Surge model ensemble forecasting

Surge model ensemble forecasting

Weather systems are inherently chaotic, and even with the best possible data and detailed model, there is some uncertainty about the details of a forecast.

For example a storm might pass across the UK further north or south, which can affect severity and wind direction in different places. To account for this the Met Office runs an ensemble of forecasts with slightly different starting conditions. This ensemble can be used to give more advanced warning of possible risks.

Each of 36 ensemble members of the MOGREPS-UK weather forecast is applied to the ocean surge model, leading to 36 possible predictions of the surge, 6 days ahead of run time. It is often the case that there is a wide spread in this forecast towards the end of the period. The "deterministic" run is the current best estimate of the most likely forecast, predicting 2 days ahead of the run time.

Latest ensemble forecast

This is the latest ensemble surge forecast.

There are 36 lines for each site, offset 1 metre between each site. The variable shown here is surge residual, so for total water levels it must be added to the tide predictions. Also marked on the plot are the times of high water at each site as pink or green triangles. Phases of the moon are provided, and the pink-yellow bar indicates the approximate spring-neap tidal cycle. Spring tides (yellow), which follow full and new moon, are in general larger than neap tides (pink) which following the waxing or waning half-moon. Hence a large surge residual combined with a spring tide would be a cause for particular concern.