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Bushcraft Weather

Trampers First Aid < Bushcraft >

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Weather Made Simple

Disclaimer
almost everything written here are gross generalisations which are true only in a limited range of circumstances.

What Causes Weather?

  • BAD weather is due to LOW pressures. A low pressure region is called a low, cyclone, or depression.
  • GOOD weather is due to HIGH pressures. A high pressure region is called a high or anticyclone.
  • WIND occurs when pressure is changing (cg. going from a Low to pressure region).

Weather Systems Move...

  • all weather systems comes to us from the WEST
  • cyclones rotate clockwise
  • anticyclones rotate anticlockwise

This Means That

  • Northerly (or rather NW) winds indicates that a cyclone bad weather is on its way
  • Southerly (or rather SW) winds indicates that an anticyclone good weather is on its way

Other factors

  • Cyclones are generally preceded by some visible weather signs: high cloud, ring around sun, gray sky, hogs backs etc. These indicate that pressures are getting low and bad weather is coming.
  • Anticyclones are generally preceded by a sort but sharp period of cold squally southerlies, with clear periods in between squalls.

When the weather hits NZ...
As a rough rule, areas facing the weather take the brunt, areas on the lee side are sheltered, remembering that NZ actually runs SW to NE this means that:

  • during cyclones (northerly winds) the West side of NZ gets bad weather while it is fine (but often windy) on the East
  • when an anticyclone is approaching (southerly winds) the East side of NZ gets “bad weather while it is fine on the West
  • mountainous areas in the middle (Tararuas, Ruapehu) get bad weather in both these cases;

“Normal” weather cycle

All these factors add up to a normal weather pattern which cycles through every 5 or 6 days.

  1. Northerly winds. High cloud building up (1 day)
  2. wet weather on the west; encroaching further east. Dry but windy on the east (1 or 2 days)
  3. winds turning to the south, temperatures getting low. Possibly snow to low levels (1 day)
  4. fine on the west but cold squaliy southerlies over the rest of the country (1 day - 2 weeks!)
  5. fine over the whole country (1 or 2 days)
  6. go to step 1

Reading Weather Maps

Even a glance at a weather map can give you a good feel for what the weather will do ever the next few days. Worthwhile doing before you head into the hills. Things you will see on a weather map are:

  • an H indicates a High Pressure = fine weather. -
  • an L indicates a Low Pressure bad weather.
  • the number beside the L or H1 tells you how high/low the pressure is. This gives you an idea of how bad the weather is going to get!
  • A short curved line indicates a FRONT, which a region of particularly wet weather
  • the lines on the map are called ISOBARS (lines of equal pressure). These tell you the wind direction - the wind generally follows these lines
  • the strength of the wind is indicated by how close together the isobar lines are.

Northern Hemisphere

Note: in the Northern hemisphere Cyclones and Anticyclones rotate in the opposite direction! (but weather still comes from the West). There NW=good weather coming, SW=bad weather coming.
WeatherMap.png: 1293x776, 467k (2014 Jul 21 06:27)

Weather map

The numbers on the weather map give you the pressure = an indication of just how high the high is (or low the low is).
In this example

  • southerly winds over the whole country (moderately strong)
  • southerly front sweeping across the south island (at Wellington in half a day)
  • fine weather to arrive in one or two days time

Bushcraft Course - Lecture 3 Weather, Hypothermia, Teamwork

Weather 'The barometer doesn’t affect the weather much on the coast' Charlie Douglas

Forecasts

  • general forecast
  • mountain forecast
  • mountain Radio

High Country Weather -

  • air temperature decreases approximately 6° per 1,000 metres of altitude gain
  • bushline ends at approximately 1,200 metres
  • weather is better on the lee of ridges

Weather Signs

  • high cloud movement indicates more general weather patterns
  • increasing lowering cloud indicates worsening weather
  • hogs backs indicate high winds and bad weather

Weather Maps

  • weather generally moves from west to east
  • H (anticyclone) brings good weather
  • L (low) brings unsettled weather

An approaching cold front brings increasing north-west winds, rain, and a change to colder southerly winds, perhaps with snow. Weather often clears from the south

Hypothermia

Serious hypothermia is when the body’s core temperature drops below 37° Heat loss may be due to either one or a combination of: Cold, Wet, Wind The situation may be exacerbated by exhaustion, body weight, immobility

Mild Condition :

Shivering, cold hands and feet, loss of dexterity, pain from cold

Severe Condition

Shivering decreases or stops, loss of reasoning and recall, confusion, abnormal behaviour, victim appears drunk, very clumsy, slurs speech, denies problem and may resist help, victim becomes semi-conscious to unconscious and muscular rigidity increases

To Guard Hypothermia

Eat high energy food, drink frequently, keep warm and dry (avoid excessive sweating), keep head, hands and neck protected, avoid fatigue (consider redistributing loads), consider seeking shelter, and if setting out in cold, wet, or windy conditions be on continual lookout for symptoms

Treatment :

The aim is to prevent further heat loss and to rewarm the victim’s core

  • organise shelter (huddle with the victim)
  • get the victim into a sleeping bag
  • provide high energy drink and/or food only if the victim is fully conscious
  • get another (warm) person into the sleeping bag with the victim (if possible)
  • don’t warm the victim rapid}y by rubbing hands/feet and don't give alcohol

Teamwork

Stay together, look after one another, leaders should generally include everyone in decision making

Confucious says: 'keep positive and enjoy yourself'

Category
Bushcraft

Page last modified on 2015 Jan 12 21:21

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