There's a pretty good chance you've heard about the heat wave coming to the east coast next week. Here at New England Storm Center, we first mentioned the possibility of above average temperatures for next week this past Monday and brought up the potential for a heat wave this past Tuesday. Since then, this heat wave has been widely publicized, and for good reason, as signals have been very strong and adamant that this heat would be on its way.
Monday will act as a transition day from the comfortable weekend weather to the scorching heat wave. A warm front will lift through New England during the day, likely bringing an increase in clouds and possibly a shower or two as it does so. Both temperatures and humidity will be on the increase, but overall, seasonable for mid-June. Tuesday will see the heat dome begin to set up to New England's southwest, a favorable position to send temperatures soaring in New England amid a southwest flow.
Tuesday through Thursday will likely be the peak of the heat with many areas seeing their first heat wave of the season during this time frame. An official heat wave in New England is at least three consecutive days with a high temperature of 90° or higher. Interior areas shouldn't have much of a problem reaching into the 90s during these three days. Coastal areas may get some relief from localized sea breezes on Tuesday. This could also prevent an official heat wave in the city of Boston if the city fails to reach 90°.
Wednesday and Thursday still look to be the peak of the heat for most (western New England may see their peak on Tuesday, but temperatures will likely only vary by a couple degrees in this time frame anyway) with most areas reaching well into the 90s and the typical warm spots of New England pushing toward upper 90s. These warm spots would namely be the Connecticut River Valley, Merrimack Valley and possibly the Champlain Valley. If clouds remain at bay for the most part, some areas could get to the century mark.
This heat dome will bring with it some very impressive temperatures aloft by New England standards. Temperatures at the 850mb level, which is about 5,000 feet above sea level, will surge towards the upper 70s, which indicates an exceptionally warm air mass aloft.
For some sort of idea on this level of warmth at this height, Mt. Washington's summit is 6,288 feet above sea level and their all time record high temperature is 72°. 500mb heights will also be (possibly) increasing to nearly 600 dam (decameters). It's rare for heights to reach this extent in New England and is a strong signal for big time heat.
500mb height (decameters) for Wednesday (June 19), showing values in the 594-597 dam range:
Along with the very high actual temperatures, dew point levels will also be rising to their highest point of this still young summer season. Dew points in the mid to upper 60s for most will add a level of stick to the heat and cause heat index values to rise above the actual temperature. Widespread heat index values will likely be in the 95-105° range with 100+ most likely in the Connecticut River and Merrimack Valleys. The high end of this range borders between heat advisory and excessive heat warning.
There is the potential for some daily record highs to fall, which is a pretty lofty goal to reach in mid-June as these records are all well into the 90s. Record highs for major cities across New England on June 19 (Wednesday) are all in the mid or upper 90s.
Whether or not records are reached will likely come down to the extent of cloud cover, which would keep temperatures from reaching their full potential. One record to watch is the all time high record in Caribou, Maine, which is 96°. The current forecast has Caribou reaching 95° on Wednesday.
The main limiting factor, which we've been alluding to all this week, is the potential for clouds and/or unsettled weather to ride around the ridge and into New England. The ridge is looking like it will be centered close enough to New England to keep the area largely dry. With that said, increased clouds will be possible at times with some widely scattered thunderstorms, especially into Thursday. Potential timing of these features could keep some areas from reaching expected forecast highs.
All big heat in New England must end, and this may come on Friday as signals show the ridge getting suppressed southward with disturbances dropping into New England along a cold front. Being a week out, and days before the heat begins, any sort of timing on the end remains fuzzy and this is just an early indication. The Climate Prediction Center's 8-14 day outlook (which currently covers June 22-28) favors continued above average conditions (of course, continued above average conditions doesn't mean continued 100° heat).
