First Major Winter Storm of 2019

[snowchaser01]

MetService CANTERBURY HIGH COUNTRY forecast for Saturday mentions heavy rain turning to snow at all levels. I presume this means above 500m?

Thats the thing with what the MS zones, the 'CANTERBURY HIGH COUNTRY' takes in my area and extends out as far as Cheviot, its not what you would call high country

So going by that, does that mean they are expecting snow as low as cheviot? "snow to all levels"

[Bradley]

Thats the thing with what the MS zones, the 'CANTERBURY HIGH COUNTRY' takes in my area and extends out as far as Cheviot, its not what you would call high country

So going by that, does that mean they are expecting snow as low as cheviot? "snow to all levels"

They seriously aren't suggesting snow down to 190m asl for Culverden on Saturday? They need to be more careful with their wordings, based on current data from all models that is 100-200m lower then anyone else is forecasting...

[talbotmj15]

I see MS not really that interested in this event. Seem very reluctant to put out numbers. Tony T has said snow to 400m. Tony what numbers are you seeing falling at these levels? EC is quite bullish going with 20cm at 400m. Personally i dont see this. Thoughts Tony?

[Cyclone Tracy]

FYI - EC 18Z upgraded Canterbury snow accum above 700m over a wide area by 20cm on Saturday. Snow level still down to around 400m. The west wiggle of the low meant more moisture available. Of course that will wiggle again on the next 00Z run

[TonyT]

I see MS not really that interested in this event. Seem very reluctant to put out numbers. Tony T has said snow to 400m. Tony what numbers are you seeing falling at these levels? EC is quite bullish going with 20cm at 400m. Personally i dont see this. Thoughts Tony?

5-10cm above 500m, a few cm to 400m. I dont really see this as a big snow maker for the lower high country, but the ski fields will love it. Brief heavy rain early Saturday morning could be interesting on the Plains. I think the interest in this system is how widespread the shitty weather will be for pretty much everyone in the country, rather than any one area getting it particularly bad.

[Bradley]

I see MS not really that interested in this event. Seem very reluctant to put out numbers. Tony T has said snow to 400m. Tony what numbers are you seeing falling at these levels? EC is quite bullish going with 20cm at 400m. Personally i dont see this. Thoughts Tony?

5-10cm above 500m, a few cm to 400m. I dont really see this as a big snow maker for the lower high country, but the ski fields will love it. Brief heavy rain early Saturday morning could be interesting on the Plains. I think the interest in this system is how widespread the shitty weather will be for pretty much everyone in the country, rather than any one area getting it particularly bad.

GFS going for 10mm approx for Christchurch in it’s 00z run, NIWA’s computer going for 80mm with EC somewhere in between, no surprises I guess with the positioning of the low pressure system anyone’s guess 48 hours out...

[snowchaser01]

Yes, Niwa going for the low hanging around in Pegasus Bay, whereas GFS has it all the way up near Welly...

[snowchaser01]

Also, both EC and GFS are picking at least 20cm for Hanmer Springs. Interesting as it is only at 330m... maybe the models are picking some sort of advection...

[NZ Thunderstorm Soc]

Rain band layer accumulating, now to the west. Should, at least see some flashes to the west this evening.
Some light sferics on the AM band.

[TonyT]

Also, both EC and GFS are picking at least 20cm for Hanmer Springs. Interesting as it is only at 330m... maybe the models are picking some sort of advection...

Neither model has the resolution to distinguish between the town at 330m and the surrounding ranges at double or treble that elevation. Remember that models are guidance, not a forecast.

[snowchaser01]

Also, both EC and GFS are picking at least 20cm for Hanmer Springs. Interesting as it is only at 330m... maybe the models are picking some sort of advection...

Neither model has the resolution to distinguish between the town at 330m and the surrounding ranges at double or treble that elevation. Remember that models are guidance, not a forecast.

Yep, I am aware. Was just pointing something out that I had noticed. Not a forecast... just guidance.

[Richard]

Thats the thing with what the MS zones, the 'CANTERBURY HIGH COUNTRY' takes in my area and extends out as far as Cheviot, its not what you would call high country

So going by that, does that mean they are expecting snow as low as cheviot? "snow to all levels"

No, it wont snow this low

[Chris W]

Looks like MetService don't currently expect any warning thresholds to be exceeded for Canterbury, but they at least mention snow to 800m and I'd think it's certainly possible for it to fall a bit lower than that. They probably have their outlook about right, given the uncertainty in the location of the low off the South Island, with the possibility of severe gales if it positions itself close to Banks Peninsula, and probably not enough rain or snow in any case to justify a warning - again for Canterbury.

[Bradley]

Looks like MetService don't currently expect any warning thresholds to be exceeded for Canterbury, but they at least mention snow to 800m and I'd think it's certainly possible for it to fall a bit lower than that. They probably have their outlook about right, given the uncertainty in the location of the low off the South Island, with the possibility of severe gales if it positions itself close to Banks Peninsula, and probably not enough rain or snow in any case to justify a warning - again for Canterbury.

