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The European Center for Medium Range Weather Forecasting Model or ECMWF is a medium range forecast model that is issued twice daily at 00UTC and 12UTC. The ECMWF was developed in 1997 by the European Center for Medium Range Weather Forecasts. The ECMWF is a 168-hour model, and is located on the left side of the main page of the e-Wall as shown below in figure 1.

Figure 1: Location of the ECMWF Model on the left side of the e-Wall.

The ECMWF is located in the “Extras” section of the e-Wall on the left wall of the main page. To view the ECMWF model, click on either the 00UTC or 12UTC run of the model (depending on the time of day). You could click on one of the hours at the top left corner of the page to view the ECMWF for that hour, or you could also use your mouse and scroll over each hour to produce a loop of the images. The model output is displayed in a four-panel map as shown below in figure 2.  Note that the aerial coverage of this map is a little larger than it is for the traditional WRF and GFS models.

Figure 2: A sample 4-panel display of the ECMWF model.

The four panels in figure 1 above are as follows:

            Upper-Left: 500mb Heights and Vorticity

            Lower-Left: 700mb Relative Humidity

            Upper-Right: Surface Pressure and 1000-500mb Thickness

            Lower-Right: 850mb Temperatures and Relative Humidity

What does each panel mean?

500mb Heights and Vorticity Panel

The 500mb Heights and Vorticity Panel can be used to describe the steering flows of the atmosphere. The steering flows of the atmosphere are located about 20,000 feet up (roughly halfway through the atmosphere) and generally direct major weather systems across the country. The black contours are isohypse (lines of constant height), and are contoured every 6 dm (the values on the isohypse are in decameters, i.e. 570 would actually be 5700m). Lower heights are usually found to the north while higher heights are usually found off to the south.

The red and purple shading on the map indicates areas of vorticity in the atmosphere. Vorticity is a measure of rotation throughout the atmosphere. Vorticity can either strengthen or weaken storm systems. Areas of red shading on the panel indicate positive vorticity, while areas of purple shading indicate negative vorticity. The darker the shading is, the stronger the vorticity. Areas of positive vorticity can strengthen areas of low pressure, and are sometimes referred to as “upper-level disturbances” or “upper-level energy”. The numbers on the map near areas of vorticity indicate the magnitude of the vorticity.

700mb Relative Humidity Panel

The 700mb Relative Humidity Panel is an important panel used by meteorologists. The green and brown shading indicates the amount of relative humidity in the atmosphere at 700mb. (NOTE: This is NOT the relative humidity found at the surface).  The green shading represents areas with a 700mb RH greater than 70% as indicated by the legend below the panel. Darker green shaded regions represent areas with 700mb RH greater than 90%. Light brown areas are regions where 700mb RH is less than 30%, with dark brown areas less than 10%. White areas on the map indicate regions where the RH is between 30% and 70%.

Meteorologists use the 700mb RH to predict areas where clouds and precipitation may develop. For more information on how to use the 700mb RH to forecast, please visit the Forecasting Page here.  

Surface Pressure and 1000-500mb Thickness Panel

The Surface Pressure and 1000-500mb Thickness Panel is useful when predicting where storm systems are moving and the type of precipitation that may fall from them. The black contours on this panel are isobars, (lines of constant pressure), and are contoured every four millibars (mb). Some of the isobars are labeled with numbers that usually range from 960mb (a strong low-pressure system), to 1050mb (a strong high pressure system). Low pressure systems are denoted by a red “L” while high pressure systems are denoted by a blue “H”.

The red and green dashed contours on the map are 1000-500mb thickness contours. The 1000-500mb thickness is the average depth of a column of air from 1000mb (surface level) to 500mb. The thickness can also be inferred to be the average temperature of a column of air from 1000mb to 500mb. The red dashed thickness contours are primary thickness contours (contoured every 30dm, the value on the thickness contours is in decameters), while the green dashed contours are secondary thickness contours (contoured every 6dm). The three primary thickness contours on the panel above are 510dm, 540dm, and 570dm. Thickness values lower than 510dm usually represent a dry, arctic air mass found in Canada or along the northern portion of the United States during winter, while thickness values higher than 570dm usually represent a warm and moist tropical air mass from the south. Thickness values can also be very useful in forecasting the different precipitation types associated with storm systems during the winter season. More information on this can be found here.

850mb Temperature, and Relative Humidity

The 850mb Temperature and Relative Humidity panel is used by forecasters to get a general sense of what is going on in the lower-levels of the atmosphere just above ground level. The 850mb level is about 1500m above ground level, and is a valuable level to use when forecasting the different precipitation types associated with major winter storms.

 The 850mb relative humidity (like the 700mb relative humidity), is scaled from 0% to 100%, with low humidity values shaded in a dark brown, and high humidity values shaded in a dark green. The difference between the relative humidity at 700mb and the relative humidity at 850mb is that the 850mb RH samples the lower-levels of the atmosphere and can be used to determine if low clouds such as stratus will form.  It can also be used to give an estimate of the low level moisture in the atmosphere if you know the temperature of the air.

The other contours on the map are isotherms. The black contour on the map labeled with a 0 is the 850mb 0°C isotherm. Intermediate isotherms in intervals of 2°C are shown as well, with the -10°C isotherm shown as a blue dashed line, the -20°C shown as a either a pink dashed line, the 10°C isotherm shown as a solid orange line, and the 20°C isotherm shown as a solid red line. Dashed isotherms indicate regions where the 850mb temperature is below freezing while solid isotherms indicate regions where the 850mb temperature is above freezing.  The 850mb temperatures can also be useful in predicting the different precipitation types associated with storm systems during the winter season. More information on this can be found here.

Model Biases

One of the main model biases with the ECMWF model is that it tends to overdevelop mid-level and upper-level cyclones across the southwestern United States. The reason for this is that the model is not fast enough to move a system out from the desert southwest and actually slows the system down and further develops it in place. The model also seems to have a warm bias when it comes to forecasting mid-level and upper-level tropospheric heights, and the resulting thickness calculations. The model also has a tendency to “bomb-out” extratropical cyclones along the east coast of the United States too prematurely.

On the reverse side, out of all of the medium range forecast models, the ECMWF generally performs the best with driving arctic fronts down the east slopes of the Rocky Mountains.

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This site was last updated 05/07/08