New Zealand Climatology Flashcards
(36 cards)
What is a Northwesterly wind most often associated with?
- A pre fontal situation
- Cold front travelling Northeast in a trough between eastward migrating high-pressure systems.
What happens to the wind when the cold front passes? Why does this occur?
- Changes to a southwesterly
- Due to angular momentum, where there is denser air following the front (colder air behind), and angular velocity is lower in front of the front (because air is less dense ahead of the front.)
What are the effects of the Northwesterly winds on meteorological conditions in the West Coast of New Zealand? What happens as the front approaches from the southwest?
- Initially Cc or Ac appear along the West Coast of the South Island, but only near Mt Taranaki in the North Island. Terrain plays a large role in the significant precipitation formation on the West Coast of the South Island.
- Low cloud bases and precipitation in Fiordland and South Westland.
- Cloud cover thickens and merges so that both West Coasts.
What happens to the wind strength at the Cook-Strait and Foveaux Strait during a cold front? What are the turbulence and visibility like?
- Northwesterly turns to gale force strength.
- Nil or light turbulence and fair to good visibility outside precipitation.
What influence do the mountain ranges in New Zealand have on the East Coast in a Northwesterly wind?
- East is free of clouds
- Influence of the ranges include:
- Much drier conditions
- Turbulence to low levels
- Good visibility
What is the orographic factor in New Zealand responsible for on the East Coast in a Northwesterly wind?
- Fohn winds and warm temperatures on the East Coast of the South Island and also in the Wairarapa and Hawkes Bay.
- The Northwesterly wind brings moist energy latent air (moisture from the ocean) plus the moisture from the cold front, that air is being mechanically lifted by the ranges, and as it does so, there is a change of state, therefore a latent energy release.
- Thus the warm temperature coming from the windward side to the lee side, warming the East Coasts
In a strong westerly, where are severe turbulence and rotor action likely to be located?
Lee of main mountain barriers
Why are Southwesterly winds strong?
Due to strong, unstable anti-cyclonic airflow associated with the high-pressure system centre in the Tasman Sea and travelling eastward behind a trough.
What are the effects of a Southwesterly wind on the weather in the West Coast of New Zealand?
- Generally unstable, expect cumulus clouds along both West Coasts.
- In very unstable conditions, isolated thunderstorm activity is likely to occur.
- Little turbulence except in the vicinity of active CB clouds.
- Visibility poor in heavy showers beneath a CB to really good visibility in fine and cold conditions outside CB’s.
What are the effects of a Southwesterly wind on the weather in the East Coast of New Zealand?
- Some cumulus clouds but with higher bases than the West Coast.
- Turbulence in the immediate lee of high ground, usually moderate, could limit light aircraft - particularly outlets of valleys which are orientated along the run of the wind.
- Good visibility apart from the occasional shower due to cumulus cloud patches.
- The high ground of both islands experience SCT to BKN cloud formations, particularly in areas facing Southwest.
What weather conditions will occur if there is a SSW wind?
- The East coasts of both islands will be cloudy with relatively clear skies on the West Coast - especially South Island West Coast. A variance of 10º from south-west is all that’s needed.
Will VFR flight be affected on the West Coasts? If so, how?
No, aside from the presence of passing showers on the West Coasts, and in mountainous terrain.
What are the effects of a Southeasterly wind on the weather in the Eastern Flank of an anti-cyclone situated SW of NZ?
- Typical cold and unstable airstream weather.
- Turbulence due to unstable conditions and cumulus cloud developments.
- Cumulus cloud developments.
Will VFR/IFR flight be affected on the East Coasts? If so, how?
- VFR flights on both East Coasts can be affected by passing showers due to cumulus clouds.
- VFR flights and potentially IFR flights can be interrupted when extensive cloud formation occurs.
What are the effects of a Southeasterly wind on the weather in the Western Flank of deep slowly travelling depression East or SE of New Zealand?
- More extensive cloud and precipitation than normal.
- When the situation occurs in winter or early spring, snow to low levels experienced along the Eastern seaboard of New Zealand - as far north as Hawkes Bay.
- This brings in really cold weather, including low freezing levels.
- Inland regions such as the Alps and the high plateau of the North Island receive thick snow - causing road closures e.g. Arthur’s Pass, Desert Road.
- Both West Coasts generally free from significant cloud. - West Coast of South Island - fine weather and good visibility.
- Turbulence in the lee of mountains.
Will VFR flight be affected?
Marginal in the west, virtually impossible in the East.
When and where is the ‘normal progression scenario’ found?
- Most common in the middle of summer and winter.
- Most common found in the Australasian region.
What is the normal progression scenario consistent with?
- Undisturbed high altitude long wave pattern, flowing anticyclones and troughs steadily eastward.
What is the typical sequence of this normal progression scenario? How long can this sequence last for?
- Passage of an anti-cyclone, then a cold front, then another anti-cyclone.
- Up to 6 to 8 days.
What happens as the cold front moves off from New Zealand and to the East? What are the weather conditions associated with this movement?
- The Northwest airflow becomes consistent.
- Strong to gale force winds through both Cook and Foveaux Strait.
- Increasing cloudiness on both Wests Coasts and clear conditions in the East.
- Clear conditions because of the Southern Alps in the South Island.
Where is the cold front first experienced in terms of the Normal Progression Scenario? What are the associated weather conditions.
Cold front first experienced in South Westland, where low clouds, heavy showers and poor visibility severely limit flying operations.
Will the East Coast experience the same conditions as the West Coast of the South Island as the Cold Front goes past?
No, East Coast experiences similar conditions but with a higher cloud base, and less severe frontal weather.
How far north does the West Coast of the North Island experience the same weather conditions as the West Coast of the South Island? Where is it less affected?
- Up to Taranaki
- Waikato, Auckland and Northland
What does the East Coast of the North Island experience as the Cold Front moves through NZ?
Passing showers and noticeable wind change from a Northwesterly to a Southwesterly.
