Topic: Rain collection suggestions (given and requested)

[tomcj2]

I have been collecting and reporting data only since the middle of November.  It is a simple enough task, but already I have a few questions and observations to make it even easier.

1)  don't drop the gauge. The second day I didn't get the outer tube on the bracket correctly, it fell and cracked the inner tube about 1/2 inch from the top. I sealed it with a solvent (IPS WELD-ON #16).  The clerk at Tap Plastics was surprised that it had broken as, in his words, "you should be able to take a hammer to polycarbonate".

2) I just ordered a second gauge.  I will have one outside, and the other one  upside down, drying out in my office.  From now on I will only have to make 1 trip outside to  replace the gauge and then return to my warm, dry kitchen to take the reading. This should also give me a more accurate measurement during times of heavy rain as I would not be missing any rain during the few minutes I take while reading the single unit.

3) I have tried weighing the gauge to calculate the rain without much success.  The dew on the exterior will add up to 9 grams to the tare weight.  I am going to try wiping the exterior off, remove the funnel (the funnel would be hard to dry)  and then measure the gross weight.  I would only want to use this method in the event of a rain day with more than 1 inch so lessen the risk of loosing water when pouring from the large to the small tube, and even then I would use the weight method of double checking my data. Any suggestions?

On a side note I was surprised and disappointed that my VP2 appears to be reading 25% low.  After I have collected a couple of months data I will crunch the numbers and request help in deciding what to do about it, such as put in an offset, and change the data in VWS. 

[92merc]

On the VP2, make sure your sensor suite is level. Mine was off when I first moved in.  I was running about that 25% off too.  Eye-balling it, it didn't look bad.  But it was off.

Since then, I've taken down the suite off the roof and put it on a post in the backyard.  I also put my manual rain gauge right next to it.  Only time I notice a difference now is when it's windy out and rains.  Otherwise, I'm spot on now.

[WeatherBeacon]

...
1)  don't drop the gauge. The second day I didn't get the outer tube on the bracket correctly, it fell and cracked the inner tube about 1/2 inch from the top. I sealed it with a solvent (IPS WELD-ON #16).  The clerk at Tap Plastics was surprised that it had broken as, in his words, "you should be able to take a hammer to polycarbonate".
...

My outer tube broke, too, about 3 weeks after getting it.

[ocala]

Tom.
On your VP rain gauge reporting incorrectly. Take off the rain bucket. Underneath the tipping mechanism there are adjustment screws.
Fill your manual gauge with with a selected amount of water.
Pour that in a styrofoam cup with a pin hole at the bottom.
Sit the cup in the rain bucket then see what total you get on the console.
Adjust the screws as necessary.
I did this with mine and calibrated it as close as .02. However on heavy rain events it is off more.
Use this link here for more info on calibrating your gauge.
http://www.weatherstations.co.uk/vp_faqt2.stm

[George Richardson]

Ocala

This seems to me to be the best calibrating instruction I have ever seen. I do have a couple of questions. How much "rain" would make a good test and how long would it take to carry out. Second, how do you read the testing "rain" without it getting into your computer/internet records? As far as amount, I was thinking in the 1/2" range. What say you?

As far as a cautionary note on adjusting; there is an adjustment screw under each tip bucket and they both must be adjusted exactly the same amount ie. number of turns and direction of turns. I think on the Davis VP2, a full rotation is 5 to 6% (check me on that!)

FWIW

George

[ocala]

George a 1/2 inch should do just fine.
As for the hole in the cup, try different sizes. A small one would get a better calibration but a large one would get more over flow during the tipping process thus causing a lower reading on the console. I would find a value somewhere in the middle, but I would lean toward the calibration of the smaller hole.
As for the bogus data, you could unplug the rain connection at the ISS and count the tips but that would be boring.
I would just let the software take the data and go back later and edit it. I use WL so it was pretty easy. Not sure how VWS or WD handle that.
Also if you have a website I would disable the FTP process while doing it.

[racenet]

Just remove the datalogger, do the test and then edit the added total from the test out of the console. Put it all back together. The software will have no idea of anything different. 



Bob

[ocala]

Just remove the datalogger, do the test and then edit the added total from the test out of the console. Put it all back together. The software will have no idea of anything different. 



Bob

There you go.

[SlowModem]

tom said I would only want to use this method in the event of a rain day with more than 1 inch so lessen the risk of loosing water when pouring from the large to the small tube

I keep the small inner tube in the house now since I have read that  it will freeze and crack in the cold.

I learned my lesson a couple of months ago when we had around 4 inches of rain in a 24-hour period.  Be sure and put the funnel into the small tube before pouring the big tube into the small tube.  Also, be sure to have a firm grip on both!  Pour slowly.  It can get messy.  (that's the voice of experience talking!) 

[tomcj2]

I am glad that I live in an area that seldom gets snow.  Doing the measurements is a cold, time consuming process.  I did learn that the process can be speeded up by transferring the core sample to a large Pyrex measuring cup, cover it with plastic wrap and melt it in the microwave.

I purchased a second CoCoRaHS rain gauge and it does make life easier.  Only 1 trip outside, and I can do the measurement in my warm kitchen.  The other advantage is that the gauge I put out every day is totally dry so there is no possibility of submitting an erroneous report of a "Trace Percipitation"

[W Thomas]

I usually grab the collector from the post in the early am as I go on my hourly wood run   or when I warm up the truck, bring it inside and do the melting and measuring. After all that's through I wipe it as dry as possible and return it to the mount on the way out.

I have really thought a lot about pointing a camera at the collector and reading from inside LOL!

[wxtech]

3) I have tried weighing the gauge to calculate the rain without much success.  The dew on the exterior will add up to 9 grams to the tare weight.  I am going to try wiping the exterior off, remove the funnel (the funnel would be hard to dry)  and then measure the gross weight.  I would only want to use this method in the event of a rain day with more than 1 inch so lessen the risk of loosing water when pouring from the large to the small tube, and even then I would use the weight method of double checking my data. Any suggestions?

Tom,
About weighing the rain; I have a NWS Fischer-Porter weighing rain gauge.  It records a month of rain.  It has a resolution of only 1/10 inch.  But it is 100% accurate with the NWS Standard Rain Gauge (& CoCoRaHS gauge). 
Maybe you can pour your daily rain accumulation into a monthly rain container and weigh the big container at the end of the month.

We talked about rain measuring inaccuracies; misreading or rounding off daily rain amounts may become a few hundreths of an inch after a month or two.  A manual long-term rain gauge that did not get emptied daily would then be more accurate than a daily rain gauge.

All needed is a big water jug with a CoCoRaHS gauge funnel fitted to the top.  Wrap a blanket around the jug to prevent sun exposure causing evaporation.  The rain amount collected in the jug should equal the amount reported to CoCoRaHS.

[port1]

  One of the biggest advantages of having the manual rain gauge is to verify the accuracy of the tipping calibration of your weather station gauge.  Both of mine are spot on.

[Chris H.]

...
1)  don't drop the gauge. The second day I didn't get the outer tube on the bracket correctly, it fell and cracked the inner tube about 1/2 inch from the top. I sealed it with a solvent (IPS WELD-ON #16).  The clerk at Tap Plastics was surprised that it had broken as, in his words, "you should be able to take a hammer to polycarbonate".
...

My outer tube broke, too, about 3 weeks after getting it.

Ice cracked the funnel on mine. But it isn't falling apart yet..I've had it for almost 3 years now (my how time flies)