Cool-Season High Wind Events in the Northeast U.S.
description
Transcript of 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
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
Climatology: Subcategories
Focus on these for composite analysis
MSLP (hPa, solid); precipitable water (mm, shaded); 1000–500 hPa thickness (dam, dashed); 1000 hPa total wind (kt, barbs); initial report (star)
Southeast Composite: Surface
HY (N = 71)
PG (N = 45)
(mm)
t = 00 h
Six Hourly Southeast Composite Cyclone Track: Pure Gradient vs. Hybrid; MSLP (hPa) is boxed; initial NE report (star)
Southeast Composite: Cyclone Track
PG (N = 45)
HY (N = 71)
t = 00 h
Loci of initial report
−24 h
+24 h
HY Southeast Composite: Cross Section
HY (N = 71)
(%)
θe (K, black); relative humidity(%, shaded); vertical motion (μb s−1, solid; red-upward, blue-downward); total wind (kt, barbs); initial report (star)
θe (K, black); relative humidity(%, shaded); vertical motion (μb s−1, solid; red-upward, blue-downward); total wind (kt, barbs); initial report (star)
PG Southeast Composite: Cross Section
PG (N = 45)
(%)
MSLP (hPa, solid); precipitable water (mm, shaded); 1000–500 hPa thickness (dam, dashed); 1000 hPa total wind (kt, barbs); initial report (star)
PG Southwest Composite: Surface
PG (N = 55)
t = 00 h
(mm)
t = 00 h
(%)
PG (N = 55)
PG Southwest Composite: Cross Section
θe (K, black); relative humidity(%, shaded); vertical motion (μb s−1, solid; red-upward, blue-downward); total wind (kt, barbs); initial report (star)
Composite sounding taken at the location of composite initial NE report at t = −06 h, t = 00 h, and t = +06 h
PG (N = 55)
PG Southwest Composite: Sounding
• Resulted in two fatalities• Caused $3.5 million in
damage in New York State
• Produced 85 kt wind gust recorded at Saratoga County Airport
• Accumulated most high wind reports in the NE (267 total reports)– 242 gradient reports– 25 thunderstorm reports
• Fits the HY southeast and PG southwest paradigms
Gradient
Thunderstorm
All High Wind Reports
85 kt gust at 15 Z
17 Feb 2006: Overview
Six Hourly Cyclone Track: MSLP (hPa) is boxed; initial NE report (star)
17 Feb 2006: Cyclone Track
−24 h
+24 h
17 Feb case
HY composite (N = 71)
t = 00 h
Loci of initial NE report
16 Feb 2006: Surface
(mm)
MSLP (hPa, solid); precipitable water (mm, shaded); 1000–500 hPa thickness (dam, dashed); 1000 hPa total wind (kt, barbs)
t = −12 h18 Z
storm reportsComposite
17 Feb 2006: Surface
(mm)
MSLP (hPa, solid); precipitable water (mm, shaded); 1000–500 hPa thickness (dam, dashed); 1000 hPa total wind (kt, barbs)
t = 00 h06 Z
storm reportsComposite
17 Feb 2006: Surface
(mm)
MSLP (hPa, solid); precipitable water (mm, shaded); 1000–500 hPa thickness (dam, dashed); 1000 hPa total wind (kt, barbs)
t = +12 h18 Z
storm reportsComposite
17 Feb 2006: Radar/Surface Obs17 FEB 06: 12 Z
t = +06 h
17 Feb 2006: Radar/Surface Obs17 FEB 06: 12 Z
t = +06 h
Gradient
Thunderstorm
Lightning
17 Feb 2006: Radar/Surface Obs17 FEB 06: 15 Z
t = +09 h
Multiple Bowing Segments
Post-Frontal Gusting
Pre-Frontal Gusting
17 Feb 2006: Radar/Surface Obs17 FEB 06: 15 Z
t = +09 h
Gradient
Thunderstorm
Lightning
17 Feb 2006: Radar/Surface Obs17 FEB 06: 18 Z
t = +12 h
17 Feb 2006: Radar/Surface Obs17 FEB 06: 18 Z
t = +12 h
Gradient
