Cool-Season High Wind Events in the Northeast U.S. Jonas V. Asuma, Lance F. Bosart, Daniel Keyser Department of Atmospheric and Environmental Sciences University at Albany/SUNY John S. Quinlan, Thomas A. Wasula, Hugh W. Johnson, Kevin S. Lipton NOAA/NWS, Albany, NY Master’s Thesis Seminar 8 July 2010 NOAA/CSTAR Grant NA07NWS4680001
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Cool-Season High Wind Events in the Northeast U.S.
Cool-Season High Wind Events in the Northeast U.S. Jonas V. Asuma , Lance F. Bosart , Daniel Keyser Department of Atmospheric and Environmental Sciences University at Albany/SUNY John S. Quinlan, Thomas A. Wasula , Hugh W. Johnson, Kevin S. Lipton NOAA/NWS, Albany, NY - PowerPoint PPT Presentation
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Cool-Season High Wind Events in the Northeast U.S.
Jonas V. Asuma, Lance F. Bosart, Daniel Keyser
Department of Atmospheric and Environmental Sciences University at Albany/SUNY
John S. Quinlan, Thomas A. Wasula, Hugh W. Johnson, Kevin S. Lipton
NOAA/NWS, Albany, NY
Master’s Thesis Seminar8 July 2010
NOAA/CSTAR Grant NA07NWS4680001
• Motivation– Cool-season high wind events can
be damaging and in some cases challenging to forecast
• Objectives– Assess frequency of high wind
events– Identify mechanisms that lead to
severe surface winds– Present case study of one
extraordinary event
Overview
From Ashley and Black (2008)
Fatalities due to various wind-related hazards, 1980–2005.
Nonconvective wind fatalities
Tree-related nonconvective wind fatalities
• Background
• Data/Methodology
• Climatology
• Composite Analysis
• Case Study
• Synthesis/Conclusions
Outline
• Thunderstorm wind climatology– Kelley et al. (1985): Nontornadic
severe thunderstorm wind• Thunderstorm winds driven by
evaporatively-cooled downdrafts– Downbursts (Fujita and Byers 1977),
bow echos (e.g., Fujita 1978), derechos (Johns and Hirt 1987)
– Mesovortices can modulate location of strongest winds (e.g., Trapp and Weisman 2003)
• Johns (1993): – Described favorable cool-season
pattern for development of squall lines with extensive bow echo-induced wind damage
Background: Thunderstorm winds
From Johns (1993)
From Kelley et. al (1985)
• Kapela et al. (1995) constructed a checklist of features associated with the occurrence of strong post cold-frontal winds:– Strong unidirectional flow throughout the troposphere,
tropospheric-deep cold advection, steep low-level lapse rates, subsidence, presence of a dry intrusion, strong isallobaric gradient
• Niziol and Paone (2000): Identified typical cyclone track associated with high winds impacting Buffalo, NY– Also noted many features determined by Kapela et al. (1995)
Background: Gradient winds
t = −12 h t = 00 h t = +12 h
LL
L
• McCann (1978) determined necessary conditions for convective storms to produce high winds without lightning:– Small amount of potential instability, synoptic scale lifting, strong
winds at 3 to 5 km above surface• Conditions met during winter
• Koch and Kocin (1991) and Browning and Reynolds (1994) studied high-wind producing rain bands– Noted importance of dry intrusion on rain band and high wind
development– High winds occurred during and shortly after cold front passed
• Van den Broeke et. al (2005) studied the lightning production of two low CAPE, high shear convective lines– Conclusions suggest the occurrence of high wind during the cool
season not as dependent on CAPE as in the warm season
Background: Case Studies
• Climatology– NCDC thunderstorm and high wind reports– National Lightning Detection Network (NLDN) data
• Composites– NCDC thunderstorm and high wind reports– NCEP/NCAR 2.5° Reanalysis data
• Case Studies– NCDC thunderstorm and high wind reports– 1° Global Forecasting System (GFS) analyses– WSI 2-km NOWRAD Radar composites– National Lightning Detection Network (NLDN) data– Hourly surface observation data
Data
• Event determination– Domains: High wind reports from the Northeast (NE) for
15 Oct 1993 through 31 Dec 2008
– High wind definition: Wind measured ≥ 25 m s−1 or damaging winds of any magnitude
– Event definition: Any series of storm reports that are separated from each other by ≤ 12 h
• Events defined by type:– Pure Gradient (PG): Only gradient wind reports– Hybrid (HY): Both thunderstorm and gradient wind reports– Pure Convective (PC): Only thunderstorm wind reports
• PG events: If lightning struck within 1° radius and 1 h from any gradient wind report, PG event becomes HY event
Methodology (1 of 2)
• Composite– HY and PG event types subdivided based upon location
of initial NE report relative to surface cyclone• Northeast, Southeast, Southwest, Northwest quadrants• PC events subdivided into trough and ridge categories
– Composite time (t = 00 h): Determined to be hour (00, 06, 12, or 18 Z) closest to initial NE report
• For reports at 03, 09, 15, or 21 Z earlier hour chosen• Events composited by event type and subcategory
– Created report-relative composites• Grids shifted to location of initial NE report• Composites centered on centroid of initial NE reports for each
event type and subcategory
Methodology (2 of 2)
Shaded represents the percentage of the total days (N = 3260) studied that high winds occurred.
Climatology: High-wind daysGradient Thunderstorm
(%)
Shaded represents the percentage of the total days (N = 3260) studied that high winds occurred.
Climatology: High-wind daysGradient Thunderstorm
(%)
Histogram depicting the frequency of occurrence based upon the type of event
Climatology: Event type
Histogram depicting the frequency of occurrence based upon the month in which the initial NE report occurred
Climatology: Yearly
Histogram depicting the frequency of occurrence based upon the month in which the initial NE report occurred
Climatology: Monthly
Histogram depicting the frequency of occurrence based time of the initial NE report
Climatology: Hourly
Histogram depicting the frequency of occurrence based upon the number of reports accumulated
Climatology: Societal ImpactEvents that accumulated > 100 reports:
HY: 27; PG: 2; PC: 0Approximate average reports per event:
HY: 60; PG: 20; PC: 11
Histogram depicting the frequency of occurrence based either the location of the initial report or upper-level flow pattern
Climatology: Subcategories
Histogram depicting the frequency of occurrence based either the location of the initial report or upper-level flow pattern
• Strong forcing associated with the passage of a front in the presence of a potentially unstable air mass leads to development of a convective line– Vertical differential θe advection and an upper-tropospheric dry
intrusion lead to mid-level drying
• Deep cold-air advection in the presence of steep low-level lapse rates and strong low-level flow leads to high winds behind the cold front– Boundary layer stability and kinematic profile favorable for