Heat and Humidity Peak Before a Cold Front Brings Storms Thursday

Temperatures will tick up a notch today as ridging will peak, with widespread 90s likely region-wide (80s in the mountains and right at the coast). Along with the heat will bring continued humidity. Widespread dew points in the 70s Wednesday and Thursday will bring feels-like temperatures well into the 90s to around 100° for typical warm spots (mainly the Merrimack, Connecticut River and Champlain Valleys). A heat advisory is up for a large portion of New England.

While today will be mainly dry, the overall atmospheric conditions may support isolated storm activity, similar to what occurred yesterday (a vast majority of the region stayed completely dry, but a couple localized areas popped a storm yesterday). Forcing will be weak and mid-level ridging will do its best to keep everyone dry, but a moisture-rich atmosphere, hot temperatures and marginal instability may allow for a couple storms to pop up here and there once again.

On Thursday, a frontal system will likely begin to approach New England. This will allow for more widespread storm and shower activity across New England. With that said, this activity does not appear to be widespread enough (or early enough in the day) to prevent temperatures from reaching well into the 80s and low 90s once again. Dew points well into the 70s will be possible in some places, leading to a tropical feel.

There may be two rounds of convection/storms on Thursday. The first would likely develop in the mid-morning to early afternoon hours due to a pre-frontal trough (which can be seen on the graphic above, represented by the dotted line). This activity would likely be much more widely scattered or isolated in nature. The second would come later in the afternoon and into the evening as the cold front actually crosses the region. Exactly how these two rounds play out will affect the overall impacts.

Should the first wave end up more widespread, the atmosphere will have trouble recovering for the second round later in the day and the cold front would pass with much less activity. If this first wave ends up producing little activity and the cold front arrives sooner, storms will be more widespread later in the day. If this scenario plays out, the severe weather threat will be increased, as the parameters for strong storms will be much higher with the second round, should the atmosphere remain unstable.

Below: HRRR showing potential weather around midday Thursday (1st image) and late-afternoon to early evening Thursday (2nd image):

As of Wednesday morning, the overall trend has sped up the cold front slightly. This will give western New England the best chance for more widespread storm activity (and stronger storms) with the second round as the first round is currently likely to develop farther east. The main ingredients for severe weather will be in place with plenty of instability and effective shear. Moisture will remain very high, with a tropical-like air mass in place. The cold front will provide strong lift and forcing.

The parameters for stronger storms will peak later in the afternoon and evening. As stated before, if activity earlier in the day is more widespread, the severe threat would be reduced as the atmosphere would not be able to recover in time for later in the day. The main severe threat will be damaging winds. Given the potential for discrete cells and overall shear profiles, it's possible New England sees its first tornado of the season as well. Western New England is currently under the "marginal" category (level 1 of 5) for severe storms, but this could very well be bumped to the "slight" category (level 2 of 5) should current trends hold.

Friday will likely begin a cooling trend for New England as the cold front slowly slides through the region. Friday, however, will have the potential to be another very warm day for southern and central New England as the front likely won't fully pass through until later in the day. With that said, the front has been trending faster, so Friday has been trending cooler. Humidity will drop off for everyone by the afternoon.