Heavy showers/possible thunderstorms, Nov 16th -20th

[spwill]

I thought I would start a thread for this.
Incoming moisture from today and upper level cooling from tomorrow will help generate some heavy showers and possible thunderstorms on Wednesday and Thursday, particularly in the afternoons/early evenings. The North Island looks most in the firing line with the influx of rich moisture. See how much heating can occur and where the convergences set up.

More heavy shower and thunderstorm risk is currently modelled for Friday and over the weekend.

[Storm Struck]

Yes it is looking very fruitful for the North Island the next few days, and probably the best day for the South Island is Thursday afternoon evening.
Inland but we will see some heavy showers out on the plains too.
I've been keeping an eye on Sunday too although seems to be flip flopping abit in the models.
50+mm potential there for Canterbury late Friday through Saturday which will be very welcome.

[jamie]

Looks like potential for 5 days of thunder in a row


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[Tornado Tim]

Metservice Thunderstorm outlook:

Updated at 8pm Tuesday - Central North Island risk increased to high, moderate risk added to Gisborne ranges, low risk of severe thunderstorms added to western Northland.

A warm moist airmass will cover New Zealand on Wednesday, while temperatures cool aloft. This is expected to lead to a very unstable atmosphere over the North Island in the afternoon and evening with heavy showers and thunderstorms in many areas.

There is a moderate to high risk of scattered thunderstorms during the afternoon and evening about many North Island areas as indicated on the chart.

These thunderstorms will produce localised heavy rain, and there is a risk some of the thunderstorms could be severe about western Northland, and central North Island areas from western Waikato through the central high country to Hawkes Bay and northern Wairarapa with localised downpours of 25-40mm/h. Rainfall rates of this intensity can cause surface and/or flash flooding and make driving conditions hazardous.

Severe Thunderstorm Watches for localised downpours may be issued for some North Island areas on Wednesday, and people within these areas are advised to stay up to date with the latest forecasts.

A low risk of thunderstorms covers other North Island areas, and the southern half of the South Island, as indicated on the chart.

No other thunderstorms or significant convection expected over New Zealand during this period.

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[Tornado Tim]

Today's storms will most likely form a convergence boundary, where the NE will meet the west. Lots of daytime surface heating and sufficient moisture.
But convergence is the trigger today. MLCAPE values around 700j/kg and Lifted indices around -3.5 indicate moisture is there.
Very little to no SHEAR today and a slow steer - So storms will be pulse multi-cell if they form.

Risk factors: Very Heavy Rain - possible flash flooding risk (Convergence zone not expected to move a whole much expect more westwards towards the coast)
If westerly onshore sea-breeze collapses, the risk decreases significantly.

[Tornado Tim]

Updated Metservices Thunderstorm Outlook:

A warm moist airmass covers New Zealand, while temperatures cool aloft. This is expected to lead to a very unstable atmosphere, especially over the North Island this afternoon and evening, with heavy showers and thunderstorms likely in many areas.

There is a moderate to high risk of thunderstorms this afternoon and evening about much of the North Island, with a lower risk continuing into the night, as indicated on the chart. These thunderstorms will produce localised heavy rain, and there is a risk some of the thunderstorms could be severe about western Northland, and central North Island areas between Waikato and Wairarapa, with localised downpours of 25-40 mm/h.

A Severe Thunderstorm Watch for localised downpours has been issued for some North Island areas.

Meanwhile, there is a low risk of thunderstorms occurring about the Canterbury High Country, inland Otago, Fiordland and Southland from afternoon. However, for parts of Fiordland and Southland the risk is considered moderate this afternoon and evening. Any thunderstorms that occur will produce localised heavy rain.

No thunderstorms or significant convection expected elsewhere in New Zealand today.

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[spwill]

I'm in Katikati today but come back to Auckland through Waikato late afternoon.

[Tornado Tim]

I'm in Katikati today but come back to Auckland through Waikato late afternoon.

If looking good, feel free to meet us Waikato crew and lets get a chase on

[spwill]

I'm in Katikati today but come back to Auckland through Waikato late afternoon.

If looking good, feel free to meet us Waikato crew and lets get a chase on

See how things go, tomorrow would work better for me.

[spwill]

A rather quiet day in the Waikato for shower activity. I drove through Waikato this morning and back again late afternoon, there was a lot of low cloud cover which is a dampener for the shower development. See how tomorrow goes, upper levels are cooling tomorrow.

[Richard]

For here its encouraging to starting the first signs of the unstable conditions this early in the morning.
It looked a bit like this yesterday which lead onto the weak storm about 10 kms north later on.

17th nov.JPG

[Tornado Tim]

At least the atmosphere has cooled today from yesterday, hoping that today will pan out a bit better than yesterdays flop.

Humid conditions over New Zealand with cool temperatures in the upper atmosphere mean very unstable conditions are likely today.

Essentially the whole of the country has a low risk of thunderstorms for parts of the day, and for clarity, no low risk areas are delineated on the chart.

Within all moderate risk areas, there could be localised heavy rain associated with thunderstorms producing intensities of 10 to 25 mm per hour.

There is moderate risk of thunderstorms this morning and afternoon about Waitomo, Taranaki and western Whanganui, while the rest of the North Island, excluding most of Northland, Kapiti and Wellington has a moderate risk of thunderstorms this afternoon and evening. Within this area, the risk of thunderstorms is high during the afternoon for southern Waikato to central North Island, across to Central Hawkes Bay, through the Tararua District and into parts of Wairarapa and there is moderate risk of severe thunderstorms for these places, bringing localised downpours with intensities of 25 to 40 mm per hour.

There is also a moderate risk of thunderstorms this afternoon and evening about inland places of the South Island.

This evening and tonight, a moderate risk of thunderstorms develops about northern Northland.

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[spwill]

We want to see the sun out.

[Razor]

We want to see the sun out.

Thats looking unlikely so far here in ChCh

[Richard]

Looking brighter to the north, the shower currently is close to passing over, after this if the sun does come out she'll be humid and steamy

[darcyplumb]

Lower level cloud is clearing in Ashburton at the moment but there is a decent layer of high cloud to be dealt with as well.

[Richard]

Lower level cloud is clearing in Ashburton at the moment but there is a decent layer of high cloud to be dealt with as well.

No low cloud here thankfully.

[darcyplumb]

Very humid here now with a light south easterly. Still some high cloud but the sun is well and truly shining through it. 19 degrees and climbing.

[Razor]

Low cloud and light drizzle in Lincoln

[Storm Struck]

Lots of high and mid level cloud here, humid on 19C and a light NE.
We had a few spots of rain around 11am from a shower down from the north, should be some good heavy showers tonight though.

[darcyplumb]

Inland along the foothills looks very volatile. Towers all the way along. Very impressive.

Edit to add that high cloud looks to be clearing here now with some weak cumulus developing.

[darcyplumb]

Radar showing the beginnings of a cell near Mt Peel.

[NZ Thunderstorm Soc]

Nothing much happening around here. Lot of clagg cloud around but with a humid feel to it despite the light southerly.

[Razor]

Moderately steady shower through Lincoln just now

[Razor]

Looks like potential for 5 days of thunder in a row


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So its an official "Thunderwave" then?