Meteorologists use many tools to predict the weather. They use past data such as temperature observations, real-time data such as radar and satellite images, and models that look into the future. Many different parameters are plotted using the numerical forecast models, which are generated using computers. The models consist of numerical equations which use current conditions as the inputs. The resulting outputs are forecasts for what is likely to happen in the future, based on those initial conditions. There are many different models that all attempt to do the same thing. The Global Forecast System model is used in this visualization.
Unequal heating and cooling over the planet, along with its rotation, creates different pressures across latitudes, longitudes and altitudes. Higher pressures are typically associated with fair weather, such as clear skies, but may also create conditions such as persistent hot or cold patterns (e.g., heat waves). Areas of low pressure are associated with storms, as dropping pressure allows moisture in the air to form clouds or precipitation. Boundaries between high and low pressure are called "fronts". This imagery shows the latest outputs of the NOAA Global Forecast System weather model for mean sea level pressure (MSLP). Blue areas are high pressure; orange/brown areas are low pressure. The Global Forecast System weather model updates every six hours and provides predictions for 10 days (240 hours) out from the start time, in three-hour time increments.