Potential Nationwide Snow Event Sunday 8th August 2021

[talbotmj15]

It seems both EC and GFS are picking some big snow snow numbers for the eastern plains of Canterbury 50cm to 200m. Still 5 days away but latest model runs are showing a severe event. Even has ChCh seeing 20cm. Seems abit far fetched to me at this stage but certainly worth watching.

[Bradley]

GFS is predicting 15cm snow down to 100m for mid-Canterbury and upwards of 40-50cm for 300m asl and above. From memory GFS also predicted 5-10cm for Christchurch for the end of June system and was way off for that system, seems like it constantly exaggerating these kind of events so I'm leaning more towards EC which only has 1-2cm above 100m...

[Lawrence]

Certainly could be very interesting.Frankly I think Canterbury as a whole is well overdue a sea level event.And looking at the extreme events that have been befalling New Zealand recently I wouldn't doubt something spectacular knocking us when we least expect it.

[Growler]

yep this looks like fun for Otautahi!

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[Cantab03]

Latest run just through for GFS still showing very cold weather for Sunday afternoon through until the early hours of Monday morning. Slight tilt to be more southwest now on Monday now, where as before hand GFS has this lasting right through until Tuesday with good moisture. I think this indicates that the GFS was being a bit rogue and it is starting to move more into alignment with the Euro model now (which tends to be the better out of the 2 models. Does seem to be stronger model agreement that Sunday will be a wintry evening however, I think we will see quick clearance through Monday however!

[talbotmj15]

GFS is bei g consistent. Even Access, ikon, CMC all leading close to GFS. EC seems to be the outlier model currently.

GFS is going for a major system. GFS going for 20cm plus to Chch with 35cm above 100m and 50cm to 250m plus.

Big numbers. Certainly one to watch. Warnings will go out today i suspect. Especially for farmers. M/S now have it in there Severe Weather Outlook referring to a very cold outbreak.

[Bradley]

GFS is bei g consistent. Even Access, ikon, CMC all leading close to GFS. EC seems to be the outlier model currently.

GFS is going for a major system. GFS going for 20cm plus to Chch with 35cm above 100m and 50cm to 250m plus.

Big numbers. Certainly one to watch. Warnings will go out today i suspect. Especially for farmers. M/S now have it in there Severe Weather Outlook referring to a very cold outbreak.

It will be interesting to hear Tony’s thoughts on this system after this mornings run of EC being consist with its previous runs a non-event for mid-Canterbury below 300m whereas all the other major models has the low a lot closer to Canterbury and a pretty major low level snow event if their forecast numbers come off…

[Chris W]

Probably a lot of changes to come in the model runs over the next couple of days, while it can get excited about cold the GFS op run today is looking interesting for either snow or heavy rain to low levels with strong winds on Sunday and the Metservice outlook will be one to watch over the next couple of days. MS 3-day maps have heavy precipitation over mid-north Canterbury from early in the day. Stratosphere and troposphere coupling for a vigorous outbreak over the weekend in some form.

[Bradley]

Probably a lot of changes to come in the model runs over the next couple of days, while it can get excited about cold the GFS op run today is looking interesting for either snow or heavy rain to low levels with strong winds on Sunday and the Metservice outlook will be one to watch over the next couple of days. MS 3-day maps have heavy precipitation over mid-north Canterbury from early in the day. Stratosphere and troposphere coupling for a vigorous outbreak over the weekend in some form.

Looking at Tony's update from last night he was leaning fairly convincingly towards EC with "a 50% chance of a few cms on the eastern plains" and I can see why with EC usually being better then GFS when it comes to winter storms...

[TonyT]

GFS has consistently been the outlier in terms of the location, timing, and intensity of the low pressure trough. Its snow output seems to be in la-la land but the consistency with which it generates that from run to run and through a large majority of its ensemble runs means we shouldn't dismiss it. Ikon and EC are less bullish on snow totals because they locate the depression further north and not as deep. I think we are starting to see a convergence as GFS is pushing its system a little further north compared to yesterday's guidance and EC is bringing theirs back a little further south. I suspect in 24 hours time they will be closer agreement around a midpoint. But bottom line is, don't expect to travel very far on Sunday and look after your lambs.

