December 5-6, 2020 Storm Observations and Nowcast

[wokeupthisam]

About 1 foot, tough to measure due to late drifting.  Just a pasting for the first 3/4 of the storm, snowed hard with temp at 32.2 most of that time.  Power went out at 10:30pm and still out.

 

[Lava Rock]

Power back on after 20hrs. Feels and looks wintery

[rimetree]

Under performed here. 2" measured this morning. Snow was nice to look at last night and very wintery feel today with some blowing snow. Went for a walk around the neighborhood and noticed the crackling sound in the trees when the wind blew enough to fracture the ice clinging to the branches. My old place in Nottingham must have done fairly well.

[STILL N OF PIKE]

I know nobody cares but in the name of accuracy my measurements were actually at about 200 feet higher elevation than I thought , going back and cross referencing topo maps and measurements taken at a couple notable spots (where trail bent 180 and Just shy of A pleatau with open view of Monadanock) . My ski tracks altitude wasn’t reading and I shouldn’t have listed the elevation before checking .

[jbenedet]

Still getting stink bugs and leaf footed bugs in my place. 

Lawn is green. 

A few herb plants I never harvested in the garden are still alive..

Met Winter still a ways off....

 

[Weatherlvr]

7 hours ago, dendrite said:

Hooksett damage

Northfield damage

 

Other than the cable line, nbd here. I saved the bamboo and birches with frequent shaking. The birches will hopefully recover. As for my parents, at least they’ll get more sun. 

We ended up with nothing here across the lake is white recorded a 39.5 mph gust sustained 25.4mph winds at 10pm to 12am last night.  

[Lava Rock]

As soon as I put genny away, power went back off. Classic

[Damage In Tolland]

Just now, Lava Rock said:

As soon as I put genny away, power went back off. Classic

Yes!

[Yukon Cornelius]

44 minutes ago, Lava Rock said:

As soon as I put genny away, power went back off. Classic

We just got ours back after about 14 out. Changed the oil and got the genny all put away and just hoping we don’t lose it again.  My connection is outside at the opposite end of the house, so dragging that beast out of the garage last night at 1:00am through the frozen cement and dropping limbs is not the kind of fun I’m looking to repeat. 

[Great Snow 1717]

58 minutes ago, jbenedet said:

Still getting stink bugs and leaf footed bugs in my place. 

Lawn is green. 

A few herb plants I never harvested in the garden are still alive..

Met Winter still a ways off....

 

Lawns have the look of  mid to late April. As of friday there were a few dandelions in the yard.

[Lava Rock]

We just got ours back after about 14 out. Changed the oil and got the genny all put away and just hoping we don’t lose it again.  My connection is outside at the opposite end of the house, so dragging that beast out of the garage last night at 1:00am through the frozen cement and dropping limbs is not the kind of fun I’m looking to repeat. 

Ours back on. I'm leaving genny out for the night just in case. Spectrum cable back on line too

[Deck Pic]

North of Presque isle.  26, +SN, roads are all packed and pretty icy. 

[backedgeapproaching]

DC to Presque Isle, that is one hell of a chase.

[40/70 Benchmark]

DEC

6

 

 

12-5-20 Rain to Snow Verification: A Matter of Lift

12-5-20 Rain to Snow Verification: A Matter of Lift

Friday Warmth Not Overcome.

It is difficult to fault anyone for having been skeptical of an impending large snowfall on Friday afternoon, as temperatures were a spring like 55-60 degrees across the region.

 

 

 

It can and has happened before in the past, however, it goes without saying that everything has to go "right", or wrong, depending on one's perspective. This is because such a warm antecedent airmass leaves virtually no margin for error within the atmosphere. Everything needs to go precisely according to plan, or else the result is the couple inches of slush that many areas saw on Saturday afternoon:

 

 

vs the forecast:

 

This was a respectable forecasting effort in such a challenging system, but obviously as implied above, something did not go according to plan. First of all, the primary critique of this forecast effort is that it did emphasize the importance of elevation enough with respect to snowfall. While topography was considered in a general sense, as the Connecticut river valley had a lighter forecast range of 2-5", the map failed to address just how much snowfall varied by elevation even in Worcester county and northern Connecticut. Secondly, snowfall was over forecast in much of eastern Mass, which had nothing to do with elevation and everything to do subtle nuances in the mid levels of the atmosphere.

