NZ Weather Forum

Looks extremly cold too me. GFS going big on the cold air. Coldest air ive seen in a decade if this comes off.

A rather non-eventful day here with grey high cloud cover and not much wind especially with this system moving over the country.
About 3 spits of rain fell.
Today's maximum was 16.4C.

Nothing historic in the last few model runs of EC and GFS but things are still looking cold from next weekend onwards, perhaps a few flurries down to 200m-300m asl on the plains at this stage...

I think its abit more than a run of the mill system. GFS putting 20cm in Chch City. Has 2m above 800m around Arthurspass.

I add to that. 50cm for Invercargill and Dunedin.

talbotmj15 wrote: ↑Fri 03/06/2022 12:58 I think its abit more than a run of the mill system. GFS putting 20cm in Chch City. Has 2m above 800m around Arthurspass.

The first map you put up was only until the 12th June so that is the system I was referring to. You are now talking right up to the 18th June
in the new map so yeah if you want to look 2 weeks ahead then for sure, it's going to be wild in those 4 days from 14th June to 18th June

will be great for the Ski fields
Currently not much snow on Mt Ruapehu yet

talbotmj15 wrote: ↑Fri 03/06/2022 12:58 I think its abit more than a run of the mill system. GFS putting 20cm in Chch City. Has 2m above 800m around Arthurspass.

If it was a couple of days out, I'd be thinking oh wow. But it's over a week. Lets see how the models show it a lil closer please.

But it's over a week. Lets see how the models show it a lil closer please.

true
but
with more flights occuring across this part of the globe now there is more data into the models on the upper level conditions and it seems to me
that the models have become more accurate again

How much snow is it saying now Talbot with the latest run? I don’t have access to that map you do

Both EC and GFS outputs have a large snow system at play. Significant event for some and less for others. Plains might get bugga all but others heaps.

I find a useful measure of the likely severity of a winter system is the ensemble output for snow on the ground in Christchurch. Now, this is not a very reliable forecast of snow for Christchurch, because we know the models are missing some pretty key parameters - they won't take account heat island effects, and they dont have the resolution to model well microdynamics which come into play like airflow over and around Banks Peninsula and other complex topography in the South Island, sensitivity to the "critical south-westerly" airflow direction and variations in the lower tropospheric temperature structure, and others. All of these are vital ingredients in the snow forecasting mix, but missing from global model calculations. Which is why many times people complain that "the snow which was forecast didn't arrive". They are assuming the model output is a forecast. It is not, and should not be taken as such.

However, if the models are putting snow on the ground in Christchurch, then that tells us that the mesoscale dynamics and temperature structure COULD BE suitable for low level snow SOMEWHERE. And multi-run ensembles can tell us how likely that is, The latest 12Z ensemble runs from ECMWF have 16 out of 50 runs with some very light snow for Christchurch between the 10th and 16th, mostly around the 13th. So thats a 32% chance. The GFS is more bullish, with 20 out of 30 runs showing some snow fall, mostly on the 12th and 13th. So thats about 60% chance. 3 of the GFS runs show a fall in excess of 5cm. Note that the GFS is well known for generating a lot more low level snow than the ECMWF, and usually too much. All the more reason NOT to consider its raw output a forecast. Its also worth noting that the Canadian ensemble (which is based on the GFS) has no runs showing snow.

Another way of evaluating potential risk is to look at trends from one model run to the next. GFS has generated low level snow in all of its last 10 control runs. ECMWF has snow in 4 of its last 10, but not the most recent.

IMHO the best way to interpret this data AT THIS TIME is to say there is a clear signal for a period of very cold, active weather coming up in 10 days time, and it is likely to be cold enough and active enough to generate some low level snow for parts of the South Island. Anything more specific than that is opening yourself up to likely disappointment until we get closer to the event.

Both EC and GFS are consistent on a major storm system dropping lots of moisture. Even has cold air and light as far north as Auckland.

Arthurspass and southern South Islsnd including the west coast show crazy amount of snow and cold. Arthurspass has well over 1m in the village!

Latest EC Numbers

Long way to go yet but I’m guessing this is a predominantly SW airflow at the moment?

Yes looks very southwest.

Razor wrote: ↑Sun 05/06/2022 08:39 Yes looks very southwest.

Thank you. Nothing for me to get excited over then. Just the hideous cold wind for us in Ashburton.

talbotmj15 wrote: ↑Sun 05/06/2022 08:08 Latest EC Numbers

I’d take that map and it’s low level snow prediction with a grain of salt, it’s also saying 12cm of snow for Greymouth haha

Looks more like western and southern areas of the south to be hit the worst. Watch out Queenstown an areas south.

Should be a good event for Qtwn with getting the ski season going. See how the models look in 2 or 3 days time.

Bradley wrote: ↑Sun 05/06/2022 10:28

talbotmj15 wrote: ↑Sun 05/06/2022 08:08 Latest EC Numbers

I’d take that map and it’s low level snow prediction with a grain of salt, it’s also saying 12cm of snow for Greymouth haha

Second rule of forecasting - Always apply common sense to computer generated model output before using it.

Latest EC putting slot more moisture in Canterbury. Time will tell if its just a rogue. Hopefully its the beginning of a wind direction shift.

What I see coming up for my area is a lot of spillover rainfall with cold winds from the west.

Richard wrote: ↑Mon 06/06/2022 11:38 What I see coming up for my area is a lot of spillover rainfall with cold winds from the west.

Yes, and probably some thunder and hail also.

I must be missing something with this system, it has never shown any consistency, other then a rogue run every now and again, for any snow below 300m at all on the plains, for either model. It certainly is being hyped up though by certain people who must be seeing something I’m not