December 5-6, 2020 Storm Observations and Nowcast

[powderfreak]

A friend at Sunday River had a tape measure and looked like 17-18”.

[dryslot]

10 hours ago, PhineasC said:

I should have bought a yardstick.

lol, That's a rookie mistake, You're no in Kansas anymore Dorothy.

[dryslot]

3 hours ago, moneypitmike said:

Anyone who scored the most and how much from this?  I'm guessing it was Jeff.

Nope, 5.5" garbage ratios.

[MaineJayhawk]

5 or 6" in North Waterboro.  Dense, too.  Shit would stick to my shovel when I tried to throw it.

[ORH_wxman]

1 hour ago, OceanStWx said:

Trying to dive deep to figure out what the real failure point was here, because I don't really think it was forcing. The QPF was pretty good, right ballpark anyway, clearly there was strong f-gen in the right location relative to the storm. 

I keep coming back to our 00z sounding last night with DGZ up around 500 mb. That's not a great spot and indicative of a pretty torched air mass. Dropping less than dendrite ratios into a deep near freezing layer primed snow to melt at the surface. Even when rates were decent. There was a lot of 1/2 to 3/4SM snowfall that normally would accumulate if your flakes weren't already near slush by the time they reach the ground. Honestly the 04.12z NAM forecast soundings weren't bad in the vicinity of GYX, and it should've been a bigger red flag to me. 

We were running with ratios around 7:1, but they needed to be lower than that given the environment we were working with. Elevations did better because it shrunk the near freezing layer that flakes had to fall through and kept near surface temps slightly cooler. 

I have to go back and find that great paper about dendritic and ice crystal growth but I also remember from it that it talked about how the well-formed dendrites/ice crystals will latently cool more efficiently when they melt than marginal ice crystals. So kind of a double whammy there in a super marginal air mass. 

There was a ton of QPF that fell in the CCB...agreed on that. So it wasn’t like we got dried out over E MA. It just ended up basically being sleet ratios there. 

[OceanStWx]

2 minutes ago, ORH_wxman said:

I have to go back and find that great paper about dendritic and ice crystal growth but I also remember from it that it talked about how the well-formed dendrites/ice crystals will latently cool more efficiently when they melt than marginal ice crystals. So kind of a double whammy there in a super marginal air mass. 

There was a ton of QPF that fell in the CCB...agreed on that. So it wasn’t like we got dried out over E MA. It just ended up basically being sleet ratios there. 

I wasn't positive of that, but intuitively it makes sense. If you create a crystal at -5C it's going to take less heat to warm it up to 0C than if you create a crystal at -12C. Even if your crystal structure may be more delicate. 

[ORH_wxman]

3 minutes ago, OceanStWx said:

I wasn't positive of that, but intuitively it makes sense. If you create a crystal at -5C it's going to take less heat to warm it up to 0C than if you create a crystal at -12C. Even if your crystal structure may be more delicate. 

Yeah if you’re throwing a bunch of marginal ice crystals at relatively warm temps (like around -5C as you said) into a layer at 32-33F, that sounds uglier than throwing a bunch of hooked dendrites at -10 to -14C into that same layer. 

[OSUmetstud]

10 minutes ago, ORH_wxman said:

I have to go back and find that great paper about dendritic and ice crystal growth but I also remember from it that it talked about how the well-formed dendrites/ice crystals will latently cool more efficiently when they melt than marginal ice crystals. So kind of a double whammy there in a super marginal air mass. 

There was a ton of QPF that fell in the CCB...agreed on that. So it wasn’t like we got dried out over E MA. It just ended up basically being sleet ratios there. 

Is it a mass issue? Melting large aggregated dendrites would remove more heat from the environment than smaller flakes? 

[CoastalWx]

3 minutes ago, OSUmetstud said:

Is it a mass issue? Melting large aggregated dendrites would remove more heat from the environment than smaller flakes? 

I think spatial area coverage too. Big hooked dendies will be efficient in cooling.

[OSUmetstud]

Without the drier dewpoints you also lose any heat of vaporization effects, which is about 8 times larger than the heat of fusion. So you're only left with heat of fusion and a smaller contribution of sensible heat from the flakes themselves. 

[ORH_wxman]

2 minutes ago, OSUmetstud said:

Is it a mass issue? Melting large aggregated dendrites would remove more heat from the environment than smaller flakes? 

Yeah I’m not sure. The temperature of the ice matters too. I’ll have to search for the paper I mentioned...I think I have it saved on my pc downstairs. It’s like my go-to source for this kind of stuff. It talks about everything including how you can get ice crystals in areas close to the ocean as low as -4C to -5C due to the salt nuclei being far more efficient at warmer temps. 

