The temperature at Logan airport was 92 degrees Wednesday afternoon, making it the second 90-degree day of the year thus far. On average there are 14 of these days in Boston, but closer to 20 farther inland. The building heat has prompted a severe thunderstorm watch for the western part of the area and has now been extended eastward this evening to affect Greater Boston.
The humidity has also increased, with dew points well into the 60s, and this has prompted that line of showers and storms to form and march eastward. Some of these storms have strong gusty winds and hail, and the requisite thunder and lightning.
In order for thunderstorms to make it into eastern New England, there has to be some upper-level support or they will fall apart. Today is the 16th day in a row without any rain and we could really use some. If the storms hold together as they approach the coastline then we could see some beneficial rainfall, but also the risk of damaging weather. I would say there’s a 50-50 chance these storms fall apart before they reach the coastline.
By tomorrow morning, the cold front that has brought this round of showers will be east of New England. The air will slowly dry out throughout the day and temperatures will be up between 78 and 83. It actually looks like a very nice afternoon.
The problems start to arrive this weekend. A low pressure area will ride a stalled frontal boundary to our south later Friday. This will likely bring some shower activity, especially overnight Friday. How close the weather system comes will determine whether we see some light showers or more significant rain — either way, it’s not going to be a lot. Whatever rain there is will end early Saturday.
The weather the second half of Sunday into Monday is dependent upon another area of clouds and precipitation and just how that area tracks. As I look at the latest computer guidance it appears that the chance of rain will actually start to re-increase Sunday afternoon, peaking overnight and into the first part of Monday.
There may actually be the opportunity for some more beneficial rain in this next round. Some of the models give us over half an inch of rain while others are less bullish, keeping it all to the south and east.
After the 90 degree weather of Wednesday, temperatures in the 60s this weekend will feel noticeably different — but those Memorial Day readings will be way closer to average than our current heat spell.
Follow Dave Epstein on Twitter @growingwisdom.