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withgeneral offshore flow at the surface. Nearly all coastalstratus is restricted to Baja California. With normal in-land penetration of hazy marine air prevented by theoffshore flow, the coastline appears with remarkableclarity, as do interior landmarks such as mountains andthe Salton Sea. Snow cover on the Sierra Nevada providesa fixed reference in this and succeeding pictures.Even while clear conditions prevailed, evidence of eddyformation first appeared during the early morning hoursof the 27th with

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David M. Schultz, Derek S. Arndt, David J. Stensrud, and Jay W. Hanna

bands over such a widespread area clearly indicates that they were not a local phenomenon like lake effect. In addition, the bands in Fig. 2 were only detected close to the radar, indicating that they were relatively shallow boundary layer features. Several mechanisms for the formation of these bands are possible. Gravity waves above convectively active boundary layers have been observed by Kuettner et al. (1987) and modeled by Clark et al. (1986) . The long-lived north–south-oriented bands in

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Vortex Look-Alikes: Juxtaposition of an Arizona Tornado and Dust Devil

Sherwood B. Idso

phenomena; yet, in this instance, an earlier photoof the tornado-waterspout (Fig. 2) showed it extendingfrom the base of a moderate-sized cumulus convectioncell. Although these two types of vortex wind motion arethus readily differentiated from each other in this case,there are other circumstances in which they are not soeasily distinguished. In particular, I refer to the vorticesthat form in association with duststorm frontal boundaries, whose precise identity is still unresolved. Ingrain(1973) has

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.In this example, the upper Ievel cloud system, which isthought to be responsible for the major precipitation, iseasily identified in the picture. The boundary of thestratus is also clearly dehed. If the precipitation mech-anism described here is correct, the satellite picture givesinsight into the timing and area of occurrence of precipita-tion under these conditions.REFERENCEBergeron, Tor, "The Problem of Artificial Control of Rainfall on theGlobe: 11. The Coastal Orographic Maxima of Precipitation

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ConvectivePlume and a Dust Devil," Journal of Applied Meteorology,Lensho\v, Donald H., "Airbornc Mrasurement,s of At,mosphericBoundary Layer Structure," Stdies of the Effrds of Variationsin Roundar?l Conditions on the ..ltnzospheric Boundary Layer,Department of Meteorology, University of Wisconsin, Madison,Saunders, Peter M., "Sca Smoke and Steam Fog." Qtcarterly Journalof ihc Royal Meteorological Society, Vol. 90, No. 384, London,England, x-. 1964, pp. 155-165.Warner, J., and Telford, J. W., "Convection

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Bradley M. Muller, Christopher G. Herbster, and Frederick R. Mosher

conditions at the surface and 850 hPa at 1200 UTC 12 September 2006 are shown in Fig. 4 . The prevailing surface airflow over the ocean as reported by buoy stations is climatologically typical [i.e., northwesterly at around 5 m s −1 (10 kt)]. Several stations in the vicinity of the south-central California coast were reporting fog or mist. At 850 hPa there was a west–east-oriented ridge of high pressure north of the Grover Beach area resulting in offshore (easterly) flow above the boundary layer over

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Ernani de Lima Nascimento, Gerhard Held, and Ana Maria Gomes

and moist conditions in central SP under moderate conditional instability. This quantitative analysis, however, was limited by the lack of observations on the mesoscale. Farther downstream, over central-eastern SP, where the tornado was observed, surface temperatures were lower but the combination of a northwesterly LLJ and northeasterly surface winds promoted strong speed and directional vertical wind shear, especially at low levels. In addition, the local boundary layer displayed very high

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Eric A. Hendricks, Brian D. McNoldy, and Wayne H. Schubert

structural variability. Note the extra observation at 1400 UTC 23 Jul from the U.S. Air Force WC-130J reconnaissance aircraft. 3. Environmental analysis To help understand the relative roles of the internal and environmental processes in the rapid intensification and deepening of Dolly prior to landfall, analysis of the environmental conditions in the vicinity of Dolly are presented here. Four critical environmental parameters for tropical cyclone intensity change are the deep-layer vertical wind shear

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Bryce J. Weinand

dissipating in extreme eastern Texas and western Louisiana at 1500 UTC on 18 April 1999. This article describes the atmospheric conditions at the time of the eddies and identifies factors that may have contributed to their formation. 2. Synoptic conditions During the days of 17 and 18 April 1999 there was a highly amplified circulation pattern over North America. A large, positively tilted trough evident on the 400-mb map for 1200 UTC 17 April 1999 ( Fig. 4 ) extended well into the middle sections of the

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Brandon J. Vogt and Stephen J. Hodanish

gradient, with the highest densities typically occurring more than halfway up mountain slopes. The author offered several possible explanations for the variability in stroke density in the mountainous areas, including surface-driven turbulence, terrain roughness, along with height and slope variations of the surface electrical boundary conditions. Bourscheidt et al. (2009) , in an analysis of lightning flash density over sections of the Rio Grande do Sul state of Brazil, also observed the greatest

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