The METAR at 1450Z reported:

• VCTS-SHRA = thunderstorms in the vicinity and light showers
• Visibility: 9999 (10 km or more)
• No direct mention of a thunderstorm overhead (however, "CB" were reported)

The SPECI at 1512Z reported:

• TSRA = Thunderstorm with rain, meaning the thunderstorm is now occurring at the station
• Visibility reduced to 6000 m
• No major change in temperature or wind from previous METAR

Therefore, the SPECI was triggered due to the thunderstorm starting at the station (TS) and the increased intensity of precipitation (RA), a significant change in weather that warrants an updated report.

METAR provides a snapshot of the current weather conditions observed at an airport at a specific moment in time. These reports reflect actual weather observations, not forecasts, and are typically issued every 30 minutes in Europe. Unlike TAFs, METARs have no forecast period, they are valid only at the time of observation.

SPECI refers to a “Special Aerodrome Meteorological Report.” Like METARs, SPECIs report real-time weather conditions, but they are issued outside the regular schedule when significant changes occur between routine METAR updates. SPECI shall be issued whenever changes in accordance with the following criteria occur:

a) when the mean surface wind direction has changed by 60° or more from that given in the latest report, the mean speed before and/or after the change being 5 m/s (10 kt) or more;
b) when the mean surface wind speed has changed by 5 m/s (10 kt) or more from that given in the latest report;
c) when the variation from the mean surface wind speed (gusts) has increased by 5 m/s (10 kt) or more from that at the time of the latest report, the mean speed before and/or after the change being 7.5 m/s (15 kt) or more;
d) when the onset, cessation or change in intensity of any of the following weather phenomena occurs:

— freezing precipitation
— moderate or heavy precipitation (including showers thereof)
— thunderstorm (with precipitation);

e) when the onset or cessation of any of the following weather phenomena occurs:

— freezing fog
— thunderstorm (without precipitation);

f) when the amount of a cloud layer below 450 m (1500 ft) changes:

1) from SCT or less to BKN or OVC; or
2) from BKN or OVC to SCT or less.