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March 2017

A Foot of Heavy Snow North, Tons of Sleet Possible in Central New England

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A rain/snow mix will expand across New England on Friday, though with most communities experiencing temperatures well above the freezing mark, overall impact will be very limited during the daylight hours.  In Western New England, it’s a different story, where steadier snow during the day will start accumulating on roads, and that trend will expand east around and shortly after sunset, resulting in deteriorating roads in Central and interior Northeast Massachusetts Friday evening.  Along the coast, an onshore wind combined with a 40° ocean probably means limited impact even Friday evening.  Heaviest precipitation will fall overnight Friday night into early Saturday morning – mostly rain for Connecticut, Rhode Island and Southeast Massachusetts with over an inch of beneficial rain, but from Northern Connecticut to interior Eastern Massachusetts points north, and increasing amount of wintry mix is expected.  In fact, for many around the Massachusetts Turnpike, very limited snow falls Friday night, but a change back to sleet and snow is possible Saturday after a period of rain – in these spots, an inch or two of snow is possible. The suburbs northwest of Boston should pick up three to four inches of snow with a prolonged period of sleet, and those in North-Central and higher terrain of Western Massachusetts should pick up around half a foot with plenty of sleet.  Sleet can serve as ball-bearings of ice under tires, so travel will become treacherous for the deep interior Friday night into Saturday morning, and if any freezing rain mixes in, a glaze of ice would occur, as well.  Farther north, amounts continue to increase into the hills and mountains of Vermont and New Hampshire, where up to a foot of heavy, wet snow may cause power outages Saturday morning, while Maine will see a bit less moisture, limiting snowfall to just shy of a foot in the mountains, around half a foot in Portland, and only a couple of inches from Midcoast Downeast.

LKN_ACCUMS_BOSTON_ACTIVE (16)Winds won’t be exceptional with this storm, though you’ll feel the stiff, chilly wind gusting to 35 mph on Saturday, which will make the mix of rain, sleet and snow all that much more pelting.  Along the coast, the northeast wind coupled with an early afternoon high tide should cause some splashover.  By Saturday late day and evening, everything will have tapered substantially, setting us up for a lovely day of melting on Sunday and a great day for the Red Sox home opener on Monday.


Snow, Sleet and Freezing Rain In the Friday Forecast

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Nice day today with plenty of sun tho a bit cool, highs near 50 but a breeze thru lunch. Wispy cirrus clouds later mean a storm is coming. Lots to consider with the event for Friday/Friday Night/Sat and I'm hearing questions from many. Here's what I can offer for answers...

LKN_FRONTS_BOSDMA (13)Light snow moves into New England during the early morning along the NY State line, but takes its time filling in east. By midday Friday, snow is likely to be falling all the way east into Boston's MetroWest, but intensity will be light at first. Snow intensity picks up during Friday afternoon. The impact of this will be somewhat offset by temps above freezing. Near the coast, a developing east wind on Friday ensures our 40° ocean will play a role, encouraging very wet snow and rain. Deeper inland, air only marginally cold to support snow,surface & aloft. Just 1 or 2 degrees important for snow vs sleet vs frz rain vs rain. In a case like this, unfortunately not much trust can be put in computer forecasts of precipitation type...they vary greatly from run to run. Particularly when it comes to sleet vs. freezing rain, the difference in cold layer depth required is quite small, but important. 

For snow, typically, we'd be looking at a 10 to 1 or 13 to 1 ratio of snow to water. That is, 1" of rain = 10-13" of snow. Not this time. The relative warmth not only at ground level but also deep thru the cloud layer will really cut back on snow to water ratios in this event. Low ratios means wet snow means sloppy snow means not very good accumulation...for most. Not all. There comes a point in northern extent where u hit enuf cold to stay mostly snow and that's probably extreme N.Central MA/Route 2 northward - From that point north, elevation makes a diff & increases snow amounts. LKN_ACCUMS_BOSTON_ACTIVE (14)Farther south,keep in mind warmth aloft,so hills don't matter as much. Another point for Friday: relatively light intensity coupled with temps above freezing means limited *daylight* road impact Central/East. Interestingly, it's during day Fri - before the warmth aloft changes precip type - where elevation matters, roads slicken in hills/mountains. Once you get toward evening Fri, sun angle decreases then sunset & this allows temp fall. Roads worsen, snow sticks better. Expect heaviest precipitation to fall overnight Friday night into early Sat AM - see the map here for Saturday morning setup.  

From a New England perspective, some will hit a foot of snow, likely to be in the Southern Greens, SW NH into the Whites. In the Boston area, we'll find a lot of rain mixing in at the coast, lots of sleet mixing inland. Given the very small difference in cold depth between sleet and freezing rain, have to watch the extended ice potential closely. There's rhyme & reason to hilite areas of possible extended icing. Tho I think mostly sleet for those areas, frz rain would be big ice storm. All rain on Cape Cod, but an inch of rain, all tolled.

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Just As Spring Nudges In, Winter To Battle Back

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I’ve heard from so many of you: “When is the sun coming back?!”  The answer has been, “Wednesday,” and here we are…while the sun won’t be abundant, most of us will see some breaks today.  In addition to providing an emotional boost, emerging sunshine will have an impact on temperatures, affording the opportunity for most of New England to rise through the 40s, and for Southern New England to reach and exceed 50 degrees.  With continued drying of the air and atmosphere, temperatures near freezing overnight Wednesday night won’t result in black ice development, so Thursday should be a quiet weather day right out of the gate, with ample sunshine and pleasant air as highs once again reach 50 degrees.  Our next storm approaches Friday, and though precipitation has been in the forecast for some time, it’s looking more and more like enough cool air will hold on for a mix with snow for some…and change to snow for others.  In fact, for deep interior Southern New England, Central and Northern New England, accumulating snow seems likely.  Just how much snow accumulates Friday and Friday night depends on how strong cool air can hold on, but the potential exists for a few inches in places like North-Central and Northwestern Massachusetts, and as much as half a foot or more in some of the higher terrain of Central and Western New Hampshire into Vermont and perhaps the mountains of Maine!  An onshore wind will keep clouds, showers of flakes and drops, and cool air in place Saturday, with drying likely Sunday, though sun may be limited.  The trend for Monday’s Red Sox home opener continues to be drier and nicer, and though showers return for the middle of next week in our exclusive Early Warning Weather 10-day forecast, temperatures look to be decidedly more spring-like.


