of storms but no necessarily decrease the severity of storms.
While storms may be isolated they have the potential to be quite severe. High-end severe reports and even tornadoes are possible in western New England and New York today. What makes the threat even more difficult to ascertain is the mesoscale convective system that has developed over Ontario and Lake Ontario. Not sure how that will impact downstream development.