BACKGROUND OF THE SEVERE WEATHER SITE

PURPOSE OF THIS WEBSITE:

These website provides an outlook to the risks on severe weather over the Benelux region.

 

Technicaly, we use color codes to indicate the possible treath of the weather on the society. The collor indicates the RISK (which is in fact a combination of the PROBABILITY and the strength of the IMPACT) on inconvenience fo the society, with:

 

green = NIL (no problems expected)

yellow = SLGT (slight risk on inconveniences)
orange = MDT (moderate risk on inconveniences)

red = HIGH (high risk on inconveniences or moderate risk on very high inconveniences)

purple = EXTR (very dangerous situation expected)

 

We also provide some comments on the blog, which particularly is reserved for people who have some knowledge about meteorology. For the moment, the texts are provivided in Duth only.

 

WIND

 

Warnings for wind gusts (non-convective) are made using a matrix based on probability and the height of the expected gust value. The resulting color gives you an estimation of the risk and impact strength of this parameter. For the period October-April:

 

gust / prob.	< 10 %	10 - 30 %	30 - 60 %	60 - 80 %	> 80 %
< 90 km/h
90 - 110 km/h
110 - 130 km/h
130 - 150 km/h
> 150 km/h

 

For the period May-September:

 

gust / prob.	< 10 %	10 - 30 %	30 - 60 %	60 - 80 %	> 80 %
< 80 km/h
80 - 100 km/h
100 - 110 km/h
110 - 130 km/h
> 130 km/h

 

SNOW / ICE

 

Snow warnings are made for snowfall rates (cm/24h), under the conditions that all the fallen snow accumulates on the ground. If there is already a snow cover on the ground, this depth is not taken into account!

 

For the snow cover in the lower regions (<400 m), a matrix is used based on probability and expected snow rate. The resulting color gives you an estimation of the risk and impact strength of this parameter

 

snow rate / prob.	< 20 %	20 - 50 %	50 - 65 %	65 - 80 %	> 80 %
< 3 cm
3 - 8 cm
8 - 15 cm
15 - 30 cm
> 30 cm

 

For the snow cover in the higher regions (mainly the Ardennes region >400 m), an other matrix is used based on probability and expected snow rate. The resulting color gives you an estimation of the risk and impact strength of this parameter

 

snow rate / prob.	< 20 %	20 - 50 %	50 - 65 %	65 - 80 %	> 80 %
< 8 cm
8 - 15 cm
15 - 30 cm
30 - 60 cm
> 60 cm

 

Beside this snow, also clear ice due to precipitation on the roads plays a role in the warning system (ice layer in mm/24h)

 

ice / prob.	< 10 %	10 - 30 %	30 - 60 %	60 - 80 %	> 80 %
ice layer <1 mm
ice layer 1 - 5 mm
ice layer > 5 mm

 

SEVERE CONVECTIVE STORMS

 

For the warnings of severe* convective storms,  a matrix is used, based on the probability of severe convection and the foreseen strength of the convection. The resulting color gives you an estimation of the risk and impact strength of this parameter.

 

severe* convection / prob.	< 10 %	10 - 30 %	30 - 60 %	60 - 80 %	> 80 %
severe* convection
very severe* convection (with hail>3 cm and/or gusts >120 km/h)

 

(* hail > 1.9 cm and/or convective wind gusts >90 km/h and/or a tornado and/or flash floods of > 60 mm/3h)

 

On the map, the type of severe weather is mentioned as follow :

 

WIND : wind gusts (all types)

T-STORM : thunderstorms