December 5-6, 2020 Storm Observations and Nowcast

[40/70 Benchmark]

Just now, Typhoon Tip said:

Not sure I understand this... the 5/6 pm attenuation of radar ( I just provided ) was not in the afternoon ?

My idea here is that a critical backing/timing therein ...around that 5 to 6 pm time frame, coincided with a rad attenuation as well as a ground truth abatement/weakening of the event - and trying to figure out exactly why. 

Now, the shadowing and downsloping is a geophysical truism -.  Regional air motion going from elevation to lower elevation, pulls the atmosphere down and offsets UVM, but also ..compressional drying do to PV=NRT of the entire mass... The total phenomenon causes what is referred to as 'rain shadowing'  ... 

When this thing closed off at all those levels and the flow was paralleling ( more so than less...) through the deeper troposphere to surface, ...I think it's bit too cutely coinciding with rad/ground truth to not implicate the models as yet again, over doing that back shit.

I like that fraud thing ..funny... Yeah, I remember Bruce was big on that back-lash. 

 

Exactly my point....even before the precip abated, I was not accumulating efficiently.

[40/70 Benchmark]

4 minutes ago, OceanStWx said:

There was definitely beam attenuation going on with BOX. Winds were starting to turn west of north (which is why the dome was attenuated in that direction), so the storm was going to begin to wind down. Like Will mentioned though LWM still had 0.34" between the hours of 5 and 7, so it's not like it was spitting out. It just was shitty snowflakes and a shitty environment to keep them frozen for very long.

Exactly...and as I said to John, it was struggling to accumulate all afternoon in that area.

[Typhoon Tip]

10 minutes ago, OceanStWx said:

There was definitely beam attenuation going on with BOX. Winds were starting to turn west of north (which is why the dome was attenuated in that direction), so the storm was going to begin to wind down. Like Will mentioned though LWM still had 0.34" between the hours of 5 and 7, so it's not like it was spitting out. It just was shitty snowflakes and a shitty environment to keep them frozen for very long.

See ...to me this doesn't really refute the shadowing tendency - that example. 

That's easily explained to me as being proximity -related, where ( literally ...geometrically ) LWM is still closer to the 700 mb core and was not getting 'd-sloped' just yet?   

[Typhoon Tip]

12 minutes ago, 40/70 Benchmark said:

Exactly my point....even before the precip abated, I was not accumulating efficiently.

Oh yeah yeah yeah... 

Right - I noticed this too out here.  There were other aspects going on in the whole of this thing's dizzying array of 'I wish we could have that week of our lives back' - lol.. 

No but I noticed between 2:30 ( ~ ) and 4:30 pm, we had moderate snow here ... and the stack depth never changed from 3"   ... That's all a different discussion aspect for me though - 

My thing is really why the sudden dwindling took place - Chris hints that the wind going N somehow attenuated the radar and he may and likely is right - it's his technology. Hahah... However, whether the rad was disrupted or not... we definitely had nothing more than street lamp sparking wet flurry mist from 4: 30 /5 o'clock out my way, right when rad did that.  

Maybe it was just bad luck timing that the rad decides to hide and seek that way.  Nice - fits this piece of shit's luck curve anyway ..  In the end, we didn't get snowed on as much... As far as that goes, yeah, it's probably both, like you say - ...some shadowing, and a lot of wasted life following this asshole storm

[STILL N OF PIKE]

30 minutes ago, 40/70 Benchmark said:

It was both.....sure, precip cutoff early in the evening, but it had been accumulating like shit all afternoon, despite heavy fall rates.

There was certainlty a myriad of reason even among different locations

To Johns point and what i saw...Some was actually fall rates like KBED. Look at their observations...They had one hour where they exceeded .10 in the bucket after 250pm. That was not going to get it done. If that was known ahead of time nobody would have forecast near 6" for KBED . HRRR seemed to  hint at  this for that area Sat am.

KBED had hourly totals of 

.09  .10 .15 .08 .03 ending 350 450 550 650 750   .45 over 5 hours of max snow forecast time. Fall rates were an issue in KBED

A spot like LWM seemed more like it was more Surface temps as you mentioned .. they were 1f too mild and you needed an extra 250 to 300' to make a difference. I know in Derry a bit NNW of you they did pretty well (around 6") at 400'

In Maine CP it seemed definitely more of the issue that LWM had.  

 

 

[40/70 Benchmark]

3 minutes ago, STILL N OF PIKE said:

There was certainlty a myriad of reason even among different locations. Some was actually fall rates like KBED. Look at their observations...They had one hour where they exceeded .10 in the bucket after 350pm. That was not going to get it done. HRRR seemed to  hint at  this for that area Sat am

A spot like LWM seemed more like it was more Surface temps as you mentioned .. that were 1f too mild and you needed an extra 250 to 300' to make a difference. I know in Derry a bit NNW of you they did pretty well (around 6") at 400'

 

 

I can tell you that it was low level temps IMBY....may have been overcome due to greater evap cooling had lift been in SGZ, and we had better dendrites, but that was not the case......so we rotted between 33.8 and 34.0 during bulk of heavy precip.

