Another questionable spotter report

[rdale]

How do you train people to estimate rain rate?

1) I can't believe this info was passed on to the NWS by net control and 2) I am a little shocked that the NWS office sent them out as rainfall totals.

For all we know this could have been a storm total of 0.04" of rain in a minute. Strange.


..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0640 PM HEAVY RAIN CHERRY VALLEY 42.24N 88.96W
08/13/2010 E2.00 INCH WINNEBAGO IL AMATEUR RADIO

ESTIMATED RATE OF 2 INCHES AN HOUR AT USBUS20 AND I39.

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0604 PM HEAVY RAIN ROCKFORD 42.27N 89.06W
08/13/2010 M2.50 INCH WINNEBAGO IL TRAINED SPOTTER

2.5 INCHES AN HOUR REPORTED AT I20 AND I39


&&

 

[Lanny Dean]

I am unsure how this exactly is "giving spotters everywhere a bad name"
While I agree there is no real way to "measure" rainfall rates per hour, per say, I do not understand how this is giving anyone a bad name?

I suspect that the local NWSFO utilized rainfall rates via the WSR88D and then matched them up to the area and reports in question.

The title of your thread makes no sense to me at all. Maybe a better outline would have been "Another Questionable Spotter Report"

 

[rdale]

I suspect that the local NWSFO utilized rainfall rates via the WSR88D and then matched them up to the area and reports in question.

The 88D doesn't do rain rates either...

My point is that there isn't a training class in the world that 1) teaches this or 2) requests this information.

Title fixed

 

[Tim Shriver]

"My point is that there isn't a training class in the world that 1) teaches this or 2) requests this information."

The WFO here asks for rain fall measurements and rates all the time.
A good weather station can do this.

They do have things on the NWS sites for measuring rain and
have had it in a spotter class or two over the years.

Wow, they also train us how to measure snow too..

Always thought rdale lived in a different world..

Tim

 

[MatthewCarman]

"My point is that there isn't a training class in the world that 1) teaches this or 2) requests this information."

The WFO here asks for rain fall measurements and rates all the time.
A good weather station can do this.

They do have things on the NWS sites for measuring rain and
have had it in a spotter class or two over the years.

Wow, they also train us how to measure snow too..

Always thought rdale lived in a different world..

Tim

Rdale was discussing a report about estimating rainfall. If you measure rainfall it is not an estimate because you know what the exact measurement is. Nothing was ever mentioned about measuring rain. If you know of a weather station that can estimate rain pretty good please explain? I always thought a rain gage measured rain and that a weather station such as GRLevel3 could only guess what could be occurring within a storm. I am not trying to be a jerk so don't take this the wrong way. I am just confused with your post.

 

[Lanny Dean]

The 88D doesn't do rain rates either...Title fixed

Does not do rain rates? Maybe I should have said precip algorithms, AKA
Precipitation Processing System...produces radar-derived rainfall products in real time for forecasters in support of the National Weather Service’s warning and forecast missions. It transforms reflectivity factor measurements into rainfall accumulations and incorporates rain gauge data to improve the radar estimates. The products are used as guidance to issue flood watches and warnings to the public and as input into numerical hydrologic and atmospheric models.

Now that you have fixed your title, maybe it would behoove you to change your post?
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[Andrew Herron]

What if the rain gauge was away from the house and he could only look from his window?

I'd say that would be worthy of calling it an estimation.

Just saying, we do not know the situation beyond the report and there are assumptions being made. If you'd like, I can continue to come up with possibilities that could suggest it was not the spotter at all. Let me know, I've not much to do tonight.

 

[rdale]

A good weather station can do this.

Sure can. But hopefully the spotter and/or net control is smart enough to realize that rainfall rate information by itself is useless, and does the right thing (i.e. asks for more information) before sending.

The 2.5" per hour report can mean anything. It could mean .04" in a minute. Does that harm you in any way? Cause torrential flooding? Nope. It could also mean 10" have fallen in the last four hours. Is that better information? Yep.

They do have things on the NWS sites for measuring rain and have had it in a spotter class or two over the years.

Please show me the training material on their site for teaching spotters how to estimate rainfall rates.

Does not do rain rates?

Correct. There is no 88D product that says "2.5 inches falling per hour over Chicago".

