Status: Finalised Material from: Linus, Fernando
1. Impact
The floods in the Midlands and North England last week have been in the news after 8 October. The worst affected area was around Sheffield and Doncaster. We learnt from the News that in some places the daily totals exceeded the monthly mean amounts. But this per se do not justify the impact on the ground we watch on the TVs, but was a combination of a wet month and heavy rainfall on the day.
https://www.bbc.co.uk/news/uk-england-50384178
2. Description of the event
Accordingly with the MetOffice, last October the North Ireland and Scotland saw near to drier conditions whiles the rest of the territory was above the average of the month while the Midlands and NE England received significant amounts, specially late in the month.
Focusing on the observation mean inside a 1x1 degree box (4 observations) around Sheffield and Doncaster, the plot below shows the daily accumulation (thin black) and accumulated since 11 September (thick black). The accumulation from the observed climatology is in grey. The wet anomaly started in end of September, and over two month the accumulation is twice the average. The day with the highest accumulation was 7 November (measured 8 October 00UTC).
The panels below show the synoptic evolution on 7 October together with the precipitation accumulation (06UTC-06UTC). The Met Office analysis charts shows a multi centre surface low moving slowly to south-east and and a occluded frontal surface stalled in England causing significant amounts of rainfall. The verification chart of rainfall for the period 07@06 to 08@06 shows few places with amounts exceeding 30 mm in 24 hours and 50mm or more in one location.
The plots below show analyses of MSLP and 6-hour precipitation forecasts every 12h hour between 6 and 8 November.
The plots below show the analyses of z500 (contours) and t850 (shade) from 6 to 8 November.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show observations and forecasts of 24-hour precipitation valid from 7 November 00UTC to 8 November 00UTC. Albeit the synoptic low and frontal system is present in all forecast up to 5 days ahead, the location is only captured from 1 day before.
3.3 ENS
The plots below show EFI and SOT for total precipitation valid 7 November.
The plot below shows the evolution of forecast for 1-day precipitation valid 7 November for the 1x1 degree box outlined in the HRES plots above. The plot includes ensemble (blue box-and-whisker), HRES (red dot) and model climate (red box-and-whisker).
The evolution of forecast shows a shift in the rainfall around 6 November. This shift is supported by the displacement of the barotropic low as we can see from the dalmatian plots below. The forecast started on 05@12 shows a split/shift of the cyclonic feature when we compare with the forecast initiated 24 hours later. As expected the former shows a large spread with the two cyclonic features farther apart.
