Breezer, Blazer, One Liner: All things that describe the last 3 days of the hot spell. Read on.
Breezer: A hot day for sure today across much of the region, but again a sea breeze developed along the MA East Coast and has progressed inland into the I-95 belt including Boston’s Metro West. This is more of a sea breeze than I had been expecting, and was likely enhanced by an outflow boundary left behind by a cluster of thunderstorms moving off the coast of Maine late last night – recall something like this happened last week too. Also, the disturbance that I thought might kick of storms southwest of Boston is a no-show. However, some pop up storms did get going in the heat in south central and southeastern NH this afternoon, including a severe cell. This activity may briefly try to survive as it encounters lift near the sea breeze boundary in the 495 belt in the last hour of the afternoon to very early evening, but as the sun sinks, this activity should disappear. The ocean air that came into the region is already warming due to the hot land so not a whole lot of additional relief is to be had. In fact, a developing southwest wind later this evening may make it feel a little warmer to hotter in areas that had cooled down, as the dew point will come back up in these areas after having been knocked down along with the temperature from the sea breeze.
Blazer: Friday will be the hottest day of this stretch as a west southwest wind gets cranking. The plus of the wind will be that it will provide ventilation, but it will drive the heat right to the beaches that had enjoyed several days of relieving sea breezes. The only spot that will see a little modification will be where a west southwest wind comes off water (portions of the South Coast, Cape Cod and Islands). Despite the heat, the lack of instability Friday will limit the thunderstorm threat, with only a minimal risk of an isolated pop-up storm.
One Liner: The heat is going to break as a cold front crosses the region on Saturday afternoon and evening. The timing of this front is critical, as the air will be unstable and it will still be hot. This is a classic setup for a squall line of thunderstorms to form in NH/VT/NY and then move east southeast across MA/CT/RI. There is severe storm potential, with the main threat being damaging straight line wind and potential microbursts. This may all occur in one line of storms, which at least eliminates the need for tracking multiple lines and clusters of storms. A single squall line does not mean that everybody will see severe weather either. We will have to see how the line sets up and moves, and its timing. If it occurs too early, before we have maxed out our heating for the day, it wouldn’t have as much time to grow to full potential. If it waited until much later in the evening, it would be arriving after the heat had started to ease and may also be a little weaker. Somewhere in the middle, and we’re talking a more potent line. This will be watched closely.
After that, a “refresher” course: A new air mass, much more comfortable, will be in place for Sunday and the start of next week! Enjoy that before humidity tries to make a come back by the middle of next week (probably without the extreme heat though).
Updated forecast for southeastern New England (southern NH, eastern MA, and RI)…
THROUGH SUNSET: Partly cloudy. Isolated showers and a few thunderstorms southern NH and northeastern MA may produce a few brief downpours. Temperature from near 80 MA Coast to near 90 further inland. Wind varying from a weakening sea breeze eastern areas, variable 5-15 MPH elsewhere.
OVERNIGHT: Partly cloudy. Stuffy. Lows upper 60s to middle 70s. Wind variable to WSW 5-15 MPH.
FRIDAY: Mostly sunny. Slight risk of an isolated thunderstorm. Sultry. Highs in the 90s, potentially about 100 in a few locations, and may hold in the middle to upper 80s some areas of the South Coast, Cape, & Islands. Wind WSW to SW 10-20 MPH gusting as high as 30 MPH.
FRIDAY NIGHT: Mostly clear and hazy. Muggy. Lows 70-80, warmest in urban centers. Wind SW 5-15 MPH.
SATURDAY: Hazy sunshine through early afternoon. A line of thunderstorms expected from west northwest to east southeast (first in NH and northern MA, later in RI and southeastern MA) sometime during the mid afternoon through early evening hours. Potential for strong to severe storms with damaging wind. Very humid. Highs 85-95, hottest interior eastern MA, coolest Cape Cod and Islands. Wind SW 10-20 MPH and gusty, becoming variable and potentially strong and gusty near thunderstorms.
SATURDAY NIGHT: Thunderstorms ending, lastly over Cape Cod and the Islands. Partly cloudy. Lowering humidity. Lows in the 60s. Wind shifting to NW 5-15 MPH.
SUNDAY: Partly cloudy. Highs 80-85. Wind NW 5-15 MPH.
MONDAY: Mostly sunny. Low 60. High 80.
TUESDAY: Partly sunny. Low 60. High 78.
WEDNESDAY: Mostly cloudy. Chance of showers. Low 60. High 76.
THURSDAY: Variably cloudy. Chance of showers/thunderstorms. Low 64. High 82.