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December 16-17, 2020 Storm Observations and Nowcast


wdrag
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11 hours ago, wdrag said:

Snow measuring: CoCORAHS guidance is deepest in 24 hours from time it began for storm total (greater 24hrs, clean the board and add whatever hours beyond). 

However, not all offices do that. I know in Mt Holly,  to limit snowmelt and or drifting problems, clean the board every 6 hours.  That's what I'll be doing at 845PM tonight.

Mat from NJ Climate Center may be commenting-adding on.  

 

 

 

 

When the guidance on measuring snow changed several years ago (and for the life of me I can't find when it happened, but I remember that it did indeed happen), the instructions included that the board would no longer be wiped at a phase change.  I've never agreed with that. As a hypothetical example:

1. In a 20 hour period 3" sleet falls with 1.00" liquid followed by 6" snow with 0.5" liquid.  Total precip =1.50" Daily Snow measured = 9"

2.  Same scenario but the snow falls first and gets beaten into unconsciousness by the sleet.  (assuming for this exercise that the snow and sleet depth at end was 6") Total precip = 1.50" Daily Snow measured = 6"

The exact same precip fell in both storms and its all still lying on the ground, but a casual observer would easily conclude that the event where 9" was measured was bigger than the 6" event.

You can make inferences based on the liquid equivalent, but in the end you are losing information about the amount of snow and sleet that fell.  In many ways snow depth and SWE are more important metrics, but snowfall is a different statistic and is what most of us are more interested in :)

That being said, there were a lot of phase changes tonight.

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3 minutes ago, NorthShoreWx said:

When the guidance on measuring snow changed several years ago (and for the life of me I can't find when it happened, but I remember that id did indeed happen), the instructions included that the board would no longer be wiped at a phase change.  I've never agreed with that. As a hypothetical example:

1. In a 20 hour period 3" sleet falls with 1.00" liquid followed by 6" snow with 0.5" liquid.  Total precip =1.50" Daily Snow measured = 9"

2.  Same scenario but the snow falls first and gets beaten into unconsciousness by the sleet.  (assuming for this exercise that the snow and sleet depth at end was 6") Total precip = 1.50" Daily Snow measured = 6"

The exact same precip fell in both storms and its all still lying on the ground, but a casual observer would easily conclude that the event where 9" was measured was bigger than the 6" event.

You can make infereneces based on the liquid equivalent, but in the end you are losing information about the amount of snow and sleet that fell.  In many ways snow depth and SWE are more important metrics, but snowfall is a different statistic and is what most of us are more interested in :)

That being said, there were a lot of phase changes tonight.

I've had the same discussion with several people since the change and I agree with you 110% for the same reason. Unfortunately those in power do not.

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Concerned about CLI DB.  Someone please correct me.  I see the excellent midnight CP 6.5" yet, the CLI does not show this as a record. XMACIS does. Why the difference between XMACIS Daily Almanac and the OKX CLI  (5.3 vs 7.0).  Thank you very much in advance. 

Almanac for New York-Central Park Area, NY (ThreadEx)
December 16, 2020
Daily Data Observed Normal Record Highest Record Lowest
Max Temperature M 43 63 in 1971 19 in 1886
Min Temperature M 32 48 in 1971 7 in 1876
Avg Temperature M 37.2 55.5 in 1971 14.5 in 1917
Precipitation  M 0.12 2.25 in 1974 0.00 in 2017
Snowfall  M 0.2 5.3 in 1948 0.0 in 2019
Snow Depth  M - 10 in 1960 0 in 2019
HDD (base 65)  M 28 50 in 1917 9 in 1971
CDD (base 65)  M 0 0 in 2019 0 in 2019

 

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Be thankful for whatever we get.  I forgot... NWS doesn't have snow climo anymore for POU, MPO. So I guess we won't know for sure on amounts per NWS CLI. Just have to regionalize average the nearby CoCORAHS etc values. BDR daily RER snowfall 6.5",  ABE 9.2, PHL 6.3 - the latter PA values not daily RER's. 

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Jackpot areas so far: 25-28" reports very near BGM (3 reports 25 or more), and multiple 20's IPT. Here's a look at reports that posted thru 350AM. 

Power outage problem did materialize as I anticipated. That is good news. 

Have not looked at guidance since 930PM last night.

 

Screen_Shot_2020-12-17_at_4_00.15_AM.png

Screen_Shot_2020-12-17_at_3_59.26_AM.png

Screen_Shot_2020-12-17_at_3_59.48_AM.png

Screen_Shot_2020-12-17_at_4_00.01_AM.png

Screen_Shot_2020-12-17_at_4_00.56_AM.png

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6 hours ago, RU848789 said:

As of 9 pm we have 5.75" OTG - slowed down a bit the last 30 min with the radar break; hoping it picks back up soon.  Pretty happy so far.  Would love to get to 10".  26F now.  

