Snowbands during the Cold-Air Outbreak of 23 January 2003

Abstract

A cold-air outbreak east of the Rocky Mountains on 23 January 2003 produced banded clouds and snow across the central and southeastern United States. The bands occurred through two processes: 1) thermal instability in the planetary boundary layer produced horizontal convective rolls (HCRs) over widespread areas, and 2) lake-effect processes downstream of small lakes (fetch Ͻ 100 km) produced localized bands. Characteristics of the observed bands associated with the HCRs, such as horizontal scale, depth of circulation, orientation, duration, and dynamics, are explored through observations, previous literature, and theoretical models. Snow from clouds produced by HCRs over land during the cold season has not been extensively studied previously. In this event, cold-air advection over the warm ground led to an upward sensible heat flux, promoting the occurrence of the HCR circulations. As the surface temperature decreased, the height of the lifting condensation level decreased, eventually forming cloud bands within the ascending portion of the HCR circulations. Ice crystals are inferred to have fallen from a large-scale precipitation system aloft into the cloud bands in the planetary boundary layer, which was within the favored temperature regime for dendritic growth of ice crystals. The ice crystals grew and reached the surface as light snow. This seeder-feeder process suggests one way to anticipate development of such snowbands in the future, as demonstrated by other similar events on other days in Oklahoma and Illinois. As the cloud bands were advected equatorward, they ingested drier air and dissipated. Among the several lakeeffect bands observed on 23 January 2003, one notable band occurred downwind of Lake Kentucky. Midlake convergence of the land breeze may have initially produced a narrow cloud band that broadened as the land breeze ended. That the snowbands due to the HCRs and lake effect were both associated with heat and/or moisture fluxes from the earth's surface highlights the potential importance of ground-and water-surface temperature measurements for accurate numerical weather prediction.

Snow bands over the Gulf of Finland in wintertime

“…Associated with these convective cells, some narrow offshore bands of weak precipitation perpendicular to the coastline were simulated, mainly between 258 and 278E, as recorded by the radar. The morphology and the quasistationarity of these observed and simulated snow bands strongly suggest that they developed from horizontal convective rolls (HCR) (Schultz et al, 2004). The mechanism is well-known (e.g.…”

“…Over an open sea, this convection typically produces two structures: cellular convection or horizontal convective rolls (e.g. Kuo, 1963;Miura, 1986;Shirer, 1986;Schultz et al, 2004), depending on the atmospheric stability, the vertical shear and the horizontal wind. In contrast to the open sea, constrained water bodies take on a greater variety of structures near land.…”

Snowbands over the English Channel and Irish Sea during cold‐air outbreaks

“…This works well because the two are usually well correlated, but occasionally a situation arises where using the wind direction is a poor predictor of band orientation (e.g. Schultz et al, 2004).…”

Technical challenges and solutions in representing lakes when using WRF in downscaling applications

“…Lake-effect precipitation has also been documented outside the Great Lakes as well, such as in Lake Champlain (Tardy, 2000;Laird et al, 2009), Lake Tahoe , and the Great Salt Lake (Carpenter, 1993;Steenburgh and Onton, 2001). A review by Schultz et al (2004) states that lake-effect snowfall has been observed to occur over lakes with fetches of only 30 to 50 km, citing prior studies over Bull Shoals Lake of Arkansas (Wilken, 1997) as well as Lake Tahoe and Pyramid Lake in Nevada Huggins et al, 2001). Interactions between the lakes and surrounding regions are also strong in tropical environments as well.…”