Storms for upper N.I. - Jan 8

jamie · Unread post by **jamie** » Wed 06/01/2016 10:23

What are people's thoughts regards Friday? Some decent numbers except upper temps look a bit warm.

Tornado Tim · Unread post by **Tornado Tim** » Wed 06/01/2016 13:52

jamie wrote:What are people's thoughts regards Friday? Some decent numbers except upper temps look a bit warm.

Despite the relatively warm upper level temps, there is lots of divergence caused by an upper level jet and latent heat as quite a significant portion of the atmosphere is forecast to be saturated on Friday afternoon.

The Setup is not going to be picturesque as there is going to be a ton of cloud and lots of rain, but in terms of a getting a storm it looks quite good.
The SFC forecast for Friday afternoon NNW, Upper levels NW to WNW, that will bring in a potent amount of moisture. If forecasts come true, theta-e temps nearing 60°C in places!

Front seems to come in a little later in the evening, so it looks like this is prefrontal activity.

jamie · Unread post by **jamie** » Wed 06/01/2016 19:14

00z run still looks good. The cloud looks to be the spoiler of the day. Will be lots of it but still plenty of juice for storms to fire. I look forward to see what metservice think in their outlook tomorrow.

NZstorm · Unread post by **NZstorm** » Wed 06/01/2016 21:57

Fridays set up looks like the best thunder potential over the North Island since November. Keep an eye on how much lightning occurs in the Tasman tomorrow as that will be a pointer to Friday.

I will still be in the South Island on Friday. A little thunder potential over east Otago Friday pm with the polar jet.

Tornado Tim · Unread post by **Tornado Tim** » Thu 07/01/2016 10:18

Very strong wind is also another possible feature associated with tomorrows forecasted storms, exposed parts of the country could get gusts in excess of 100km/hr esp on the main mesoscale cold front.

Nev · Unread post by **Nev** » Thu 07/01/2016 10:59

This morn's TC outlook for tomorrow arvo looks pretty good…

MetService - Thunderstorm Outlook

Valid to: Midnight Friday 8 Jan 2016
Issued at: 10:46am Thursday 7 Jan 2016

A front should cross the North Island during the afternoon and evening followed by a trough. During the afternoon there is a high risk of thunderstorms with rainfall rates of 10 to 25mm per hour affecting the northwest of the North Island from Taumarunui and Taupo northwards to Northland and the Coromandel Peninsula. In this area there is also a low risk that a few of the thunderstorms will be severe with rainfall rates of 25 to 40mm per hour with one or two damaging tornadoes. There is a broader low risk of thunderstorms affecting the northern half of the North Island during the afternoon and evening.

Elsewhere, no risk of thunderstorms or significant convection.

MetService T-storm Outlook for Nov 8, pm.png

Nev · Unread post by **Nev** » Thu 07/01/2016 11:06

Thought this event might be worthy of a separate thread...

jamie · Unread post by **jamie** » Thu 07/01/2016 11:25

I'll be floating around tomorrow and will chase anything worth while.

Tornado Tim · Unread post by **Tornado Tim** » Thu 07/01/2016 11:30

The EHI's are quite elevated for this setup too, not enough to cause alarm but I can see why Metservice included a low risk of a Damanging Tornado....

Rogue · Unread post by **Rogue** » Thu 07/01/2016 11:50

Is there anywhere to view an EHI chart for New Zealand? I can see EHI on the GFS soundings (from BSCH), but would be nice to pinpoint the max value across the country

spwill · Unread post by **spwill** » Thu 07/01/2016 21:05

Thunderstorms occurring in the trough in the Tasman this evening, a sign of the instability heading for the NI. A steamy afternoon tomorrow even in heavy showers, dewpoint will be around 20C.

jamie · Unread post by **jamie** » Thu 07/01/2016 21:47

So will there be elevated thunder on the front in the morning leaving muggy conditions for the trough in the afternoon to ignite into decent storms?

Tornado Tim · Unread post by **Tornado Tim** » Thu 07/01/2016 22:26

Metservice starting to pull all the stops on this:
AM:

Metservice wrote:A front is expected to move across the upper South Island and over the west of the North Island during the morning. Broad scale Warnings and Watches are in effect for many places.

There is now a high risk of elevated thunderstorms affecting the northwest of the South Island during the period and the west of the North Island during the morning. Generally rainfall rates of 10 to 25mm per hour can be expected but there is an additional moderate risk that some of these thunderstorms will be SEVERE with rainfall rates in the 25-45mm/hr range. There is a surrounding low to moderate risk extending from Coromandel Peninsula to Taupo to Kapiti, across much of Marlborough and down into inland Westland as depicted on the chart. Elsewhere, no risk of thunderstorms or significant convection.

756c-1521aab9b00-1521e886000-1521b1dbdfc.0 (1).png

PM:

Metservice wrote:The front will cross the North Island during the afternoon and evening followed by a trough. During the afternoon there is a high risk of thunderstorms with rainfall rates of 15 to 25mm per hour affecting the northwest of the North Island from Taranaki to Taupo to eastern Bay of Plenty. Within this area there is a moderate risk that some of these thunderstorms may become SEVERE with localised downpours of 25 to 45mm/hr. Later in the afternoon from inland Auckland to inland Waikato, there is a low risk of one or two small tornadoes as the trough passes. There is a surrounding lower risk of thunderstorms depicted on the chart covering areas northwest of a line from East cape to the Tararaua range.

Elsewhere, no risk of thunderstorms or significant convection.

756c-1521aab9b00-152211b8e00-1521b2c8ba7.0.png

jamie wrote:So will there be elevated thunder on the front in the morning leaving muggy conditions for the trough in the afternoon to ignite into decent storms?

