Large Rain Event Canterbury and high altitude snow. 29-31st May 2021

[snowchaser01]

Very litttle rain so far here in the City. 4mm in total and it's now stopped. Hoping the heavy feed zone hits us soon as forecast.

Looooong way to go yet...3 day map update on MS this morning predicted a slight clearance around mid afternoon before returning harder and faster a few hours later.

[NZ Thunderstorm Soc]

Definitely raining down here in Geraldine. Had 35.1mm so far today from around midnight. and still raining with no evidence of it easing up.

[mikechamble]

Just been across the city from Halswell back home to parklands. Rain out Halswell was becoming more persistent but had cleared up as i headed back east.

Traffic though, was awful. Not sure what it is about rain that causes almost everyone to forget how to drive properly. And this before the real event has even started. Best to be well off the roads by then.

[Orion]

Raining, thick overcast, dark enough to need lights on indoors really;

feels cold: 7.8°C.

[Chris W]

Coming on to a shower in Lyttelton now with a slight increase in the wind strength. I can see some evidence of that jet starting to form up as there are some purple specs on the edge of the rain band. Evidence of shadowing for the city from the peninsula, but how much remains to be seen.

[Razor]

Looking through the Ecan gauges, approaching 50mm in a few sites now, Geraldine and Mt Somers for eg

[snowstormwatcher]

Yeah river levels haven't gone up to much yet though.
Based on past experiences it takes a lot more rain to get the rivers flooding when the soil is dry like it has been lately compared to if the soil was sodden.

[NZ Thunderstorm Soc]

Looking through the Ecan gauges, approaching 50mm in a few sites now, Geraldine and Mt Somers for eg

A bit of flooding in our street at the moment, spent yesterday clearing leaves out of the gutter outside but to no avail. Still flooding.

[Razor]

Rakaia Rain radar offline? That rain band just totally vanished from Canterbury, has to be a tech issue surely

[TonyT]

34mm so far in Amberley, street gutters are full to overflowing, and the drainage swale at the back of our property is full and flowing fast.

[Razor]

34mm so far in Amberley, street gutters are full to overflowing, and the drainage swale at the back of our property is full and flowing fast.

Just 3.6mm here so far but it looks to be picking up

[Razor]

Rakaia Rain radar offline? That rain band just totally vanished from Canterbury, has to be a tech issue surely

Back on, phew

[Tuppence]

8.5mm of rain from 4.30pm yesterday to 8.15am this morning in Rakaia. A brief heavy burst half an hour ago but other than that nothing out of the ordinary here.

[NZ Thunderstorm Soc]

Rakaia Rain radar offline? That rain band just totally vanished from Canterbury, has to be a tech issue surely

Back on, phew

Yes, the Otago Radar at Hindon was doing the same thing this afternoon, showing a bunch of heavy showers moving towards Dunedin, then all of a sudden disappearing, except for the 120k option.?

[Cantab03]

Rain just can't get any momentum here. 5mm so far. I think some level of sheltering is occurring, despite the heaviest rain period not starting for a few hours. On a side note, have hit 100mm for YTD.

[03Stormchaser]

Currently in Wellington, so will miss this. Still very early in this event, although have seen some images of flooding in Mid Canterbury.

[Orion]

Rain splattering on an east-facing window now.
Temp. gone up to 10.9°C.

[NZ Thunderstorm Soc]

Yes, back to a more easterly faction here too with it being a bit milder. 10.7C at 6pm.
I can remember with easterly wind factions can be quite wet in this sort of weather scenario.
I hope it doesn't rain into my woodshed which faces to the north/NE.

[Awhituobs]

better rain bands developing heading for CHCH now

[TonyT]

RaIn has eased off here now, and cloud breaking a little, and temperature has pushed up 2 degrees. I suspect the passage of a warm front.

[Cyclone Tracy]

The nocturnal low-level jet is going to induce a parade of new vortices north east of Pegasus Bay tomorrow morning heading WSW towards the Canterbury coast tomorrow afternoon.

[snowchaser01]

Radar starting to really kick off now. Just starting to properly set in region wide. Extremely problematic.

[TonyT]

12Z ECMWF ensemble rainfall is closing in nicely now we are less than 3 days out. So the range (for Christchurch, by Monday night) is 50-115mm with the mean at 80mm and the control run at 85mm. Slightly less of the region in the 150mm+ zone now, but most areas other than then far eastern Plains in the 100-150mm range.

The narrow feed of near gale force easterly winds into Pegasus Bay briefly between midnight and 6am Sunday morning (that CT identified earlier - good job!) has to be a concern as it coincides with a high tide (around 6am) and the area is likely to have already received 50mm of rain. Significant easterly swells will be generated. The potential impact on river/lagoon mouth drainage and possible erosion potential in that brief time period need to be highlighted.

0Z EC ensemble not much changed from 12 hours earlier, with a range of 55-125mm with a mean of 80mm and the control run at 95mm (for Christchurch by Monday night). However, the EC operational run now has 95mm, the first time in a while that this value has exceeded 90mm for the event. Almost all of the Canterbury region is showing event totals of 125mm+ apart from the rain shadow area around Banks Peninsula.

Also worth noting that the low level easterly jet due to peak into Pegasus Bay 3-5am tomorrow morning is now modelled as stronger than it was this morning.

[Cantab03]

Rain picking up in Christchurch over the last 30 minutes. Up to 8mm here now for the day.

Some current totals via ECAN:

Mt Somers 116mm
Geraldine Forest 71mm
Mt Hutt 58mm
Ashley Gorge 54mm
Whitecliffs 45mm
Waimak Esk 42mm

Several stations will be in triple figures come morning.

[03Stormchaser]

Rain picking up in Christchurch over the last 30 minutes. Up to 8mm here now for the day.

Some current totals via ECAN:

Mt Somers 116mm
Geraldine Forest 71mm
Mt Hutt 58mm
Ashley Gorge 54mm
Whitecliffs 45mm
Waimak Esk 42mm

Several stations will be in triple figures come morning.

Looking at the current rain bands moving in and how heavy the rain appears on radar, I think nearly all will be in the triple digits. Christchurch included.