…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

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.

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

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)

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

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!

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

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

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

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

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

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

Damage Survey 16 Apr 2011 Several reports of observed funnels Narrow swath(s) (generally ~50-100 yd width) Scalloped path(s)

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)

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)

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

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

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

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

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

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

Case: 13 Oct 2011 TDWR Loop DCA Eastward shift of circulation center by ½ - ¾ mile from 1726-1728 UTC Added second circulation track for survey What happened?

References Atkins, N.T. and M. St. Laurent, 2009: Bow Echo Mesovortices, PartI: Processes That Influence Their Damaging Potential. Mon. Wea. Rev. 137, pp 1497-1513. Atkins, N.T. and M. St. Laurent, 2009: Bow Echo Mesovortices, Part II: Their Genesis. Mon. Wea. Rev. 137, pp 1514-1532. 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.