[OSUmetstud]

2 minutes ago, ORH_wxman said:

Yeah I’m not sure. The temperature of the ice matters too. I’ll have to search for the paper I mentioned...I think I have it saved on my pc downstairs. It’s like my go-to source for this kind of stuff. It talks about everything including how you can get ice crystals in areas close to the ocean as low as -4C to -5C due to the salt nuclei being far more efficient at warmer temps. 

Right, I usually use -6 out here and then -8 in Ontario, but it's just an estimate because of the stochastic nature of cloud droplets. 

[It's Always Sunny]

2 minutes ago, CoastalWx said:

I think spatial area coverage too. Big hooked dendies will be efficient in cooling.

Goes back to what you said originally though Scott how most places didn't see flakes flourish in the DGZ. I remember looking at soundings and x-sections yesterday and saw the same thing. Best lift was either above or below it (at least the stations I was looking at). 

[ORH_wxman]

1 minute ago, OSUmetstud said:

Without the drier dewpoints you also lose any heat of vaporization effects, which is about 8 times larger than the heat of fusion. So you're only left with heat of fusion and a smaller contribution of sensible heat from the flakes themselves. 

Yeah this almost certainly a factor too. Even in warm spring storms, if you have a dry polar high sitting up there, it can be a nice source of drier dewpoints feeding into the storm to help cool the low levels even if temps were 55F the day before. 

There was probably a combo of factors that hurt further east. Less loft in the DGZ, lack of drier dewpoints up north to help advect in a source of lower level cooling. 

[ORH_wxman]

Just now, It's Always Sunny said:

Goes back to what you said originally though Scott how most places didn't see flakes flourish in the DGZ. I remember looking at soundings and x-sections yesterday and saw the same thing. Best lift was either above or below it (at least the stations I was looking at). 

And the best zone that had decent lift in the DGZ was further west over ORH county into adjacent S NH...so they had the double advantage of better DGZ lift plus some elevation. It’s probably why you saw like 9-12 inches of snow there while Ray in Methuen was struggling to get 2”. You hardly ever see that type of gradient unless he was mostly raining which wasn’t the case. 

[mahk_webstah]

3 hours ago, OceanStWx said:

Well I think a problem is that clown maps (especially these realistic looking ones) are a relatively new feature. Because of how they are generated, you rarely end up seeing more snow than they spit out. 

Point taken.  It still seems like there are more misses these days and model gyrations.  It is not just the maps because you help us see reality.  The Euro no longer dependable, gfs kinda new.  It all just seems less can be counted on from models these days although maybe it is the bias that comes from paying attention more.  It wouldn’t surprise me though that the pace of climate change fooks with the analogue data; Tip has talked about this.  I’m not a scientist so can’t provide any reliable analysis.  But if the Mets don’t feel the models are worse with these storms, then you are probably right since you work with them every day.

[alex]

12.2" here this morning; light snow continuing. Very scenic snow, it's like snow maker stuff. Cemented to the trees. 

[It's Always Sunny]

1 minute ago, ORH_wxman said:

And the best zone that had decent lift in the DGZ was further west over ORH county into adjacent S NH...so they had the double advantage of better DGZ lift plus some elevation. It’s probably why you saw like 9-12 inches of snow there while Ray in Methuen was struggling to get 2”. You hardly ever see that type of gradient unless he was mostly raining which wasn’t the case. 

Yeah looking at METARs this morning I was seeing several hours of snow reports for lots of places along the coast but then only saw like 1-2" total.  Unique event for sure and most places changed over sooner than modeled (even though we knew that would probably happen).

[CoastalWx]

Not to beat a dead horse, but it helped in the October 30 storm. I was getting fluff in the aftn from efficient snow growth. Part of the reason we saw record snow. 

[MJO812]

2 hours ago, NorEastermass128 said:

0.0” final. 
 

0.0” season to date.

 

Welcome to my area

[Ginx snewx]

Rain totals

[It's Always Sunny]

I know I'm speaking for others but events like these always leave a dent in forecasting confidence because there have been many times where the best lift wasn't quite in the DGZ but still yielded great amounts and then you have yesterday's storm that pretty much puts us back in check. I remember earlier this year (I forget the date Will probably knows lol) but mid level dry air was a potential issue which made many of us poo-poo it but most of SNE ended up doing really well. If I can find the date I'll update this post but point being that was a storm that left a dent as well.

EDIT: December 11, 2019 event with the mid-level dry pocket.

