Weather

We have stocked Ken Ring's book in the bookshop for the last 3 years now. Seems to sell less and less each year. You have to make sure you sell the last copy before Jan 1 because the first thing people do after that is look up what the weather is supposed to be today and then put it back on the shelf. My philosophy with the weather is to basicly look outside and see what it is like and then make plans from there. Also be prepared for anything at any time of year. I would very rarely cancel a trip because of weather but will usually have a plan B incase we cannot complete what we want to do. I always carry storm gear, including mitts, woolly hat and fleece pants and overtrou, even in summer. I find that the weather forecasts are usually pretty good. The main issues are with timing, a front may come on faster than predicted or slower, but it usually happens sometime. Then there is the issue of local microclimates. The Met service themselves admit that they cannot predict for local microclimates. Usually the locals with an experienced eye for the weather will predict it better.

I have been thinking a bit more about the issue of the weather after the last two weekends where we had dire weather predicted but it hasn't really turned out too bad, at least in the Bay of Plenty it hasn't been too bad. I think with the new weather format on the TV1 news where they give a teaser at the beginning of the news and then halfway through, they tend to sensationalise the weather a bit. Talk of severe weather warnings and all sorts of things and then when it actually comes to the weather report, it isn't that bad. A string of depressions comming across the Tasman with a norwester followed by a front and then a souwester is just normal stuff really.

If it's a short trip I try to have an alternative; most of my tramping is Lewis / Arthurs Pass or Nelson Lakes, so I use the Canterbury foothils or Kaikoura region as a plan B. I've found forecasts in the short range to be in the right ballpark. In fact a guy who spent heaps of time in Arthurs Pass region gave me a guideline relating the number of norwester isobars over the south island to how far east the rain will reach. Haven't tested it out too hard, but it seems to be about right. Having said that, I'm always equipped for the worst. But good weather increases the enjoyment factor (and lessens the moaning from the brother in law) For longer trips the forecast more than a few days out is usually no use at all and I just take it as it comes.

and theres my problem with the established media. Its the crying wolf thing that concerns me. Miss enough good days tramping because they forcast dire extremes and somebody is going to get caught when they give up and go only to find that this time they where right. You can hear the press already as they say we told you so while completely side stepping the fact that they got it wrong too many times before.

What was the rule of thumb regarding the number of isobars? I've been told 3 means don't go to the main divide. Also I've been told if the sirface barometric pressure isobar is less than 1016 then the system will behave more like a low than a high. I check out multiple sites e.g. FNMOC (US Navy), snowforecast.com (UK but created by a kiwi), down here in Chch, I use Tony Trewinnard's sites i.e. fencepost and ATS. The VUW forecast thumbnails are good to print off and take with you. They were right for 6 days ahead for one of my recent trips. My last trip however I only checked one site and we got stuck in the hut for an extra day waiting for the rivers to go down. Serves me right for being lazy.

My partner is compiling statistics for heavy rain warnings from MetService versus the actual outcome at Arthur's Pass. I think the MetService have to be cautious to cover their arse. However, one weekend we changed our plans to go to a more eastern dry range which was good and a friend died on the main divide due to heavy rainfall.

I think the Metservice would be the first to admit that their forecasts can seem inaccurate but in general I have found them to be pretty good. The are never going to be able to predict if a shower will actually happen or when exactly the front will arrive but at least they tell you that the conditions are there and what is likely to happen. Recently I have found that a predicted front moving up the country has often run out of steam by the time it gets to Rotorua so often predicted bad weather just doesn't happen. It is a good idea to make yourself familiar with the weather patterns when in the hills. On a trip in Nelson Lakes a few years ago we tramped all day in rain, camped out the night and woke up to a beautiful day, quite cold and a dusting of snow on the tops. I told another tramping party that the weather would now be settled for a couple of days and they could confidently continue with their plans. They were impressed with my "local knowledge". But really it is only general knowledge of how weather systems function over NZ and what all trampers should know.

Regarding norwesterly isobars and the Main Divide: 2 isobar lines cross the south island: east of the Main Divide (ie anything further east than Arthurs Pass) usually OK 3 isobar lines: east of Craigeburn Range / Cass usually OK (Craigeburn and Cass wet) 4 isobar lines: further east than Torlesse / Big Ben ranges / Porters Pass is OK. (that only leaves foothills such as Oxford forest, Lees Valley, Mt Thomas) 5 or more, bad weather reaches across the Canterbury Plains. As above, NO GUARANTEES! These are what someone once told me; the few times I have tested it it seemed to work. I would be interested to know if anyone else finds it to be right or wrong.

Hi Chris1, it will be good to check out your rule of thumb. cheers.