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New England May Weather Outlook: Spring vs Summer

May is an interesting month weather-wise as summer weather tries to kick start amid typical spring conditions. This can often lead to an up and down month in the temperature department. This year appears to be no exception. See the forecast below.



TEMPERATURES


May will begin with zonal flow in place, meaning the jet stream lays relatively flat across the United States. This will generally keep colder air locked to the north of the region. With that said, typical spring features will generally keep more mild temperatures out of the picture at least for eastern New England during this first week of the month. These features being frontal systems keeping clouds around, an onshore flow and backdoor cold fronts. Western New England will generally have a more mild start to the month.



Heading into week two of the month (the first full week of May), a trough will likely begin to dig into the west with a ridge building into the east (you can see this pattern beginning to develop amid the more zonal flow in the map above). This will support a general warm-up beyond this weekend for New England. At this point, the position of the ridge doesn't favor a significant warm-up and typical spring factors (mentioned above) will need to be watched for eastern New England.




This warm-up for the start of next week may not last too long as the western trough will likely push eastward. This will re-introduce clouds and showers back into the forecast with a potential cool-down. At this point, a cool-down doesn't look significant, it may be a return to near average temperatures for early May after a brief stint above average.


While New England may end up on the warm side of the trough axis, the warmest temperatures (relative to average) are more favored for the east coast south of New England, as seen in the Climate Prediction Center's 8-14 day outlook, which currently covers May 8-14.



Heading toward the middle of the month, signals point toward general zonal flow continuing. This would support a more progressive pattern with troughs and ridges moving through relatively quickly. This may lead to up and down temperatures, similar to what's being seen here at the start of the month. This is supported by the fact that the Climate Prediction Center mentions "anomalous troughs" over the eastern United States in their week 3-4 discussion.


A generally zonal flow can be seen by looking at both the NAO index and PNA index. A positive or negative NAO favors ridging or troughing in the east while the PNA does the same for the west. Both the NAO and PNA remain near neutral, around the same level. This supports zonal flow. On top of that, Arctic Oscillation is also expected to remain around neutral after starting the month tilted negative.



We'll need to watch the trends to see if this holds heading toward the end of the month. If a blocking pattern can get set up at some point later in the month, cooler temperatures could filter into the eastern United States. The charts above only show the forecast through the middle of the month. As one would expect looking weeks in advance, there are mixed signals or whether or not a block will set up for the second half of the month.


Overall, we're predicting an up and down month temperature-wise, which should be expected in a transitional month as it is. Whether New England ends up skewed toward warmer than average or cooler than average is tough to say and will likely vary across New England with western areas skewing warmer than eastern areas, as per usual.



PRECIPITATION


New England will be generally active and unsettled to start the month, which is expected for early-May, with frontal systems bringing a lot of clouds and showers to the region. The rainiest time of the near-term forecast should be Saturday night into Sunday (May 4-5).


With zonal flow in place, these systems will likely skew toward being weaker and less impactful with less rainfall. This occurs as storm systems are more quickly pushed across the US in this setup, which doesn't give them time to strengthen.



So, systems will continue moving through New England, but they should be low-impact events. With an overall active pattern, precipitation will have a better chance to skew slightly above average. Overall, we're thinking it will be a near-average month precipitation-wise.


LOOKING BACK


At the beginning of April, New England was in the midst of a very active pattern off high-impact storms with another major snowstorm bearing down on the region. On top of that, the total solar eclipse was quickly approaching. With all of that going on, it was simply a bit too chaotic to get an April weather outlook released at the start of the month. With that said, March panned out generally as expected in our outlook with generally colder conditions at the end and above average precipitation.


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