"tmin" 24-hour minimum of 2-metre temperature in degrees Celsius (°C) spatially averaged over the native grid area (5 kilometres)
"tmax" 24-hour maximum of 2-metre temperature in degrees Celsius (°C) spatially averaged over the native grid area (5 kilometres)
"tmean" 24-hour average of 2-metre temperature in degrees Celsius (°C) spatially averaged over the native grid area (5 kilometres)
"precipitation" 24-hour (OR monthly for "monthly forecast" and "departures (anomalies)" requests) accumulation of precipitation of all types in millimetres (mm) spatially averaged over the native grid area (5 kilometres)
"minhumidity" 24-hour minimum relative humidity at 2-metres above the surface as a percentage of saturation point (%), spatially averaged over the native grid area (5 kilometres)
"maxhumidity" 24-hour minimum relative humidity at 2-metres above the surface as a percentage of saturation point (%), spatially averaged over the native grid area (5 kilometres)
"hail" 24-hour average of precipitation rate or intensity in millimetres per second multiplied by 1000 (mm/s x 1000), spatially averaged over the native grid area (5 kilometres)
"wind" 24-hour average of wind speed at 10 metres above the surface in metres per second (m/s), spatially averaged over the native grid area (5 kilometres)
"solar" 24-hour average of incoming solar radiation at the surface in Watts per metre squared (W/m2 (daily mean)), spatially averaged over the native grid area (5 kilometres)
"Soilmoisture" Volumetric soil water layer 2 at a depth of 7cm to 28cm; reported either as a monthly mean, or as a absolute departure 'anomaly'
Hazard Indices or 'Scores' are generated by comparing forecasts against a 15-year climatology dataset derived from the UERRA MESCAN-SURFEX 4.5km reanalysis product. Documentation and further information is available from the Copernicus Climate Data Store (CDS).**
Both the daily ensemble weather forecast data and observations are statistically processed to generate confidence intervals at each decile (10th, 20th, 30th, 40th, 50th, 60th, 70th, 80th, 90th, 100th). An index unit of 5.0 indicates a forecast that is on par with the historical measurements (from UERRA reanalysis) spanning the years 2004 to 2018. A shift of one decile category unit in the seasonal climate forecast increases the likelihood of more extreme weather, and increases the hazard index by one unit.
"hail" Hail Indices are calculated by comparing the 80th centile of ensemble forecasts of aggregated ERA-5 derived convective precipitation rate (hail)/ H80 against closely spatially matched measurements of daily precipitation rates from recent history. Index values of 1 indicate that the likelihood of intense convective precipitation is low, while an index of 9 indicate that hail or intense precipitation events are more likely within the seasonal period (potentially crop, building or other infrastructure/ asset damage). **Compared against Copernicus ERA-5 observations/ WeatherLogistics' model climatology.
"solar" Solar Indices are calculated by comparing the 20th centile of ensemble forecasts of ERA-5 derived aggregated daily average solar radiation (solar)/ S80 against closely spatially matched measurements of solar radiation from recent history. Index values of 1 indicate that the likelihood of extreme cloudless days is low, while an index of 9 indicate that the extreme sunlight exposure is more likely within the seasonal period (potentially exacerbating drought or heat-stress if combined with high temperatures). **Compared against Copernicus ERA-5 observations/ WeatherLogistics' model climatology.
"wind" Wind Indices are calculated by comparing the 80th centile of ensemble forecasts of ERA-5 derived aggregated daily average wind speed (wind) / RH80 against closely spatially matched measurements of relative humidity conditions from recent history. Index values of 1 indicate that the likelihood of extreme windy days is low, while an index of 9 indicate that high winds are more likely within the seasonal period (potentially leading to crop lodging, or building or other infrastructure/ asset damage). **Compared against Copernicus ERA-5 observations/ WeatherLogistics' model climatology.
"aridity" Aridity Indices are calculated by comparing the 20th centile of ensemble forecasts of ERA-5 derived aggregated daily minimum and maximum relative humidity/ RH20 against closely spatially matched measurements of relative humidity from recent history. Index values of 1 indicate that the likelihood of extreme aridity is low, while an index of 9 indicate that the extreme aridity is more likely within the seasonal period (potentially to agricultural soil moisture deficits, or exacerbation of drought conditions if combined with high temperatures and/ or low precipitation). **Compared against Copernicus ERA-5 observations/ WeatherLogistics' model climatology.
