Troughing to Remain Dominant Over New England

The upper-level low responsible for the frontal passage across New England will remain north of New England through the end of this week. This will promote broad cyclonic flow across the northeast. Broad cyclonic flow is synonymous with partly to mostly cloudy skies building in the afternoon, cool temperatures and breezy conditions. This time will be no exception as this will be the general weather for Thursday and Friday.

Below: 500mb height anomaly showing the upper-low north of New England keeping us in a rather deep trough:

The deep trough and cold pool aloft will promote plenty of cloud formation both today and tomorrow afternoons. Moisture is rather meager, so shower activity will likely remain rather spotty and isolated. With that said, the instability associated with the cold pool will likely allow for some activity both afternoons. Showers will be most numerous across the mountains and northern Vermont, closer to the center of the upper low.

Below: HRRR showing potential weather late this afternoon:

By this weekend, the trough axis will begin to shift eastward while high pressure builds in from the west. Overall, broad troughing is expected to persist over the region while surface high pressure keeps the region dry (something that was in question earlier in the week). This will allow for continued partial sunniness, but also continually dropping temperatures, with widespread highs in the mid 40s north to mid 50s south by Sunday.

Widespread freezing temperatures are expected for overnight lows heading into the weekend and early next week. By Sunday and Monday mornings, widespread lows in the 20s north to mid 30s south are likely. At this point in the season, only southern Connecticut is apt to still receive frost and freeze alerts.

Our stretch of rather mild mid-fall temperatures has ended for most (eastern Maine will remain generally milder for a couple more days). Each day will likely be a notch cooler than the last through early next week. This will come as an area of Canadian high pressure continues to build into New England, resulting in a brisk northwest flow. It certainly won't be notably cold given we're quickly approaching November; generally seasonable temperatures are expected over the next week or so.

Looking toward the middle and end of next week, a large-scale blocking pattern reminiscent of a Rex Block may set up (this block involves an area of high pressure directly north of an area of low pressure). A large, strong and expansive ridge to the north of New England is likely to form. This will force New England into continued troughing while the ridging remains across Canada.

Below: 500mb height anomaly late next week showing a ridge over eastern Canada, with troughing locked farther south:

This large-scale setup will promote a slow-moving area of low pressure to impact New England around the middle to end of next week. A piece of northern-stream energy will likely drop southward into the Midwest due to the aforementioned ridging. This northern-stream system is looking increasingly likely to spawn a secondary low off the east coast by next Wednesday or Thursday, which would likely move offshore of New England right around Halloween, bringing a period of rain and possibly wind.

Below: Current weather map for next Thursday (October 30), showing what is described in the paragraph above:

There are a couple factors that will determine the level of impact this system will have on New England. The first is the strength and exact location of the ridge over eastern Canada. Looking at the 500mb graphic above, northern New England is more on the edge of the ridge and trough. How far north impacts get in New England will be determined by the exact location. Southern New England will likely see the bulk of the storm.

The other side will be the exact strength and track of the low pressure system. Naturally, the farther the secondary low remains offshore, the lower the impacts will be across a smaller portion of the region. Some guidance shows a strong low pressure system passing just offshore. Couple this with a strong area of high pressure to the north, and a period of heavy, windswept rain will be likely for southern and maybe central New England.

Another factor will be Melissa, which will likely get pushed well offshore of the east coast, but could inject tropical moisture into the system. Overall, this storm could go either way at this point (on being high impact or low impact) with massive spreads in guidance.