For more than thirty-five years in this business I have wrestled with the conundrum of predicting summer time showers and thunderstorms. Accurately forecasting a shower or thundershower hinges on monitoring the ever changing atmospheric boundaries and vertical profile.
In the warm season, convective storms seem to randomly blossom in the heat of the day and then drift in the relatively light steering winds overhead. A valued colleague in Indianapolis once declared that thunderstorm formation is not random; there is a trigger to ignite the towering cumulus cloud. Boundaries can be subtle. Identifying where a specific boundary might form two days out is next to impossible.
Regrettably, meteorologists are still left with providing clients the proverbial thirty percent chance when it comes to crafting a forecast on sultry summer day.
So, decades after I began my forecasting career, the precipitation probability dilemma remains. If you tend to be an optimist, you could infer that there is a seventy percent chance for no rain.
Forecasters in National Weather Service office collaborate the seven day forecast to mosaic the weather regionally and nationally. Twice a day they present their case for the decisions they have made in formulating your forecast.