Thunderstorm
Lightning
500 hPa Z (hPa, solid); CAPE (J kg−1, shaded);1000–500 hPa shear (kt, barbs)
17 Feb 2006: CAPE/Shear
t = +06 h12 Z
storm reports
t = +12 h18 Z
storm reports
(J kg−1)
17 Feb 2006: Dry Intrusion
(%)
ERI42 N, −90 W 42 N, −60 WBGM BOS
12 Z
ERI BGM BOS
θ (K, red); relative humidity(%, shaded); potential vorticity (10−6 K m2 s−1 kg−1, black)
17 Feb 2006: θe Advection
ERI42 N, −90 W 42 N, −60 WBGM BOS
12 Z
ERI BGM BOS
θ (K, solid), θe advection (10−4 K s−1, shaded), potential instability (K km−1, dashed)
(10−4 K s−1)
17 Feb 2006: Frontogenesis
ERI42 N, −90 W 42 N, −60 WBGM BOS
12 Z
ERI BGM BOS
[K (100 km)−1 (3 h)−1]
θ (K, solid), Petterssen front. [K (100 km)−1 (3 h)−1, shaded], vertical motion (μb s−1, dashed; red-upward, blue-downward)
17 Feb 2006: Wind Profile
θ (K, solid), vertical motion (μb s−1, dashed; red-upward, blue-downward),
total wind (kt, barbs)
ERI42 N, −90 W 42 N, −60 WBGM BOS
12 Z
ERI BGM BOS
17 Feb 2006: Dry Intrusion
(%)
ERI42 N, −90 W 42 N, −60 WBGM BOS
18 Z
ERI BGM BOS
θ (K, red); relative humidity(%, shaded); potential vorticity (10−6 K m2 s−1 kg−1, black)
17 Feb 2006: θe Advection
ERI42 N, −90 W 42 N, −60 WBGM BOS
18 Z
ERI BGM BOS
(10−4 K s−1)
θ (K, solid), θe advection (10−4 K s−1, shaded), potential instability (K km−1, dashed)
ERI42 N, −90 W 42 N, −60 WBGM BOS
18 Z
ERI BGM BOS
[K (100 km)−1 (3 h)−1]
θ (K, solid), Petterssen front. [K (100 km)−1 (3 h)−1, shaded], vertical motion (μb s−1, dashed; red-upward, blue-downward)
17 Feb 2006: Frontogenesis
ERI42 N, −90 W 42 N, −60 WBGM BOS
18 Z
ERI BGM BOS
θ (K, solid), vertical motion (μb s−1, dashed; red-upward, blue-downward),
total wind (kt, barbs)
17 Feb 2006: Wind Profile
MSLP (hPa, solid), 12-hr centered pressure change (hPa (12 h)−1, dashed);
1000 hPa isallobaric wind (kt, barbs)
17 Feb 2006: Isallobaric Wind
+24
−28
t = +06 h12 Z
t = +12 h18 Z
+28
−32
storm reports storm reports
• 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
turbulent momentum transport– Isallobaric wind likely enhanced low-level flow
Case Study Conclusions
• This work represents the first time thunderstorm AND gradient wind events have been looked at from a climatology and composite perspective
• 17 Feb 2006 case is consistent with previous studies of cool-season high wind events
• HY events tend to be the highest impact events
• HY synoptic set up is essentially a combination of the composites constructed by Niziol and Paone (2000) and the conceptual model of Johns (1993)
Synthesis/Conclusions
Conceptual Model of the typical HY event
Synthesis/Conclusions• HY event
conceptual model
• High wind threat area in red shading
Tstorm
Gradient
• Lance and Dan• John, Tom, Hugh, and Kevin• Stuart Hinson at NCDC• Fellow graduate students
– Most notably: Ben, Natalie, Melissa, Tom, Jay, Nick, Heather, Alan, Matt
• Professors and Faculty– Ross, Kevin, Vince, Paul, Mathias, Chris, Ryan, etc.
• And of course, my family
Thank You!
Conceptual Model of the typical HY event
Conceptual Models• One PG event
model
• Average number of reports:– total
• High wind threat area in red shading
Gradient
Southeast Composite: Surface
HY (N = 71)
PG (N = 45)
t = 00 h
12 h centered composite pressure change (hPa per 12 h, dashed); MSLP (hPa, solid); ageostrophic wind (kt, barbs)