Heavy Rain Risk Sunday Night/Monday

WolfeIRE

The HIRLAM suggest that Connaught and Donegal, along with the upper Midlands will see the most rain tonight and tomorrow. A lot of places will escape with the odd shower or two. Thursday looks to be the best day of the week before Friday brings another band of rain across the country from the west.

pauldry

Chicken Run wrote: »

so
rain gauges
can I make one at home ??
I'm bored and can't work cos it's raining...
Normally gauge the amount of rain by what's in the horse's empty feed bucket but it tipped over in the wind.

Best way to make a rain gauge thats simple,

Get a 2 litre water bottle from supermarket flat bottom (ooh)better
Cut off top quarter as even as possible
put this back into bottle upside down
paper clip both sides for added support
put bottle into a pot of stones or something to hold it steady and level
put in a cool place that gets little sun to avoid evaporation
measure mm with ruler after a days rain;)

Su Campu

pauldry wrote: »

Best way to make a rain gauge thats simple,

Get a 2 litre water bottle from supermarket flat bottom (ooh)better
Cut off top quarter as even as possible
put this back into bottle upside down
paper clip both sides for added support
put bottle into a pot of stones or something to hold it steady and level
put in a cool place that gets little sun to avoid evaporation
measure mm with ruler after a days rain;)

Measuring the depth of water that way does not convert into mms rainfall as quoted officially. 1mm rainfall means a depth of 1.0mm over an area of 1.0m², ie. 1 litre. So a bottle with a small "funnel" will catch only a fraction of that litre, therefore you will need to take the area of the funnel into account. Measure this area, and divide it into the number of mms of water you measure in the bottle.

Eg. your bottle has a diameter of 15cms, so a radius r of 7.5cms (0.075m). It's area will be pi*r², (3.142 x 0.075²) = 0.0177m²

If you measure say 2.5mm in the bottle after a day, then your actual rainfall will be

2.5 / 0.0177 = 141.2mm (a lot!). To measure a small rainfall amount (say 5mm, you would only have a depth of 0.09mm in your bottle - impossible to measure accurately. That's why it's good to have as large an area as possible feeding into a narrow bottle, like a graduated cylinder.

Danno

From a standard 5" gague 10mm rain weighs 127g.

pauldry

Crikey?

So better take out that applied Maths book then:)

Joe Public

Su Campu wrote: »

Measuring the depth of water that way does not convert into mms rainfall as quoted officially. 1mm rainfall means a depth of 1.0mm over an area of 1.0m², ie. 1 litre. So a bottle with a small "funnel" will catch only a fraction of that litre, therefore you will need to take the area of the funnel into account. Measure this area, and divide it into the number of mms of water you measure in the bottle.

Eg. your bottle has a diameter of 15cms, so a radius r of 7.5cms (0.075m). It's area will be pi*r², (3.142 x 0.075²) = 0.0177m²

If you measure say 2.5mm in the bottle after a day, then your actual rainfall will be

2.5 / 0.0177 = 141.2mm (a lot!). To measure a small rainfall amount (say 5mm, you would only have a depth of 0.09mm in your bottle - impossible to measure accurately. That's why it's good to have as large an area as possible feeding into a narrow bottle, like a graduated cylinder.

I don't think pauldry's simple method would be too far out as to be useful enough as a rough guide. The tolerance may be ~ +/- 10%. If he put 16 such bottles side by side in a large square formation they would all roughly fill by the same height over a period of a few hours rain.
Even if he had a bottle with a base surface area of 1.0m² and a bottle with a base surface area of .25m² they would both fill to more or less the same height. It may not be official but it will give Chicken Run something to peck at.

lucernarian

Su Campu wrote: »

Measuring the depth of water that way does not convert into mms rainfall as quoted officially. 1mm rainfall means a depth of 1.0mm over an area of 1.0m², ie. 1 litre. So a bottle with a small "funnel" will catch only a fraction of that litre, therefore you will need to take the area of the funnel into account. Measure this area, and divide it into the number of mms of water you measure in the bottle.

Eg. your bottle has a diameter of 15cms, so a radius r of 7.5cms (0.075m). It's area will be pi*r², (3.142 x 0.075²) = 0.0177m²

If you measure say 2.5mm in the bottle after a day, then your actual rainfall will be

2.5 / 0.0177 = 141.2mm (a lot!). To measure a small rainfall amount (say 5mm, you would only have a depth of 0.09mm in your bottle - impossible to measure accurately. That's why it's good to have as large an area as possible feeding into a narrow bottle, like a graduated cylinder.

I'm think I'm not following this. It could be that I'm thinking about this arseways. But surely the depth only has to be adjusted if there's a funnel being used? I.e. If rain is being collected from a large area and concentrated into a smaller glass jar or beaker (like a 5" gauge) then the actual rain depth would have to be adjusted accordingly. If a funnel with 20cm^2 area collects rain into a cylinder with 10cm^2 cross sectional area, then the depth in the cylinder would have to be simply halved to get the appropriate depth.

With something of uniform diameter, like a flat bottomed cylinder or a box, then only the depth need be recorded even if it's ability to accurately collect rain is suboptimal.

Also, where are the units in that calculation?! 2.5mm/17,700mm^2 = 0.00014mm^-1 which is not a valid unit of volume.:)

Su Campu

To_be_confirmed wrote: »

I'm think I'm not following this. It could be that I'm thinking about this arseways. But surely the depth only has to be adjusted if there's a funnel being used? I.e. If rain is being collected from a large area and concentrated into a smaller glass jar or beaker (like a 5" gauge) then the actual rain depth would have to be adjusted accordingly. If a funnel with 20cm^2 area collects rain into a cylinder with 10cm^2 cross sectional area, then the depth in the cylinder would have to be simply halved to get the appropriate depth.

With something of uniform diameter, like a flat bottomed cylinder or a box, then only the depth need be recorded even if it's ability to accurately collect rain is suboptimal.

Also, where are the units in that calculation?! 2.5mm/17,700mm^2 = 0.00014mm^-1 which is not a valid unit of volume.:)

No wait, you're both right - I'm the one who got it arseways! There should be no calculation required as long as the two diameters are the same. D'oh! :rolleyes:

And on my planet, mm^-1 is a valid unit of volume!! :pac::pac:

No more late night posts by me!

lucernarian

Su Campu wrote: »

And on my planet, mm^-1 is a valid unit of volume!! :pac::pac:

No more late night posts by me!

Well if it makes you happy:D

I'm glad I didn't haul out the auld physics book, it's got more calculus and vector planes than you can shake a stick at...

kc66

This thread made for interesting reading, seeing as I was stuck out in that weather for most of Sunday night / Monday morning with only a t-shirt on me. Never saw anything like it. Electric picnic was great.

fishmahboi

Anybody got info about the rain on thursday night?

Deep Easterly

fishmahboi wrote: »

Anybody got info about the rain on thursday night?

Yes, we have no information yet, but when THEY let us know, thou'st will be the first to know...;)

Ya wide?

irishh_bob

several reports on rte last night and today suggested that today would start off wet but would become increasingly dry by afternoon and evening , in the north east , we got the exact opposite , heavy rain for about an hour and a half straight from 5 pm - 6.30

you would need a different forecast for every parish in this country

wild handlin

fishmahboi wrote: »

Anybody got info about the rain on thursday night?

Due to sweep in from the SW around mid-day and quickly spread to the rest of Ireland by nightfall, with heavy and thundery bursts expected according to RTE weather this evening.