ICAO附件3 <1.4 Use of probability groups>

The probability of occurrence of an alternative value of a forecast element or elements should be indicated, as necessary, by use of the abbreviation “PROB” followed by the probability in tens of per cent and the time period during which the alternative value(s) is (are) expected to apply.
出现其他的预报元素的可能性，必要时可用“PROB”加上出现的可能性和出现的时间段来表示

The probability information should be placed after the element or  elements forecast and be followed by the alternative value of the element or elements.
这种可能性的报文，应该放在预报元素和其他预报元素之间

The probability of a forecast of temporary fluctuations in meteorological conditions should be indicated, as necessary, by use of the abbreviation “PROB” followed by the probability in tens of per cent, placed before the change indicator “TEMPO” and associated time group.
出现短暂浮动的气象条件的可能性，可用“PROB”加上出现可能性，放在“TEMPO”时间之前。

A probability of an alternative value or change of less than 30 per cent should not be considered sufficiently significant to be indicated.
如果出现其他气象值的可能变化少于30%，则不用表明这种变化

A probability of an alternative value or change of 50 per cent or more, for aviation purposes, should not be considered a probability but instead should be indicated, as necessary, by use of the change indicators “BECMG” or “TEMPO” or by subdivision of the validity period using the abbreviation “FM”. The probability group should not be used to qualify the change indicator “BECMG” nor the time indicator “FM”.
最后这段太拗口了，翻译不出来。

因此，PROB + TEMPO 连着出现的情况时，表示的是TEMPO出现的可能性，也就是间歇性出现的可能性。比TEMPO更弱。