The current three- to seven-day forecasts Americans have come to rely on for planning everything from weekend picnics to hurricane evacuations rely heavily on constant updates from satellites that orbit Earth’s poles measuring temperature, moisture and a host of other variables that define the planet’s ever-changing weather. Early Tuesday, NASA plans to launch the first of four state-of-the-art polar orbiters for the National Oceanic and Atmospheric Administration, a $1.6 billion weather satellite that will monitor the entire planet as it rotates below, feeding computer models the data they need to make increasingly accurate predictions.