An Observational Study of Cold Season–Banded Precipitation in Northeast U.S. Cyclones

Abstract

A climatological and composite study of banded precipitation in the northeast United States during the cold season (October–April) is presented. Precipitation systems in the northeast United States in April 1995 and from October 1996 to April 2001 that exhibited greater than 25.4 mm (1 in.) of rainfall, or 12.7 mm (0.5 in.) liquid equivalent, were identified as cases for study. A total of 111 cases were identified during this period, of which 88 had available radar data. Of these cases, 75 exhibited banded structure whereas 13 did not. A band classification scheme was developed from a subset of study cases. Application of the classification scheme to the 88 cases revealed that banded cases can exhibit a variety of banded events during their evolution. Single-banded events were the most common (48), followed by transitory (40), narrow cold frontal (36), multi (29), and undefined (9). Further investigation of the single-banded events highlighted banded structure in the comma-head portion of storms, with 81% of these events exhibiting a majority of their length in the northwest quadrant of the surface cyclone. Composites were calculated for cases exhibiting single-banded events in the northwest quadrant of the surface cyclone and for nonbanded cases to distinguish synoptic and mesoscale flow regimes associated with banded events and nonbanded cases. The banded composite was marked by cyclogenesis and the development of a closed midlevel circulation. This flow configuration was associated with deformation and strong midlevel frontogenesis northwest of the surface cyclone center, which coincided with the mean band position. The nonbanded composite exhibited a much weaker cyclone located in the confluent entrance region of an upper-level jet. The absence of a closed midlevel circulation in the nonbanded composite limited deformation and associated frontogenesis northwest of the surface cyclone. Cross-section analysis through the respective composite frontogenesis maxima showed that the banded composite frontal zone exhibited stronger and deeper frontogenesis and weaker conditional stability than the nonbanded composite frontal zone. Case studies from the northeast United States confirm the composite results, highlighting the importance of deep-layer frontogenesis coincident with weak conditional stability. These results are in qualitative agreement with the Sawyer–Eliassen equation, which predicts that the frontogenetical response will be enhanced (reduced) in the presence of small (large) moist symmetric stability.

A Comparison of CMIP3 Simulations of Precipitation over North America with Observations: Daily Statistics and Circulation Features Accompanying Extreme Events

“…Such deficiencies may stem from the inability of the models to resolve or accurately simulate some of the processes that generate extreme precipitation in the northeastern part of North America. These processes can include moist convection and tropical cyclones in the warm season (Dai 2001;Christian et al 2003;Riemann-Campe et al 2009;Kunkel et al 2010;Kunkel et al 2012;Manganello et al 2012), mesoscale precipitation bands associated with extratropical cyclones (Novak et al 2004), and other features of the synoptic atmospheric structure that were not explored in this paper (Milrad et al 2010). The atmospheric circulation patterns during extreme events in northern Canada are interesting in that they appear to result in low-level moisture flow that originates from the Pacific Ocean in winter and Gulf of Mexico in summer (Figs.…”

SYNOPTIC METEOROLOGY | Fronts

“…Instead, the flow may consist of convective elements embedded within the ascent (the so-called escalatorelevator paradigm of Neiman et al, 1993) or may be characterized by banded convective precipitation (e.g., Novak et al, 2004).…”

The use of potential vorticity inversion to evaluate the effect of precipitation on downstream mesoscale processes

“…The manner in which moisture, lift and instability organize to create frozen precipitation in either banded or non-banded form has been previously investigated by Nicosia and Grumm (1999), Banacos (2003), Jurewicz and Evans (2004), Novak et al (2004) and Moore et al (2005), among others. This research demonstrates that the mesoscale processes (frontogenesis, conditional and symmetric instability) attendant with frozen precipitation can be viewed as the result of interactions between largescale conveyor belts.…”