It transforms reflectivity factor measurements into rainfall accumulations

Exactly. It gives you estimated accumulations. Such as "2.3 inches fell since 5pm" or "5.2 inches fell in the last 3 hours." Not rain rates.

What if the rain gauge was away from the house and he could only look from his window?

If you can watch your rain gauge fill up from the back window and tell me how fast it is filling up per hour based on a few minutes of observing, I'll buy you an electronic weather station

 

[Lanny Dean]

rdale,
your statement is incorrect regarding the 88Ds precip algorithms/rainfall rates. It can and does estimate rainfall totals. Wonderful article here:
http://www.srh.noaa.gov/mrx/research/precip/precip.php

IMO this thread is going nowhere. Have a great weekend rdale.

 

[Chris Nuttall]

Sorry for staying off-topic, but I think what rdale is trying to say is that the 88Ds do not display precipitation rates, which is correct. The only products produced are products depicting accumulation. The 88D precip algorithms do calculate rain/snow rates, but these are used in producing the accumulation products and in external applications, such as the Flash Flood Monitoring Program (FFMP).

 

[rdale]

8 It can and does estimate rainfall totals

Which we all are in agreement on. So let me back up to avoid confusion.

If someone asks you "how much rain did you get from that storm?" would you choose to answer them:

1) "I picked up 1.14 inches"
2) "I picked up 3.35 inches per hour"

Answer #1 tells you exactly how much rain the storm left you with. Answer #2 does not, since it does not include a timeframe. Answer #2 is useless, because that could mean you received a tenth of an inch, or you could have received 12 inches.

That's my point. Spotters are not taught anywhere to estimate rainfall rate. First - it's impossible. Second - it's useless.

I'm looking forward to seeing Tim Shriver's training material on rainfall rate estimation. Most spotters can't even get wind estimation right, so I'm interested in seeing how Tim gets his gang to do that and add value to those reports - since I've shown you how they are worthless.

 

[cedwards]

I don't see that as a questionable spotter report at all.
It is "ESTIMATED" heavy rainfall rate. The exact number does not matter much. Maybe he should have specified for "for the last 30 minutes" But a heavy rainfall can leas to flash flooding and IMO should be called in.

He estimated a number rather than saying "It is raining really heavy right now". Some people want quantitative numbers rather than "lots", "big", ...

 

[rdale]

But a heavy rainfall can leas to flash flooding and IMO should be called in.

Heavy rainfall - yes. Heavy rainfall rate - not really. As I pointed out, the report could have been 0.04" in a minute and the shower ended, which is a 2.5" per hour rainfall rate.

Some people want quantitative numbers rather than "lots", "big", ...

True. But that's back to my first question again - how do you teach people to estimate rainfall rate? When you look at the drops, what factors are you taking in to consideration to come up with a number? Or is it just a WAG, in which case giving a number is WORSE than "lots" and "big"...

 

[cedwards]

how do you teach people to estimate rainfall rate?

Sometimes, you can't teach everything. Let people use their own judgment. Net control could have easily asked him how long it has been falling at that rate, if he wanted more details.

This was an ESTIMATION! take it for what it is worth. If you need more details, ask.

 

[rdale]

This was an ESTIMATION! take it for what it is worth. If you need more details, ask.

Thanks for confirming my point exactly!

It was worth nothing without more details. So why didn't NCS get those details, and why didn't the NWS office get them too? That's the topic for a thread on a different forum

 

[jdrenken]

Hopefully when the new MPAR comes into full scale deployment these types of questions won't be brought up because the local NWS will look at their system and say yes or no to a report like this.

 

[Mike Bates]

We had this issue about two months ago here in Colorado. NWS was swamped by spotter giving estimated rates per hour. Some weather stations can provide this information but it is where ever the station and the local spotters do not carry weather stations with them that could measure rain.

After discussion with the NWS Severe Weather Coordinator, we changed to reporting measured rain over a period of time 15, 30, or 60 minute intervals. This provided actual measurements and in some cases we reported at 10 minute intervals since there was lots of flooding in the area.

Rainfall rate per hour based on my experience is a very subjective number and there is no good way without instruments to provide good data...I guess I am saying in this case, estimates just to not work unless you have lots of experience reviewing lots of measured cases.

