NZ Weather Forum

Another round of possible severe warned storms coming tomorrow, worthy of a thread. Parts of Otago need this like a hole in the head

Issued METSERVICE at 11:27am Wednesday 6 Jan 2021

Valid from Noon Thursday 7 Jan 2021 to Midnight Thursday 7 Jan 2021

The front to the west of the country moves over the northwest of the South Island in the afternoon, and onto southwest of the North Island in the evening, bringing a low risk of thunderstorms from late afternoon. Over the north of the South Island, there is an increase in instability with, and following the front, and there is a moderate risk of thunderstorms about Nelson, Buller, northern Westland and Marlborough in the afternoon and evening, mainly about the ranges. These thunderstorms if they ocur could bring localised heavy rain of 10 to 25 mm per hour, and hail 10 to 20 mm in diameter.

Over the south of the South Island, afternoon heating and surface wind convergences are expected to produce showers an thunderstorms in some areas. About inland areas of North Otago, Dunedin, Clutha, Southland, southern Fiordland, as well as in Central Otago, there is a high risk of thunderstorms during the afternoon and evening. While about remaining areas of inland Fiordland, the Southern Lakes, coastal Otago and south Canterbury south of about Ashburton, there is a moderate risk of thunderstorms. These thunderstorms if they occur could bring localised heavy rain of 10 to 25 mm per hour, and hail 10 to 20 mm in diameter. However in the high risk area there is also a low risk some of these thunderstorms could become SEVERE, producing localised downpours of 25 to 40 mm per hour. Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips. Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain. Note, the low risk of SEVERE thunderstorms could be increased to moderate tomorrow.

The set up tomorrow isnt as good as the weekend we had. Wind convergences looks to be more inland near foothills/ mountains. And the shear tomorrow isnt there like the weekend.

Looks good for Otago/Southland and Nelson Lakes etc. (except for the unwanted heavy rain that is) but I looked earlier and saw nothing at all for mid/north/coastal Canterbury. So enjoy, those who are in those risk areas!

Edit - MS have amended the moderate area to come up to about Rolleston, looks from GFS like there is a band of convective activity that comes up the coast about teatime but there doesn't seem much in it.

Chris W wrote: ↑Wed 06/01/2021 14:33 Looks good for Otago/Southland and Nelson Lakes etc. (except for the unwanted heavy rain that is) but I looked earlier and saw nothing at all for mid/north/coastal Canterbury. So enjoy, those who are in those risk areas!

Edit - MS have amended the moderate area to come up to about Rolleston, looks from GFS like there is a band of convective activity that comes up the coast about teatime but there doesn't seem much in it.

So long as it doesn't muck with the cricket at Hagley- in the unlikely event they need tomorrow!

I'm really not seeing that much greatness for tomorrow, definitely lacking alot of ingredients including cold upper air and strong upper jet.
All we have is daytime heating and wind convergences, so an overall low risk for me and perhaps moderate south Canterbury North Otago where the moisture is higher and there's good orographic lift in the converging zone.
Hail 10mm at maximum.
I could be wrong though, but some much needed rain on the way for sure.
We had just over 62mm in the week leading up to Christmas, since then it's been less but temperatures have remained average.

Looks like a fairly high risk of inland storms for Otago/Southland today due to the upper level trough. A La Nina style set up in which convection develops over the foothills and higher terrain inland. Coastal dewpoints are 15C to 16C this morning and that moisture will work its way inland during the day. Geraldine may catch an afternoon thundery downpour.

NZstorm wrote: ↑Thu 07/01/2021 07:57 Looks like a fairly high risk of inland storms for Otago/Southland today due to the upper level trough. A La Nina style set up in which convection develops over the foothills and higher terrain inland. Coastal dewpoints are 15C to 16C this morning and that moisture will work its way inland during the day. Geraldine may catch an afternoon thundery downpour.

Yes i thought any storms will stay down that way. Inland
Timaru/ southwards, any hail wont be big today. It doesn't look overly promising for Canterbury plains as it did few days ago.
I think ill stick to my original plans and head off to akaroa today for a nice walk. Not that excited about todays set up

The cloud clearance is a couple of hours away with the center of the low slowly moving towards the top of the SI, so, will be interesting even though the upper air is not overly cold .

Moderate area extended into my area this morning, so no hoping in the jigger and driving anywhere today.

Gold/Brown Central Otago must be green at the moment.

spwill wrote: ↑Thu 07/01/2021 08:59 Gold/Brown Central Otago must be green at the moment.

Last late summer was like that too when I was down there.

I wasn't seeing that level of risk! A learning opportunity.

MS have issued a severe TS watch for the high risk area. Severe as mentioned on the chart due to heavy rain, the upper air isn't cold enough for large hail.

mikestormchaser wrote: ↑Thu 07/01/2021 08:12

NZstorm wrote: ↑Thu 07/01/2021 07:57 Looks like a fairly high risk of inland storms for Otago/Southland today due to the upper level trough. A La Nina style set up in which convection develops over the foothills and higher terrain inland. Coastal dewpoints are 15C to 16C this morning and that moisture will work its way inland during the day. Geraldine may catch an afternoon thundery downpour.

Yes i thought any storms will stay down that way. Inland

Southland was a typo Mike. Should have read Canterbury.

Southland in the hunt too though, inland again. Would you really expect these to make it to the coast though?

Chris W wrote: ↑Thu 07/01/2021 09:28 Southland in the hunt too though, inland again. Would you really expect these to make it to the coast though?

Looks more Otago/Canterbury. Christchurch could be in the frame too.

See how we go then, I'm not used to this kind of setup where the normal Canterbury TS/severe TS conditions (cold uppers, shear, NE vs SW) are replaced by those more akin to the North Island with higher DPs. If it's looking fun after work I might head inland for a look-see.

Just light rain in Southland.1.5mm so far.Overcast and mild

I think the MS risk levels today relate mostly to slow moving heavy showers dumping a lot of rain in one area in a short amount of time.

If I was chasing thunderstorms in Central Otago today I would be hoping for a lot less of the current cloud cover into the afternoon

Sun has been out most of the morning in Amberley and looking at the satellite image much of Canterbury. Looking west now:

Not looking all that interesting down here @ the moment, as compared to the first 3 days of this year,
Clouds are gathering but no pregnancy in them. Warm and humid here with light winds from the SE to East direction..

Certainly plenty of heating around these parts, had been 28deg a short time ago along with some decent looking cloud about.

Some showers on the radar. They have some wheels on too out of the nw. That seems strange, doesn't it?

More development:

A bit more fruitful after my last posting, Cu development going on to the south of here, roughly the same area of that supercell the other day but nothing much showing up on the radar.

Rain just starting in Rakaia

Just overcast down here