This forecast fell apart. During light southerly conditions (from the about the end of September to April), a small heat low develops inland around the Nelson Lakes area and draws cooler air from the coast via Marlborough. As the cool maritime air moves inland it condences and forms cloud. Marlborough completely claggs in. http://dl.getdropbox.com/u/2492379/061107%20easterly%20drawn%20into%20BHE.jpg It then takes a reasonably stiff west or NW breeze at ridge top level (1000m) overnight to flush the cloud out of the region, otherwise it stays until winds freshen the following day. Despite ridge top winds freshening from the west last night, they didnt reach sufficient strengths to peal all the cloud away before dawn. No other forecast providers picked it either.

Partial clearance allowed more cooling to take place shortly before dawn around Wairau Valley township and upper Waihopai Valley than expected. Other regions as predicted.

Cloud did not clear in the Wairau Valley until shortly before sunrise and as a result temperatures did not cool as expected. Light frost recorded in parts of the Awatere Valley as predicted.

Temperatures cooled more than expected in parts of the Awatere Valley giving light frost. It seems to do this when there is a shift in ridge top wind directions from southerly to NW, possibly cancelling drift winds at lower elevations within the valley. At present very difficult to predict.

http://dl.getdropbox.com/u/2492379/141009.pdf

http://dl.getdropbox.com/u/2492379/131009.pdf