Weather

2. Aims of Session Understand the effects that the weather has on you and your activities. Where to look for weather information How to interpret that information to make an informed decision about your activities These are the aims of the session. In the first part I will cover long term forecast and what you need to be looking for prior to your expedition; in the second half I�ll cover how to spot the signs of incoming bad weather when your on your expedition. These are the aims of the session. In the first part I will cover long term forecast and what you need to be looking for prior to your expedition; in the second half I�ll cover how to spot the signs of incoming bad weather when your on your expedition.

3. Where does our weather come from? Why do we need to know about the weather? The weather has a profound effect on the walking environment. So to know what the weather will doing for the duration of your expedition is an essential part of the planning process. The final decision about itinerary, route etc could ultimately depend on the weather so its important to have a basic understanding The air can swirl towards Britain from all different directions. As it comes towards is it picks up the properties of whatever it is crossing. If the air comes from over the sea? (wet/rain). If the air comes over land? (dryer). Most common air flow to the UK is polar maritime (cold and wet). Then Tropical maritime (warmer but still wet). The names are not important but thinking where it has come from is. This idea will generally work where ever you are on expedition.Why do we need to know about the weather? The weather has a profound effect on the walking environment. So to know what the weather will doing for the duration of your expedition is an essential part of the planning process. The final decision about itinerary, route etc could ultimately depend on the weather so its important to have a basic understanding The air can swirl towards Britain from all different directions. As it comes towards is it picks up the properties of whatever it is crossing. If the air comes from over the sea? (wet/rain). If the air comes over land? (dryer). Most common air flow to the UK is polar maritime (cold and wet). Then Tropical maritime (warmer but still wet). The names are not important but thinking where it has come from is. This idea will generally work where ever you are on expedition.

4. Air Pressure The air flows that we seen in the previous slide are generated by PRESSURE: (point out High and Low pressure areas) Low Pressure is turbulent and volatile, it produces bad weather. High Pressure is slow and stable, it generally produces good weather. Note: high pressure can also produce bad weather ie. Electrical storms etc. Draw attention to different pressures, low lows = bad weather and high highs = good weather. The wind runs roughly along the isobars � the closer the isobars, the stronger the wind, similar to contour lines. Lows circulate anti-clockwise Highs circulate clockwise The air flows that we seen in the previous slide are generated by PRESSURE: (point out High and Low pressure areas) Low Pressure is turbulent and volatile, it produces bad weather. High Pressure is slow and stable, it generally produces good weather. Note: high pressure can also produce bad weather ie. Electrical storms etc. Draw attention to different pressures, low lows = bad weather and high highs = good weather. The wind runs roughly along the isobars � the closer the isobars, the stronger the wind, similar to contour lines. Lows circulate anti-clockwise Highs circulate clockwise

5. Effects of Air Pressure Air pressure determines wind and weather patterns. Air pressure determines wind and weather patterns.

6. The Effect of Wind in the Mountains Wind can have a tremendous effect on morale and safety. Strong winds can make conditions feel considerable colder that the ambient air temperature and pin down an unsuspecting party on an exposed ridge. Wind behaves differently in the mountains and is influenced by the shape of the land. Wind accelerates uphill due to it being squeezed between the earth and the troposphere. Its also accelerates through cols etc for the same reason. Wind can have a tremendous effect on morale and safety. Strong winds can make conditions feel considerable colder that the ambient air temperature and pin down an unsuspecting party on an exposed ridge. Wind behaves differently in the mountains and is influenced by the shape of the land. Wind accelerates uphill due to it being squeezed between the earth and the troposphere. Its also accelerates through cols etc for the same reason.

7. Wind and its effect on us! Highlight the wind chill is based on an ambient temp of 5 degrees C. The ambient air temp will decrease as the air moves up the mountain this will increase the wind chill. Wind at 900m is 2 to 3 times what it is at sea level Do not underestimate wind chill Highlight the wind chill is based on an ambient temp of 5 degrees C. The ambient air temp will decrease as the air moves up the mountain this will increase the wind chill. Wind at 900m is 2 to 3 times what it is at sea level Do not underestimate wind chill

8. Rain Rain or hail preceding or during a walk will have a profound effect on the party. Morale will be lowered by rainfall, especially if you do not have good quality waterproofs which increases the risk of cold injury. It will also effect the going underfoot, making rocks very slippery and progress slowerRain or hail preceding or during a walk will have a profound effect on the party. Morale will be lowered by rainfall, especially if you do not have good quality waterproofs which increases the risk of cold injury. It will also effect the going underfoot, making rocks very slippery and progress slower

9. Temperature How cold is it going to be, especially in the wind? Choice of clothing and spares can be modified according to the temperature. When planning you expedition, its important to know that temperature changes with altitude as this will influence your route As you go higher it gets colder. This rate of change is known as the Lapse Rate. Temperature drops at a rate of 1 deg per 200m when the air is cloudy and wet and 1 deg per 100m when the air is clear and dry and How cold is it going to be, especially in the wind? Choice of clothing and spares can be modified according to the temperature. When planning you expedition, its important to know that temperature changes with altitude as this will influence your route As you go higher it gets colder. This rate of change is known as the Lapse Rate. Temperature drops at a rate of 1 deg per 200m when the air is cloudy and wet and 1 deg per 100m when the air is clear and dry and

