Synoptic and Mesoscale Aspects of Ice Storms in the Northeastern United States A43C-0145 American Geophysical Union 2012 Fall Meeting San Francisco, CA 3–7 December, 2012 Research supported by NOAA/CSTAR Grant: NA01NWS4680002 Christopher M. Castellano1*, Lance F. Bosart1, Daniel Keyser1, John Quinlan2, and Kevin Lipton2 1Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY 2NOAA/NWS/WFO Albany, NY *Corresponding author email: [email protected] Ice Storm Climatology Motivation Summary: Climatology N = 137 • Ice storms endanger human life and safety, undermine public infrastructure, and disrupt local and regional economies NTOT = 137 NSYN = 25 • 81.8% of ice storms were local, regional, or subsynoptic, while only 18.2% were synoptic • Ice storms are historically prevalent and destructive in the northeastern U.S. • Ice storms present a major operational forecasting challenge Figure 1. Map indicating the 14 county warning areas (CWAs) included in the climatology. Figure 2. Archetypical surface synoptic weather patterns associated with freezing precipitation east of the Rocky Mountains. Caption and figure reproduced from Fig. 2 in Rauber et al. (2001). Objectives Figure 3. Number of ice storms impacting each county during the 1993–2010 period. Figure 4. Frequency distribution of ice storms by spatial coverage. • Ice storms were primarily associated with Type G (N=65), Type BC (N=30), or Type EF (N=25) synoptic weather patterns Figure 5. Distribution of total ice storms (blue) and synoptic ice storms (red) by event type. Summary: Composite Analysis Composite Analysis: Type G Events (N=24) Similarities • Establish a cool-season climatology (Oct 1993–Apr 2010) of ice storms in the northeastern U.S. A • Ice storms are coincident with an upstream trough, an amplifying downstream ridge, and confluent upper-level flow over eastern North America • Identify environments conducive to ice storms and dynamical mechanisms responsible for freezing rain A′ • Provide forecasters with greater situational awareness of the synoptic and mesoscale processes that govern the evolution of ice storms 10 m s−1 • Ice storms are accompanied by low- to midlevel moisture transport and warm advection 10 x 10−11 K m s−1 A Data and Methodology Figure 6. Composite 500-hPa geopotential height (black, every 6 dam) and anomalies (shaded, every 30 m). Ice Storm Climatology Figure 7. Composite 850–700-hPa layer-averaged wind (arrows, m s−1) and 0°C isotherm (dashed red), precipitable water (green, every 4 mm), and standardized precipitable water anomalies (shaded, every 0.5 σ). Figure 8. Composite 300-hPa wind speed (shaded, every 5 m s−1), 1000–500-hPa thickness (dashed, every 6 dam), and mean sea level pressure (black, every 4 hPa). Figure 9. Composite 700-hPa temperature (dashed, every 3 K), Q-vectors (arrows, 10−11 K m−1 s−1), and RHS Q-vector form of QG omega equation (shaded, every 2.5 x 10−16 K m−2 s−1). A′ 5 m s−1 5 cm s−1 Figure 10. Frontogenesis [shaded, every 1 K (100 km)−1 (3 h)−1], potential temperature (black, every 2 K), wind speed (green, every 5 m s−1), vertical velocity (dashed red, every 5 μb s−1), and ageostrophic circulation (arrows). 1. Any event listed as an “Ice Storm” 2. Any event with significant ice accretion (≥ 0.25 in) 3. Any event with damage attributed to ice accretion Differences A • Type G events are preceded by a deep cold-air intrusion, whereas Type BC events are preceded by persistent warm air aloft • Classified ice storms by spatial coverage: Counties Affected Local ≤3 AND ≤3 Regional 4–12 AND ≤6 A′ CWAs Affected Subsynoptic 13–48 AND ≤6 Synoptic > 48 OR >6 • Partitioned ice storms by synoptic weather patterns commonly associated with freezing rain (Fig. 2) Composite Analysis • Identified 35 ice storms impacting the ALY CWA 10 m s−1 10 x 10−11 K m s−1 A Figure 11. As in Fig. 6, except for Type BC events. Figure 12. As