This page gives a short description of the extended forecast graphical products available on the web.

Ensemble mean anomaly

These products are similar to seasonal forecasting graphical products but with weekly means instead of monthly means. Over each point of the map, atmospheric variables such as 2-metre temperature, total precipitation, mean sea-level pressure or surface temperature, have been averaged over a weekly period:

Runs Period
Thursdays
  • day 5 to 11
  • day 12 to 18
  • day 19 to 25
  • day 26 to 32
Mondays:
  • day 1 to 7
  • day 8 to 14
  • day 15 to 21
  • day 22 to 28

The weekly means have been averaged over the 51 members of the real-time forecast and the 660 members of the back statistics (11 members x 20 years x 3 forecast runs). The Weekly anomaly - Extended range forecast charts display the difference between the ensemble mean of the real-time forecast and the ensemble mean of the back-statistics. The graphical products therefore displays the shift of the forecast ensemble mean from the estimated "climatological" mean (created from ensemble runs over the past 20 years).

A Wilcoxon-Mann-Whitney test (WMW-test), see for instance Wonacott and Wonacott 1977), has been applied to estimate whether the ensemble distribution of the real-time forecast is significantly different from the ensemble distribution of the back-statistics.

  • Regions where the WMW-test displays a significance less than 90% are blank.
  • Regions where the WMW-test displays a significance exceeding 99% are delimited by a solid contour (blue or red depending on whether the anomaly is positive or negative respectively).

The blanking of "non-significant" shifts does not mean that there is no signal in the blanked regions, but only that, with the particular sampling we have, we cannot be sure that there is a signal. For this reason, there are likely to be many areas where a signal is real but remains undetected.

This product is currently limited to surface temperature, 2-metre temperature, total precipitation and mean sea level pressure.

See corresponding graphical products: Weekly anomaly - Extended range forecast

Probability

The probability charts (Weekly probability anomaly - Extended range forecast) display the probability that the predicted anomaly is greater than zero. As for the ensemble mean anomaly charts, the anomalies are calculated by subtracting the model climatological mean from the real time ensemble forecast. The maps are also based on weekly means.

As per ensemble mean anomaly a Wilcoxon-Mann-Whitney test (WMW-test), see for instance Wonacott and Wonacott 1977), has been applied to estimate whether the ensemble distribution of the real-time forecast is significantly different from the ensemble distribution of the back-statistics.

  • Regions where the WMW-test displays a significance less than 90% are blank.
  • Regions where the WMW-test displays a significance exceeding 99% are delimited by a solid contour (blue or red depending on whether the anomaly is positive or negative respectively).

The blanking of "non-significant" shifts does not mean that there is no signal in the blanked regions, but only that, with the particular sampling we have, we cannot be sure that there is a signal. For this reason, there are likely to be many areas where a signal is real but remains undetected.

See corresponding charts:  Weekly probability anomaly- Extended range forecast

Tercile maps

From the 660-member ensemble of the back statistics (11 members x 20 years x 3 forecast runs ), three equally probable domains are defined: below normal, normal and above normal. The probability of the back-statistics (model climatology) in each domain is 33%. The upper tercile map displays the probability of an anomaly above normal and the lower tercile displays the probability of an anomaly below normal. It is calculated from the number of ensemble members in the real time forecasts which display an anomaly within the above-normal domain defined from the model climatology. If there is no signal (the ensemble distribution of the real time forecast is not significantly different from the ensemble distribution of the model climatology), then the tercile map will indicate a probability close to 33%. Therefore, the probability range 20-40% has been blanked, in order to indicate regions where the model does not predict a significant shift of ensemble distribution from model climatology.

See corresponding charts: Weekly terciles- Extended range forecast

Multiparameter outlook

This products displays geopotential height at 500 hPa and anomalies of 10-metre wind, 2-metre wind and sunshine duration on a same plot. This product is available only for Europe.

See corresponding charts: Multiparameter outlook- Extended range forecast

Plumes

This product displays the time evolution of the ensemble forecast of geopotential at 500 hPa, 12-hour accumulated precipitation and temperature at 850 hPa over several European cities. The 51-ensemble distribution of real-time monthly forecasts has been categorised in 12.5% intervals (shading) together with the median (solid line).

