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Through a new, feature-based approach to
post-processing ECMWF is developing a suite of products that
provide synoptic insights into ensemble handling. These web page
products aim to represent, objectively and in a variety of ways,
the location and behaviour of near-surface, synoptic-scale
features, such as fronts, frontal waves, cyclonic features and
cyclonic feature tracks, in the ensemble forecasts. The features
represented are those typically associated with adverse weather:
barotropic lows, frontal systems and frontal waves.
Co-location masking, using a feature-type
hierarchy and a minimum separation threshold, helps to keep all
cyclonic features 300 km or more apart. Mean sea level pressure, as
estimated from 1000 hPa geopotential height and temperature, is
also shown as a reference point on many plots. A tracking algorithm
has been used to follow the cyclonic features as they evolve in
each ensemble member. As a severe weather event approaches, the new
products can indicate that there is an increasing risk of a major
storm system in the area of interest, they highlight the track that
the system is likely to take and they also suggest the degree of
confidence that can be placed in that track (see Figure
58).
Figure
58: A still image of EPS
member 15 on 30 January 2011, 12 UTC + 228 hour forecast. Likely
positions of fronts and troughs are indicated by lines and
important synoptic features by filled circles.
The inherent automation should vastly reduce
the amount of time forecasters need to spend analysing the ensemble
and deterministic output. Since synoptic
‘features’ have historically been used, in part, to
highlight the likelihood of severe weather occurring, these
products inherently focus, by proxy, on this potential (see further
Hewson, 2009; Hewson and Titley, 2010).
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