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titleSt Jude wind-storm key highlights

The case study will look at one of several severe wind-storms that hit Europe in late 2013 (see handout of ECMWF article by Hewson et al, ECMWF Newsletter 139).

  • On the 28th October 2013 a small, severe wind-storm named St Jude in the UK, hit the UK & north-western Europe.
  • A total of 19 people were killed across Europe, 5 in the UK.
  • The return period of the event based on wind-gust observations show the 10yr return period was exceeded along the North Sea coast.

  • From the 23rd October, the ECMWF forecast predicted a greater than 70% probability of a severe wind event (greater than 60kt, 31m/s, at 1km) over southern England. A signal for the storm was evident from the 21st October.
  • On the 24th October, the UK MetOffice issued an amber alert for wind-speed across southern England placing the potential impact in the highest category.

  • The cyclone first appeared as a cold front wave, south of Nova Scotia over the Atlantic, late on 25th October.
  • It deepened and moved rapidly east then northeast, with the storm centre reaching southern Sweden late afternoon on the 28th.
  • The most rapid deepening occurred between 06-12UTC on the 28th between eastern England and the North Sea where when the strongest wind gusts were observed.

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  • HRES : T1279 (16km grid) highest resolution 10 day forecast
  • ENS : Ensemble (50 members), T639 (34km grid) for days 1-10, T319 (70km) days 11-15.

 

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titleTeams

 We suggest these exercises are best done by small groups working in teams.

Suggestions are made in the exercises for how each team can work on different data.

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titleTeam : Getting started
  1. Start with an_1x1.mv with mapType=1 to see the large scale.
    Everyone should plot the mean-sea-level-pressure (mslp) and 10m wind-gust, over each 3hr period, (wgust10) plots. Remember you can overlay two or more variables as shown above and use animation.
  2. Each team member can then choose their own parameters; look at the fields on different pressure levels; use the smaller geographical area (mapType=0) to compare with the observations.
  3. Discuss the storm characteristics and development.

If you prefer to see multiple plots per page rather than overlay them, please use the an_2x2.mv macro.

 

Task 2: Visualise operational

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HRES forecast

 

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titleThe HIRES forecast

The ECMWF operational forecast is called HIRESHRES. The model runs at a spectral resolution of T1279, equivalent to 16km grid spacing.

Only a single forecast is run at this resolution as the computational resources required are demanding. The ensemble forecasts are run at a lower resolution.

Before looking at the ensemble forecasts, first understand the performance of the HIRES HRES forecast.

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titleAvailable forecast dates

Data is provided for multiple forecasts starting from different dates, known as different lead times.

Available lead times for October 2013 are: 24th, 25th, 26th and 27th.

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titlePlot HIRES HRES forecast

 For this task, use the metview icons in the row labelled 'Oper forecast'

oper_2x2.mv              works in a similar way to the an_2x2.mv icon used in the previous task where parameters from a single lead time can be plotted.

oper_to_an_runs.mv   plots the same parameter from the different forecasts for the same verifying time. Use this to understand how the forecasts differed, particularly for the later forecasts closer to the event.

oper_to_an_diff.mv     plots a single parameter as a difference between the operational HIRES forecast and the ECMWF analysis. Use this to understand the forecast errors from the different lead times.

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