Status:Finalised Material from: Linus

 

Discussed in the following Daily reports:


Picture

1. Impact

On the 14 March strong wind and precipitation hit northern Scandinavia together wind precipitation. The station Stora Sjofallet in Sweden measured 36 m/s in mean wind and 47 m/s in the gusts (purple and black in the plots). After the storm, a ski resort in the area had a major avalanche, probably an effect of the snowfall and wind.


2. Description of the event


The figures above show the 24-hour maximum wind speed (left) and wind gusts (right) for the 14 February. Along the Norwegian coast several stations had gusts more than 35 m/s. The Stora Sjofallet station is the purple and black dots respectively in the figures. The station is on the eastern end of a lake. On the western side the station Ritsem is located, with much lower wind speeds.

3. Predictability

  

3.1 Data assimilation

 

3.2 HRES

HRES 24-hour wind gusts and MSLP
13 Mar 00UTC
14 Mar 00UTC
12 Mar 00UTC

The figures above show example of wind gusts forecast for 1, 2 and 3 days before the event. Also the three day forecast was good for the event.

10-meter wind speed and wind gusts for Stora Sjofallet (67.5N, 18.2E) for forecasts (red) and observations (red). Forecast initialised is14 March. For the Friday (14 March) the forecast had wind speeds around 5 m/s but the observed was 36 m/s. However, the wind gusts were in the better forecast with a peak on 38 m/s but missed the observed maximum. Except the maximum, the wind gusts forecast were very good.

The figure above show the forecast from 14 March 00UTC (same as above) but for Ritsem (57.7N, 17.5E). Here the maximum wind speed on the Friday was 10 m/s.The mean wind was therefore ok while the wind gusts here were clearly overestimated.

Ritsem is located along the same long-narrow lake as Stora Sjofallet. However, the gap between the mountain ridges is very narrow at the site of Stora Sjofallet, and the station is well-known for the channelling effect of the wind.

The figures above show the orography from T1279 (HRES, left) and T3999 (right). In the left plot the observation stations are plotted where Ritsem is in the western end and Stora Sjofallet on the eastern end of the narrow lake (although I think Stora Sjofallet should be somewhat more left than plotted). Here we see that the lake is not properly resolved in the orography for T1279, while it looks better in T3999. My experience is that 5 km is not enough resolution for this gap, one rather need 1 km or 500m.

3.3 ENS


The CDF is for wind speed (left) and wind gusts (right) for Stora Sjofallet, valid on the 14 March. Here we see that the wind was extreme for the area.

3.4 Monthly forecasts

3.5 Comparison with other centres


4. Experience from general performance/other cases

 

5. Good and bad aspects of the forecasts for the event

  • The synoptic forcing of the event was well forecast 2-3 days before the event.
  • For Stora Sjofallet, the mean wind was far too low but the wind gusts were ok
  • For Ritsem, the mean wind was not very strong, as in the forecast, but the wind gusts were too high.
  • Is this an effect of sub-grid variability or a more general mountain problem?
  • Is the gust/mean wind ratio realistic for this case?


6. Additional material