Status:Ongoing analysis Material from: Linus
1. Impact
Around 22 April was unusually cold in large parts of central and Western Europe, resulting in a late frost during the bloom of fruit trees and vine. This might have became worse due to the warm spring before this event.
2. Description of the event
The evaluation of the cold temperatures will focus on 3-day minimum temperature 22-24 April in a 0.25x0.25 box around Troyes, France (centre point 48.3N, 4E). The point was chosen because of the nearby wine districts.
The plots below show analyses of T850 and z500 from 19 April to 25 April.
The plot below shows the 2-metre temperature anomaly from ERA5 for 22 to 24 April.
The plot below show daily mean (based on 00 and 12UTC) temperature over western France (land points inside 50-55N, 2-7E) based on ERA5. Daily values (thin), 7-day running mean (thick) and daily climatology (dashed). The time series starts 1 August 2023 and ends 5 May 2024.
3. Predictability
3.1 Data assimilation
3.2 HRES
3.3 ENS
The plots below show evolution for 2-metre temperature for Troyes, France in observations (black), ENS control (purple) and ENS members (cyan). The cooling rate in the forecast seems to be somewhat slow compared to the observations.
The plots below show EFI for 3-day temperature 22-24 April. All forecast visualised here (earliest from 16 April) captured the general structure of the cold event.
The plot below shows the forecast evolution for the 3-day (22-24 April) minimum 2-metre temperature in the 0.25x0.25 box around Troyes, France, going back 30 days before the event. The evolution plot includes:
Analysis - green dot
Mean of observations - green hourglass
Extended-range ensemble purple box-and-whisker
Model climate based on extended-range (pink) based reforecasts with 200 fields. Climate maximum as triangle.
Model climate based on medium-range (cyan) based reforecasts with 200 fields. Climate maximum as triangle.
3.4 Monthly forecasts
The plots below show forecasts of weekly temperature anomalies for 22-28 April.
The plots below show forecasts of weekly z500 anomalies for 22-28 April.
3.5 Comparison with other centres
4. Experience from general performance/other cases
5. Good and bad aspects of the forecasts for the event
- Cold anomaly captured around 1.5 week before the event.
- Week 3 and earlier forecasts were for a warm anomaly.