Risk of Severe Thunderstorms This Afternoon/Evening
An approaching cold front may trigger strong to severe thunderstorms this afternoon and evening across southern New England. Vertical wind shear is very strong due to a low-level jet in excess of 50 knots (at around 5000 feet) and a mid-tropospheric jet approaching 100 knots. Instability looks to be marginal, however. Yet, it can take less instability for strong thunderstorms when the wind shear is so strong. A warm front will pass through southern New England this morning with scattered showers and possibly even some embedded thunder. It’s questionable whether southern New England will truly get into the warm sector with breaks in the cloud cover to allow enough heating to significantly destabilize the air mass (recall that an unstable air mass is characterized by very warm low level temperatures and relatively cold air aloft). If that should take place, then the potential for more widespread severe weather increases considerably.
There looks to be also low-level wind shear not only with respect to speed but direction as well. That low-level directional as well as speed shear is measured by helicity, which looks to be elevated ahead of the approaching cold front. Consequently, an isolated tornado or two cannot be ruled out.
If thunderstorms do develop this afternoon, they may take the form of short lines with strong wind gusts. There could also be an isolated low top supercell or two with a non-zero tornado risk.
Taken altogether, the potential exists for a few afternoon/evening thunderstorms to produce damaging winds. The risk extends across all southern New England but would appear greatest in western MA and western CT where the instability may be greatest. Also, any thunderstorms will likely move very rapidly in a generally west to east direction. As noted by the National Weather Service, there is uncertainty regarding severe weather later today, but should it occur, the impact could be high.
People involved in outdoor activities (including boating) this afternoon and evening should monitor National Weather Service forecasts, radar imagery, and any warnings. Be ready to seek immediate shelter if a Severe Thunderstorm Warning (or Special Marine Warning for those on the water) is issued or the sky begins to look threatening.
Looking ahead, Friday and weekend weather looks to feature seasonable temperatures and comfortable humidity. There remains a potential for fairly widespread and significant rain to develop across southern New England on Monday.
Beyond southern New England, the remnants of short-lived Tropical Storm Arthur may dump as much as 10 to 20 inches across portions of the Gulf states. This could produce life-threatening flash flooding. The moisture associated with remnants of Arthur will likely pass out into the western Atlantic well south of New England early this weekend.
Next Message
The next message will likely be the significant weather weekly outlook to be issued Monday June 22.
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The National Weather Service monitors the weather 24/7 and updates forecasts, watches, and warnings as necessary. For most of southern New England, refer to your local Weather Forecast Office for the latest forecast/warning information at weather.gov/box. For information from other Weather Forecast Offices, go to weather.gov and click on the location of interest on the map.
The frequency of this blog will depend upon the nature of the weather threat and availability of the author. Thus, for the latest information on weather forecasts and warnings, refer to the National Weather Service, which monitors and forecasts the weather 24/7.
Blue Hill Observatory and Science Center (BHOSC)
The BHOSC maintains a continuous daily observation record that dates from February 1, 1885 without interruption and provides educational information on weather and climate to area students and the community at large. Your support of BHOSC is much appreciated and enables this nonprofit organization to maintain the long-term climate record at the Blue Hill Observatory (longest continuous record in North America) and provide valuable educational resources on weather and climate via outreach to schools, site visits/tours, webinars, and conferences. For more information on the Blue Hill Observatory and Science Center, explore bluehill.org.
Message issued June 18, 2026 by:
Bob Thompson
Retired National Weather Service Meteorologist
Blue Hill Observatory and Science Center Board member
