NZ Weather Forum

Darkening clouds near Akaroa since about 4.30pm, but only a few brief spits so far.

No point getting even remotely excited about this one,haven't brothered to even look to the south for the hour or so.

spwill wrote:I see the NW flow was moist, Chch dewpoint was 12C with the northwester this afternoon, the dewpoint has dropped with the wind change. often there is a dewpoint rise with the southerly change

Yes I thought this interesting also, there would've been some method in putting out a moderate risk of TS's. There isn't a garantuee of storms with that level of risk anyway but the potential is there for a chance of thunder and looking at some things you can sort've see it (upper air warm though, pheww). Imagine if there was that little extra bit of a certain ingredient and a small storm fired, then it would all be well done! lol. One treads a delicate line with forecasting....... I look forward to the next chance!

Cheers
Aaron

Don't worry Aaron, we aren't even in December yet so I'm sure we'll have plenty more opportunities for ye old chase. In the main time, a certain brand new camera travels towards my mailbox ...

I see MS had 28.9C for Timaru Aero yesterday before the change, 28.2C for Chch Aero and Hastings, and 28.0C at Kaikoura Aero.

Warmish, humid night here, with a min of 16.1C (DP 14-15C) after 25.2C late yesterday. No measurable rain here yet though, unlike the city it seems.

I like what GFS has thrown out thismorning for a week out today. Im craving good storms so much so that im getting excited a week out. How silly of me. No harm in watching and waiting. Been about a month if not more since the models even hinted at a good low.

whats the bet this last gasp frontal drizzle comes back tomorrow morning on the easterly change

Some light showers around, on the humid side today with dewpoints 15 - 16C, currently 19C.

Lovely afternoon here now with low cloud clearing and blue dome skies, 17 in this part of the woods with no wind so feels nice. Not looking forward to Wednesday and Thursdays weather here with strong Northeasters forecast.

It was a humid night here last night, but today is definitely cooler compared to yesterday, thanks to the SW change. It's been a dry November here - just like last Nov. 39mm this month, 30mm for Nov 2010.

Fantastic afternoon in Invercargill, has been good all day. There was some picture perfect cumulus out nice and low before, too bad I didn't have my camera. 14°C out there now, which is supposed to be todays high. Expecting 11 more than that tomorrow, might pay for me to go find my shorts

Boy this was unexpected, storms going off in the Waikato
Update: Distant Thunder

Good to see the photo, can see distant Cb from Ak, fine here now.

This set up always looked weak in the models. But its that time of year.

6.30 PM Radar Image.....

good timing with the SE convergence change then with some afternoon heating

I am keeping an eye of Friday, looking like we get some moisture+upper trough with possible pm thunder activity over inland North Island. Looks semi promising on the latest 00Z run of the gfs. But the gfs has been fluctuating a bit.

Great to see the pics Tim.

Daam dam dam! I am in palmy. I had to leave Hamilton at 1. On drive down it looked awesome watching it all brew up. Gutted I missed the action. I'll be in taihape and palmy for the next week.

Whenuapai's sounding didn't show any unstableness today, instead it showed one big cap!

This is why I wish they did Balloon Soundings for Hamilton, so you you could get an idea of the upper air temps and wind flow along the trough when these types of events come to rise.

Nice stuff Tim! How do you overlay the radar image like that? That would be handy. Haven't had a chance to look at models the last few days as am in the process of moving, within Chch.

In regards to the Skew T thought I'd do a bit of playing around and see how the GFS model performs compared to the Skew T from NZWP at I think 10am this morning? I've got two locations here for the modeled Skew T's, one is Auckland and the other the Cambridge area. Mind you I did these for modeled Skew T's for 1pm and 4pm, obviously the 1pm one will be 3 hours after the weather balloon went up but I think it provides a pretty good idea.

Note, in these Skew T's below I've used GFS (NOAA ARL READY) data and input the txt figures into this Skew T program I use called Boltware. The surface data I have adjusted slightly however to represent actual surface conditions, I've set dewpoints a little lower then what some weather stations were reading in certain areas to allow for some mixing however it won't be to much (not like chch and it's NW's! lol)

Here is the Auckland modeled Skew-T at 00z (1pm):



I think compared to the NZWP sounding in the morning the model has done farily well, shows the cap there.

And here is the Waikato Skew-T at 00z.



So we have slightly higher elevation but not much. Main things to note are no cap and higher surface temperatures! Starting to look unstable!

