South Island snow - July 6-10

[einzack]

You might want to add a few more province's to that title (in a few more runs)

Indeed - could be an interesting few days if this comes to fruition here. I know these computer gen ones aren't worth worrying about, but I thought I'd post it anyways.

[Nev]

You might want to add a few more province's to that title (in a few more runs)

Suggest a more appropriate thread-title and mods will happily change it.

Unfortunately it's usually the area-specific 'Facebook Forecasters' of late that hastily start these threads seeking 'peoples thoughts'. Maybe if those who have actually been discussing these possible events in the previous days were given the chance to start new threads, we might end up with more appropriate thread-titles (spelling/grammar notwithstanding).

[hozza95]

http://www.weatherwatch.co.nz/content/s ... -next-week ww posted this just need now, intersting

[Tim S]

Weatherwatch's forecast seems the most common sense forecast out there at the moment. Although I feel even they are getting a bit carried away with the models. All of the polar blasts this year have been exaggerated by the models and I feel this will be no exception. I would love to be proved wrong though!

[Bradley]

Well said Nev, I have to say the wordings that CWU used last night when describing the event for next week had some scary similarities to what Tony said on his Blueskies update…

Anyway looking at this mornings EC update the moisture levels for inland areas has increased up to around the 50mm mark (from about Darfield and further inland) but the moisture levels for
coastal areas has halved to around 15mm, good news is though it has snow down to sea-level again whereas last night’s run had it gone altogether! GFS also going for the same kind of forecast
as this…

[TonyT]

http://www.weatherwatch.co.nz/content/s ... -next-week ww posted this just need now, intersting

Ha ha, that is hilarious - such an Auckland-centric view of the South Island's weather "just think of it as a few showers"!

[Bradley]

Tony is it just me or does the latest run of ACCESS have that low affecting parts of Canterbury now on Friday and Saturday as well?

[Tim S]

http://www.weatherwatch.co.nz/content/s ... -next-week ww posted this just need now, intersting

Ha ha, that is hilarious - such an Auckland-centric view of the South Island's weather "just think of it as a few showers"!

I think they were referring to the fact that the snow wont be widespread as rain would be, more isolated in nature like showers. That is what i read it as meaning anyway.

[TonyT]

Tony is it just me or does the latest run of ACCESS have that low affecting parts of Canterbury now on Friday and Saturday as well?

The end point of this event is probably going to be the hardest part to forecast accurately, but also probably the least important. These southerly flows have a habit of dragging on for longer than the models suggest, so it is possible, but I wouldn't be too concerned with it at present, whats important is to get the main course in the oven, worry about the desert later.

BTW Blue Skies latest update is on the FB page, and already out to clients, will be on the Farmlands site soon. Not a lot of change to yesterday, but just pulled back a little on the sea level snow.

[Tim S]

Tony, I notice on your forecast you have 30-50cm for areas above 200m, this seems a lot for a southerly fed system as generally the air is a lot colder hence holds a lot less moisture meaning snowfalls are generally a lot lighter than say an advective snow event. Or is there something I'm missing?

[matttbs]

I see metservice are starting to come onboard with this. Predicting snow to "near sea level" Tuesday and Wednesday on the rural section

[TonyT]

Tony, I notice on your forecast you have 30-50cm for areas above 200m, this seems a lot for a southerly fed system as generally the air is a lot colder hence holds a lot less moisture meaning snowfalls are generally a lot lighter than say an advective snow event. Or is there something I'm missing?

If you work off 10:1 ratio for snow to equivalent rainfall (i.e. a mm of rain gives about a cm of snow) then a rainfall of 30mm should give about 30cm of snow, no rocket science needed. You are right, a 30cm fall from a southerly is at the higher end of the range, but it has certainly happened before. You need to check out the models and see the moisture which is getting carried into the trough over the North Island, so its not just the southerly airflow which will influence how much snow falls, but proximity of the trough to the north. And we all know how flighty they can be...

Also perhaps take into account this is a 2-3 day event, so you dont need heavy snow rates to accumulate the 30cm.

[talbotmj15]

You might want to add a few more province's to that title (in a few more runs)

Suggest a more appropriate thread-title and mods will happily change it.

Unfortunately it's usually the area-specific 'Facebook Forecasters' of late that hastily start these threads seeking 'peoples thoughts'. Maybe if those who have actually been discussing these possible events in the previous days were given the chance to start new threads, we might end up with more appropriate thread-titles (spelling/grammar notwithstanding).

