Page History

...

• instantaneous (e.g. probability 10m wind speed exceeds 20m/s as a given time),
• calculated over a time interval (e.g. probability precipitation exceeds 50mm during a defined 12 hour period).  This is possible because the values are themselves originally computed as values accumulated over some (shorter) time interval. 

Probability of precipitation

Probability of precipitation (PoP) totals include all precipitation types (rain, snow, etc. but not hail) in mm of rainfall or rainfall equivalent falling in 6 hour or 12 hour periods using colour shading.   As a rough guide 1 mm rainfall equivalent approximates to 1 cm of snowfall.

Probability of extreme gusts

Probabilities for extreme wind gusts are computed as probabilities over 24 hours because it is considered more important to know that an extreme wind gust might occur than to know the precise time.

...

Fig8.1.1-8: As Fig8.1.1-7 with the probability of wind ≥10m/s.  There is a higher probability (dark blue) in the area west of Ireland where the pressure gradient is uncertain although the direction is fairly certain.  The ensemble mean (Fig8.1.1-6) would not suggest such strong winds.  There is very low probability (white) south of Greenland where the gradient is generally light but the direction is uncertain.   Chart taken from ecCharts.  Light blue >25%, Blue >50%, Dark blue >75% probability.

Probability of combined events

Additionally, ecCharts can display the probability of a combination of events occurring together.  For example:

...