It's no secret that New England's weather has been dominated by high pressure for the past couple weeks. Except for a couple weak, unassuming features, this will continue for another several days, at least. One of these weak features will drop into northern New England today as a cold front. This front may trigger a couple brief, weak showers, mostly across New Hampshire and Maine. While a quick shower can't be 100% ruled out anywhere in New England today, many more areas will stay dry wire to wire versus areas that see a shower.
This front will stall out across northern New England thanks to the nearby high pressure. The front will weaken and eventually wash out on Saturday. This could allow for a couple more quick showers on Saturday, but moisture will be so limited, anything will have trouble developing and will likely stay in the higher terrain. High pressure begins to slide offshore this weekend, allowing an onshore flow and a slight cool-down for the coastal plain. Temperatures will remain warm and above average through at least early next week.
What is now post-tropical Francine is now well inland across the south. The ridge over the northeast will cause the remnants of Francine to remain well south of New England. The system has cut off from the main flow since the ridge of high pressure in the north has closed off the path through the northeast, which is where the storm would naturally want to go. With this path closed off, the system will rain itself out over the south as it dissolves.
This ridge of high pressure over the north and the remains of Francine over the south sets up a specific type of blocking pattern. This type of block is commonly known as a Rex Block (named after the meteorologist who discovered it). This block involves an area of high pressure located directly north of an area of low pressure. This setup blocks the low pressure from traveling north and west along the jet stream, which is what all storms want to do.
This type of block often leads to a flip-flop of what is expected with the weather with warmer and calmer weather in the north and cooler and unsettled weather in the south. This is what will be happening this weekend. In this case, the remnants of Francine act as the low pressure system. As with most blocking patterns, these setups can be stubborn and slow to break down, leading to stagnant weather.
1st image below: Weather map for Saturday showing the high-over-low Rex Block set up. 2nd image below: Temperature departure from average on Saturday, showing a pool of cooler air over the south from Francine while above average warmth remains across the north:
As stated above, this block (along with any blocking pattern) will likely be stubborn and break down slowly. So, the question becomes, how long can things stay this way? After this weekend, the blocking high will continue to sit in place near New England. Monday and Tuesday will be more of the same, with above average temperatures and mainly sunny skies.
Heading into the middle of next week, things may get a bit more interesting. You'll notice an area of low pressure off the southeast coast on the map above. This low will want to creep northward early next week. It will be slow moving and will run into the blocking high, but it could be what's needed to budge this setup. With that said, most guidance does keep the system just south of New England, but some models are beginning to trend farther north with the system.
The National Hurricane Center has their eye on this potential system. The system will likely form along a stalled frontal boundary over the southeast. From there, it may develop some tropical characteristics as it meanders around the coast. The NHC gives this system a 30% chance of developing into a subtropical or tropical system within the next week. While there's plenty of time for things to change with this system, it will represent New England's next chance for appreciable rainfall and not until mid to late next week at the earliest.
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