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. 1 , bottom right) where the isentropic surfaces are approximately level and the height dependence of temperature on the slope is similar to that above the center of the basin ( Whiteman 2000 ). Sheridan et al. (2014) found approximately horizontal isentropic surfaces in a valley with less than a 1% downvalley slope, a curve in the valley axis, and a valley constriction. Dorninger et al. (2011) found that strong cold pools in enclosed basins are generally well protected from wind events above
. 1 , bottom right) where the isentropic surfaces are approximately level and the height dependence of temperature on the slope is similar to that above the center of the basin ( Whiteman 2000 ). Sheridan et al. (2014) found approximately horizontal isentropic surfaces in a valley with less than a 1% downvalley slope, a curve in the valley axis, and a valley constriction. Dorninger et al. (2011) found that strong cold pools in enclosed basins are generally well protected from wind events above
1. Introduction Cold pools are evaporatively cooled areas of downdraft air that spread out horizontally underneath a precipitating cloud. They can be an important focus for the development of new convective cells, since some of the environmental air that approaches a cold pool is lifted up and over it ( Byers and Braham 1949 ; Purdom 1976 ; Wilson and Schreiber 1986 ). The development of new cells along the boundary between the cold pool and the environment, commonly called the outflow
1. Introduction Cold pools are evaporatively cooled areas of downdraft air that spread out horizontally underneath a precipitating cloud. They can be an important focus for the development of new convective cells, since some of the environmental air that approaches a cold pool is lifted up and over it ( Byers and Braham 1949 ; Purdom 1976 ; Wilson and Schreiber 1986 ). The development of new cells along the boundary between the cold pool and the environment, commonly called the outflow
1. Introduction Surface cold pools are areas of evaporatively cooled downdraft air that have spread out beneath a precipitating cloud. In midlatitudes, cold pools are common, play an integral role in the development of new convective cells along their leading edge, and are known to be the primary mechanism for the sustenance of multicell thunderstorms and convective lines (e.g., Markowski and Richardson 2010 ). In tropical cyclones (TCs), cold pools are believed to be less common due to the
1. Introduction Surface cold pools are areas of evaporatively cooled downdraft air that have spread out beneath a precipitating cloud. In midlatitudes, cold pools are common, play an integral role in the development of new convective cells along their leading edge, and are known to be the primary mechanism for the sustenance of multicell thunderstorms and convective lines (e.g., Markowski and Richardson 2010 ). In tropical cyclones (TCs), cold pools are believed to be less common due to the
1. Introduction Atmospheric cold pools are cold pockets of air formed in downdrafts by the evaporative cooling of clouds or raindrops ( Charba 1974 ; Goff 1976 ; Zipser 1977 ; Black 1978 ). These cold downdrafts expand horizontally upon reaching the surface, lasting for a few hours while forming gust fronts that reinitiate convective processes, resulting in more rain. Mechanical lifting of warm moist air at the edges of the cold pool fronts triggers new precipitating convective cells
1. Introduction Atmospheric cold pools are cold pockets of air formed in downdrafts by the evaporative cooling of clouds or raindrops ( Charba 1974 ; Goff 1976 ; Zipser 1977 ; Black 1978 ). These cold downdrafts expand horizontally upon reaching the surface, lasting for a few hours while forming gust fronts that reinitiate convective processes, resulting in more rain. Mechanical lifting of warm moist air at the edges of the cold pool fronts triggers new precipitating convective cells
1. Introduction Valley cold pools (VCPs), which are shallow layers of cold air trapped in a valley or basin ( Whiteman et al. 2001 ), are common in the western United States during winter. Numerical forecasts of basic variables, such as temperature and humidity, are known to be problematic during VCPs, which makes for difficulty in anticipating the various forms of hazardous weather, such as fog or freezing rain that can occur. In this study, the North American Mesoscale Model (NAM) forecasts
1. Introduction Valley cold pools (VCPs), which are shallow layers of cold air trapped in a valley or basin ( Whiteman et al. 2001 ), are common in the western United States during winter. Numerical forecasts of basic variables, such as temperature and humidity, are known to be problematic during VCPs, which makes for difficulty in anticipating the various forms of hazardous weather, such as fog or freezing rain that can occur. In this study, the North American Mesoscale Model (NAM) forecasts
