NZ WEATHER

Question 1

What are the three main influences on NZ climate

Answer 1

1. Oceanic environment with high average water vapour content
2. High relief with strong orographic effects, bigger contrasts between E-W vs. N-S
3. Location in region of travelling highs and lows with strong westerlies

Question 2

What produces a high westerly index over NZ?

Answer 2

1. Lows at high latitudes
2. Strong ridging at 30deg south
3. strong upper level westerlies that advects systems eastward

Question 3

What is the sequence of a high westerly index?

Answer 3

1. Ridge of leading High
2. Pre-frontal NWs
3. Trough & associated front
4. Post frontal SWs

Question 4

High Westerly index sequence: the ridge

Answer 4

Fine condxns, scattered Cu or Sc, westerlies & sea breezes.
Low cloud beneath inversions or early morning fog in valleys is common

Question 5

High Westerly index sequence:
Pre frontal NW’lies

Answer 5

• Approach of front
• Flow turns NW with drop in pressure.
• Marked orographic effects
• West of ranges: heavy rain & TS
• East: thickening high & middle cloud

Question 6

High Westerly index sequence: Post frontal SW’lies

Answer 6

• After ront moves through, sudden wind chg to SW
• Brief rain from Ns
• Large increase in pressure

Question 7

What is a low westerly index situation characterised by

Answer 7

1. East or NE winds across much of NZ.
2. A low pressure system within NZ latitudes
3. Upper level flow tends N-S.
4. SFC pressure features move slowly.

Question 8

What affects low westerly index the most?

Answer 8

Trough line between anticyclones

Question 9

Low westerly index sequence?

Answer 9

1. Pre warm front
2. Warm front passage
3. Warm sector
4. COld front passage

Question 10

Low westerly index sequence: pre warm front

Answer 10

• Airflow is N/NE & warm/moist.
• RH increase as air moves south, minor ascent results in cloud/precip
• Terrain exposed to north will receive rain & low cloud.

Question 11

Low westerly index sequence: Warm front passage

Answer 11

• as front appchs, rain falling from middle cloud saturates air below, low cloud forms.
• very poor vis & bases only few 100ft.

Question 12

Low westerly index sequence: Warm sector

Answer 12

• As front passes wind tends more NW
• middle & high cloud clears but areas W of ranges still get orographic rain & low cloud.
• areas E of ranges get warm & sunny condxns

Question 13

Low westerly index sequence: cold front passage

Answer 13

• behind cold front & depression, airflow is S’ly
• East coast: low cloud & drizzle
• as front clears, ridge of high pressure is produced