The proceedings of the Second International Congress on Psychotronic Research included several papers on dowsing. Apostol and Dumitrescu (1975) presented an abstract on their work. They found that the electric potential between dowsers’ palms was correlated with a number of variables such as galvanic skin response, magnetic field, soil temperature, and atmospheric pressure. They found that the ‘dowsing area’ (an undefined term) was correlated to geophysical anomalies and that its extent showed a diurnal variation. 
http://www.tricksterbook.com/ArticlesOnline/Dowsing.htm

Major - Major Discovery -

An approaching low pressure system induces more humidity. The reason enhanced forecasts occurred after visiting a steam room is because the steam room has enhanced humidity. Also the ocean/beach has increased humidity when a low front occurs.

The reason many gifted individuals receive their inspiration at night in their dreams, especially during winter, is because low pressure occurs more heavily during the nightime/early morning hours. (when a low pressure front is coming (and they do, all the time) it signals not only a change in the weather, but a drop in the barometric pressure.) High pressure systems are “domes of density” that press down, while low pressure systems are akin to “atmospheric valleys” where the density of the air is less. If we decrease the air pressure, the air tends to rise into the higher levels of atmosphere where temperatures are colder.  As the capacity to hold water vapor diminishes, the vapor rapidly condenses and clouds (which are composed of countless billions of tiny water droplets or, at very high altitudes, ice crystals) will develop and ultimately precipitation will fall. 

There is an internal sensing mechanism that is responsible for detecting the future. During certain times this detection mechanism becomes more affected by outside stimuli, which results in an inaccurate rv session.  At other times this internal mechanism is "strengthened" and not affected by outside disturbances or interruptions.

Favorable Geographic Locations

Areas with strong winds occurring on occasion, with stormy weather at latitude of Oregon and below
Grey Rock substrata outside of a magnetic anomaly occurring location
between 2 earthquake fault lines 
near a major river or coastline with ocean waves
in a valley where wind flows through an area that retains a "bubble" of cool as warmer temperatures begin to occur
An eastwards facing slope that does not get afternoon sunshine 

Both the Portland and Topanga locations happen to lay at the outside "ring" of a magnetic anomaly - a good zone for doing the scan.

Favorable Conditions

Just after or before an active magnetometer within 24 hours

After 3 or more days of declining atmospheric air pressure

The last 24 hours before a sharp rise in air pressure after it has been in decline the last 3 days.

Declining in X-ray background Flux Levels

Solar wind entering the 350 speed level and has not gone past the 50% mark towards an increase in solar wind speeds (may be optional, if major favorable conditions are present)

The above conditions carry enhanced clarity 3 to 5 days after a major solar flare, increase in sunspot activity. 

Boosters: 
Full moon
KP above 11 and below 7
Apogee moon
Sundays