NZ Weather

Question 1

What are the three main influences on NZ WX

Answer 1

1. The surrounding ocean environment with high average water vapour content
2. High relief, with strong orographic effects, giving bigger contrasts b/t E and W than N and S
3. The countries location in a region of travelling highs and Lows with strong Westerlies and variable WX

Question 2

High Westerly index in NZ

Answer 2

• Positive West to East flows dominate for 90% of the time in NZ
• Usually characterised by a Low pressure systems at high latitudes and strong ridging at 30 deg S.
• Results in SFC and upper level Westerlies, as well as variable and changing WX

Question 3

Low Westerly index in NZ

Answer 3

• When NZ gets (negative westerlies) - East or NE winds about 10% of the time.
• Usually characterised by a low pressure system flanked by high pressure systems. These systems move very slowly and can bring days of Easterlies over NZ = droughts etc.

Question 4

Critical SW flows: WSW characteritics

Answer 4

• Flows onshore to west coast of SI = Showers and wind

- Wind shadow with no CLD or SH experienced East of NZ

Question 5

Critical SW flows: SSW characteristics

Answer 5

• Flows onshore to east coast of SI - wind and SH experienced here as well as East coast of NI
• Wind shadow with no CLD or SH experienced west of SI and through Central/BoP areas in the NI

Question 6

Critical SW flows: SW characteristics

Answer 6

• Flows onshore to the bottom of the SI = wind and SH experienced here as well as clipped edges of east coasts.
• Wind shadow with no CLD or SH experienced over upper NI and SI

Question 7

Aviation Climatological region 1: Southland (6)

Answer 7

1. Sheltered from WNW through N and NE
2. Exposed from ENE through S to W
3. Strong winds about coast, esp in summer
4. Severe turb frequent, esp in N to W flow
5. In unstable SW, SHRA with poor vis and low CLD is common
6. Radiation FG frequent in winter, can persist in inland valleys

Question 8

Aviation Climatological region 2:Eastern SI (6)

Answer 8

1. Sheltered from NNE through W to SW
2. Exposed from NE to SE to SSW
3. Channeled WSW to NNW winds through mntns = strong winds on coastal plains, esp in spring/autumn
4. Strong NW winds = Severe turb/rotors/lee activity/downdrafts.
5. Moist Easterly winds = extensive low CLD, SHDZ and poor vis in coastal areas.
6. Radiation FG common in winter, can persist in inland valleys

Question 9

Aviation Climatological region 3: Westland SI (7)

Answer 9

1. Sheltered from ENE through SE to SSW
2. Exposed from SW through NW to NE = heavy RA, poor vis and low CLD
3. Onshore flow stronger to the South and far North
4. When flow is perpendicular over the ranges, winds over the alps are very strong b/t 5 - 12,000ft
5. In SE flow, severe turb, Lee waves, downdrafts and rotor streaming occur.
6. Radiation FG rare near coast due strong katabatics, advection FG is common
7. Radiation FG common in sheltered inland valleys in winter

Question 10

Aviation Climatological region 4: Nelson (7)

Answer 10

1. Exposed only from N and NE. Blenheim exposed to E. All CLD/low vis occur in these directions
2. Sheltered from all other directions
3. Sounds exposed to flows from WNW
4. Radiation FG not common
5. Advection FG occasional with moist Northerlies in N or Easterlies in Blenheim
6. Strong convection occurs in all season (esp summer)
7. Strong NW winds = severe turb, rotors, lee waves, downdrafts. Rotor streaming in strong Easterlies

Question 11

Aviation Climatological region 5: SW NI (7)

Answer 11

1. WX and climate dominated by cook strait gap that deflects all flows to N-NW or S-SE
2. Manawatu gorge also channels winds towards W-NW and E-SE
3. Both Cook straight/Manawatu gorge are very windy
4. Exposed to W to NW flows everywhere, and S to SE in WLG. Poor WX associated with these winds.
5. Severe turb and downdrafts common in WLG/Cook strait in NW winds
6. Radiation FG rare due strong winds. Can occur in Horowhenua and far N of zone, esp in winter
7. Advection FG occasional in moist NW or NE flows

Question 12

Aviation Climatological region 6: East coast NI (5)

Answer 12

1. Sheltered from SW through N to NE (except woodville in NW)
2. Exposed from NE through E to S
3. These directions are stable = advection FG, Low Stratiform CLD, Poor vis in RA or DZ, and severe icing above FZL
4. Strong NW winds accompanied by severe turb, rotors, lee waves, downdrafts
5. Radation FG less frequent

Question 13

Aviation Climatological region 7: N of NI (6)

Answer 13

1. Exposed to winds from N quadrant
2. Sheltered from Southerlies, esp in the S
3. N flows are stable = advection FG, low stratiform CLD, poor vis in RA and DZ, severe icing above FZL
4. Worst WX in NE flows ahead of ex tropical Lows coming from N. Exposed coast worst affected
5. Prevailing winds are SW, esp in winter = frequent, heavy SH, however BOP is sheltered.
6. Radiation FG most common in late spring/early summer, esp in waikato valleys.