Challenges of Forecasting in the West - NOAA

Categorize mesoscale circulationsinto two types:1. Free (internal) circulations/disturbances:• Occur as a result of an instability inherent within the fluid (someprecip bands, MCCs, jetstreaks, polar lows, squall lines,hurricanes)• To predict, look at “background” flow to determine what instabilitiesmay be present2. Forced circulations/disturbances:• Owe their existence, at least in part, to an external boundary of thesystem• External forcing controls location and influences the scale of thesystem• To predict, need to be familiar with local physiographic featuresand complicated mesoscale dynamics