New England June Weather Outlook: Transitional Weather Expected

It is now meteorological summer. Average temperatures across New England continue their trek upwards. Through the month, daily average highs rise a good 10°. A majority of New England sees average highs reach the 80° mark by the end of the month, near the start of astronomical summer (June 20 this year).

Summary: The overall weather pattern will likely be shifting through the month, which will result in cooler stretches followed by warm-ups and back again, as evidenced by how the month is starting out. Overall, the way the pattern is setting up may result in a mild June with odds tilting toward above average temperatures and around average precipitation. Read below for the in-depth discussion.

TEMPERATURES

After spending much May under persistent troughing, New England will be spending the next few days under a firm ridge of high pressure. This will bring some long-awaited summer heat to the region with widespread 80s to low 90s expected for Wednesday and Thursday.

Below: 500mb heights on Wednesday afternoon, showing a warm ridge building over the east:

This will be rather short-lived, however, as a slow-moving frontal boundary approaches and crosses New England late this week through the weekend. This boundary will produce more clouds and showers beginning Friday, bringing temperatures back down. This drop in temperatures is more likely to bring New England back to seasonal averages for early June rather than well below average.

This will come as a familiar pattern re-establishes itself over the United States: a firm ridge will rebuild over the west coast while a trough develops over the center of the country and Great Lakes. This will bring the heat to the west coast with little indication of any big-time warmth east of the Rockies. The trough will be centered to New England's west, so New England itself likely won't be centered under the full cool-down, but rather just the edge of it, so near average temperatures are currently favored next week, with a slight lean toward above for Maine, who will be the furthest removed from the trough.

Moving into week two of the month, the established trough over the Great Lakes will likely gradually shift eastward. With that said, it is favored to weaken significantly as it does so. This weakening of the trough helps to keep New England in the orange on the map above, but confidence is low as the exact evolution of the trough and surface features next week will ultimately determine how temperatures play out. No big-time summer heat is currently expected. Given the overall uncertainty, seasonable temperatures are currently expected with a potential warm-up coming toward the end of the week.

Below: Euro showing 500mb height anomaly evolution from Sunday (June 8) through Thursday (June 12). You can see the trough over the Great Lakes shift east, but weaken quite a bit as it does so:

Heading toward the middle of the month, a major pattern could begin to develop, the start of which can be seen on the graphic above. The firm ridge over the west coast is expected to weaken throughout next week and is likely to be replaced by troughing late in the week. While there isn't as strong of a signal for firm ridging in the east, a trough in the west would support the return of summer heat after a period of slightly cooler weather.

Below: 500mb height anomaly late next week showing a trough dig into the northwest:

Overall, the middle of June is appearing to be a transitional time from one pattern to the next. This transition time will likely include a period of a more zonal flow, which occurs when the jet stream lays generally flatter across the country. This flow lowers confidence in long-term forecasts.

With that said, a transitional period like this would tend to favor mild pacific air across much of the country, so generally warmer than average conditions are favored by the Climate Prediction Center's current 8-14 day outlook (shown below). Again, the overall confidence in this period (June 12-17) is lower due to the transitional nature of the pattern, which will put a high emphasis on small-scale factors that can't be predicted this far out.

With the confidence reduced in the evolution of the pattern during the middle of June, late June remains under increased uncertainty as well (which is typically the case when trying to look multiple weeks out). Overall, positive height anomalies are favored to stretch from the southwest, across the northern plains and into New England. Remember this is the general large-scale pattern and does not take into account small-scale factors that will affect day to day weather and temperatures.

Overall, we're predicting a generally mild June that has a better chance to end above average than below average. With that said, there may be multiple up and down periods throughout the month with cooler stretches followed by warm-ups and back again.

PRECIPITATION

After a period of ridging and dry weather, more unsettled weather looks to re-enter the picture for New England for later this week and into the weekend. At this point, a weak trough followed by a period of more zonal flow could support near to above average precipitation for New England through the middle of June. With New England on the edge of the trough followed by a weaker trough moving through New England, the region has a lower chance of above average precipitation than the rest of the east during the first half of the month.

With that said, there are some reasons to believe the region will end up with above average precipitation. This weekend's frontal boundary will support the chance for torrential downpours with very high moisture content being acted upon by a cold front. Through the month, increased flow north from the Gulf could support high humidity and continued heavy downpour events amid thunderstorms. Even if all-day washouts are few and far between, the potential for multiple "scattered downpour" days could result in precipitation adding up when all is said and done with the month.

LOOKING BACK

May ended up generally warmer in the front half with a much cooler finish. In our outlook, we stated that confidence was low heading toward the middle of the month, mainly due to how troughing over the south would play out. This trough turned into persistent troughing across the east for the second half of May, leading to long periods of cloudy and wet weather punctuated by a couple late-season nor'easters. This undercut the potential for a warming trend in the second half of the month and kept things on the cool side.

Below: Temperature departure from average for the first half of May (1st image) and the second half of May (2nd image), showing the opposite of what we generally predicted: