A SPECI (Special Meteorological Report) is issued when there is a significant deterioration or improvement in weather conditions. According to ICAO standards, one of the criteria is when cloud cover becomes BKN (broken, 5-7 octas) or OVC (overcast, 8 octas) below 1500m (or below lowest minimum sector altitude). SCT (scattered, 1-4 octas) does not qualify for a SPECI.