Tropical Atmospheric River 13-17 Dec

[NZ Thunderstorm Soc]

The Manawatu copped a bit of rain this afternoon with flooding reported in Feilding, with some thunderstorms reported in that area.

[JP.]

Metservice rainfall forecast for Christchurch city tomorrow is over 95mm in the 24 hours. I’ve never seen a daily total forecast that high in years.

Christchurch has surface flooding when totals reach 40-50mm so we could have some terrible issues if we do get 95+

[Bradley]

Metservice rainfall forecast for Christchurch city tomorrow is over 95mm in the 24 hours. I’ve never seen a daily total forecast that high in years.

Christchurch has surface flooding when totals reach 40-50mm so we could have some terrible issues if we do get 95+

That amount will be modified down the closer we get to the event…

[JP.]

That amount will be modified down the closer we get to the event…

Interesting because they have just changed it to 121mm in 24 hours

[Awhituobs]

57mm here yesterday, 22mm so far today
145mm for the month
(verified with a normal rain gauge as well)
the hills here give orographic rain effect in a N to NE wind flow
104mm total since the start of the rain

[Chris W]

MS rain charts/UK model have increased rainfall rates for Canterbury tomorrow, starting with Kaikoura and working its way south into the latter half of the day. It could be an overestimate but after June I'd be wary of saying that, though at this stage it looks like Ashburton at least gets off more lightly than Selwyn and areas further north. Hopefully rainfall rates stay low enough for long enough to allow drainage to mitigate totals.

[Razor]

yes the metservice model is starting to approach 100mm for Christchurch City. I think Banks Peninsula is the area to watch the most along with the Kaikoura mountains and all that orographic effect

[Bradley]

That amount will be modified down the closer we get to the event…

Interesting because they have just changed it to 121mm in 24 hours

Both EC and GFS are going for under 50mm for Christchurch until Thursday morning which will be the most likely outcome...

[Rogue]

Well the stream behind my house is nearly back up to the level it reached last week, which itself was the highest other residents have seen in at least six years. No real risk to my house but do worry about the base of the retaining wall... Also reports of significant flooding of property around Paraparaumu. Well and truly over this weather!

IMG_20211214_091651.jpg

[David]

56mm so far. With another 25mm+ expected. Just what was needed after almost 4 weeks of negligible rain!

[darcyplumb]

MS rain charts/UK model have increased rainfall rates for Canterbury tomorrow, starting with Kaikoura and working its way south into the latter half of the day. It could be an overestimate but after June I'd be wary of saying that, though at this stage it looks like Ashburton at least gets off more lightly than Selwyn and areas further north. Hopefully rainfall rates stay low enough for long enough to allow drainage to mitigate totals.

Water table is still incredibly high here in Ashburton after the June event and subsequent rainfall since then. Metservice have significantly increased expected rainfall for us over the next 48 hours which concerns me. Ashburton River still only has temporary stopbank protection at the June breakout sites and we know how close the town stopbank got to being overtopped. Certainly an event I am keeping a very close eye on.

[Bradley]

I see the TC has been named:
TC Ruby

Do we not start each season from 'A" now?

Metservice has just released a heavy rain warning for Christchurch with 110-160mm accumulating which is double what GFS and EC are forecasting, what are you seeing Tony? Are the major models playing this down a bit in your opinion?

Periods of heavy rain. Expect 110 to 160 mm of rain to accumulate, especially north of Christchurch. Peak rates of 15 to 25 mm/h. Note, heavy rain is expected to ease north of Christchurch after midnight Wednesday.

[spwill]

Dry to wet here in two days, 70mm in total here at my place. Looks like another spell of heavy rain this evening.


Thunder rsk showing up for Waikato tomorrow afternoon, see how the ingredients look tomorrow morning.

[TonyT]

Do we not start each season from 'A" now?

Metservice has just released a heavy rain warning for Christchurch with 110-160mm accumulating which is double what GFS and EC are forecasting, what are you seeing Tony? Are the major models playing this down a bit in your opinion?

Periods of heavy rain. Expect 110 to 160 mm of rain to accumulate, especially north of Christchurch. Peak rates of 15 to 25 mm/h. Note, heavy rain is expected to ease north of Christchurch after midnight Wednesday.

