Weatherwatch with Irv Lee

The Colour of the Weather

With a legal duty to check the weather, and an interest in self preservation, many GA pilots have realised that Actuals (METARs) and Forecasts (TAFs) for nearby or en route military bases are often available much earlier in the morning than those from civilian airfields.

Checking military data, now very easy with the Internet, helps with early warning or encouragement for getting the most out of your flying day, especially as daylight hours get shorter. The presence of an official forecaster at most military bases also gives the advantage of allowing the trends for the two hours following observation to be indicated on the METAR itself.

Inspection of military meteorological data, obtained either by Internet or telephone, reveals the little understood colour codes seen on military METARs, (but not TAFs), or used verbally to sum up both actuals and forecasts.

Checking by telephone with a military base might reveal that they are 'green but hope to be white before lunch'. Blue ('BLU') and white ('WHI') are the codes to give hope to the VFR GA pilot. Don't be fooled by 'Green', as this can indicate weather under VFR limits in the Class D around some military bases.

Other colours indicate poor conditions for the GA pilot, as they are designed for decision-making between precision and non-precision instrument approaches or even diversions.

Examine the following military METARs for different ends of the UK at the same time:

(Lyneham) 110850 EGDL 110850Z 21015KT 9999 BKN006 OVC010 11/10 Q0987 YLO NOSIG=

(Kinloss) 110850 EGQK 110850Z 08007KT 9999 FEW020 BKN250 01/03 Q0986 BLU NOSIG=

The first METAR, from Lyneham, situated west of my home airfield, doesn't need detailed investigation. 'YLO' (=Yellow), combined with the no significant change ('NOSIG') indicates it's better for me stay in the clubhouse on the ground looking for FLYER, rather than being a flyer looking for the ground. Yellow indicates visibility less than 3700 metres, or a cloud base less than 700ft, or both.

Friends in the north of Scotland have more hope, as the 'BLU' (=Blue) code and the 'NOSIG' from Kinloss indicates cloud and visibility are good for GA flying.

The UK military colour codes only summarise the worst of cloud and/or visibility, therefore wind and trends could still ruin the day.

There is no colour code system yet designed for civilian VFR pilots in the UK, but the Germans have 'GAFOR'. This service, Internet or telephone based, uses a similar colour coding idea (but be warned, different definitions to UK military colours), plus an extra sub-code to indicate whether a 'poor' colour is due to bad visibility, low cloudbase or both.

An annual Internet subscription or a premium rate phone call summarises the colours and sub-codes by region in Germany. In fact, you get three groups of codes, covering six hours in two-hour time bands, updated every three hours, so the bands move forward throughout the day.

UK Military METAR Colour Codes

Black - Airfield closed for non-Met reasons.

Red - Cloud under 200ft, and/or Visibility under 800m.

Amber - Better than Red, but cloud under 300ft, and/or Visibility under 1600m.

Yellow - Better than Amber, but cloud under 700ft, and/or Visibility under 3700m.

Green - Better than Yellow, but cloud under 1500ft, and/or Visibility under 5km

White - Better than Green, but Cloud under 2500ft, and/or Visibility under 8km

Blue - Cloud 2500ft or above and Visibility 8km or more

'Cloud' in this case is the lowest cloudbase designated as SCATTERED or worse.

This article first appeared in FLYER magazine's November 2000 edition