Grasshopper’s 2024 New Zealand Snow Season Outlook, Mid-July Update – Unsettled Weather Regimes Imminent

July 16th, 2024
Blue skies and cold, dry chalky snow in Mt Hutt this week.  After a period of fine weather, peak season will see unsettled weather for New Zealand’s resorts. Photo: Mt Hutt

 

Mountainwatch | The Grasshopper

With June clocking in as a very mild and drier than normal month across New Zealand ski fields, largely thanks to a slow-moving Tasman Low of exceptional longevity through mid-month, it’s fair to say the fields were snow-ploughing along last month with very modest additions to the snow-pack in June. A significant low from the Southern Ocean got the season’s ski-tips pointing straight down the mountain at the start of July though, with some 30-50cm of fresh snow racking up for most of the resorts on the 1st/2nd of this month.

However, this was the last significant natural snow most resorts have seen as a massive high pressure has dominated across the weather maps through the rest of the first half of July (see figure 1). This has kept any weather fronts at bay the last couple of weeks and has provided us with some very welcome cold, low humidity weather conditions with snowmaking going into overdrive at the resorts. The snow-guns are humming away! Add in the string of blue-bird and low wind days on the mountains and we have been treated to great weather for the first week of the school holidays in NZ.

As we enter week two of the holidays, the groomers are the place to be with the pistes looking fantastic and the resorts continuing to open more lifts every day. The back-country remains rather thin and icy with early season conditions still prevalent, so if you do venture off the piste ride with care and watch for hazards.

MSLP anomaly patterns for June (left) and the first two weeks of July (right). Blue shades indicate lower than normal pressure, green/orange shades indicate higher than normal pressure. Note that neither of these two set ups are partuicarly favourable for snowfall in New Zealand (we really want big low-pressure anomalies SE of the country), but at least July has offered predominantly southerly airflows and colder temperatures to allow for great snow-making conditions. Images courtesy of NOAA Physical Sciences Laboratory.

A month of two halves with unsettled weather regimes imminent

Our big high has now departed eastward and opened the door to a much more unsettled outlook for the second half of July. Whilst an uptick in the number of fronts moving onto the country enhances our chances of natural snowfalls, unfortunately we are returning to a milder spell of weather over the coming days with rain more likely than snow on North Island slopes, and not a huge amount of promise beyond some dustings higher up for South Island resorts. More variable on-mountain conditions too with wind and poor visibility becoming a player.

Next week offers some good potential for low pressures to return to favourable positions to the east of South Island with temperatures lowering, and the possibility of some decent snowfalls, with perhaps the best offerings at the Canterbury fields early in the week. Early signs for some further southerly flurries towards next weekend too.

Seasonal Weather Models do a 180 in July, but what does it mean for NZ?

As we head into August and September, and the peak of the NZ snow season, it looks like the seasonal weather models have spent a bit too much time in the terrain park…July model runs have done a large 180 (see figure 2)! Previous model ideas maintained higher than normal pressures across the Tasman Sea and NZ through these months, but the latest modelling suggests low pressure anomalies will now dominate south of Australia and in the Southern Tasman Sea through the period. As a result, a much more unsettled outlook has developed for New Zealand and the North Island in particular.

There are some fairly compelling reasons for this shift with global model drivers like ENSO and IOD now firmly neutral, short-term drivers well and truly in charge and some very interesting developments in the stratosphere over recent weeks (more to come on this in our Australian Seasonal update later this week…check it out!).

ECMWF seasonal forecast MSLP (top) and Precipitation (bottom) anomalies from the June (left) and July (right) model runs for August/September/October. Note the massive jump in the MSLP anomaly patterns in particular. Images courtesy of ECMWF.

What that means is we can expect a fairly wild ride of weather over the coming months and lots of week-to-week variability. August in particular could see a lot of weather systems roll through, with wind, rain, snow, mild and freezing conditions occurring across time frames of a few days, not a few weeks as we have seen with the slower weather progressions of winter so far.

So, this isn’t necessarily good or bad news for seasonal snow falls, with natural snow-makers looking quite frequent over coming weeks/months, but it does mean keeping up with my forecasts on Mondays, Wednesdays and Fridays will help you maximise your riding potential in changeable weather regimes!