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

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Presentation on theme: "Gatzen, Groenemeijer: Forecasting tornadoes using model- and sounding derived parameters."— Presentation transcript:

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

2 Introduction A: Importance of sounding information doing convective forecasts

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) = T Td * T 500 [°C] K index = T Td T (T-Td) 700 [°C] Sweat index = 12*Td *(TOTL-49)+2*U *U *(0.2+sinf) where f=(wind direction 500 -wind direction 850 ), 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) = T Td * T 500 [°C] K index = T Td T (T-Td) 700 [°C] Sweat index = 12*Td *(TOTL-49)+2*U *U *(0.2+sinf) where f=(wind direction 500 -wind direction 850 ), 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, (A.C. Frenks)

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

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 1.Find soundings taken in the proximity of severe weather events (here: tornadoes) 2.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 radiosonde observations Dec 1975 – Aug 2003 (thanks to KNMI, DWD, KMI) severe weather reports from Dutch voluntary observers (VWK) Data sets Sinds 1974 Vereniging voor Weerkunde en Klimatologie (VWK)

29 Data soundings associated with:number hail ( cm) hail (>= 3.0 cm) tornadoes F0 tornadoes F1 tornadoes F2 waterspouts thunder ( only) all soundings67816

30 results…

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

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

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

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

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

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

38 0-1 km A.G.L. storm-relative helicity (m 2 /s 2 ) 0-1 km shear high with F1, esp. F2 tornadoes.. US studies: high values favor supercell tornadoes (e.g. Rasmussen, 2003).

39 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. Some conclusions

40 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 Some conclusions

41 back to Christoph…. 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, 21 st 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.

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 Using parameters: A scenario for a weather pattern associated with critical values T H 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 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 L L H H 1005

45 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 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 Using parameters: A scenario for a weather pattern associated with critical values Would this scenario be associated with a tornado outbreak? L L H H 1005

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

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

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

51 23 June, 2004: 850 hPa height, theta-e

52 23 June, 2004: MUCAPE, deep layer wind shear

53 23 June, 2004: MUCAPE, low level wind shear

54 23 June, 2004: LCL height

55 23 June, 2004: LFC height

56 Soundings from north-central Germany. Proximity soundings were not available. Soundings indicate... rather weak CAPE winds veer strongly with height strong low level wind shear rather low LFC heights Note: Models did indicate SW-erly surface winds

57 Conclusions Sounding information is essential for convective forecasts.

58 Conclusions Sounding information is essential for convective forecasts. Parameters derived from model soundings give a good overview when plotted on maps.

59 Conclusions Sounding information is essential for convective forecasts. Parameters derived from model soundings give a good overview when plotted on maps. They make it easy to compare different models or model runs.

60 Conclusions Sounding information is essential for convective forecasts. Parameters derived from model soundings give a good overview when plotted on maps. They make it easy to compare different models or model runs. Parameters without physical meaning are not used by Estofex. Learning magical numbers associated with complex variables wont increase our knowledge about tornado forecasting.


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