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

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

Introduction B: Sounding-derived parameters using parcel-theory

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

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

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

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

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

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

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

Introduction B: Sounding-derived parameters using parcel-theory

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

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

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

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

Is it useful to use them on horizontal maps? 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:

Is it useful to use them on horizontal maps? 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.

Is it useful to use them on horizontal maps? 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.

Is it useful to use them on horizontal maps? 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.

Complex parameters using “significant” levels 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

Complex parameters using significant levels 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.

“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.

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)

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

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?

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

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

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

Data soundings associated with: number hail (2.0 - 2.9 cm) tornadoes F0 tornadoes F1 tornadoes F2 waterspouts thunder (1990-2000 only) 46 47 24 37 6 26 2045 all soundings 67816

results…

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…

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+

(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)…

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

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

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

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..

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..

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.

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

(ask me if you want to see this slide again) 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….

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)

Using parameters: A scenario for a weather pattern associated with “critical” values T H 592 584 576 568 560 552 500 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

Using parameters: A scenario for a weather pattern associated with “critical” values 1015 1020 1010 L H 1005 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

A scenario for a weather pattern associated with “critical” values Using parameters: A scenario for a weather pattern associated with “critical” values 31 14 27 22 19 16 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

A scenario for a weather pattern associated with “critical” values Using parameters: A scenario for a weather pattern associated with “critical” values 31 14 27 22 19 16 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

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

Using parameters: A scenario for a weather pattern associated with “critical” values 1020 1015 1010 L H 1005 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.

Using parameters: 23th June, 2004 Estofex Christian Schöps

23 June, 2004: 500 hPa height, wind speed

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

23 June, 2004: MUCAPE, deep layer wind shear

23 June, 2004: MUCAPE, low level wind shear

23 June, 2004: LCL height

23 June, 2004: LFC height

Soundings from north-central Germany 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

Conclusions Sounding information is essential for convective forecasts.

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

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.

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 won’t increase our knowledge about tornado forecasting.