Chance of Rain in a Town.

[TheOracle]

I have built a calculator which will tell you how often it actually rains in your town.

Pick a town and a month and it tells you how many days in a hundred actually see rain. Second tab: pick a job and it tells you the odds of getting enough dry days in a row to finish it.

Anyone interested can have a look here: https://southafricafacts.co.za/chance-of-rain-calculator-south-africa/

 

[EmmanuelGoldstein]

 

[FiestaST]

 

[Gordon_R]

Just curious: Why how many days in a month get rain, out of 100, when most months have 30 days?

Wikipedia gives some data on this, at least for CT. Table from Jan to Dec (plus annual).
Average precipitation days (≥ 0.1 mm)
1.8 1.8 2.5 5.0 7.4 10.1 9.1 9.3 6.8 4.2 4.0 2.6 64.6

 

[FiestaST]

https://files.catbox.moe/oejmwr.pdf

 

[TheOracle]

Just curious: Why how many days in a month get rain, out of 100, when most months have 30 days?

Wikipedia gives some data on this, at least for CT. Table from Jan to Dec (plus annual).
Average precipitation days (≥ 0.1 mm)
1.8 1.8 2.5 5.0 7.4 10.1 9.1 9.3 6.8 4.2 4.0 2.6 64.6

It's a percentage, not a count out of 100 days. June reads 27, so 27% of June days, which is about 8 days in a 30 day month. January reads 5, so about 1.5 days.

Your Wikipedia row counts any day with 0.1 mm or more, so every trace of drizzle is a rain day there. Mine uses the Weather Service standard of about 1 mm or more, which is why the year comes out at 52 instead of 64.6.

Also worth flagging: Cape Town has no published rain-day normal to check against, so the tool labels it "seasonal pattern checked", the shape of the year is solid but the exact day counts rest on the national calibration. It says so on the page when you pick it.

Fair point on the wording though. I've changed it, the headline now reads "About 8 of June's 30 days see meaningful rain" with the percentage underneath.

You may need to refresh your browser to get the latest code.

 

[Gordon_R]

It's a percentage, not a count out of 100 days. June reads 27, so 27% of June days, which is about 8 days in a 30 day month. January reads 5, so about 1.5 days.

Your Wikipedia row counts any day with 0.1 mm or more, so every trace of drizzle is a rain day there. Mine uses the Weather Service standard of about 1 mm or more, which is why the year comes out at 52 instead of 64.6.

Also worth flagging: Cape Town has no published rain-day normal to check against, so the tool labels it "seasonal pattern checked", the shape of the year is solid but the exact day counts rest on the national calibration. It says so on the page when you pick it.

Fair point on the wording though. I've changed it, the headline now reads "About 8 of June's 30 days see meaningful rain" with the percentage underneath.

You may need to refresh your browser to get the latest code.

I'm happy with that explanation, and update. I ran the applet on my phone earlier, and on my desktop now. The screen dimensions and layout do differ, but both are acceptable.

P.S. The difference in rainfall between Newlands/Kirstenbosch and the CT airport is about 3:1, but I'm sure you know that. Edit: And if you get 0.1mm at the airport, Kirstenbosch will probably get 10mm...