It looks like upper levels will desaturate as the day progresses, but I just checked the sounding for the frontal passage, the elevated convection is narrow (380hpa to 250hpa) accumulating to less than 3km of vertical height for free parcel rise before hitting the trop, but the section is fully saturated, so taking into account potential temps such as theta-e and a much steeper lapse rate at that height, a high resulting risk of Lightning with the passage.

The Cloud in this type of setup for Friday PM anyway will have less impact as the NW to N flow will be keeping that temp up and moisture high. Any additional Sun will help but its not essential like in heat pulse type storm setups as other dynamics are at play here such as the upper level jet creating divergence which increases the SFC wind when parcels rise to fill in the divergence which drags in more moisture etc.....

Tornado Tim · Unread post by **Tornado Tim** » Thu 07/01/2016 23:03

Severe Thunderstorm Watch also issued:

Metservice wrote:This watch affects people in the following weather forecast districts:
Northland
Auckland
Great Barrier Island
Coromandel Peninsula
Waikato
Waitomo
Taumarunui
Bay of Plenty
Rotorua
Taupo
Taranaki
Nelson
Buller
Westland
A front is expected to move onto the northwest of the South Island in the early hours of Friday morning, onto the west of the North Island from about dawn and then cross the upper North Island (north of a line from Taranaki to East Cape) during the afternoon. There is a high risk of thunderstorms moving through these areas from west to east during the period with locaised rainfall rates generally expected in the 10 to 25mm/hr range. However, there is a moderate risk that some of these thunderstorms may become SEVERE with localised downpours of 25 to 45mm/hr possible.
Such rainfall rates may last one to two hours and have the potential to cause 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. More specifically, higher population areas such as Auckland city and Hamilton city can expected this threat to move through during the afternoon hours.
Note: A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area. People in these areas should be on the lookout for threatening weather conditions and listen for possible Severe Thunderstorm Warnings.

Issued by: Paul Mallinson

littleheaven · Unread post by **littleheaven** » Fri 08/01/2016 00:06

For once I find myself both not working and child-free tomorrow afternoon so I'll be taking the opportunity to get out amongst it. I see Civil Defence has now flagged it on Twitter as something to keep an eye on.

NZstorm · Unread post by **NZstorm** » Fri 08/01/2016 07:22

I am in Wanaka so won't be chasing storms today.

Its usual to see wind shear in January with thunderstorms over the upper North Island! The shear adds the potential for severe wind gusts 90km/h +

The 850mb dewpoint for Auckland this afternoon is 14C, moist air!

jamie · Unread post by **jamie** » Fri 08/01/2016 07:32

It's incredibly moist air thismorning. Everything is wet but has been no drizzle. Almost like fog.

Who is going to chase today? I'm happy to meet up somewhere and take a car load....company car = free chasing.

NZstorm · Unread post by **NZstorm** » Fri 08/01/2016 07:33

I'll post the jet stream chart for the record today. 00Z.

A subtropical jet moving onto upper North Island. Polar jet over the south. Enhanced lift between the two jets will occur over the North Island.

Tornado Tim · Unread post by **Tornado Tim** » Fri 08/01/2016 08:26

jamie wrote:It's incredibly moist air thismorning. Everything is wet but has been no drizzle. Almost like fog.

Who is going to chase today? I'm happy to meet up somewhere and take a car load....company car = free chasing.

Yes I will most probably chase today, but I am not sure how much we will be able to see.....
Im in the Raglan office today, so I can see whats starting to come in and can take off whenever

The trip over was quite interesting as front hit, moderate to heavy rain and a bit of an elevated gust front that didnt effect the surface.

Metservices Update for today:

Metservice wrote: A front is expected to move across the upper South Island and over the west of the North Island during the morning. Broad scale Warnings and Watches are in effect for many places.

There is now a high risk of elevated thunderstorms affecting the northwest of the South Island during the period and the west of the North Island during the morning. Generally rainfall rates of 10 to 25mm per hour can be expected but there is an additional moderate risk that some of these thunderstorms will be SEVERE with rainfall rates in the 25-45mm/hr range. There is a surrounding low to moderate risk extending from Coromandel Peninsula to Taupo to Kapiti, across much of Marlborough and down into inland Westland as depicted on the chart.

Additionally during the morning there is a moderate risk of a few thunderstorms about eastern areas of Gisborne and northern Hawkes Bay.

Elsewhere, no risk of thunderstorms or significant convection.

jamie · Unread post by **jamie** » Fri 08/01/2016 08:48

Interesting....nothing about the afternoon?

Orion · Unread post by **Orion** » Fri 08/01/2016 08:51

Auckland Civil Defence notification as at 8:44am:
http://www.aucklandcivildefence.org.nz/ ... cy-status/

Nev · Unread post by **Nev** » Fri 08/01/2016 08:59

jamie wrote:Interesting....nothing about the afternoon?

Yeah, it would also be really helpful if Tim could include the issue and validity date/times, particularly as they are often updated throughout the day. Saves having to double check them all the time.

NZstorm · Unread post by **NZstorm** » Fri 08/01/2016 09:16

Like any summertime storm set up, there will need to be decent surface heating to get the surface based storms, otherwise convection stays elevated. Temps need to get to 25C.

jamie · Unread post by **jamie** » Fri 08/01/2016 09:18

Thanks for your thoughts Steve.

I see Paul is on the desk today....the latest thunderstorm outlook includes afternoon and it's wild!!!!!! Paul if your reading this and have the time, what are your personal thoughts on today's setup. Would you have a top spot to be at?

spwill · Unread post by **spwill** » Fri 08/01/2016 09:20

GFS showing lifted index of -6 in Waikato this afternoon, the model picking up on daytime heating.

I fly down to Dunedin this afternoon so can't chase. I must organise a window seat

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