I'll do a live stream at 1pm to cover this. The main models are looking good in my opinion but I seem to be interpreting more rain from them than you are..

[JP.]

I'll do a live stream at 1pm to cover this. The main models are looking good in my opinion but I seem to be interpreting more rain from them than you are..

Hi Tony, where are your livestreams found? I looked on FB but could only see some older ones.

Thanks

[TonyT]

I'll do a live stream at 1pm to cover this. The main models are looking good in my opinion but I seem to be interpreting more rain from them than you are..

Hi Tony, where are your livestreams found? I looked on FB but could only see some older ones.

Thanks

Blue Skies Weather 2.0 on Facebook. I got hacked back in April, and had to set up a new page. I can't access the old one, I've been locked out, and no way to delete it.

https://www.facebook.com/BlueSkiesWeather2.0

To be fair to Bradley, the 12Z operational run of the ECMWF was very much at the low end of the ensemble range for Christchurch rainfall.

[Bradley]

Hi Tony, where are your livestreams found? I looked on FB but could only see some older ones.

Thanks

Blue Skies Weather 2.0 on Facebook. I got hacked back in April, and had to set up a new page. I can't access the old one, I've been locked out, and no way to delete it.

https://www.facebook.com/BlueSkiesWeather2.0

To be fair to Bradley, the 12Z operational run of the ECMWF was very much at the low end of the ensemble range for Christchurch rainfall.

Thanks Tony, I look forward to your livestream at 1pm!

[Awhituobs]

the rain band moving south over northland is impressive!

[Richard]

Screenshot 2021-12-14 at 17-31-41 Culverden Weather Forecast and Observations - MetService New Zealand.png

This sort of rainfall rate is something more common seen for the West Coast, not Culverden. Never seen such a high accumulation rate from the MS for here before. I'm sure others from around Canterbury must have noticed the amount of unstable cloud around today, really did have an ominous look to it.

[Razor]

Screenshot 2021-12-14 at 17-31-41 Culverden Weather Forecast and Observations - MetService New Zealand.png

This sort of rainfall rate is something more common seen for the West Coast, not Culverden. Never seen such a high accumulation rate from the MS for here before. I'm sure others from around Canterbury must have noticed the amount of unstable cloud around today, really did have an ominous look to it.

Certainly noticing that instability in the sky here in ChCh in the past hour or two. Brooding skies. Somewhere will get a good drenching tomorrow, but these 'atmospheric river' set ups tend to be a tough thing to pin the tail on in terms of biggest effects. My guess is Kaikoura Coast and Banks Peninsula Outer Bays, but its only a guess. Gone are the dry starts to summer of the past 4-5 years, classic La Nina

[Richard]

Gone are the dry starts to summer of the past 4-5 years, classic La Nina

Yes, there's a pattern that seems to have become common over the last few years where Dec is generally cool and cloudy, and then the summer switch gets turned on after new year

[darcyplumb]

Screenshot 2021-12-14 at 17-31-41 Culverden Weather Forecast and Observations - MetService New Zealand.png

This sort of rainfall rate is something more common seen for the West Coast, not Culverden. Never seen such a high accumulation rate from the MS for here before. I'm sure others from around Canterbury must have noticed the amount of unstable cloud around today, really did have an ominous look to it.

We are in Hanmer Springs for the night. The unstable looking sky caught my eye on a number of occasions today.

[Razor]

Good lord, the Metservice precipitation model for Christchurch now gives 170mm + for the event. Thats gotta be a rogue output, surely

[darcyplumb]

Good lord, the Metservice precipitation model for Christchurch now gives 170mm + for the event. Thats gotta be a rogue output, surely

I would hope for Christchurch’s sake that we don’t see that sort of number.

[Cantab03]

Good lord, the Metservice precipitation model for Christchurch now gives 170mm + for the event. Thats gotta be a rogue output, surely

That was what 3 day map was showing earlier this afternoon and this evening, but its just updated again and pulled back somewhat. Still very decent rain but Thursdays rainfall is clearing a lot earlier on metservice model run now, instead of the very heavy falls lasting to midday.