Average leading order stability properties of a dynamical system may be quantified via Lyapunov exponents. Using a barotropic circulation model of the atmospheric flow, regional Lyapunov exponents are calculated in terms of enstrophy of the flow. The role of large-scale flow as well as the synoptic scale eddies is examined for the stability of the flow during zonal and meridonal (blocking) regimes. It is noted that the meridonal flow regime is more stable relative to more frequent zonal flow regime. Using NCEP grided re-analyzed data, a case study of a blocking event occurring over continental US during the month of March 2003 is presented to elaborate the relative role of stability of the two regimes.