1. Introduction Below clouds, the partial evaporation of precipitation may cool the air sufficiently to generate unsaturated downdrafts, which spread horizontally when reaching the surface in the form of density currents. As these so-called cold pools expand, they lift the warmer adjacent air masses, leading in some situations to the creation of new convective cells ( Craig Goff 1976 ; Warner et al. 1979 ; Böing et al. 2012 ; Torri et al. 2015 ; Li et al. 2014 ). This triggering has
1. Introduction Below clouds, the partial evaporation of precipitation may cool the air sufficiently to generate unsaturated downdrafts, which spread horizontally when reaching the surface in the form of density currents. As these so-called cold pools expand, they lift the warmer adjacent air masses, leading in some situations to the creation of new convective cells ( Craig Goff 1976 ; Warner et al. 1979 ; Böing et al. 2012 ; Torri et al. 2015 ; Li et al. 2014 ). This triggering has
1. Introduction Life cycles (formation, maintenance, and breakup) of cold-air pools in sinkholes and valleys of different scales have been studied for more than 30 years. The majority of these (semi-) analytical and numerical modeling studies focused on the processes responsible for cold-air-pool breakup. Among these are dissipation of the cold-air pool by convective boundary layer growth after sunrise ( Whiteman and McKee 1982 ), convective boundary layer growth due to heated sidewalls and
1. Introduction Life cycles (formation, maintenance, and breakup) of cold-air pools in sinkholes and valleys of different scales have been studied for more than 30 years. The majority of these (semi-) analytical and numerical modeling studies focused on the processes responsible for cold-air-pool breakup. Among these are dissipation of the cold-air pool by convective boundary layer growth after sunrise ( Whiteman and McKee 1982 ), convective boundary layer growth due to heated sidewalls and
incursions of cold air masses into a region that result in an episode of anomalously low surface temperatures (e.g., Konrad 1996 ; Walsh et al. 2001 ; Cellitti et al. 2006 ). TPVs are cold-core features and are associated with anomalously cold air throughout the depth of the troposphere (e.g., Cavallo and Hakim 2010 ). Several studies show evidence of tropospheric-deep cold pools located within and beneath TPVs and upper-tropospheric cyclonic PV anomalies (e.g., Defant and Taba 1957 ; Boyle and
incursions of cold air masses into a region that result in an episode of anomalously low surface temperatures (e.g., Konrad 1996 ; Walsh et al. 2001 ; Cellitti et al. 2006 ). TPVs are cold-core features and are associated with anomalously cold air throughout the depth of the troposphere (e.g., Cavallo and Hakim 2010 ). Several studies show evidence of tropospheric-deep cold pools located within and beneath TPVs and upper-tropospheric cyclonic PV anomalies (e.g., Defant and Taba 1957 ; Boyle and
1. Introduction Mesoscale convective systems (MCSs) form an integral part of the West African monsoon ( Flamant et al. 2007 ; Marsham et al. 2013a ) and account for more than 80% of the annual rainfall in most of the Sahel ( Mathon et al. 2002 ; Dhonneur 1973 ). Cold pools produced by MCSs are important for a number of reasons: they are a key mechanism for maintenance of the MCSs, and for secondary initiation of new cumulonimbus systems; they transport substantial amounts of cold air
1. Introduction Mesoscale convective systems (MCSs) form an integral part of the West African monsoon ( Flamant et al. 2007 ; Marsham et al. 2013a ) and account for more than 80% of the annual rainfall in most of the Sahel ( Mathon et al. 2002 ; Dhonneur 1973 ). Cold pools produced by MCSs are important for a number of reasons: they are a key mechanism for maintenance of the MCSs, and for secondary initiation of new cumulonimbus systems; they transport substantial amounts of cold air
1. Introduction Observational and numerical studies have long indicated the key role of precipitation-laden downdrafts in the formation of cold pools and a significant cold-pool impact on the surface–atmosphere exchange and on the initiation of subsequent convection (e.g., Houze and Betts 1981 ; Tompkins 2001 ; Khairoutdinov and Randall 2006 ; Grabowski et al. 2006 ; Schlemmer and Hohenegger 2014 ; Feng et al. 2015 ; Torri et al. 2015 ). Cold-pool formation and evolution involves
1. Introduction Observational and numerical studies have long indicated the key role of precipitation-laden downdrafts in the formation of cold pools and a significant cold-pool impact on the surface–atmosphere exchange and on the initiation of subsequent convection (e.g., Houze and Betts 1981 ; Tompkins 2001 ; Khairoutdinov and Randall 2006 ; Grabowski et al. 2006 ; Schlemmer and Hohenegger 2014 ; Feng et al. 2015 ; Torri et al. 2015 ). Cold-pool formation and evolution involves
