Unpredictability of Tornado Occurrence: the Atypical Case of Cassacco, ITALY, Winter F2 Tornado

Transcription

1 Title and Authors Unpredictability of Tornado Occurrence: the Atypical Case of Cassacco, ITALY, Winter F2 Tornado by (1) Gallai I., (1,2) Giaiotti D. B., (3,4) Gladich I., (1,2) Stel F. dario.giaiotti@osmer.fvg.it (1)ARPA FVG - OSMER - Visco (UD) - ITALY (2)ESSL - Wessling - GERMANY (3)University of Trieste - Trieste - ITALY (4)ICTP - Trieste - ITALY 1

2 Outline of the presentation Description of the severe weather event and related damages Description of the forecast procedure and forecast result Consideration on the quality of mesoscale simulation Comments on the event predictability 2

3 Classification of the event Tornado F2/T4 - At least another F0/T1 observed that day in the area :30 UTC - More than one intense vertical vortex in the event Storm Chaser: Paolo Zamparutti Photos and report 3

4 Location on the event Friuli plain NE Italy 4

5 Radar VMI sequence No mesocyclone signature both in Reflectivity and Doppler fields No intense CG lightning activity 5

6 Radar VMI sequence 6

7 Radar VMI sequence 7

8 Radar VMI sequence 8

9 Radar VMI sequence 9

10 Radar VMI sequence 10

11 Radar VMI sequence 11

12 Radar VMI sequence 12

13 Radar VMI sequence 13

14 Radar VMI sequence 14

15 Radar VMI sequence 15

16 Radar VMI sequence 16

17 Radar VMI sequence 17

18 The environment - WMO RDS 00UTC and 12UTC 18

19 The environment - boundaries, jets, wind shear and instability No boundaries (both thermal and moisture) Slight instability No upper level jets Significant shear Tornado 19

20 Was the environment prone for severe storms occurrence? It was not, according to the worldwide used empirical rules NOT Forecasted VGP = S (CAPE) 1/2 20

21 WRF simulation of the event: some details. 3 DOMAINS NESTING (TWO WAY NESTING) Domain 1 : 36x18 50km Domain 2 : 91x46 10km Domain 3: 96x96 2 km Vertical levels ( 31 levels) Initialization: ECMWF ANALYSIS and topography enhanced by 20% Average wind direction Pseudo-Temp considered for the study 21

22 WRF Pseudo-Temp thermodynamic analysis CAPE and SREH for the 4 selected grid points Pseudo-Temp Tornado 22

23 WRF Pseudo-Temp vs real Radiosounding environment 4 grid points from: 00 UTC to: 15 UTC CAPE vs SHEAR diagram brings analogue information No boundaries (both thermal and moisture) 23

24 Conclusions A damaging F2/T4 Tornado occurred in an environment considered not prone to severe storms. The event was NOT forecasted - Missing Alarm. High resolution mesoscale numerical simulations do not produce an environment prone to to severe storms. Even in case of operational availability of very good mesoscale numerical forecasts the event wont be forecasted. At present the predictability of significant tornado events is affected by NOT negligible uncertainties. This is a sufficient condition to transform the atmospheric hazard in an atmospheric risk This case suggests that more work is required on the understanding of tornado prone (mesocyclones) environments. 24

25 Location on the event (cont d) Path at F2/T4 about 400 m 25

26 WRF simulation of the event: Some details (cont d). Initial time UTC ending time UTC time resolution output: 30mn Map Projection (suggest lambert) : MERCATOR # 3 DOMAINS NESTING (TWO WAY NESTING) # Domain 1 : 36x18 50km # Domain 2 : 91x46 10km #DOMAIN 3: Horizontal Dimension X: 96 Horizontal Dimension Y: 96 Distance between grid points (km): 2 Vertical levels ( 31 levels) #Initialization: WPS with ECMWF ANALYSIS and topography enhanced by 20% #Physical options: MICROPHYSICS OPTION: Thompson et al graupel scheme 8 RADIATION PHYSICS LONGWAVE rrtm scheme 1 SHORTWAVE Dudhia scheme 1 SURFACE LAYER OPTION: Monin-Obukhov scheme 1 LAND_SURFACE OPTION: Thermal diffusion scheme 1 BOUNDARY-LAYER OPTION:YSU Scheme 1 CUMULUS OPTION: no cumulus parametrization 0 26

27 WRF Pseudo-Temp at WMO location 00UTC and 12UTC 27

28 Title of slide Regional Agency for Environmental Protection of 28