Latest run of EC still bullishly going for 20cm down to 300m asl for places like Sheffield and Methven, nothing to 200m asl at all so an interesting 24-36 hours coming up in terms of model forecasts and guidance for this event

[Cyclone Tracy]

UKMet 00Z going for a low 970's cyclonic gyre just off coast from Christchurch Saturday AM. Looks like a sting jet scenario. When interacting jet streams running at 300 km/h + are involved, things can escalate quite quickly.

[talbotmj15]

Seems interesting that EC still super keen on big snow numbers given its the more reliable model. GFS not that keen at all. Im picking somewhere inbetween. The position of that low is very critical. On a side note its crazy windy here.

[NZstorm]

EU looks like snow to 100m mid to north Canterbury Saturday.

[Bradley]

Latest run of EC this morning now going for snow on Saturday right down to sea level for Canterbury Only a few centimetres but still a huge upgrade overnight...

[talbotmj15]

Tony why do you believe theres still such distance between the models on 48 hours out. GFS vs EC. Which do you see as being more accurate with this setup?

[snowchaser01]

Latest run of EC this morning now going for snow on Saturday right down to sea level for Canterbury Only a few centimetres but still a huge upgrade overnight...

This EC run has thrown out 11cm for Chch on Saturday... I don't believe that for a second but EC definitely seems like the more consistent model for this event so far.

[TonyT]

Tony why do you believe theres still such distance between the models on 48 hours out. GFS vs EC. Which do you see as being more accurate with this setup?

Neither model is accurate. You make your first mistake in assuming that either of them could be. They are providing you with guidance about what might happen. They dont know what is going to happen, any more than you or I do. Stop assuming that each model run is an attempt at the truth, and see it as an opinion. Your opinion changes as you get more data and according to the various biases you carry around in your head. The models are no different. There is a range of possible outcomes with very small changes to the initial inputs - try to look at some of the ensemble model sets and you will see significant variation across 20 or 50 runs of the same model with essentially the same inputs. I'll try to post some examples later this morning when I have more time.

PS - models have consistently been more bullish about low level snow potential in Canterbury for the Tuesday/Wednesday storm next week than this weekend. Just saying.

[snowchaser01]

Tony why do you believe theres still such distance between the models on 48 hours out. GFS vs EC. Which do you see as being more accurate with this setup?

Neither model is accurate. You make your first mistake in assuming that either of them could be. They are providing you with guidance about what might happen. They dont know what is going to happen, any more than you or I do. Stop assuming that each model run is an attempt at the truth, and see it as an opinion. Your opinion changes as you get more data and according to the various biases you carry around in your head. The models are no different. There is a range of possible outcomes with very small changes to the initial inputs - try to look at some of the ensemble model sets and you will see significant variation across 20 or 50 runs of the same model with essentially the same inputs. I'll try to post some examples later this morning when I have more time.

PS - models have consistently been more bullish about low level snow potential in Canterbury for the Tuesday/Wednesday storm next week than this weekend. Just saying.

Tony with all due respect, no one is assuming that the model runs are an attempt at the truth. We are aware they are purely guidance. The question simply was why you believe there is so much difference between EC and GFS.. one of them must be closer to the truth.

[Razor]

Neither model is accurate. You make your first mistake in assuming that either of them could be. They are providing you with guidance about what might happen. They dont know what is going to happen, any more than you or I do. Stop assuming that each model run is an attempt at the truth, and see it as an opinion. Your opinion changes as you get more data and according to the various biases you carry around in your head. The models are no different. There is a range of possible outcomes with very small changes to the initial inputs - try to look at some of the ensemble model sets and you will see significant variation across 20 or 50 runs of the same model with essentially the same inputs. I'll try to post some examples later this morning when I have more time.

PS - models have consistently been more bullish about low level snow potential in Canterbury for the Tuesday/Wednesday storm next week than this weekend. Just saying.

Tony with all due respect, no one is assuming that the model runs are an attempt at the truth. We are aware they are purely guidance. The question simply was why you believe there is so much difference between EC and GFS.. one of them must be closer to the truth.

Thank you Tony for the comprehensive reply. Without expert views like yours and CT and a few others around here us more amateur types (I am one) would chase our tails far too often.

I also am more interested in the second system. I think because its been so long since a decent weather system here in Canterbury that we are all getting a bit wound up over what may well fizzle ( myhunch only), comparatively speaking

[snowchaser01]

Tony with all due respect, no one is assuming that the model runs are an attempt at the truth. We are aware they are purely guidance. The question simply was why you believe there is so much difference between EC and GFS.. one of them must be closer to the truth.

Thank you Tony for the comprehensive reply. Without expert views like yours and CT and a few others around here us more amateur types (I am one) would chase our tails far too often.

I also am more interested in the second system. I think because its been so long since a decent weather system here in Canterbury that we are all getting a bit wound up over what may well fizzle ( myhunch only), comparatively speaking

As always your input is appreciated Razor, currently can't see too much with the second system. It doesn't look overly cold anyway (just my opinion).

Let's just see how this one plays out, but i think it goes without saying that everyone around here appreciates the knowledge and input that Tony and CT provide.

[Chris W]

Interesting, MetService rain maps/UKMO output now show the low crossing the middle of the South Island, with greater rain and ramping up the wind in mid-Canterbury as well as a lot of snow over Arthur's Pass. I'd expect changes in the outlook this morning unless that is an outlier.