New England October Weather Outlook: Warmth Persists?

It's officially the month of Halloween, pumpkins, fairs and fall foliage. Average high temperatures drop about 12 to 15 degrees from October 1st to October 31st. The region will also lose nearly an hour of daylight from the start to the end of the month as well.

Summary: This October will likely feature a predominantly trough-in-the-west-ridge-in-the-east pattern. This is poised to bring a warmer than average month to New England overall (with the inevitable ups and downs that come with a changing season, of course). The region is also poised to see the continuation of below average rainfall. Read below for the in-depth discussion.

Fall color unfolds at Lincoln Woods in New Hampshire. Photo by Phil Evenden

TEMPERATURES

New England is starting off October with a fall chill, but that chill won't last very long. The high pressure system pumping this cooler air mass into the region will sink southward this weekend, centering across the Mid-Atlantic. This will create a southwest flow and warm air advection. After Thursday, each day will be steadily warmer than the last through the middle of next week. A large upper-level ridge will continue to build into New England, allowing temperatures to push a good 10-15° above average by early next week. This is a classic trough-in-the-west-ridge-in-the-east pattern.

Heading toward the middle of next week, a gradual change in the upper-level pattern is expected to be underway. The main change through the course of next week will be a slow de-amplification of the jet stream. When the jet stream is amplified, there are pronounced troughs and ridges (hence the trough-in-the-west-ridge-in-the-east pattern). Both the western trough and eastern ridge are expected to weaken.

In New England, this will support temperatures crashing back down to reality by midweek. At the surface, a cold front will cross New England, likely in the Wednesday to Wednesday night time frame. The return flow ahead of this front may allow for one more mild day Wednesday before temperatures come back down for the rest of the week (October 9 onward).

Below: Height anomaly from this weekend through next week, showing a deamplifying pattern:

Despite the de-amplification of the pattern, weak troughing is expected to be maintained in the west and general ridging is expected to be maintained in the east as we head toward the middle of the month. This would support near to above average temperatures generally continuing.

As always, this doesn't mean everyday will be warmer as we head into the middle of the month, but the average to above average days will likely continue to outnumber the below average days. Riding is expected to be more centered across the center of the United States, which would keep the most above average temperatures to our west.

Heading into the second half of the month, the pattern is favored to re-amplify, back toward a more pronounced trough-in-the-west-ridge-in-the-east setup. It should be noted that longer-term guidance is in good agreement on this general setup returning, with the Climate Prediction Center saying guidance is in "remarkably good agreement".

The exact location and orientation of the western trough remains the main point of contention. The center of the ridging is currently favored to set up across eastern Canada and into the Great Lakes and Midwest. This would keep the highest temperatures relative to averages to New England's west, but, at this point, there's not much pointing toward sustained cooler weather.

Overall, we're predicting a warmer than normal October for New England. There will be the inevitable cool-downs and temperature swings (like what's happening here at the very beginning of the month). The main uncertainties will be just how amplified the pattern becomes after the de-amplification in the middle of the month, and where the center of ridging sets up. As stated before, there's just not much pointing toward any sustained cooler than average weather right now.

PRECIPITATION

New England remains entrenched in an overall very dry pattern to start off October. This will generally continue through the first week of the month. With high pressure centered to New England's south and west, the region will remain completely dry through the weekend and into early next week. It will be areas west of this high pressure that will have better shower chances due as they will be on the moist return flow of the high, as opposed to New England, which remains on the drier side.

New England's next shot at widespread rain will come around the middle of next week with the arrival of a potent cold front. When looking at the big picture for October as a whole, it would support a drier month overall with sporadic rain chances. The question on whether the month ends up drier or wetter than average may come down to how much rain those sporadic chances can produce.

There's a saying that goes something like "when in a drought, forecast a drought." This basically means that the deeper the drought, the more difficult it can be to get rainfall to help alleviate the drought. With that said, and the overall potential for broad ridging, we're predicting a below average month for rainfall.

LOOKING BACK

September panned out almost exactly as predicted. We predicted a near average month in the temperature department. We noted that there were some signals for a cooler end to the month, which increased overall uncertainty for the month. This cooler solution was not able to take hold, which led to a slightly above average month overall, but it was pretty close to average for a majority of the region. We also stated that there would likely be multiple ups and downs throughout the month, which did occur.

Below: Average temperature departure for September (1st image) and Boston's daily temperature chart, showing the multiple ups and downs (2nd image):

We also predicted a below average month in the precipitation department, which did pan out for most. Overall, precipitation was highly varied across the region. The driest city was Portland, which saw only 50% of average precipitation this month. The only city that was above average was Providence, which saw over six inches of rain (150% of normal). This was mainly spurred by last week's soaking, which saw a slow-moving storm move over the city, resulting in a flash flood warning.