Using Met Eireann station data to augment a daily weather diary

Iwannahurl

I have a Commuting Weather Diary on the go in the Galway City forum: http://www.boards.ie/vbulletin/showthread.php?t=2057085431

I'm now thinking of using data from Met Eireann's Synoptic and Rainfall stations to make comparisons with the individual diary reports.

What are the practical considerations with obtaining and using such data?

The context is that 47% of Galway City residents live 4 km or less from their place of work or education. That would be about a 15-minute cycle, for example, which means that hourly rainfall data are only indicative.

It's obvious that, for example, a high level of "hourly" rainfall could occur in the form of an intense 5-minute shower. In practical terms that would still leave a 55-minute window for a rain-free commute of 4 km or less.

Any suggestions for how best to use available rainfall data for the purposes of such an exercise?

piuswal

What is the ultimate purpose of your exercise or project?

Iwannahurl

The overall objective is to produce a tally of the number of trips where rain actually fell during the commute.

I'm focusing on the school run, which in my case is less than 4 km, as it is for 47% of the Galway City population.

I hope to use the Met Eireann data to augment (or ideally confirm) the self-reported data. Some people have tried to suggest that self-reports are not reliable.

Harps

Lumi's weather station is probably your best bet, I think there's a met station in the University but don't think all the data is readily available whereas Lumi could probably give you an hourly breakdown of whatever you need

piuswal

Met Eireann's 15min radar data would probably be their most useful data for what you have in mind, combined with what ever non ME rain data you can get locally.

How you get it from the web I have no idea but I'm sure there is someone about that can solve that problem.

Contacting their Climatological Division might be worth considering.

Iwannahurl

Coincidentally, I just started to wonder last night whether historical radar info might be available.

piuswal

Then talk to

Climatology and Observations Division

018064260

octo

Interesting question. You can get a "rainfall duration" figure from those fine officers at MÉ climate division for your nearest station, which would be Athenry. This is defined as the duration of precipitation where the precipitation rate exceeds 0.1 mm/hour.

You'll then need an estimate of, on average, how long people are commuting for each day. Try to get an accurate figure. Say, for example, 0.75 hours. Then get an average rainfall duration from MÉ for your local station, say something like 0.2. Then multiply it out as follows:
(Average hourly rainfall duration) * (number of commuting hours) * (number of commuting trips) = Number of times per year to get wet !!

Rough Guess as follows:
0.2 * 0.75 * 400 = 60 wet trips/year.

Harps

Iwannahurl wrote: »

Coincidentally, I just started to wonder last night whether historical radar info might be available.

Available from netweather if you're willing to pay a one off subscription, weatheronline also have a free archive though it's more awkward, the only way I know of using it is to manually type each date and time into the url which could take ages depending on how much info you'd looking for

Iwannahurl

octo wrote: »

Interesting question. You can get a "rainfall duration" figure from those fine officers at MÉ climate division for your nearest station, which would be Athenry. This is defined as the duration of precipitation where the precipitation rate exceeds 0.1 mm/hour.

I was beginning to ponder that one also. I wasn't aware that rainfall duration data were available.

Duration of precipitation is key, as hourly rainfall data are indicative but not sufficiently informative in the context of 'exposures' of, say, 15-30 minutes.

Take for example this excerpt from the Galway City commuting weather diary:

Trip: morning school run, 6 km round trip.
Mode: cycle.
Weather: no rain during outward leg.
Comment: left house without rain-gear because wasn't raining. Delayed a bit before return leg and got caught in a shower. Sheltered for a few minutes and then resumed journey. Arrived home dry.

What I am hoping for is data that would confirm the veracity of such qualitative self-reports.

Though accurate, the bland fact that X mm of rain fell between 08:00 and 09:00 on that date does not describe the experience, which is that it was perfectly possible, with a little adaptation, to commute 3 km each way that morning without getting wet.

Hopefully rainfall duration figures will fill out the canvas a bit more.

Is there a definition (in mm per hour, presumably) of light, moderate and heavy rain, I wonder? Can qualitative descriptions such as "light shower", "constant drizzle" or "heavy downpour" be drawn from the figures?

Iancar29

I really don't get the idea of this op lol .

Why not use radar to determine travelling weather ?

Iwannahurl

1. I'm not as knowledgeable about met stuff as some (presumably most) people here.
2. Only just realising that I can use Met Eireann's radar info to augment the daily diary, along with weather station data.
3. The object of the exercise is to create a record of rainfall during the daily commute (mostly the school run in my case).
4. Daily data can be used to confirm self-reports 'going forward' but I may also need to use historical data, as some posters are trying to cast doubt retrospectively on the self-reports.
5. The context of all this is the apparently persistent belief that rainfall in Galway City is such that it acts as a real deterrent to cycling and walking, even over commuting distances of 4 km and less. <Snip>

octo

Iwannahurl wrote: »

5. The context of all this is the apparently persistent belief that rainfall in Galway City is such that it acts as a real deterrent to cycling and walking, even over commuting distances of 4 km and less. <Snip>

I think you have the wrong approach. Open scientific enquiry shouldn't be about 'proving' anything. You should be prepared to accept the answer to your question, whether it validates your hypothesis or not.

Iwannahurl

octo wrote: »

I think you have the wrong approach. Open scientific enquiry shouldn't be about 'proving' anything. You should be prepared to accept the answer to your question, whether it validates your hypothesis or not.

Where exactly is my approach incorrect? Where have I used the word "prove" in the manner you suggest? And where have I indicated that I am not prepared to accept the outcome of the exercise?