Introduction

A forecast 'bust' is typically associated with a sudden and pronounced drop in forecast performance. The standard way of assessing the performance of a single forecast is to calculate how well the height of the 500-hPa pressure field (Z500) agrees with the observed outcome. The agreement is typically quantified by calculating the area-averaged root-mean-square error (RMSE) or the spatial anomaly correlation coefficient (ACC).

This case study looks at an example of a 'forecast bust' from April 2011 over Europe. The reference for this case study is:

Rodwell, M.J. and Coauthors, (2013). Characteristics of occasional poor medium-range weather forecasts for europe. Bull. Am. Meteorol. Soc., 94(9) 1393–1405. DOI: http://dx.doi.org/10.1175/BAMS-D-12-00099.1

Rodwell, M. J., and Coauthors, 2012a: Characteristics of occasional poor medium-range forecasts for Europe. ECMWF Newsletter, No. 131, ECMWF, Reading, United Kingdom, 11–15.
Rodwell, M. J., and Coauthors, 2012b: A case study of occasional poor medium-range forecasts for Europe. ECMWF Newsletter, No. 131, ECMWF, Reading, United Kingdom, 16–24.

Case study aims

Possible approaches to studying this case are:

  • Characteristics of forecast bust compared to analyses.
  • Role of organised convection over the USA.
  • Understanding Rossy wave development associated with the forecast bust.
  • Use of ensembles.
  • Sensitivity to parametrized physics processes, particularly vertical mixing.

Initial conditions

Case study initial conditions are provided on the OpenIFS ftp site. The ftp site is password protected, only licensed institutes may be provided with the ftp password. Please contact openifs-support@ecmwf.int.

The initial conditions are available for different resolutions and start dates. The experiment ids listed below are created at ECMWF and used for identifying the model forecasts on the ECMWF archive system (for those with access).

Note that ERA-Interim has a horizontal resolution of T255.

 As OpenIFS is a spectral model, the 'T' number refers to the triangular truncation in spectral space. Equivalent grid resolutions are:
T159 ~ 125km resolution, T255 ~ 80km, T511 ~ 40km, T799 ~ 25km, T1279 ~ 16km.

The number of vertical levels is given after the letter 'L' e.g. L62 means 62 vertical levels.

Please note that higher resolutions progressively require more processors and computer memory to run.

 ResolutionExp idStart datesAnalysisFilenameFile size
T255L91gj3e2011/04, 8th, 10th, 12th, 00ZOperationalT255_gj3e_2011040800.tgz
T255_gj3e_2011041000.tgz
T255_gj3e_2011041200.tgz		78Mb
(each)
T511L91gj3g2011/04, 8th, 10th, 12th, 00ZOperationalT511_gj3g_2011040800.tgz
T511_gj3g_2011041000.tgz
T511_gj3g_2011041200.tgz		290Mb
(each)
T1279L91gj3h2011/04, 8th, 10th, 12th, 00ZOperationalT1279_gj3h_2011040800.tgz
T1279_gj3h_2011041000.tgz
T1279_gj3h_2011041200.tgz		1.7Gb
(each)

All initial data supports 10 day forecasts. Additional days are available (not all are provided due to space constraints), please contact openifs-support@ecmwf.int.

To uncompress and unpack using the tar command:  tar xzvf T255_gj3e_2011040800.tgz

Acknowledgements

The figures on this page are taken from a project on this case study by Lauri Tuppi, University of Helsinki. We are grateful for permission to reproduce them here.

 

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Figure shows ACC (%) of a 6 day forecast initialized on dates shown over Europe. (courtesy Lauri Tuppi, University of Helsinki).

 

 

 

Figure shows 500hPa geopotential height at 16th April 2011 00UTC. Top figure shows the OpenIFS forecast, T255L91, the lower panel is from ERA-Interim. Although the forecast predicted a blocking situation over Europe, this did not occur. (courtesy of Lauri Tuppi, University of Helsinki).

 

 

 

Figure shows the forecast of CAPE and significant error in position and magnitude of CAPE over USA, 6 hrs into forecast, initialized from 10/4/2011 00Z. (courtesy Lauri Tuppi, University of Helsinki)