201410 - Rainfall - Norway

 Status:Ongoing analysis Material from: Linus

Discussed in the following Daily reports:

http://intra.ecmwf.int/daily/d/dreport/2014/10/28/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/10/29/sc/

Picture

1. Impact

In the end of October 2014 heavy rainfall affected south-western Norway and caused the worst flooding in the area since 1892.The worst affected area was inland Bergen and around Voss.

Photos and a video showing the effects of the flooding can be found on the Norwegian television homepage: http://www.nrk.no/sognogfjordane/forti-husstandar-i-flam-kan-snart-fa-flytte-heim-1.12015077 (you can find the video if you scroll down)

2. Description of the event

 The series of plots below shows short forecasts of MSLP and precipitation starting from 20 October to 29 October. During the whole 9 day period a more or less continuous rainfall affected south-western Norway, caused but a persisting low over Iceland bringing moist air from south-west towards Norway. Scotland was affected by heavy rainfall during the period as well.. The most intense rainfall occured between 26 and 28 October.

The plots below shows observed accumulated precipitation for the stations Takle (61.03N, 5.28E, left) and Modalen (60.86N, 5.97E, right). The accumulation start 1 October. The normal October rainfall for Takle is 407 mm. The station Modalen was established 2008 and therefore are no normal values available (facts from yr.no). For both stations we see a rapid accumulation since the 22 October.

The next plot shows the 3-day accumulated precipitation for the period 26 October 06z to 29 October 06z. Almost all stations north of 60N and west for 8E had more than 100 mm/72h and a few stations measured more than 200 mm.

The plot below shows the red warning for south-western Norway for the 28 October.

3. Predictability

3.1 Data assimilation

3.2 HRES

Results focusing on 27 October 18z to 28 October 18z (24-hour)

The plot below shows the observations from the period:

The plots below are for the 24-hour accumulation from HRES (16 km).

The plots below are for the 24-hour accumulation from ENS control forecast (32 km).

The plots below are for the 24-hour accumulation from NCEP ensemble control forecast (64 km?), retrieved from TIGGE. Interestingly one of the forecasts manged to produce very high precipitation although the low resolution.

NCEP CF (24-hour)
There are no images attached to this page.

The plots below are for the 24-hour accumulation from DMI ensemble control forecast (5.5 km), retrieved from TIGGE-LAM. Here we start to the orographic features in the precipitation.

The plot below shows a forecast run initialised 27 Oct 00z with TC1279 (8km) resolution and cycle 41r1. Compared to HRES orographic features are more apparent and the peak in the precipitation matches the maximum from the observations.

3.3 ENS

The plots below show EFI and SOT for precipitation over the period 26-28 October, from different initial times. Already the forecast from 20 October had increased EFI values for the actual period and the forecast from the 23 October had a very strong signal.

3.4 Monthly forecasts

Coming soon.

3.5 Comparison with other centres

See section 3.2.

3.6 EFAS

The plots below shows hydrographs (in terms of return periods) for the outflow from Vangsvatnet (60.63N, 628E). The red line is for the ECMWF HRES and the blue for COSMO-EU from DWD (8 km resolution). The COSMO-EU had a much stronger signal than both ECMWF HRES and ENS for this river.

4. Experience from general performance/other cases

• Central European flooding in 2013 (ECMWF Technical Memo 723)
• Balkan flooding in 2014 201405 - Rainfall + flood - South-eastern Europe

5. Good and bad aspects of the forecasts for the event

• Early warning from EFI

6. Additional material