Saturday December 4 2021 Forecast (8:49AM)

72 Comments

COMMENTARY

Reminder for model watchers: Do NOT get hung up on anything you see beyond 3-days in advance. A perfect example, the day 5 forecast between the 00z run for the Canadian, US, and European models all differ enough that a forecast made verbatim from each of them would look like a forecast for 3 different low pressure systems impacting the region. And this applies to everybody regarding their weather app forecasts beyond a couple days. Some of this guidance is already 24 hours off on day-of-impact with things under a week away, and when they have the right day other things are wrong. Do yourself a favor and listen to meteorological discussions that have taken into account glaring model issues in this weather pattern…

DAYS 1-5 (DECEMBER 4-8)

A chilly weekend is in store for us but nothing outrageously cold. The remains of a dissipating clipper low will be moving in today and you’ll notice it in the form of clouds. These clouds have the potential to release a few snowflakes but the air is dry enough that they may never reach ground where they fall. A sliver of high pressure brings fair weather for Sunday. Timing worked out for a generally nice weekend, but we’re still in an active pattern and there will be two low pressure systems to contend with before this 5-day period ends. The first one will be a strong low that I’m confident will be heading east northeastward from the Great Lakes across southeastern Canada on Monday. Its warm front will come through during the early to mid morning when we have our best chance of rain. After that, it’s time for a warm wind from the southwest behind the warm front and ahead of an approaching strong cold front. The wind will be quite gusty so if you have outdoor decorations vulnerable to wind you’ll want to secure them before this weekend is over, if you have not done so already. While the region is in the warm sector, the atmosphere will be unstable enough so that we may see a couple of isolated showers and even thunderstorms Monday afternoon favoring the South Coast region. It would be these that would have the best potential to produce damaging wind gusts, even show some rotation. The timing of Monday’s cold front appears to be evening, after sunset, from west to east, and it should produce a band of rain showers, a few of which may be heavy and contain small hail, with even the possibility of a thunderstorm. Gusty, shifting winds will occur with the passage of this front. Following the frontal passage will come a sharp temperature drop and Tuesday, while dry, is going to be up to 30 degrees colder than what we have Monday. Classic La Nina temperature roller coaster pattern. This cold air sets up the potential for frozen precipitation for at least portions of the region for the next low pressure threat, which is Wednesday. Keeping in mind this is day 5, the only thing I can say at this point is this low track will be much further south than Monday’s, passing over or just south of New England, with highest probability of snow/sleet being over interior locations and a higher chance of mix/rain closer to the coast. Fine-tuning of both the low’s track and resultant precipitation type and intensity/accumulation will take place as this event gets closer, and after we improve the focus a little bit for tomorrow’s blog post, it will be Monday’s discussion will contain much more detail on the system. I will tell you that I’ve already seen snow amounts mentioned somewhere in media for this system. I will not say where, but I will say that I highly disagree with such a practice for any system that far in advance and most especially for something occurring in the situation I discussed in my commentary…

TODAY: Sun/cloud mix. Highs 36-43. Wind W up to 10 MPH.

TONIGHT: Variably cloudy. Slight chance of a very light snow shower. Lows 21-28. Wind NW up to 10 MPH.

SUNDAY: Mostly sunny. Highs 37-44. Wind N up to 10 MPH.

SUNDAY NIGHT: Increasing clouds. Chance of light rain overnight. Lows 30-37 evening, rising into the 40s overnight. Wind variable under 10 MPH evening, S 5-15 MPH overnight.

MONDAY: Cloudy with a chance of rain early, then mostly cloudy to partly sunny. Slight chance of an isolated rain shower or thunderstorm near the South Coast in the afternoon. Highs 61-68. Wind SW 10-20 MPH, gusts 30-40 MPH and slight chance of gusts above 40 MPH.

MONDAY NIGHT: Mostly cloudy evening with a passing rain shower and potential downpour with possible thunder and/or small hail west to east. Partly cloudy overnight. Lows 33-40. Wind SW 10-20 MPH gusting 30-40 MPH and potentially higher in any convective activity, shifting to NW from west to east.

TUESDAY: Partly cloudy. Temperatures steady 33-40. Wind NW 10-20 MPH with higher gusts, diminishing later in the day.

TUESDAY NIGHT: Increasing clouds. Lows 23-30. Wind variable up to 10 MPH.

WEDNESDAY: Cloudy. Rain and snow likely. Highs 33-40. Wind NE 5-15 MPH.

DAYS 6-10 (DECEMBER 9-13)

The active weather pattern continues but model guidance is not reliable. Best guess is that a weak low pressure area brings a minor precipitation threat December 10 and a stronger one tracks north of the region later in the period with a milder surge and a rain chance of some kind.

DAYS 11-15 (DECEMBER 14-18)

Mild and active pattern to start with a chance or two of unsettled weather from passing systems through the middle of this period and then the chances of a return to some cold for later in the period.

