Laurier Williams'

Australian Weather News & Links

How To Do It Yourself Page

Various items in the lists can look so complex they frighten the non-boffins away. The humble explanations on this page aren't designed to make you an expert, but they may make your learning curve easier.

Print this page out and so that you can work from it.


The READY system (updated 07/01/00)

This site allows you to plot maps of Australia, or any part of Australia or the globe, showing a wide range of current or forecast weather elements at the surface or in the upper atmosphere. You can also produce a diagram which shows the actual or forecast vertical sounding through the atmosphere at any location. Perhaps best of all for the casual user, you can produce a meteogram for any location, showing the forecast rain, temperature, wind, cloud, humidity and other variables. Work through these once, and you'll be surprised at how easy, yet how powerful, this system is to use. I'd suggest you print out these instructions, and work from the paper!

All this information is produced from the US NCEP Medium Range Forecasting model, and comes in two flavours:

The AVN 191km model is run four times daily, based on observations made globally at 00, 06, 12 and 18 hours UTC. It is produced quickly and is usually available about 5 hours after observation time -- i.e. around 3 and 9 am and 3 and 9 pm Eastern Standard Time. It only looks 72 hours or 3 days ahead, but shows the weather in 6-hourly time steps.

The MRF 191km model is run twice daily, based on observations at 00 and 12 UTC. It takes longer than the AVN version to produce because it "waits" for more observations to come in, then number-crunches the forecast out to 15 days. It is typically available about 9 hours after observation time -- i.e. around 7am and 7pm EST -- and shows the weather in 12-hourly time steps.

In using all these products, remember that forecast accuracy drops off rapidly after about 5 days -- sooner at times of unstable weather patterns -- and that the forecast produced by a professional forecaster working with several computer models is almost always more accurate than the forecast of a single model.

How to plot a map

Let's say you want to plot a map for part of Australia showing expected rainfall and the pressure pattern (i.e. standard weather map) for some time in the future. Here's what you do:

  1. On the ARL Mapping page, go to the Forecast Model Graphics, Interactive Forecast Maps (Java Based) line, and select AVN/SH 191km or MRF/SH 191km, depending on which model you want to use. This takes you to a second screen.
  2. Click on the part of Australia for which you want a map. This takes you to a third screen.
  3. Change zoom factor to 10.0
  4. Change No overlay to overlay
  5. For Field 1 select Accumulated Precipitation and change contour type to color filled and contour interval to 3.
  6. Leave Field 2 unchanged so as to get sea level pressure at the surface using colour lines at the default interval
  7. Choose the date and time for the chart.
  8. Click the Request Plot button, and shortly you will start receiving the requested chart. It shows the rain amount forecast for the 6 or 12 hours up to the time you requested, and the standard weather map at that time.
  9. To get the same information for different time periods, click the back button on your browser, and select a different time -- the rest of the information on the form stays the same unless you alter it.
  10. Finally, play around with different settings and choosing different fields.

How to plot a meteogram

  1. On the Meteogram line, select AVN 191km or MRF 191km, depending on which model you want to use. This takes you to a second screen.
  2. Here you indicate the location for your meteogram in one of three ways -- city code (e.g. yssy for Sydney), latitude/longitude, or by simply clicking on the map of Australia. For this demonstration, enter yssy as the WMO ID, then click next. This takes you to a third screen.
  3. On this final screen, leave the starting date/time as it is, but change the forecast duration to 72 hours. Change the graphics size to anything you like.
  4. You can customise what you get using the rest of the form, but for now just click the Default Meteogram Request Meteogram button.
  5. In the meteogram you get, the precipitation, 2 metre temperature and barometer are graphed out for the next three days -- the dates and times are at the bottom of the chart. You also get the 500mb Thickness and 850mb Temperature. Don't worry if you don't have a clue what these are! You can return to the previous screen by hitting your browser's back button, and then use the customising boxes to get exactly what you want. A good selection for the average user is wind flags, cloud cover, precipitation, 2m temperature (i.e. air temperature) and either Mean Sea Level pressure or 2m relative humidity. Important: Be sure to select the radio button for "user's choice of up to 5 fields to plot", and use the "request meteogram" button at the foot of the page.

