New NWS snow measurement guide

[famartin]

http://www.nws.noaa.gov/om/coop/reference/Snow_Measurement_Guidelines.pdf

 

It is my understanding that the primary goal of the re-write is to "reduce snowfall inflation", which some believe the previous guidelines encouraged.

[Absolute Humidity]

http://www.nws.noaa.gov/om/coop/reference/Snow_Measurement_Guidelines.pdf

 

It is my understanding that the primary goal of the re-write is to "reduce snowfall inflation", which some believe the previous guidelines encouraged.

Probably the most significant change is the elimination of clearing your board every 6 hours during snow fall. Instead the new guidelines want everyone to only measure the total depth every six hours and to report your maximum depth (within a 24 hr period) at the end of said 24 hr period. So no more board cleaning every 6 hrs. They feel this has a tendency to inflate totals as I agree.

[famartin]

Probably the most significant change is the elimination of clearing your board every 6 hours during snow fall. Instead the new guidelines want everyone to only measure the total depth every six hours and to report your maximum depth (within a 24 hr period) at the end of said 24 hr period. So no more board cleaning every 6 hrs. They feel this has a tendency to inflate totals as I agree.

 

An additional change of significance is that snow that melts and re-accumulates is not to be factored in; only the maximum new depth during the 24-hour period is to be reported as snowfall.  Previously you would have factored melting into your total.

 

Example: Previously, if 5" fell, 2" melted, then another 4" fell, your total was 9".  Now you just report the maximum depth (in this case, likely 7").

[Absolute Humidity]

An additional change of significance is that snow that melts and re-accumulates is not to be factored in; only the maximum new depth during the 24-hour period is to be reported as snowfall.  Previously you would have factored melting into your total.

 

Example: Previously, if 5" fell, 2" melted, then another 4" fell, your total was 9".  Now you just report the maximum depth (in this case, likely 7").

It sure does make sense since that fallen total of 9" never lived on the ground all at once. Case in point, my Jan 26-27 2010 total of 17.3" would likely be around 15" since two inches of round one were lost due to mixing issues for several hours that day depending on the interval.

[famartin]

It sure does make sense since that fallen total of 9" never lived on the ground all at once. Case in point, my Jan 26-27 2010 total of 17.3" would likely be around 15" since two inches of round one were lost due to mixing issues for several hours that day depending on the interval.

Depends on how you look at it.  If, say, you were shoveling or plowing... did you shovel/plow 9" or 7"?  You probably cleared your walkway/roadway more than once during the storm, so...

[Stebo]

I think this is a bad policy change, to me it is more that you are measuring the maximum snow depth of an event. I mean what if you have an event that starts as snow, goes to ice and then back to snow. You might have maybe a maximum of 4" of depth throughout the event but could easily get two times as much snow to fall.

[famartin]

I think this is a bad policy change, to me it is more that you are measuring the maximum snow depth of an event. I mean what if you have an event that starts as snow, goes to ice and then back to snow. You might have maybe a maximum of 4" of depth throughout the event but could easily get two times as much snow to fall.

There is, as you are of course aware, a climatological element called snow depth.  I fear, however, that it is often ignored, even by those in the climate field who perhaps should be paying more attention to it.  Perhaps it is just because "snowfall" gets a lot more media hype compared to "snow depth".  I feel the latter is a better climatological element.  Snowfall's usefulness is more "weather" than "climate".

[NorthShoreWx]

An additional change of significance is that snow that melts and re-accumulates is not to be factored in; only the maximum new depth during the 24-hour period is to be reported as snowfall.  Previously you would have factored melting into your total.

 

Example: Previously, if 5" fell, 2" melted, then another 4" fell, your total was 9".  Now you just report the maximum depth (in this case, likely 7").

 

Thanks for posting that Ray!

