Tuesday morning severe weather: what went wrong?
This morning, a very intense line of storms moved across southern New England, particularly Rhode Island and southeastern Massachusetts, as well as Long Island, associated with a cold front that is currently tracking across the region. There were dozens of severe weather reports as the line of storms crossed the region, with many trees and power lines knocked down and damaged buildings. The strongest wind gust was reported in Charlestown, RI, where winds were clocked at 83 mph at 6:40 am this morning. WLNE meteorologist Chelsea Priest (@ChelseaPriest) shared some impressive pictures from her own parents’ backyard in Warwick, RI, as did WPRI news anchor Brian Yocono (@BrianYocono) out of Cranston, RI.
— Chelsea Priest (@ChelseaPriest) August 4, 2015
— NortheastWeatherWx (@NEWeatherWx) August 4, 2015
Review of the storm
The intense storm complex developed rather suddenly over Long Island and New York City near sunrise. The first severe weather reports were shortly after 4:30 am over Nassau County, and increased greatly over Suffolk County. However, the storm was most severe in Rhode Island and southeastern Massachusetts as it moved east-northeast between 5:00 and 7:00 am with widespread severe winds and some gusts over 75 mph (including the aforementioned 83 mph wind report). Even the marine layer did not slow down these storms, as there were severe gusts reported even on the tip of Cape Cod. In Rhode Island alone, more than 125,000 customers lost power, which was more than the number that lost power during Hurricane Sandy in 2012, and represents more than one-quarter of the state’s total customer base.
The Storm Prediction Center did not issue a watch, and only issued a Mesoscale Discussion with weak wording at 5:59 am this morning, believing that only isolated strong to damaging wind gusts and some hail was possible. However, shortly thereafter, NWS Taunton issued a very strongly worded Severe Thunderstorm Warning for much of the region, mentioning 80 mph wind gusts and calling it a “very dangerous situation”, which is what verified. As far as I know, no one was injured in southern New England or Long Island, however, at least 2 people were killed and 20 injured in northern New Hampshire near Lancaster on Monday afternoon when a circus tent collapsed during strong winds.
Why did such an intense storm hit?
You might be wondering how such an intense storm could develop in the early morning hours, when daytime heating is at its minimum, and become so powerful seemingly unexpectedly? There were hints that could be found, but also some limitations. Notice the image below showing the CAPE values in the area. For the time of day, they were quite high (about 1,500 J/kg) near the coast. However, just offshore, the CAPE values increased to about 3,500 J/kg, which is exceptionally high for early morning and indicates a very high amount of instability. The juice was clearly there, but the question was whether or not it would be high enough onshore for severe weather. The lifted index, indicating the temperature differences in the atmosphere from the surface to about 20,000 feet, was also exceptionally high, indicating an extremely unstable air mass. Near the coast the Lifted Index was near -5 and just offshore was about -9, which is typical of higher-end severe weather episodes and more often seen in the Plains and Midwest than in the Northeast. Combined, they allowed for a narrow area of extreme instability to form and produce severe storms with widespread damaging winds. The area was relatively narrow, focused near the coast.
Some other thoughts
First, it is important to remember to take severe thunderstorm winds seriously. They can be as strong as in a weak (or even strong on rare occasions) tornado, and tend to last longer with much more widespread damage. This was not a derecho as it did not last nearly long enough, but the winds were still very impressive.
The danger is much greater outdoors, as we saw yesterday with the tent collapse. Every outdoor venue and every major event needs to have a severe weather plan and a safe place to go if severe weather strikes. Outdoor venues are greatly at risk since it does not take extreme events (like an intense tornado) to cause death and destruction to them – even wind gusts of 50 mph can bring down tents or damage trailers and knock down trees. It is imperative to keep in touch with the weather as storms can hit very suddenly during the summer months, especially on warm, humid days when the air mass is unstable. Weather radios are extremely important as well and can be livesavers!
Forecaster Craig Ceecee (@EternalWeather1)