In typical spring fashion, this latest soaking will be spread over a few days in three waves of precipitation. It starts today with an increase in clouds along with light, scattered showers. The main rain event will take place from Thursday afternoon through Friday. This system's rain will combine with snowmelt across the north, leading to potential runoff issues.
CMC showing the batches of rain moving through from noon Wednesday through Friday night:
WAVE 1: WEDNESDAY
On Wednesday, a weak system will skirt through New England, bringing a round of showers from west to east in the afternoon and evening (for areas farther east). These showers will be more pronounced across northern and western New England. A few rumbles of thunder will be possible across Vermont.
Expected weather Wednesday evening:
WAVE 2: THURSDAY
On Thursday morning, the main storm complex will be in the vicinity of the Great Lakes Region. This will slowly lift the system's warm front through New England during the day. This will spread another round of rain showers into the region. These showers will again be on the lighter side for the most part. They will also likely be scattered around, so some will be drier on Thursday than others. The general idea of Thursday is to expect some showers around during the day.
Expected weather late morning Thursday:
Once the front passes, there will be a lull in the rainfall. This lull likely won't be totally dry, but shower activity will become more isolated and light. Thursday will not be an all day washout. Snowmelt will be continuing across northern New England, which will allow rivers to begin rising in northern New England.
WAVE 3: THURSDAY NIGHT-FRIDAY
This is when a majority of rain will fall across New England during this time frame. New England will be within the system's warm sector during this time, allowing a strong southerly flow. This will bring plenty of moisture into New England, leading to periods of moderate to at times heavy rainfall. Showers will fill in through Thursday evening into the overnight from southwest to northeast.
Euro showing potential weather Friday morning:
The heaviest of the rain will likely move through from the early morning hours Friday through the midday hours for most with showers continuing in the afternoon. Maine will likely see the steadier rain linger into Friday afternoon. The system does appear to be progressive, which will help keep rain totals down. A general half an inch to an inch and a half of rain is expected with up to two inches in the mountains.
While the progressive nature of the system is helping to keep rainfall amounts lower, especially compared to previous storms over the past few months, there are still some flooding concerns. The southerly position of the low-level jet will allow terrain-enhancement, with the White and Maine mountains seeing the most rainfall. There could also be some rumbles of thunder, mainly in western New England.
Storm Prediction Center thunderstorm outlook for Friday:
These areas will also be seeing the most snowmelt. Warm and humid (for April) conditions will allow for the ripe snowpack to melt out rapidly. Some areas could see 2-3 inches of water equivalent melt out of the snow. All of this could lead to immediate runoff and river flooding. At this point, more minor flooding looks to be most common, but there could be pockets of more notable flooding if the higher rainfall amounts register. With all of New England saturated, isolated, minor issues could be seen in southern New England as well.
This system will also bring gusty winds to the region Thursday night to Friday morning. While a strong low-level jet of 80 to 85mph will cross New England, there will likely be a decent inversion that will keep the strongest winds from reaching the surface. An inversion is basically a warm layer of air aloft with cooler air trapped below. This can prevent the stronger winds from getting below the inversion layer. With that said, gusts up to 50mph will be possible near the coast.
BOSTON MARATHON OUTLOOK
As of now, the Boston Marathon is looking dry. A trough may dig into New England Sunday night into Monday morning, which will need to be watched over the coming days. A warming trend looks to ensue leading up to the race, providing a mild day for the city with highs potentially reaching well into the 60s. It may be a good day for spectators, but a bit warm for runners.
Winds are looking to be out of the west, providing a tail wind for runners. This westerly flow will help boost the temperatures closer to the city of Boston itself, but, being April, we always need to watch for a potential sea breeze to develop that would cool off Boston and Brookline versus the towns and cities farther inland in the afternoon.