The (now long) anticipated heat wave for New England will be arriving this week, with highs well into the 90s at least one day for everyone with many seeing two to three days with 95+° heat. The heat dome will begin to break down late this week.
MONDAY
Monday will act as a transition day for New England. Both heat and humidity will build during the day, but not nearly to the extent that will occur later in the week. A warm front will lift into the region during the day, marking the beginning of the increase in humidity.
Increased clouds and quick, spot showers will be possible as the front passes, but otherwise it will be a partly cloudy, dry and warm day. Highs will be in the 80s for most, with 70s holding on along the coast and across northern Maine.
TUESDAY-THURSDAY
As has been talked about for several days now, the middle of this week is going to be scorching hot as a heat dome sets up to New England's southwest. This position is favorable to send very high temperatures and high humidity levels into New England. Widespread 90s are likely across New England during this stretch for at least one day with central and southern New England reaching 90° all three days. The Connecticut River and Merrimack Valleys will likely jump well into the 90s and possibly approach 100°.
Heat Advisories have been issued across New England with Excessive Heat Watches remaining in effect for the lower Connecticut River and Merrimack Valleys. With dew points reaching well into the 60s, heat index values will reach into the 95-105° range for many during this stretch. Heat Advisories are for heat index values ranging from 95° to 105° while Excessive Heat Warnings are issued for values of 105° or higher. With the valleys of southern New England on the edge of that 105° threshold, the watch remains in effect for now.
This heat will be coming with exceptionally warm air aloft. 500mb (about 18,000 feet above sea level) heights will rise to nearly 600 dam (decameters). It's rare for heights to climb to this extent in New England and is a strong signal for serious heat in the region.
Also, the 825mb level (about 5,000 feet above sea level) will climb toward the low 70s. For an idea on this temperature at this height, Mt. Washington's summit stands at 6,288 feet and their all time high temperature is 72°. Daily, monthly and even a couple all time highs (we're watching Caribou and Frenchville for that) could be broken this week.
With the heat and humidity will always come the chance for stray, pop up showers and storms. These will be mostly likely across the northern tier of New England through Thursday. Many more areas will stay dry during this time than areas that see a storm. A cold front will begin to approach the northern third of New England, allowing for more storms to fire there in the afternoon. While humidity levels are high at the surface, they actually dry out a bit moving aloft, which will help limit storm development until the front approaches.
Euro showing the increased chance for storms and showers Thursday afternoon as the front approaches:
FRIDAY & WEEKEND
On Friday, the heat dome will begin to flatten and get suppressed to New England's south as a cold front moves into the region. This will begin to break the heat, though it will likely still get pretty warm on Friday with 80s north and 90s continuing south. The front will likely trigger more widespread showers and storms across southern and central New England with lingering activity possible across the northern tier. The timing of the front, which is still a point of contention among models, will determine the level of heat and storms on Friday.
Heading into the weekend, the front will be slow moving as it gets blocked by the high pressure to the south. This may cause the front to become a stationary boundary, leading to a mainly cloudy and unsettled weekend with thunderstorm chances continuing. Temperatures are looking to fall back to more seasonable levels by the weekend, but humidity may remain increased.
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