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

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Presentation Transcript
slide2

Introduction A:

Importance of sounding information doing convective forecasts

http://physics.uwstout.edu/wx/Notes/

slide3

Introduction B:

Sounding-derived parameters using parcel-theory

slide4

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

slide5

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

slide6

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

slide7

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

slide8

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

MUCAPE

slide9

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

MUCAPE

LCL

slide10

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

MUCAPE

LCL

LFC

slide11

Introduction B:

Sounding-derived parameters using parcel-theory

slide12

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

CAPE

CIN ~ 0 J/kg

SBCAPE

MUCAPE

slide13

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

MUCAPE

LCL

slide14

Introduction B:

Sounding-derived parameters using parcel-theory

CAPE

CIN

SBCAPE

MUCAPE

LCL

LFC

slide15

Introduction C:

Sounding-derived parameters in horizontal forecast charts

Is it useful to use them on horizontal maps?

slide16

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:
slide17

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.
slide18

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.
slide19

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.
slide20

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
slide21

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.
slide22

“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.
slide23

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)

slide24

Sounding-derived parameters associated with large hail and tornadoes in the Netherlands

study done at Institute for Marine and Atmospheric Research Utrecht

slide25

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?
slide26

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
slide27

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

slide28

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

slide31

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…

slide32

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+

slide33

(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)…

slide34

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

slide35

Average soundings

LARGE HAIL F0 F1+

note the distribution of parcel buoyancy with height

slide36

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

slide37

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..

slide38

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..

slide39

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.
slide40

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

slide41

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….

slide42

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)
slide43

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
slide44

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
slide45

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

slide46

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
slide47

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?

slide48

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.

slide49

Using parameters:

23th June, 2004

Estofex

Christian Schöps

slide56

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
slide57

Conclusions

  • Sounding information is essential for convective forecasts.
slide58

Conclusions

  • Sounding information is essential for convective forecasts.
  • Parameters derived from model soundings give a good overview when plotted on maps.
slide59

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.
slide60

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.
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