Is there any data that shows the likelyhood of rain falling at a particular instant in the UK

[mike57]

You can find data for 'rain days' but that doesn't really tell me what I am interested in, at a given moment what is the likelyhood that rain will be falling at a given location. It will obviously vary by area, season, possibly even time of day (Summer showers tend to 'pop up' in the afternoon). Its purely for personal interest, but interests me. As part of my exercise regeim I go for a bike ride at roughly the same time each day. I take a picture at the same location each day, and have prepared some interesting collages showing the changing seasons. The thing that surprises me is how few days its actually raining, it may have been raining, or about to rain, but the days when its actually raining are quite infrequent.

[Roger J Smith]

Mike, I would imagine that some stats must exist for this, have seen them for other locations in different countries, and the statistical foundations are probably similar for the UK. Had a look at the NEWP portion of the EWP (England and Wales precip) and just rough estimates, some precip falls on about 40 per cent of days overall, varying from 50-50 in late autumn, winter and early spring to 30-70 in summer. But as you say, that does not tell you the frequency of precip at any given hour of the day. In the stats that I have seen, for any given day that has some precip, the percentage chances of it including any given hour are only in the neighborhood of 20-30 per cent, so that multiplied by the already partial amount of days to which that applies gives something like 6 to 20 per cent figures overall, with the values near 20 being in the wettest part of the year. Does that line up with your experience? My experience would be how often there is enough rain to affect one's day on the golf course or hiking trails (I don't bike) so what you say is roughly my perception too, the actual number of times that I have been seriously affected by rain on these outings is fairly low compared to the percentage of days that have any rain. Of course in both cases we have some control over the situation and can plan to be outside when it's not likely to rain. So that would have to be factored in, a more valid experiment would be a "robot" outdoor enthusiast oblivious to weather forecasts who might randomly be outside in rain that we might consciously avoid. 

Also those stats refer to precip within an hour, which is probably the most detailed time scale that most researchers would have any data to study, but once you get to 20% chance per given hour, I think the percentage chance for any minute within that hour is almost the same, as it usually rains fairly continuously for one to three hours in most events, sometimes longer than that. I do remember one occasion when I was filming a desert thunderstorm and it was raining hard across the road from where I was standing and never rained while I was outside the car on my side of the road. 

Edited November 14, 2021 by Roger J Smith

[mike57]

On 14/11/2021 at 22:46, Roger J Smith said:

So that would have to be factored in, a more valid experiment would be a "robot" outdoor enthusiast oblivious to weather forecasts who might randomly be outside in rain that we might consciously avoid. 

Also those stats refer to precip within an hour, which is probably the most detailed time scale that most researchers would have any data to study, but once you get to 20% chance per given hour, I think the percentage chance for any minute within that hour is almost the same, as it usually rains fairly continuously for one to three hours in most events, sometimes longer than that. I do remember one occasion when I was filming a desert thunderstorm and it was raining hard across the road from where I was standing and never rained while I was outside the car on my side of the road. 

Thanks for the reply, yes it coincides with my experience. I am not quite the robot outdoor enthusiast that you refer to, but not far from it, I work from home, and am away from my screens for an hour starting nominally at 12, when I go for my bike ride. Outside weather is less likely to affect the exact timing, the main impact is business things, overrunning meeting, zoom call etc. If its really foul I might leave it and see what its like at tea time when I finish, but over the last 20 months thats only probably 4 or 5 times as even if its wet and windy I find I benefit from the break, and 4 days in February when the ice and snow was bad enough to make riding a normal bike stupid.

When looking at the granularity within an hour I would say that in the UK that it maybe halves again if you are thinking minute by minute, in summer we get showery days where rainfall maybe lasts 10-15 mins. Theres maybe enough data in my pictures now to quantify it, roughly 70 weeks of data 5 days each week, well over 300 days.

The thumbnail from Climate-Data.org below gives the spread of rainfall over the year for my nearest town which is Bridlington.