New England has been visited by a spring staple: a cut off low pressure system. These are systems that have become completely detached (or cut off) from the main flow. This often happens in the spring as the polar jet stream weakens and begins to move northward for the summertime. In this case, a blocking high pressure downstream is preventing the system from exiting through in a timely manner.
HRRR showing the system meandering around the south of New England over the next 48 hours:
These systems can be notoriously difficult to predict as they are cut off from the Main flow. This allows the storm to basically make its own rules; stalling out, moving westward and making loops over the region. This can go on for days, even up to a week at a time before moving away, bringing persistent clouds, cool temperatures and showers.
With this storm, it was looking for several days like it would stay well south of New England, with only the outer fringes making it to the region. Yesterday, the system began to trend farther and farther north, leading to an uptick in the showers and showers intensity. As of 7am, 2-4+ inches of rain has fallen across southern Rhode Island and Connecticut.
Rainfall since Wednesday evening (as of 7am):
Throughout today, another 1-2 inches of rain will be possible across these areas as bands of heavy rain cycle into the area very slowly. This has prompted a flood warning for much of Rhode Island and the Massachusetts South Shore until 9:30am. A rather sharp cutoff in steady rain has set up to the north of these areas, leading to much lighter rain.
HRRR showing expected weather around mid-afternoon today:
The extent of steady rain north of Rhode Island and Connecticut will be determined by just how far north the system can meander. If this was wintertime, determining snow totals with this one would be very daunting as areas to the south would likely have seen a decent thump while a very sharp cutoff to just flurries would have occurred farther north. But we digress.
This particular cutoff low will be with us through the rest of today and into tonight as the system slowly dives back south and east, away from New England. This will gradually shut off shower chances from north to south this afternoon and evening. At the same time, a stationary front over northern New England will begin to move once again and clear the region by Friday evening. High pressure will help dry out the atmosphere, leading to a mainly dry Friday with some sun possible.
The weekend has been trending drier as a system has trended farther to the south of New England (which we did mention was a distinct possibility in our "Weather This Week" article on Monday). Most of New England is looking mainly dry for the weekend, although still on the cooler side for eastern areas amid an onshore flow. The region will remain under broad cyclonic flow, so brief, spot showers will be possible. Showers may be most numerous across Vermont.
Euro showing scattered showers around during the day on Saturday, but there will be plenty more dry hours than wet hours:
Yesterday we mentioned the chance for a larger warm-up next week. This still remains on track as ridging ahead of a trough in the Great Lakes will likely bring a southerly flow and high pressure bringing drier, sunnier weather. If this holds up (still an "if"), summer-like weather will be on the docket to start the work week next week. A sea-breeze is likely to keep temperatures down along the coast. The trough will push east later in the week.
CMC showing temperature departure from average for Monday (1st image) and Tuesday (2nd image). Note the distinct sea breeze influence:
