weather

outdoors toc =Weather = introductory video: media type="custom" key="10119333" width="140" height="140"

Sources of information
You need to know where to get accurate weather information //before// going intothe wilderness. the source will depend upon where you are going and what you plan to do. this preparation is especially important if you are going to an unfamiliar area.

UK sources of weather information
[|Mountain weather information service] (for UK mountain/hill areas)  [|Metcheck.com] (click the hobbies tab then mountaineering) Met office [|mountain weather forecasts]

Weather maps
[|Weather charts]  [|UK Met Office synoptic charts]

Weather developments
[|Air masses (UK)] [|Video on air masses]  [|UK climate]  [|Weather systems]

Crossed winds rule (northern hemisphere)
<span style="font-family: Georgia,serif;">Stand with back to the wind (free of local effects such as tall buidlings, narrow valleys etc). <span style="font-family: Georgia,serif;"> If the upper wind (clouds) comes from your left the weather will deteriorate. <span style="font-family: Georgia,serif;"> If the upper wind (clouds) comes from your right the weather will improve. <span style="font-family: Georgia,serif;"> For increased accuracy stand with your back to the direction of the lower clouds or rotate 30 degrees to the right from the surface wind behind you

<span style="font-family: Verdana,Geneva,sans-serif;">Identification of cloud types, wind speed and temperature
<span style="font-family: Georgia,serif;">//From the UK met office website:// <span style="font-family: Georgia,serif;">The ten main types of cloud can be separated into three broad categories according to the height of their base above the ground: high clouds, medium clouds and low clouds. <span style="font-family: Georgia,serif;">**High clouds** are usually composed solely of ice crystals and have a base between 18,000 and 45,000 feet (5,500 and 14,000 metres). <span style="font-family: Georgia,serif;">**Medium clouds** are usually composed of water droplets or a mixture of water droplets and ice crystals, and have a base between 6,500 and 18,000 feet (2,000 and 5,500 metres). <span style="font-family: Georgia,serif;">**Low clouds** are usually composed of water droplets — though cumulonimbus clouds include ice crystals - and have a base below 6,500 feet (2,000 metres).
 * <span style="font-family: Georgia,serif;">Cirrus - white filaments
 * <span style="font-family: Georgia,serif;">Cirrocumulus - small rippled elements
 * <span style="font-family: Georgia,serif;">Cirrostratus - transparent sheet, often with a halo
 * <span style="font-family: Georgia,serif;">Altocumulus - layered, rippled elements, generally white with some shading
 * <span style="font-family: Georgia,serif;">Altostratus - thin layer, grey, allows sun to appear as if through ground glass
 * <span style="font-family: Georgia,serif;">Nimbostratus - thick layer, low base, dark. Rain or snow falling from it may sometimes be heavy
 * <span style="font-family: Georgia,serif;">Stratocumulus - layered, series of rounded rolls, generally white with some shading
 * <span style="font-family: Georgia,serif;">Stratus - layered, uniform base, grey
 * <span style="font-family: Georgia,serif;">Cumulus - individual cells, vertical rolls or towers, flat base
 * <span style="font-family: Georgia,serif;">Cumulonimbus - large cauliflower-shaped towers, often 'anvil tops', sometimes giving thunderstorms or showers of rain or snow

<span style="font-family: Georgia,serif;">A change from the highest (cirrus) clouds to the loest (stratus) ones often indicates the arrival of a warm front. The warm front itslef often includes nimbostratus clouds - these will bring rain. <span style="font-family: Georgia,serif;">Altostratus clouds cause the appearance of a halo around the sun or moon - a halo around the moon at night may well herald rain in the morning.

<span style="font-family: Georgia,serif;">[|Clouds]

<span style="font-family: Verdana,Geneva,sans-serif;">Effects of weather on route selection & level of activity
<span style="font-family: Georgia,serif;">Winds will be greater on ridges and in between hills (in saddles and, especially, valleys) - on windy days plan routes to stay on the lee side of ridges as much as possible.

<span style="font-family: Verdana,Geneva,sans-serif;">Links
<span style="font-family: Georgia,serif;">[|Mountain weather] <span style="font-family: Georgia,serif;">[|weather basics] <span style="font-family: Georgia,serif;">[|Understanding weather] <span style="font-family: Georgia,serif;">[|weather systems]

<span style="font-family: Verdana,Geneva,sans-serif;">Books
<span style="font-family: Georgia,serif;">[|Weather for hillwalkers and climbers] <span style="font-family: Georgia,serif;"> [|Instant weather forecasting]