10. Sources of Information Internet www.mwis.org.uk; www.metoffice.gov.uk Tourist information Mountain rescue bases Newspapers Television & radio Look around! Check the forecast as close to the time of the expedition as possible to obtain the most accurate information. Where do we find this information: There is a huge choice as to where we can get our weather information. Each source has it�s own pros and cons. In your hand out there is more detail on how to find these sources. TV-Usually too general but easy to access and interpret. Radio-Whole spectrum of usefulness from radio 1 to radio 4, Shipping and outdoor reports most useful, Easy to get on little hill radio, Easy to miss the time slot. Newspaper-Whole variety from the Sun to the Telegraph, Some have specific activities forecasts for the weekends Telephone-Good choice of specific products, Sometimes hard to follow, Difficult to share with group for decisions, Expensive Fax-All of the choice of the telephone but on paper to share, Can be really specific to area and give a good record of how the weather has developed, Expensive Internet-Huge choice of different forecasts for different activities and different areas, From a written description to synoptics and satellite images to web cams at the summit of Cairngorm, Great when you can get to it but who take the lap top on exped. Local Knowledge-Only as good as the �expert� you are talking to, Can be very specific. Folklore-Some are very reliable e.g. red sky at night. Yourself- Seeing fronts coming in, seeing patterns of weather in a new area, getting to know your area Where do we find this information: There is a huge choice as to where we can get our weather information. Each source has it�s own pros and cons. In your hand out there is more detail on how to find these sources. TV-Usually too general but easy to access and interpret. Radio-Whole spectrum of usefulness from radio 1 to radio 4, Shipping and outdoor reports most useful, Easy to get on little hill radio, Easy to miss the time slot. Newspaper-Whole variety from the Sun to the Telegraph, Some have specific activities forecasts for the weekends Telephone-Good choice of specific products, Sometimes hard to follow, Difficult to share with group for decisions, Expensive Fax-All of the choice of the telephone but on paper to share, Can be really specific to area and give a good record of how the weather has developed, Expensive Internet-Huge choice of different forecasts for different activities and different areas, From a written description to synoptics and satellite images to web cams at the summit of Cairngorm, Great when you can get to it but who take the lap top on exped. Local Knowledge-Only as good as the �expert� you are talking to, Can be very specific. Folklore-Some are very reliable e.g. red sky at night. Yourself- Seeing fronts coming in, seeing patterns of weather in a new area, getting to know your area

11. Things that can indicate a change in the weather Cloud formations are the main indicator in approaching bad weather. These are the clouds that can indicate the onset of a change in the weather Cirrus clouds indicate fair weather in the immediate future � they can also be an indication of bad weather within the next 36 hours Stratus are low-lying solid clouds they bring drizzle or light snow. Cumulus clouds � if low clumps floating across the sky, there will be fair weather; vertical growth can indicate the start of a large storm. Cumulonimbus clouds are cumulus clouds that have grown vertically. These clouds bring stormy weather such as rain, lightning and hail. Things that can indicate a change in the weather Cloud formations are the main indicator in approaching bad weather. These are the clouds that can indicate the onset of a change in the weather Cirrus clouds indicate fair weather in the immediate future � they can also be an indication of bad weather within the next 36 hours Stratus are low-lying solid clouds they bring drizzle or light snow. Cumulus clouds � if low clumps floating across the sky, there will be fair weather; vertical growth can indicate the start of a large storm. Cumulonimbus clouds are cumulus clouds that have grown vertically. These clouds bring stormy weather such as rain, lightning and hail.

12. Predicting Bad Weather Weather systems bring a sequence of descending clouds as the bad weather approaches. Observation of devolving clouds can help you anticipate weather changes. A progression from high wispy or cirrus clouds through to lower layers or stratus clouds is a clear indication of an approaching warm front and subsequent unsettled weather. Cirrostratus clouds often form a halo around the sun or moon, so a halo around the moon is often a good early warning sign of rainfall arriving in the morning so don�t leave your stuff outside the tent!Weather systems bring a sequence of descending clouds as the bad weather approaches. Observation of devolving clouds can help you anticipate weather changes. A progression from high wispy or cirrus clouds through to lower layers or stratus clouds is a clear indication of an approaching warm front and subsequent unsettled weather. Cirrostratus clouds often form a halo around the sun or moon, so a halo around the moon is often a good early warning sign of rainfall arriving in the morning so don�t leave your stuff outside the tent!

13. Remember Hills are more likely to have their own micro-climate and localised wind. High pressure: Summer � protect yourself against the sun Winter � wrap up warm Low pressure: Layers; wet weather gear Check the forecast before going into the hills Forecasts do not take account of wind chill Be prepared to change your plans in bad weather