Status:Ongoing analysis Material from: Linus, Esti, Tim
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Discussed in the following Daily reports:
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The two animations below compare forecasts from the raw ECMWF Ensemble with forecasts from the ecPoint post-processed version of that, for thresholds, respectively, of 150 and 300mm/12h. Probability of exceedance in percent is shown. Turis, where 666mm were provisionally recorded during this period, lies 10km south of the middle of three black markers (which is itself at the site of Chiva where very high totals were also registered).
The raw ENS forecasts provided good guidance here from 4 days in advance, albeit with a large underestimation versus the point values. That said there is some jumpiness in the locations forecast to be at greatest risk. And also in the time sequence of probabilities, with for example a big jump to lower probabilities apparent between the last two forecasts issued.
In relative terms the ecPoint forecasts are spatially and temporally more consistent, with the area south of the middle black dot shown to be at highest risk throughout. Plus this is for a higher threshold rather closer to what was observed.
The third (static) graph plot shows a time sequence of the maximum 99th percentile ecPoint value seen over the broader Spain area, in the 5 days leading up to the event. The peaks were all in the general vicinity of Turis. Here we again see consistency in ecPoint forecasts, and a signal that grows in magnitude with shorter lead times, which is what one would expect as confidence grew and the spread of the driving raw ensemble reduced somewhat. In the last two forecasts values are very close to the Turis observation, albeit that this still represents a low probability within the gridbox. Against that we have selected the wettest known place to verify against, and note also that, not far away, in Valencia itself, less than 10mm rainfall was recorded in this period, so huge local variability.
The adjacent map plot shows an estimate from the ERA5-ecPoint product, of the 200-year return period of 24h rainfall (this comes from the ecPoint probabilities, and as such is a non-parametric estimate, so no "tail fitting" is involved). The Turis area value is shown with a black line on the graph - evidently all the 99th percentile ecPoint forecasts in the lead up showed well above this value.
Raw ENS probabilities of >150mm/12h (valid time 06-18UTC 29th October 2024), from successive forecasts, at 12h intervals, from 25 Oct 00UTC to 29 Oct 00UTC (see titles)
Same as Raw ENS animation above, but output is from ecPoint, for a higher threshold: >300mm/12h.
Graph shows the maximum of the 99th percentile ecPoint field in forecasts leading up to the event (over Spain, but always, in practice, close to Turis). The map shows a 200-year return period estimate for 24h gauge-based rainfall totals from ERA5-ecPoint (data from 2000-2019).
3.4 Monthly forecasts
The plots below show forecasts of weekly precipitation anomalies for 28 October - 3 November.
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