After much of New England experienced a full week without precipitation, things are changing once again. The change back to unsettled weather begins this afternoon for northern New England as a trough approaches. This trough will send a wave of energy into northern New England, igniting showers and storms. An upper-level low to New England's northwest will send its fronts toward New England on Thursday, bringing wet weather back for everyone by then.
For Wednesday, scattered thunderstorms are expected to begin to develop by midday and continue to pop up through the afternoon and into the evening. Storms are most likely to occur across New Hampshire (specifically central and northern New Hampshire) and western Maine. With that said, there is at least a slight chance of a storm anywhere in northern New England. Southern New England is expected to remain dry today.
GFS showing potential weather this afternoon:
The main threat with today's storms will be the potential for torrential rainfall causing minor and localized flooding issues. Dry conditions over the last week will help to reduce any flood risk today, but storm training (when multiple storms move over one area) will be a possibility. Any area that sees multiple storms today could see minor issues. Storms will also be slow moving initially before picking up speed later in the afternoon.
As for severe storms, the trend has been more favorable for them to develop, though the threat is still looking pretty isolated with more non-severe cells likely than severe ones. The four main ingredients will be present in northern New England, though some will be rather muted.
There will be plenty of moisture and lift, but shear and instability will be more modest. Shear has generally increased, which is the main reason for the bump in this potential. As for instability, CAPE values will likely be in the 800-1,200 range, which is not all that impressive. With the potential for stronger updrafts, small hail will be the main threat severe-wise (severe storms don't take into account the potential for torrential rainfall).
After today, New England's pattern will shift, moving the ridge to New England's east with a trough developing to the west. New England has been in the warm and drier center of an omega style blocking pattern, but now this pattern will be shifting east, putting New England on the cloudier and unsettled side of the block.
This unsettled weather kicks off for all of New England on Thursday as a cutoff low north of the Great Lakes sends its warm front into New England. A surface low will likely develop and track through New England through Friday morning as well. This will allow for a shield of rain to move from southwest to northeast across New England during the day.
How far north the warm front pushes will determine how far north in New England the shield of downpours will reach. As of now, it looks like the front will clear southern New England, but may struggle to lift into northern New England. The atmosphere will be moisture rich, so torrential downpours could develop.
WRF-ARW showing potential weather around mid-morning Thursday:
The main batch of showers will continue to lift northeast through New England in the afternoon, likely beginning to fall apart as it does so. In the afternoon, showers will become more isolated, but they will be around for the entire day. If the initial batch of rain moves through quickly enough, some breaks of sun will be possible in the early afternoon. Should this happen, a round of thunderstorms may develop for the late afternoon or evening.
WRF-ARW showing potential weather around late afternoon Thursday, highlighting the potential development of storms in western New England:
With a moisture-rich environment, some areas of potential downpours are likely to develop within the initial batch of rain. With the variable intensity of rainfall, total amounts will likely be variable from area to area. A broad 0.25-0.75 inches of rain is likely with localized spots seeing 1-2 inches, depending on where exactly the heavier downpours set up. These downpours could lead to some minor flooding concerns, mainly in the order of urban and poor drainage flooding. Dry conditions beforehand will again help to mitigate this issue.
A blocking pattern and cutoff can only mean one thing for New England: the unsettled weather will last for days. While Thursday will likely be the wettest day of the stretch with the most widespread rainfall, plenty of clouds and showers will hang around as long as that cutoff low keeps spinning to the north and west of New England. This will likely last until at least early next week.
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