Modèle:
GFS (Global Forecast System) Global Model from the "National Centers for Environmental Prediction" (NCEP)
Mise à jour:
4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC
Greenwich Mean Time:
12:00 UTC = 13:00 CET
Résolution:
0.5° x 0.5° for forecast time <= 384 hrs
Description:
The Lifted Index (LI) is defined as a rising parcel's temperature when it reaches
the 500 millibars level (at about 5,500m or 18,000 feet asl), subtracted from
the actual temperature of the environmental air at 500 mbar. If the Lifted
Index is a large negative number, then the parcel will be much warmer than its
surroundings, and will continue to rise. Thunderstorms are fueled by strong rising air, thus the
Lifted Index is a good measurement of the atmosphere's potential to produce
severe thunderstorms.
The Lifted Index (LI) |
RANGE IN K |
COLOR |
AMOUNT OF INSTABILITY |
THUNDERSTORM PROBABILITY |
more than 11 |
BLUE |
Extremely stable conditions |
Thunderstorms unlikely |
8 to 11 |
LIGHT BLUE |
Very stable conditions |
Thunderstorms unlikely |
4 to 7 |
GREEN |
Stable conditions |
Thunderstorms unlikely |
0 to 3 |
LIGHT GREEN |
Mostly stable conditions |
Thunderstorm unlikely |
-3 to -1 |
YELLOW |
Slightly unstable |
Thunderstorms possible |
-5 to -4 |
ORANGE |
Unstable |
Thunderstorms probable |
-7 to -6 |
RED |
Highly unstable |
Severe thunderstorms possible |
less than -7 |
VIOLET |
Extremely unstable |
Violent thunderstorms, tornadoes possible |
GFS:
The Global Forecast System (
GFS) is a global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up to 16 days in advance, but with decreasing spatial and temporal resolution over time it is widely accepted that beyond 7 days the forecast is very general and not very accurate.
The model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour.
NWP:
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
http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746.