A Comparison of Two Banded, Heavy Snowstorms with Very Different Synoptic Settings

Abstract

Two banded, heavy snowstorms that occurred over the northern mid-Atlantic region are compared and contrasted. On 6-7 January 2002, a narrow, intense band of heavy snow was observed, along with several other weaker bands, embedded within a large area of moderate snow. On 19-20 January 2002, a single, broader band of heavy snow was observed, embedded within a broken area of light snow.The synoptic-scale settings associated with these two storms were strikingly dissimilar. In the first case, strong quasigeostrophic (QG) forcing for ascent was present just to the south of the heavy snowfall area. A highly amplified longwave trough was located over the Mississippi River valley, while a compact shortwave trough moved northward, up the east side of the longwave trough. The result was robust cyclogenesis off of the midAtlantic coast. In the second case, the relatively weaker QG forcing for ascent was located much farther southwest of the snowband. The flow aloft was much less amplified, with weaker cyclogenesis occurring off of the midAtlantic coast.Analysis of the frontal scale environments for both cases indicated that the snowbands were each associated with the collocation of midtropospheric frontogenesis and reduced stability. In the first case, evidence is shown that a layer of potential symmetric instability (PSI) was located just above a deep, sloping zone of frontogenesis, in the presence of deep near-saturated conditions. In the second case, evidence is shown that a layer of potential instability (PI), associated with rapidly decreasing relative humidity with height, was located just above a shallow, sloping zone of frontogenesis. In addition, it is shown that a particularly favorable thermal environment for snowflake growth and accumulation became collocated with the heavy snowband. It is hypothesized that the differences in the intensity and horizontal extent of the bands observed with these two events resulted from differing atmospheric responses associated with the areal extent of large-scale and frontogenetical forcing, moisture availability, degree of instability, and specific thermal profiles.

Banded Convection Caused by Frontogenesis in a Conditionally, Symmetrically, and Inertially Unstable Environment

“…In this paper, we calculate the instability parameters using the both the geostrophic wind and the total wind. In general, calculations performed using the geostrophic wind indicated more instability, as found in previous studies (e.g., Clark et al 2002;Jurewicz and Evans 2004;Novak et al 2006). Whether the geostrophic or total wind is more appropriate in calculating symmetric and inertial instability parameters remains an open question (e.g., Gray and Thorpe 2001;Novak et al 2006, 19-21;NielsenGammon and Gold 2007).…”

“…2713).] In contrast, others prefer using the total wind (e.g., Gray and Thorpe 2001;Clark et al 2002;Jurewicz and Evans 2004;Novak et al 2004Novak et al , 2006. In this paper, we calculate the instability parameters using the both the geostrophic wind and the total wind.…”

Correlations between Analyses and Forecasts of Banded Heavy Snow Ingredients and Observed Snowfall

“…While much research and forecaster training during the past several years has focused on applying these concepts to major snowstorms, a growing body of case study research indicates that events associated with lighter snowfalls also feature many of the same signatures commonly associated with heavier snow events (e.g., Banacos 2003;Schumacher 2003;Jurewicz and Evans 2004;Evans 2006;Novak et al 2006;Wagner 2006). The implication of this finding is that some of the conceptual models that have been applied to forecasting heavy snow can also be applied to forecasting lighter snowfall events.…”

Comparison of Ensemble Kalman Filter–Based Forecasts to Traditional Ensemble and Deterministic Forecasts for a Case Study of Banded Snow

“…Frequently associated with extreme snowfall (e.g., Martin 1998;Nicosia and Grumm 1999;Gaffin et al 2003;Jurewicz and Evans 2004;Moore et al 2005;Market et al 2006;Cronce et al 2007), banded snow is not always resolved or well forecast by numerical models. Predictability issues are compounded by the high degree of uncertainty in synoptic-scale (200-1000 km) flows in the presence of moist convection (e.g., Zhang et al 2003;Zhang 2005;Zhang et al 2007).…”

“…Bands have been noted along cold and warm fronts (Houze et al 1976;Nicosia and Grumm 1999;Novak et al 2004), and in the commahead region of midlatitude cyclones during the cool season in the northeast United States (Novak et al 2004). When forecasting for banded snow, there are several ingredients that can be used to predict the likelihood of banding (e.g., Wiesmuller and Zubrick 1998; Nicosia and Grumm 1999;Schultz and Schumacher 1999;Wetzel and Martin 2001;Jurewicz and Evans 2004;Novak et al 2004;2010;Moore et al 2005). These include a midlevel (;700 hPa) frontogenesis (F) maximum northwest of the surface low, where …”