Rainfall rate unrealistic or possible??

[Great Cornholio]

I'm not home right now so I don't have Cumulus to look at, but under all time records my max rainfall rate is over 8 inches per hour. To me that seems like it would be pretty high. So how many bucket tips would that be and is it even a realistic value? We were both out of town for a few days so the computer was off so Cumulus downloaded the data from the data logs of the station. So just wondering if it was a glitch.

The thing that got me really thinking about this is because I live in the Nashville TN area and we have gotten a lot of rain over the past 2 days. My station has over 9.5 inches of rain since about 1400 GMT 5/1. I was curious so I asked the wife what the rain rates were the past 2 days and one was a little more than 3 inches and one more than 4 inches. And she said it was raining pretty hard. So that makes me think that the 8 inches may be unrealistic, but before I edit my all time records I wanted to see what you guys thought. I've only had the station up since the holidays so not much heavy rain for me to go by.

[Gina]

I don't know what counts as very heavy rain in Tennessee but 2 inches an hour in the UK is considered very exceptional and results in pretty devastating flooding. It has been known known but is very rare. I can't remember what the cumulative amount per day was - it could have been that much. A bucket tip is 0.3mm so about 83 per inch.

So, my thoughts are :- 8" an hour seems too much for the rate but 9.5" over 2 days is a lot but I'm pretty sure we've had that much over here occasionally, with consequent flooding.

[mcrossley]

I would check the daily total rainfall figures with a local met. station if possible. But the rate figure is calculated over a 5 minute 'window', so if you have some short, very heavy downpours, the rate can be much higher than the daily total might suggest.

I'm not sure if there is a 'standard' met office definition of rainfall rate - I'm sure there must be somewhere? - but the length of the 'window' it is averaged over will have a big effect on the calculated figure.

[steve]

The rain rate is calculated from a 5 minute period, so a short, very heavy downpour could produce a high hourly rate, but a rate of 8 in/hr equates to over 50 tips in 5 minutes. It's certainly possible - a foot of rain fell in about 40 minutes once in Missouri. But from the other figures you're quoting, my guess would be that the station is 'inventing' some of it.

[Great Cornholio]

The rain rate is calculated from a 5 minute period, so a short, very heavy downpour could produce a high hourly rate, but a rate of 8 in/hr equates to over 50 tips in 5 minutes. It's certainly possible - a foot of rain fell in about 40 minutes once in Missouri. But from the other figures you're quoting, my guess would be that the station is 'inventing' some of it.

TN is right on the border of Tornado Alley so we do get some pretty nasty thunderstorms with very heavy downpours. I just wasn't home and the computer wasn't on so I wasn't sure if it was something that was way out of the realm of possibility. So I will leave that as my all time record.

As for the amount of rain in the past 2 days..I wish I could say that some of it was fake rain, but Nashville has seen record amounts of rain and massive flooding. We got lucky. Just 20 miles to the NW and the total rain was about 14 inches, about 50 or so miles NW was even worse with doppler radar estimates of over 22 inches of rain. Needless to say a lot of Nashville is under water at the moment. Lucky for me my house is apparently at the very top of a very small hill in the neighborhood. Water is in my back yard but still has a long way to go until it gets to the house. Houses to left and right of mine have flooded yards, but most look like even though the water is up to the houses, it is not deep enough to be inside the houses. Different story to the left of my house were 2 houses down the water sounds like it is about 3 or 4 feet deep so water is definitely in that house. There is no way out of the neighborhood since the road out is under at least 1 foot of water. To give you an idea of how close the water is from me each house has an average lot size of 0.5 to 1.0 acres so pretty close together so water is not that far away. Of course I haven't seen any of this in person since I'm out flying around the country. Also hope I have a car when I get home as I have no idea if the employee lot at the airport flooded..the airport had just shy of 13 inches of rain. If I do have a car I have no idea if I can make it home as many of the roads I have to drive on to make it home have been or still are under water so no idea if they have been "washed out". Get off of work in 2 more days so guess I'll find out then...

[steve]

I've just been reading about the recent rainfall in TN on the BBC News site, and I withdraw what I said about it probably being a problem with your station!

[dhrandy]

You can check http://www.wunderground.com/auto/wxmap/ and see what other weather stations around you are getting if you catch it while it's happening or around the same time.

[Great Cornholio]

I've just been reading about the recent rainfall in TN on the BBC News site, and I withdraw what I said about it probably being a problem with your station!

Its pretty bad from what I hear. Earliest I will be able to get home (based in Washington DC so have to get off work and get on a plane to Nashville) will be Wed evening. Assuming I have a car when I get back I'm not sure if I will be able to get home as I hear a lot of roads are still under water or have been washed out...but hopefully most of those problems will be fixed by the time I get there. Oh yeah on a side note the river that runs thru downtown Nashville was at the highest its been since 1937 (when I saw tv at 1800 GMT 5/3) and was forecast to keep rising for at least another day.

As far as the station goes its never reported fake rain before that I haven't physically contributed to. I have the station mounted on a short pole that is mounted to a corner post of my 6 ft tall privacy fence (so the whole station is about 10 ft above ground) I know now that thats too high for the temp and rain and too low for wind, but it works for me...although I may try to move the temp sensor to a spot with more shade as it seems to report higher temps than it probably actually is outside. Anyways the only time that fake rain has happened has been a few times when I've opened the gate to the fence and it has shaken the station causing a "bucket tip".


I've checked out that map and the "interactive wundermap" and have found that for the most part my station comes close to what most stations in the area report. Although the airports and tv stations tend to report slightly higher wind speeds and for some reason my high temps tends to be a few degrees F warmer, but my low temps tend to be a few degrees colder..but the difference is only 3 to 5 degrees so I can live with it..although I may try to find a shady spot for my temp sensor..even though that still wouldn't solve the colder low temp issue...or at least in my head it seems like it wouldn't fix it.