Significant Severe Weather Threat Later Today

1630z SWODY1

After two bouts of severe weather last night with a spectacular lightning display, gusty winds, and large hail in Litchfield County the real show may not be until later today.

The Storm Prediction Center has upgraded portions of southern New England to a “moderate risk” which means a 45% chance or greater likelihood of severe weather within 25 miles of any given point.

Much like last Wednesday (during the Hampden County tornado) the instability in the atmosphere is extreme. When CAPE exceeds 3000 j/kg instability is high when it exceeds 5000 j/kg it’s extreme and that’s what is in place just to our west thanks to high dew points and a remnant elevated mixed layer aloft.

16z SBCAPE (Courtesy: SPC Mesoanalysis)

Though there will be moderate to strong shear in the atmosphere capable of producing rotating updrafts (and subsequently large hail) the tornado threat is low. The wind shear today is mostly speed shear as opposed to directional shear. Last Wednesday winds turned rapidly with height (directional shear) which is favorable for tornadoes particularly when that change happens in the lowest mile or two of the atmosphere.

Today’s severe weather event will likely bring an organized squall line capable of producing destructive winds. Out ahead of the squall line any storms that organize will be capable of producing large hail and potential a brief/isolated tornado but nothing like last Wednesday.

12z NAM 6 Hour Forecast 500mb Heights and Vorticity

The atmosphere will remain capped until 2 or 3 p.m. and then we’ll see things explode to our northwest. The cap will be weakened as a disturbance moves in from the west resulting in large-scale ascent. As 500 mb heights fall you generally see the removal convective inhibition (known as CIN and pronounced “sin”)  and thunderstorms start to fire.

I expect the significant severe weather threat to exist down to the Connecticut shoreline today as well. These are the kinds of events that pose a severe weather risk for the entire state.

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