NZ Weather Forum

Looks like a potentially very nasty system with snow to near sea level in places across the SI Tues to Thurs.

Um...

TonyT wrote: ↑Sun 03/06/2018 19:22Um...

That is very interesting

TonyT wrote: ↑Sun 03/06/2018 19:22Um...

I don’t even know what kind of weather event that map represents haha

TonyT wrote: ↑Sun 03/06/2018 19:22Um...

Possibly another non event for Rakaia south...looked exciting yesterday

Yea not showing much for the plains. I expect some of the moisture to come back as well. Given it went from major to nothing. I think the low will come abit closer to NZ again. Certainly interesting to watch.

Just noticed the Metservice 3 day maps are completely at odds with most major models? Aparently these are updated every 6 hours so i would have expected it to have backed off. Just confirms my suspicions that the moisture levels will come back up in the next few runs unless others have some other ideas on this?

Obviously most of the snow inland over the higher terrain with heavy falls in Canterbury. But coastal zones including Canterbury plains will get some wintry precip out of this system. Isolated thunder as well near the coast. Warmer air comes into the south late Wednesday or Thursday with warm front by the looks.

Metservice have issued a heavy snow watch for Southland and Otago this morning.

Moisture levels on the increase again...interesting few days ahead.The weekend looks mild following the cold snap.

Dean. wrote: ↑Mon 04/06/2018 18:11 Moisture levels on the increase again...interesting few days ahead.The weekend looks mild following the cold snap.

Yep GFS now going for around 40mm for Christchurch so a fair increase, the real test will be tonight’s run of EC in about 2 hours, if that keeps the amount of moisture around the 15-20mm mark for Tuesday night/Wednesday then the level of disruption will be moderate but not severe for areas above 300-400m...

Bradley wrote: ↑Mon 04/06/2018 18:18

Dean. wrote: ↑Mon 04/06/2018 18:11 Moisture levels on the increase again...interesting few days ahead.The weekend looks mild following the cold snap.

Yep GFS now going for around 40mm for Christchurch so a fair increase, the real test will be tonight’s run of EC in about 2 hours, if that keeps the amount of moisture around the 15-20mm mark for Tuesday night/Wednesday then the level of disruption will be moderate but not severe for areas above 300-400m...

Post ECs run up later..cheers

Last couple of EC runs have kept the current NI depression well out in the Pacific and not really interacting with the cold pulse from the south. Access is keener to develop the interaction. The 0Z EC has pushed the snow level back up a few hundred metres to keep most of the Plains clear, but its still keen on giving Banks Peninsula a coating, and keeping the cold air around a little longer into Thursday.

Yeah EC really hasn’t liked this system for nearly 2 days now, that low is just too far off the coast for this to be anything other then a moderately strong winter cold front - unless of course the model EC uses isn’t picking something up...this will be a good test to see if the major models really are struggling because of such factors as the recent SSW as some people have alluded to...

Thats interesting Tony that its lifted. GFS,CMC still hovering between 520-522thk. Both seem to be picking up some kind of interaction with that low. I would be sceptical with a run lifting the levels so quickly. But i also think the EC is slightly better at predicting snow events. But for overall weather i find the GFS pretty good 2 days out. GFS has lifted the moisture level too i see about 15-20mm more.

Rain, heavy falls possible at first. Snow down to 400 metres. Southerlies, gale about the coast at first.
Issued: 11:43pm 4 Jun

Met S Methven's precipitation accumulation chart certainly doesn't match there forecast, looking like a non event when there so much contradiction

Yeah this mornings run of EC is depressing reading if you’re a snow lover, snow level lifted to 300-400m for Canterbury and only 15-20mm now. Oh well still a nice wee top up for the aquifers I guess so not all is lost

my 2 bobs worth.

Should see some sort of secondary circulation off the old Tasman low in around 6 hours. Looking at the current water vapour image, reasonable amount being detected near the -40c 500 hPa cold pool. Should get a clearer picture this afternoon on how the mid levels look as it approaches the SI.

Latest MS watch is out for heavy snow in canterbury above 400m including BP. Includes significant accumulations in some areas. Im wondering if they are picking up the recirculation of moisture from the Low thats now east of NZ.

talbotmj15 wrote: ↑Tue 05/06/2018 10:18 Im wondering if they are picking up the recirculation of moisture from the Low thats now east of NZ.

No is the short answer. The moisture is coming up from the south seas.

The warm front early Thursday is interesting as the milder air comes in very quickly from the SW.

850mb temps for midnight Wednesday.

As moisture is a hot topic in this thread, here is a freely available tool to see near real time precip water levels through the layers of the troposphere. I have this set this to between the surface and 850 hPa (1,500m), if you click on the layer you can change the levels of the atmosphere and see Total Precip Water. For this event, 850 to 700 hPa is important. http://tropic.ssec.wisc.edu/real-time/m ... anim=html5

As of 11am (23:00 UTC), you can see the 2nd low starting to circulate and moisture moving SSW to South from the pacific. The cold trough has a lot less moisture as you would expect and will push the pacific surface low SE before the surface low cuts back towards NZ dragging warmer air.

Latest guidance is showing a difference of 17 to 21c from the sea surface to 850 hPa along the SI east coast around 1 to 6am tomorrow morning. Prime for cold convection and beefy coldies to launch onto land when the wind direction is at its most southerly. IMO this would be the best time for Christchurch to get snow as a super cooling process would be underway in that area.

In the meantime, I’ll continue to browse and chew the popcorn

Metservice now forecasting snow down to 200m for Canterbury on Wednesday morning...

Thats about time. Pretty bad from them given this has been well below 400m for days. I think sometimes they are abit conservative. Cheers for that info CT.

talbotmj15 wrote: ↑Tue 05/06/2018 12:19 Thats about time. Pretty bad from them given this has been well below 400m for days. I think sometimes they are abit conservative. Cheers for that info CT.

To be fair to Metservice EC is only forecasting snow down to 350m-400m mark and has been for the last 2 days or so which is in line with -5C or -6C at 850hpa...

Wet flakes falling to 200m here with the band of heavy rain, looks like it'll be over pretty soon though.