WV images to diagnose WV images to diagnose the context favourable for the context favourable for

deep convectiondeep convectionPatrick Santurette

Forecast Laboratory METEO-FRANCE

Christo GeorgievNational 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 < -18 dg, grey when 6.2 BT >= -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, EX 1 : Strong thunderstorms with hail, southwest of France, due to destabilisation by upper-level PV advection due to destabilisation by upper-level PV advection (1)(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 2006 12 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, EX 1 : Strong thunderstorms with hail, southwest of France, due to destabilisation by upper-level PV advection due to destabilisation by upper-level PV advection (2)(2)

> necessity to add information:

WV 6.2 µm Image WV 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 UTC1200 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