Cool-Season High Winds 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

NROW XI Albany, NY5 November 2009

NOAA/CSTAR Grant NA07NWS4680001

Overview

• Motivation– Cool-season high wind events can be damaging

and in some cases challenging to forecast– Structure and environment of such events needs

to be rigorously investigated• Objectives

– Provide climatological basis for forecasting– Compare large-scale patterns that typify event

types– Contrast convective potential of the environment

for event types

Outline

• Data• Methodology• Results of Climatology• Results of Compositing• Conclusions

Data

• Climatology– NCDC Thunderstorm and High Wind reports

• Composites– NCEP/NCAR 2.5° Reanalysis data

• Climatology– Temporal Domain: 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 ≥ 2 reports

separated by 12 h before and after initial and final report

• Events defined by type:– Pure Gradient (PG): No thunderstorm wind reports– Pure Convective (PC): No gradient wind reports– Hybrid (HY): Both thunderstorm and gradient wind reports

Methodology (1 of 4)

• Climatology– Spatial Domain: Greater Northeast– 575 total events

• 187 HY events• 223 PG events• 165 PC events

Methodology (2 of 4)

Reports

0.5° Barnes Analysis of spatial distribution of All wind reports

• Composite– Spatial Domain: Northeast (NE)– 358 total events

• 158 HY events• 156 PG events• 44 PC events

Methodology (3 of 4)

0.5° Barnes Analysis of spatial distribution of All wind reports

Reports

Methodology (4 of 4)

• Composite– Composite time (t = 0): 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

– Created report-relative composites• Grids shifted to location of initial Northeast report• Composites centered on centroid of initial Northeast

reports for each event type

Climatology: Monthly Frequency

Oct Nov Dec Jan Feb Mar Apr0

10

20

30

40

50

60

70

80

Hybrid Pure Gradient Pure Convective

Ev

en

ts

N = 575

Climatology: Annual Frequency

1994–1995

1995–1996

1996–1997

1997–1998

1998–1999

1999–2000

2000–2001

2001–2002

2002–2003

2003–2004

2004–2005

2005–2006

2006–2007

2007–20080

10

20

30

40

50

60

Hybrid Pure GradientPure Convective Total

Ev

en

ts

N = 575

• Events per cool season:– PG: most events– PC: least events

• Annual variability:– PG: largest variability– HY: least variability

N = 14 years

Hybrid

Pure G

radie

nt

Pure C

onvective

0

5

10

15

20

25

Mean

Outliers

Ev

en

tsClimatology: Annual Variability

Whiskers encompass inner 90% of data

Climatology: Event Variability

N = 27,644

N = 575

2–2525–50

50–7575–100

100–150

150–200

200–300

300–400

400–500

500–6000

20

40

60

80

100

120

140

160

Hybrid

Pure Gradient

Pure Convective

Reports

Ev

en

ts

N = 575

• PC and PG events tied to seasonal cycle of convection– Dynamically vs. thermodynamically driven

• HY events have largest impact (more reports per event)– Max in Apr but not uncommon in other months– Likely dynamically AND thermodynamically driven

• Interseasonal variability possibly associated with seasonally averaged storm track

Summary of Climatology

Composite Analyses: Surface

Composite initial NE report (star); MSLP (every 2 hPa, black);precipitable water (mm, shaded); 1000-hPa θ (every 4 K, red), total wind (≥10 kt, barbs)

(mm)

276 K

Pure Convective N = 44

L

H

H

Pure Gradient N = 156

H

LL

H

N = 158Hybrid

H

Composite Analyses: 850 hPa

Composite initial NE report (star); 850-hPa Z (every 30 m, black), temperature (every 4°C, dashed);1000–850-hPa lapse rate (K km−1, shaded), wind shear (≥15 kt, barbs)

(K km−1)

0°C

Hybrid N = 158 Pure Gradient N = 156

Pure Convective N = 44

Composite Analyses: 500 hPa

Composite initial NE report (star); 500-hPa Z (every 6 dam, black), lifted index (K, shaded); 1000–500-hPa thickness (every 6 dam, red) and wind shear (≥ 40 kts, barbs)

(K)

540 dam

Pure Convective N = 44

Pure Gradient N = 156Hybrid N = 158

Composite Analyses: 300 hPa

Composite initial NE report (star); 300-hPa Z (every 10 dam, black), total wind speed (m s−1, shaded); mslp (every 2 hPa below 1014 hPa only, dashed);jet max (J) and surface low (L) labeled

N = 156Pure Gradient

Pure Convective N = 44

(m s−1)

Hybrid N = 158

L

L

LJ

J

J

• HY and PC cyclones located north of initial report; PG cyclone located east of initial report

• PC events tend to be most moist, least stable – PG events tend to be least moist, most stable

• HY and PG upper-level wave patterns more amplified compared to PC composite– Suggests stronger dynamical processes

• HY report occurs in warm sector in advance of cold front– PG report occurs in region of cold air advection– PC report occurs on warm side of zonally oriented

baroclinic zone

• Jet structures vary by event type

Composite Summary

• HY events associated with favorable dynamic AND thermodynamic environments– PG events maximize in Dec: dynamically driven– PC events maximize in Apr: thermodynamically driven

• Interseasonal variability likely due to variations in storm track– HY event: cyclone track north of domain– PG event: cyclone track east of domain

Conclusions

ja124521@albany.edu

Extra Images

Climatology: Frequency of Reports

Oct Nov Dec Jan Feb Mar Apr0

50010001500200025003000350040004500

Monthly Frequency

Gradient Tstorm

Repo

rts

N = 28,872

94–9596–97

98–9900–01

02–0304–05

06–070

500

1000

1500

2000

2500

3000

3500

Yearly Frequency

Gradient Tstorm

Repo

rts

N = 27,644

0 to 33 to 6

6 to 99 to 12

12 to 1515 to 18

18 to 2121 to 24

0500

1000150020002500300035004000

Diurnal Frequency

Gradient Tstorm

Repo

rts

N = 28,872

Climatology: Frequency of ReportsPopulation N = 27,751

0.5° Barnes Analysis of spatial distribution of Population

Climatology: Frequency of ReportsPopulation N = 27,751

0.5° Barnes Analysis of spatial distribution of Population

Major Population area

Climatology: Frequency of Reports

0.5° Barnes Analysis of spatial distribution of All wind reports

All N = 28,540

Climatology: Frequency of Reports

0.5° Barnes Analysis of spatial distribution of All wind reports

All N = 28,540

Major Population area

Gradient

Thunderstorm

Population

Climatology: Frequency of ReportsGradient N = 16,907

0.5° Barnes Analysis of spatial distribution of Gradient wind reports

Climatology: Frequency of ReportsGradient N = 16,907

0.5° Barnes Analysis of spatial distribution of Gradient wind reports

Major Population area

Climatology: Frequency of ReportsThunderstorm N = 11,633

0.5° Barnes Analysis of spatial distribution of Thunderstorm wind reports

Climatology: Frequency of ReportsThunderstorm N = 16,907

Major Population area

0.5° Barnes Analysis of spatial distribution of Thunderstorm wind reports