NZ Climatology

Question 1

What effect does the Waitakeres and Coromandel ranges have on AKL?

Answer 1

W: protects AKL from SW & W winds
C: protects AKL from E winds and therefore prevents low cloud bases and rain

Question 2

What are the most common winds in Auckland? When are they most likely and how strong are they?
What effect will a tropical cyclone have on wind?

Answer 2

SW (most common) spring/summer.
NNE even throughout the year.
When +20kt often due SW. If +30kt due passing cold front. Rarely ever +G50kt.
Bottom of TC will move NW-SE hence NE—E—SE winds

Question 3

When is the sea breeze most common in AKL?
How strong is it and what direction does it blow?
What can help/destroy the sea breeze?

Answer 3

SSW 5-10kt Oct-Mar.
SW wind will help enhance breeze to 20-25kt and extend upto 3000ft, whilst a NE breeze may eliminate it entirely or significantly weaken it so it only reaches 5-600ft (strong shear).

Question 4

When does the land breeze occur in AKL?

From what direction and speed?

Answer 4

ENE 5-10kt.
Starts around midnight.
Common in summer and winter but will start later/weaker in winter.

Question 5

Is turbulence common in AKL?

Answer 5

No surface friction is uncommon.

Thermally induced friction around hills is more common.

Question 6

When is radiation fog common in AKL?

What winds can enhance/destroy it?

Answer 6

April to August under high pressure conditions.
Will generally form 0300 and dissipate 0900.
Less issue with fog when NNE winds
More fog when W/NW winds and will form 2200 and persist longer (due Waitakeres blocking wind) especially over Papakura channel.
A sea breeze as the day begins to warm the land may cause fog to blow over airport.

Question 7

What is the most common cause for low cloud in AKL?
What are some other causes?
How high can cloud be expected and how long will it last?

Answer 7

Moist NE is the most common cause with cloud bases 5-600ft, as low as 300ft. Can persist 24h and will be lower of Manawatu Heads.
Slow moving SF will have cloud bases 300ft and rain if wind is moist NNE. Can last 12h.
Wind from W/SW with low SE NZ can bring instability and rain, Cb and cloud to 100ft

Question 8

When is poor vis most common?

What are common reasons?

Answer 8

Poor vis due to low cloud is often absent in summer and worst may-aug and is worst with N/NE winds less 20kt
Due to rain in most common due to frontal passages and will last 1-2h.
Due to pollution is worst in light wind and stable air conditions.

Question 9

What effect does terrain have on Wellington airport winds?

Answer 9

NI/SI produce a channeling effect through the Cook St, prevailing winds are NNW/SSE. Hills either side of the airport provide additional channeling which causes a N/S wind

Question 10

Does the surface wind follow more or less the gradient wing at Wellington?
Describe common reasons for northerly and southerly winds. What percentage of winds are N/S?

Answer 10

Due to complex terrain surface winds do not always follow the gradient wind.
98% of the time the wind will be N or S.
Northerly are common with trough/depression moving E in spring/early summer. The accompanied CF will bring NW winds 50-60kt.
Southerly winds are common in winter with highs over SI or low over/east of NI. Sudden S winds can be experienced with a squall line through the region with winds of 50kt lasting 30-40min.

Question 11

When does the sea breeze in Wellington occur? (Year/day)
What requirements are there for this formation?
What direction is the breeze?
What can enhance the sea breeze?

Answer 11

Occurs late Oct-Apr. Requires sufficient surface heating and anti cyclonic conditions (high/col) when the pressure differences is low between sea/land.
Occur 0900-1800, reduced hours in spring/autumn and rare in winter.
Is normally SSE 6-12kt. Although with weak pressure gradients, can have weak S ar one end of RWY and N at the other end.
A 12-14kt SB May occur if wind above friction layer is E/NE as Rimutaka/Tararua ranges shelter winds, allowing SB to prevail…will die down in evening.

Question 12

When does a land breeze at Wellington occur? From what direction?
What can influence this?

Answer 12

Occurs all year round from NNE, with weak pressure gradients.
In winter LB can occur mid afternoon.
Katabatic effects from N/NE can influence the strength and time of day.

Question 13

What degree of turbulence can be expected when there is a northerly/southerly wind on landing and T/O phase?

