Sunday December 6 2020 Forecast (8:29AM)

43 Comments

COMMENTARY

Good morning (or afternoon depending on when you see this) WHW readers! A quick review of the expectations and results of yesterday’s storm and some additional thoughts. This was a system that for many days was expected as a possibility “around the weekend” with many model forecasts just a handful of days before the event having it as a low pressure system tracking through the Great Lakes and a rain event here, in which the biggest challenge would have been whether or not the warm front was going to pass the entire region before the cold front arrived. It would have been too warm for anything other than rain to be involved in the precipitation shield. But many forecasters knew better that a solution such as that, or any other solution for that matter, that far in advance with recent and ongoing model performance issues was not something that you could look at and have any confidence in whatsoever. Hence, the forecasts (at least mine and probably many others) were written in vague terminology, which should always be used to reflect uncertainty. There is nothing wrong with uncertainty in the scientific process. If not for it, we’d lose our desire to learn and improve. As we got closer to the event, and it become more and more obvious that the track and development of the low center, and precise details around both, would leave the tiniest margin for error for making or breaking our forecasts on it, I can speak for myself and others when I say the challenge become the real deal. One of my colleagues noted how a 1 or 2 degree difference could literally make the difference between an inch of snow and over a half foot of snow, and the 1 or 2 degree difference was not just the temperature at the surface, but the temperature throughout the entire depth of the storm from surface to top of clouds. That one small aspect, before we include all other aspects, went very much into determining a much bigger outcome, as noted by a comment on yesterday’s blog, the final snow numbers. This, not necessarily through any fault of their own, is what the general public is looking at. Joe Public doesn’t really care what my temperature forecast is for 850 millibars, if the wind direction is from direction 20 or 330 (yes it makes a difference), or any of that. Joe Public wants to know how much snow he has to shovel, or plow. And I get that. Unless one is a weather geek, they’re not looking at forecasts and listening to media for discussions of a storm’s dynamics, they just want to know what, when, and how much. I assure you every forecaster out there gave it their all in trying to figure this one out. Some forecasts worked out OK, some did not. Some worked out great in some areas and poorly in others. That’s the nature of what we do, and this was a prime example of that. We saw a lot of good forecasts for nearly every detail of this system, from its evolution and its track, to its precipitation timing and marginal temperature profile, snow being dependent on precipitation intensity in bands we had to try to forecast development of, and intensity of, and worry if these bands would even form enough at all to do what we expected. How ironic that, in many (not all) areas, that the only aspect of the forecast that didn’t work out as well was the ONE that most people were most interested in. Most of them didn’t care that the 1 to 2 1/2 inches of rain forecast before any mixing and changing did indeed occur, and as a result gave our drought yet another gut punch. That’s some good news. Ah, so Joe Public may have any number of reactions. He may be posting on social media this morning that “they got it wrong again! what a great job where you can be wrong and still get paid” (old joke, heard it before), or he may be a snow lover who is just angry that only a slushy inch or two of snow fell when he was expecting 6 and a perfect forecast, or he may be happy because even though he doesn’t mind some December snow, that we didn’t have enough to bring down a hundred more trees in his city putting most people in the dark for a day or longer, and causing more damage. People have their reactions, and that’s fine. But no matter what we expect and how we react, I’d like to remind all of them for a moment to remember what goes into making these predictions, and how easily they can go awry, and how often they don’t compared to how often they do. I say this, not because I think more folks than usual are bent out of shape about the snow aspect of this system, but because it’s important for us to try to understand what goes into doing a job, and I don’t mean just weather forecasting. This can be applied to any position, and a couple that come to mind immediately are first responders, which goes without saying, and utility workers. Yes, it sucks when the power is out for any length of time, but understanding why it may take some time for them to get to the line down the street that was cut by one branch, while there are hundreds and maybe even thousands of others just like that, and that yours can’t always be first, is very important. The set-up for doing these jobs isn’t perfect, and will never be perfect, but people in these do the best they can. The same with weather, really. Forecasting is never going to be something we ever achieve perfection in, but doing the best you can should never be thought of as failure. Aspects of a forecast may fail sometimes, but a strong effort is always a success.

