Saturday December 19 2020 Forecast (8:20AM)

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DAYS 1-5 (DECEMBER 19-23)

A true weather nut will be fascinated by the contrast across our area during the nighttime hours leading up to sunrise when I started writing this blog. While many areas were clear and calm with significant radiational cooling over a fresh snow cover, dropping temperatures into the teens and single digits, even to near zero in some locations, cloud cover (with a few snow flurries) and a breeze did their job holding temperatures up in the 20s to even around 30 along the South Shore of MA and especially Cape Cod, and even Cape Ann from Gloucester through Rockport, as the western edge of the northerly air flow behind our recent storm continued unimpeded by the low friction of the ocean water. As today goes on, our temperatures will find themselves much more uniform across the region by early afternoon in comparison to how they started out the day, but it will be a cold day, albeit with plenty of sunshine, which will start to fade later in the day as we get an increase in high and mid level cloudiness in advance of our next disturbance. Unfortunately this will interfere with the view of Jupiter & Saturn, which draw ever closer in the sky on the way to their Grand Conjunction in just 2 days. But the weather has the say, and these clouds are going to move in, and the disturbance causing them will bring slightly milder air but also the chance of some light rain & snow shower activity on Sunday. This will not be a big deal, with rain showers most likely in coastal areas and Cape Cod while interior sections see a better chance of snow showers, where a minor accumulation could result in few slick spots. This system moves out Sunday evening, but probably again not in time to see the planets, leaving us one more chance on the day-of Grand Conjunction, Monday, also the Winter Solstice. But will see see it even then? That’s a good question. I have been keeping an eye on the potential evolution of another storm to threaten us on Tuesday, although the leaning has been for this to stay mostly offshore. But the evolution of this system may be a little different than I’d envisioned earlier, with 2 piece of energy not getting close enough to join up and create a larger storm. If this is indeed to be the case, what we will see is the southern energy sliding offshore south and east of us Monday with some high cloudiness that could exit in time for evening twilight planet viewing, and cloudiness from the northern piece of energy, while approaching via the Great Lakes, still holding off far enough to the west so as not to bother the view. Hoping this is how it turns out! Regardless, that northern energy is expected to dive across the region Tuesday with cloudiness and some snow shower activity (perhaps rain showers Cape Cod with more marginal temperatures), but not a big storm. Behind that comes high pressure and dry weather for Wednesday.

TODAY: Mostly sunny. Highs 30-37. Wind W 5-15 MPH.

TONIGHT: Variably cloudy. Lows 20-27. Wind SW up to 10 MPH.

SUNDAY: Mostly cloudy. Periods of light snow/mix/rain, frozen precipitation most likely Boston north and west, with rain more likely to the southeast. Highs 33-40. Wind variable 5-15 MPH.

SUNDAY NIGHT: Mostly cloudy early, then clearing. Lows 21-28. Wind W 5-15 MPH.

MONDAY: Early and late sun, a period of cloudiness between. Highs 35-42. Wind W 5-15 MPH.

MONDAY NIGHT: Clouds return. Lows 23-30. Wind variable 5-15 MPH.

TUESDAY: Mostly cloudy. Snow showers likely, except rain or snow showers South Coast. Highs 34-41. Wind NW 5-15 MPH, higher gusts.

TUESDAY NIGHT: Clearing. Lows 15-22. Wind NW 5-15 MPH.

WEDNESDAY: Mostly sunny. Highs 31-38. Wind W 5-15 MPH.

DAYS 6-10 (DECEMBER 24-28)

High pressure shifts offshore with dry but a little milder for December 24. Low pressure attempts a track northwest of New England for early December 25 but how much warm air gets into the region is questionable. While guidance will show a strong surge of southerly air, warmth, and a good slug of rain, I have my doubts this is exactly how it plays out. While we may eventually get into the “warm sector”, it will likely be difficult at first and also modified by snow cover, which will still very much be around in most of the region, and the rainfall along the frontal boundary that sweeps through from the west may be a much narrower area than depicted by models at this time. Cold air likely returns rather quickly by later December 25 hanging around for the remainder of this period as high pressure builds across the Great Lakes and into eastern Canada.

DAYS 11-15 (DECEMBER 29 – JANUARY 2)

High pressure eastern Canada, low pressure approaching from west may bring a wintry weather event to start this period followed by a brief shot of cold, then moderation with more tranquil weather as 2021 arrives. This is a low confidence forecast at this time.

42 thoughts on “Saturday December 19 2020 Forecast (8:20AM)”

  2. Well we might not win the with snowfall contests here, but the cold mornings in our deep valley sure do measure up. -4 at my house this morning. Yep, that’s negative.

