New Zealand Local Weather Forum
General Category => General Discussion => Topic started by: JennyLeez on July 16, 2012, 07:32:30 PM
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I know this has been covered in other forums but having asked a few members of late I have been given varied answers.
So here we go.
What do you class as a Rain day?
What do you class as a Wet day?
and What do you class as a Precipitation Day.
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A day that had some rain[/color]
What do you class as a Wet day? A day when its rained most of the day
and What do you class as a Precipitation Day.A day (24hours)When you have recorded rain
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Rain day = any rainfall that is enough to record in a rain gauge
Wet day = any day with rainfall >= 1.0mm
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Ok I was given this.
Precip day or rain day = 0.2mm or more.
Wet Day = 1.0mm or more
Food for thought.
Now Cumulus users dont show any rain until 1 tip and that 1 tip would = 0.3mm.
Therefore Cumulus users would never have a reading of 0.2mm where as WD users would.
So do WD users have more of a chance of a rain day over Cumulus users :)
There is also a 50% chance if that is the total for the day that it in fact be dew and not rain....yes?
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The tip amount depends on the rain gauge, not the weather software. After one tip Cumulus shows 0.2mm for me
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Fortunately, or unfortunately, how you define the various descriptions of rainfall is vague. It is a good thing in some respects, as the ability of some equipment to measure rainfall is suspect, because the mechanics, electronics and software employed do not provide a consistent result. It is also quite good to keep the definitions vague because rain gauge catchment areas are generally too small to provide accurate measurement of small amounts of rainfall. Rainfall expressed in mm per square meter or Litres per square meter is a simple and recognised standard and your ability to measure low levels of rainfall depends on the size of the catchment and its placement relative to any other objects. This is nicely vague, it depends what you have and where it is, relative to your own definition of rainfall, relative to your ability to measure it. My own personal view is that if it is raining or has been raining, it is a wet day, but to quantify it, I use anything above 0.04 mm as the definition of a wet day but in my system that represents a collected rainfall in excess of 2 Litres. I don't actually think that there is significant benefit from splitting the definitions beyond wet or dry unless it is coupled to other factors which can give an indication of its effect or relationship to a particular area.
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Just to throw in my thoughts. NIWA considers a rain day is 1.0mm or more (according to thier historical averages for rain days) . I see alot of wx stations on this forum regularly record 0.2/0.3mm daily & from my own experience especially in winter this is caused more often than not by dew which from my research does not constitute percipitation unless it was fog! I edit out these 0.2's as I catch them to keep my percipitation stats correct, Some later version Cumulus have since last dry/wet day which restarts the count as soon as the bucket has tipped.
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The Bureau of Metrology in AU:
Rain day
A rain day occurs when a daily rainfall of at least 0.2 mm is recorded.
In the States, NOAA defines a rain day as greater or equal to .01" = 1/100" = 0.25mm
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Perhaps the Australian definitions are appropriate for most purposes :
Extreme Temperature Indices Definition
Very hot days Annual count of days with maximum temperature > 40°C
Hot days Annual count of days with maximum temperature > 35°C
Very hot nights Annual count of nights with minimum temperature > 25°C
Hot nights Annual count of nights with minimum temperature > 20°C
Cold days Annual count of days with maximum temperature < 15°C
Very cold days Annual count of days with maximum temperature < 10°C
Cold nights Annual count of nights with minimum temperature < 5°C
Frost nights Annual count of nights with minimum temperature < 0°C
Warm days Percentage of days with maximum temperature > 90th percentile
Warm nights Percentage of nights with minimum temperature > 90th percentile
Cool days Percentage of days with maximum T < 10th percentile
Cool nights Percentage of nights with minimum T < 10th percentile
Highest maximum temperature Annual maximum value of daily maximum temperature
Highest minimum temperature Annual maximum value of daily minimum temperature
Lowest maximum temperature Annual minimum value of daily maximum temperature
Lowest minimum temperature Annual minimum value of daily minimum temperature
Warm spell duration Annual count of days with at least 4 consecutive days when daily maximum temperature > 90th percentile
Cold spell duration Annual count of nights with at least 4 consecutive nights when daily minimum temperature < 10th percentile
Growing season length Annual (1st July to 30th June) count between first span of 6 or more days with daily mean temperature > 15°C and first span of 6 or more days with daily mean temperature < 15°C
Extreme Precipitation Indices Definition
Wet days Annual count of days with daily precipitation ≥ 1 mm
Heavy precipitation days Annual count of days with daily precipitation ≥ 10 mm
Very heavy precipitation days Annual count of days with daily precipitation ≥ 30 mm
Maximum 1-day precipitation Annual maximum 1-day precipitation total
Maximum 5-day precipitation Annual maximum consecutive 5-day precipitation total
Very wet day precipitation Annual total precipitation when daily precipitation > 95th percentile
Extremely wet day precipitation Annual total precipitation when daily precipitation > 99th percentile
Annual total wet day precipitation Annual total precipitation on wet days (daily precipitation ≥ 1 mm)
Simple daily intensity Annual total precipitation divided by the number of wet days (daily precipitation ≥ 1 mm)
Consecutive dry days Maximum number of consecutive days with daily precipitation < 1 mm
Consecutive wet days Maximum number of consecutive days with daily precipitation ≥ 1 mm
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WD can be set to ignore a tip that is dew
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Cumulus Users have to manually remove.
Thats easy enough but unfortunately it does not correct the last 24 hour value or last hour. If you wish to correct those it means mucking around with day files.
Definitely not ideal.
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Cumulus could have been setup better in that respect. But the day files are where I do it from. Just have to remember cumulus cant be running when you edit them.
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Yep same here.
Steve fixed this a week ago. So thats a help :)
Fix for high hourly rain timestamp being set when no rain
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A rain day is when I think about staying in bed all day and a wet day is when I do just that. A good book, a hot drink to sip and a snuggly bed, a day dreams are made of is a wet day on the hill top!
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My thoughts exactly Babs. Well put ;D
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Its a wet day I should be in bed!
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But going to restaurants and eating chocolate cake is ok... ;)
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thats what you do on a rain day haha