A brief synopsis of Johnson and Mapes: Mesoscale Processes and Severe Convective WeatheroverviewAdvective ProcessesExamples of mesoscale Differential AdvectionExamples of Convergence LinesSlide 6Dynamical processesSlide 8Slide 9Slide 10Triggering of convectionSlide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20A brief synopsis of Johnson and Mapes: Mesoscale Processes and Severe Convective WeatherFrom Severe Convective Storms sections 3.3b, 3.3c.1, 3.4ByMatt Goughoverview•Advective Processes and examples that lead to severe weather•Dynamical Processes and examples•Convective triggering mechanismsAdvective ProcessesMoisture Advection•Increases CAPE and lowers LFCSynoptic scale Differential Advection•Destabilizes atmosphere•Provides vertical wind shear•establishes capping inversionsConvergence Lines•Preconditioning and triggering convectionExamples of mesoscale Differential Advection•Low-level jets with high θ(e) overrunning fronts and cold-pools (bow echoes).•Flow of moist boundary layer air out from beneath an inversion•Transport of clouds and moisture aloft downstream of mountain barriers (dry microbursts)•Short periods of jet streak circulations and boundary layer heatingExamples of Convergence Lines•Warm and cold fronts – associated with Mesoscale cross-front circulations.•Precipitation driven downdrafts (gust fronts)•Drylines – usually needs to be coupled with other mechanisms.•Land and Sea breezes – convergence of offshore or onshore flow.• Mountain/Valley breezes – upslope flow in western US providing convergence and lifting.Off the east coast of Florida in the morning.Dynamical processes•Upper level jets•Lower level jets•Coupling of upper and lower level jetsDynamical processesUpper level jetsDynamical processesLower level Jets•Enhancement of moisture and temperature advection.•Increased low level convergence•Increase in vertical wind shearCoupling of upper and lower level jets•Upper level conv. forces low level jet Coupling between indirect circulation and cold cold front.Triggering of convectionMechanisms can operate in isolation•Storms along a gust frontor in combination•Gust fronts colliding with each otherTriggering of convectionLocal ProcessesBuoyancy driven circulation•Thermals, horizontal convective rolls, overshooting buoyant eddies.Terrain Forcing•Lee-side convergence, thermally-induced lifting, flow deflection, and surface inhomogeneities.Lee side convergenceTriggering of convectionAdvective Processes•Convection along convergence•Cold/warm front lifting•Gust fronts, sea breezes, and drylinesUsually the intersection of these features cause severe convection.Cold front liftingTriggering of convectionDynamical Processes:•Horizontal Convective Rolls (operate in conjunction with other processes)•Gravity waves (in tropics – small CIN)•Horizontal shearTriggering of convectionCombined Lifting Processes:•Boundary layer rolls intersecting with convergence lines •HCRs intersecting with sea breezes.•Dryline convection: mesoscale lows, HCRs, fronts, and gravity waves.•Gust fronts with terrain, gravity waves, etc.Denver, CO, 17 Jul