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Example Charts

The extratropical cyclone diagrams provide a comprehensive display of the variation between the forecasts of each member of the ensemble regarding positions of fronts, depth of depressions, and strength of winds at 1km altitude. In the examples the features near Brittany relate to an extreme windstorm which in terms of European losses was the major windstorm of thr 2016of the 2016-17 winter.  For interpretation of the charts see a guide to using cyclone database products.

Fig8.1.15-3: An example of a chart showing positions of fronts diagnosed from ensemble members (see legend below chart for details) illustrating the variation in positions.  DT 00UTC 03 March 2017, T+84 VT 12UTC 06 March 2017.

Fig8.1.15-4: An example of a "Dalmatian Plot" showing the centres of cyclonic features coloured to show an analysis of the cyclone class as derived from ensemble members (see legend below chart for details) showing the variation in forecast positions.  DT 00UTC 03 March 2017, T+84 VT 12UTC 06 March 2017.  Note that not all the spots denote genuine low pressure centres; it is only the barotropic lows (black spots) that are guaranteed to be.

Fig8.1.15-5: An example of a "Dalmation Plot" showing the centres of cyclonic features, coloured to show an analysis of the forecast maximum wind strength, at 1km altitude, within 300km of each centre derived from ensemble members (see legend below chart for details).  Chart highlights show the variation in positions and intensity.  DT 00UTC 03 March 2017, T+84 VT 12UTC 06 March 2017.  Note several members suggest a maximum wind of 65-85kn in the vicinity of northwest France.

Fig8.1.15-6: An example of a chart showing the percentage of ensemble members predicting a cyclonic feature point will track within 300km in a 24-hour period T+72 to T+96 (i.e. 00UTC 06 March to 00UTC 07 March 2017).  DT 00UTC 03 March 2017, T+84 VT 12UTC 06 March 2017.  Only cyclonic features with a maximum wind speed exceeding 60kn at 1km altitude within 300km of the centre at some point in the 24h period are included.  A probability greater than 60% (darker orange) is shown over the western English Channel and NW France.  For a cyclonic feature moving west-to-east in this part of the world the strongest winds will ordinarily be found to the south of the low track.  This needs to be taken into account - indeed it is important for the user to not misinterpret the shading on these strike probability charts as being like a simple wind gust probability chart.