How to plot a vertical sounding

  1. On the Forecast Soundings line, select AVN 191km or MRF 191km, depending on which model you want to use. This takes you to a second screen.
  2. Here you indicate the location for your meteogram in one of three ways -- city code (e.g. yssy for Sydney), latitude/longitude, or by simply clicking on the map of Australia. For this demonstration, enter yssy as the WMO ID, then click next. This takes you to a third screen.
  3. Leave everything on this screen as it is, and click the Request Plot button at the bottom of the page. If you're familiar with upper air diagrams, you'll recognise the familiar Skew-T LogP diagram. If you haven't got a clue what a Skew-T LogP diagram is, here's a simple explanation. Imagine you're in a balloon going straight up above Sydney. The thick red line shows the temperature trace, and the green line the humidity as you rise. The heights aren't shown in feet or metres, but by the pressure that a barometer you had with you would show -- pressure drops as you go up. The pressure is shown down the left side of the plot. 700 hectopascals (or millibars) is about 10,000 feet up, and 500hPa is about 18,000 feet. To read the temperature, follow the thin diagonal red line from the thick red trace up to the temperature figures on the right of the plot. The humidity is a bit trickier. It is given as a dew point. If you don't know what this is, it doesn't matter -- just remember that the closer it is to the temperature trace, the moister the air is. Finally, the wind direction and speed are given by the flags down the right side of the plot, with the wind blowing from the flag or feather into the vertical line.
  4. Because you requested the default plot, what you got was the actual conditions at Sydney Airport at the initial time for the model data. Now experiment by hitting your browser's back button, and selecting different forecast times, or an animation.

If you're developing an interest in meteorology, playing with these professional forecasting tools while observing the weather day after day will help both your understanding of the weather and your understanding of the tools!


Real-time data plots from GDAS

Global Data Assimilation System Real Time Data Plots CPC. Using global data gathered at 00, 06, 12 and 18 UTC daily, this site allows you to plot maps of Australia (or anywhere else) showing about 70 meteorological variables at the surface or 16 upper levels for the most recent observation time or any time during the past 5 or 6 weeks.

This gem of a location needs a few basic driving skills; then it's up to your own depth of meteorological knowledge as to how far you take it. Available to you is the full surface and upper air data for the past 5 or 6 weeks, including the latest set, normally only 6 to 12 hours old. The wizzardry here has been put together by the folk at NCEP, and uses the same GrADS software that produces the COLA/US MRF Australian weather charts which are currently the best on the web.

The following demo will take you through the steps to produce a chart; after that it's over to you to play with all the other possibilities.

  1. Clicking the link above will take you to the first of two pages. The first page asks you to select a data set control file, sci-speak for "how do you want to look at this stuff." You can look at the data for pressure levels through the atmosphere (1000hPa, 925hPa, etc) which will be mostly what you'll want to see. Or you can look at non-pressure level data (basically precipitation, max and min temperature and outgoing long wave radiation). In each of these categories, you can look at the latest analysis, or any six-hourly analysis over the past month or so. For this demo select pgb_simple_last.ctl, which says you want to look at a simple subset of the latest available data.
  2. In the options, click "include variable definitions" to give brief explanations of what the abbreviations on the next screen mean.
  3. You can leave the type of plot blank for now -- you'll get a map by default. Click on "Next Page"
  4. Now you are on the second page, where you have to select a variable to map. Click on Temp
  5. In the select level box select 700 -- that's the 700 hectopascal pressure level, about 10,000 feet up.
  6. In the extra operation box select to convert from degrees K (Kelvin) to degrees C unless you're more comfortable with deg K
  7. You can't change the next line on this input screen, because data is only available here for the latest observation set. If you had clicked one of the selections on the first screen that said every six hours, you could select any set of observations from the past few weeks here.
  8. For Map projection click Aust
  9. For contouring click shaded + lines
  10. For plot size click 640 x 480 which will fill most screens
  11. Click plot and wait (about 10 to 20 seconds unless the traffic's bad) for your chart
  12. Finally, play with some of the other variables. Simple ones include SLPres (normal weather map or isobaric chart), PrcWater (the number of kilograms of water you'd get if you squeezed a column of air 1 meter square and the full height of the atmosphere like a sponge!), RHum (Relative humidity at various levels), Omega (how fast the air is rising (unstable) or falling (stable) at each level) and winds (speed and direction - 250hPa is a good level for the jetstream).
  13. If you get nothing returned to you, it probably means that data for that variable at that time is not available or possible - the software is not smart enough to stop you asking for things that don't or can't exist.
  14. Have fun!