Building ridge will bring heat, severe wx chances through July

Within a pattern which has been well discussed for a week or more, changes are afoot during the middle to latter part of this week. The troughing and cooler air, which had become a mainstay over the Northeast US over the past several weeks, will be replaced by increased atmospheric ridging. Warmer air and heat, with temperatures over 90 F, is expected to push into the area by the middle part of this week, and last through the weekend.

This airmass will be marked by mid level temperatures warming up quite dramatically. Temperatures at the 850mb level, or 5000 feet above the ground, will warm to 20 C or above – often times the “demarcation line” for a heatwave in this part of the country. On both Wednesday and Thursday, 850mb temperatures will approach or exceed this 20 C threshold over parts of the area, and not surprisingly forecast models have indicated temperatures in the mid 90’s on both days.

With this warmth, along the periphery of a mid level atmospheric ridge, will come increased atmospheric instability. In fact, the presence of a weak elevated mixed layer will lead to impressive instability numbers. Multiple disturbances riding along the northern edge of the ridge could lead to several opportunities for strong to severe thunderstorms beginning on Thursday and lasting through Saturday.

The main forecast uncertainty, at this range, is the intricate details of each atmospheric disturbance. Not surprisingly, forecast models have been jumping back and forth a bit with the evolution and intensity of each individual piece of energy. Overall, though, weaker atmospheric wind shear should limit the potential for organized severe storms until late in the week. Models are focusing in on later Friday into Saturday for potential severe weather, with better wind fields arriving in the Northeast US along with high instability.

Regardless of what happens with this weeks severe weather threat, the long range pattern is beginning to come into focus. Shifting tides (no pun intended) with tropical forcing, namely the MJO phase, and a changing stratospheric vortex with a lack of high latitude blocking, are likely to lead to increased ridging over the Central and Eastern United States. After a transient trough late this weekend and early next week, forecast models suggest ridging similar to this weeks will return — but with more vigor.

Rising mid level heights and warm mid level temperatures could, again, support heat by the middle to latter part of next week. Not surprisingly, with the ridge axis to our north, multiple opportunities for strong to severe thunderstorms would again be likely, especially as height falls begin later in the week with an active pattern continuing over Southeast Canada.

Stay tuned over the next few days for further updates and information as we head into what looks like an active, warmer, and more stormy summer pattern.