Tuesday, 21 February 2012

How do I conduct an extreme weather watch?

This blog post is for Year 12 students at Bethany School.  During this Extreme Weather unit a practical skill you need to learn is how to monitor the weather during an extreme weather event.  The only problem with this is that by definition such an event is unusual and therefore unlikely, though not impossible, to occur during the six weeks on this topic.  The only way to find out if we are having any extremes is to keep a close eye on the weather. There are three approaches to recording the weather and the first two are shown below.  You need to practice and become confident in developing these skills.
Assignment: Click here for further details on this week's assignment.  
Click here to download a pdf copy of this blog post.  

Approach A: Weather Log Book (Fieldwork)
The first approach is the way people have recorded the weather since the mid 18th Century.  This log book measures 4 types of weather: temperature, precipitation, cloud cover and wind direction.  Apart from the temperature, all the others can be recorded using your eyes and a sense of direction.  Here’s a quick practical guide on how to record each of these weather variables:
  1. Temperature (measured in degrees Celsius °C). To measure temperature will need a thermometer.  Mr Simmons and Mrs Lindsey both have weather display consoles which show the live temperature at Bethany School. 
  2. Precipitation. This is any water falling from the sky and comes in 4 forms: rain, snow, sleet and hail.  The graphic below shows the common precipitation symbols you can use.  You can easily make your own rain gauge using a plastic drinks bottle, ruler and some sellotape!
  3. Cloud Cover (measured in oktas).  To measure the amount of cloud cover you need to estimate how many eighths (or oktas) of the sky are covered in cloud.  Clear skies = 0 oktas, overcast (fully cloudy) = 8 oktas. The graph below shows the cloud cover symbols you can use.
  4. Wind Direction. Wind direction is the direction FROM which the wind blows e.g. a cold Northerly wind (from the Arctic) or a warm Southerly wind (from the Tropics).  To measure this you need to know where North is.  Mrs Lindsey has compasses you can borrow in her classroom.  You can use the map of the school below to help you.  Be careful to measure wind direction away from buildings as wind is funnelled around them and will give you a wrong reading.  If you are practically inclined you can make your own wind vane like the one in my garden. 
  5. Other measurements.  If you want to measure more weather you can also record cloud type. Cloud types are closely linked to the passage of a depression and there is a sequence of cloud types ahead of a warm front. Watching the clouds can help you to produce your own weather forecast.  The diagram below shows the 10 main cloud types arranged by shape and altitude.  The diagram below shows which symbols to use.
This chart shows standard weather symbols which you could use in your weather log book
This cloud ID chart shows the ten main cloud types

Approach B: Automatic Weather Station (Research)
 The Geography department owns and manages the school’s Automatic Weather Station (AWS).  The mast is securely attached to the Science block fire escape and broadcasts data wirelessly to the two weather display consoles.   Data is also sent to a PC and uploaded to the internet every 15 minutes.  You can download this sampled data using the following address: http://www.skylink-pro.com/schools/bethany/index.php . Here’s a practical guide on how to use the AWS data.

  1. Front page. This gives you a snapshot of the weather data for Bethany School. The map of the British Isles displays weather readings from airport weather stations and is useful for analysing spatial patterns in temperature and wind speed.
  2. Site History.  This gives you a more detailed set of graphs for all the weather instruments on the weather station. If you click on these graphs you will get an even more detailed graph! http://www.skylink-pro.com/schools/bethany/history.php?stationid=T069
  3. Data.  This gives you the data in table form and you can select the date to research the actual weather. http://www.skylink-pro.com/schools/bethany/data.php?stationid=T069
  4. Windrose. This gives you the wind direction in an impressive wind rose graph. http://www.skylink-pro.com/schools/bethany/windrose.php?stationid=T069
  5. Reports.  This displays daily weather data for the current month. http://www.skylink-pro.com/schools/bethany/reports.php?stationid=T069
Site History graphs.  Click on these to get even more detailed graphs
Data.  This displays all the weather data in table form
Wind Rose.  This graphic shows the wind direction.
Reports. Shows you the monthly summary & daily highs and lows - helpful for spotting Extreme Weather. 

Approach C: Rain Radar, Surface Pressure and Twitter
In addition to the fieldwork and research approaches above we would also like you to pull in some other data from the internet these are: rain radar maps, surface pressure charts and Twitter. 
  1. Rain radar.  This gives you actual data of where and how heavy precipitation is.  These maps are sampled every 30 minutes. http://www.metoffice.gov.uk/weather/uk/radar/
  2. Surface Pressure Charts.  These maps are forecasts maps of weather which show isobars (lines of equal pressure), weather fronts and the location of depressions and anticyclones (Highs and lows).  http://www.metoffice.gov.uk/weather/uk/surface_pressure.html
  3. Satellite Images.  These images show you the pattern of cloud cover and are sampled every 30 minutes. http://www.sat24.com/?culture=en
  4. Blogs.  Matt Hugo's blog provides more detailed analysis of Jet Stream movements.  http://matthugo.wordpress.com/
  5. Met Office WOW. The Met Office runs a site for people and organisations to upload their AWS data.  You can zoom in and out of maps and select different weather variables.  http://wow.metoffice.gov.uk/
  6. Twitter.  We recommend you sign up for a free Twitter account and follow the following Twitters:
Click on these images below to see the actual live webpages. 

Deciding your sampling approach
You need to practice using both of these approaches.  An important decision you need to make is your sampling interval.  You can record the once a day for 1 week or pick one day and monitor the weather at 7 hourly intervals throughout the day.  If you are working in a group perhaps one person can do weekly sampling and the other can do hourly sampling.

Deciding your weather recording format
Finally you need to decide on how to record the weather in your log book.  I recommend adapting the weather log book table shown at the start of this post. 

Happy Extreme Weather watching! :)

To see an example of an extreme weather watch please click on these link to Extreme Weather (Snow) 4/5th February 2012 or Extreme Weather (Lightning) 28th June 2011.