An Unusual Hailstorm on 24 June 2006 in Boulder, Colorado. Part I: Mesoscale Setting and Radar Features

An unusual, isolated hailstorm descended on Boulder, Colorado, on the evening of 24 June 2006. Starting with scattered large, flattened, disk-shaped hailstones and ending with a deluge of slushy hail that was over 4 cm deep on the ground, the storm lasted no more than 20 min and did surprisingly lit...

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Bibliographic Details
Published in:Monthly weather review 2008-08, Vol.136 (8), p.2813-2832
Main Authors: SCHLATTER, Paul T, SCHLATTER, Thomas W, KNIGHT, Charles A
Format: Article
Language:English
Subjects:
Air
Air parcels
Boundary layer
Boundary layers
Convective available potential energy
Density
Doppler sonar
Earth, ocean, space
Echoes
Exact sciences and technology
External geophysics
Global positioning systems
GPS
Hail
Hailstones
Hailstorms
Ice
Laboratories
Meteorological conditions
Meteorology
Moisture content
Mountains
Potential energy
Precipitation
Radar
Radar signatures
Reflectance
Storms
Surveillance radar
Vegetation
Vertical shear
Vertical wind shear
Weather
Wind
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Summary:An unusual, isolated hailstorm descended on Boulder, Colorado, on the evening of 24 June 2006. Starting with scattered large, flattened, disk-shaped hailstones and ending with a deluge of slushy hail that was over 4 cm deep on the ground, the storm lasted no more than 20 min and did surprisingly little damage except to vegetation. Part I of this two-part paper examines the meteorological conditions preceding the storm and the signatures it exhibited on Weather Surveillance Radar-1988 Doppler (WSR-88D) displays. There was no obvious upper-tropospheric forcing for this storm, vertical shear of the low-level wind was minimal, the boundary layer air feeding the storm was not very moist (maximum dewpoint 8.5°C), and convective available potential energy calculated from a modified air parcel was at most 1550 J kg−1. Despite these handicaps, the hail-producing storm had low-level reflectivity exceeding 70 dBZ, produced copious low-density hail, exhibited strong rotation, and generated three extensive bounded weak-echo regions (BWERs) in succession. The earliest of these filled with high reflectivities as the second one to the south poked up through precipitation-filled air. This has implications for low-density hail growth, as discussed in Part II.
ISSN:0027-0644
1520-0493
DOI:10.1175/2008MWR2337.1