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mer 26.10 09 GMT
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Max. wind velocity NAM Modèle


NAM: North American Mesoscale Forecast System "NOAA"

Mise à jour:
4 times per day, from 0:00, 06:00, 12:00 and 18:00 UTC
Greenwich Mean Time:
12:00 UTC = 14:00 CEST
Maximum wind velocity of convective wind gusts
The method of Ivens (1987) is used by the forecasters at KNMI to predict the maximum wind velocity associated with heavy showers or thunderstorms. The method of Ivens is based on two multiple regression equations that were derived using about 120 summertime cases (April to September) between 1980 and 1983. The upper-air data were derived from the soundings at De Bilt, and observations of thunder by synop stations were used as an indicator of the presence of convection. The regression equations for the maximum wind velocity (wmax ) in m/s according to Ivens (1987) are:
  • if Tx - θw850 < 9°C
    wmax = 7.66 + 0.653⋅(θw850 - θw500 ) + 0.976⋅U850
  • if Tx - θw850 ≥ 9° C
  • wmax = 8.17 + 0.473⋅(θw850 - θw500 ) + (0.174⋅U850 + 0.057⋅U250)⋅√(Tx - θw850)

  • Tx is the maximum day-time temperature at 2 m in K
  • θwxxx the potential wet-bulb temperature at xxx hPa in K
  • Uxxx the wind velocity at xxx hPa in m/s.
The amount of negative buoyancy, which is estimated in these equations by the difference of the potential wet-bulb temperature at 850 and at 500 hPa, and horizontal wind velocities at one or two fixed altitudes are used to estimate the maximum wind velocity. The effect of precipitation loading is not taken into account by the method of Ivens. (Source: KNMI)
La prévision numérique du temps (PNT) est une application de la météorologie et de l'informatique. Elle repose sur le choix d'équations mathématiques offrant une proche approximation du comportement de l'atmosphère réelle. Ces équations sont ensuite résolues, à l'aide d'un ordinateur, pour obtenir une simulation accélérée des états futurs de l'atmosphère. Le logiciel mettant en œuvre cette simulation est appelé un modèle de prévision numérique du temps.

Prévision numérique du temps. (2009, décembre 12). Wikipédia, l'encyclopédie libre. Page consultée le 20:48, février 9, 2010 à partir de

These charts are for guidance only, actually gusts may be considerably higher than those shown.

Max. wind velocity NAM mer 26.10.2016 09 GMT
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