NZ Weather Forum

Models seem to be keen on a reasonably decent advection snow event above 400m.

Lewis pass could see as much as 50-75cm of snow.

Picking up on Metservice’s wording here, not too surprising given the late change in the GFS the past couple of days:
https://www.metservice.com/warnings/sev ... er-outlook

“ During Thursday and Friday, there is low confidence that a rain warning will be needed for all of the North Island and also for eastern and southern Marlborough, far northern Canterbury Plains and the Canterbury High Country north of about Mt Cook. Confidence increases to moderate for The Tararua Range, Taranaki and the central North Island High Country on Thursday and for eastern Bay of Plenty, much of Gisborne and Hawkes Bay, Wairarapa, Wellington, Kaikoura Coast and ranges, southern Marlborough and northern Canterbury during Thursday and Friday as indicated on the chart. Snow is also expected in Marlborough and Canterbury to 500 metres at this stage, but this could possibly be lower as we get closer to the event.”

EC 00Z showing an energetic downwind latent heat release on Thursday evening into North Canterbury. Solid ocean effect if that verifies.

A fairly decent polar trough moving north Thursday and heavy snow in the Canterbury ranges. Some lighter falls to 400m inland valleys?

Mt Hutt ski field will be happy with the prognosis. And looks to be more of these cold events later in June on gfs.

Off to Reefton on Friday via Arthurs Pass, so will interesting to see the snow there ....and along the Alps.

Both EC and GFS just can't agree on this event. With less than 24hours they seem to disagree with moisture amounts and snow levels.

NZ Thunderstorm Soc wrote: ↑Tue 16/06/2020 22:56 Off to Reefton on Friday via Arthurs Pass, so will interesting to see the snow there ....and along the Alps.

I doubt NZTA will let you through under current policy

On that. Big meeting at 6pm. Castlehill village. NZTA and Selwyn Mayor fronting up. Hall holds 40 odd people. Yet word is hundreds are expected. Lol.

Would be a laugh if NZTA got caught up there by snow and isaacs closed the road. Lol. Hahaha

Latest UK 00Z putting a few centimetres down to 300m early tomorrow morning near Ashburton and Geraldine

Cyclone Tracy wrote: ↑Wed 17/06/2020 17:20 Latest UK 00Z putting a few centimetres down to 300m early tomorrow morning near Ashburton and Geraldine

. The southerly has gone through here, nothing on the radar, well yet. Wait and see

Looks another inland event if anything. Snow to 400m
Canterbury high country/twizel/ tekapo will get more snow. And inland north Canterbury

What the heck... Metservice modelling 80mm plus for Chch all of a sudden? Insanity!!!!

Razor wrote: ↑Wed 17/06/2020 20:40 What the heck... Metservice modelling 80mm plus for Chch all of a sudden? Insanity!!!!

Don’t take any notice of the 48 hour guidance rainfall figures when it suddenly jumps up massively like that, it’s happened many times before in moderate rain events and will be corrected tomorrow morning

Snowing in Alexandra tonight....seems much lower than forecast levels

Dean. wrote: ↑Wed 17/06/2020 21:50 Snowing in Alexandra tonight....seems much lower than forecast levels

Both GFS and EC have between 7-10cm of snow forecast for Alexandra tonight and overnight, interesting though MetService only forecasting rain for Alexandra, not even sleet. Work experience kid must have been on duty when the forecasts were done this afternoon

Razor wrote: ↑Wed 17/06/2020 20:40 What the heck... Metservice modelling 80mm plus for Chch all of a sudden? Insanity!!!!

I saw metservice's rain models and thought it was to much. So checked other GFS models and doesn't match metservice. So i doubt it would be 80mm

Dean. wrote: ↑Wed 17/06/2020 21:50 Snowing in Alexandra tonight....seems much lower than forecast levels

Anything settling yet Dean?

Bradley wrote: ↑Wed 17/06/2020 22:10

Dean. wrote: ↑Wed 17/06/2020 21:50 Snowing in Alexandra tonight....seems much lower than forecast levels

Anything settling yet Dean?

Not sure...just reading the Severe weather NZ comments on Facebook...whoever runs that?

Dean. wrote: ↑Wed 17/06/2020 22:12

Bradley wrote: ↑Wed 17/06/2020 22:10

Anything settling yet Dean?

Not sure...just reading the Severe weather NZ comments on Facebook...whoever runs that?

With 850hpa temps of -3C at the moment above Alexandra, no warm advection element something very strange is going on to be snowing under those conditions at 150m asl...

Often see this with snow events were the precipitation provides the cooling and the snow level drops. I think evaporative cooling is the correct term for it.

Bradley wrote: ↑Wed 17/06/2020 22:17 With 850hpa temps of -3C at the moment above Alexandra, no warm advection element something very strange is going on to be snowing under those conditions at 150m asl...

.....?

Interesting that central Otago temperatures were up to 18C today and now some winter precip tonight, with temps near zero.

NZstorm wrote: ↑Wed 17/06/2020 22:25 Often see this with snow events were the precipitation provides the cooling and the snow level drops. I think evaporative cooling is the correct term for it.

Iv heard of this aswel, isnt when the precip is so heavy it drags the freezing level down quite significantly? Aaron was telling me about it ages ago. Something along those lines.

mikestormchaser wrote: ↑Wed 17/06/2020 23:30

NZstorm wrote: ↑Wed 17/06/2020 22:25 Often see this with snow events were the precipitation provides the cooling and the snow level drops. I think evaporative cooling is the correct term for it.

Iv heard of this aswel, isnt when the precip is so heavy it drags the freezing level down quite significantly? Aaron was telling me about it ages ago. Something along those lines.

Yes, I think the better name for it is snow melt cooling. A fairly typical process with inland snow events. You need fairly heavy precip to get the process going.

Bradley wrote: ↑Wed 17/06/2020 21:44

Razor wrote: ↑Wed 17/06/2020 20:40 What the heck... Metservice modelling 80mm plus for Chch all of a sudden? Insanity!!!!

Don’t take any notice of the 48 hour guidance rainfall figures when it suddenly jumps up massively like that, it’s happened many times before in moderate rain events and will be corrected tomorrow morning

It's actually ramped up. Over 100mm now