Heat wave next week

A prolonged heat wave is likely for much of the Northeast next week.

The upper level trough that brought the refreshing cool/dry weather to the region for the last few days will shift east into the northwest Atlantic by tomorrow. In its place, a broad subtropical ridge will build into the Ohio Valley and eventually the northeast by Sunday. Strong high pressure currently over the Great Lakes will slowly slip southeast, backing winds across the northeastern US. This will unleash a very hot airmass from the southwest.

There are some timing differences between model forecasts as to when the ridge pushes into New England. The GFS in particular is a outlier, developing and retrograding an upper low from the offshore trough, preventing the ridging from building in on Sunday. The GFS still eventually lifts the low north and heights rise by Tuesday.

All other model forecasts keep the low further east and north. 500mb heights rise above 588dm by Monday evening on all guidance, and in some cases reach up to 594dm on Tuesday. This is also supported by the teleconnections as the NAO and AO become more neutral to slightly positive.

The ECMWF brings 850mb temperatures up to 20C into New England as early as Sunday afternoon and becomes very robust with the heat as high pressure shifts further east early next week. Eventually the ridge over the eastern US bridges with ridging over the Atlantic by late Tuesday into Wednesday. During this period, the ECMWF launches 850mb temperatures to between 22C and 25C!!! Most other model guidance is not quite this hot, but there is a consensus for between 17C and 20C every day next week.

Just as a reminder, a heat wave is defined as at least three days with high temperatures of at least 90 degrees. In the last 20 years, Keene has experienced seven heat waves. The longest was July 6-10, 1993. There is overwhelming support for a heat wave next week, possibly lasting five to as long as six days: Sunday through Friday!!! In addition, the peak of the heat wave will likely be Tuesday and Wednesday when high temperatures could possibly reach the upper 90's, to even near 100 in portions of southern New England!! As the Atlantic ridge builds westward, humidity will increase as well. There is a high probability that excessive heat warnings will be issued for a few days next week.

A short wave trough will move through the Great Lakes regions sometime late next week into the following weekend. Model guidance has a wide spread in terms of timing and amplitude, but regardless we should see relief from the heat by the following weekend.