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The spread in the 00Z Sunday T+36h forecasts, reproduced below as a single frame (left), is especially striking, showing an ordinary but active autumnal frontal wave (green dots = 55-60kts) in a few members, through to a once-in-a-lifetime intense (red = 75-80kts) low in rather more members. Example snapshots from each of these two categories are shown to the right. This is a 'nightmare scenario' for forecasters, but at the same time probably gives a true reflection of uncertainty in what appears to have been a dynamically very sensitive situation. It would seem, perhaps, that uncertainty at other times was under-estimated?? The intensity range (as inferred from colour range) in forecasts from slightly earlier times, on the dalmatian animations above, seems, curiously, to have been less.
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EFI for 10-metre maximum wind gusts can be seen here: from 38r2 (ps) and 40r1 (ps) suites. There is no significant difference between both managing to give a signal of anomalous wind even 7-days in advance but unluckily weakening the storm in Sunday's forecasts. That was the main concern expressed by the local forecasters during the member state visit to the Netherlands later that week. They presented at the meeting the following results from the HRES which show that a forecast from the Sunday 12UTC run just after they had issued a warning suddenly made the storm substantially weaker (right plot).
HRES MSLP, wind and wind gusts forecasts for different lead times started from longer ones (left to right).
Comparing the CDFs from three locations: one in East England, second in the Netherlands and third in Denmark, where hurricane-force wind gusts were observed, show that in the runs where the storm was weaker the 40r1 suite had bigger spread than 38r2.
EAST ENGLAND (OBSERVED WIND GUSTS > 35 M/S):
38R2 40r1
THE NETHERLANDS (OBSERVED WIND GUSTS > 35 M/S):
38R2 40r1
DENMARK (OBSERVED WIND GUSTS > 40M/S):
38R2 40r1
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CDF for wind gusts (left) and maximum mean wind speed (right) for Reading valid on the 28 October. Different colour represents different initial times and the o-suite (38r2, solid) and e-suite (40r1, dotted). Comparing different initial times, the forecast from 26 October (green and black), were the most severe. For the forecasts from the 27 October the wind speed was less. This is partly because the development of the cyclone occurred later and therefore had not reached such a deep stage when it passed over Reading. Comparing e-suite and o-suite, we see that the winds (both mean and gusts) are less in the e-suite and o-suite.
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