[Lawrence]

GFS is bei g consistent. Even Access, ikon, CMC all leading close to GFS. EC seems to be the outlier model currently.

GFS is going for a major system. GFS going for 20cm plus to Chch with 35cm above 100m and 50cm to 250m plus.

Big numbers. Certainly one to watch. Warnings will go out today i suspect. Especially for farmers. M/S now have it in there Severe Weather Outlook referring to a very cold outbreak.

Rural Weather seems to be on to it at this point.

https://www.ruralweather.co.nz/content/ ... and-4-maps

[Nev]

Rural Weather seems to be on to it at this point.

https://www.ruralweather.co.nz/content/ ... and-4-maps

That's a cut-n-paste from WeatherWatch...

https://www.weatherwatch.co.nz/content/ ... and-4-maps

[Bradley]

Rural Weather seems to be on to it at this point.

https://www.ruralweather.co.nz/content/ ... and-4-maps

That's a cut-n-paste from WeatherWatch...

https://www.weatherwatch.co.nz/content/ ... and-4-maps

Look like at this point the only groups or organisations talking up the GFS forecast are the Facebook weather groups lol

[TonyT]

Rural Weather seems to be on to it at this point.

By no means the only ones Lawrence.

[TonyT]

Look like at this point the only groups or organisations talking up the GFS forecast are the Facebook weather groups lol

On the face of the GFS numbers are from la-la land. If that was just a one-off run from GFS I would happily ignore it. But its been like that 6 runs now, each supported by very solid ensemble runs. It has to be taken seriously as a credible possible scenario, even if perhaps not currently the most likely scenario.

[TonyT]

Thought it might be interesting and potentially useful to post here all the current synoptic predictions for midday Sunday. These will either be from the models' 12Z or 18Z runs. As you can see, still a lot of variation as to the location and intensity of the wave depression. That feeds back into the uncertainty around precipitation totals and snow levels.

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[Razor]

But bottom line is, don't expect to travel very far on Sunday and look after your lambs.

Mrs Razor is travelling home from the West Coast on Sunday, sounds like an early start to travel is recommended!

[TonyT]

But bottom line is, don't expect to travel very far on Sunday and look after your lambs.

Mrs Razor is travelling home from the West Coast on Sunday, sounds like an early start to travel is recommended!

Don't even try. Seriously. Stay put and stay safe.

[Razor]

Mrs Razor is travelling home from the West Coast on Sunday, sounds like an early start to travel is recommended!

Don't even try. Seriously. Stay put and stay safe.

Tony this potentially is a serious issue. There's a major trail running event in Reefton this weekend. Race day looks great (Saturday) but hundreds of competitors are travelling from all over the South island, and will be trying to travel home on Sunday after the race prizegiving. Its possibly the biggest date on Reefton's calendar for visitors this year

[TonyT]

Don't even try. Seriously. Stay put and stay safe.

Tony this potentially is a serious issue. There's a major trail running event in Reefton this weekend. Race day looks great (Saturday) but hundreds of competitors are travelling from all over the South island, and will be trying to travel home on Sunday after the race prizegiving. Its possibly the biggest date on Reefton's calendar for visitors this year

All I can say is someone has 48 hours to make some decisions.

[talbotmj15]

Latest GFS run is in. Seems to be very similar to last run. Showing 50cm from 200m above and 35cm from about 100m. So amazing that GFS is being so consistent. Is it consistently wrong? Im not sure. Its been the same for about 3 days with nearly every run being identical.

[Northsouth]

Except the low has moved about 300km north before jumping over the alps in the last 36 hours. GFS pulling north, EC pulling south. They will meet somewhere in the middle. Looks decent north of about Hurunui.

[jamie]

Looks like a lot of place in the north island could see snow, that haven’t seen snow in years, or not since 2011.


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[Razor]

Metservice 3 day graphic has much reduced/ very little impact for Canterbury. Its all moving north rapidly to be almost entirely a West coast/ Nelson and then North Island event

Be interesting to see how it plays out and who is right

[Lawrence]

Looking more like a North Canterbury event in this model.

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