Answer 13

LANDING:
N: Bumpy on approach and landing
S: Approach bumpy but smoother landing
TAKE OFF:
N: Turbulent until 3000ft
S: Little to none climbing out of Lyall Bay. Low level turbulence when Cook St wind 240-290*, and due to hills to W of airport low level shear 500-1000ft.

Degree of turbulence is proportional to wind direction fluctuations

Question 14

How often will fog occur at WLG? During what season?

What are the common causes?

Answer 14

Occurs Jan-Mar 5 times a year.

A southerly wind can blow fog from EC SI upwards. Or very rarely radiation fog in Hutt Valley blown S by NE winds.

Question 15

Describe how a moist northerly or southerly airstream will produce low cloud

Answer 15

N: Cook St is generally covered with low cloud but WLG protected by high ground to the north. Lee waves can form so cloud base not uniform, but is lower over Cook St. If due to trough or front, OVC over airport and well to south (approach side) with strong wind, rain and poor vis.
S: ONLY with low/mod strength winds. Low pressure system to N or NE WLG with high over Canterbury but relatively weak PG. Or a weakening tropical depression travelling south along EC NI can produce long periods of low cloud.

Question 16

What wind direction produces more low cloud?

When is low cloud most common?

Answer 16

Southerlies less than 20kt.
Jan-Mar is worst, May-Jul optimal.
Reduced vis to rain is typically 1-3000m, but is not as common as reduced vis due to low cloud.

Question 17

What are the main orographic influences of CHC airport winds?

Answer 17

Southern alps 90km to west.
Port hills 15km SE at 2000ft.
Canterbury plains.
Mainly the alps and Cook St will affect wind.

Question 18

What is the predominant surface wind at CHC? When will this wind typically blow?

Answer 18

NE
Is most frequent in summer as the sea breeze is a major contributing factor. Often very cool temperature.
When 3000ft wind is NNW through to NNE, the surface wind is NNE. Is most common with high to E or SE of Canterbury and is due to effect of Alps and Port Hills.

Question 19

Explain the NW wind on CHC.

When is it likely to occur?

Answer 19

Is a hot and dry Föhn wind that brings turbulent flying conditions. Is most likely to occur ahead of cold fronts moving from the SW.
When 3000ft wind between SSE/SW, the wind at the airport is SW.

Question 20

How often is wind above 20kt at CHC?

What direction are these winds typically?

Answer 20

3% are +20kt.

Slightly less than 50% S Or SW, with the remainder from NW or NE.

Question 21

When (year/day) is the sea breeze common at CHC? How strong and from what direction?

Answer 21

Is most common Oct-Apr starting 1-2h after sun rise, peaking 3h later and ceasing 3h after sunset. Requires a weak PG.
Is approximately 15kt NNE

Question 22

When do land breezes occur at CHC?

What assists them?

Answer 22

On clear sky nights with weak pressure gradients. Katabatic winds can help assist land breezes. Will start 1-2 hours after the sea breeze has ceased.

Question 23

What wind directions bring turbulence to CHC.

Any other ways create turbulence?

Answer 23

The airport is relatively free of turbulence with a sea breeze but will have large amount of it when the NW sets in.
In NW, there will be low level wind shear with moderate to severe turbulence, and as NW sets in turbulence will reach ground level.
Other ways include convective heating over crop plains which can result in Cb/hail and turbulence

Question 24

Is fog common at CHC? What type is most common and how does it form?
Can any other types of fog form? How?

Answer 24

Yes, approximate 45 days per year.
Radiation fog most common, will occur on clear nights with weak pressure gradient from a NE wind, before fog forms will become light NW.
Evening fog may clear around 0000 but form again just before sunrise.
Advection fog may occur from Pegasus Bay (NE) or Waimakariri River (N) and blow over, slight lifting of fog from surface will occur as it approaches the airport. Not as common but may also occur Lake Ellesmere from south which is less likely to lift.

Question 25

Describe the different ways low cloud can form over CHC

Answer 25

High/ridge to E or SE which creates E winds blowing low cloud from ocean or Pegasus bay over 2-300ft
Depression/low E or NE will create SW over land (airport protected by Banks Peninsula) and SE over sea with cloud 1-1500ft.
After CF SW winds occur with cloud base 1000ft, E of Banks Peninsula will receive more low cloud.

Question 26

What are the main causes for poor vis in CHC?

What winds produce the best/worst vis?

