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December 5-6, 2020 Storm Observations and Nowcast


Baroclinic Zone
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12 hours ago, ORH_wxman said:

When everyone was flipping to snow ahead of schedule I thought it was going to be a positive bust...LOL. Shows how quickly things can change. I was sure that the 128 belt was gonna get rocked. They were changing over around 2pm and it looked excellent for hours...but they just never mustered the intensity after the flip. The low level temps were a problem but I’m still surprised. I guess maybe the lift wasn’t quite lining up perfectly in DGZ which really helps in marginal setups. You need everything to go right...esp at lower elevations and perhaps that was the one ingredient missing in an otherwise perfect opportunity to overcome the marginal near-sfc layer. 

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. 

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4 minutes 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. 

That’s a good point about dropping flakes in a near 32 layer that is thousands of feet thick. 

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1 minute ago, Lava Rock said:
37 minutes ago, PWMan said:
0.5” in Scarborough

Really? I thought they were frcsting 5" or so

And I ended up with 2.9" 

It was probably more, but I was fast asleep when the snow ended and the board was a wind blown/compacted 0.4" after my 2.5" midnight ob.

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20 minutes 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. 

Yea when I flipped and started accumulating fast I thought for sure 12 was a distinct possibility. This quieted my appetite, but I’m already craving more! Thankfully it’s December and not late Feb. Any 12+ potential and I’m on the road these days, gotta enjoy my 30s no regrets!

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1 hour ago, OceanStWx said:

It takes some stones to forecast a significant period of 3:1 or worse ratio. 

I had a general 3-5" in my Portland/Augusta/Bangor forecast when I left on Friday, but given what the NWS and folks on the board were discussing, I was really worried I was going to bust low. I'm glad there was such a struggle in that regard. Lack of drier dewpoint advection and strong lift but in the wrong spot kinda makes sense to me. Given the lack of good antecedent airmass, there's more bust potential if things don't align. 

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13 minutes ago, STILL N OF PIKE said:

This storm was impossible to forecast in CP of Maine 

We’re about 1/2 mile from the ocean. Wouldn’t be surprised if there’s more west of Route 1.  Good discussion earlier about the torched layer and how it likely inhibited accumulation even with decent intensity. When we started to flip around noon I figured we were primed for a thumping.

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