NZ Weather Forum

Bloody wet in Franz Josef!

SH6 is closed overnight between Fox Glacier and Mokarara, so it's a fairly long detour between Wanaka and Franz.

The thunderstorm outlook said

"However there have been lightning strikes detected and observed from wave cloud over Canterbury and North Otago this morning, and there is a moderate risk of a few further lightning strikes about Canterbury and Kaikoura this morning and early afternoon. Note, these are technically not thunderstorms, but lightning strikes from wave clouds aloft."

If they're not thunderstorms, what are they then?

Cloud to cloud lightning in a wave cloud is something I have only ever experienced once here in Wellington in 20 years. But when it happens it is VERY impressive. The fact I was woken from a very deep sleep by a said wave cloud thunder clap, AND it showed up on the geonet quake drums shows how much energy can be released!!

Post from 2012 And the GeoNet quake drum close up at the time.

dogmelon wrote: ↑Wed 02/02/2022 22:55 The thunderstorm outlook said

"However there have been lightning strikes detected and observed from wave cloud over Canterbury and North Otago this morning, and there is a moderate risk of a few further lightning strikes about Canterbury and Kaikoura this morning and early afternoon. Note, these are technically not thunderstorms, but lightning strikes from wave clouds aloft."

If they're not thunderstorms, what are they then?

Flashes

I noticed the lack of lightning too.Despite the forecast there were no thunderstorms anywhere on Blitzortung yesterday arvo across NZ.

A wave cloud essentially is an elongated and perhaps thinner anvil of a Thunderstorm. Its just the updraft that caused it is far enough away from it and technically can be disconnected from the storm that formed it. Lightning strikes from the anvil in cumulonimbus are fairly common.

The lightning that forms from waveclouds and anvils in Thunderstorms tends to be quite strong and is usually postive in polarity. The reason for this is the Cloud to ground Lightning at that height has to overcome a very large resistance of around from 5 to 9KM of air to travel to earth.

Reason why it can strike in sequence more like a typical thunderstorm is due to the updraft (or lift mechanism) upstream pumping more charge (water vapour getting charged from lift) up into the upper atmosphere (wether that be from a jet stream, orography induced uplift etc). This process is external to the cloud, where as a Thunderstorms updraft is internal.

This process is different from Elevated Thunderstorms, as an elevated Thunderstorm is basically a Thunderstorm that operates with half or less of atmosphere to form itself in the upper atmosphere. The mechanics that feed an elevated Thunderstorm and a wavecloud can be similar if not the same though.

Hope that makes sense.

MetService tweet gives rainfall totals for 18 hours to 1pm today (Weds 2nd Feb) with a maximum value of 189mm at Mt Aspiring National Park. I would guess quite a bit more has fallen since then.

https://twitter.com/MetService/status/1 ... 0439913472

A NIWA tweet gives a figure of 335mm at Ivory Glacier for the 17 hours to 5pm on Wednesday 2nd Feb.

https://twitter.com/NiwaWeather/status/ ... 0969205761

No alerts on the west coast rivers this morning, Haast is up over 5.3m and doing close to 3000 cumecs but overall at the moment (early Thurs am) rainfall intensities are declining.

https://envirodata.wcrc.govt.nz/dashboa ... vels.php#1

Highest rainfall total I can see is Tuke River inland from Ross at Tuke Hut, 528.5mm for 24 hours and 633.5mm this week.
https://envirodata.wcrc.govt.nz/dashboa ... infall.php

Higher intensity rainfall is further north for the rest of this event, so northern Westland and Buller/Grey in the firing line as well as Nelson/Tasman/Golden Bay.

Chris W wrote: ↑Thu 03/02/2022 08:34
Higher intensity rainfall is further north for the rest of this event, so northern Westland and Buller/Grey in the firing line as well as Nelson/Tasman/Golden Bay.

Worried about Westport township with 124mm yesterday, 51mm forecast today and 121mm forecast for Friday. Friday could be the sting in the tail

Westport EWS (NIWA) at the WCRC page (have edited my last post) is 113.6mm for the last 24 hrs, 137.8mm so far this week.

24hr before and after view of the river below Fox Glacier from Wednesday morning vs today. Via webcam on Windy.com

Buller civil defence advising people to self-evacuate from Westport:
https://twitter.com/NZcivildefence/stat ... 15tcMsS05Q

No one posting here this afternoon. Thinking of our Westport people, looks like the focal point for Friday

Noticed that Metservice have indicated that rain is to return to Southland today as the Tasman Sea cloud returns to the province.Raining lightly in Northern Southland currently.

lots of rain mid/north westland on the rain radar currently and lots more to come!

Numbers are pretty big in some of those rain gauges for the event so far

Top 5 to date:
Tuke Hut 849mm
Waiho at Douglas Hut 761mm
Cropp Rv at Waterfall 756mm
Haast Rv at Cron 669mm
Ivory Rv at Gorge 643mm

https://envirodata.wcrc.govt.nz/dashboa ... infall.php

Wow. It looks as though some of those places will easily top a metre of rain. That's a phenomenal amount of water when you think of the area involved, then when you think about how steep some of those West Coast catchments are, no wonder the rivers rise so quickly.

Mandatory evacuations have been ordered for parts of Westport:

https://www.arcgis.com/apps/webappviewe ... 2%2C102100

Both the Buller and Hokitika Rivers have just gone through their alarm flows.

Rain still tipping down on those WCRC gauges- The Tuke Hut 12mm shy of 1000mm for the event (probably surpassed it as I typed this)

The Buller river has been rising steadily over the course of the day but is now rising quite quickly. I feel for the people of Westport. Awful that they are experiencing this again.

Looks like the rain is easing in the Westport Area. Small but useful mercy 4 hours out from high tide

Tuke Hut 1,177mm as tweeted by NIWA just now, Westport 287mm:

https://twitter.com/NiwaWeather/status/ ... mef7w&s=19

For the WCRC stations I looked earlier and Bald Hill/Buller River was over 450mm for the week, Inangahua River copped a lot as well. Link in earlier messages.

Chris W wrote: ↑Sat 05/02/2022 13:44 Tuke Hut 1,177mm as tweeted by NIWA just now, Westport 287mm:

For the WCRC stations I looked earlier and Bald Hill/Buller River was over 450mm for the week, Inanghahua River copped a lot as well. Link in earlier messages.

Must be like being in a massive downpour that lasts for a few days instead of a few hours that we're used to elswhere in NZ.