Two Cold Fronts to Bring Rounds of Rain/Storms to New England

After another stretch of dry and quiet weather for New England, the region's next shot at more active weather will come Thursday night through Sunday morning. Multiple rounds of showers and storms will be possible during this time frame as a deep trough forms across the Midwest and Great Lakes regions. This trough will send two cold fronts through New England to close out the week, bringing a widespread rainfall and scattered storms to much of the region.

The first cold front will cross New England tonight into Friday morning. This cold front will likely weaken and fall apart across New England. The best shot at widespread showers and a good rainfall will be across the western half of New England and northernmost areas, before the front dies out. This front on its own will likely bring minimal rainfall amounts, with the most widespread showers occurring during the overnight hours tonight. Spot showers will be possible Friday afternoon, but a vast majority now look to stay dry after the morning wave.

Below: Potential weather during the pre-dawn hours tonight (1st image) and Friday afternoon (2nd image):

After Friday's front, the trough's main cold front will swing through New England Saturday through Sunday morning. This front will be stronger and hold together as it crosses New England, allowing for more widespread rainfall and higher rainfall amounts across the board. The higher chances of a longer lasting, steady rainfall on Saturday will be across western and northernmost New England. Areas east of the Connecticut River and south of the mountains are currently more likely to see a period of scattered showers and thunderstorms Saturday afternoon and evening rather than periods of rain all day.

This front will likely enter into western and northernmost New England during the morning hours Saturday. The front will gradually slide southeast through the day, expanding the rain chances south and east as the day goes on. Northern interior New England may see bouts of rain throughout most of the day, especially by late morning or early afternoon onward.

Southern New England and northern New England's coastal plain will likely see more by way of scattered storms pop up late in the day. Areas near the coast of southern New England may not see storms pop up until late evening or early night Saturday as the front has continued to trend slower.

Below: RGEM showing potential weather early Saturday afternoon (1st image) and Saturday evening (2nd image):

These two fronts combined will likely drop a widespread quarter of an inch to inch of rain across New England. Rainfall amounts will gradually drop moving south and east in the region as the front takes longer to reach, leading to a shorter window of rainfall. Across interior northern New England, it's possible some will see upwards of 1-2 inches of rain. Terrain enhancement will likely be needed to reach closer to 2 inches, however.

An area of frontogenesis will likely occur across northern Vermont and New Hampshire stretching into interior Maine. Frontogenesis refers to the strengthening of a front, which can often lead to a band of heavier snowfall during winter storms. Since we're in early September, the band of heavier snow is replaced by steadier rain. Rainfall rates are expected to be on the gentler side outside of any thunderstorms, with hourly rates likely not exceeding 0.5 inches an hour.

While severe weather isn't expected at this time, areas that see the front cross in the afternoon and evening may see some stronger ones with gusty winds. Areas that will see the best chance for afternoon storms will have the lowest instability. Areas that have higher instability that would favor severe storms likely won't see much activity until later in the evening, when the overall instability starts to fade.

This system will bring a surge of summer-like temperatures and dew points to the region. Ahead of the cold fronts will see a moist, southerly flow develop. The humidity will peak on Saturday ahead of the main front. Friday night looks to be warm and breezy, likely the warmest night New England has had in a couple weeks. Dew points will likely be well into the 60s on Saturday with widespread 80s for high temperatures (outside of northern Vermont). Both temperatures and humidity will be on the downfall on Sunday once the front clears the region.

Below: Temperature departure from average early Saturday afternoon. You can probably see where the cold front is located:

This cold front is looking like it may take on more of an anafrontal setup. When most cold fronts cross New England, they advect cooler and drier air into the region, allowing precipitation chances to diminish (this setup is known as katafrontal). When an anafrontal setup occurs, the cold air rapidly pushes against the warmer air ahead of the front, causing the warmer air to rise over the colder air behind the front, resulting in clouds and precipitation behind the front rather than clearing.

This anafrontal setup may allow for clouds and showers to linger Sunday morning, especially near coastal areas. Gradual clearing remains expected as the day goes on Sunday. Clouds may linger across New England for much of the day. Heat and humidity that built on Friday and Saturday will be erased. Next week will likely be yet another one on the cooler side for New England relative to early September averages.