Discussed in the following Daily reports:
Material from: Linus, Mohamed, Ivan
Discussed in the following Daily reports: |
On 16 April Storm Hans brought extreme precipitation to the southern Alps, locally more than 400 mm/24h in a few locations according to high-density observations. In high altitude it fell as snow. The cyclonic system was named Hans. Connected to the same system, an IF1 tornado was registered near Verona in northern Italy on 17 April.
The evaluation of the precipitation will focus on 24-hour rainfall on 16 April 06UTC - 17 April 06UTC for a 0.5 degree box centred on the Simplon Pass (46.2N, 8.1E) between Switzerland and Italy (see maps below for outline).
The plots below show analyses of MSLP and 6 hour rainfall from 14 April 00UTC to 17 April 00UTC, every 12th hour.
The plots below show analyses of z500 and T850 from13 April 00UTC to 17 April 00UTC, every 24th hour.
Observations (left) and analysis (right) for the event
Control forecast (IFS 9-km resolution)
DestinE (IFS 4.4km resolution)
AIFS deterministic (AIFSv1.0 ~0.25 resolution)
AIFS ensemble perturbed member 1 (AIFS-CRPS ensemble ~0.25 degree resolution)
EFI (based on IFS 9-km ensemble)
24-hour precipitation valid 16 April (00-00UTC). Already the forecast from 10 April had a signal in EFI for the event.
Forecast Evolution plot
Almost from 15 days before the event the ensemble means in the IFS ensemble were above the m-climate mean. From 6 April (10 days before the event) the signal started to gradual increase in the ensemble. On 10 April the ensemble mean crossed the 99th percentile of the model climate and around 3 days before the event the ensemble mean crossed the model climate maximum.
Legend:
Observation - green hourglass
Analysis - green dot
ENS CF - red dot
DestinE - dark-green dot
AIFS-single - cyan dot
ENS distribution - blue
AIFS-ENS-CRPS distribution - pink
ENS m-climate - cyan
ENS m-climate maximum - black triangle
The plots below show hit (green), misses (purple) and false alarms (cyan) of predicting precipitation above the 99th percentile of model climate, based on the ensemble mean.
Forecasts for the z500-predictor for extreme precipitation over the Central Alpine region (see Dorrington et al. fore details: https://doi.org/10.1002/qj.4622). The forecast is based on the 100-member sub-seasonal ensemble. Thanks to Josh Dorrington (Uni. Bergen) for the figures.
Same as above but for the Integrated Water Vapour flux predictor.
From around 5 April, both predictors showed anomalous high values, giving an early indication for conditions favourable for extreme precipitation around 14-17 April.
The plots below show forecasts of weekly precipitation anomalies for 9-15 September.
The plots below show forecasts of weekly z500 anomalies for 9-15 September.
