Gatzen, Groenemeijer: Forecasting tornadoes using model- and sounding derived parameters

1. Gatzen, Groenemeijer: Forecasting tornadoes using model- and sounding derived parameters

2. Introduction A: Importance of sounding information doing convective forecasts http://physics.uwstout.edu/wx/Notes/

3. Introduction B: Sounding-derived parameters using parcel-theory

4. Introduction B: Sounding-derived parameters using parcel-theory CAPE

5. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN

6. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE

7. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE

8. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE MUCAPE

9. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE MUCAPE LCL

10. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE MUCAPE LCL LFC

11. Introduction B: Sounding-derived parameters using parcel-theory

12. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE CAPE CIN ~ 0 J/kg SBCAPE MUCAPE

13. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE MUCAPE LCL

14. Introduction B: Sounding-derived parameters using parcel-theory CAPE CIN SBCAPE MUCAPE LCL LFC

15. Introduction C: Sounding-derived parameters in horizontal forecast charts Is it useful to use them on horizontal maps?

16. Introduction C: Sounding-derived parameters in horizontal forecast charts Is it useful to use them on horizontal maps? • Horizontal cross sections provide barely enough information for convective forecasts:

17. Introduction C: Sounding-derived parameters in horizontal forecast charts Is it useful to use them on horizontal maps? • Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented.

18. Introduction C: Sounding-derived parameters in horizontal forecast charts Is it useful to use them on horizontal maps? • Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented. • Looking at forecast soundings or vertical cross sections yields required information, but it takes time to find regions of interest.

19. Introduction C: Sounding-derived parameters in horizontal forecast charts Is it useful to use them on horizontal maps? • Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented. • Looking at forecast soundings or vertical cross sections yields required information, but it takes time to find regions of interest. • Parameters highlight interesting regions as well as selective variables and are helpful... • ...to get a brief overview. • ...to compare different numerical models.

20. Introduction C: Sounding-derived parameters in horizontal forecast charts Complex parameters using “significant” levels • Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C] • K index = T850 + Td850 - T500 - (T-Td)700 [°C] • Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf) • where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49

21. Introduction C: Sounding-derived parameters in horizontal forecast charts Complex parameters using significant levels • Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C] • K index = T850 + Td850 - T500 - (T-Td)700 [°C] • Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf) • where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49 • We do not use them for tornado forecasting. • Using them requires a guide of “magical” numbers - and not physical understanding of the weather situation.

22. “One-slide introduction” of myself… • Pieter Groenemeijer • (almost) M.Sc. in Meteorology • Utrecht University • Oklahoma University (spring semester 2002) • 2002 and 2004 European Severe Storms Conferences (Prague, León) • ESWD (European Severe Weather Database) • “Sounding-derived parameters associated with large hail and tornadoes in the Netherlands“ • Co-initiator of ESTOFEX (with Johannes Dahl and Christoph Gatzen), Oct, 2002.

23. Sounding-derived parameters associated with large hail and tornadoes in the Netherlands Pieter Groenemeijer (IMAU; ESTOFEX), Aarnout van Delden (IMAU) F3 tornado near Deil, 25-06-1967. (A.C. Frenks)

24. Sounding-derived parameters associated with large hail and tornadoes in the Netherlands study done at Institute for Marine and Atmospheric Research Utrecht

25. Main questions • What sounding-derived parameters can be used to forecast tornadoes? • ………………….. large hail? • sub-question: • How do the results differ from studies from the United States?

26. Basic idea • Find soundings taken in the proximity of severe weather events (here: tornadoes) • Find if they have special characteristics (w.r.t. other soundings) • method: look at parameters • that represent something physical • and that have been studied before

27. Proximity soundings What is a proximity sounding…? Used definition: • within 4 hours of the sounding (before or after) • within 100 km from a point that is advected by the 0-3 km mean wind from the sounding location at the sounding time

28. Data sets • radiosonde observations Dec 1975 – Aug 2003 (thanks to KNMI, DWD, KMI) • severe weather reports from Dutch voluntary observers (VWK) Sinds 1974 Vereniging voor Weerkunde en Klimatologie (VWK) http:/www.vwkweb.nl

29. Data

30. results…

31. Most-unstable CAPE (MUCAPE) Number of events  US studies: MUCAPE highly variable with tornadoes. Strong tornadoes may occur with low CAPE when shear is high maximum  75th perc. median  25th perc. MUCAPE not very high with tornadoes…

32. Most-unstable CAPE released below 3 km A.G.L. US studies: Davies (2004) has found a relation between tornado occurrence and high CAPE below 3km (in his study M.L.CAPE)... MUCAPE<3km high with F0, not with F1+

33. (most-unstable) LFC height (m) US studies: Davies (2004) has found a relation between low LFC and tornado occurrence LFC relatively low with tornadoes (esp. F0)…

34. LCL height (50 hPa mixed layer parcel) US studies: Low LCL favors significant tornadoes, e.g. Craven et al. (2002) LCL not sign. diff. between tornadic and thunder

35. Average soundings LARGE HAIL F0 F1+ note the distribution of parcel buoyancy with height

36. 0-6 km A.G.L. bulk shear (m/s) US studies: strong tornadoes often occur with supercells associated with >20 m/s 0-6 km shear (e.g. Doswell&Evans, 2003) 0-6 km bulk shear high with F2 tornadoes

37. 0-1 km A.G.L. bulk shear (m/s) US studies: strong 0-1 km shear favours for sign. tornadoes (e.g. Craven et al., 2002). 0-1 km shear high with F1, esp. F2 tornadoes..

