Weather It Is (Some Explanation)

Hi:

(What are "mb" and what is an "ensemble?")

mb are abbreviation for millibars.  Near the surface (or rather sea-level), the pressure is around 1000 mb (lower in storms, higher in fair weather).  We often look at the weather at 850 mb (1500 meters), 700 mb (around 3000 meters up), and at 500 mb (5000 meters) to better understand or predict changes in the weather.  Certain temperatures or moisture indicate the possibility of thunderstorms and/or snow.

An ensemble is multiple forecasts of the same event (or day ahead), where each forecast is (often) made by changing the initial conditions (observations) a little bit, to see how our lack of knowledge affects the forecast.  When there is very little spread (standard deviation) among the ensemble members, it means that the signal in the forecast is more important than any error in our knowledge.

Barry Lynn