https://www.caa.co.uk/media/3hwj223x/safety-sense-03-winter-flying-version-9.pdf

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Know the weather codes!

Whether you’re just learning to fly, or have had your PPL for many years, it’s easy to forget what the codes used in a Metar, TAF and on Form 215 mean. After all, how often do you see ‘SNSH’ through the summer months?

The key weather codes you need to know through the winter season are SN (snow), GR (hail), GS (snow pellets) and TS (thunderstorms). 

Codes usually seen throughout the year include BR (mist) and FG (fog). But did you also know BC (patches) and MI (shallow)? These are added to weather reports to denote the character of the fog.

Some Metar reports also contain runway state information. Have you seen something like 27599392 before?

This strip of numbers refers to the runway number (27), what is deposited on the runway (5: in this case meaning wet snow), the extent of the contamination (9: indicating 51 to 100%), the depth of contamination (93 meaning 15cm), and the braking action (92: indicating medium or poor).