1. …or… Why Everyone Needs a TDWR (in 25 Slides or Fewer)
Applying Conceptual Models for Non-Mesocylonic Tornadoes in Quasi-linear Convective Systems to National Weather Service Tornado Damage Surveys
…or…
Why Everyone Needs a TDWR
(in 25 Slides or Fewer)
Matthew R. Kramar
Senior Forecaster
WFO Baltimore/Washington

2. Motivation
QLCS tornadoes occur frequently in WFO LWX forecast area, but have been difficult to warn for:
environments favorable for their formation were not anticipated adequately
temporal duration often is smaller than the temporal resolution of the NWS WSR-88D scanning strategies
mechanisms by which QLCS tornadoes are generated, until recently, were not very well-understood.

3. Tornadogenesis Distilled
Updraft tilts & stretches the vortex lines
Rear-flank downdraft (RFD) tilts and packs streamwise vortex lines under the updraft

4. QLCS mesovortices Atkins and St. Laurent (2009) conceptual model
Streamwise vorticity tilted and stretched by updraft and surging gust front
Produces single vortex along leading edge where upward motion maximized
From Atkins and St. Laurent (2009)

5. Extrapolation to QLCS tornadogenesis
QLCS rear inflow jet (RIJ) or localized surge of gust front serves purpose of RFD
Streamwise vortex lines are tilted and stretched along leading edge of surge
Updraft and accelerating airflow over the surging gust front provide stretching
Vortex is shed from leading edge of surge as boundary segment accelerates

6. Extrapolation to QLCS tornadogenesis
Inherently a non-mesocyclonic process
A tornado in QLCS is inextricably linked to its mesovortex. Why?
In the right environment, this process can be cyclic!

7. Terminal Doppler Weather Radar
WFO LWX has four TDWRs, affording unique coverage of the Washington DC metro area
Scanning strategy offers one-minute temporal resolution on lowest tilt reflectivity/velocity

8. Case: 16 Apr 2011 Abridged synoptic features:
Negatively-tilted 500mb wave ejecting across north-central Appalachians
Strong forcing for ascent as upper jet streak crosses region
Negatively-tilted surface trough lifting northeastward
Modest instability, high shear
7-8 m/s shear in lowest ½km, with vorticity vector predominantly in the streamwise direction
Expected
Storm Motion

9. Case: 16 Apr 2011
Loop of KLWX
No obvious gate-to-gate velocity signatures, except perhaps in Carroll County
But, notable hook echoes and reflectivity notches suggest decent rotation
15- to 20-minute duration circulation tracks

10. Case: 16 Apr 2011
Loop of TIAD
Five, shorter-lived circulation tracks with the original southern track alone!

11. Case: 16 Apr 2011
Loop of TBWI
Another perspective showing several shorter-lived circulation tracks

12. Diagnosed Circulation Tracks
Several potential damage tracks diagnosed with just a little effort
Circulations often are short-lived
What about the damage survey?

13. Damage Survey 16 Apr 2011 Several reports of observed funnels
Narrow swath(s) (generally ~ yd width)
Scalloped path(s)

14. Damage Survey 16 Apr 2011 Scalloped paths make perfect sense…
Line often has strong eastward component to motion
Vortex is shed poleward from leading edge of surge (provides component perpendicular to forward track of circulation)

15. Case: 31 Jul 2009 Abridged synoptic features:
Broad trough over CONUS, with low-amplitude shortwave trough over Ohio
Weak surface trough east of the Appalachians
Warm, exceptionally moist airmass east of Blue Ridge Mountains
Steep low-level lapse rates available upon boundary-layer mixing; wide low-level CAPE profile
Although low-level winds appeared weak at 12Z, 40kt southwesterly low-level jet was forecasted to develop at 925mb, which would lengthen the hodograph significantly and increase low-level shear (map at 01/00Z confirms its development)

16. Case: 31 Jul 2009 Loop of KLWX Significant velocity couplet
Leading-edge hook echo
Suggests a single circulation track to the southwest of New Market

17. Case: 31 Jul 2009 Damage swath surveyed
These 4 trees snapped
Damage swath surveyed
Began narrow, widened considerably at end
Debris field exhibited circulation/ convergence
Limits of significant tree damage defined tornadic width

18. Case: 31 Jul 2009 Damage swath surveyed
One tornado…8 minute duration…path width varied…
…and then we found another damage point

19. Case: 31 Jul 2009 Loop of TIAD Two individual circulations noted
Leading-edge hook echoes
The circulation paths crossed and briefly were concurrent!!!

20. Summary QLCS tornadoes:
Form along leading edge of gust front surge/RIJ, where vertical accelerations enhanced
Tracks tend to be scalloped in shape
Generally narrow, focused damage swath
Can be generated cyclically in the right environment

21. Summary QLCS tornadoes:
Leading-edge kink
Leading-edge weak hook echo
QLCS tornadoes:
Often accompanied by brief, subtle signatures in reflectivity:
Outflow inflection point
Subtle, leading-edge hook echo
Leading-edge inflow notch concurrent with rear weak-echo channel
Important to recognize that not all mesovortices are tornadic

22. Case: 13 Oct 2011
TDWR Loop DCA
Eastward shift of circulation center by ½ - ¾ mile from UTC
Added second circulation track for survey
What happened?

23. References
Atkins, N.T. and M. St. Laurent, 2009: Bow Echo Mesovortices, PartI: Processes That Influence Their Damaging Potential. Mon. Wea. Rev. 137, pp
Atkins, N.T. and M. St. Laurent, 2009: Bow Echo Mesovortices, Part II: Their Genesis. Mon. Wea. Rev. 137, pp
J.M. Esterheld and D. J. Giuliano, 2008: Discriminating between Tornadic and Non-Tornadic Supercells: A New Hodograph Technique. Electronic Journal of Severe Storms Meteorology. 3, No 2.
Kramar, M.R. and K.M. Olmstead, 2010: A ‘Survey’ of Tornadoes and their Environments in the WFO Sterling, VA Forecast Area . Oral Presentation, Northeast Regional Operational Workshop XII, Albany, NY.
Appreciation is extended to Frederick County MD Department of Emergency Preparedness and to WFO LWX forecaster Greg Schoor for their graphical contributions to this presentation.