I’m going to make this version of the summer outlook fairly quick, simple, and to the point. Our drought now essentially behind us, and the pattern having been wet, it’s obvious we are not going into summer 2017 the way we did just a year ago. The pattern in the spring was wet, with a cold March, a milder April, and a very cool May (the coolest since 2005 and the first below normal May in many parts of the region since 2008). What follows is a short summary of what I expect for the summer. I have observed forecasts from colleagues, NOAA, and other professionals and I will say that I’m in general agreement with most of them.
SUMMER 2017 OVERVIEW
A pattern of blocking at high latitudes has resulted in a pattern of frequently cool, often cloudy, and occasionally wet weather for New England during the last several weeks, and this general idea will continue into the early and mid part of June, though as climatology dictates, we continue to warm slowly as we advance the calendar so the direct impact, while less, will still be noticeable when compared to daily normal values, especially for temperature. As we move into late June, we should see a shift of the pattern as blocking weakens and dissipates, and a more zonal flow takes over. This will allow more episodes of westerly flow and more seasonable warmth with occasional spikes of heat alternating with brief cool-downs as air masses change with passing systems on a more progressive jet stream. Heading into the heart of summer, provided a forecast El Nino is slow to develop, and I suspect it will be, we should see an occasional Bermuda High setup as high pressure in the western Atlantic occasionally retrogrades (backs westward) toward the East Coast. During these times we will see our higher humidity, some heat, and episodic showers/thunderstorms. The shower activity this summer will be more prolific than that of last summer, keeping overall precipitation amounts near to above normal and preventing a slip back into drought. This, along with what ends up being a warmer middle and end, will skew temperatures to near to above normal. So the theme of summer 2017, after its cool start, will be warm and wet.
Current pattern of blocking and frequent troughing in the Northeast continues through mid month with precipitation above normal and temperatures below normal. Pattern breaks down around the summer solstice and the last third of the month will be warmer and drier with passing systems in a more progressive jet stream flow causing brief shower/thunderstorm threats.
Temperature: Below normal.
Precipitation: Above normal.
The first half of the month should feature the pattern that is established during the latter third of June. The second half of the month will feature an alternating between the early July pattern and a more humid and showery Bermuda High pattern. Though this type of pattern does not typically produce all day rains, we’d have to be on the lookout for some tropical moisture feeds that could provide days with frequent showers/thunderstorms.
Temperature: Near to above normal.
Precipitation: Near to above normal.
Take the pattern of the second half of July and continue it for August, but with more emphasis on Bermuda High and less so on westerly flow and progressive jet stream. Should be a warm and humid month with episodic showers and thunderstorms. Though we cannot predict very far in advance whether or not a tropical storm or hurricane will threaten the region, or any part of the US coast, we can say that a Bermuda High pattern can leave the East Coast vulnerable, should a storm form and be in the right position to get around the western side of such a high pressure area.
Temperature: Above normal.
Precipitation: Near to above normal.