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, NY 5 November 2009 NOAA/CSTAR Grant NA07NWS

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 N = 575

Climatology: Annual Frequency N = 575

Events per cool season: – PG: most events – PC: least events Annual variability: – PG: largest variability – HY: least variability N = 14 years Climatology: Annual Variability Whiskers encompass inner 90% of data

Climatology: Event Variability N = 27,644 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 Pure GradientN = 156 N = 158Hybrid

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°C0°C HybridN = 158 Pure GradientN = 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 GradientN = 156 Hybrid 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

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

Extra Images

Climatology: Frequency of Reports N = 28,872 N = 27,644 N = 28,872

Climatology: Frequency of Reports Population N = 27, ° Barnes Analysis of spatial distribution of Population

Climatology: Frequency of Reports Population N = 27, ° 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 Reports Gradient N = 16, ° Barnes Analysis of spatial distribution of Gradient wind reports

Climatology: Frequency of Reports Gradient N = 16, ° Barnes Analysis of spatial distribution of Gradient wind reports Major Population area

Climatology: Frequency of Reports Thunderstorm N = 11, ° Barnes Analysis of spatial distribution of Thunderstorm wind reports

Climatology: Frequency of Reports Thunderstorm N = 16,907 Major Population area 0.5° Barnes Analysis of spatial distribution of Thunderstorm wind reports