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M I C H A E L L . J U R E W I C Z , S R . A N D C H R I S T O P H E R G I T R O
N O A A / N W S, B I N G H A M T O N, N Y
N O RT H E A ST R E G I O N A L O P E R AT I O N A L W O R K S H O P1 0 D E C E M B E R 2 0 1 3
The Utility of Considering Dual-Pol Radar Signatures in the Tornado Warning Process
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Outline
MotivationPrevious ResearchMethodology / Latest ResultsSummary / ConclusionsFuture Work
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Motivation
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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
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Previous Research
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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
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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
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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
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Methodology / Latest Results
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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
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Radar 4-Panel from Central New York at 2010 UTC, 26 July 2012
* EF -1 tornado was on the ground at this time (near Elmira, NY)
* Once again, note the westward displacement of Kdp maxima (lower right) versus Zdr maxima (lower left)
* Also, note the developing arc-shaped region of enhanced Zdr (lower left)
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Radar 4-Panel from Central New York at 2010 UTC, 26 July 2012
* EF -1 tornado was on the ground at this time (near Elmira, NY)
* Once again, note the westward displacement of Kdp maxima (lower right) versus Zdr maxima (lower left)
* Also, note the developing arc-shaped region of enhanced Zdr (lower left)
Zdr Maxx
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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)
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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°
280°300°
320°340°
0
10
20
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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
2
3
4
5
6
Mean Null Sep-arationMean Tor Sep-aration
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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
20
30
40
50
60
70
80
Mean Null SRMMean Tor SRM
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Summary / Conclusions
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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 stormsAlthough 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
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Future Work
Publish resultsDevelop methods to make Zdr/Kdp
separations easier to recognize in real-time Continue to evaluate these processes in
coming convective seasons
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Questions ?