WV images to diagnose the context favourable for deep convection Patrick Santurette Forecast Laboratory METEO-FRANCE Christo Georgiev National Institute of Meteorology and Hydrology, Bulgarian

2 13 UTC11 UTC About pre-convective environment and WV information  WV Imagery information 6.2  m imagery is (almost the only) information about upper-level 7.3  m gives information about low- to mid-level  Potential instability pronounced when upper-levels cold and dry whilst low-levels moist and warm, so potential instability when: warm brightness temperature on 6.2  m and cold brightness temperature on 7.3  m  So making the difference 6.2 BT – 7.3 BT can provide an instability index > But pre-convective environment is NOT ONLY potential INSTABILITY Necessity to add information about the motion field as regards to the low-level forcing on ascending motion … IR, 925 hPa wind, θ’ w 850 hPa, 12 UTC WV BT difference (WVBTDiff = 6.2  m BT – 7.3  m BT); dark blue for BT difference -18 to -10 dg C, light blue - 10 to -5, green -5 to 0, yellow for > 0 dg. If WVBTDiff = -39 dg, light grey when 6.2 >, = -39 dg AND 7.3 <, = -19dg. Convection develops after 12 UTC from Greece to Bulgaria inside the light grey area.

3 EX 1 : Strong thunderstorms with hail, southwest of France, due to destabilisation by upper-level PV advection (1) Hail near Toulouse, highway temporarily closed Infrared Image (colour), WV_6.2 µm (BT>= -39°C, grey shade), lightening Z,T 500 hPa 24 Sep UTC Upper-level dry and cold air overhanging warm moist air at low level Convection development

4 EX 1 : Strong thunderstorms with hail, southwest of France, due to destabilisation by upper-level PV advection (2) > necessity to add information: WV 6.2 µm ImageWV 7.3 µm, BT < - 19°C 6.2 – 7.3µm, 10 m MOCON analysis WV 6.2  m = observation of upper-level moisture flow and upper-level dynamics (PV anomalies) WV 7.3 µm = observation of low- to mid-level moisture flow 1100 UTC 1200 UTC Low-level convergence (LLConv) for example is a crucial parameter Strong convection is NOT ONLY potential INSTABILITY, motion field is crucial Necessity to add information as regards to the low-level forcing on ascending motion - Superimp. of LLConv on WVBTDiff can help as precursor of convective development as regards to upper-level divergence, as regard to ground parameters evolution? … Radar 15 UTC