On account of the finescale convergence, radars generally see the dryline as a reflectivity “fineline” (e.g., Wilson et al. The mature dryline is often a remarkably fine boundary with a substantial humidity jump and significant convergence over the depth of the convective BL ( Miao and Geerts 2007). The large-scale convergence along the dryline is attributed to the formation of a heat trough in the lee of the Rockies (e.g., McCarthy and Koch 1982 Parsons et al.

The dryline has clear diurnal characteristics and becomes more defined during the afternoon hours, when it tends to move eastward, at least in the absence of synoptic changes ( Bluestein 1993, p. To a first order, the dryline can be viewed as the intersection of the top of a level, capped boundary layer (BL) containing the mT air mass and the sloping terrain east of the Rocky Mountains (e.g., Schaefer 1974). The dryline is a well-defined atmospheric boundary observed over the southern Great Plains, between hot dry air to the west and air of maritime tropical (mT) origin to the east. Also shown are the least squares fits for the points with Δ θ υ < 0, and a theoretical dependence of density current speed on Δ θ υ for three values of density current depth D. Scatterplot of the dryline propagation speed relative to the ambient flow ( U rel) against Δ θ υ. Trend of the propagation speed of the dryline fineline. 9 but for the humidity difference, Δ q υ. The times of solar noon and sunset (both on 1 and 31 May) in Lubbock are indicated.Īs in Fig. The linear regression line is shown as well. Scatterplot of the difference in mixing ratio vs the difference in virtual potential temperature (moist side − dry side), between stations on opposite sides of the dryline, at any time before sunset. (a) Skew- T diagram and (b) hodograph for AMA (black lines) located 12 km west of the dryline, and MAF (gray lines), located farther south and ∼75 km east of the dryline, at 0000 UTC. The sea level pressure contours (2-hPa interval) are based on the North American Mesoscale (NAM) model initialization. The official analysis of the dryline and the outflow boundary is inaccurate, so these boundaries have been redrawn, based on additional surface station data, radar data, and soundings. The frontal analysis is the official version from the National Weather Service. The fineline in (a) and (b) is a westward-propagating outflow boundary, which had occluded the surface dryline around 2230 UTC. A north–south orientation is 0°.Īs in Fig. Histogram of local dryline orientations within the area of view of the LBB radar. The stations were located on the moist side of the boundary during the respective periods. 2) and (b) between 00 UTC (labeled as XSLS and XWVS in Fig. Saturation point analysis ( Betts 1984) for two WTM stations (a) between 20 UTC (labeled as XPTS and XRLS in Fig. The scale can be inferred from the range rings, shown at 40-km intervals. The station ID is shown below the station. The unconventional numbers, on the right of the station location, are the virtual potential temperature θ υ (K) and the mixing ratio q υ (g kg −1). The conventional parts of the station data are the wind barbs, the temperature T (☌), and the dewpoint T d (☌). The color field (with key bar on the left) is the 0.5° elevation base reflectivity (dB Z) from LBB. Stations used are Amarillo, TX (AMA) Dyess Air Force Base, TX (DYX) Frederick, OK (FDR) Lubbock, TX (LBB) Midland–Odessa, TX (MAF) and San Angelo, TX (SJT).Įxample of a dryline fineline and WTM station observations at 2340 UTC. The preferred longitude of drylines at 0000 UTC is based on the dryline climatology by Hoch and Markowski (2005). The gray circles, with a radius of 70 km, represent the typical clear-air coverage of the boundary layer. Map of WSR-88D radars and highways in West Texas.

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