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Severe Thunderstorm Outbreak; Flash Flooding Possible Thursday in New England

Updated 7:30am Thursday

Just days after a historic flooding event struck Vermont, the state is now facing the threat of severe thunderstorms and additional flash flooding. An area of low pressure will move to New England's northwest tomorrow. This setup will put New England in the warm sector of the system, allowing heat and humidity to build into the region. As the system sends a wave of energy into Vermont, it will allow numerous thunderstorms to develop, with some turning strong to severe.

There is a chance for morning showers across most of New England, but the line of impactful thunderstorms likely won't begin to fire until mid-afternoon in western areas as a cold front is dragged through the region. This front will touch off the line of storms. The above setup allows for ample growth of severe thunderstorms, including supercell storms. The storms have been trending toward a later start time, more in the evening than the afternoon.

HRRR suggests a 30-45% chance of severe thunderstorms in the 5pm-9pm time frame for western New England. This later timing is a big reason why eastern New England is not nearly as likely to see strong to severe storms. The line of storms will likely arrive in these areas well after sunset, after daytime heating and instability has dwindled. It's worth noting that most of the time, a few isolated rogue storms fire ahead of the front, but the most widespread activity likely won't be until later.

HRRR showing storms just entering Vermont at 6pm:

This later start time for the storms has pushed the area where severe and strong storms are most likely further west.

The biggest threat with the storms will be the formation of microbursts, causing damaging winds. Hail will also be a threat. With the possibility of supercells, and an adequate amount of shear, an isolated tornado is also possible. This threat is very low, a 2% chance in the area in yellow on the map above, but whenever this risk is above 0% in New England, it's worth mentioning.

As the evening progresses into the night, the threat will transition from a severe thunderstorm threat to a flash flood threat. Slow moving showers and storms will be possible throughout the evening and night, with storm training possible (this is when multiple storms move over the same area).

1-3 inches of rain is possible from this system from central and southern Vermont, central and southern New Hampshire and western Massachusetts. The threat for flash floods, unfortunately, is the highest across Vermont. Central and southern areas could once again see numerous flash floods.

This is due, in part, by the fact that the area is still running off flood waters from earlier in the week. The other reason is that central and southern Vermont is where storm training is most likely to occur. This system will slow recovery efforts. It needs to be noted that this event will not be a repeat of Sunday to Monday. Another nine inches of rain will not fall.

The unsettled weather pattern will continue beyond Thursday with parts of New England in the Weather Prediction Center's outlook for excessive rainfall on Friday, Saturday, Sunday and Monday (this does NOT mean all those days will be washouts). The hyperactive pattern will continue through much of next week.



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