Now for the 03z (4pm) Auckland sounding:



A slightly higher surface temperature (possibly could've plotted it at 20C going by other stations) but still it's quite stable looking, model performs fairly well.

Here is the 03z Waikato modeled sounding:



High surface temperatures in the afternoon brings an unstable airmass! Infact some weather stations recorded higher temperates / dewpoints then I've put down so it could have been even more unstable but I've cut it back a little bit to be conservative and there is always the chance some stations may record slightly higher figures then actually occured.


So my conclusion from this is that the model has performed pretty well. If you think there could be storms in the afternoon, go ahead and put in your forecasted afternoon temperatures and dewpoints for your area of focus. It may not be a real sounding but it could give you a good idea of what may happen! Interesting stuff.

Cheers
Aaron

A 1.5deg start to the day here and a warm one coming up ,though i dont reckon there will be the temperature range as it was a few days go

On Monday snowstormwatcher wrote: I dont know why metservice take there Tempertures for Fairlie out at Kimbell which is 10-15km west of Fairlie, tempertures are usually diffrent out there. It was much hotter than 27 in town [Sunday]. Stevenson screen at the high school recorded 30.1. and I recorded 31.

Yes, fair comment. I'm a little puzzled as well, particularly as there'd be no historical value at Kimbell.

I also compared the overlapping months of May, June and July, 2009 between NIWA's old Fairlie school-site (probably not the same school) and MS's new Kimbell site. T-maxs at the old site did indeed often read 2-3 degrees higher. However, T-mins could also sometimes be up to 8 degrees lower. Initially not a bad site, but some of their notes later described the screen exposure as 'near to poor', i.e. nearby there seems to have been additional concrete paving, extensions to buildings, including shrub planting, some eventually reaching more than 2.5m in height, spraying of grass around the screen, and a tree to the NW of the wind-vane growing taller than the vane itself.

Having said that, if the screen at Fairlie High School is out in the open, it sounds like it could have the potential to be one of the few 'official' sites to record more than 30.0C this month (second only to MS's rounded 31C at Hanmer Springs, which NIWA don't appear to recognise?).

Below are a few other top T-maxs c/o NIWA for this month. Note that Waione in the Wairarapa is the only N.I. site that I can find to get near 29C (second highest being Napier Aero's 27.9C on the 21st)...

29.8C Leeston (28th)
29.7C Christchurch, Kyle St (28th)
29.5C Middlemarch (27th)
29.3C Culverden (27th)
29.0C Cheviot (27th)
28.9C Timaru Aero (28th
28.9C Waione (27th)
28.8C Hanmer Forest (27th)
28.8C Snowdon (27th)
28.7C Rangiora (28th)
28.6C Waipara West (27th)
28.6C Methven (27th)

Hey Aaron, what you can do to get the Radar Overlayed is copy the radar image url and make a new image overlay in google earth, paste the url image and position it where the radar is covering.
As for the soundings you posted (for Waikato), the GFS has upper atmosphere way too dry to support any storms.
You also might want to try some really good software written by Storm Chaser Tim Vasquez called "Digital Atmosphere" it can do pretty much any weather plotting you can throw at it.

Usually what happens in a storm situation is that upper air temps are dry anyway, but usually there is a mid point usually around 850 to 750mb where the updrafts take in moisture an heat and then saturate it and carry it further up (known as the LCL or Lifted Condensation Level) but yesterday it was atypical due to the storms not even hitting the tropopause.

You can usually get a very good indication of wether a storm has hit the tropopause or not by seeing what type of CB it is:

Cumulonimbus Incus: The Crown on top means the updraft in the cloud couldnt go any higher(due to a non favorable environment above) and instead spreads out.

As opposed to a Cumulonimbus Calvus: Pictured in this post, as it shows that it hasn't developed the "crown" or hasn't hit the tropopause yet.

Since that it didnt hit that height it seems that the optimum SFC temps and Dp's (around 18°C) caused a good enough lapse rate for lightning to occur.

NZstorm wrote:I am keeping an eye of Friday, looking like we get some moisture+upper trough with possible pm thunder activity over inland North Island. Looks semi promising on the latest 00Z run of the gfs. But the gfs has been fluctuating a bit.

Great to see the pics Tim.

Yes it looks like there could be some storms for BOP Waikato?

Before we move on to December weather - NIWA's October stats. summary is not visible yet!