 

Proficient Snowflake Production Can Compensate for Marginal Thermal Profile

There is a great deal more to forecasting snowfall than the temperature on the thermometer outside. Snowflakes, or "dendrites" are optimally produced between a temperature of -12 to -18 celcius in the mid levels of the atmosphere. This is referred to as the "snow growth zone". The high quality dendrites that are proficiently produced within this region accumulate very efficiently. In order to get rates that heavy, there is a tremendous amount of "lift", or rising air that is needed to produce the very heavy rates of +1-2" per hour. It is possible to have perfect dendrites falling at only light intensity when lift of paltry, and conversely, ample lift can be occurring outside of the optimal snow growth zone, which is what took place yesterday in eastern Massachusetts. This does not necessarily preclude a heavy snowfall, assuming that low level temperatures are cold, however, yesterday the forecast did not have that margin for error, since we were relying on perfectly formed dendrite falling at very heavy rates owed to well placed lift. We needed everything to go as planned, and it did not. A superior snowfall forecast requires accurately forecasting the temperature at the surface, the temperature at all other levels of the atmosphere, as well as the amount of lift, and where said lift is located relative to that -12C to -18C optimal snow growth region. There is zero margin for error with respect to any of this when temperatures are as marginal as they were yesterday.

 

Forecast Thought Process

The forecasting yesterday was for several inches of snow to the northwest of Boston, however, only about 2-5" actually accumulated. The reason was that Eastern Mass Weather underestimated the importance of the fact that the best lift was located slightly beneath the snow growth region, which greatly limited snowfall since the lower levels of the atmosphere were slightly above freezing.

 

There was no question that sufficient lift would exist, as the developing storm created a strong temperature gradient in the mid levels of the atmosphere, which is called "frontogenesis".

 

 

However, what is evident is that the area in question immediately to the north and west Boston is on the eastern edge of said lift, which further complicated the forecast.

 

Here is the sounding at Lawrence, MA:

 

 

The thought process was that it would be "good enough" for 5-8" of pasty snowfall, but it was not. There was 2-5" of slush. This was the forecasting error. Had the temperature been 1-2 degrees colder, and the lift been slightly higher, then the forecast would have been for 12-18" of snow. An accurate snowfall forecast is a complex endeavor that incorporates the consideration of a myriad of different factors on a continuum, which necessitates a great deal of critical thinking. A far cry from the linear process of simply considering the low level temperature and the amount of water falling from the sky that many people believe it to be.

 

Compare this to the sounding to the west in Worcester:

 

 

 

This is why the Worcester county forecast of 8-12" verified nicely, with the exception of the lowest elevations. Low level temperatures were slightly colder with some elevation, and the strongest lift, which was perfectly centered it he snow growth region, directly traversed the area.

Conclusions

This was a solid, albeit flawed forecasting effort that will inform future endeavors this throughout the boreal 2020-2021 winter season. Since this is a la nina season, there will likely be many marginal scenarios that will both hone and challenge forecasting skill.

 

Final Grade: B

 

 

 

 

[40/70 Benchmark]

Should have stuck with First Call back east.

 

[weathafella]

A Tipesque verification blog from Ray.

[Damage In Tolland]

8 minutes ago, weathafella said:

A Tipesque verification blog from Ray.

He had you at hello?

[Heisy]

Tip alluded to this, but something I noticed was when I did flip to snow it stuck to all surfaces practically immediately. In my life in philly I had never seen that during a changeover event. It always took some time for pavement to accumulate. When the fatties were falling it stuck and accumulated pretty much evenly to every surface. This seems kind of odd considering ratios were bad. When that had happened I thought for sure we might bust high or at least do close to expectation. I didn’t notice the melting aspect until the tail end of the deformation zone where I imagine temps might have climbed up a tad. 

[CoastalWx]

Not sure if anybody noticed, but after it cleared on the outer cape, that had some gusts 70-90mph. Mini 05.

[HoarfrostHubb]

ORH set record daily rainfall (1.97”) and snowfall (9.6”)  records yesterday.  Wtf?

[dendrite]

23 minutes ago, HoarfrostHubb said:

ORH set record daily rainfall (1.97”) and snowfall (9.6”)  records yesterday.  Wtf?

Water equiv

[Typhoon Tip]

I looked at the modeled contouring at the traditional sigma levels ...

the 850, 700 and 500 mb lvls

these cyclonic components collocated upon the same axis at nearly the same time and when that happened the wind backed NNW ... right around 21z

1/2 hr later the winds at the surface here, NW of I495, went 350 and flurry mist mixture became the primary fall rate and type. Basically ... our wind shift coincided with vertical stacking and storm loss. 

I have seen this too often in the past and that wind backing tandem. 
 

yeah ... we lost DGZ because the coupled atmosphere stretches when the flow down slopes ... compensating for synoptic UVM forcing.  
 

