Loaded Gun – But No Trigger

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If you like big storms you’ve got to love a sounding like this. A plume of very steep mid level lapse rates, known as an elevated mixed layer, is streaming east toward the northeast. This sounding shows the EML in place over Windsor Locks Wednesday afternoon. Temperatures in the mid levels of the atmosphere cool very rapidly with height – on the order of 8 to 8.5 C/km between 500 and 700mb – almost dry adiabatic!!!

The result is a tremendous amount of CAPE. This type of sounding is what’s called a loaded gun. If the cap (which is sizable) can be broken the resulting thunderstorms can be explosive. Thankfully, it seems unlikely the cap will be broken. Connecticut will be in the midst of a brutally hot day with a ridge of high pressure cresting overhead.

Mike Ekster and Pete Banacos published a paper about the presence of EMLs in a staggeringly high percentage of severe weather days that resulted in fatalities or injuries (53% and 49%, respectively) in the northeast. Most memorable high end severe weather events in the northeast have occurred with an elevated mixed layer overhead (1953 Worcester tornado, 1973 West Stockbridge tornado, 1985 Pennsylvania super tornado outbreak, 1989 Hamden tornado, 1995 Connecticut hailstorm, 1995 super derecho, 1998 Labor Day derecho and tornado outbreak, 2011 Springfield tornado to name a few). While many large severe weather outbreaks have occurred on an EML day the presence of an EML does not guarantee severe weather – in fact there are many days where the “cap” is too strong to overcome and no thunderstorms result even though instability is sky high.

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The airmass on Wednesday is going to be extremely hot for the time of year. 850 mb temperatures are progged to be hotter on Wednesday than they’ve been all summer! +20 to +22C 850 mb temperatures are forecast across southern New England that should allow the mercury to soar into the 90s. If winds can stay westerly and clouds can stay away 95-98F is possible in the valley!

A few notes about this setup. If thunderstorms can break through the cap upstream we’ll have to watch them closely here in Connecticut. At this point I’m not expecting much but if a rogue storm forms it could be quite severe. By Thursday the EML plume exits to the east and instability wanes while deep layer shear and forcing increases. We could see a round of severe weather on Thursday but at this point the coverage and intensity is still unclear. Worth watching.

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One thought on “Loaded Gun – But No Trigger

  1. Once again, I am baffled by the spectacle of dry (and therefore heavy) air remaining aloft over moist (and therefore lighter) air for 2000 miles. Can anybody explain? Does the extreme altitude/relative warmth of the air compensate for its lack of water vapor?

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