Finescale Surface Observations of the Dryline: A Mobile Mesonet Perspective

Mobile mesonet line normal, time-to-space converted data analysis on three meridional drylines that occurred in west Texas on 10 June 1999 and 5 May 2000 are presented herein; two occurred in a quiescent environment on 5 May 2000. Based on the data, the mixing zone across the dryline was composed of a series of large horizontal moisture differentials that were highly variable in width, ranging from 5 km down to several hundred meters. The largest dewpoint differential sampled was 10.0°C over 185 m. Concurrent with a deceleration of dryline movement to nearly stationary, and while moisture differentials strengthened, surface-based mesoscale vertical circulations with horizontal diameters of 2 km down to less than 300 m were resolved in the data, and visual observations were made of numerous, strongly rotating dust devils. The estimated diameters of the largest dust devils were ∼80-100 m and ∼1 km deep, and these persisted for tens of minutes. All vortices were found to move along or adjacent to the zones of moisture differential. Additionally, when the circulations were observed, spatially isolated cumulus clouds located along the dryline exhibited rapid vertical development. It is plausible that the vortices protect an ascending air parcel by inhibiting mixing, thus allowing the parcel to reach its local lifting condensation level and level of free convection with relatively greater buoyancy than parcels not contained in vortices.