72 thoughts on “Saturday December 4 2021 Forecast (8:49AM)”

  2. Thanks TK.

    A system passing “over or just to the south of New England” isn’t going to bring snow to Logan this time of year. On to the next “rain” event! 😉

    Just as well as my property is now full of leaf drop until the landscapers can come. This is what happens due to a late foliage season.

    1. That’s quite inaccurate, actually. Where would a system have to pass to bring snow to Logan this time of year? It’s not that simple. You could have a system pass NORTH of here and still bring snow (probably with a changeover, but still snow). And I’m not sure why Logan matters so much. Nobody lives there except seagulls. And we all know that it is pretty much irrelevant when it comes to representing the weather for the rest of the city 90% of the time. 😉

      Boston has a shot at accumulating snow from the Wednesday system as it stands right now.

      2. I can attest to the fact that 12/9/78 had thunder snow in Boston. Mac and I watched the lightning from our honeymoon room overlooking the Charles at the Hyatt Cambridge.

        1. Vicki, I don’t recall the thunder snow. All I do recall is that the 1978-79 winter was pitiful in terms of snow. I forget the specific amount. Off the top of my head, maybe like 27 inches? I can look it up later for the exact amount.

          Now I understand why 12/9 means so much to you. 🙂

          1. Haha. Yes it does mean a lot. Oddly, there have been a number of quite large snows right around or on that date. I surely don’t think every dec 9 snows. But when I see the potential anywhere near, I have wonderful memories of Mac and some tears….like now 🙂

  6. With regards to TK’s discussion about the 3 models.

    6Z GFS

    https://maps1.pivotalweather.com/maps/models/gfs/2021120406/114/prateptype_cat.conus.png

    https://maps1.pivotalweather.com/maps/models/gfs/2021120400/150/snku_acc.us_ne.png

    0Z Euro

    https://maps3.pivotalweather.com/maps/models/ecmwf_full/2021120400/120/prateptype_cat_ecmwf.conus.png

    https://maps3.pivotalweather.com/maps/models/ecmwf_full/2021120400/150/sn10_acc.us_ne.png

    0Z CMC

    https://maps2.pivotalweather.com/maps/models/gdps/2021120400/114/prateptype.conus.png

    https://maps2.pivotalweather.com/maps/models/gdps/2021120400/150/snku_acc.us_ne.png

    I’ll take door #3 please. 🙂

    1. All I can say is that the cold high is in decent position North of us, so if we get a decent track, it could snow even in Boston.
      Euro is the most South And the GFS is the most North. CMC is sort of in the middle but a bit South as is the ICON.

      NAM is coming into range soon.

    3. Of course keeping in mind That we are looking at day 5…

      If it makes you feel any better, I think the GFS is overdone and the ECMWF is underdone.

      1. And the CMC is just right? The Goldilocks scenario????

        Now let’s see what corrections the 12Z runs make.

  7. Good morning and thank you, TK.

    Looking as if we may bookend the 9th. My tree has been up for a bit, but I like to put ornaments on it on the 9th. It is interesting that 43 years ago, Mac and I decorated our tree around the 7th so we’d have it done before his parents arrived from Rome prior to our wedding. Back then, it was literally the only tree or decoration to be found. Now decorations go up much earlier. I love it.

    1. Very interesting indeed. I actually could read the Twitter link.
      I used to have an account, but I deleted it when unknown crazy people started following me???????????? Oh well.

      Btw, current Boston Buoy (16 NM Due East of Boston) water
      temperature is: 50.9 degrees
      Average is: 47.13
      Departure: + 3.77 degrees

      Logan is TOAST with the wind coming in from the ocean.

        2. No necessarily. Depends on direction and wind speed
          and of course precipitation intensity.

          If the wind is 45 degrees or less, it is coming over
          slightly colder water and has more of the Cold High Influence. As the wind approaches 90 degrees, FORGET ABOUT IT!!

          It is always tricky. I have seen it snow this time of year
          with a NE wind and water temps normal. Also have seen it rain as well.

          2. I remember one time in the 70s During November.
            We had a reasonable system and the wind was
            ENE and it was raining. As the system moved Eastward, the winds backed. As the wind reach 45 degrees snow started mixing in and when the wind made it to about 30 degrees or so, it flipped to all Heavy snow. It was awesome. Not sure of the final accumulation, but it was something in the order of 3-5 inches. Not a blockbuster by any means, but by November standards it was pretty awesome.

            1. The 70s was a decent decade for snow, if I recall. The 2020s remain to be seen of course just getting started.

              The 80s as I recall were somewhat paltry in terms of snowfall.

              The 90s…WOW!!!

              1. The 70s was a mixed snow decade. We had some very notable storms and some absolute dud winters in there.

        3. In most cases with this set-up, yes, but a north wind would negate that. And even sometimes Logan can be raining when the rest of the city is frozen precipitating.