"cold" Cold Indices are calculated by comparing the 20th centile of ensemble forecasts of 24-hour minimum daily temperatures (tmin)/ TMIN20 against closely spatially matched measurements of temperature conditions from recent history. Index values of 1 indicate that the likelihood of extreme colder-than-average daytime minimum temperatures is low, while an index of 9 indicate that the extreme cold night-time weather is more likely within the seasonal period (potentially frost or crop damage).
"drought" Drought Indices are calculated by comparing the 20th centile of ensemble forecasts of dry days/ PR20 (where precipitation exceeds 0.1 millimetres per day) against closely spatially matched measurements of drought conditions from recent history. The minimum threshold of 0.1mm avoids multiple decile probability of occurrence categories of zero precipitation, which is commonplace in arid climates. Index values of 1 indicate that the likelihood of extreme drier-than-average conditions is low, while an index of 9 indicate that that extreme drought is more likely within the seasonal period (potentially water shortages linked to crop failure and domestic water supply and quality issues). See further information on the Drought Index.
"heat" Heat Indices are calculated by comparing the 80th centile of ensemble forecasts of 24-hour maximum daily temperatures (tmax)/ TMAX80 against closely spatially matched measurements of temperature conditions from recent history. Index values of 1 indicate that the likelihood of extreme warmer-than-average daytime maximum temperatures is low, while an index of 9 indicate that the extreme daytime heat is more likely within the seasonal period (potentially overheating of buildings if during the summer or warmer seasons).
"humidity" Humidity Indices are calculated by comparing the 80th centile of ensemble forecasts of ERA-5 derived aggregated daily minimum and maximum relative humidity/ RH80 against closely spatially matched measurements of relative humidity conditions from recent history. Index values of 1 indicate that the likelihood of extreme humidity is low, while an index of 9 indicate that the extreme daytime humidity levels are more likely within the seasonal period (potentially linked to crop pests/ disease or heat-stress if combined with high temperatures). **Compared against Copernicus ERA-5 observations/ WeatherLogistics' model climatology.
"precipitation" Flood Scores are calculated by comparing the 80th centile of ensemble forecasts of wet days/ PR80 (where precipitation exceeds 1.0mm per day) against closely spatially matched measurements of hydrological conditions from recent history. Index values of 1 indicate that the likelihood of extreme wetter-than-average conditions from heavier downpours is low, while an index of 9 indicate that that extreme precipitation (potentially flash flooding) is more likely within the seasonal period. See further information on the Precipitation Index.
"spi" SPI (Standard Precipitation Index) is calculated by comparing the 50th centile of ensemble forecasts of non-drizzle days/ PR50 (where precipitation exceeds 0.3 millimetres per day) against closely spatially matched measurements of hydrological conditions obtained from recent history. The minimum threshold of 0.3mm is a calibrated value to account for less reliable observations of lighter precipitation events. Index values of 1 indicate that the weight of the season (or month) indicates more drier-than-average days, while an index of 9 indicate that excess precipitation days (potentially leading to groundwater flooding or extended wet periods) are likely to be more frequent than average. Caution neeed to be exercised, since kurtosis and skew of the local distribution of daily precipitation days may produce regional artefacts that may affect the quality of the analysis. See further information on the SPI.
"EXCEEDANCES" Exceedance curves compare daily precipitation from a collection of realizations (ensemble members) at different intensities. These are compared directly against spatially correlated UERRA reanalyses from a 15-year history between the years 2004 and 2018. Where the forecast curve exceeds/ subceeds the historical reference at a precipitation intensity threshold, the rate of precipitation is likely to be more/ less intense.
"GDD" Growing Degree Days (otherwise known as Heating Degree Days), reports the accumulated daily average mean temperature over a rolling 7-day (weekly period) i.e.
Σ(tmean)t+1 + Σ(tmean)t+2 + Σ(tmean)t+3 + Σ(tmean)t+4 + Σ(tmean)t+5 + Σ(tmean)t+6 + Σ(tmean)t+6 + Σ(tmean)t+7,
The daily timeline runs from t = 0 days (for the first calendar month of the seasonal climate forecast) to t ≈ 92 at the end of the calendar month 3. Rather than the traditional definition, a baseline temperature of zero degrees Celsius (0°C) is used in these graphical charts, and any period of sub-zero temperatures are accumulated and are subtracted from the rolling 7-day accumulated thermal units. Lower/ upper confidence intervals in the seasonal climate forecasts are supplied as 10th/90th and 25th/75th shading bands, while a real-time climatology reference is also provided. **Compared against WeatherLogistics' model climatology.
*Contains modified Copernicus Climate Change Service information 2022. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.