A bar fly's guide to snow forecasting

Ruapehu Bulletin, Volume 14, Issue 686, 13 May 1997, Page 10 (Supplement)

A bar fly's guide to snow forecasting

Or, how^^^^^^y/Adiabatic Lapse T rick' to predict the Turoa car park temperature based on the gauge outside the Ohakune Hotel Te all like to predict what's happening up Y/V/ there on the mountain during a storm. "Y eah V ▼ man, it mu|| be dumping!" — "I reckon there mustbe lOfeetof snow^already!" — "We'llbe skiing by next weekend" sort of comments can be heard over the roar of laughter at the 0 hakune pub about now. A quick glance at the Ohakune Hotel temperature/clock board above the Summit Bar entrance and how would I know that we'd be lucky to get Mt Ruapehu' s summit sprinkled with a dusting? 'Adiabatic Lapse' is how. Generally speaking, and we all know how accurate weather forecasters are, clear air cools at 1°C per 100 vertical metres. Not much use, you say, because you don't need to be a meteorologist to work out that it doesn't snow when it's clear. During a storm air cools at 0.6°C per 100m. So if 'Ski FM' says it's 12°C in Ohakune is it snowing 'up there'? Ohakune is at 650m, Turoa's base area is 1600m, that's a difference of 950m. 950m divided by 100m =9.5,9.5x0.6 (adiabatic lapse) = 5.7°C, so it's about 6°C cooler. Ohakune' s temperature is 1 2°C , minus 6 = 6°C. Sorry , it' s not snowing at the base, more likely only around the top of the Bacardi T-Bar at 2322m. But if it's 6°C in Ohakune then it's probably snowing down to the 13km barrier on the road because it usually snows 200-300m below freezing level. So for it to be snowing at the Turoa's base area it needs a freezing level of about 1850m, or about 7-8°C in Ohakune. To work it out for yourself: 1850m, required freezing level, minus 650m (Ohakune' s elevation) = 1 200m. 1 200m divided by 100m = 12 x 0.6 (adiabatic lapse) =7.2°C. So if it's 7°C in Ohakune, lets celebrate! Even if it's 10°C in Ohakune, it should still be snowing around the top of the Giant, building up a base. Editor's note: So if I'm in lying on the beach in Wellington and it's 1 1°C, then it's snowing at the car park, right? Wrong — nobody lays on the beach in Wellington because all the sand has blown away.