            1. I’ve seen that as well, but likely not as many times as JPD since he’s one of the oldest WHW members here. 😉

  10. 12Z GFS coming in fairly robust, but just a tad too far North for much of SNE. Healthy dump of snow farther North.

    https://maps1.pivotalweather.com/maps/models/gfs/2021120412/108/prateptype_cat.us_ne.png

    Kuchera Snow

    https://maps1.pivotalweather.com/maps/models/gfs/2021120412/126/snku_acc.us_ne.png

    From MA Pike Northward, this run keeps 850 mb and 925 mb temps below freezing. So along the coast looks to be a cement type snow with perhaps mixing or changing back and forth and/or a change to rain

    Could be an interesting day. BUT let’s see what the other
    models have to say.

    So, is this the GFS slowing correcting to the Euro?
    Or will they meet half way. I find this to be fascinating.

  13. The GFS today is getting cooler today with that system middle of next week but wide range of possible outcomes showing up in the ensembles. I would love to go home to snow on the ground. Just no delaying or canceling my flight 🙂

    1. Isn’t that the one Sak said picked up on the storm I have now forgotten? I need to find which storm and write it down somewhere. The big wind one. Anyone?

    1. Why so much so this year? because of the pattern we are in or
      because the models plain and simply Suck?

      It seems years ago, they were better.

      1. Models are never all that trustable beyond day 3, and they are worst (IMO) in fast-flowing patterns because the error starts sooner and expands more quickly regarding short-wave timing and evolution. A lot more ripples on the rope. More chance for things to “go wrong” with the model projection.

  21. The GFS is trending towards what the other models are showing which makes sense with the background states of the atmosphere such as MJO and other parameters currently in place. The GFS is not handling showing its own MJO and TELLE forecasts all that well on the operational runs.

  22. This is well-deserved criticism that I have NO problem stating. At least one local TV station showed a snow map for Wednesday on their Saturday night weathercast. To me, that’s NOT WISE at all. Far too soon. That’s the nice way to put it. I’ll leave it at that.

  23. NWS pretty bullish this morning…

    It appears increasingly likely that at least part of southern New
    England could see its first widespread accumulating snow of the
    season. The dynamics are impressive. The 00z GFS shows a decent
    storm intensifying close to the 70W/40N benchmark with deformation
    band forming across the CWA. Omega within the favorable
    Dendritic Growth Zone of -12 to -18C looks to be in the 15-20
    unit range, along with negative 700-500mb equivalent potential
    vorticity and good 700mb frontogenesis should help set up a
    decent mesoscale band sometime Wednesday afternoon into evening.
    The question will be whether it is cold enough for 1 inch per
    hour snowfall rate to materialize and how much snow can
    accumulate before potential mixing or changeover to rain
    especially along the Boston- Providence corridor. Ensemble model
    guidance (GFS, EC and GEM) have continued to advertize decent
    probability of 24 hour 3-plus inches snowfall, with consensus of
    at least 40-50 percent for Wednesday into Wednesday night
    across interior MA and CT, using uniform 10:1 snow to liquid
    ratio. Dependent on how impressive the cold air injection is,
    this ratio could potentially be a little higher. In fact, the
    GFS shows SLR of around 14 to 16:1.

    While it is still too premature to go into possible snowfall
    accumulation, would like to see greater signal for formation of
    deformation band across the CWA especially when the Convection-
    Allowing Models come into range by Sunday night/Monday morning.
    Given it is a fast-moving system, snowfall rates will likely have to
    approach or exceed an inch per hour for Warning criteria snowfall (6
    inches averaged over a forecast zone in a 12 hour period). There is
    above average uncertainty with the Boston-Providence corridor
    because either it could be a mostly rain event or it could be the
    sweet spot for significant snowfall accumulation if the colder air
    holds its ground and the deformation band sets up in the vicinity.
    So plenty for snow lovers to ponder over and continually monitoring
    over the next couple of days. For now, really don`t have the
    confidence to come up with a snowfall map until the Hi-res ensemble
    guidance (HREF) comes into range but we have time to fine-tune the
    specifics.

    1. It’s interesting that yesterday afternoon they were talking about unreliability of deterministic guidance and we all could see the GFS op was an outlier to suddenly analyzing the GFS op run like it’s the leader when it’s still clearly somewhat of an outlier.

      1. Totally agree and 6z gfs is even father South correcting more and more towards other guidance.
        smells like an outlier to me.
        Wouldn’t be surprised if it ends up a complete miss to the South.

        2. Given that this morning’s 7:30AM discussion is still talking about last night’s weather – and mentioning “Great Lakes” and “the waters” (non specifically referring to the Atlantic waters just to our east) in the same sentence, I’m going to guess that there is someone rather in experienced on shift.

          And I’m not sure I would be comfortable talking about snowfall rates, deformation bands, and snow:water ratios at this point, but more power to the person who ventures out on that limb for day 4 based on a model that doesn’t even agree with its own ensemble…

          1. I will phrase my comment carefully. There are two young, enthusiastic forecasters who work at Norton. When the discussion text skews to the most significant possible outcome, I know if I check at the bottom as to who was responsible for writing that particular timeframe, it is without fail one of the two young forecasters I reference above.

            It is not they, it is one individual who chose to frame the forecast discussion as written. He wrote the discussion last night and the night before.

            Read NYC or ALY discussion. You will see this is not NWS group think.

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