Status:Ongoing analysis Material from: Linus
1. Impact
In the end of November and beginning of December north-western Europe was it by a cold spell. During the period e.g Munich was hit by severe snowfall causing travel disruptions, and also in the Lake District in UK snow caused problems. In Sweden Visby on the island Gotland set a new cold temperature record for November with -15.1C (station since 1859), and Uppsala measured the deepest snow in November with 33 cm (observation record of snow since 1904) (summary on https://www.smhi.se/bloggar/vaderleken-2-3336/rekordstort-novembersnodjup-i-uppsala-och-koldrekord-i-visby-1.202456 , in Swedish).
2. Description of the event
The plots below show analyses of T850 and z500 from 25 November to 1 December.
The plot below shows the 2-metre temperature anomaly from ERA5 for the week 27 November to 3 December.
The plot below show daily mean (based on 00 and 12UTC) temperature in Hamburg based on ERA5. Daily values (thin), 7-day running mean (thick) and daily climatology (dashed).
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show analysis of 3-day temperature 28-30 November forecasts from 25 November from IFS (ENS control), AIFS, PanguWeather and Graphcast.
3.3 ENS
The plots below show EFI for 3-day temperature 28-30 November. For north-western Europe the signal appeared between 22 and 23 November.
The plot below shows the forecast evolution for the 3-day (28-30 November) 2-metre temperature in the box around Hamburg in the map below, showing the analysis for the same period. The evolution plot includes medium-range ensemble (blue), daily extended-range forecasts (purple) and model climate based on medium-range (cyan) and extended range (pink) reforecasts with 1800 fields. The analysis in included in green dot and observation in green hourglass.
The plot below show CRPS (shade) for z500 over Europe. The x-axis shows the valid dates and the y-axis the forecast lead time. The dashed diagnostics represent individual initial dates.
3.4 Monthly forecasts
The plots below show forecasts of weekly temperature anomalies for 27 November to 3 December.
The plots below show the same as above but for z500.
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 signal of the cold was captured from around 22 November for north-western Europe. The forecast before had large errors in z500 as well.