Scattered Storms Today will Usher in Cooler, Less Humid Air for New England

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. It will be another fairly hot day, even though yesterday was very likely the hottest day. Humidity will peak today ahead of the cold front. Dew points well into the 70s will be possible in some places, leading to a tropical feel.

There may be two main 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 and warm air advection (which can be seen on the graphic below, represented by the dotted line). This activity would likely be much more widely scattered or isolated in nature and mainly focused across the higher terrain.

New England. The second round would come later in the afternoon and into the evening as the cold front actually crosses the region. This second round will likely be the main round and feature generally more storms, though coverage is still expected to be scattered in nature rather than widespread. Exactly how these two rounds play out will affect the overall impacts.

Below: HRRR showing potential weather early this afternoon (1st image) and this evening (2nd image):

Should clouds linger for a while after the first round, and if the first round produces more storms than anticipated, 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 clouds clear quickly, 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.

The cold front will likely cross New England this evening through the overnight hours. This will give western New England the best chance for more widespread storm activity (and stronger storms) as it will arrive during peak daytime heating. Storms will begin to weaken and wane as they push eastward late in the day. The northern tier of New England will have the highest chances for severe storms as they will be closest to the low pressure system and see the strongest forcing.

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.

There are limiting factors, especially for central and southern New England. First, lapse rates (the rate of temperature decline with altitude) are poor when it comes to supporting severe weather. Lift and forcing for storms will also be much weaker across southern New England, which may significantly limit overall coverage of storms.

Overall, coverage will likely be more scattered rather than widespread across all of New England. 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. Poor lapse rates will keep the large hail threat lower. The chances for more widespread hail would come within the first round.

Friday through early next week will see cooler weather and lower humidity (for the most part). Temperatures will likely fall right around seasonal averages with upper 70s to mid 80s dominating this stretch. Humidity levels will generally be lower, but another system on Sunday will lift a warm front into New England, bringing a brief surge. That system's cold front will quickly erase the humidity for Monday. The system will likely ignite scattered showers and storms for Sunday as well.