the utility of considering dual-pol radar signatures in the tornado warning process

MICHAEL L . JUREWICZ, SR. AND CHRISTOPHER GITRO

22 N D U.S. /CANADA GLOMW15 MAY 2014

ANN ARBOR, MI

The Utility of Considering Dual-Pol Radar Signatures in the Tornado Warning Process

Outline

MotivationPrevious ResearchMethodology / Latest ResultsSummary / ConclusionsFuture Work

Motivation

NWS ER Tornado Warning Statistics for 2012-2013

* Tabulated for the WFO’s in our study (ALY, BGM, BOX, BTV, BUF, CAR, CTP, GYX, OKX, PBZ, and PHI)

* Total of 62 events for these offices; with 27 of them fully warned and 8 partially warned; for a POD = 0.5 (well below expected performance standards)

* FAR stats (0.79) were similarly below established goals

Previous Research

Drop Size Sorting / Zdr Arc

* Enhanced Kdp (blue) gets displaced left of enhanced Zdr (orange) via preferential size sorting

From Romine, et. al, 2008

* Conceptual schematic of differing hydrometeor descents and Zdr arcing

From Kumjian and Ryzhkov, 2009

Radar 4-Panel from Northern Alabama at 1620 UTC, 27 April 2011 (from Crowe, et. al, 2012)

Click icon to add picture* EF -1 tornado was on the ground at this time (near Trinity, AL)

* Note the westward displacement of Kdp maxima (lower right) versus Zdr maxima (lower left)

* Also, note the arc-shaped configuration of the Zdr pattern (lower left)

ZH

ZDR KDP

SRV

Radar 4-Panel from Northern Alabama at 1620 UTC, 27 April 2011 (from Crowe, et. al, 2012)

Click icon to add picture* EF -1 tornado was on the ground at this time (near Trinity, AL)

* Note the westward displacement of Kdp maxima (lower right) versus Zdr maxima (lower left)

* Also, note the arc-shaped configuration of the Zdr pattern (lower left)

ZH

ZDR KDP

SRV

Zdr Max

Methodology / Latest Results

Methodology

Favorable initial results (Crowe, et. al, 2012) were further put to the test over the Northeastern U.S. (New England, NY, PA, and NJ) 30 Storms (17 Non-tornadic and 13 Tornadic) were chosen from

the 2012 and 2013 convective seasons, each within a potentially favorable synoptic environment for tornadogenesis: ML CAPE > 700 J/kg 0-6 km Shear > 40 kt 0-1 km Shear > 20 kt 0-1 km SRH > 100 m2/s2

Many radar/storm-scale parameters were tabulated at the lowest tilt Including specific Zdr and Kdp maximum values, and their separation

distances (nmi) AWIPS/GR2 Analyst sampling and distance measuring tools

Statistical Correlations

Strongest correlations to tornadic development (either same volume scan or in the near future): Zdr and Kdp separation (nmi) – 0.50 Maximum gate-gate shear (kt) – 0.38 Maximum SRM increase within a volume scan – 0.30 Existence/development of a Zdr arc – 0.23

Given approximately 300 data points (radar volume scans), these values are statistically significant to the 99th percentile (Gibbons, 1976)

Elmira, NY Tornado Event (July, 2012)

Seneca County, NY Null Event (May, 2013)

Polar Plot of Kdp maxima (red for tornadic storms and blue for non-tornadic storms) versus Zdr maxima (center point)

* All 30 storms in the database represented

* Note the typically much larger horizontal separation for tornadic storms (red)

* For the non-tornadic storms (blue), little separation was typically seen (data points tightly clustered around the center of the plot)

360° 020°040°

060°

080°

100°

120°140°

160°180°200°220°

240°

260°

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300°320°

340°

0

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Horizontal Separations (nmi, y-axis) of Zdr and Kdp maxima over time

* Looking at +/- 3 volume scans from T=0

* T=0 is either the time of initial tornado touchdown or tornado warning issuance (null events)

* Note the large differences in separation magnitude between T-2 and T=0

T - 3

T - 2

T - 1

T = 0

T + 1

T + 2

T + 3

0

1

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Mean Null Sep-arationMean Tor Sep-aration

Trends of Maximum Gate-Gate Shear (kt, y-axis (Storm Relative Motion)) over time

* Once again, looking at +/- 3 volume scans from T=0

* T=0 is either the time of initial tornado touchdown or tornado warning issuance (null events)

* Rotational velocity couplet seems to spike in intensity near T=0 for tornadic storms T -

3T - 2

T - 1

T = 0

T + 1

T + 2

T + 3

0

10

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Mean Null SRMMean Tor SRM

Summary / Conclusions

Take Home Points

Horizontal separation of Zdr and Kdp maxima via drop size sorting (enhanced low-level helicity) seemed to be a reliable indicator of tornadogenesis Matches previous research well over the Southeastern U.S. Initially promising results perhaps warrants consideration in

the tornado warning processGate-gate shear values tend to maximize right

around the time of touchdown (T=0) in tornadic storms

Although there was a general tendency for Zdr arc formation in Northeast U.S. tornadic storms, drop size sorting appeared to be the more readily apparent phenomenon via radar interrogation

Future Work

Publish resultsDevelop methods to make Zdr/Kdp

separations easier to recognize in real-time Future collaborative research likely with UAH, Penn

St. CSTAR group, Univ. of Albany CSTAR group, and perhaps WDTB

Continue to evaluate these processes in coming convective seasons

Questions ?