JEFFREY D. KELLEY
NOAA/NWS Weather Forecast Office
Hastings, Nebraska
DAVID M. SCHULTZ
Center for Atmospheric Science, School of Earth and Environmental Sciences
University of Manchester
United Kingdom
RUSS SCHUMACHER
Department of Atmospheric Science, Colorado State University
Fort Collins, Colorado
29th Conference on Weather Analysis and Forecasting, June 4-8, 2018
ABSTRACT
On 25 December 2016, a 984-hPa cyclone departed Colorado and moved into the Northern Plains. As this occurred, a nearby stationary arctic front was drawn into the circulation, wrapping cyclonically around the equatorward side of the cyclone. An intense mesoscale wind maximum formed within the cyclone’s comma head and descended to the top of the boundary layer where its leading edge became collocated with the arctic front. Steep lapse rates associated with cold air advection mixed the high winds to the surface, resulting in a narrow swath of winds exceeding 26 m s-1 from northeast Colorado to southwest Minnesota. The highest recorded wind gust was 35 m s-1 at Aurora, Nebraska. The formation and existence of this mesoscale wind maximum was associated with mountain waves and severe downslope winds over Colorado and Wyoming. The arctic front provided a stable layer, facilitating the transport of the downslope winds away from the immediate lee slope of the mountains and into the circulation of the cyclone. Despite an entirely different physical mechanism for this wind maximum, it exhibited similarities with a sting jet: origin in the mid-troposphere within the comma head, acceleration and descent of air out of the tip of comma head to the top of the boundary layer, decrease in temperature and relative humidity, and an existence separate from the cold conveyor belt of the cyclone.
Characteristics of this mesoscale wind maximum will be examined, along with evidence for its origination and evolution over time.
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