Weather forecasts for film makers, what does it all mean?

Some of the most important and difficult production decisions involve weather predictions. There are now a wide variety of sources to obtain information. 

See MediaWeather.tv

Additionally there are excellent commercial services with the advantage of being  able to talk personally to a forecaster (albeit at a cost). Forecasters understandably tend to use a range of technical terms as a form of verbal shorthand.

To assist you, here follows a 'decode' of the most commonly used meteorological terms.

Warm Front   High, overcast gradually lowering cloud, light then heavy rain. The total passing of this front may take 2 - 3 days. If you want grey light and rain, great if not, shoot interiors.

Cold Front    Sharp showers, gusting winds then clear blue skies and another heavy shower etc (possible thunder in the Summer). These quickly changing conditions are often a production nightmare. After the front passes in 1 - 2 days, there is often stunning visibility and bright sunshine.

The weather chart indication of a warm front is xxx generally remembered as 'warm tits' whilst the indication of a cold front is xxx generally remembered as 'cold tits'. You may never look at a weather chart in the same way again! Occlusions termed as Warm or Cold, they have similar weather as warm or cold fronts but take less time to pass.

Anti Cyclone/High Pressure normally good weather, an area of long lasting stable conditions.  In Summer it gets hotter and stickier, with decreasing visibility due to air pollution. In Winter prolonged fogs can occur, if you need good visibility shoot as soon as you can after the arrival of an anti-cyclone.

Depression/Low Pressure Area/Trough Normally poor weather.

Deep Depression particularly bad weather.

Isobars Lines drawn on a weather chart showing areas of the same pressure, presenting the layout of the weather.  The closer the lines are together, the stronger the wind. Wind direction is always forecasted and reported "from", therefore a Northerly wind is from the North. The term 'Backing' means changing direction anti-clockwise, and 'Veering' clockwise.

Beaufort Scale is a maritime system of applying a number of wind speeds:

No.   Description 









10     

Diurnal Temperature Variation  The lowest temperature is just before sunrise and maximum temperature occurs not at midday but at 2-3pm. This seems irrelevant but affects many weather aspects; any cloud cover decreases the temperature difference.
Weather Forecast, notes
Land/sea breezes Temperature imbalance between land and sea causes onshore wind in the day time and offshore at night. Due to Diurnal variation, maximum wind strength occurs in the afternoon.  If you want to shoot a relaxed scene on the top of the cliffs (subject to light), try to shoot in the morning.

Clouds (or how much sunshine can we expect?). There are numerous individual titles for cloud types, but they can be broken down into two main types.

Stratus   =layer cloud, no direct sun, amount of light depends on thickness of cloud.
Cumulus =towering type, sun then shade etc.

There are also three altitudes 'low' = low, 'alto' = medium, 'cirro' = high. The only other name to remember is 'cumulo numbus' = thunderstorms.

Fog = visibility less than 1,000m. Mist = visibility 1 -10km. The classic localised fairyland mists will only form with overnight clear skies, cool moist air and a light wind. If there is no wind, a dew forms and if a strong wind, cloud forms.

Burn Off is a terms which has more film than meteorological use for the re-absorption of visible moisture and thus improvement in visibility, often confused with thermal lifting of mist as the earth's surface warms. If either hasn't happened by mid-afternoon, forget it.

Finally, there are often request to 'phone around' to get a better forecast. It should be understood that the Met Office compile all the weather data at their headquarters in Bracknell (they have the most powerful computer in the world there). The general situation and forecasts are then transmitted out to the many weather information services. Local airfields may or may not have a Met Office but are often used as a recording centre and have a localised knowledge of the interpretation and how it affects their area; but with the availability of pre-recorded area forecasts, many are now reluctant to help.

Forecasts beyond three days tend to be unreliable, long range non existent.

There are many who study meteorology who believe that in recent years (since they got it so wrong in the storms) that forecasts have tended to become pessimistic. Meteorologists probably work on the theory that you'll never meet a disappointed pessimist.

This is not helpful to us as film makers, thus the more that you can cross reference and self interpret weather charts the better.

At the end of the day and this is entirely serious, especially in hilly and mountainous areas, it is often the local farmer or fisherman who may not know about global climatology but can probably predict more accurately the weather in their specific area.
Light Breeze
Gentle Breeze
Moderate Breeze
Fresh Breeze
Strong Breeze
Near Gale
Gale
Strong Gale
Storm Force
Leaves rustle
Leaves and twigs move
Raises dust
Small trees sway
Difficulty with umbrellas
Difficulty to walk against wind
Roof slates blown off
Structural damage
Trees uprooted