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1. Introduction It is well established that some clouds contain supercooled liquid water (SLW), which poses an icing hazard for the aviation industry ( Sand et al. 1984 ). Under favorable conditions, supercooled large drop (SLD) icing can occur, such as from freezing drizzle and freezing rain ( Pobanz et al. 1994 ; Cober et al. 1996 , 2001a ; Cober and Isaac 2012 ; Bernstein et al. 2019 ). SLD icing is particularly hazardous to aircraft as current deicing techniques do not in general
1. Introduction It is well established that some clouds contain supercooled liquid water (SLW), which poses an icing hazard for the aviation industry ( Sand et al. 1984 ). Under favorable conditions, supercooled large drop (SLD) icing can occur, such as from freezing drizzle and freezing rain ( Pobanz et al. 1994 ; Cober et al. 1996 , 2001a ; Cober and Isaac 2012 ; Bernstein et al. 2019 ). SLD icing is particularly hazardous to aircraft as current deicing techniques do not in general
1. Introduction Freezing precipitation, defined by the American Meteorological Society's Glossary of Meteorology as freezing rain, freezing drizzle, and freezing fog ( Glickman 2000 ), can have a devastating effect on many industries, including transportation, energy, agriculture, and commerce. In addition to freezing precipitation, ice pellets at the ground often are an indication of freezing precipitation aloft, which can have a detrimental effect on aircraft ( Zerr 1997 ; Bernstein et al
1. Introduction Freezing precipitation, defined by the American Meteorological Society's Glossary of Meteorology as freezing rain, freezing drizzle, and freezing fog ( Glickman 2000 ), can have a devastating effect on many industries, including transportation, energy, agriculture, and commerce. In addition to freezing precipitation, ice pellets at the ground often are an indication of freezing precipitation aloft, which can have a detrimental effect on aircraft ( Zerr 1997 ; Bernstein et al
1. Introduction Freezing precipitation has been well documented as the cause of extensive damage to property, utility service wires, and disruption to surface transportation ( Regan 1998 ; Rauber et al. 1994 ; Martner et al. 1992 ; Bendel and Paton 1981 ). Primarily thought of as surface phenomena, freezing drizzle and freezing rain can extend from the surface to altitudes of 10 000 ft or more ( Jeck 1996 ), have been observed as high as 20 000 ft ( Cober et al. 1999 ; Isaac et al. 1999
1. Introduction Freezing precipitation has been well documented as the cause of extensive damage to property, utility service wires, and disruption to surface transportation ( Regan 1998 ; Rauber et al. 1994 ; Martner et al. 1992 ; Bendel and Paton 1981 ). Primarily thought of as surface phenomena, freezing drizzle and freezing rain can extend from the surface to altitudes of 10 000 ft or more ( Jeck 1996 ), have been observed as high as 20 000 ft ( Cober et al. 1999 ; Isaac et al. 1999
drizzle occurs and the sounding is everywhere colder than 0°C. In these cases, freezing precipitation forms through the warm rain process ( Bocchieri 1980 ; Huffman and Norman 1988 ; Rauber et al. 2000 ). Czys et al. (1996) note that their 1995/96 experience suggests that this situation is “a highly localized phenomena.” Based on initial successes, CZ developed a simple isonomogram that could be used with soundings as a diagnostic tool to distinguish freezing rain and ice pellet occurrences. The
drizzle occurs and the sounding is everywhere colder than 0°C. In these cases, freezing precipitation forms through the warm rain process ( Bocchieri 1980 ; Huffman and Norman 1988 ; Rauber et al. 2000 ). Czys et al. (1996) note that their 1995/96 experience suggests that this situation is “a highly localized phenomena.” Based on initial successes, CZ developed a simple isonomogram that could be used with soundings as a diagnostic tool to distinguish freezing rain and ice pellet occurrences. The
1. Introduction Accurate forecasts of aircraft icing and supercooled large drops (SLD; freezing drizzle and freezing rain) conditions are of great importance to aviation safety. In fact, new aircraft icing regulations were enacted in January 2015 to introduce a new icing certification rule, section 25.1420 ( FAA 2014 ), and a FAA engineering standard (“Appendix O”) that defines SLD environments for certification of affected aircraft. Past icing forecast algorithms were developed by applying
1. Introduction Accurate forecasts of aircraft icing and supercooled large drops (SLD; freezing drizzle and freezing rain) conditions are of great importance to aviation safety. In fact, new aircraft icing regulations were enacted in January 2015 to introduce a new icing certification rule, section 25.1420 ( FAA 2014 ), and a FAA engineering standard (“Appendix O”) that defines SLD environments for certification of affected aircraft. Past icing forecast algorithms were developed by applying
and surface precipitation type or amount of cloud cover present, a gridded analysis of the 0000 surface airways observations (SAOs) was performed. A latitude–longitude (lat–long) grid of 0.25° lat × 0.25° long boxes was created over the United States. The precipitation or greatest cloud coverage (when precipitation was not occurring) reported by the SAO closest to the centroid of each grid box was assigned to that box. Six categories were used for precipitation: snow, rain, drizzle, freezing rain
and surface precipitation type or amount of cloud cover present, a gridded analysis of the 0000 surface airways observations (SAOs) was performed. A latitude–longitude (lat–long) grid of 0.25° lat × 0.25° long boxes was created over the United States. The precipitation or greatest cloud coverage (when precipitation was not occurring) reported by the SAO closest to the centroid of each grid box was assigned to that box. Six categories were used for precipitation: snow, rain, drizzle, freezing rain
1. Introduction and background Branick (1997) found that notable freezing rain or freezing drizzle occurs in about 24% of all winter weather events across the continental United States. Proper preparation by utility, transportation, and public safety entities for these freezing rain events requires accurate forecasts of ice accumulation on various surfaces. As icing takes place during a freezing rain event, it ultimately results in two different types of ice accumulation that contribute to the
1. Introduction and background Branick (1997) found that notable freezing rain or freezing drizzle occurs in about 24% of all winter weather events across the continental United States. Proper preparation by utility, transportation, and public safety entities for these freezing rain events requires accurate forecasts of ice accumulation on various surfaces. As icing takes place during a freezing rain event, it ultimately results in two different types of ice accumulation that contribute to the
hydrometeors in the thermodynamic energy balance, an alternate method was formulated to diagnose the simulated liquid water fluxes based on mutually independent drop size ranges. We separate the total water content into nonprecipitating types, which is the drop population with diameters of less than 80 μ m (cloud water), and precipitating types with diameters of 80–300 μ m (drizzle) and greater than 300 μ m (rain). The computational procedure is described in the appendix . The simulated liquid water
hydrometeors in the thermodynamic energy balance, an alternate method was formulated to diagnose the simulated liquid water fluxes based on mutually independent drop size ranges. We separate the total water content into nonprecipitating types, which is the drop population with diameters of less than 80 μ m (cloud water), and precipitating types with diameters of 80–300 μ m (drizzle) and greater than 300 μ m (rain). The computational procedure is described in the appendix . The simulated liquid water
. Icing conditions occurring close to the ground are particularly dangerous for aircraft during takeoff and landing. Here freezing rain and freezing drizzle containing SLDs are quite frequent not only in Canada ( Stuart and Isaac 1999 ) and the United States (e.g., Bernstein et al. 1998 ; Bernstein 2000 ), but also in Europe ( Carrière et al. 2000 ). Freezing rain and drizzle have however also been reported at altitudes as high as 10 000 and 20 000 ft MSL, respectively ( Jeck 1996 ). Of course, the
. Icing conditions occurring close to the ground are particularly dangerous for aircraft during takeoff and landing. Here freezing rain and freezing drizzle containing SLDs are quite frequent not only in Canada ( Stuart and Isaac 1999 ) and the United States (e.g., Bernstein et al. 1998 ; Bernstein 2000 ), but also in Europe ( Carrière et al. 2000 ). Freezing rain and drizzle have however also been reported at altitudes as high as 10 000 and 20 000 ft MSL, respectively ( Jeck 1996 ). Of course, the
also results in ice accretion at the surface, but does not require a >0°C warm layer ( Bocchieri 1980 ; Huffman and Norman 1988 ; Rauber et al. 2000 ). Precipitation forms not as snow, but instead as rain or drizzle via collision and coalescence. This typically occurs with upward motion in shallow, low-level saturated layers lacking active ice nuclei. This formation mechanism most commonly produces freezing drizzle, though Rauber et al. (2000) also identified several freezing rain cases in
also results in ice accretion at the surface, but does not require a >0°C warm layer ( Bocchieri 1980 ; Huffman and Norman 1988 ; Rauber et al. 2000 ). Precipitation forms not as snow, but instead as rain or drizzle via collision and coalescence. This typically occurs with upward motion in shallow, low-level saturated layers lacking active ice nuclei. This formation mechanism most commonly produces freezing drizzle, though Rauber et al. (2000) also identified several freezing rain cases in
