Abstract
This study investigates the synoptic/mesoscale dynamics responsible for an unusually heavy southern US snowstorm that occurred on February 11-12, 2010, using reanalysis, observations, and numerical simulations. This record breaking snowfall event represents an example of multiple upper level and low-level jets (LLJs) and their accompanying baroclinic zones. The analysis reveals the following synoptic scale processes as significant contributors: (1) upper level jet splitting and merging, (2) advection of cold arctic air at low levels by a large anticyclone, and (3) an incoming upper level shortwave trough. In addition to the synoptic scale processes, the following mesoscale features played a major role in this snowstorm event: coexisting potential (convective) instability and conditional symmetric instability, terrain blocking, and a double LLJ development process. Sensitivity experiments including (1) limiting the orographic effects of elevated plateau in Texas and the Sierra Madre Mountains in Mexico by reducing the terrain height to 225 meters, (2) the microphysics/latent heating effects, and (3) surface fluxes on the development and intensity of the snowstorm were also conducted by turning these options off in the numerical model. Of all three experiments, the surface flux experiment displays the least amount of influence on the developing frozen precipitation bands.
Highlights
During February 11-12, 2010, a snowfall event broke many records across the southern regions of the US
During the genesis of extreme moist convection over west Texas ∼0600 UTC 11 February (see Figure 15(a), where vertically erect isentropes can be seen near 28.5∘N, 29.5∘N, and 31∘N), the aforementioned precipitation bands formed close to the adjustments leading to the dual level jets (LLJs) convergence zone
Prior studies indicating common synoptic scale features of southern US snowstorms were examined in the case study analysis of the record breaking Deep South Snowstorm February 11-12, 2010, by employing multilevel, multiscaled observations, reanalysis data, and numerical simulations
Summary
During February 11-12, 2010, a snowfall event broke many records across the southern regions of the US. Following the publication of this manuscript, Uccellini et al [4,5,6] and Whitaker et al [7] published a sequence of manuscripts that focused on the role of jet streaks and the interaction of the streaks with the coastal front and a subsequent tropopause folding event that produced a multistage evolution and intensification of this cyclone They employed primarily upper air observational analyses and mesoscale numerical simulation studies to diagnose key multiscale processes. It is germane to point out that prior to the most rapid offshore cyclogenesis, record snowfalls were observed from western North Carolina to southern New Jersey within the cold air damming region Similar to these Presidents’ Day event analyses, Uccellini and Kocin [8] and Kocin et al [9] both performed analyses of multilevel explosively developing coastal storms in the same region.
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