Another Batch of Rain, Downpours for New England this Saturday

The stalled frontal boundary that's been waffling around New England will very slowly push eastward through the region today as a cold front. Another area of low pressure will ride along the front, bringing another period of rain and thunderstorms from west to east later this morning and into the afternoon. This final round of showers will again be capable of producing bouts of heavy downpours.

The main batch of rain will break out along the cold front across western New England Saturday morning. This batch of rain will steadily move eastward through the afternoon, arriving in Maine and eastern Massachusetts by early to mid-afternoon. This batch will likely be steady rain with scattered to numerous embedded downpours.

Some thunderstorms will likely also be mixed in. Isolated showers and thunderstorms will likely develop across northernmost New England in the afternoon on the backside of the front while central and southern New England deal with the main batch of rain and storms.

Below: HRRR showing potential weather around midday today (1st image) and mid-afternoon today (2nd image):

The main feature with today's showers and storms will be the continued threat for torrential downpours. Moisture will remain highly elevated ahead of the front. A widespread half inch to inch of rain is likely through today. Areas that get under torrential downpours will see more, possibly in the 2-4 inch range, similar to yesterday. Overall, rainfall totals will again be highly varied from community to community today.

A flood watch has been issued for areas that saw multiple inches of rain on Friday. A widespread 1-3+ inches of rain fell across southern Vermont, southwest New Hampshire and portions of central Massachusetts. Maximum rainfall of 2-3 inches of rain is being shown for today's system, and if this falls in areas that saw the most rain Friday, additional flooding issues could arise. As of now, the axis of heaviest rain today is generally being shown a bit farther east than where it set up yesterday.

One of the issues today is that while the main batch of rain will be pushing eastward, the embedded downpours could take a more northeast route as they move parallel to the frontal boundary. This could lead to some storm training and slow-moving storms and downpours. Forcing for showers and storms will be strong along the front, especially with an area of low pressure moving along it.

With the same air mass remaining over New England today, the environment remains moisture-rich. Precipitable water values (which measures the amount of water vapor in the atmosphere) are highly elevated, with values in excess of 1.5 inches. This indicates a moisture-rich atmosphere that will be primed for downpours within the rain and storms. With that said, the kind of numerous thunderstorms that were seen yesterday are unlikely to repeat. Today will be more like one blob of rain rather than many storms scattered around.

Below: Precipitable water values today, showing a very-moisture rich environment streaming up the eastern US and into New England:

The Weather Prediction Center has placed southern New Hampshire and central Massachusetts in the "slight" category for excessive rainfall today (which is level 2 of 4). With yesterday's rain, the threshold for flash flooding to occur has dropped to 1-2 inches of rain within 1-3 hours. The greatest chance of additional issues will be across southern New Hampshire and Vermont as generally more rain is expected in northern New England than southern New England today.

Instability is much lower today than it was yesterday due to the earlier arrival of the rain and thicker cloud cover, so the thunderstorm threat is much lower as well. There will likely be enough to allow for some rumbles of thunder within the downpours, but severe weather is not expected.

After a few days and many rounds of showers and storms later, the boundary looks to clear out by Sunday, setting up a drying trend. New England's next system looks to approach around next Tuesday. After cooling off this weekend and into early next week, signals point toward a rebound back to more summery conditions for the latter part of next week.