See corresponding charts: Monthly forecast plumes- Extended range forecast

Members

This graphical products (also called stamp maps) is also an extension of an ENS product. It contains 51 stamps. Each stamp represents one ensemble member forecast of geopotential at 500 hPa or mean sea-level pressure. For mean sea-level pressure stamps, the 8 and 16 degree isolines of temperature at 850 hPa are also displayed as cyan and red lines respectively. The stamp maps display the instantaneous fields at days 5, 10, 15, 20, 25 and 30. Weekly means (defined as week1: day 5:11, week2: day 12:18, week3: day 19:25 and week4 day 26:32) are also displayed. As for the plumes, this product is not bias-corrected.

See corresponding charts: Mean sea level pressure and z500 stamps- Extended range forecast

Clusters

This graphical products is based on a method of regime clusterization used in ENS (see ECMWF Technical Memorandum 317). Six pre-defined patterns for the Atlantic/Europe region of geopotential at 500 hPa have been determined using several years of ERA15 data. The patterns represent different equiprobable weather regimes. Each member of the ensemble real-time monthly forecast of geopotential at 500 hPa is assigned to the closest pattern for different time steps (5, 10, 15, 20, 25 and 30 days). The products display the patterns computed by averaging all the ensemble members that fall within the same cluster, along with the number of ensemble members that fall within each cluster.This product has also been extended to weekly means. The variability in the population of each cluster from one week to the next is also displayed. This product is not bias-corrected.

See corresponding charts: Weather regime clusters- Extended range forecast

Hovmoeller diagram

The Hovmoeller diagram displays the time evolution of the ensemble mean anomaly of geopotential height at 500 hPa or 1000 hPa , averaged over the latitude band 35N-60N (Northern Extratropics) or 25S and 50S (Southern Extratropics). The anomaly has been computed by averaging all the members of the real-time forecast and subtracting the ensemble mean of the back-statistics (model climatology). Therefore, the graphics display anomalies with respect to the climate of the past 20 years. The x-axis represents the longitude, and the y-axis represents the time evolution (from top to bottom). Since it is an ensemble mean, the structures are much more detailed in the first days of the forecast (top part of the graphics) than in the last days (bottom part). Contours are plotted every metre. Shaded areas represent the ensemble spread and are displayed only when the amplitude of the anomaly exceeds 2 metres. The value of the spread increases sharply during forecast.

See corresponding charts: Time-longitudes diagram- Extended range forecast

Large scale mean flow

"Large scale mean flow" shows 500 hPa geopotential anomaly of the ensemble mean averaged over periods of one week.

See corresponding charts: Large scale mean flow- Extended range forecast

MJO graphical products

The Madden-Julian Oscillation (MJO) is a main source of predictability on the monthly time scale. The MJO is characterized by an eastward propagation of convection along the tropical band, typically initiated over the Indian Ocean. Several MJO forecast products are available:

- MJO index plot which displays the time evolution of the MJO predicted by ENS. described by a multivariate MJO index (Wheeler and Hendon 2004 Mon. Wea. Rev. vol. 132, 8 p 1917-1932).

- Time-longitudes section of ensemble mean anomalies of outgoing long-wave radiation, zonal wind at 850 hPa and velocity potential at 200 hPa averaged over a tropical band (15N-15S).

- Stamp maps of the  time-longitudes sections of anomalies of outgoing long-wave radiation, zonal wind at 850 hPa and velocity potential at 200 hPa averaged over a tropical band (15N-15S) for each ensemble member (51 stamps).

See corresponding charts: MJO index- Extended range forecast

Tropical storm

Two graphical products display monthly forecast of tropical storms:

- Tropical storm frequency or accumulated cyclone energy. This product shows the predicted  tropical storm frequency or accumulated cyclone energy (sum of the square of the estimated maximum sustained velocity of every active tropical storm at six-hour intervals) calculated over the same weekly periods than the other monthly forecast products and averaged over an ocean basin. The forecasts have been calibrated using the ensemble re-forecasts and past observed tropical storm data. This product is very similar to the seasonal outlook of tropical storm frequency but for a weekly period instead of a full season.

 - Tropical storm probabilities. This product shows a grid point map of tropical storm strike probability (probability of a tropical storm passing within 300km), calculated over weekly periods. This product is similar to the tropical cyclone activity maps produced for the medium-range forecasts.

References:

Wonacott, T.H. and R.J. Wonacott, 1977: Introductory statistics.John Wiley, 650 pp.

See corresponding charts: