General April Weather

[NZstorm]

A significant amount of lightning in the Tasman this morning as a potent polar trough interacts with moist air.

Thunderstorms will affect the west of the North Island tomorrow morning. An isolated tornado/severe wind gust report not impossible.

Weather gradually settling down from mid week as a high builds in, back to more traditional April weather.

[spwill]

I think the general trend for the rest of April will be westerly pattern.

[einzack]

Very strong NE wind down this way today. Very unusual for us to have a NE wind this strong. Easily gale strength. House shaking at times. It's causing some issues with my beer-making.

[Orion]

^ I noticed "white horses" streaming up Otago Harbour this morning when I looked on the albatross webcam http://www.doc.govt.nz/royalcam - the bird seems to have hunkered down in the wind

[NZ Thunderstorm Soc]

Very strong NE wind down this way today. Very unusual for us to have a NE wind this strong. Easily gale strength. House shaking at times. It's causing some issues with my beer-making.

Been sort of calm here all day with a light SW drift for much of the day. Nice NW Arch though, this afternoon.
I see that it has been rather windy in ChCh and Dunedin, with the ENE, with Jeff having a high wind run in Hillmorten of 246 km.

[Razor]

Spent most of the day today at Castle Hill. Wonderful up there. Extremely strong NE here in town. MS projecting around 20mm overnight for us, seems on the high side?

[NZ Thunderstorm Soc]

A bit of sporatic lightning way out to the west from here, late this evening. Seems distant.
Looks like the West Coast is getting it.

[Chris W]

In Wellington. Great weekend's weather especially yesterday, but hoping for some sparks this morning.

[melja]

On the boat Marlborough sounds, weather has turned very wild!

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[Cyclone Tracy]

GEFS ensemble 1504 18Z and some runs before it, has picked up a sudden stratospheric warming (SSW) event over Antarctica towards the end of April, which is mixing down the layers of the stratosphere. If this pans out, zonal winds will transfer into the troposphere, weaken the polar vortex and transport cold air northward towards NZ. That late season monsoonal burst might be triggering the ripple effect at these levels. Sea surface temperatures are expected to remain well above normal over the next month.

It's still early but IMO, if the American ensemble is correct, I think something epic is brewing for the middle May that will affect North and South Islands.

[SnwAddct]

GEFS ensemble 1504 18Z and some runs before it, has picked up a sudden stratospheric warming (SSW) event over Antarctica towards the end of April, which is mixing down the layers of the stratosphere. If this pans out, zonal winds will transfer into the troposphere, weaken the polar vortex and transport cold air northward towards NZ. That late season monsoonal burst might be triggering the ripple effect at these levels. Sea surface temperatures are expected to remain well above normal over the next month.

It's still early but IMO, if the American ensemble is correct, I think something epic is brewing for the middle May that will affect North and South Islands.

What was the last example of this scenario? How was the weather impacted for NZ etc? Do we have any dates for said event to look back on?

[TonyT]

What was the last example of this scenario? How was the weather impacted for NZ etc? Do we have any dates for said event to look back on?

Major SSW events are quite rare in our hemisphere (less common than over the arctic). I think there have only been a few this century. Minor ones are more common, we see them every couple of years, but I dont know where we could find a list of them. Too early to say how major this one will be. They usually manifest as a significant injection of polar air (i.e. cold) into lower latitudes. This affects temperatures and storminess. They often will disrupt the polar jet stream in a major way, so weather systems get "out of sync" the usual latitude belts.

[Cyclone Tracy]

Good question and reply from Tony.

The warming in the stratosphere at those levels should be taken seriously. Whether it happens is still debatable. The side effects from the marine heatwave in the Tasman is unprecedented, so there is no historical comparison for this set up that I'm aware of. I've also checked a reliable temperature forecast run for 23rd to 30th April from NAEFS and it has a bullseye on the Tasman for abnormally high temperatures again.

An extreme sudden stratospheric warming event has just occurred in Feb this year above the Artic which delivered the 3 versions of the 'Beast from the East' to western Europe. Some suggest that initial evidence is pointing to a vast area of tropical storms including Cyclone Gita that triggered the warming in the Stratosphere over the Artic, as part of a meteorological 'butterfly effect'.

[NZstorm]

Looks like a return to summer next week with fine Anzac Day.

A little area of storms crossing the top of Northland today. Yesterdays set up did not eventuate for Auckland, possibly because the forcing was not good enough.

[Cyclone Tracy]

That multicell cluster NW of Auckland is now showing around -50c cloud tops and heading SE.

[spwill]

See if that incoming thunder activity can hold up.

Up to 25C at Greylynn today, dp has been around 17C.

[Cyclone Tracy]

That Auckland bound cell is decaying to a standard shower for now, still sparking around Northland though.

Hit 24c today back to 23c with a DP of 18c

[David]

Yeah quite impressed with the temperature today, up to 24.3C in Howick, warmest this month. A little surprising considering that it wasn't even 15C last Wednesday.

[Razor]

Some unplanned NW rain here this evening

[Cyclone Tracy]

I was half expecting the GEFS ensemble to calm down on it's sudden stratospheric warming event by the end of the month but it's doing the opposite. Each run over the last 4 days has locked onto this event and it now has significant mixing down into the lower stratosphere. Upper stratosphere now showing a more extreme 20c anomaly around the end of April over Antarctica and holds a warming period of around a week for the event. Atmospheric alarm bells will sound if this comes off in 10 days and pulses of the polar vortex will balloon into the ridge over a bubbling warm Tasman by mid to late May. Considering the SST's, I've never seen a set up like this, maybe someone has?..... interesting indeed.

[mikestormchaser]

I'd keep eye on the sky tomorrow evening for Canterbury. I see a chance of heavy showers/hail with the SW flick tomorrow evening

[NZ Thunderstorm Soc]

Will be out at a do at Rangitata Island tomorrow night. Will keep an eye out but not expecting anything.

[mikestormchaser]

Will be out at a do at Rangitata Island tomorrow night. Will keep an eye out but not expecting anything.

Will be coastal if anything John. There is a wee bit of unstable air around tomorrow with a SW trigger around 5pm 500mb temp -28 -30 total totals is high at 57 as at 6pm just off the coast of Christchurch

[NZstorm]

Looking like Banks Peninsula the most likely spot for a possible TS today. Problem in Canterbury will be the westerly ahead of the southerly change. Ideally want a NE which is not signaled in any modeling. Dps' will be good off the coast 10C.

[mikestormchaser]

Looking like Banks Peninsula the most likely spot for a possible TS today. Problem in Canterbury will be the westerly ahead of the southerly change. Ideally want a NE which is not signaled in any modeling. Dps' will be good off the coast 10C.

Will either take a drive to birdlings flat tonight or watch the lightning from home in rolleston.
Should be some nice looking clouds atleast