Case studies
Storm Xaver
On the 5 December 2013 a large and violent cyclonic storm hit the North Sea region and several adjacent countries. Problems were caused both by the high wind speeds and the related storm surge. The surge reached 6 metres in Hamburg for example and was the highest along the England east-coast for 60 years. In the aftermaths of the cyclone a blizzard hit Sweden. The storm system was named Xaver by Berlin's Free University; other names assigned elsewhere include Bodil, Sven and St. Nicholas (Hewson et al., 2014). T he cyclone developed around 00 UTC on 4 December northeast of Newfoundland and it was situated between converging northerly and southerly airstreams. Due to the westerly wind jet accelerated by the convergence, the cyclone moved to northeast and east, deepening explosively. It had an intense meso-vortex hanging back to west, which enhanced the strong wind (see Figure 1 ). The cyclone was presented in the operational forecasts 8-9 days before the event and the forecasts indicated the very strong wind gust 3-4 days in advance. (Although some strength overestimation over Germany as well as timing error in surface pressure were concluded.)
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Figure 1: 24-hour maximum wind gust (m/s) on 5 December with mean sea level pressure (white contours; hPa) on 12 UTC on 5 December from the operational forecasts at 00 UTC on 3 (left) and 5 December (middle) and from the observations (right). | ||
Storm Desmond
Storm Desmond caused severe flooding, travel disruption and a power outage across northern England, parts of Scotland and Ireland on 5 December 2015. Cumbria in northwestern part of England is one of the worst affected regions with more than 200 mm of rain in 24 hours recorded in that area. Storm Desmond broke the United Kingdom's 24-hour rainfall record, with 341.4 mm of rain falling in Honister Pass, Cumbria. On Saturday, 5 December, UK Met office issued a red warning of heavy rain for Cumbria. The cyclone also led to flooding in southern Norway.
Orographical enhancement of precipitation played a major role in the event and the operational model of the ECMWF picked well the highest rainfall amounts over the orographical barriers. However, the forecast underestimated the peak values of about 100 mm in 24 hours in Cumbria and overestimated the precipitation amount in lee of the hills ( Figure 2 ).
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Figure 2: 24-hour precipitation amount (mm) between 6 UTC on 5 December and 6 UTC on 6 December, based on ECMWF operational IFS forecast at 00 UTC on 5 December (left, with cyan contours for the mean sea level pressure at 12 UTC on 5 December) and observations (right). | |
Model experiments
Several experiments have been conducted with OpenIFS for both cases with the aim to test the effect of starting date and forecast length, initial condition as well as spatial resolution to the forecast quality. The details of experiments are summarized in Table 1 .
Table 1: Settings of the experiments achieved for Storm Xaver and Storm Desmond. | ||||||
| Initial condition | Resolution | Starting date | Time step | Output frequency | ||
|---|---|---|---|---|---|---|
Xaver | 1. | ERA-Interim | T255L91 | 1 Dec 2013 | 2700 s | 3h |
| 2. | ERA_Interim | T639L137 | 900 s | 3h | ||
| 3. | ERA5 | T255L91 | 2700 s | 3h | ||
| 4. | ERA5 | T639L137 | 900 s | 3h | ||
D e s m o n d | 1. | ERA-Interim | T255L91 | 1 Dec 2015; 2 Dec 2015; 3 Dec 2015; | 2700 s | 3h |
| 2. | ERA-Interim | T639L137 | 3 Dec 2015; 4 Dec 2015 | 900 s | 3h | |
| 3. | ERA-Interim | T1279L137 | 3 Dec 2015; 4 Dec 2015 | 600 s | 3h | |
| 4. | ERA5 | T255L91 | 3 Dec 2015; 4 Dec 2015 | 2700 s | 3h | |
| 5. | ERA5 | T639L137 | 3 Dec 2015; 4 Dec 2015 | 900 s | 3h | |
- download from download.ecmwf.int/openifs/evalution
Post-processing step
- how to prepare data for plotting
Metview macros
- where they are, how to set them up .. etc
Catalogue
References
Hewson, T. , Magnusson, L. , Breivik, O. , Prates, F ., Tsonevsky, I. , de Vries, H.J.W. , 2014: Windstorms in northwest Europe in late 2013. ECMWF Newsletter 139, 22–28. [ PDF ]