I have found a very cool web site with a good consolidated  weather forecast as well as historic data.  It is:

CLICK HERE (GUIYANG PAGE)

Weather for Monday SAMPLE DATA

Narrative from ChinaTravelGuide.com

SAMPLE DATA
SEE LINK ABOVE

Guiyang nestles in the southwest of China, on the eastern side of the Yunnan-Guizhou Plateau. It has a pleasant moist subtropical climate with plenty of sunlight and ample rainfall. It does not have intense heat in summer or severe cold in winter. Guiyang weather is fresh and humid without any sandstorm. The agreeable climate makes it a cozy city for living.

A yearly average temperature of Guiyang is about 15C (59F). July is the hottest month of the year with an average of 24C (75F) while January is the coldest one, averaging a temperature of 4.6C (40F). This place features four distinctive seasons, with winter to be the longest one.

Its genial year-around weather contributes a lot to its popularity among travelers. However, due to the changeful weather on the Yunnan-Guizhou Plateau, it is recommended to take rain wear along with you whenever you go out. A folding umbrella is indispensable! Due to its topography, the things for anti-solar radiation should be fully prepared. Mornings and evenings can often be rather cool so a windproof coat is necessary.

If you are lucky enough to visit in March or April, you can experience a lot of traditional Miao festivals. From April 30 to May 7 there is the Baiyun National Kites Festival and from June to August is the Hongfeng Lake Tourism Festival, lasting nearly two months. The best seasons for visiting the Huangguoshu Waterfall near Guiyang are summer and autumn when the scenery is the most splendid. The good weather means that travelers can visit at any time of the year. However, the best weather there is in late August.