Status:Ongoing analysis Material from: Linus
1. Impact
During 19-22 November the east coast of Sweden was hit by strong snowfall. For example Stockholm was affected and got 30-40 cm.
2. Description of the event
The plots below show the snow depth over Sweden from 19 to 22 November (all 06UTC).
The plot below shows example of radar image from 21 November.
The plots below show the z500 and T850 evolution in analyses from 17-22 November. Before the start of the event a cut-off low propagated from the east.
The plots below show the analyses of MSLP and 6-hour precipitation from 19 Nov 00UTC to 22 Nov 00UTC, every 12th hour. The short forecast developed the precipitation bands of the Baltic.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show concatenated 6-hour forecasts (first plot) an HRES forecasts with different initial times, all for 72-hour precipitation valid 19 Nov 00UTC to 22 Nov 00UTC. Between forecasts from 16 and 15 Nov (two last plots) there is a large change in the precipitation over the Baltic.
The plots below show z500 and T850 valid 19 November 00UTC from HRES forecasts with different initial times. Between the forecasts from 16 Nov and 15 Nov (step 72h vs step 96h) we see a shift in the position of the cut-off low.
3.3 ENS
The plots below show EFI and SOT for 3-day snowfall for the period 19-22 November.
The plot below shows the forecast evolution plot for 72-hour precipitation valid 19 November 00UTC - 22 November 00UTC for the box over southern Stockholm. Mean of observations - green hourglass, concatenated 6-hour forecasts - green dot, HRES –red, ENS blue box-and-whisker, Model climate – red box-and-whisker. Triangle marks the maximum in the model climate based on 1200 forecasts. Also here the jump between 15 and 16 November is clear.
The plot below shows the forecast evolution plot for T850 for 19 November 00UTC for a point in southern Sweden. Mean of observations - green hourglass, concatenated 6-hour forecasts - green dot, HRES –red, ENS blue box-and-whisker, Model climate – red box-and-whisker. Triangle marks the maximum in the model climate based on 1200 forecasts. The cold spell was captured from 13 November and onwards, while longer forecasts favoured a warm anomaly.
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
- Captured the cold spell around 6 days ahead
- Captured the cut-off low over the Baltic 4 days ahead that led to the precipitation
- Snow accumulations needs to be investigated