More Consistent Summer Heat Set to Arrive for New England

A warm front will slowly approach today, allowing for warm air advection to occur aloft. This will set up a very warm stretch, starting tomorrow. Heading into this evening and overnight, this warm air advection will allow for showers to develop from west to east across the region. Despite warm air advection aloft, flow at the surface will be more easterly due to a weakening area of high pressure offshore. This will allow for a continued onshore flow and keep temperatures cooler for most. Interior Maine will be the warmest today.

Below: Temperature departure from average this afternoon:

On Wednesday, a weak system will pass just to the north of New England. This will lift a warm front through the region, allowing warm air advection to occur at the surface. This will bring both temperatures and humidity up a notch from Tuesday. This system will allow for scattered shower development throughout the day and plenty of clouds around. With New England entering the warm sector of the system, the atmosphere will become moisture-rich, the potential for showers to become briefly heavy during the day. These showers and clouds will help keep temperatures in check for Wednesday, but the warm-up will be underway.

New England will remain in the warm sector on Thursday, with conditions more favorable for higher heat and humidity. Temperatures aloft will peak on Thursday, allowing for the hottest day of the week. A stronger frontal system will cross New England during the day, allowing for a stronger southwest flow, which will mitigate any sea breeze. Widespread highs in the 80s to near 90° are possible for southern and central New England. The northern tier will be kept cooler with more clouds and precipitation closer to the center of the system.

On top of the heat, humidity levels will also get pumped up on the strong southwest flow. Dew points will likely reach their highest point of the season thus far. Each day will see a tick up in humidity levels through Thursday, when dew point values likely peak around the 70° mark. This will bring heat index values well into the 90s for southern and central New England in what will be the first truly hot and humid day of the season. Again, the northern tier of New England, particularly northern Maine, will be cooler (but humid).

Thursday's frontal system will also likely trigger a line of scattered thunderstorms Thursday afternoon and into the evening. This line will come ahead of the system's cold front, expected to cross the region later Thursday into the overnight hours. The timing of when the cold front crosses the region will determine coverage and timing of storms as well as how potent they’ll be.

Should this front cross more toward the evening or overnight, the storm chance will be lowered. As of now, the western half of New England will have the best chance of seeing storms erupt in the afternoon. With favorable timing of the cold front passage, strong to severe storms will be possible. The four main ingredients for severe thunderstorms will be in place, and this threat will be the focus of tomorrow's article. Western New England will have the highest chance for severe weather Thursday.

Below: Storm Prediction Center thunderstorm outlook for Thursday:

The cold front will have crossed New England by Friday. This front will be a rather strong one, with an impact on both temperatures and humidity. Dew point levels will drop back into the 50s for many, erasing the very high humidity. Temperatures will likely fall back to seasonal averages for late-June, with mid 70s north to mid 80s south dominating, so it will still remain warm, but not scorching hot. A secondary cold front may swing through on Friday, igniting a few spot showers, but the day will likely end up mostly dry and calm.

Heading into next week, it looks like a trough-in-the-west-ridge-in-the-east pattern will develop, setting the stage for more full-on summer heat early next week. While the exact details and magnitude of the potential heat are not set in stone a week out, the large-scale setup will be in place for some big heat.

A strong ridge of high pressure looks to become centered to New England's southwest. This ridge is currently advertised with a height of 590-594 decameters extending into New England (the higher the decameters, the stronger the ridge and therefore, the higher the temperature potential), which would support highs in the 90s in late June for New England.

Below: Euro showing geopotential heights early next week, with high heights being shown around a strong area of high pressure in the east:

The main question for New England when it comes to how hot it will get will have to do with the northern extent of the high pressure. The system will be set up to New England's south and west. The issue will be sorting out how far north the ridge manages to extend. Should it extend far north, it would help keep New England dry and scorching hot. If it gets suppressed farther south, it would open the door for showers or thunderstorms to round the top of it and enter New England. This would help tamp down temperatures. Should this occur, temperatures early next week will trend lower.

Below: Temperature outlook for next week. You can see high confidence in above average heat to New England's south and west, but confidence does begin to drop moving north and east in the region: