Soaking Rain Incoming to New England Before Period of Drier Weather

The main wave of low pressure along our latest stalled cold front will move up the east coast and will very slowly cross over southern New England Friday into Saturday. This will bring a widespread soaking rain to New England from southwest to northeast Friday into Saturday morning. Torrential downpours embedded within the steady rain will be possible.

Showers will be ongoing for most of Friday for western New England. It will likely take some time for more widespread activity to push eastward toward the coastal plain. For eastern areas, widespread rain currently looks to hold off until later in the day Friday. Much of Maine may end up mostly dry through the afternoon.

Below: HRR showing potential weather Friday early afternoon (1st image) and Friday evening (2nd image):

For many, the peak of the rain and the greatest potential for downpours will come more toward Friday evening. The rain will continue to steadily push northeastward Friday night into Saturday morning. The area of low pressure will be slow to cross southern New England, so showers will be slow to break down Saturday. Wrap-around showers will continue to be possible through at least the first half of Saturday for many. A general drying trend from west to east is likely for the second half of Saturday.

Below: HRRR showing potential weather early Saturday morning (1st image) and early Saturday afternoon (2nd image):

This low pressure system will be one to slowly meander its way eastward as it will be sitting between two ridges of high pressure. A deep southerly flow will allow for increased moisture to stream into New England ahead of the system. This deep moisture will be acted upon by a strengthening surface low pressure system as it phases with the upper-level, cutoff low, allowing for steady to at times heavy rainfall. A widespread 1-3 inches of rain is likely across much of New England by Saturday evening.

The bull's eye for up to three inches of rain continues to look like it will be focused over the Berkshires, southern Green Mountains and into the Litchfield Hills. This will come as a modest easterly low-level jet will allow for upslope enhancement in these areas, basically allowing for more frequent heavier downpours. This area will also likely see the effects from frontogenesis (the strengthening of a frontal boundary).

A flood watch is in effect for much of interior New England outside of Maine and northern Vermont. With wet conditions already coming into this event, streams and rivers are running on the high side. A handful of rivers are currently expected to reach action stage all around New England as grounds remain saturated and rivers and streams are running high from earlier this week. Minor flood stage is forecast for the Connecticut River, Hoosic River and Housatonic River.

Rainfall rates within the downpours could reach up to 0.25 to 0.5 inches an hour, though rates over 0.3 inches an hour aren't expected to last very long as they will be convection-based. Downpours will also likely remain progressive, meaning they aren't likely to sit over one area for a prolonged period of time.

The threshold for flash flooding to occur is currently 1-1.5 inches of rain in an hour or 1.5-2.5 inches of rain in three hours. This keeps the chance for flash flooding on the lower end. The Weather Prediction Center has all of New England in the "marginal" category (level 1 of 4) for excessive rainfall.

All of this still looks to move out in time for Mother's Day. Starting next week, a pattern shift will occur that places New England under ridging rather than the constant troughing over the past week and a half. This will likely lead to a gradual warming trend with widespread temperatures returning to the 70s and possibly low 80s for interior areas by early next week. With high pressure around, an onshore flow will likely create a sea breeze, keeping the coast cooler. Overall, a trough-in-the-west-ridge-in-the-east pattern may develop.