Status: Ongoing analysis Material from: Linus
1. Impact
On 26 may the regions around Stockholm, Sweden experienced heavy rainfall, with local flash floods as a result. The region got 45-50 mm and locally up to 60 mm.
2. Description of the event
The plot below shows observations of 24-hour precipitation in SYNOP observations (from www.ogimet.com)
The plot below shows the interpolated daily precipitation on 26 May from SMHI.
The plot below shows the radar image from 26 May 12UTC from SMHI.
The plots below show analyses of MSLP and short forecasts of precipitation from 25 May 00UTC to 27 May 00UTC. The heavy rainfall on 26 May as associated with a frontal system approaching from south, with a secondary cyclone forming over the eastern Sweden.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show 24-hour precipitation for 26 May in HRES forecasts from 26 May 00UTC (first plots) to 22 May 00UTC (last plot), every 24 hours. HRES from 22 May had a stronger cyclonic development over eastern Sweden what pushed the frontal zone to the south on the backside.
3.3 ENS
The plots below show EFI for 24-hour precipitation on 26 May in forecasts from different initial dates.
The plot below show the evolution of forecasts for 24-hour precipitation in a 1x1 degree box around Stockholm (see outline in the plots above) on 26 May. The plot includes HRES (red dot), ENS CF (purple dot) ENS distribution (blue box-and-whisker) and model climatology (red box-and-whisker). The forecast system started to pick up the signal around 22 May, got more intense on 23 May 12UTC and made a final jump on 25 May 12UTC.
The plots below show cyclone feature plots valid 26 May 12UTC, with the colour of the cyclone position dependent on the maximum rainfall associated with the feature.
3.4 Monthly forecasts
The plots below show weekly precipitation anomalies for the week 24-30 May in extended-range forecasts with different initial dates.