 

Although it is clear about snow that accumulates, melts and then accumulates more, I don't see something that would specifically address a situation with phase changes that do not cause melting, for example a significant period of sleet sandwiched between periods of accumulating snowfall.  Max depth could be misleading in this example.  In the past snow was measured at phase changes, then the board was wiped,

 

Eliminating the 6 hour board clearing actually makes things easier.

 

I make my snowfall measurements for the actual day (12AM - 11:59PM), but usually measure melted precip around 9AM.  Does that need to get synchronized?  That might pose some logistical problems.

[Absolute Humidity]

Depends on how you look at it.  If, say, you were shoveling or plowing... did you shovel/plow 9" or 7"?  You probably cleared your walkway/roadway more than once during the storm, so...

Good point.

[famartin]

Thanks for posting that Ray!

 

Although it is clear about snow that accumulates, melts and then accumulates more, I don't see something that would specifically address a situation with phase changes that do not cause melting, for example a significant period of sleet sandwiched between periods of accumulating snowfall.  Max depth could be misleading in this example.  In the past snow was measured at phase changes, then the board was wiped,

 

Eliminating the 6 hour board clearing actually makes things easier.

 

I make my snowfall measurements for the actual day (12AM - 11:59PM), but usually measure melted precip around 9AM.  Does that need to get synchronized?  That might pose some logistical problems.

 

The new guidelines are very clear:  Only maximum snow depth on the snow measurement board during the 24-hour period is to be reported as snowfall.  There will no longer be any board clearing at phase changes or storm interruptions.  The most interesting example of this is if you have a 2" snowfall, it completely melts, and then another 2" falls... your snowfall is now to be reported as 2", since that is your maximum snow depth on your snow board.  Previously, you would've added them together.  That practice is now forbidden.

 

As far as your snow vs. precip measurements... what are you reporting them to?  If its just your own personal records, you can do them whenever you like.  If you are using them for CoCoRaHS, then ideally they would be synchronized.

[Stebo]

There is, as you are of course aware, a climatological element called snow depth.  I fear, however, that it is often ignored, even by those in the climate field who perhaps should be paying more attention to it.  Perhaps it is just because "snowfall" gets a lot more media hype compared to "snow depth".  I feel the latter is a better climatological element.  Snowfall's usefulness is more "weather" than "climate".

Yes, the thing too with respect to airports many do measure hourly snowfall changes, which is where you get the SNINCR group in the observations when you get an inch+ in an hour. Does this go away from observing?

[famartin]

Yes, the thing too with respect to airports many do measure hourly snowfall changes, which is where you get the SNINCR group in the observations when you get an inch+ in an hour. Does this go away from observing?

I don't think those are affected at all.  These guidelines are meant primarily for NWS climatological observations.  Note also that 6-hour measurements followed by board-clearing will still continue at airport Contract Weather Observation stations, snow-paid observer stations, and NWS offices. 

[Stebo]

I don't think those are affected at all.  These guidelines are meant primarily for NWS climatological observations.  Note also that 6-hour measurements followed by board-clearing will still continue at airport Contract Weather Observation stations, snow-paid observer stations, and NWS offices. 

 

Well then there is a disconnect there, as you are going to have one group with much higher totals compared to the other.

[Chicago Storm]

The new "guidelines" are terrible.

 

With the new guide you're pretty much tracking snow-depth (for a max) through the given day.

 

The biggest issues will be in events that feature high wind, marginal temps and changing precip types. For example, say you have an event that features changing precip types. You start off with snow in the early morning hours that accumulates 2". You then transition to rain for several hours during the day, with the previous snow accumulation melting. Precip changes back over to snow during the evening with new accumulation of 4". The new guidelines would say you only had 4" of snow, when in reality you had 6" fall and accumulate.

 

The same can be said the the other aforementioned issues.

[Chicago Storm]

I don't think those are affected at all.  These guidelines are meant primarily for NWS climatological observations.  Note also that 6-hour measurements followed by board-clearing will still continue at airport Contract Weather Observation stations, snow-paid observer stations, and NWS offices. 

