New England August Weather Outlook: It's Still Summer

We're into the final month of meteorological summer. High temperatures have peaked and will begin their descent. This descent starts slowly with average highs only dropping a few degrees from the start to the end of the month. The drop in average temperatures will really begin next month.

Summary: The large-scale pattern for August will likely favor hot, summery weather for much of the month. With that said, the general ups and downs we've seen through the summer are expected to continue, with bouts of cooler days sprinkled into the warmth. A generally dry month is also possible, but certainly not locked in. Read below for the in-depth discussion.

The Green Mountains on a summer evening. Photo by John Howard

TEMPERATURES

New England will be starting off August with surface high pressure dominating the region. Troughing aloft has allowed a cooler start to the month relative to average, however, a warming trend is now underway as this troughing gives way to ridging. Overall the start of August is looking very seasonable with high temperatures hanging right around seasonable levels for much of the upcoming week. The dry air mass with high pressure in place will allow for cooler and comfortable overnight lows as well.

In the near-term, Monday will be the warmest day of the week ahead of a cold front that will help bring temperatures back down. Overall, a mainly zonal flow and generally quiet weather will allow for mild and seasonable temperatures to persist through much of next week. Toward the end of next week, a large-scale ridge is expected to form across eastern Canada. This is consistent with a positive NAO (North Atlantic Oscillation) Index, which is expected to strengthen and last through at least the middle of the month.

Below: Upper-level height anomalies showing the ridge building over eastern Canada later next week:

After a mainly seasonable week, this building ridge will likely support rising temperatures heading into next weekend and into the beginning of week two. This comes as trends have shown the above average heights associated with the ridge expanding southward into the northeast US. The main question for New England will be the strength of the ridge and if it breaks down sooner than what's currently being shown.

This, along with surface features, will determine just how warm it may end up getting during this time (in the August 8-12 range). Trends toward a stronger ridge over Canada is seen in the Climate Prediction Center's 6-10 day outlook, which currently covers August 7-11, which shows above average temperatures being favored across the northeast and Great Lakes. With the ridge centered over Canada, northern New England has the highest chance at above average temperatures, with those chances lowering moving southward.

Heading toward the middle of the month, there's not much signal for a widespread or major shift within the overall pattern. That is to say that a positive phase of NAO is generally expected to persist. This supports troughing across the high-latitudes of northern Canada and Alaska with general ridging farther south, toward southern Canada and the northern United States.

Below: Euro showing forecast upper-level height anomalies from August 10-15, which favors a positive NAO setup:

With that in mind, continued above average warmth is currently expected for New England heading into, and potentially beyond, the middle of the month. That's not to say every single day will be hot and humid as this overall setup does not take into account surface features (which can't be predicted this far out). These surface features (mainly cold front) will likely continue to bring cool-downs after hot stretches, as has been the case for the entire summer. With that said, hotter days will likely outnumber cooler ones.

The one caveat in this forecast is the potential for a weak trough or cyclonic flow over the northern Plains, Mississippi Valley and into the southeast. This is currently poised to keep these areas closer to averages rather than above average. Should this trough trend farther north or east, New England would trend cooler as well, which will be something to watch. The Climate Prediction Center currently has New England with a 70-90% chance of above average temperatures around the middle of the month.

Heading toward the end of the month, individual models show little signals for major change. With that said, at this range, there will always be a large spread in potential outcomes. The other issue in the long-term is that this month's forecast uses the presence of a positive NAO heavily. NAO and other teleconnections are generally weaker and have less of an influence on overall weather during the summer months. This makes it more difficult to say with any kind of confidence that warmer than average weather will continue, but at present, that is the favored outcome.

Overall, we're predicting an above average August as a whole. With that said, we also expect the ups and downs that we've had for much of the summer to continue as well. That means, while hotter days are favored to outnumber cooler ones, we expect relief to continue to move into the region throughout the month rather than consistent and persistent heat all the time.

PRECIPITATION

With a ridge and surface high pressure persisting over New England to start off the month, it will be a dry beginning. The Weather Prediction Center's current seven day forecast shows less than a tenth of an inch of precipitation through next Saturday. While spot showers and storms here and there will be possible in the upcoming week, the next chance for more widespread precipitation may not come until late next week when Tropical moisture advects northward.

Current seven-day precipitation outlook:

With little signal for major change within the overall pattern heading through the month, it may lead to a drier month as a whole, though that will come down to surface features. One big issue with August precipitation outlooks (and September into October) is the fact that hurricane season will be reaching its peak activity. Whether New England sees a direct impact from a tropical cyclone or remnants moving through, it could drastically alter how precipitation ends up being for the region.

LOOKING BACK

July played out exactly as expected. We predicted that bouts of hot weather would be continuously replaced with shots of cooler weather. We also said that the bouts of hotter weather would override the cooler weather to create an above average month as a whole. Much of the region landed 1.5-3° above monthly averages. There were distinct cool-downs sprinkled through the month, as seen on Boston's daily temperature chart below. Precipitation ended up right around average, which we also predicted.