[Lava Rock]

38 minutes ago, OceanStWx said:

Right. Kind of had a partial pupu platter and could never complete the order. 

We had rates, but not the dendrites or low level cold. A little low level cold (elevation) went a long way in this event to help save things. Valleys needed one or the other (dendrites) to come through and neither did. 

In the 8yrs we've lived on tenney hill, this storm produced the largest snowfall gradient over very small elevation changes. A friend of ours lives on Sebago and they only received 1.5". We got 11.5" at 730', yet areas just down the road at ~300' had about half. When I got down towards windham, even less. It's nice when living at some elevation produces during early and late season events. doesn't happen often, but this was the best for us.

[Typhoon Tip]

Marginality ftl ... ugh. 

It's almost like it was "marginal + .5"

Like, you know ... you can have "marginal -1"  or "marginal +1" ?           

Some situations will look marginal and it's excruciatingly tedious if not all but impossible to really differentiated one 'marginal' appeal from another, but the "synergistic" tendency - which do to being emergence-dependent ...doesn't exist until it does, so cannot really be pre-assessed in that sense - will be warmer -vs- cooler.  I've seen marginal situations go either direction, usually, unexpectedly.  Maybe the "-1" and "+1" in the sketch numbers above are the synergistic tendencies - nice... solid sci-fi material right there.  But hey - 

It does ( I'm being a little hypothetical on this particular turn of thought ) seem that we are in an era now where marginal flop direction tendency tries to find the +1s. 

It's "flop direction" ... I sort of snarked in half seriousness about this as being one of those 'intangible gems' about changing climate ...  

[ORH_wxman]

1 hour ago, Typhoon Tip said:

See ...to me this doesn't really refute the shadowing tendency - that example. 

That's easily explained to me as being proximity -related, where ( literally ...geometrically ) LWM is still closer to the 700 mb core and was not getting 'd-sloped' just yet?   

I dunno...the max snowfall for the eastern zones in MA was really like 4-8pm on the model guidance....I agree the models did seem to go on too long after that, but the core of the best stuff was forecasted mostly late afternoon and early evening....which from a rate standpoint, largely verified. Maybe we're having two different discussions here.....

1. Did downsloping affect things later on? Yes. The precip after 7-8pm did not really match model guidance which suggested perhaps 2-3 more inches for E MA even at modest 7 or 8 to 1 rations.

2. Was downsloping the main reason for the lack of snowfall accumulation between 4-7pm? No (IMHO). I think our cross sections are explaining that better with the "perfect storm" of toxic brew....as Chris said, the lower elevations needed either slightly more LL cold or for dendrites to overcome the lack thereof, and we couldn't get either. Places like BED and LWM were getting heavy white rain...slamming plenty of precip into the buckets, but just not accumulating it on the ground.

[Typhoon Tip]

28 minutes ago, ORH_wxman said:

I dunno...the max snowfall for the eastern zones in MA was really like 4-8pm on the model guidance....I agree the models did seem to go on too long after that, but the core of the best stuff was forecasted mostly late afternoon and early evening....which from a rate standpoint, largely verified. Maybe we're having two different discussions here.....

1. Did downsloping affect things later on? Yes. The precip after 7-8pm did not really match model guidance which suggested perhaps 2-3 more inches for E MA even at modest 7 or 8 to 1 rations.

2. Was downsloping the main reason for the lack of snowfall accumulation between 4-7pm? No (IMHO). I think our cross sections are explaining that better with the "perfect storm" of toxic brew....as Chris said, the lower elevations needed either slightly more LL cold or for dendrites to overcome the lack thereof, and we couldn't get either. Places like BED and LWM were getting heavy white rain...slamming plenty of precip into the buckets, but just not accumulating it on the ground.

hahaha - ...perfect, 'nough said

Yeah, I'm not insinuated ( ...at least I hope - ) that down sloping at a synoptic scale was the whole dagger... 

This was like Cesar on March 15, where - like you hint .. - every douche in the room took turns with the knife.   lol. 

I dunno...radar flushed to light and inspite of attenuating beams and so forth... we went light... like, physically, right then... where the rad flushed light -

Fit did... Bed did... Lunenberg did. Auburn did...I know folks in these areas, and they all were texting me, 'where's the storm?' 

I'm like oh god - 

Frankly?  I'm just glad this isn't March 15 and they're going, 'where's winter' 

[SJonesWX]

at mi casa, it flipped to snow at around 10:45 after about .3” of rain. temp dropped from 36 to 33, and we just rotted on either side of 33 for the rest of the day. the ground got white quickly, and seemed to accumulate quickly. But it was so wet, it just never stacked up. driving around yesterday you could tell that even slightly higher elevations got mor accumulation. interesting storm.

[FXWX]

On ‎12‎/‎5‎/‎2020 at 5:34 PM, dryslot said:

I had it made.

Nice...  I like the look and style... Nothing online the looks anywhere near as nice...