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Climatological Aspects of Freezing Rain in the Eastern U.S. Christopher M. Castellano, Lance F. Bosart, and Daniel Keyser Department of Atmospheric and Environmental Sciences University at Albany, State University of New York, Albany, NY John Quinlan and Kevin Lipton NOAA/NWS/WFO Albany, NY - PowerPoint PPT Presentation
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Climatological Aspects of Freezing Rain in the Eastern U.S.
Christopher M. Castellano, Lance F. Bosart, and Daniel KeyserDepartment of Atmospheric and Environmental Sciences
University at Albany, State University of New York, Albany, NY
John Quinlan and Kevin LiptonNOAA/NWS/WFO Albany, NY
Northeast Regional Operational Workshop XIII3 November 2011, Albany, NY
NOAA/CSTAR Grant: NA01NWS4680002
Motivation and Objectives
Data and Methodology
Freezing Rain Climatology
Significant Freezing Rain Events
Summary
Outline
Freezing rain undermines public infrastructure, disrupts local and regional economies, and endangers human life and safety
Freezing rain presents a major forecast challenge due to the combined influence of synoptic, mesoscale and microphysical processes
Freezing rain is historically most prevalent and destructive in the eastern U.S.
Motivation
Fig 2. Changnon (2003). The amount of loss (millions of dollars expressed in 2000 values) from ice-storm catastrophes in each climate region during 1949–2000. Values in parentheses are the average losses per catastrophe.
Fig 3. Changnon (2003). The number of ice-storm catastrophes in each climate region during 1949–2000. Values in parentheses are those catastrophes that only occurred within the region.
Motivation
Construct a long-term (1975–2010) climatology of freezing rain for the eastern U.S.
Identify significant freezing rain events based on duration, ice accretion/damage, spatial characteristics, and thermal structure
Determine synoptic-scale environments and mesoscale features conducive to significant freezing rain events
Provide forecasters with greater situational awareness of synoptic and mesoscale processes that modulate the evolution of freezing rain events
Objectives
Construct a long-term (1975–2010) climatology of freezing rain for the eastern U.S.
Identify significant freezing rain events based on duration, ice accretion/damage, spatial characteristics, and thermal structure
Determine synoptic-scale environments and mesoscale features conducive to significant freezing rain events
Provide forecasters with greater situational awareness of synoptic and mesoscale processes that modulate the evolution of freezing rain events
Objectives
Freezing Rain Climatology:– Acquired hourly surface observations for 91 first-order stations
from NCDC’s Integrated Surface Database– Analyzed the temporal and spatial variability of freezing rain and
freezing drizzle
Significant Freezing Rain Events:– Identified significant freezing rain events at two stations:
Greensboro, NC [GSO] and Worcester, MA [ORH]– Generated synoptic composite maps for significant events at
each station using 2.5° NCEP/NCAR reanalysis data
Data and Methodology
Geographical domain: 32°N, 90°W – 48°N, 66°W
Freezing rain event: 1+ h of measureable freezing rain (FZRA) and/or freezing drizzle (FZDZ)
Significant freezing rain event: 6+ h of measureable freezing rain (FZRA) observed within a 24-h period
Data and Methodology: Definitions
* Sequential FZRA/FZDZ observations must be within 6 h of each other to be considered part of the same event
ORH
GSO
Domain and First-Order Stations
Average number of hours of freezing rain/freezing drizzle per season.
Climatology: Freezing Rain Hours
Average number of freezing rain events per season.
Climatology: Freezing Rain Events
Average number of significant freezing rain events per season.
Climatology: Significant FZRA Events
Percentage of freezing rain events qualifying as “significant.”
Climatology: Significant Event Ratio
Identified 38 significant events at GSO and 44 significant events at ORH
Examined 500-hPa geopotential heights and anomalies
Examined 300-hPa wind speed, 1000–500-hPa thickness, and mean sea-level pressure
Examined 850–700-hPa layer winds, precipitable water, and standardized precipitable water anomalies
Performed analyses at t = 0 and t − 24 h preceding events
Analysis of Significant Freezing Rain Events
500-hPa geopotential height (black contours, every 60 m) and anomalies (shaded, every 30 m)
N = 38
500-hPa geopotential height (black contours, every 60 m) and anomalies (shaded, every 30 m)
N = 38
N = 38
300-hPa wind speed (shaded, every 5 m s-1), 1000–500-hPa thickness (dashed contours, every 6 dam), and mean sea-level pressure (solid contours, every 4 hPa)
N = 38
300-hPa wind speed (shaded, every 5 m s-1), 1000–500-hPa thickness (dashed contours, every 6 dam), and mean sea-level pressure (solid contours, every 4 hPa)
850–700-hPa layer wind (arrows, m s-1), 850–700-hPa layer 0°C isotherm (dashed contour), precipitable water (green contours, every 4 mm), and standardized precipitable water anomalies (shaded, every 0.5 σ)
N = 38
850–700-hPa layer wind (arrows, m s-1), 850–700-hPa layer 0°C isotherm (dashed contour), precipitable water (green contours, every 4 mm), and standardized precipitable water anomalies (shaded, every 0.5 σ)
N = 38
500-hPa geopotential height (black contours, every 60 m) and anomalies (shaded, every 30 m)
N = 44
500-hPa geopotential height (black contours, every 60 m) and anomalies (shaded, every 30 m)
N = 44
300-hPa wind speed (shaded, every 5 m s-1), 1000–500-hPa thickness (dashed contours, every 6 dam), and mean sea-level pressure (solid contours, every 4 hPa)
N = 44
300-hPa wind speed (shaded, every 5 m s-1), 1000–500-hPa thickness (dashed contours, every 6 dam), and mean sea-level pressure (solid contours, every 4 hPa)
N = 44
850–700-hPa layer wind (arrows, m s-1), 850–700-hPa layer 0°C isotherm (dashed contour), precipitable water (green contours, every 4 mm), and standardized precipitable water anomalies (shaded, every 0.5 σ)
N = 44
850–700-hPa layer wind (arrows, m s-1), 850–700-hPa layer 0°C isotherm (dashed contour), precipitable water (green contours, every 4 mm), and standardized precipitable water anomalies (shaded, every 0.5 σ)
N = 44
Greatest frequency of freezing rain hours observed east of the Appalachian Mountains, in upstate New York, and in central New England
Sharp gradients in frequency exist across the Appalachians and along the Mid-Atlantic and New England coasts
Greatest frequency of significant events also occurs east of the southern Appalachians and in the interior Northeast
Higher percentage of freezing rain events qualify as significant in the Southeast than anywhere else
Summary: Freezing Rain Climatology
Freezing rain events are coincident with an amplifying 500-hPa ridge along the East Coast, an upstream trough between the Rockies and the Midwest, and negative 500-hPa geopotential height anomalies to the northeast
Freezing rain events occur near an equatorward entrance region of a confluent 300-hPa jet, within a 1000–500-hPa thickness ridge
Freezing rain events feature low-to-midlevel moisture transport and warm-air advection via deep southwesterly flow
Summary: Significant Freezing Rain EventsSimilarities
ORH events feature more amplified upper-level height anomalies, thermal trough/ridge patterns, and moisture anomalies than GSO events
GSO events primarily rely on Gulf of Mexico as sole moisture source, whereas ORH events likely rely on Atlantic Ocean as an additional moisture source
GSO events are typically associated with cold-air damming east of the Appalachians
ORH events are typically associated with ageostrophic northerlies that reinforce cold air on the poleward side of a mature warm front
Summary: Significant Freezing Rain EventsDifferences