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New England's Cool and Unsettled Weather Pattern

New England has been in a generally unsettled and cool pattern over the past few days, mainly due to the setup of zonal flow. This occurs when the jet stream lays flatter across the region, or is positioned more west-to-east rather than north-to-south (meridional flow). When this type of flow is in place over New England, it can send multiple rounds of low pressure through the region, since the jet stream acts as a steering current for these systems.

Zonal flow is also synonymous with unimpactful weather as systems don't have the time or amount of energy needed to strengthen as they move through the un-amplified pattern. This has been the case this week with more "inconvenience" weather with non-flooding rains and no wind. The exception was, of course, the thunderstorms Wednesday that brought torrential downpours and large hail, but that was isolated and attributed to a temporarily primed atmosphere for strong storms to develop.

This flow can also be thanked for the persistently cool temperatures that have set up for New England since the warmth at the beginning of the week faded. Without ridging in the jet stream, warmer temperatures farther south don't have much of an access point to get into the northeast. Add in a cool, onshore flow, plenty of clouds blocking the sun and occasional showers and the region stays cool, or at least closer to seasonable levels for some.

With that said, this upcoming weekend has trended drier over the past 36 hours thanks to a southward trend in an area of low pressure. This system will pass south of New England on Saturday before moving northeast, well offshore. This keeps a majority of the rainfall out of New England.

HRRR showing expected weather Saturday early afternoon. You can see the system well offshore with a low chance for spot showers around New England due to broad cyclonic flow. Dry air will make it difficult for any shower to develop:

Weak high pressure will try to build in, allowing for at least partial sunshine for Saturday. New England will be under broad cyclonic flow, so intervals of clouds and spot showers will be possible. A digging jet stream will keep the region persistently cool this weekend.

On Sunday, an upper level closed low becomes centered over New England. This keeps the region under broad cyclonic flow. It will likely be generally more cloudy and showery than Saturday. There should be many more dry hours vs wet hours for most, though there is a spread among models on just how widespread shower activity will be.

There is a spread on shower activity for Sunday afternoon, but we think the GFS is a good middle ground right now, showing light showers scattered around:

That upper level closed low can be seen on the 500mb height & wind map for Sunday afternoon. A closed low is a low with a distinct center of circulation. The circulation of a closed low can be completely encircled by isobars or height contour bars.

Heading into next week, the trends have been more toward a less amplified pattern (or more zonal flow). We mentioned that zonal flow would likely have a bigger impact on New England's weather this May in our monthly outlook. A less amplified pattern will keep the systems rolling through New England.

This starts with a brief ridge of high pressure for Monday quickly followed by another low pressure system for later Tuesday into Wednesday. A warming trend is likely for next week as winds shift to a more southerly direction ahead of the Tuesday system.

The main flow will feature a split flow across the United States, which will continue to keep any big time, summery, warm ups out of the picture for New England. The preliminary outlook for next week features seasonable temperatures, though there's mixed guidance on whether it'll end up on the cooler or warmer end of the spectrum.



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