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Daily Thunderstorm Chances Continue for New England This Weekend

A stalled frontal boundary over southern New England will slowly begin to lift northward as a warm front this weekend. This front will provide the focus for showers and storms throughout this weekend. Thunderstorm chances appear to be more limited to southern New England on Saturday afternoon before expanding into northern New England for Sunday. Storms will have the chance to become strong to severe both days.

Looking at Saturday, the threat for storms will be concentrated to the south of the warm front, in the system's warm sector. This will be across southern New England along with southern Vermont and southern New Hampshire. After a mainly cloudy morning, storms will likely move through at their usual time, starting in the early afternoon for western areas and moving generally southeast throughout the afternoon and into the evening. Scattered showers and maybe a rumble of thunder will be possible farther north today.

HRRR showing potential weather late this afternoon:

As for severe storms, they will likely shape up in the same manner they did on Friday, and around the same areas as well. Connecticut and western Massachusetts will see the best opportunity for stronger storms. Damaging winds and large hail will be the greatest threats. There will be sufficient shear, lift and moisture present in the warm sector, but instability will be a big question mark.

CAPE values are expected to reach the 1,000-1,500+ range and lapse rates (rate of the decrease in temperature with height) will be steep, indicating an unstable atmosphere. The big issue will be cloud cover. If the sky remains mostly overcast today, the atmosphere will not be able to de-stabilize as much and would therefore reduce the severe threat.

Along with the severe threat, there will also be the potential for storms to produce torrential downpours on Saturday. This may result in localized, more minor flooding issues. This potential looks to be the highest across the same areas that were hit with heavy rains and storms yesterday. The extent of this issue will depend on whether storm training or back-building can develop. This will be most likely within the warm sector across southern New England. Overall, this threat has declined for much of New England since yesterday.

On Sunday, the system responsible for the warm front will lift to the north of New England, pulling the warm front farther north in New England. This will expand the thunderstorm threat (and strong thunderstorm threat) to include more of northern New England. With a northward trend in the low’s track, it has pushed the more widespread, steady rain event farther north, into Canada and northern Maine. Scattered showers and storms will be possible overnight Saturday into Sunday morning

HRRR showing potential weather Sunday mid-morning. Note the blob of widespread, steady rain being shown to generally stay in Canada:

After the morning activity, showers and storms should become generally more isolated for most of New England; far northern areas may stay in the rain for much of the day and northern Maine may see a washout (but these areas will see a lower thunderstorm chance). With that said, there will likely be activity around throughout the day, though it won’t be a total washout outside of northern Maine.

The main line of more impactful storms has been trending toward a later start-up time. This line looks to begin to get together in western New England around mid-afternoon before moving east-southeast through the rest of the afternoon and into the evening. While this timing isn’t locked in, the basic idea is that storms will be isolated early in the afternoon and generally fill in as the afternoon and evening wear on.

HRRR showing potential weather from mid-afternoon through the evening Sunday:

As for the severe threat for Sunday, it will be centered across a larger portion of New England and the ingredients for severe weather will also be generally heightened. This has led to the Storm Prediction Center placing a larger portion of the region in the “slight” category (level 2 of 5) for thunderstorms. As of now, the greatest risk in storms will be strong winds, but large hail and isolated tornadoes can’t be ruled out right now. Sunday remains a fluid situation and the storm threat could increase or decrease depending on today’s trends.

As stated above, damaging wind gusts will be the greatest threat in any storms due to an unusually strong (for summer) low-level jet. With that said, shear profiles are impressive with some models, particularly over New Hampshire and Vermont. It will also be plenty moist with humidity rising in the system’s warm sector. Lapse rates will also likely be steep once again. This kind of setup is conducive for the formation of rotating supercells.

The Storm Prediction Center has Vermont, most of New Hampshire and western Massachusetts in a 5% risk for tornadoes. This basically means there is a 5% chance of a tornado in any given spot in these areas. This threat is very low overall, but the risk is there for some cells to rotate. Again, this threat could decrease depending on trends today, especially in regards to the placement of the warm front and how far north it pushes during the day Sunday.

Storm Prediction Center tornado threat for Sunday:

The flash flood threat has been pushed northward for Sunday, which we did mention was a distinct possibility yesterday. The greatest threat for potential flash floods will be over northern Maine, where 1 to 2 inches of rain could fall during the day Sunday with localized higher amounts anywhere a torrential downpour sets up. Torrential downpours will be possible with any storm that forms in New England, so isolated issues can’t be ruled out for most of New England.

One last quick thing to mention is that temperatures will remain hot and humid for Connecticut and portions of western Massachusetts. A Heat Advisory remains in effect through Sunday for Connecticut away from the coast and portions of Hampden and Hampshire county. If Hartford can get to 90° today and tomorrow, this would become a seven day heat wave for the city, the longest on record in June.



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