I'm looking for a weather API which has information on what the weather is "About to do..." (within as short a time as possible).
For instance, I could put in Mountain View, CA and retrieve: "About to starting raining in 10 minutes..."
(So far, I've only found the daily weather condition.)
Is this available anywhere?
Airports (and other instances) publish weather information regularly as a METAR report (which describes the current weather) and a TAF report (which describes what's coming, with probabilities).
If you were to check the weather for Stockholm (Sweden) you first find an airport there (I choose Arlanda for this example). The ICAO code for Arlanda is ESSA (Europe Sweden Stockholm Arlanda). Luftfartsverket, the Swedish authority for air space control, consolidates all metar published into one page, and taf at another making it easier to get an overview.
This info was current at the writing of this post:
METAR: ESSA 020850Z 28005KT 9999 FEW014 BKN015 M07/M08 Q1006 RWY 19 ICE
0-10 PCT 1 MM FC 0.50 RWY 26 ICE 0-10 PCT 1 MM FC 0.47 NOSIG=
TAF: ESSA 020530Z 0206/0306 29007KT 9999 SCT014 BKN035 PROB30
0206/0306 4000 -SN BKN008=
You need to read the linked Wikipedia articles for information on the parsing. This following is just a part of what they tell you. The metar is taken 08:50 zulu time (gmt+0), about 10 minutes ago, wind speed at 5 knots, good visibility, -7 degrees celsius. The taf is older, (05:30 zulu time) and indicates some snow (-SN).