This makes it even more lol worthy.

[famartin]

Well then there is a disconnect there, as you are going to have one group with much higher totals compared to the other.

 

It would seem that way.  The goals communicated to me by those who made this change essentially consisted of "forcibly" lowering COOP snowfall totals, since many COOPs are poor snowfall reporters in the first place; these guidelines would bring the better reporters down towards the poor reporters, making everyone closer together overall.  I am paraphrasing, but it was pretty clear based on what was said.

[OHweather]

Well then there is a disconnect there, as you are going to have one group with much higher totals compared to the other.

I don't measure snow for the NWS right now so this doesn't directly impacting me, but reading through the linked PDF and this thread, this is an issue that popped into my mind.

 

If you have a system that has a change to rain or a mix, or perhaps snow, a break with some melting, and then additional snow after one of those things occurs you'll get a much lower maximum depth if you only clear your board every 24 hours than if you clear it every 6 hours and add the maximum depths from those periods.

 

What also doesn't make sense to me is the example famartin gave of say 2" of snow falling, completely melting, and then another 2" falling now forbidden to be reported as 4". If this occurs at an airport or another location that clears their boards every 6 hours it would be reported as 4" if it fell in two different 6 hour periods...someone who clears their board once a day it would be reported as half of that. Heck even if all of that occurred in a 6 hour period (as unlikely as it may be to have all that happen in such a short period) it seems like a severe misrepresentation of how much snow fell. 4" of snow falling is 4" of snow, it shouldn't be counted as say 2" in this example just because that was the maximum depth during the given time period.

 

But again that's just me, I don't measure for the NWS but am concerned a bit about how this will all play out.

[Stebo]

It would seem that way.  The goals communicated to me by those who made this change essentially consisted of "forcibly" lowering COOP snowfall totals, since many COOPs are poor snowfall reporters in the first place; these guidelines would bring the better reporters down towards the poor reporters, making everyone closer together overall.  I am paraphrasing, but it was pretty clear based on what was said.

Wouldn't it make more sense to work with the COOPs and help with training them to measure better. I know that probably boils down to a 'no' due to lack of funding but to me that would make more sense than changing things like this.

[famartin]

Wouldn't it make more sense to work with the COOPs and help with training them to measure better. I know that probably boils down to a 'no' due to lack of funding but to me that would make more sense than changing things like this.

Perhaps, though there is some belief that COOPs have never been that great with snowfall and it would be best to work on a "standard, low-ball measurement guide".  At least, that's my interpretation of what has been said to me about this.  Therefore, keeping COOPs "low" would be in keeping with climatological practices of the past.

[famartin]

If you have a system that has a change to rain or a mix, or perhaps snow, a break with some melting, and then additional snow after one of those things occurs you'll get a much lower maximum depth if you only clear your board every 24 hours than if you clear it every 6 hours and add the maximum depths from those periods.

 

Correct.  This is apparently a goal of the new guidelines.

[Stebo]

Perhaps, though there is some belief that COOPs have never been that great with snowfall and it would be best to work on a "standard, low-ball measurement guide".  At least, that's my interpretation of what has been said to me about this.  Therefore, keeping COOPs "low" would be in keeping with climatological practices of the past.

 

 

Oh trust me, I understand that there is a bit of a fluff up so to speak from some COOPs but I'd like to think that most are within the range of error. I mean I don't think this is a situation where your paid observers are well below the COOPs.

[Stebo]

Correct.  This is apparently a goal of the new guidelines.

 

That is a bad goal then, 4" is 4" not 2". I mean hell what if the snowfall fell during a blizzard and got blown off the snow board, you could very well low ball the snowfall by several inches then.

[famartin]

Oh trust me, I understand that there is a bit of a fluff up so to speak from some COOPs but I'd like to think that most are within the range of error. I mean I don't think this is a situation where your paid observers are well below the COOPs.

