Conditions over the Netherlands,01 March 2008, 00 and 03 UTC (Rob Groenland, KNMI)

This image reveals measurements (in numbers) of gusts during 1st March 2008 over the Netherlands. The coloured areas are interpolated analyses. We see that near the coast (with one exception near the Belgium boarder) gusts between 27 and 33 m/s occured (54 and 64 knots, Beaufort 10 to 12). Further to the East lower gusts were reported (19 to 25 m/s, 38 to 50 knots).

This image shows convection in potential unstable layer (marked by A). The jet axis (according to wind speed in 300 hPa) was directed along the line B. The position of the upper cold front can be found at the line marked by C.

Note: You can click on the legend).

We see from this image that all structures (moved fast to southeast. In the meanwhile the convection line can be clearly seen (D).

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The hodogram at the radiosounding station De Bilt shows the wind direction (in that the wind is streaming) and the wind speeds [m/s]. The numbers at the line shows the heigght [hPa] of the corresponding measurement. For example, At 781 hPa a west-northwest wind was measured of a about 35 m/s.

From this hodogram a linear windprofile can be derived with increasing wind from about 10 m/s at 993 hPa to almost 30 m/s at 916 hPa that is equivalent to a stroing vertical wind speed. Therefore, convection development at the cold front is likely (Bader, 1995). The image reveals a little directional wind shear and cold air advection around 700 hPa (wind backed with height).

In the radiosounding measurement from De Bilt we recognise a moist layer up to about 2.5 km above the surface. Above that there was a layer of about 1 km depth with potential unstable air. The strong wind shear (20 to 70 knots between surface and 850 hPa) is also visible from this image.

This image is a 3h-forecast of the potential wet bulb temperature (Theta W). Decreasing values are typical for potential unstable air. This The simulation reveals potential instability between the surface and about 800 hPa north of about 52°N (very clearly north of about 53.5°N). The position of the convection line was at this time approximately along 52°N.

The KNMI weather radars perform a 14-elevation volume scan every 5 minutes and for each scan radar reflectivity and radial velocity are measured. This images shows the reflectivites in about 1500m height.

We see from this radar image a line shaped with relatively high reflectivites (brownish to red pixels, i.e., 35 to about 45 dbZ). This is related to the convective line that extended across the Netherlands. Near the radar location we find even some pixels with more than 50 dBz. However, it is questionable into what extend this is realistic. We see several bow forms at the line indicating regions of strong gusts.