10.5, 10.6, 10.7, 10.8 Lower tropospheric fronts and air masses

Drylines

Large-scale gradients between climatologically humid and dry air mass source regions

How might drylines strengthen

Into distinct air mass boundaries due to a combination of confluent air flow, subsidence inversions, and topography

Where are drylines primarily identified

The Southern Great Plains of the US

Quiescent drylines

Form without any major synoptic fronts or low-pressure systems

dominated by the diurnal cycle of PBL processes (moves east during the day, moves west at night)

Active drylines

Exist in an environment with a nearby shortwave trough and surface cyclone/front system

Forms south of the low and east of the cold front

Drylines are primarily located by…

a sudden moisture gradient

Pre-frontal windshifts

May form by both synoptic and mesoscale processes

significant for the organization of convection

occasionally may experience sufficient frontogenesis

Derechos

Large-scale convectively driven straight-line wind storms

Propagate over damage paths of several hundred kilos

The lower troposphere in low latitudes is strongly driven by

the background climatological patterns of flow and convergence that influence organized and general convection

Significant components of synoptic variability involve either…

extratropical interactions or transient low-pressure systems along the “moist margins”

Cold air damming

Cold dense air that is blocked by a topographic barrier

Cold air damming was first referenced because of

wintertime cold air “wedges” of high pressure east of the Appalachian Mountains