 

I don't know how most CoCoRaHS observers are measuring.  If they are doing it by the way the training teaches, they are probably measuring at storm's end (max depth) and clearing, versus clearing every 6 hours.  I recently made a map of last winter's snowfall in NJ, and you wouldn't really be able to tell which stations were 6-hourly and which were 24-hour.  I think the bigger difference was between observers who measured conscientiously at max depth, versus those who waited until ob time. 

 

I've had my parents use the 6-hourly method.  It was said to me that the 6-hour method inflates snowfall, yet they were the LOWEST in their county.  Maybe its because I make sure they use the board the right way.  I suspect there are observers who set the board back into the same hole every 6 hours, and obviously that COULD inflate snowfall.

[Stebo]

I don't know how most CoCoRaHS observers are measuring.  If they are doing it by the way the training teaches, they are probably measuring at storm's end (max depth) and clearing, versus clearing every 6 hours.  I recently made a map of last winter's snowfall in NJ, and you wouldn't really be able to tell which stations were 6-hourly and which were 24-hour.  I think the bigger difference was between observers who measured conscientiously at max depth, versus those who waited until ob time. 

 

I've had my parents use the 6-hourly method.  It was said to me that the 6-hour method inflates snowfall, yet they were the LOWEST in their county.  Maybe its because I make sure they use the board the right way.  I suspect there are observers who set the board back into the same hole every 6 hours, and obviously that COULD inflate snowfall.

I could see this, but I don't think it is that big of an issue compared to what will be happening now with the severe low balling of snowfalls.

[NorthShoreWx]

... this change essentially consisted of "forcibly" lowering COOP snowfall totals, since many COOPs are poor snowfall reporters in the first place; these guidelines would bring the better reporters down towards the poor reporters, making everyone closer together overall.  I am paraphrasing, but it was pretty clear based on what was said.

Sounds like common core applied to snowfall measurements

[famartin]

I could see this, but I don't think it is that big of an issue compared to what will be happening now with the severe low balling of snowfalls.

The biggest impact will be on those (probably few) COOPs which do do 6-hour measurements; they may now report lower.  The other impact will be on those events with change-overs, or multiple snowfalls in a 24-hour period with melting in between; those events will get lowered measurements compared to previously.  At least at those COOPs with conscientious snowfall observers.  Like I said, many don't have them.

[Absolute Humidity]

I just checked CocoRaHS and they do not mention the six hour board clearing method. Not sure if they ever did. Their measuring guidelines sound pretty similar to these new ones if not more simplified. Rarely do I clear off the board in intervals and almost exclusively measure the total at end of a snowfall then report. I suspect most folks would do it this way but who knows.

[famartin]

I just checked CocoRaHS and they do not mention the six hour board clearing method. Not sure if they ever did. Their measuring guidelines sound pretty similar to these new ones if not more simplified. Rarely do I clear off the board in intervals and almost exclusively measure the total at end of a snowfall then report. I suspect most folks would do it this way but who knows.

Likely correct, which is why enforcing a "lowered" total on all is probably going to make measurements more consistent.  Consistently a little low, of course.  Though EWR, PHL and ACY certainly didn't stand out as "high" on the snow map I made, and I *know* they are using the 6-hour method.  My parents also didn't stand out. 

[Absolute Humidity]

Likely correct, which is why enforcing a "lowered" total on all is probably going to make measurements more consistent.  Consistently a little low, of course.  Though EWR, PHL and ACY certainly didn't stand out as "high" on the snow map I made, and I *know* they are using the 6-hour method.  My parents also didn't stand out.

True, though our snowfalls last year were rather uniform, beginning to end events with little or no breaks or mixing In between.

[famartin]

True, though our snowfalls last year were rather uniform, beginning to end events with little or no breaks or mixing In between.

 

This is true.  I did also do maps for the prior winters.  I don't recall my parents, EWR or ACY standing out in any of them... though the observer at PHL kinda did.