Welcome to...Astronomical Spring 2017!

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Welcome to astronomical spring, as of just prior to 6:30 this morning!  Of course, I say "astronomical spring" because in the world of meteorology, we tend to view March, April and May as the spring season, as that tends to be when weather patterns change.  Of course, snow and cold is often still a part of early spring, but in general, weather patterns begin shifting considerably in the month of March, and that's when we see a noticeably uptick in average daily temperatures.

Astronomical seasons work differently, based upon the solstices and equinoxes.  The onset of spring is marked by the Vernal Equinox - referring to equality of day and night...or at least pretty close to it.  Truly, the Vernal Equinox marks the day and time at which the sun crosses the imaginary line directly above the earth's equator, called the "celestial equator," which very nearly reflects equal day and night length, though not quite - for instance, here in New England we've already passed our closest time of equal day and night, with today bringing 12 hours, 9 minutes and 37 seconds of daylight.

So what else is at work here?  It's all about tilt: the earth's axis tilt of just over 23 degrees means at times we in the Northern Hemisphere tilt toward the sun, at times we tilt away, and sometimes...twice a year...we don't tilt toward or away...we just tilt "sideways" - and those two times are equinoxes.  So, today, the Spring Equinox, our earth still tilts at 23.4 degrees, but finds no solar favor north or south.  So, as we in the Northern Hemisphere ring in the start of astronomical spring, the Southern Hemisphere is heralding in autumn, preparing for their tilt away from the sun in the months to come.

What this all means for us in New England is a big change in weather over the next several weeks.  Take Boston as an example for the region:

  • Our daily average high temperature rises from 46° today, to 78° by the last day of the spring season!
  • Our nightly average low temperature rises from 32° today, to 61° by season's end.
  • Normal rainfall for spring in Boston is 11.5" of precipitation.
  • We gain about 3 hours and 7 minutes of light - from 12 hours, 9 minutes and 37 seconds today...to 15 hours, 17 minutes and 1 second by the last day of spring.

In short, the average spring in New England takes us to a whole new weather world than where we've been, and while it will surely come with some ups and downs (like the arctic air en route for later this week), know that we are rounding the bend quickly to the warmer season.

-Matt


Lots of Talk About a Tuesday Storm - Is It For Real?

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There's already buzz about the storm showing up in our 10-day forecast for next Monday night through Wednesday.  One thing you know I cherish with our team at NBC Boston and NECN is avoiding hype and sensationalism, and delivering reliable facts...or at least reliable guidance that we hope is as close to the end result as you'll find.  So: what's the deal on Tuesday and Wednesday - hype or real?

Let's start with the probability of a storm occurring at all:  it's very high.  Those of you who follow our NBC Boston and NECN forecasts closely know that I spent two years with colleague Aaron Perry formulating our exclusive, in-house computer guidance to provide us with 10-days of critical weather information.  Though our team is not bound to the output from our guidance, certainly we take it very seriously, since we've home-grown the technology to feed it.  The NBCU (NBCUniversal) Forecast System is showing a 90% chance of precipitation on Tuesday - four full days from today.  That's huge.  We tend to really sit up and take notice when the probability that far out rises to 50%, so to be so high is a sure sign to us that all the pieces are there for a sizable storm.

Next item: what is most certain about the storm?  Wind.  There is excellent agreement that the wind will significantly exceed normal thresholds Tuesday (less so, Wednesday)...though wind direction still is dependent upon storm track...a track into New England would mean an east wind becomes southeast, then northwest.  A track offshore means a northeast wind becomes north, then northwest.  Either way, utility companies and customers should be aware there is an increased risk for power outages Tuesday.  Winds of this magnitude raise two more flags: coastal flooding potential and, if enough snow, blizzard conditions.  Coastal flood parameters aren't exceptional given the height of the tide with relation to the moon, but while the tide may not be so high as a base level, it's high enough that if the winds really crank, an early afternoon tide on Tuesday and again overnight Tuesday night surely could produce some coastal flooding.  The potential for blizzard conditions hinges upon rain or snow...

Final Item:  Snow or rain?  The likely answer to this is: both.  The bigger question is how much of each...with arctic air from the weekend lingering through Monday and precipitation slated to arrive Monday night into Tuesday morning, this surely suggests at least a burst of snow will occur at the onset of the storm.  How long snow lasts before changing to rain - if at all - is entirely dependent upon both the storm track and rate of intensification.  A storm track up the coast and into Eastern New England or scraping along the coast will mean a propensity for an east and east-southeast wind to develop, carrying relative warmth off the 40 degree ocean waters and promoting a change to rain at the coastline.  If the storm moves a bit farther east, I mentioned above this promotes a more northerly wind...which would help to hold antecedent cold in place and produce more snow.  Reality may lay in the middle - a coastal front that stalls inland over Eastern New England, making for inland snow and a change to coastal rain...but again, it's too early to say.  As we close in on the event, the texture of storm development and forecast temperature profile will become clearer.

-Matt