in Fig. 7, except for Type BC events. Figure 13. As in Fig. 8, except for Type BC events. Figure 14. As in Fig. 9, except for Type BC events. A′ 5 m s−1 5 cm s−1 Case Study: 11–12 Dec 2008 Ice Storm Impacts Synoptic Evolution Mesoscale Dynamics • 74 counties and 8 CWAs affected • Numerous reports of ice accretion exceeding 0.50 in (1.27 cm) • More than 1 million customers lost power 1200 UTC 11 Dec 2008 1800 UTC 11 Dec 2008 081212/0600 GYX (Gray, ME) Case Study • QG forcing for ascent, frontogenesis, and ageostrophic transverse circulation are notably stronger during Type BC events Summary: Case Study • Significant icing occurred on the cold side of a warm front associated with a northeastward moving surface cyclone (a) Figure 16. Map highlighting the 74 counties impacted by the 11–12 Dec 2008 ice storm. • During Type G events, the Gulf of Mexico is the primary moisture source, but during Type BC events, the Atlantic Ocean also serves a crucial role Figure 15. As in Fig. 10, except for Type BC events. • Generated synoptic composite maps (2.5° NCEP– NCAR reanalysis data) and composite cross sections (0.5° Climate Forecast System Reanalysis [CFSR] data) centered on Albany, NY (KALB), for the two most common synoptic patterns • Performed analyses at the synoptic time nearest the midpoint of each event • Ice storms occur in association with quasigeostrophic (QG) ascent and frontogenetical forcing beneath an equatorward jet entrance region • Ice storms occur within a region of ageostrophic northerlies on the cold side of a surface warm font Composite Analysis: Type BC Events (N=7) • Catalogued ice storms impacting 14 NWS CWAs (Fig. 1) using NCDC Storm Data: Size • Ice storm occurrence is modulated by complex topography and proximity to large bodies of water (b) (a) (b) Figure 18. (a) 300-hPa wind speed (shaded, every 5 m s−1), 1000–500-hPa thickness (dashed, every 6 dam), and mean sea level pressure (black, every 4 hPa). (b) Precipitable water (shaded, every 4 mm), 850–700-hPa layer-averaged θe (white, every 10 K), and 850–700-hPa layer-averaged moisture transport (arrows, expressed as the product of wind velocity and mixing ratio, multiplied by 100). Figure 20. (a) Mean sea level pressure (black, every 2 hPa) and 10-m streamlines (blue). (b) 2-m temperature (red, every 2°C; dashed contour marks the 0°C isotherm). Surface elevation is shaded every 200 m. 0000 UTC 12 Dec 2008 0600 UTC 12 Dec 2008 Figure 22. Skew-T with temperature (red, °C), dewpoint (blue, °C), and wind (barbs, kts). The 0°C isotherm is highlighted in purple. • Southerly low- to midlevel winds transported high θe air poleward, providing ample moisture for heavy and prolonged freezing rain • Complex terrain enhanced the northerly surface flow poleward of the warm front, which thereby reinforced subfreezing air and strengthened the confluence and associated frontogenesis • Used 0.5° CFSR data to create maps illustrating the synoptic evolution and dynamical forcing during the 11–12 Dec 2008 ice storm • Sounding profiles were characterized by surfacebased subfreezing layers, elevated melting layers, saturated conditions, and veering low-level winds • Utilized radiosonde data from the University of Wyoming and calculated backward trajectories from the NOAA HYSPLIT model to examine the local thermodynamic environment in the ice storm region • Air parcels in the subfreezing layer arrived from interior Canada (cP air mass), while air parcels above the inversion had extensive contact with the western Atlantic Ocean (mT air mass) Figure 17. Quantitative precipitation estimates for the 24-h period ending at 1200 UTC 12 Dec 2008. From the National Mosaic & Multi-sensor QPE. (a) Figure 19. As in Fig. 18, except at 0000 UTC 12 Dec 2008. (b) (a) Figure 21. As in Fig. 20, except at 0600 UTC 12 Dec 2008. (b) Figure 23. 120-h backward trajectories ending at Gray, ME (GYX).