Computer Model Outputs

MSL Pressure/Thickness/Rainfall

These charts represent the predicted state of the atmosphere over Australia at a time stated in the top right corner. They display the mean sea level pressure, the thickness of the atmosphere between 1000 and 500hPa and accumulated precipitation in 24 hour blocks from analysis. The ECMWF charts do not display rain.

Surface Temperature/Wind

These charts display the predicted temperature, wind speed and wind direction close to the surface.

Surface Dew Point/Wind

These charts show the predicted dew point, wind speed and wind direction at the surface.

850hPa Temperature/Wind/Height

These charts depict the predicted temperature, wind direction and speed at, and height of the 850hPa pressure surface.

850hPa Relative Humidity/Wind

These charts represent the predicted relative humidity, wind speed and direction at the 850hPa pressure surface.

700hPa Relative Humidity/Wind

These charts represent the predicted relative humidity, wind speed and direction at the 700hPa pressure surface.

500hPa Temperature/Wind/Height

These charts display the predicted temperature, wind speed and direction at, and height of the 500hPa pressure surface.

500hPa Vorticity/Height

These charts show the predicted height of and vorticity at the 500hPa pressure surface.

Total Totals Index/300hPa Wind

These charts depict the Total Totals Index (TTI), wind direction and speed at the 300hPa pressure surface. The 300hPa wind speed gives an indication of the location and strength of the jetstream.

The TTI is calculated by the addition of the temperature and dew point at the 850hPa pressure surface. The value two times the temperature at the 500hPa pressure surface is then subtracted from the original calculation to result in the TTI. A TTI greater than 60 indicates the likelihood of thunderstorms occurring in that region with the possibility of some storms becoming severe.

Haines Index

These charts represent the predicted Haines Index at a given time. This index (ranging from 2 to 6) reflects the temperature difference between the 850 and 700hPa pressure surfaces, and also the dew point depression at the 850hPa pressure surface. Each of these calculations results in a score between 1 and 3. The Haines Index is the addition of these two numbers. This index is useful for fire-fighting purposes. An Index of 6 reflects a high potential for the explosive growth of a bushfire. An Index of 2 or 3 indicates a low potential.

Precipitable Water/700hPa Vertical Velocity (GFS only)

These charts display the predicted precipitable water values and vertical velocity values at the 700hPa pressure surface.

Lifted Index (GFS only)

These charts reflect the predicted Lifted Index (LI) at a given time. A positive LI value reflects a relatively stable atmosphere, unconducive to thunderstorm development. An LI value between -4 and -6 indicates a very unstable atmosphere.

CAPE (GFS only)

These charts show the predicted Convective Available Potential Energy (CAPE) at a given time. CAPE represents the amount of buoyant energy available to lift a parcel of air through the atmosphere, increasing its potential for thunderstorm development. A CAPE value of less than 1000 reflects a marginally unstable atmosphere.

Conversely, a CAPE value greater than 2500 indicates a very unstable atmosphere.

Snow Forecast

The Snow Forecast charts show the cumulative amount of precipitation expected in 24 hour blocks from analysis, plus the expected snow level. The cumulative precipitation amounts appear in a shaded grey scale for rainfall and colours for snowfall, as shown in the legends. The red contours depict the expected snow level ? any land above this point can expect any precipitation that does occur to fall as snow.

• 14:32 AEST Satellites capture huge dust storm crossing Mediterranean Sea
• 08:00 AEST A digger's letter from snowbound Gallipoli
• 15:39 AEST Summery Sydney, wintry Melbourne
• 13:00 AEST Rainfall to soak some parched areas of WA