38. 0-1 km A.G.L. storm-relative helicity (m2/s2) US studies: high values favor supercell tornadoes (e.g. Rasmussen, 2003). 0-1 km shear high with F1, esp. F2 tornadoes..

39. Some conclusions • F1 and esp. F2 tornadoes occur with higher-than-average 0-1 km shear (and SRH, but less clearly). • F0 tornadoes (and waterspouts) occur with lower-than-average 0-1 km shear values • (MU)CAPE is not extreme with tornadoes and thereby has limited value for tornado forecasting.

40. Some conclusions • MUCAPE released below 3 km / low LFC heights seem to be important for the formation of weaker (and likely non-supercellular) tornadoes…. (but of course we rather want to forecast the stronger tornadoes) • LCL heights are probably not as much a limiting factor for tornado development in the NL (and in Germany?) than in much of the U.S.A. i.e. LCL heights are practically always low enough here for tornadoes

41. References (ask me if you want to see this slide again) Craven, J. P., H. E. Brooks, and J. A. Hart, 2002: Baseline climatology of sounding derived parameters associated with deep, moist convection. Preprints, 21st Conference on Severe Local Storms, San Antonio, Texas, American Meteorological Society, 643–646. Davies, J. M., 2002: On low-level thermodynamic parameters associated with tornadic and nontornadic supercells. Preprints, 21st Conf. on severe local storms, Kananaskis Park, Alberta, Canada, Amer. Meteor. Soc., 558–592. Davies, J. M., 2004: Estimations of CIN and LFC Associated with Tornadic and Nontornadic Supercells. Wea. Forecasting, 19, 714–726. Doswell, C. A. III, and J. S. Evans, 2003: Proximity sounding analysis for derechos and supercells: An assessment of similarities and differences. Atmos. Res., 67-68, 117–133. Rasmussen, E. N., 2003: Refined supercell and tornado forecast parameters. Wea. Forecasting, 18, 530–535. back to Christoph….

42. Using parameters: A scenario for a weather pattern associated with “critical” values • In collaboration with Lars Lowinski (Meteos Munich) a scenario was designed that is characterized by “critical” values of mentioned parameters. • This scenario is based upon the synoptic situation of four tornado outbreaks over Central Europe: • Aug. 1st, 1925 (NL, five tornadoes, one F4) • June 1st, 1927 (northwestern GER, four F3/F4 tornadoes) • June 24th, 1967 (northern F, F4/F5 tornadoes) • June 25th, 1967 (NL, four F3/F4 tornadoes)

43. 568 560 552 T 576 H 592 584 Using parameters: A scenario for a weather pattern associated with “critical” values • 500 hPa level • High geopotential over southern Europe due to well-mixed airmass originating from Atlas mountains • Strong upper SW-erly jet streak coupled with negatively tilted short-wave trough

44. 1015 1020 H 1010 H L 1005 L 1010 1015 Using parameters: A scenario for a weather pattern associated with “critical” values • Surface chart • Frontal boundary with embedded frontal waves from Iberian Peninsula to northern Germany • Easterly surface winds over Germany south of Scandinavian surface high pressure system

45. 19 16 27 22 31 14 Using parameters: A scenario for a weather pattern associated with “critical” values moist maritime airmass north of the warm front rich low-level moisture underneath an inversion north of convergence line well-mixed airmass south of convergence line

46. 19 16 27 22 31 14 Using parameters: A scenario for a weather pattern associated with “critical” values • Warm sector north of the convergence zone: • CAPE • winds veer strongly with height • strong low-level wind shear • maybe low LFC heights • quasigeostrophic forcing due to WAA and DCVA

47. 1015 1020 H 1010 H L 1005 L 1010 Using parameters: A scenario for a weather pattern associated with “critical” values Would this scenario be associated with a tornado outbreak?

48. 1015 1020 H 1010 H L 1005 L 1010 Using parameters: A scenario for a weather pattern associated with “critical” values Would this scenario be associated with a tornado outbreak? We don’t know. Tornadogenesis is not well understood. Probably, this scenario is associated with an enhanced chance for tornadoes.

49. Using parameters: 23th June, 2004 Estofex Christian Schöps

50. 23 June, 2004: 500 hPa height, wind speed