Whats your problem NEV. Dont mock me or say **** on the weather forum about me and hide behind your Mod status. You know nothing about me or my knowledge of the weather. Or the fact that i worked in a government funded weather department and have studied the weather for a job. Having a go when you know nothing is pathetic. Just because i put up "thoughts people" doesnt mean anything. it was designed to get people talking about this upcoming event. Isnt that what the forums for. People to discuss the weather. Having the Mods join in on personal attacks is pretty low.

[Tim S]

Tony, I notice on your forecast you have 30-50cm for areas above 200m, this seems a lot for a southerly fed system as generally the air is a lot colder hence holds a lot less moisture meaning snowfalls are generally a lot lighter than say an advective snow event. Or is there something I'm missing?

If you work off 10:1 ratio for snow to equivalent rainfall (i.e. a mm of rain gives about a cm of snow) then a rainfall of 30mm should give about 30cm of snow, no rocket science needed. You are right, a 30cm fall from a southerly is at the higher end of the range, but it has certainly happened before. You need to check out the models and see the moisture which is getting carried into the trough over the North Island, so its not just the southerly airflow which will influence how much snow falls, but proximity of the trough to the north. And we all know how flighty they can be...

Also perhaps take into account this is a 2-3 day event, so you dont need heavy snow rates to accumulate the 30cm.

Thanks for the clarification, does seem on the high end of accumulation but as you said it has happened before.

[matttbs]

this is a weather forum not a bitch fight forum

[Razor]

Suggest a more appropriate thread-title and mods will happily change it.

Unfortunately it's usually the area-specific 'Facebook Forecasters' of late that hastily start these threads seeking 'peoples thoughts'. Maybe if those who have actually been discussing these possible events in the previous days were given the chance to start new threads, we might end up with more appropriate thread-titles (spelling/grammar notwithstanding).

Whats your problem NEV. Dont mock me or say **** on the weather forum about me and hide behind your Mod status. You know nothing about me or my knowledge of the weather. Or the fact that i worked in a government funded weather department and have studied the weather for a job. Having a go when you know nothing is pathetic. Just because i put up "thoughts people" doesnt mean anything. it was designed to get people talking about this upcoming event. Isnt that what the forums for. People to discuss the weather. Having the Mods join in on personal attacks is pretty low.

Can you take this sort of stuff to the private message area? As a dad of 7 year old twin lads, I can assure you there is little to be gained by venting in front of everyone
Ta

[Storm Struck]

Having gone over THK levels for mid next week and in line with the consistent 850mb temps, its fair to say sea level snow does look likely but its a case of how long it could fall for and how much.
Although its only one model THK goes as low as 518 around 12am Wednesday, which if you compare to the coastal Southerly event the other week which didnt have a settling of snow in the city but had flurries at one point.
The lowest THK for that event was 525 which is always borderline, but the 850 was -9c which i thought might help regardless of the high THK values.
Thats just looking at ARL there's lots of other models to be looking at as well i know, but to me anything below that 523 mark you should be getting snow given the right wind direction and topography etc.
With the air becoming freezing early Wednesday will it stay cold right through to early friday and be enough to keep snow at sea level, thats something we can consider closer to the time should this eventuate.

[Razor]

Hey team, a question- and just a laymans observation I have made over past events here in Christchurch. I've noted that there seems a 'high threshold' for sea level snow in town (apart from the odd flurry). But once it transitions to a full blown snow settling event, things somehow seem to intensify to a point where apparent actual moisture levels exceed those modelled and predicted. I say 'apparent' in recognition of the variables attached to actually measure snow depth in comparison to if it had been rain.

Seems to be a 3-5 year event when this happens.

Am I wrong in thinking that once it crosses this 'threshold' that it seems to change the game? Maybe a vague question but I hope people get where I'm coming from

[matttbs]

Hey team, a question- and just a laymans observation I have made over past events here in Christchurch. I've noted that there seems a 'high threshold' for sea level snow in town (apart from the odd flurry). But once it transitions to a full blown snow settling event, things somehow seem to intensify to a point where apparent actual moisture levels exceed those modelled and predicted. I say 'apparent' in recognition of the variables attached to actually measure snow depth in comparison to if it had been rain.

Seems to be a 3-5 year event when this happens.