Answer 26

Cloud is almost the only reason for poor vis at CHC.
All season have no reduction in vis when NW/SE (or ken SW).
When ENE/S/SW less than 20kt low cloud and drizzle may reduce vis.
When wind above 20kt all poor vis due cloud and rain is from S/SW.
May to Sep is the worst for poor vis/low cloud

Question 27

What latitudes does NZ lie between? What does this mean for the type of climate NZ has? How do the different climates differ in temperature?

Answer 27

34-47S
Very north is sub tropical, characterised by light-mod winds, high RH & reduced vis.
Rest is temperate, NI has temp fluctuations of 14c while SI is 10*c

Question 28

What parts of NZ receive more of an impact from cold fronts?

Answer 28

West coast SI, not as much NI but Taranaki will. Fronts weaken by AKL and east coasts are relatively sheltered

Question 29

How does being surrounded by ocean affect NZ?
What annual temperature fluctuations can result?
What region escapes the influence of oceanic surrounding?

Answer 29

Acts to reduce variability in temperature and increase RH.
RH is higher in winter. And is often slightly higher in WC SI.
Annual fluctuations in temperature are 7-8c on WC and 12-13 EC.
Central Otago.

Question 30

What region experiences predictable & unpredictable rainfall?
Seasonally, how does central NI & Deep South change with rainfall patterns?

Answer 30

WC SI predictable.
North NI & east coast unpredictable.
Northern and central parts of NZ have most rain in summer/least winter.
Deep South has the opposite.

Question 31

What axis does the main mountains in NZ run?

How do they deflect the westerlies?

Answer 31

NNE-SSW.
Southern Alps deflect to NE to create SW.
Far south the westerlies are maintained.
Taranaki deflects air to become NW/SW
-south of Taranaki is NW and air bends around farewell spit to create NW, which channels through the Cook St
-north of Taranaki SW which weaken

Question 32

What are the 3 main gaps in the mountain ranges?

What happens when gale force winds occur through the Cook St?

Answer 32

Fovaux st, Cook St, Manawatu Gorge.
When NW there is little low level cloud in straight other than Sc on hills N WLG. Turbulence is restricted to the friction layer.
When SE turbulence is nil/light over water and mod over land. Low cloud occurs.

Question 33

How does the westerlies creates a NE across the SI?

Answer 33

A low pressure region develops in the Lee of the southern alps which encourages air to be drawn in which curves the NW through the straight into NE. However is very strong NW it will prevail.

Question 34

What creates NW & SW winds?

Answer 34

NW is created prefrontal as a CF moves NE located in a trough situated between two highs.
SW are created by an unstable anticyclonic airflow centred in the Tas,an Sea behind a trough.

Question 35

Explain cloud formation, turbulence due to NW winds (NZ whole)

Answer 35

Cloud will initially be Cc/Ac as front approaches, especially along WC SI and Mt Taranaki. Then cloud will thicken and bases will lower, especially with precipitation in Westport/Fiordland, whilst the EC remains relatively clear. Middle layer cloud will remain over hills as trough approaches.
Wind will increase to gale force through both St and will produce turbulence on EC. Turbulence is nil/light on WC and vis is good outside of showers.

Question 36

What kind of cloud can be expected in a SW wind? (NZ whole)

Answer 36

Due to the unstable nature Cu development is common on WC, even on EC but with higher bases. May develop into Cb with isolated TS. Turbulence and visibility is good except around Cb.
EC will have good vis and some showers.
If the wind is slightly S of SW then WC will be more clear and as far north on EC as Gisborne will be cloudy.

Question 37

What will cause an SE wind?

Answer 37

High SW NZ or low to SE NZ. Both bring cold unstable airstreams, the latter will bring extensive cloud, heavier precipitation (snow if winter/early spring).
West coast is free of cloud and turbulent. EC may also have turbulence as cumulus build up.

Question 38

Describe map 1 from waypoints

Answer 38

Is a standard situation especially summer where an undistrubed long wave pattern is occurring so high-low-high-low and there may be a front attached to the lows. This creates a NW wind, bringing all the effects along with it. It will remain over an area 3-4h, but take a day to sweep country. WC SI most affected and Taranaki, far north not so much. 36-48h later will have high over country.

Question 39

Explain map 2 from Waypoints

Answer 39

The north Tasman Sea is favourable for creating warm core depressions which bring extensive cloud and gale force winds. Will create NE wind which can bring drizzle and low cloud to EC. Will reduce further as fronts approach.