Significant Severe Weather Threat Thursday

Ingredients are coming together for a sizable severe weather event on Thursday. A combination of vertical wind shear, instability, and forcing appears sufficient for a major/significant severe weather event. The Storm Prediction Center has issued a rare (for us) moderate risk.


It’s somewhat unclear how the threat will evolve tomorrow. Morning convection (remnant MCS?) may linger through a portion of the day. How quickly this clears out will determine the amount of heating/destabilization we will see. In addition the NAM/GFS do not agree on how steep mid level lapse rates will be with the NAM showing a remnant EML plume between 850mb and 600mb through a portion of the day which results in very impressive instability.

While the amount of instability is somewhat up in the air we will be in a highly sheared environment that will be favorable for supercell development.  0-6km deep layer shear should be nearly 40 knots – low level shear will also be supportive of low level rotation especially where winds remain locally backed.



With long and curved hodographs tornadogenesis is possible particularly with low LCLs across the state.

My current thinking is that several discrete supercells will develop in southeastern New York and western Connecticut after 2 p.m. (possibly as late as 5 p.m.) and move through the region. A second severe weather threat will exist after 8 p.m. with a damaging wind threat. It will be an active day with the potential for high-end/significant severe weather.

The exact details will depend on how much destabilization we see, where the warm front sets up, and where winds in the boundary layer are able to remain locally backed. Will update the blog in the morning with the latest thinking and as always the best place to turn for up to the minute weather information is Twitter – @ryanhanrahan.


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