At last! a chance to use my 5 years studying meteorology at grad school in the US:
FAIRFORD EGVA 021155Z AUTO 06005KT 9999 BKN011 14/12
You should be familiar with that bit
A3015 - Altimeter setting in inches of mercury 30.12
RMK AO2 - Remarks: its a automatic weather station (ASOS) with a precipitation measurer
SLP212 - Sea level pressure in mb: 1021.2
(the next bits look exciting but are only really for weather anoraks)
70020 - 24 hour precipitation amount (thats what the leading 7 signifies), in this case 0.20 inches.
T01380124 - Hourly temperature and dewpoint in tenths of degrees C. in this case T=+13.8C and Td=+12.4C. The Zero leading indicates they are both above freezing (i.e. T and Td of minus 5 would be T10501050).
10139 - Six hour maximum temperature in degrees C (signified by leading '1'), using the same convention as above, this case is +13.9C
20111 - Six hour minimum temperature in degrees C (signified by leading '2'), using the same convention as above, this case is +11.1C
56003 - Three hourly pressure tendency (signified by leading '5') the first number is the character of the change, '6' means lower than 3 hours ago, but is decreasing more slowly with time (or was decreasing and now steady). '003' means it has decreased by 0.03mb.
As I said these are for the anoraks, and all but the most hardcore have to look them up (I cheated on the final one there!). It really doesn't help with all the mixed units of measurement, but what can you do? There's a couple of 'exciting' webpages you can use as reference:
http://www.met.tamu.edu/class/METAR/quick-metar.html
Cheers,
Gareth.