We had 6.0" at 11 pm and then after finishing up poker around 1 am, I went out and shoveled while it was snowing mostly lightly (had sleet before then) and finished around 3 am. We got about another 1" from 11-3 for a probable final tally of 7.0", which matches up well with the 6.5-7.5" amounts I've seen in northern Middlesex County; we did get 12-16" drifts, lol. Not quite the 8-12" range I was thinking for the 95 corridor, but not that far off either. Was certainly a fun storm to track and enjoy. I had cleared the board at 11 pm and we got about 1/2" of sleet and a 1/2" of snow, which would've been about 2" if all snow (which would've been 8" total). Yeah a foot would've been nice, but I got almost as much as all last winter, so i'm pretty happy.

Was interesting to see how many of the areas predicted to get maybe 1-3/2-4", like much of SNJ near Philly (which got 6.3") and northern Ocean and much of Monmouth County ended up getting 4-7", so those areas overperformed while the 95 corridor underperformed a fair amount vs. the NWS forecasts, but weren't too bad vs. the 6-12" forecasts many had.

And the areas NW of 95 and well NW that were forecast to get 12-18" (and up to 20" in spots) busted pretty badly as I've only seen a few reports over 10" with only the Poconos getting over 12". The 8-14" for NYC/LI busted moderately, as they mostly got 4-8" with Central Park getting 6.5", more than last winter although maybe it's not quite done there yet. Turns out that it wasn't really the sleet that got us nearly as much as simply not getting the precip. The areas that got all the precip were huge swaths of central/northern PA and much of NY from Binghamton to Albany, where many locations got over 20" of snow (and some places got 30").

Some folks may still pick up another inch or so (we're getting some light snow still). And yes, my back is killng me, lol - this is why I usually shovel every 3-4" and not all at once...

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23 minutes ago, wdrag said:

Be thankful for whatever we get.  I forgot... NWS doesn't have snow climo anymore for POU, MPO. So I guess we won't know for sure on amounts per NWS CLI. Just have to regionalize average the nearby CoCORAHS etc values. BDR daily RER snowfall 6.5",  ABE 9.2, PHL 6.3 - the latter PA values not daily RER's. 

Why don't they have snow climo at POU anymore?

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3 minutes ago, jysamuel said:

Found the jackpot - once in a lifetime event going on in Upstate NY --> southern NE :blink:

Makes us look like plebeians worrying over inches while they're measuring in 2-foot increments lol 

 

Busted forecast to an incredibly positive degree. IMBY our forecast for around 18-24 still seems good but kind of pathetic in comparison, lmao.

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2 hours ago, NorthShoreWx said:

When the guidance on measuring snow changed several years ago (and for the life of me I can't find when it happened, but I remember that it did indeed happen), the instructions included that the board would no longer be wiped at a phase change.  I've never agreed with that. As a hypothetical example:

1. In a 20 hour period 3" sleet falls with 1.00" liquid followed by 6" snow with 0.5" liquid.  Total precip =1.50" Daily Snow measured = 9"

2.  Same scenario but the snow falls first and gets beaten into unconsciousness by the sleet.  (assuming for this exercise that the snow and sleet depth at end was 6") Total precip = 1.50" Daily Snow measured = 6"

The exact same precip fell in both storms and its all still lying on the ground, but a casual observer would easily conclude that the event where 9" was measured was bigger than the 6" event.

You can make inferences based on the liquid equivalent, but in the end you are losing information about the amount of snow and sleet that fell.  In many ways snow depth and SWE are more important metrics, but snowfall is a different statistic and is what most of us are more interested in :)

That being said, there were a lot of phase changes tonight.

Thanks!  I agree w you.  My guess is that there will eventually be some sort of normalization of this snowfall data, as NHC with prior history etc etc.  

 

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14 minutes ago, gravitylover said:

Why don't they have snow climo at POU anymore?

ALY can answer, but my understanding, similar to many offices... can't find and train a reliable observer within the requirements of NWS CLI to be representative of previous POU observer location.  Something like that. Takes time, effort, conscientiousness, paying attention to detail and maybe we don't pay enough. NWS has other resources including CoCoRAHS, CO-OP observers, NOHRSC, etc. 

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1 hour ago, wdrag said:

CP: I did not check, will try in an hour but if someone has the answer. The 6.5 " in CP in one day is largest since??? Thanks. 

There was a 7.0” figure in 1896. It was a 2-day figure (12/15-16) in the daily data, but all but 0.02” precipitation fell on 12/16. That may explain why all 7.0” was allocated to 12/16.

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