INTRODUCTION While instability release is like a basketball rising from the bottom of a swimming pool, lifting is caused by air being forced to rise. Forced lifting is like picking up a bowling ball from the ground or doing a bench press. The object will not rise until a force causes it to rise. It is lifting not caused by the air rising on its own. Without enough lifting, parcels of air can not be lifted to a point in the troposphere where they can rise on their own due to positive buoyancy. Instability, if it is present, can not be released without the proper amount of forced lifting for the individual situation. LIFTING MECHANISMS 1. Frontal boundaries, dry lines and outflow boundaries (low level convergence) 2. Low level Warm Air Advection 3. Upslope flow 4. Low pressure system (synoptic and mesoscale) 5. Differential heating along soil, vegetation, soil moisture, land cover boundaries (low level convergence) 6. Low level moisture advection 7. Differential Positive Vorticity Advection, jet streak divergence (upper level divergence) 8. Gravity wave PRECIPITATION FROM LIFTING Dynamic precipitation is also known as stratiform precipitation. Dynamic precipitation results from a forced lifting of air. These forcing mechanisms include processes that cause low level convergence and upper level divergence. As unsaturated air rises the relative humidity of the air will increase. Once the air saturates, continued lifting will produce clouds and eventually precipitation. Dynamic precipitation tends to have a less intense rain rate than convective precipitation and also tends to last longer. While stratiform rain is the product of lifting, convective precipitation is the product of both lifting and instability release. FORECAST MODELS Lifting is assessed on the forecast models by examining the 700 mb upward vertical dynamic motion prog and surface prog. It is also important to examine constantly updated surface charts for lifting mechanisms that occur on a time and space domain that the models have a difficult time resolving (especially in thunderstorm situations). http://weather.unisys.com/eta/4panel/eta_700_4panel.html http://weather.unisys.com/eta/4panel/eta_sfc_4panel.html http://www.rap.ucar.edu/weather/surface/java_metars/ |