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Frontal System to Bring Rain; Gusty Winds to New England: Impacts, Timing

Overnight Tuesday to Wednesday, a deepening low pressure will pass to New England's north. This system does appear that it will bring rainfall to New England in two waves: overnight Tuesday to Wednesday morning and Wednesday evening through the overnight into Thursday morning.


The first wave of rain and wind comes as more mild air surges north amid increasing southerly winds. The second wave will come through later Wednesday into Thursday as a strong cold front gets dragged across New England. This wave will be the more potent of the two. Overall, this won't be the strongest or most impactful storm New England has seen this winter, but it will bring rain, wind and a rapid temperature drop.



ALERTS



TIMING


The first wave of steadier rain will move into New England overnight tonight into Wednesday morning. The showers will lift from southwest to northeast as the southerly flow and moisture increase ahead of the main storm system.


Expected weather around midnight tonight:


Scattered showers will continue through the day on Wednesday. Most areas likely won't see a continuous rain, especially Wednesday afternoon, when the showers will become scattered around. Winds on Wednesday will be strongest across eastern Massachusetts and Rhode Island. This is when the wind advisory is in effect.


Expected weather early Wednesday afternoon:



By Wednesday evening, the main storm system will begin lifting to the north of New England. This will drag a rather powerful cold front across the region. The front will produce a heavier round of rain and stronger wind gusts as it makes its way from west to east.


Temperatures will plummet behind the front; so quickly that the rain may end as some snow. A couple inches of snow is looking possible across the White Mountains and northern Maine. Elsewhere will mainly just see some flakes at the end.


Expected weather Wednesday evening (1st image) and around 10pm Wednesday night:


The front will have pushed through the region entirely by daybreak Thursday. This will set up a much colder, but mainly sunny, day with continued wind gusts of 30-50mph.


RAINFALL


As stated before, rain will come to New England in two waves. The first will be generally lighter and more scattered around through Wednesday afternoon. This round of showers will be focused more on eastern New England, with Vermont mostly missing out.


The second round of showers will be able to produce heavier rain as atmospheric moisture increases significantly. This will allow for a line of steady rain with embedded downpours. Heavier downpours do appear to be brief, but this will allow for a widespread half inch to inch and a half of rain. This round will be seen by all of New England.



The most rain is looking to fall across Downeast Maine. Areas across northern New England that have a snowpack will see rapid melting along with the rain. Some areas of northern New England may see total snowpack loss by Thursday morning. With the frozen ground, this snowmelt will be running off into rivers along with the rain. This could result in some river rises.


Among the concerns for flooding with this system will be the potential for ice jams to develop in the foothills of Maine. River ice thickness is below average across the region. This fact will aid in the development of ice jams as the ice decays and begins to move around. The National Weather Service of Caribou calls attention to the Piscataquis, Penobscot, Mattawamkeag and Aroostook river basins specifically.


Widespread, significant flooding is not expected, but localized areas could see some issues arise, especially near smaller rivers and streams in northern New England. The areas expected to see the highest rain totals are areas with very minimal or no snowpack on the ground.


Poor drainage and flash flooding is looking to be minimal. The Weather Prediction Center does have most of New England in the "marginal" category (level 1 of 4) for excessive rainfall.




WIND


While winds will be gusty with the initial wave of rain, stronger and more widespread gusts are expected with the cold front beginning Wednesday evening. Ahead of the front, a strong low-level southerly jet will move over portions of New England. This jet will contain wind speeds of 70-90mph at 2,500-4,500 feet above sea level in places. Naturally, all of this wind won't make it to the ground.


Wind speed at the 850mb (about 4,700 feet above sea level) level showing a strong low-level jet over New England on Wednesday evening. Strongest winds are in the tan color:


The question with these events is always how much of this wind will be able to mix down to the surface? An inversion will be in place, which helps keep the strongest winds from reaching the surface. An inversion occurs when there is a layer of warmer air aloft with cooler air trapped below.



This warmer air layer can trap the strongest winds aloft. In this case, temperatures at the surface will be rising to near record high temperatures, well into the 50s in some spots. This warming of the surface will aid in mixing and weaken the inversion. Just how warm it gets will play a role in how strong the wind gusts are able to get, especially near the coast. Note that the warmer temperatures in the 50s won't be enough to completely overcome the inversion.


As the cold front pushes through, a line of convection may develop. This would also aid in mixing stronger winds down to the surface, especially inland. All of this is to say that gusts of 40-50mph will be possible for pretty much everyone in New England Wednesday through Thursday. Gusts toward 60mph will be most likely be across Maine's Midcoast and Downeast areas as well as into the Berkshires and southern Green Mountains.



With a potentially strong inversion in place, winds likely won't be able to reach their full potential. Despite this, scattered power outages are likely in places from 50+mph wind gusts.


The strongest winds Wednesday during the day will be limited to the coast and into the Berkshires. Those stronger winds will expand to everyone else by Wednesday night and into Thursday as the cold front pushes through the area.


FLASH FREEZE/SNOW


The cold front is a powerful one that will result in a rapid temperature drop. Temperatures will be dropping from the 50s down to the teens and 20s by Thursday morning. Some areas of northern New England could see a drop of up to 40°. This drop will occur in a span of less than 12 hours, with drops of 5° or more in the span of one hour. Factoring in wind chill, the drop in feels-like temperature will be even greater.



While it will be windy (which will help dry out surfaces before the drop off), this rapid of a drop will likely see areas of standing water quickly freeze. While a flash freeze likely won't cause much of an issue in this case, it's worth keeping an eye on.


With the sharp drop in temperature will come the chance for some snow at the very end of the precipitation. A quick inch or two of snow will be possible across the higher elevations of northern New England.


Probability of at least 2 inches of snow by Thursday morning:


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