[OceanStWx]

13 minutes ago, mahk_webstah said:

Point taken.  It still seems like there are more misses these days and model gyrations.  It is not just the maps because you help us see reality.  The Euro no longer dependable, gfs kinda new.  It all just seems less can be counted on from models these days although maybe it is the bias that comes from paying attention more.  It wouldn’t surprise me though that the pace of climate change fooks with the analogue data; Tip has talked about this.  I’m not a scientist so can’t provide any reliable analysis.  But if the Mets don’t feel the models are worse with these storms, then you are probably right since you work with them every day.

It's not worse, just different.

15 years ago when I was in school, models were all 80 km resolution. You would have to tease out banding potential and snowfall forecasts were more broad, with "locally higher amounts". 

Now models are finer resolution which is prone to more wobbling when they can resolve features down to 9 or 13km. Banding doesn't need to be teased out, but can be modeled, and "locally higher amounts" are explicitly forecast by guidance. So when those shift around it's far more noticeable.

[WinterWolf]

1 minute ago, It's Always Sunny said:

I know I'm speaking for others but events like these always leave a dent in forecasting confidence because there have been many times where the best lift wasn't quite in the DGZ but still yielded great amounts and then you have yesterday's storm that pretty much puts us back in check. I remember earlier this year (I forget the date Will probably knows lol) but mid level dry air was a potential issue which made many of us poo-poo it but most of SNE ended up doing really well. If I can find the date I'll update this post but point being that was a storm that left a dent as well.

Good points.  It goes both ways, sometimes we poo poo something and it still works out well because something offset the potential issue.  
 

And sometimes we see the issues and feel this or that should overcome the issue, and it doesn’t.   It’s not an exact science yet....humbling to say the least.  Looking forward to the next threat. 

[It's Always Sunny]

1 minute ago, WinterWolf said:

Good points.  It goes both ways, sometimes we poo poo something and it still works out well because something offset the potential issue.  
 

And sometimes we see the issues and feel this or that should overcome the issue, and it doesn’t.   It’s not an exact science yet....humbling to say the least.  Looking forward to the next threat. 

Yeah exactly to your point.  Like you said events that don't look so hot then do great, we pick out what went well, what overproduced, etc and we do the opposite for when we have high expectations and it doesn't materialize.

[STILL N OF PIKE]

If post 20z the winds at 850-925 veering to NNW..didn’t seem to effect the QPF that much ..could they have been responsible for a slight moderating of low level temps (via downsloping)  when they turned this direction for Central mass over to S NH and why elevation maybe played a even bigger part  than forecast for second half . 
 

BC Nashua was like 32.5 mid day and then 33.5 34 late pm and evening . 

[It's Always Sunny]

4 minutes ago, STILL N OF PIKE said:

If post 20z the winds at 850-925 veering to NNW..didn’t seem to effect the QPF could they have been responsible for a slight moderating of low level temps (via downsloping)  when they turned this direction for Central mass over to S NH and why elevation maybe played a even bigger part  than forecast for second half . 
 

BC Nashua was like 32.5 mid day and then 33.5 34 late pm and evening . 

Maybe so but that would probably happen more often during similar setups if that were the case.  Others will likely add onto this but I think it goes back to the lack of lift in the DGZ.

[wxsniss]

5 hours ago, CoastalWx said:

The weenie maps just don’t take anything important really into consideration. I hate them lol. I thought it would pound in metro west, but it did not. I do think the lift into the DGZ was only confined to a narrow area associated with the higher terrain coincidentally (I think I even said it’s possible this could be a storm that really differs from low elevation to high elevation). Therefore if it doesn’t pound dendrites, it is tough to latent cool to near 32. That’s probably a big reason. If I was on air or a NWS met, I would have busted there for sure. Hell I busted on 1-3 for BOS lol. Congrats on the little one!

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, lack of drier dewpoints, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

[ORH_wxman]

2 minutes ago, wxsniss said:

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

The lift was lowering throughout the event over E MA. There was prob more DGZ lift during the initial changeover than later on...maybe Chris or someone has easier access to the cross sections than I do at the moment, but I’m pretty sure i recall seeing the lift a bit deeper earlier in the event. 

Usually once you flip over to snow, keeping excellent DGZ isn’t a huge deal because your in the CCB and often advecting cold air into the system...but this was a unique system in which we were not so the issue ended up more glaring than it usually would be. 

[OceanStWx]

1 minute ago, wxsniss said:

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

Most likely answer is that when the changeover occurred the thermodynamic profile didn't look like what we've described. The DGZ was likely lower in the atmosphere, and over time the WCB forced it to rise. Those mid level temps were way colder at 12z (despite surface temps being near 40) than they were at 00z (despite surface temps being near 33).