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Stanley A. Changnon
and
Jonathan Burroughs

Abstract

The most damaging hailstorm ever recorded moved from eastern Kansas to southern Illinois during an 8-h period on 10 April 2001, depositing 2.5- to 7.5-cm-diameter hailstones along a 585-km path. A classic long-lived supercell storm was the cause of the record hailfalls. The record-large hailswath size, large and often windblown hailstones, and movement over portions of the St. Louis and Kansas City urban areas led to $1.5 billion in insured losses. This tristate hailstorm and other adjacent hailstorms collectively created $1.9 billion in insured losses in a 2-day period, becoming the ninth most costly weather catastrophe in the United States since property insurance records began in 1949.

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James P. Kossin
,
Brian D. McNoldy
, and
Wayne H. Schubert

Abstract

A collection of images depicting various swirling patterns within low-level cloud decks in hurricane eyes is presented and described. A possible causal mechanism for the presence of these cloud patterns is suggested by comparison of the observed cloud patterns with the evolution of passive tracers in a simple 2D barotropic model. The model is initialized with a barotropically unstable flow field that imitates the observed flows in hurricanes, and numerical integration of this field simulates vigorous mixing between eye and eyewall. During the mixing process, passive tracers initially embedded in the flow form swirling patterns in the eye that are strikingly similar to cloud patterns often observed in the eyes of hurricanes.

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Katharine M. Kanak
and
Jerry M. Straka

Abstract

Photographic documentation of a rare and enigmatic reticular cloud formation that occurred in conjunction with a thunderstorm outflow anvil on 4 June 1995 at 2230 UTC at Norman, Oklahoma, is presented. A National Weather Service vertical sounding, taken within 1 h of the occurrence of the formation at Norman, is also presented. Possible formation mechanisms for these unusual cloud features are discussed.

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John P. Monteverdi
,
Warren Blier
,
Greg Stumpf
,
Wilfred Pi
, and
Karl Anderson

Abstract

On 4 May 1998, a pair of tornadoes occurred in the San Francisco Bay Area in the cities of Sunnyvale (F2 on the Fujita scale) and Los Altos (F1). The parent thunderstorm was anticyclonically rotating and produced tornadoes that were documented photographically to be anticyclonic as well, making for an extremely rare event. The tornadic thunderstorm was one of several “pulse type” thunderstorms that developed on outflow boundaries on the left flank of an earlier-occurring thunderstorm east of San Jose. Satellite imagery showed that the tomadic storm moved northwestward along a sea-breeze boundary and ahead of the outflow boundary associated with the prior thunderstorms. The shear environment into which the storm propagated was characterized by a straight hodograph with some cyclonic curvature, and by shear and buoyancy profiles that were favorable for anticyclonically rotating updrafts. Mesoanticyclones were detected in the Monterey (KMUX) radar data in association with each tornado by the National Severe Storm Laboratory's (NSSL) new Mesocyclone Detection Algorithm (MDA) making this the only documented case of a tornadic mesoanticyclone in the United States that has been captured with WSR-88D level-II data. Analysis of the radar data indicates that the initial (Sunnyvale) tornado was not associated with a mesoanticyclone. The satellite evidence suggests that this tornado may have occurred as the storm ingested, tilted, and stretched solenoidally induced vorticity associated with a sea-breeze boundary, giving the initial tornado nonsupercellular characteristics, even though the parent thunderstorm itself was an anticyclonic supercell. The radar-depicted evolution of the second (Los Altos) tornado suggests that it was associated with a mesoanticyclone, although the role of the sea-breeze boundary in the tornadogenesis cannot be discounted.

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John A. Knaff
and
John F. Weaver

Abstract

A large, low-level thunderstorm outflow boundary was observed as it exited from beneath the cirrus canopy of Hurricane Luis following a period of intense convection in the storm’s eyewall. A description of the feature and a short summary of its behavior are presented.

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Neil F. Laird

Abstract

No abstract available.

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Hisashi Ozawa
,
Kumiko Goto-Azuma
,
Koyuru Iwanami
, and
Roy M. Koerner

Abstract

A thin rotor cloud was observed on the lee side of Penny Ice Cap in the Canadian Arctic on 21 April 1996. The cloud consisted of thin cirriform layers, so that its motion was clearly observed. By means of time-lapse camera photography, the velocity of the cloud rotation was estimated to be around 2 m s−1. It is suggested that the existence of a high humidity layer at the bottom of an inversion layer is a key factor for the formation of the thin rotor cloud.

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J. Christopher Clarke

Abstract

An unusual cloud feature was noted over the south Texas coast on the morning of 14 March 1997. This feature shares some characteristics with the “morning glory” bores that are seen along the coast of northern Australia.

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Brian A. Klimowski
,
Mark R. Hjelmfelt
,
Matthew J. Bunkers
,
Don Sedlacek
, and
L. Ronald Johnson

Abstract

No abstract available.

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Frank M. Monaldo
,
Todd D. Sikora
,
Steven M. Babin
, and
Raymond E. Sterner

Abstract

No abstract available.

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