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Check the MetEd pages for extensive information on meteorology

 

Wind levels

Wind speed in km/h is indicated at different levels for a seven day period. Levels are normally the summit and 500m intervals below the highest point. The wind speed is marked red above 60 km/h. This is an arbitrary threshold. 60 km/h is rather windy at high altitude, it may be OK on easy ground but it can make progress impossible on more technical routes.

Wind profile

Here the wind speed is indicated at all levels for a seven day period. The height is indicated as pressure levels (see the conversion charts). For 8000 m mountains is given between 5500m and 11800m approximately, for lower mountains, between 1500m and 5000m approximately. Wind speed is given in km/h, see the conversion table for other units.

T profile

Temperature profile indicated at all levels for a seven day period. The height is indicated as pressure levels (see the conversion charts). For 8000m mountains is given between 5500m and 11800m approximately, for lower mountains, between 1500m and 5000m approximately. Temperature is given in degrees centigrade, see the conversion table for other units.

RH profile

Relative Humidity profile indicated at all levels for a seven day period. The height is indicated as pressure levels (see the conversion charts). For 8000m mountains is given between 5500m and 11800m approximately, for lower mountains, between 1500m and 5000m approximately. Relative humidity is given as a percentage. A value of 100% means saturation, and therefore cloud, fogs and likely snowfalls.

Meteogram

The model outputs are given at pressure level, that is why the Y-axis shows milibars (mb) or hectopascals (hPa). The height over sea level corresponding to a given pressure changes depending on latitude, surface temperature and atmospheric temperature profile. A correspondence for the standard atmosphere is given in the charts below.

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click to enlarge in a new window

Hovmoellers

Hovmoellers (or rather pseudo Hovmoellers). First panel indicates the evolution of several parameters in a vertical profile over a week period. On the Y-axis is indicated the pressure level (see above) and on the X-axis the date. Data are plotted at 3h intervals. Background colour is relative humidity (RH) from white (0%) to grey to green (100%). High relative humidity values (over 80% - 90%) might indicate coondensation, and therefore cloud formation at the given level.

Colour contours indicate air temperature (°C). The 0°C isotherm is highlighted, which helps forecasting snow level. It is worth reminding that it can snow at higher temperatures, depending on relative humidity and temperature profile aloft. These contours, togeter with wind speed and direction can give a rough idea of air masses and fronts displacement.

Wind barbs indicate wind speed and direction. Convention is 10knots per barb, 5 knots half a barb and 50 knots per triangle. For example, wind coming from the North West at 60 knots: ; or wind from the SW at 25 knots:

CAPE Convective Available Potential Energy

CAPE is the maximum buoyant energy available to an ascending parcel of air. It is a measure of atmospheric instability, with high numbers indicating possible convective activity (and therefore thunderstorms)

TCC Total cloud Cover

The amount of cloud cover, 100% means completely overcast, 0% completely clear. The GFS model seems to overestimate the total cloud cover. Check the solar irradiation for a better estimate.

1000 - 500mb thickness

The 1000 - 500 thickess is the height difference between the 1000mb level and the 500mb level, measured in decameters (10m). As air expands with heat, a smaller thickness means colder air in between. A practical rule of thumb is that precipitation on the ground is usually as snow if the thickness is smaller tan 540.

Totals - Totals and Lifted Index

These index are useful to determine atmospheric instability and thunderstorm risk.

Totals-Totals is calculated as TT = (T850 - T500) + (Td850 - T500),
where T is air temperature, Td is dew point and the numbers indicate the pressure level.

The lifted index is the temperature difference between ambient temperature at 500mb and te temperature of an air parcel lifted to the same level (dry-adiabatically to saturation and moist-adiabatically above that).

These tables reproduced from Ohio University give a practical idea of the index meaning:

Totals - totals < 43 Thunderstorms unlikely 43-44 Isolated thunderstorms 45-46 Scattered thunderstorms 47-48 Scattered thunderstorms/ isolated severe 49-50 Scattered t-storms/few severe/isolated tornadoes 51-52 Scattered-numerous t-storms/few-scattered severe/isolated tornadoes 53-55 Numerous thunderstorms/ scattered tornadoes 56+ You don't want to know

Lifted Index > 0 Thunderstorms unlikely 0 - -2 Thunderstorms possible - trigger needed -3 - -5 Thunderstorms probable -5 - -7 Strong/severe thunderstorms. Tornadoes possible -7 - -9 Move to Alaska < -9 Yikes!

SLP Sea Level Pressure

This is obtained by the theoretical reduction of the barometric pressure to sea level. If ground level is above sea level, it shows the extrapolated pressure to sea level. It is probably the most familiar figure in weather charts, low pressure is usually associated to unstable weather conditions while a high pressure indicates stability.

Wind speed at 10m

This is the estimated wind speed at 10m above ground surface. The GFS model has a resolution of 0.5°, or approximately 50 x 50 km. Therefore the terrain is smoothed and ground level may not correspont to actual ground level at a given point. Wind barbs indicate wind speed and direction as explained above.

Temperature and dew point temperature at 2m

Air temperature and dew point at 2m above ground level (see above comment on model resolution). Dew point is the temperature to which air must be cooled in order to reach saturation. The closer the dew point to the air temperature the higher the relative humidity, if they are equal it means saturated air.

Relative Humidity at 2m

Relative humidity at 2m above ground level. 100% indictes saturation and therefore likely condensation, fog or clouds.

Short wave irradiation at surface

This is useful to check wether is cloudy or clear and gives a better idea of cloud thickness than the total cloud cover chart. An approximate idea of the thickness of cloud cover can be estimated by comparison with clear skies irradiation values in the chart below. The chart is calculated at 1000m a.s.l. for the European spots and at 5000m a.s.l. for the Everest

 

Precipitación

Indicates type and amount of accumulated precipitation over the last three hours. Note that precipitation smaller than 1mm/6h is normally unreliable.
Total / Rain
Convective precipitation
Freezing rain
snow
Ice pellets
 

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Wind Chill Index

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Conversion Table

1 meter 1 m/s 1 m/s 1 m/s 1 km/h °C * 9/5 + 32 (°F - 32) * 5/9 0 °C 0 °F 1 mb Pressure to height

= = = = = = = = = =

3.28 feet 1.944 knots 3.6 km/h 2.237 mph 0.6214 mph °F °C 32 °F -17.78 °C 1 hPa

Speed equivalences