DAYS 1-5 (DECEMBER 6-10)

Low pressure exits via the Canadian Maritime Provinces today, leaving in its wake a blustery and cold day with passing clouds and a remote chance of a few snow flakes or rain drops falling from some of these clouds. With winds still gusty, keep an eye out for loose branches that may still be caught in trees. The damage from yesterday’s storm was not too bad, but older trees still saw some broken branches and limbs from wind and in some cases wet snow. Also, temperatures having slipped into the upper 20s to very low 30s in many areas north and west of Boston early this morning has caused some ice patches to form in ground that was just wet last evening. This should melt and dry off during the day today as temperatures rise above freezing and wind and dry air work on the ground. But where some melting causes more puddles, watch for re-freezing and additional ice patches tonight. Winds diminish tonight as the Canadian low moves away. Our attention then turns to 2 things, an offshore storm developing later Monday and passing southeast of New England early Tuesday. This system is fully expected to be offshore for enough to avoid any significant impact, but its circulation will be large enough to create a northeast to north wind over Cape Cod that may carry some light showers of rain and/or snow across that area on Tuesday. In addition, a disturbance breaking off from a trough to our west will initiate some cloudiness for us here on Monday, and maybe enough for some snow showers Monday night and early Tuesday before the energy is absorbed by the offshore storm. At midweek, expect a dry and chilly Wednesday, but a disturbance moving rapidly southeastward may bring a few snow showers to the region Wednesday night and early Thursday, with a bit of a reinforcing shot of seasonably chilly air following.

TODAY: Cloud/sun mix. Slight chance of a passing sprinkle of rain or flurry of snow. Highs 35-42. Wind NW 15-25 MPH and gusty, diminishing late day.

TONIGHT: Mostly clear. Lows 18-25. Wind NW diminishing to under 10 MPH.

MONDAY: Partly to mostly cloudy. Highs 31-38. Wind variable up to 10 MPH.

MONDAY NIGHT: Mostly cloudy. Chance of snow showers. Lows 28-35. Wind NE to N 5-15 MPH except 15-25 MPH Cape Cod.

TUESDAY: Mostly cloudy to partly sunny. Chance of snow or rain showers Cape Cod. Highs 35-42. Wind N 10-20 MPH, higher gusts especially Cape Cod.

TUESDAY NIGHT: Mostly clear. Lows 20-27. Wind N to NW 5-15 MPH.

WEDNESDAY: Mostly sunny to partly cloudy. Highs 36-43. Wind variable up to 10 MPH.

WEDNESDAY NIGHT: Variably cloudy. Chance of snow showers. Lows 25-32. Wind NW 5-15 MPH.

THURSDAY: Partly sunny. Chance of snow showers in the morning. Highs 35-42. Wind NW 10-20 MPH.

DAYS 6-10 (DECEMBER 11-15)

High pressure brings fair and pleasant weather for December 11. The next low pressure system is set to impact the region on the December 12-13 weekend, but the track, timing, and intensity of the system is somewhat uncertain. The early idea is that low pressure may track through the Great Lakes and northern New England or nearby Canada, with a warm front trying to move through followed by a cold front. Frontal positions and timing in this scenario would be uncertain this far in advance, so for now just going to forecast a chance of some precipitation at times for the weekend. Fair, seasonably cold weather should follow this.

DAYS 11-15 (DECEMBER 16-20)

Watching December 16-18 as a window for potential storm threat (rain/mix/snow – still too early to know).

43 thoughts on “Sunday December 6 2020 Forecast (8:29AM)”

  1. Thank you, TK. GREAT write up. I had a few happy tears when you included first responders and utility workers. Darned if that isn’t the God’s honest truth. I think you are right that it is human nature to see what is above the surface. Often, there is far more below the surface that we just do not see.

    Tom, I’m hoping you will repost your comment here also. Both you and TK took advantage of a great learning opportunity

  2. Thanks TK. Great commentary and explanation. These two back events have my sump pump running every 90 seconds today. At least it looks like most of the upcoming week is dry! Rivers are rising too!

  7. So well written Tk. It simultaneously explains the complex nature of the forecast, while intertwining it with broader public misconceptions about meteorology and meteorologists.

    I am pleased with most of what I brought to front regarding this storm and in broad strokes the forecast worked out ok. Elevation, jackpot would be somewhere Worcester County south into NE CT or NW RI, not Worcester County North toward the Merrimack Valley. The probable less than forecast amounts in deep valleys and east coastal and adjacent urban areas. The need for hyperlocal snow forecasts with this storm as a 5 minute drive down or up the hill could yield you a completely different visual.

    Where I failed, and make no mistake, I failed, was not trusting myself or my strengths as a forecaster. Truthfully, I felt a bit burned by the October 2020 snow and also succumbed to some of outside noise regarding this storm.

