This system will involve a deep trough moving across the country. The system's primary low continues to look like it will move well north of New England, dragging its cold front across the region after a warm frontal passage. The main slug of rain will occur along a line ahead of the system's cold front. The primary area of low pressure has continued to trend northward, now likely passing over Hudson Bay in Canada with a secondary low pressure forming along the front south of New England.
Sunday is still looking like a mainly cloudy, but mainly dry day. A couple pop-up showers are possible around the region throughout the day, but a majority of the rainfall will remain to New England's west until the evening. By the evening, the main slug of rainfall ahead of the cold front will likely enter westernmost areas while lighter and scattered showers begin to fill in farther east.
Below: FV3 showing potential weather Sunday evening:
This slug of rain will chug across New England throughout the overnight hours. This is when widespread bands of steady rainfall will occur with pockets of heavier downpours. It will remain very mild Sunday night into Monday morning. There will basically be a fire hose of moisture moving up the eastern seaboard, allowing for heavier rates.
Below: FV3 showing potential weather around midnight Sunday night (1st image) and early Monday morning (2nd image):
The cold front will slow down on Monday due to a ridge of high pressure offshore, allowing for periods of rain to continue through Monday morning and into the afternoon. This will mainly be for eastern New England as Vermont, western Massachusetts and Connecticut will begin to dry out by Monday afternoon as a secondary cold front pushes into the area. This slowing down of the front will allow southeastern Massachusetts and Rhode Island to sit in the heavier bands of rain for the longest amount of time.
Below: FV3 showing potential weather around mid-morning Monday:
New England is poised to see a widespread half an inch to inch and a half of rainfall by Monday evening. The potential formation of a secondary low pressure near southern New England and the fact that the cold front will be slowing down as it moves eastward will help boost totals across southernmost New England and Downeast Maine. Northernmost New England will stand to see the least as the rainfall will be more progressive compared to farther south and east in New England.
Overall rainfall amounts may be a bit varied across the region due to the scattered nature of heavier downpours. There could certainly be locally higher amounts within the totals above due to the aforementioned scattered downpours. The overall coverage of convection will play a large role in overall totals.
The storm will be capable of creating periods of heavy rain Sunday night into Monday as a very strong southerly flow develops. This flow will allow for significant moisture from the deep south to work into New England on basically a conveyor belt working up the eastern seaboard. Precipitable water (PWAT) values may exceed 1" and potentially approach 1.30+". This indicates a moisture-rich environment given the time of year (PWATs are generally higher in the summer and takes higher values to be considered moisture-rich).
PWAT is defined as the amount of water vapor contained in a column of air if it were to be condensed and collected. Basically, the higher the PWAT value, the heavier rainfall rates can potentially get. The PWAT value does not correspond to how much rain is expected to fall, meaning that a PWAT of 1 to 1.30" doesn't immediately mean 1-1.30" of rain is expected.
Below: PWAT values overnight Sunday into Monday, showing a moisture conveyor belt from the deep south:
The ingredients will be together for significant snowmelt this time around for northern New England. Overall, 1-2.5 inches of runoff from snowmelt will combine with total rainfall. Total runoff across northern New England may come out to around 2-3.5 inches. River ice will continue to rot and break up as well. Rivers in southern and central New England will likely see river ice flushed out, however, the thicker ice across the north may present some ice jam issues as it breaks up.
There will be the potential for open water river flooding in addition to potential ice jam issues. Ice jams are more likely across New Hampshire and Maine while open water river flooding is more likely in Vermont. At this point, minor flooding is the most likely outcome for rivers with pockets of moderate flooding a possibility. A flood watch has been issued for all of Vermont.
As of this morning, the Missisquoi River in North Troy, VT; Mad River near Moretown, VT and Otter Creek at Center Rutland, VT are forecast to reach minor flood stage by Monday morning. The Swift River in Maine, Pemigewasset and Warner Rivers in New Hampshire, Hoosic River in Massachusetts and Housatonic River in Connecticut are forecast to reach action stage. These forecasts are not final and the current forecast period ends at 8am Monday.
For southern and central New England, this will be more beneficial rainfall as drought conditions persist. Severe drought status was removed from central Massachusetts and Connecticut this week, however, a moderate drought remains in place as we continue to chip away from last fall’s bone dry conditions.
Below: Current US Drought Monitor status:
A strong low-level jet of 60-75mph will also cross the region Sunday and Sunday night. Naturally, not all of this wind will make it to the ground, and southerly winds can often have trouble mixing to the surface. With that said, gusty winds will be likely during this time. They may be at their strongest Sunday afternoon, when mixing is deepest. The wind forecast has been a point of contention among guidance with some showing much higher gusts than others.
This is not surprising as strong southerly winds are often the most uncertain (versus other wind directions) when it comes to how much reaches the surface. At this point, maximum gusts of 35-45mph appears to be the most likely outcome. There will be the potential for occasional stronger gusts given the stronger low-level jet, but most of this jet's momentum is expected to stay aloft.
Below: Winds at the 850 millibar level (about 4,700 feet above sea level) Sunday evening:
This cold front is not going to usher in a much colder air mass. Ridging will build in after the system for Tuesday and Wednesday with continued mild conditions for most. The next system looks to enter the picture next Thursday into Friday. A primary looks to move north of New England with potential secondary low development over Maine. The timing and strength of the secondary low will likely determine if any changeover from rain to snow will occur. A changeover would most likely affect Maine; elsewhere (outside of the mountains) is more likely to see mainly rain at this point.
Below: Current weather map for Friday morning (March 21):
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