Am I wrong in thinking that once it crosses this 'threshold' that it seems to change the game? Maybe a vague question but I hope people get where I'm coming from

Would the june 5-6 2012 event be similar to what your talking about? If I recall correctly chch received 30cm which was a lot more than forecast if my memory serves me well

[Storm Struck]

Hey team, a question- and just a laymans observation I have made over past events here in Christchurch. I've noted that there seems a 'high threshold' for sea level snow in town (apart from the odd flurry). But once it transitions to a full blown snow settling event, things somehow seem to intensify to a point where apparent actual moisture levels exceed those modelled and predicted. I say 'apparent' in recognition of the variables attached to actually measure snow depth in comparison to if it had been rain.

Seems to be a 3-5 year event when this happens.

Am I wrong in thinking that once it crosses this 'threshold' that it seems to change the game? Maybe a vague question but I hope people get where I'm coming from

Do you mean like the July 2011 snowfall where moisture levels remained low on model outputs but doubled once the snow began falling at sea level? I think especially for Christchurch regardless of snow or not in SSW flows and sometimes southerly the likes of fresh water off Ellesmere and some kind of land enhancement increases the depth of the shower activity therefore bringing more moisture and heavier snow.
Christchurch is really a set up spot of all sorts because as we know the penninsula can suck in band activity and can also shelter depending on wind directions, i always find it fascinating to see what happens regardless of what models say because models just cant pick up these things.
Is that what you were talking about or am I way off .

The June 5-6th event was around 18cm i think, the only time i know of the city getting 30cm was 1992 and possibly 1945

[SnwAddct]

Looking good for some decent snow at Ruapehu. Lets hope it stays nice and cold..

[Bradley]

Tony is it just me or does the latest run of ACCESS have that low affecting parts of Canterbury now on Friday and Saturday as well?

The end point of this event is probably going to be the hardest part to forecast accurately, but also probably the least important. These southerly flows have a habit of dragging on for longer than the models suggest, so it is possible, but I wouldn't be too concerned with it at present, whats important is to get the main course in the oven, worry about the desert later.

BTW Blue Skies latest update is on the FB page, and already out to clients, will be on the Farmlands site soon. Not a lot of change to yesterday, but just pulled back a little on the sea level snow.

Thanks for the clarification Tony, the main event is definitely still what I'm focusing on for sure! I notice in your update you say the temp has gone up around 1C compared to yesterday's data for next week, just wondering in these kind of events which model tends to be the most reliable for temperature prediction, EC, GFS or ACCESS?

[TonyT]

I notice in your update you say the temp has gone up around 1C compared to yesterday's data for next week, just wondering in these kind of events which model tends to be the most reliable for temperature prediction, EC, GFS or ACCESS?

Generally (speaking globally here) ECMW is considered the most accurate, but they vary with each event. Best to look at each one and see if you can spot some trends which they are all showing. However, tracking trends of 1degC is a bit fraught with uncertainty.

[Razor]

Do you mean like the July 2011 snowfall where moisture levels remained low on model outputs but doubled once the snow began falling at sea level? I think especially for Christchurch regardless of snow or not in SSW flows and sometimes southerly the likes of fresh water off Ellesmere and some kind of land enhancement increases the depth of the shower activity therefore bringing more moisture and heavier snow.
Christchurch is really a set up spot of all sorts because as we know the penninsula can suck in band activity and can also shelter depending on wind directions, i always find it fascinating to see what happens regardless of what models say because models just cant pick up these things.
Is that what you were talking about or am I way off .

The June 5-6th event was around 18cm i think, the only time i know of the city getting 30cm was 1992 and possibly 1945

Yea that's the sort of event I am talking about. Once they get going (which is rare) they tend to deliver in spades. I too have wondered about the Lake Ellesmere impact, but suggest it would have to be exactly the right windflow, because otherwise Banks Peninsula ends up doing that sheltering thing, as we saw last month. Or else its too SW

So is it fair to say it could be that there is a very narrow band of wind direction that feeds these events into ChCh proper?

[Richard]

the only time i know of the city getting 30cm was 1992 and possibly 1945

The 1945 snow was about 15cm,ive got a photo of mother standing by a fence where they lived in Papanui and you can work out how deep,the snow depth from that event seems to grow deeper as the years past,its a bit like Rangiora, you hear some people say that there was '3feet', but look at old photos and there's no way there was that much.