    My strengths in this field are synoptic recognition and its impacts on sensible weather outcomes and diagnosing known model error and weaknesses, particularly in marginal situations such as this. You, know all the reasons, I am usually such a wet blanket…

    The lack of cold air available, the difficulty in generating cold all the way to the surface with 2m DP’s above freezing, ocean temperatures, misplaced banding signals in timing, location and duration. This was the completely wrong scenario to be aggressive with, yet yesterday morning I changed my thinking and added to my top range in the jackpot zone, and upped Boston to 1-3 and brought the 3-6 to within 3 miles of the coast. Relying on longer duration departure of cold fetch moisture to get some accumulation. (That happens in Maine, not too often in Metro Boston) I saw too many Kuchera and 10:1 maps floating around and some of the aggressive types jumping to 18″ and I got unduly influenced. I was on here stating how bad Kuchera is in this situation. Its calculation does not work with yesterday’s dew point issue. I mentioned if you need a snow map, use the depth or positive change maps. And you know what? The NAMs and some other short range guidance snow depth / change maps, ended up being about right, except at the highest of elevations. I thought about October, even though I knew that event was a synoptic antonym. Weakness!

    Tom, as I said before, you have a strong understanding of synoptics and climatology and their nuances. Your input is invaluable. You are teacher, beyond the classroom.

    As always, thank you to TK for hosting such a welcoming community of thought exchange.

    1. JMA I always look forward to your posts. We all do exactly what you did. It is easy to doubt yourself went you care for what you are doing and want to get it right. Sadly, meteorology is one of those fields that has so many variable.

      I agree. Tom is an exceptional teacher. I may have said that a time of two in the past 😉

  8. Thanks TK, excellent write-up as always. And a quieter weather pattern we’re entering into. Watching that 12/16-12/18 period also for a storm threat. I think beyond then we probably throw the “La Nina” switch. Even before then, we’re going to start seeing the Southeast ridge flexing later this week, but it will be transient at first. An up and down type pattern for a couple weeks.

    JMA, thanks for your thoughts also, and Tom and others for all your analysis. These storms are always a learning experience to bank for next time. And just as the October storm had no bearing on this one, this one will have no bearing on the next one. Tough start to the winter forecasting season but just gotta regroup for the next one.

  9. Good morning and thank you TK, Excellent writeup and thank you for you additions JMA and WxWatcher.

    If you don’t mind, I have some comments regarding yesterday’s event. Take them or leave them, just my thoughts:

    1. I am not angry or upset with anyone’s forecast whatsoever, I am Disappointed about the lack of snow? sure, but life goes on. The forecasters here did an outstanding job for certain. We all saw what they were working with and most of us were in agreement. Rough call for sure.

    2. I was disappointed in how long it took the column to cool. With that deepening system and the amount of rain it produced, I really thought the column might cool several hours ahead of when it actually did.

    3. yesterday AM sometime, don’t remember exactly when, I was looking at various GOES loops and I saw one in particular,
    GOES-East – Sector view: Northeast – Band 10 – 7.3 µm – Lower-level Water Vapor – IR. This showed a great deal of dry air being infused into the system when it was just of the DelMarVa. I should have posted it, but just took note, thinking crap, what if this disrupts the development of the system.

    4. When the changeover finally occurred in my location just a minute or 2 before 4PM (on cue), It was really coming down and I thought for sure that the forecast numbers for my area would come to fruition. But then not long thereafter, I noticed the radar echoes diminishing. At first I thought well that was because it had change to snow and snow doesn’t reflect as well. WRONG!!! that kind of heavy wet snow does indeed reflect very well. So, it was the beginning of the end. The dry air had interfered with the intensification process and thus we LOST the snow intensity and shortly after that, with the marginal temperatures, the temperature rose and it switched back to rain.

    Pete B mentioned dry air last night, So I think the above covers that.

    At my location, we picked up a quick slushy inch in that 1st hour before it self destructed. Only coatings in places remain,

    Very interesting day. Chalk it up to another learning experience.

  10. Thanks, TK…
    I appreciate your words, insights and writing style as always!

    But you summed it best yesterday at 5:49 when you simply stated,

    “Weather is fascinating…”

    Indeed!

    The best part of yesterday was looking at webcams from sunny and calm Nantucket while a nor’easter was raging outside here on the “mainland.”

    Go Pats! And Go Revs! The Revolution are in the MLS conference championship this afternoon against Columbus.