      1. Well, we know early cold doesn’t always mean colder later either. 🙂 Last year is a good example of that……..

    2. I didn’t visit Hampton Beach NH this morning because I’m planning to be up there Monday for daybreak (regardless of sky condition). But last year on the 3rd Saturday of December the weather was nearly identical to how it was this morning, right down to the look of the incoming waves & shallow sea smoke (saw photos from people I know who live up there).

      Figured there might be some near to slightly below zero readings in the best areas even though I didn’t put it in my forecast – probably should have.

      1. I don’t think this is the white christmas irving berlin meant. Hahaha

        I guess the tree tops will be glistening… with rain.

        1. Well, as noted above, rain may not even end up much of a factor.

          1) Models nearly ALWAYS vastly over-estimate warming when we have a snow pack.

          2) Models nearly ALWAYS over-forecast rain areas from a system like that this many days in advance.

          I would not be surprised if we barely get to 50 for a few hours and we have about 1 to 3 hours of rainfall, tops.

          It may even snow (snow showers) before Christmas Day is over, if things break just so…

  5. Yes, I don’t get all the hand wringing and armpit sweat over the white Christmas. Highs in the 30s and at best low 40s through for the next 5 days with December sun angle isn’t going to melt any snow ( you will lose more from compaction and evaporation than melting) the brief warm up and wet weather is not going to make it all go away either. Maybe on parts of the Cape? Even in my area where the snowfall totals on the ground are lower, I am confident snow will still be here. The next 7 days, will serve to naturally clean up and widen the roads, driveways, and walkways , but that’s about it.

    1. Agree on all counts.

      A white Christmas, defined as at least 1 inch of snow on the ground at 12z, will be achieved in well over 90% of New England.

      1. I remember the song fondly

        “I’m dreaming of a white christmas
        as long as there’s one inch of snow at 12z”

        I truly didn’t understand that line of the song until I was older. hahaha 🙂

  8. TK – Even if we don’t get as much rain as expected, what about fog over the deep snowpack? Will there be much of that involved?

    1. Not likely. It’s also a myth that fog eats snow. Fog does very little to snow. It is the warm air that causes that fog to form that melts snow.

      We could have a foggy period if we get into a good warm sector but I don’t expect that to be last and very long if it happens.

    1. I always like a White Christmas, I like it even better with a Christmas Eve snow storm. 🙂 But that’s the way I roll.

        1. That’s not really how it works though. Go by long-term averages to start, and then take each season’s pattern as it is.

          Boston has always averaged white Christmas 25% of the time. Caribou is nearly 100% of the time white. That’s just how it works.

          Don’t let Christmas cards and paintings skew your idea of what “should” and “shouldn’t” be. What should be, is. It’s called climate, and it’s dictated by where we live.

    1. We may have only a couple shots before we get into a pattern that’s less favorable during January and for quite some time after that…

      2. Wednesday’s storm you never know could be the biggest storm we have all winter , remember the key word is could!!

      3. After December I don’t care if there isn’t or is snow in Mass as I will be flying back down to St. Thomas January 2nd.

  11. Tk,

    Any chance the storm on Monday/Tuesday starts to come closer to us? Just looking at the gfs looks as though it wants to get a little moisture on the south shore. Thank you

    1. There is, but I sure hope it doesn’t. I’d much rather see the great conjunction of Jupiter & Saturn than get a period of rain & snow.

    1. despite the EURO ensembles the temperature range for that period look to be borderline at best with no fresh cold air intrusion making me feel that even if it does get closer and gets its act together a bit quicker than it does now, it would be more wet than white but we shall see. Wide range of temperatures possible but the models are likely over doing the warmth as the snow can act as a refrigerator.

    1. You can really do it any time. Any precipitation will be rather inconsequential but if you want nothing falling at all, earlier in the day is better.

  14. I don’t think the Canadian will catch on, but the other medium range models should start to shorten the duration of any rainfall at the end of next week as we get closer to it…

  15. I agree with TK here. I think the ECMWF is too amped, too wet, too warm at the surface for late Christmas Eve, almost through all of Christmas Day, and it will come around to a more progressive solution, with most of the rain falling in a 6 hour type window late Christmas Eve / Christmas morning and then cooler weather quickly following.

    Also agree that 12/5 – 12/25 period for winter weather is coming to a close, but the pattern identification and timing has been pretty spot on.

    Transition is coming and the pattern will be particularly less favorable for snowfall in SNE.

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