Signs of Spring?
The leaves on the poplars have only just changed colour and are dropping round here!
So is that later than or just as usual for your area?
Had an extensive trip round Otago/Southland late last month, pockets of riverside willows look stupid there, with their bare branches having a topknot of new green growth.
My NI kowhai is close to budburst, chickweed is still growing and the silver beet sown after the longest day and supposed to stand through winter is starting to bolt. We had three crops of field mushrooms for the year, spring bulbs were flowering at Queenstown late May. My Totara tree has had three distinct cycles of bright new growth, and did the same last year.
This stupid seasonal repetition has been happening for the last two or three years.
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Seasonal Weather Outlook - issued 10 June 2010 Regime Change During May the Tasman Sea and New Zealand area went from a regime that favoured lingering anticyclones to one that favoured the developing of low pressure centres. In the last week of May a large, multi-centred low deepened in the Tasman Sea and then slowly crossed the South Island and lingered near Chathams. This brought extreme amounts of rain to the southeast of the South Island. It delivered 191 mm of rain to Oamaru airport and 280 mm to Oamaru city in six days. That's about equal to the amount of rain recorded in these sites in the eight months from 20 September 2009 to 20 May 2010.
Sea Surface Temperature Pattern.Seasonal forecasting is all about watching trends that change slowly from one month to the next; trends that are related to how the planet is handling its heat budget. For us, the main item of interest is how heat is transferred from the Pacific Ocean into the atmosphere to make weather. For this, the eastern equatorial part of the Pacific is the target area to watch. After being warmer than normal since last June, the sea in this area has now reverted to near normal temperatures. So the recent El Nino has faded and we are now having neither El Nino nor La Nina conditions, and this is described as "neutral territory". Since March there has been a period of upwelling along the equatorial Pacific, causing sub surface temperatures to cool below normal, and this cooling phase is now nearing the surface, so that conditions are becoming favourable for a transition towards La Nina over the next few months. Trade winds have recently been stronger than normal near and west of the dateline, and convection has been stronger than normal over Indonesia and northwest Australia-these are factors that are consistent with La Nina conditions. However trade winds have also been weaker than normal about the Galapagos, so it looks as though the current phase of neutral conditions should continue for a few months. Recently the seas around New Zealand and in the Tasman Sea have been slightly warmer than normal in places. This may continue to act as a source for extra evaporation and cloudiness over the next few months.
The Southern Oscillation Index (SOI).The impact of La Nina or El Nino on our daily weather maps can be computed by a parameter called the Southern Oscillation Index (SOI). The SOI is compiled from the weather maps, and counts the difference in the isobars between Tahiti and Darwin. In April it dived sharply into positive La Nina territory. This was a temporary blip related to some low pressure systems that lingered near Darwin, and recently its value has relaxed but is still positive. A year in the recent past that behaved similarly is 2003, and that year stayed in neutral territory during winter. Anyone with local weather recordings from 2003 may be able to use them as a possible indicator of the impact of weather this year.
Likely weather patterns as we slip into winter.We are neither having an El Nino pattern, nor a La Nina pattern. The pattern is in-between or in 'neutral territory'. This increases the amount of variability and the possible extremes for our weather pattern. Sea surface temperatures around New Zealand may revert to near average during the next few months, and air temperature are expected to be generally milder than normal. This does not rule out a few short-term cold snaps and frosty periods that are typical of winter. Some decent snowfalls are likely for the ski fields. The main pattern this winter is expected to consist of broad troughs of low pressure moving across New Zealand. Some may be followed by periods of cold west to southwest winds with mountain snow. A few passing fronts may be followed by a period of enhanced southerly winds with hail or snow showers for eastern hills. As in May, a few low pressure systems may form in the mid Tasman Sea and move onto New Zealand,bringing periods of wind and rain. This pattern is often preceded by a burst of enhanced northwest or northerly winds bringing mild conditions. By July these lows are more likely to be more in the south, rather than the mid,Tasman Sea. Acting as a variation between the troughs, there are likely to also be some anticyclones. These have been weak in the New Zealand region lately and are expected to occasionally track across the northern Tasman Sea, bringing fogs and frost. Some of these may linger in the area east of Chatham Islands,or to north of New Zealand, and thus enhance the westerly flow onto the South Island.
SEASONAL OUTLOOK FOR CENTRAL OTAGORAIN continuing about normal.
WIND westerlies and southwesterlies.
TEMPERATURE becoming above normal after a near normal May.
SUNSHINE returning to normal after a sunny May.
SPECIALS passing fronts.
CONFIDENCE low to moderate.
Troughs and fronts arriving from the Tasman Sea are expected to vary in intensity and duration but should bring normal amounts of rain and snowfall. Some of these fronts may be preceded by bouts of northwest or northerly wind, and some may be followed by southerly winds. There should also be the typical number of cold spells this winter, bringing the usual number of frosty mornings.
SEASONAL OUTLOOK FOR COASTAL OTAGORAIN returning to normal after an extremely wet May and start to June.
WIND westerly quarter.
TEMPERATURE becoming about to above normal after a near normal May.
SUNSHINE becoming above normal after a cloudy May.
SPECIALS erratic rainfall.
CONFIDENCE low to moderate.
Wet periods are expected from passing fronts, but the main rain is expected to with episodes of easterly wind associated with low-pressure systems crossing central parts of the country. There may also be a few cold snaps,typical of winter. These are usually heralded by a large anticyclone moving onto Tasmania, and followed by a few clear frosty nights.
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