Sharp Cold Front to Bring Rain and Storms to New England Saturday

After the weak, overnight cold front, the trough's main cold front will swing through New England Saturday through Sunday morning. The higher chances of a longer lasting, steady and cool 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 widespread showers and thunderstorms later in the day rather than periods of rain all day along with warm temperatures.

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 the late morning and afternoon.

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 in the afternoon or evening Saturday as the front slowly creeps through New England.

Below: HRRR showing potential weather around midday Saturday (1st image) and late Saturday afternoon (2nd image):

The showers and storms from this cold front will likely bring a widespread half inch to inch of rain across New England. The storms have been trending toward being more widespread and longer-lasting across the region, which has led to an increase in total rainfall. An area of frontogenesis will likely occur, which will lead to a band of 1-2 inches across a rather narrow portion of the region. 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 and stronger thunderstorms.

For much of this week, it appeared this would set up over interior northern New England, but the latest trends have pushed this band farther south and east. It now looks most likely to set up across interior Maine through southern New Hampshire and into central Massachusetts. This change has come as the front has trended a bit faster, with areas farther north clearing out of the front quicker. With that said, guidance has been wobbling with this front, so it's worth continuing to watch the trends. Overall, a widespread soaking of rain will be coming regardless of where the heaviest amounts set up.

The overall severe weather threat for Saturday has trended up. Instability will likely build and overlap with effective shear, which is a good recipe for some stronger storms. The best forcing for storms will be closer to the cold front, which will likely be right across New England in the afternoon. Where exactly the front sets up in the afternoon and evening will have the best shot at a severe storm. The greatest threat will be damaging wind gusts. Large hail will be a lesser threat due to poor lapse rates. A quick spin-up tornado can't be ruled out given the setup.

There was a discussion among the Storm Prediction Center to potentially upgrade the severe threat to "slight" (level 2 of 4) from "marginal" (level 1 of 4) overnight. The threat level remained a 1 due to uncertainty over instability. With that said, a portion of New England could be upgraded later today should trends toward a more favorable environment continue. The level of instability will be the main area to watch to see whether this upgrade occurs or not.

Below: Storm Prediction Center thunderstorm outlook for Saturday as of Friday morning:

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 where the front won't cross until the afternoon or evening. Interior northern New England will see the front cross earlier in the day, leading to much cooler weather. There could be a decent temperature gradient across New England Saturday afternoon.

Below: Temperature departure from average early Saturday afternoon:

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.

This causes the warmer air to rise over the colder air behind the front. This results in clouds and precipitation behind the front rather than clearing. This setup may allow for clouds and showers to linger on Sunday, which is why Sunday has been trending in the wrong direction when it comes to nice weekend weather.