Page History
| Table of Contents |
|---|
EFI Charts
The Extreme Forecast Index and Shift of Tails are presented in chart form, either for each parameter separately, or on a composite chart that caters for temperature, precipitation and maximum gusts.
EFI Web open access charts
Fig8.1.4.7.1: To view Medium Range CDFs:
...
Colours indicate the quintile90 temperature ranges of the M-climate where only one in 10 occasions have reached greater values than shown (i.e. on only 1 in 10 occasions during the construction of M-climate for each location and on this date have the temperatures indicated by the colours been exceeded). The chart shows on only 1 in 10 occasions are mean temperatures likely to be above 15°C-20°C in parts of southern Italy and Sicily. The high EFI and locally positive SOT in these areas suggests unusually high mean temperatures may be expected. Selection of quintile10 would allow a similar assessment of how unusually cold the mean temperature in Portugal is likely to be.
Composite Multi-parameter Interactive (clickable) EFI charts
Multi-parameter interactive charts are available showing the geographical distribution of the EFI of the principal weather parameters: maximum 10m wind gust, 24hr precipitation and 2m temperature, overlaid with the ensemble mean of the MSLP field. This chart highlights areas where there is a significant difference between the ensemble forecast (ensemble) distribution and the model climate (M-climate) distribution.
...
ecCharts and Dashboard Widgets
For a location chosen by the probe tool on ecCharts or by selection of a widget on the dashboard:
...
Fig8.1.4.7.5: Examples of EFIs and CDFs from a series of ensemble runs for Valetta VT 30 Mar 2018. The location can be chosen by the user by the probe tool on ecCharts or by use of widgets on the dashboard.
Cumulative Distribution Function Diagrams
Attached to each grid point of the global EFI charts there is a CDF diagram for each of the EFI parameters, with information on M-climate at the grid point (always shown for the lead time 24-48h) and the available forecast distributions (all valid for the given day, but coming from different, consecutive ensemble runs, so the lead times vary). On the right are shown the corresponding EFI values. These diagrams can be displayed interactively by clicking on the desired location on the EFI web charts, use of the probe tool on ecCharts, or selection of the widgets on the dashboard.
...
Fig8.1.4.7.6D:CDF and associated EFI for NE Poland area. There is a strong and consistent negative EFI for temperature. The CDF traces are steep and very similar over last four forecast runs and imply high confidence in out of the ordinary cold mean temperatures about 8°C below normal.
Extreme Forecast Index (EFI) and Shift of Tails (SOT) versus Lead Time
The development and evolution of EFI and SOT over a sequence of charts can give an early insight into the likelihood of occurrence of out-of-the-ordinary weather and the confidence that may be assigned to developments. EFI values roughly indicate the extent to which ensemble members forecast values exceed the corresponding M-climate. At longer lead-times the number of such members may be quite low. However areas of SOT >1 on longer lead charts give an indication that at least some ensemble members are showing extreme values. This shows there is a risk, albeit small, of out-of-the-ordinary weather within the marked area. As the forecast lead time shortens, EFI values will indicate any increase or decrease in the number of members exceeding the corresponding M-climate value. At the same time the isopleths of SOT will show the variation in the potential for extreme values and give an increasing definition of the risk area (if there is one!).
...
Fig8.1.4.7.8: Observed rainfall totals include some above 50mm/24hr and one above 100mm/24hr over eastern Canada during the period 05/12UTC to 06/12UTC September 2018.
Very high uncertainty illustrated by EFI and SOT
The ensemble is designed to give an assessment of uncertainty. However, occasionally the uncertainty becomes very large, with additionally a potential for very high or low forecast values to occur. An example is shown in Fig8.1.4.7.9 where ensemble members showed widely differing yet potentially extreme hot or cold temperatures. These cases are relatively rare, usually associated with a sharp upper trough and associated front separating widely dissimilar airmasses. Users should accept the uncertainty and tailor their forecasts to reflect the impact on users. Certainly they should not take middle course. Some customers may require an indication of very high or very low temperatures, even if at a low probability.
...
Fig8.1.4.7.9: EFI and SOT chart VT 22-23 July 2012 (T+156-180) from ensemble DT 00UTC 15 July 2012, with associated Cumulative Distribution Function (CDF) and meteogram with M-climate for the marked position. The uncertainty is clear on the meteograms. The CDF shows some ensemble members indicating temperature values above M-climate maximum and some below M-climate minimum and thus the SOT will show values for both the warm and cold tails. This is shown on the chart where the SOT lines (black) overlap. The airmasses are clearly very different as there is a large positive EFI indicative of high temperatures over eastern Europe and a large negative EFI indicative of low temperatures over western Europe.
Additional Sources of Information
(Note: In older material there may be references to issues that have subsequently been addressed)
...
Overview
Community Forums
Content Tools