    1. Thanks, Dave, for thinking of me!!! 🙂
      Don’t have time to watch a lot of TV now, but vacation’s coming soon!
      We work through Tuesday, December 22 and go back Monday, January 4. That’s a nice, little break for necessary recharging!
      I will check out Selena!

  12. Thanks TK !

    I didn’t get up to Brant Rock this morning, went the other direction.

    In the last 6 weeks, the brook/stream at the western end of town center has gone from pools of stale water to fast flowing, nearly at bankfull.

    Nice day, we are headed out for a midday walk.

  13. TK, thank you. I just liked seeing the whole thing unfold yesterday. Didn’t care whether it was rain or snow or both. Found it interesting and educational.

  14. Worcester’s 9.6 inches of snow was a new snowfall record for the date (December 5), putting their seasonal total-to-date at 15.8 inches, which is 11.4 inches above the average of 4.4 inches through December 5.

    1. 15.8 inches was what Logan had all of last winter. It would appear that Worcester is off to a fast start. They will do well in snowfall, as they usually do.
      Come to think of it, Worcester doesn’t usually have too many below normal snowfall winters, do they? (64.1”)

      1. In order to get an “average”, you have to have a bunch of above and below normal snowfall winters to get there 🙂

      2. Worcester has about an equal amount of above normal & below normal snowfall winters. That’s where the average comes from. Sometimes a decade (or a period of years) will be skewed one way or another, such as the 1960s which had some pretty decent winters, the 1980s when tended to have less snow, and the 1990s which turned much more snowy again (just a few examples in general).

  15. Although we have an abundance of rainfall in recent weeks, we are still about 10″ behind for our yearly average which is 51.99″.
    The Taunton River at Bridgewater is healthy at 6.09″. Action stage is 7.5″ This week’s drought map has SEMass and the South Coast still in the Abnormally Dry/Moderate Drought range (valid through December 1 at 7 am).

  16. Thanks TK for the great commentary!

    The hyper local aspects of this storm with respect to the snow totals I thought were well forecasted by all. I had 3″ here but the spotter in Tolland a few miles north of me at higher elevation reported 6″. And I also see a report of 10″ in Union, about 15 miles NE of me. In the CT River Valley to my west, pretty much nothing with only 0.2″ reported at BDL.

    This was an extremely compact storm as well…at one point we had the dry slot that was practically into Boston while the back edge of accumulating snow was less than 90 miles west. This tight banding resulted in lower totals further west as well, where there was a bit more cold air to work with.

    Jackpot snow total was 12.5″ reported in both Monson (Hampden Co) and in Paxton (Worcester Co).

    Impressive rain amounts too with a report of 4″ on the Vineyard and 5.5″ in Newport County, RI.

    Peak wind gust was 68mph at Dennis.

    Here is a summary of the final rain and snow totals from the NWS….

    https://forecast.weather.gov/product.php?site=BOX&product=PNS&issuedby=BOX

  18. Looking ahead….

    Models seem to agree on our next storm system about a week from now being a massive cutter over the Great Lakes.

    They all are showing a threat in the 16-18th timeframe as well with a more southerly storm track and potentially some more cold air to work with but even the 12z GFS is showing that system tracking far enough north for all rain here. Still early….

    1. They also agreed on yesterday’s track being Great Lakes about a week ahead of time. 😉

    1. 🙂 Stop beating yourself up. I thought your forecast was truly excellent. Things happen. You’re one of the best in the business.

      1. I am beating myself up because I had this close to right and I double clutched …Less models, more meteorology.

        Thanks Old Salty (ha!) I appreciate the boost. Be well.

  22. What happened with Monday nights potential? Did it go poof? Models aren’t going to make a shift further north…Boo…I await JP post about something changing.

    You all did great! We got snow! More snow in some towns and less in others it’s what is going to happen. Keep up the good work.

    1. Yes, I saw that this morning on air. Another met beating himself up. I hope these tv mets haven’t been getting obscene comments from viewers, or negative feedback from their management.

  25. Lean colder next Saturday.
    Expect models to do something kind of funny with the next system – the big split. And maybe a lagging surprise (12-14).
    Beyond: System being modeled for around 12-17 will probably occur further south than today’s projections.

    Nice stratocumulus sunset color for some areas today. Those tend to be short-lived but rather deep orange / red colors.

  26. 00z GFS should show a bit more high pressure north and a subtle hint of more cold air further south for the weekend system in regards to the frontal boundary for New England.

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