Sunday, 22 January 2017
4E (Washington State Convention Center )
The coastal northeastern region of the United States from Delaware to Maine experiences many snow storms during the winter months. These storms often develop elongated bands with locally higher snow rates. The intense snow fall can accumulate rapidly, bringing a city to a standstill. Snow bands can also yield large gradients in snow fall over small distances which are difficult to predict. Radar observations show that snow bands lasting more than an hour occur in two main modes. Snow bands > 250 km in length usually only occur one at a time during a storm and are labeled single bands. Multi-bands are sets of roughly parallel bands each less than < 250 km in length which tend to move as a group. Individual winter storms in the Northeast can feature no bands, single bands, multi-bands, or both single and multi-bands at the same time. This study examines the interaction among concurrent multi-bands and single bands. North American Regional Reanalysis and radar data from six National Weather Service operational radars are used to assess band characteristics in the context of cyclone structure. In some storms, multi-bands will radiate away from the low pressure center and converge with a large single band, in effect fueling heavy snow within the single band. In a geographic framework, these multi-bands often move roughly perpendicular to storm motion. In other storms, snow bands are relatively stationary with respect to the low pressure center and hence move parallel to storm motion. The parallel-moving bands tend not to converge with each other. Convergent multi-bands occur in the northwest and northeast quadrants of the storm. Parallel-moving bands usually occur to the northwest of the low center. These results suggest that there may be more than one way to originate and maintain a set of multi-band snow bands.
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