I feel pretty confident you’ll see this in reanalysis. All that then added to physics of descending motion adding evaporation I think together worked against and is why the back 1/3 to 2/5ths of the event fell apart. 
 

I also like the idea of ‘melt momentum’ and tall column distance.  Didn’t help. 
 

As always the case theres probably a cocktail of reasons

[The 4 Seasons]

Here's the final storm totals for CT. Thanks everyone for all the reports. I figured this one wouldn't work out for southern CT and the valley areas so i wasn't really feelin' it enough to make a map. Also with my schedule i really didnt have the time. Attached is a screenshot from a group chat im in with a few mets from this board. I would have done very well for most of the state but busted too low for NW CT, especially that tight area around Burlington. Nailed E and NE CT especially around the Tolland to Union area.

It was pretty much all rain here except for a brief time around 12-2PM with heavy banding we changed to a 50/50 mix but never fully flipped. When the precip lightened up we changed back over to all rain and ended. Final total was Trace. 

Lets hope we can all sneak one solid event here in CT and the tri-state area before the month is over. It's been almost 3 years since the last warning even during met winter. Too long..

 

[Lava Rock]

Guess we got lucky getting our power back yesterday late afternoon. CMP estimates it'll be Weds night until everyone is restored. They made a comment this was the worst storm/outage of the century. I'm scratching my head on that one. I saw one tree across some lines on our little drive yesterday to scope things out. The lower elevations had no snow on the trees and overall, the damage looked pretty insignificant to me. I though Hurricane Irene (2011) was much worse in terms of damage.

[STILL N OF PIKE]

10 hours ago, Typhoon Tip said:

I looked at the modeled contouring at the traditional sigma levels ...

the 850, 700 and 500 mb lvls

these cyclonic components collocated upon the same axis at nearly the same time and when that happened the wind backed NNW ... right around 21z

1/2 hr later the winds at the surface here, NW of I495, went 350 and flurry mist mixture became the primary fall rate and type. Basically ... our wind shift coincided with vertical stacking and storm loss. 

I have seen this too often in the past and that wind backing tandem. 
 

yeah ... we lost DGZ because the coupled atmosphere stretches when the flow down slopes ... compensating for synoptic UVM forcing.  
 

I feel pretty confident you’ll see this in reanalysis. All that then added to physics of descending motion adding evaporation I think together worked against and is why the back 1/3 to 2/5ths of the event fell apart. 
 

I also like the idea of ‘melt momentum’ and tall column distance.  Didn’t help. 
 

As always the case theres probably a cocktail of reasons

Thank you 

On 12/5/2020 at 8:41 AM, It's Always Sunny said:

bruiser. 

that was 8am sat HRRR, the model WDRAG said to monitor for now cast

does that not show max lift in DGZ leaving at 20z (4pm) and lift in general going bye bye by 5-530pm (above DGZ) ..isn’t that a big old red flag for a 495 Given what we needed to see 

maybe I’m wrong since this was posted as a reason for a crushing by someone but I’m not confident in reading that but that is my intuition interpretation 

How would that chart be interpreted as a crushing for 5-9pm as was forecast 

[tamarack]

53 minutes ago, Lava Rock said:

Guess we got lucky getting our power back yesterday late afternoon. CMP estimates it'll be Weds night until everyone is restored. They made a comment this was the worst storm/outage of the century. I'm scratching my head on that one. I saw one tree across some lines on our little drive yesterday to scope things out. The lower elevations had no snow on the trees and overall, the damage looked pretty insignificant to me. I though Hurricane Irene (2011) was much worse in terms of damage.

Short memories?  They had over 500k customers out from the Oct. 2017 gale; that's a few thousand more than in 1998, though in '17 most were re-powered within 2-3 days while the ice storm had many thousands dark for 2 weeks +.

[Lava Rock]

Just now, tamarack said:

Short memories?  They had over 500k customers out from the Oct. 2017 gale; that's a few thousand more than in 1998, though in '17 most were re-powered within 2-3 days while the ice storm had many thousands dark for 2 weeks +.

Yeah, I don't know where or why they made that statement, but it didn't seem accurate to me.

[JC-CT]

[40/70 Benchmark]

I didn't do well Saturday, but it was apparent that I did better than Boston. There are only patches in the Everett/Chelsea area. I have fill coverage at home in Methuen.....and that 2" of concrete will not cede ground easily.

[Damage In Tolland]

19 minutes ago, 40/70 Benchmark said:

I didn't do well Saturday, but it was apparent that I did better than Boston. There are only patches in the Everett/Chelsea area. I have fill coverage at home in Methuen.....and that 2" of concrete will not cede ground easily.

Oh it sure will on Sunday