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A in Basque Country?: the 23 june 2014 case. S. Gaztelumendi 1,2 , J. Egaña 1,2 , A. Etxezarreta 3 , M. Maruri 1,2 , M. Martija 1,2 , J.A. Aranda 1,4 , P. Anitua 4

(1) Basque Meteorology Agency (EUSKALMET) (2) Mete orology Area, TECNALIA R&I, (3) ADASA (4) Emergencies and Meteorology Directorate, Securi ty Department, Basque Government Introduction

Tornado cases in Iberian Peninsula, and particularly in Mediterranean area (Catalonia, Balearic Islands, and Andalusia) are relatively often observed, on the other hand in Cantabric area (north of Iberian Peninsula) are very unusual, in fact in Basque Country none well documented and

confirmed case exist. In this work a discussion about the possibility of a tornado occurrence in Basque country (Izki area) are presented. Fig.1: Basque During afternoon of 23 june 2014, different severe affect southern part of Basque Country, with heavy , hail and gust /see Country and tornado area ECSS2015-69 for more details). Particularly, a affect the Izki area promoting large hail, heavy rain and severe wind gusts leaving hundreds of trees removed in a narrow area compatible with a tornado event. In this work we analyzed different aspects of the event and if it is compatible with tornadogenesis, mainly based on data from the Euskalmet C–band Doppler Radar sited near the affected area, in Kapildui mountain. .

Fig. 7 : PPI (dBZ) - General environment. 0.5 and 0.5 (from top to bottom), 14:22, 14:42, 14:52 and 15:02 ( During this episode, Basque Country area (see Fig.1) is affected by a from left to righ), resoltuion 0,062 cut-off low located at the west of Iberian peninsula, traveling to the east km/pixeL) and promoting instability. Difluence in high layers are significant, with weak flux at 500 hPa and 300hPa levels, at low levels convergence is present at 75 the South of Basque Country. At surface level a relative thermal low is present with undefined wind and relatively warm and humid air mass

affecting the area. These general environment favors a steep mid level 60 lapse rate that become steeper due to diurnal heating and mixing ratios of

10 g/kg advected from the sea, promoting high degree of instability (TTI 50 54/55, LI -4/-5, CAPE 1400 J/Kg ) and moderate shear values increasing during day due to approaching upper level low (0-6 km shear 10-20 m/s) 40 (see ECSS2015-69 for figures and more details).

30 environment and Radar data 20 From 13:30 a storm core quickly begins to grow getting a great vertical extent (see Fig. 2), with cloud top reaching the tropopause (13- 10 14 km) (see Fig. 3). Splitting are produced and right core is activated, dBZ being consistent with hodographs that rotates clockwise (see fig 2,3 and 4). This core continues clearly showing the characteristics of a supercell Fig. 2. MAX (dBZ) with the generation of a that can be seen in the radial sequence from image of wind in the first kilometers (velocity couplet) (see Fig 5 and 6), 13:42 to 15:22 each 10 minutes1 where a cyclonic is present coincident with hook signature in the b a (Height 1-13km. Hor res 0.062 supercell with own notch from feeder flow at low layers (see Fig 6 and km/pixel, Vert resol 7). c 0.1) Theoretically during the collapse of the supercell there is a high Fig. 4: VVP(V) Radar product , wind profile at Radar site from 12:42 probability of tornadogenesis (meter referencias), in that case Tornado to 16:52 UTC. vortex Signature (TVS) can be seen in radar imaginary. Unfurtunatly this is not the case due to lack of quality and resolution. Keep in mind that Fig. 6: 14:52 MAX 1 km to the algorithms used in the radar scan, make noise often appears false, 13 km (top) and CAPPI (V) 1km with 0,062 km/pixel especially in the sign of radial wind. (down). We can appreciate the Hock echo with (a) the In the studied case the area affected by tornado is in the rear-flank Bounded week echo from updraft region (b) the area downdraft (RFD) as can be seen clearly both that area and the main with enhanced reflectivity Fig.5. PCAPPI (1, from forward flank downdraft area of updraft and downdraft forward-flank (FFD) (see figure 6). If we 3 and 5 km (from (FFD) and (c) the Rear Flank top to bottom), consider shear present in the first meters and complex topography of the Downdraft (RFD) where 14:22, 14:42, 15:02 tornado are most probable. In (from left to right), area, transformation and potentiation of horizontal vorticity into vertical the CAPPI we can appreciate resolution 0,062 the inbound-outbound vorticity near surface is possible. If a downdraft is Involved in the tilting km/pixel ) (wind couplet in radial velocity data barbs from typical from supercelular process, vertically vorticity can be advected toward the surface HWIND), promoting tornadogenesis. mesociclonic pattern. Fig. 3: MSG HR VIS and CAPPI 2km for 13:30,14:00,14:30 and 15:00 Fig.8: Location of Radar and area Damages and impact analysis Radar affected by tornado and observed damages. Analyzed supercell leaves heavy rain and big hail in the region. In particular, the high wind affected zone is about 3 hectares of forest near Izki area (mainly pine). It present more than a hundred uprooted and 10,9 Km broken trees at different heights (from 0.5 to 5-6 meters high). Big branches and trees up to 30-40 cm in diameter are fallen in different directions, all over the area (see Fig.8). Tornado area Conclusions 23.900 m2

Euskalmet Doppler radar can't see the tornado itself, because the

radar beam gets too wide few kilometers away from the transmitter to Before After resolve such a small structure as the tornado vortex structure (TVS). But some radar data indicates the presence of different signatures from supercell structure and ingredients for potential tornadogenesis. damaged area are located in typical location of a tornado if occurs in the Rear Frank Downdraft (RFD). Even though there are no direct observers to the phenomenon, the distribution and characteristics of fallen trees are compatible with the effect of a short lived F2 scale tornado. On the other hand, small spatial and temporal scale of phenomenon are perhaps more compatible with a downburst. 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