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- The HRES forecast values are shown as a blue line on the 10-day ENS meteogram. The medium range ensemble control (CTRL) is virtually identical to HRES and is not shown.
- The 15-day ENS meteogram displays the probability distribution for each calendar day from 00UTC to 00UTC. For forecasts with data time of 12UTC the first and last 12 hours in the forecast period are excluded and only 14 (instead of 15) daily distributions are generated.
10-day ENS meteogram
Fig8.1.4-4: 10-day medium-range meteogram for Athens data time 00UTC 12 May 2017. Solid blue lines are HRES/Control. The red numbers above the precipitation panel are the greatest precipitation value reached by any ENS member. ENS extreme values cannot be ignored as the evolution of every ENS member is considered to be equally probable. Note: the forecast temperatures are at 00UTC, 06UTC, 12UTC, 18UTC each day (15-day meteograms show forecast maximum and minimum temperatures for each day). UTC is used exclusively in the meteograms and maxima or minima will occur according to the longitude (or local time) of the location in question.
15-day ENS meteogram
Fig8.1.4-5: 15-day medium-range meteogram for Dublin from ENS data time 12UTC 22 June 2023. The displayed values are for the 24hr period each day, with additionally the distribution of 10m wind direction. Note: the forecast maximum and minimum temperatures are shown for each day (10-day meteograms show forecast temperatures at 00UTC, 06UTC, 12UTC, 18UTC).
15-day ENS meteogram with M-climate
Fig8.1.4-6: As Fig8.1.4-5 with the addition of M-climate data. M-climate data is shown by colours with percentiles similar to the box and whisker scheme. The temperature box and whisker for 24 June lies confidently above the 99th percentile of the M-climate. The median wind forecast for 30 June lies above the M-climate values (above the 75th percentile of the M-climate) with the whisker extending above the 99th percentile of the M-climate. The median precipitation for the 25 June lies between the 50th and 75th percentile.
Fig8.1.4-7: Illustration of the relationship between 10day ensemble presentation and 15day presentation (truncated to 10days for ease of comparison).
Fig8.1.4-8: Illustration of the relationship between 10day ensemble presentation and 15day presentation (truncated to 10days for ease of comparison).
Weather Parameters in the Ensemble Meteograms
- Total cloud cover in the 10-day ensemble meteogram is the instantaneous forecast value in oktas (eighths of the sky covered by cloud). In the 15-day extended ensemble meteogram it is the daily average of ENS forecast values at 06, 12, 18 and 24UTC. When all members have 0 cloudiness (clear sky) or 8 oktas cloudiness (overcast), there is no line or box at all. Note:
- When the forecast is very uncertain and all cloud amounts are more or less equally likely, the columns cover almost the whole range from 0 to 8 oktas, which can be wrongly interpreted as “overcast”.
An alternative display (currently only available within the ecCharts meteogram platform) has a circle divided clockwise into eight arcs, each arc representing 1/8 cloud cover. So, for example, the arc covering 45°-90° represents 2/8 cloud cover. The shading within each arc is proportional to the number of members that forecast this particular degree of cloud cover or more.
- When the forecast is very uncertain and all cloud amounts are more or less equally likely, the columns cover almost the whole range from 0 to 8 oktas, which can be wrongly interpreted as “overcast”.
Total precipitation in the 10-day ensemble meteogram is the accumulated precipitation (sum of convective and large-scale) over 6hr periods (00-06UTC, 06-12UTC, etc). In the 15-day meteogram it is the accumulated precipitation over 24hr periods (00-24UTC). Note:
On the 10-day meteogram the box-and-whisker plot locations align with the end of the 6 hour period.
Probabilities for intervals longer than the 6hr and 24hr time intervals cannot be deduced from the ensemble meteogram.
Periods of probabilities >0% in every interval can be wrongly interpreted as uninterrupted rain.
Consideration of the median alone can be wrongly interpreted as protracted dry spells.
The precipitation shown on the ensemble meteograms cannot be directly inter-compared as the rainfall range (y-axis) varies from one location to the next and from one forecast to the next. The rainfall range is chosen separately for each ensemble meteogram so that 100% of the predicted values are covered for the 15-day ensemble meteograms, and at least 90% of the predicted values are covered for the 10-day ensemble meteograms (if the top of the distribution is beyond the scale maximum the largest 6-hourly total is shown at the top as red numbers).
- 10m wind speed in the 10-day ensemble meteogram is the instantaneous forecast value in m/s. Note this is the mean speed, not the diagnosed gust. In the 15-day ensemble meteogram as it is the 24-hour wind-speed average of ENS forecast values at 06, 12, 18 and 24UTC. Note:
- The peaks of the whiskers should not be interpreted as wind gusts. ENS products related to gusts should be used (e.g. CDF diagrams).
- The peaks of the whiskers should not be interpreted as wind gusts. ENS products related to gusts should be used (e.g. CDF diagrams).
- 10m wind direction (only shown in the 15-day ensemble meteogram) is the daily distribution of directions obtained by taking each 6-hourly forecast step for the day (50 members x 4 forecast steps at 06-12-18-24UTC) and allocating it to the relevant octant. The area of an octant is proportional to the probability of that wind direction (i.e. to the proportion of forecasts falling in that octant). The probability of each octant is shown by shading light (low) to dark (high). Note:
- The wind roses shown on the ensemble meteograms cannot be directly intercompared compared as each is scaled to the size of the most populated octant. The size of the wind rose does not refer to wind speed.
- The wind roses shown on the ensemble meteograms cannot be directly intercompared compared as each is scaled to the size of the most populated octant. The size of the wind rose does not refer to wind speed.
- 2m temperature in the 10- day ensemble meteogram is shown as instantaneous forecast values at 6-hourly intervals. In the 15-day ensemble meteogram it is shown as daily maximum and minimum temperatures (in °C). Note:
- The forecast temperature is adjusted by using a 6.5K/km lapse rate applied across the difference between the station height (as displayed in the title) and the ENS orography (the relative heights of ENS and true orography are shown in the top right corner of the meteogram web page. In some instances, some information is also included in the temperature panel title of the meteogram itself).
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