Mike - N7DQ

 

[Lanny Dean]

The 88D doesn't do rain rates either...Title fixed

???? I have noticed that you clearly avoided this and even changed your statement regard the rain rates, what gives???

 

[Steve Miller]

It's going to be funny when everyone on this board reaches the point that they don't want to report because they fear getting ripped apart by their "peers".

 

[Shane Adams]

It's going to be funny when everyone on this board reaches the point that they don't want to report because they fear getting ripped apart by their "peers".

And when it does happen, they can replace the "reports" forum with "how to be a money chaser while pretending it's about the storms".

 

[rdale]

I have noticed that you clearly avoided this and even changed your statement regard the rain rates, what gives???

I haven't avoided anything, nor have I changed my statement. You were wrong when you said the 88D gives out rain rate data. I said that, and Chris backed it up. I'm not sure what you want me to change?

Rain rates are USELESS. This issue has been around for 20+ years, and thankfully there are people that care about the quality of spotter reports and want to do something about it. Look at the SN review section. It's all about quality and making spotter reports the best they can be.

If you don't care about the quality of Skywarn info, that's your right.

But don't get all in a tizzy because there are people who say spotter reports can be improved.

 

[rdale]

It's going to be funny when everyone on this board reaches the point that they don't want to report because they fear getting ripped apart by their "peers".

That would be funny.

 

[Lanny Dean]

I haven't avoided anything, nor have I changed my statement. You were wrong when you said the 88D gives out rain rate data. I said that, and Chris backed it up. I'm not sure what you want me to change?

Rain rates are USELESS. This issue has been around for 20+ years, and thankfully there are people that care about the quality of spotter reports and want to do something about it. Look at the SN review section. It's all about quality and making spotter reports the best they can be.

If you don't care about the quality of Skywarn info, that's your right.

But don't get all in a tizzy because there are people who say spotter reports can be improved.

I am not getting "tizzy" at all, rdale, I was just trying to point out that I do not understand your statement and that IMO you are incorrect regarding the 88D's ability to calculate rainfall rates.
As far as what Chris said:

The 88D precip algorithms do calculate rain/snow rates, but these are used in producing the accumulation products and in external applications, such as the Flash Flood Monitoring Program (FFMP).

That says it all.

Again, I will direct you to a wonderful read that might help?
http://www.srh.noaa.gov/mrx/research/precip/precip.php

If you don't care about the quality of Skywarn info, that's your right.

Where is this coming from? I did not at all mention not caring about Skywarn info. If anything, I believe the request I made for you to change your original post should have been understood as such.

My mother used to tell me that I would run into people who would argue with a fence post.....

 

[rdale]

you are incorrect regarding the 88D's ability to calculate rainfall rates.

You say tomato - I say tomato.

There is no 88D product that shows rainfall rates.
Spotters should not report rainfall rates, as it is useless without other parameters (i.e. timeframe) and it is impossible to estimate.

 

[Patrick Marsh]

The current 88D networks do not measure rainfall rate. The 88D's measure the reflectivity factor and radial velocity. From the radial velocity, spectrum width can be computed as well.

From the reflectivity factor it is possible to "back out" an instantaneous rainfall rate using one of several different formulas depending on the environment. Again, this is not observed by the 88D; it is a post processed field. From the derived rainfall rates it is possible to then to a time integration to generate an estimated rainfall product.

As for rainfall rates, the smaller the time measurement, the more useful the information. Examples:

2" per hour could be composed of:

1. 0.01" per minute for 10 minutes (0.1" total), 0" per minute for 30 minutes (0" total), then 0.095" per minute for 20 minutes (1.9" total); or
2. 0.033" per minute for 60 minutes (2" total); or
3. 0.066" per minute for 30 minutes (2" total, then 0" per minute for 30 minutes (0" total)

All three of those are equivalent to 2" per hour, however at any given moment the rain rate was different. By decreasing the time component of the rate, you give a higher quality report containing more information about current rainfall intensity. However, without including how long that rate continued, it's impossible to know how much rain fell.

With that said, the best report would be to do one of the following:

1. Rain rate of 0.1" per minute for 10 minutes; or
2. Total rainfall of 1" over the last 10 minutes

Both of these reports are equivalent (1" in 10 minutes) and allows the NWS to compute the missing information (total rain in [1] and rain rate in [2]).