Page History

...

• The new product is a post-processed product, based on calibrating ENS fields, including the Control run
• It delivers probabilistic forecasts of rainfall totals for points - i.e. that would be measured by a raingauge randomly located within a model gridbox (hence the word 'point')
  
• By way of comparison the raw ENS delivers probabilities for gridbox-average rainfall (in the current ENS that means ~18x18km ~9km x 9km boxes, up to day 15)
• The term rainfall here means all precipitation types: rain, rain plus snow, snow etc., always converted into mm of rain equivalent.

...

Fig8.1.7-3: Colour fill options for a user-defined percentile (first plot, amounts in mm), and a user defined threshold (second plot, probability in %)

Fig 8.1.7-4 and Fig8.1.7-5 below show some ecCharts examples of new products, comparing with raw ENS, for lead time T+78-T+90. Because of the sophisticated post-processing undertaken, the relationship between point rainfall and raw ENS products can vary a lot, according to the amount and range of forecast rainfall totals, and the range of forecast gridbox-weather-types (which all depend also on lead time). The user-selected threshold is also of fundamental importance. However the following generalisations usually hold for map-based products, and may help forecasters to interpret the output (examples of some of these can be found on the plots below):

...