The chances of a potentially major flash flooding event for western New England have increased over the past day. A stalled cold front will combine with an area of low pressure to create a very heavy rain event. The heaviest rain is currently looking to fall across areas that were hit hardest by flash flooding this past Friday. This means several inches of rain will fall on soil that is already over saturated.
During the day Sunday, the stalled cold front will begin to push eastward as the area of low pressure off New England's coast departs. At this time, an area of low pressure will form along the frontal boundary to our west. This will help inject even more moisture into an already moisture rich atmosphere.
Rain will likely begin to overspread western areas Sunday afternoon. There could be some pop up showers and storms in the morning, but the main event will begin in the afternoon. There is a chance for strong to severe thunderstorms Sunday afternoon, although this threat is low.
The heaviest rain will likely come down Sunday night into Monday morning in western areas. The frontal system is so slow moving, it will take a while for the rain shield to get further east. Significant flash flooding is possible, mainly in Vermont, where widespread flash flooding occurred on Friday.
Those who live in flood prone areas of Vermont have been asked to have plans in place in case evacuations are needed Sunday night. There will likely be hours of steady rain with embedded heavy downpours, potentially moving over the same areas all night.
Expected weather at 8pm Sunday. You can see a sharp cutoff in rain as you work eastward in New England:
Expected weather at 8am Monday, that sharp cutoff in rain still exists:
There is a discrepancy in the models as to how long rain will linger through Monday in western areas. Despite this, it is looking likely that heavy rain will begin tapering off in the afternoon. The rain will pick up in intensity in eastern New England on Monday during the day, however, it will not be falling as hard or as widespread as western areas. This is why flooding is not as much of a concern in eastern areas, but the flood threat is still there somewhat.
By Monday, the flood concern will begin shifting from flash flooding to river flooding, particularly in Vermont. This is due to the fact that by Sunday evening, the rainfall will likely transition from scattered downpours to a widespread soaking rain.
Eastern areas will see rain and downpours through Monday and into Monday night. Again, flash flooding is possible in these areas, but it will likely not be as widespread as western areas. Eastern areas may even see their heaviest rain Monday evening and night. Total rainfall from Saturday through Tuesday could approach 4-6 inches in places across Vermont and western Massachusetts, with locally higher amounts in places where torrential downpours develop on Saturday and Sunday.
Total rainfall amounts are unlikely to be uniform given the chance for localized torrential downpours. Some areas will overachieve and some will underachieve, but a widespread 2-4 inches is possible across western areas. Flooding will be worse in some areas and better in others.
Flood watches have been issued for western and central New England. These alerts generally run from Sunday evening through Monday evening. These watches are mainly for river flooding.
While heavy rainfall and flooding is by far the primary concern with this event, there is another side developing. That is the chance for strong to severe thunderstorms Monday afternoon. Nearly all of New England is in the "marginal" category for severe storms.
These storms will have the potential to bring damaging winds and hail. Tornadoes are unlikely, but not impossible given the tropical-like setup. The overall severe threat is low at this time, a widespread severe weather outbreak is not anticipated. The severe storms that do develop could add insult to injury in areas that may have been flooded across western areas.
Stay with New England Storm Center as this event develops and gets underway.
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