Scores on ALADIN-FRANCE during the second quarter of 1999 : Comments on cloud cover and precipitations forecasts scores

(more details jean-marc.moisselin++at++meteo.fr )

Next figures show the contour plot of Heidke Skill Score (HSS) against hazardous forecast for both precipitations and cloud cover parameters from september 1997 to june 1999.

The classes used to calculate HSS are well known EWGLAM classes. Scores have been calculated over FRANCE with 00H as base. Highest values (HSS greater or equal than 35/100) are plotted in blue and smallest one in red (HSS lower or equal than 20/100).


Contour plot of HSS*100 for 6 hours cumulated precipitations ("6H fc range" means precipitations between 00h00 and 06h00). X-axis=month, Y-axis=forecast range


Contour plot of HSS for cloud cover. X-axis=month, Y-axis=forecast range


There are about 135 synoptic stations used for ALADIN precipitations verification.

The average value of HSS is 0.33 which is correct with this severe criteria.

The vertical aspect of the contour is reliable to a seasonal dependency of HSS. Values are higher in winter (sometimes more than 0.40) than in summer (sometimes lower than 0.25). It is difficult to extract forecast range dependency but we can note :

* In spring and summer a 12h cycle (HSS minimum for 6, 18 and 30H forecast ranges)

* In winter better results until the 24H forecast range

The number of synoptic stations used for ALADIN cloud cover verification varies from 40 (24H validity hour) to 130 (6H validity hour). Thus it is difficult to analyse forecast range variations.

The average value of HSS is 0.24 wich is medium.

The aspect of contours is vertical. Values are higher in winter than in summer. The decrease with forecast range (for a same validity hour) is not very high : about 0.05 in 24 hours.



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