Dartmoor, because of its height and general lack of shelter in the form of vegetation can be quite wild at times. The additonal height of Dartmoors hills and tors above that of Devon means that there is often an average temperature drop of two or three degrees and an average wind increase of five to ten miles per hour over that expected in the surrounding lowlands. Precipitation levels can also be elevated as the clouds are encouraged to drop their loads as the moist air is forced up and over the highland. These rules of thumb can easily be upgraded when a deep low pressure moves in from the Atlantic. Added to these factors, the lack of tree protection on most of the moors means that winds speeds can run unhindered as they scour the upper tors. On such gusty days shelter from the wind can often be found in the lower-lying valleys, particularly if you select a valley that runs perpendicular to the wind direction.
When looking for a weather forecast for Dartmoor, the power of the internet is always quite revealing, with a plethora of advisory channels to choose from. The: BBC, Metoffice, Metcheck, Local radio stations all provide fairly reasonable forecasts. When combined with a little local knowledge of how to interpret these forecasts for Dartmoor, then you can usually predict the weather quite accurately. Princetown, (approximately 400m a.s.l.) is usually a good place to start, if you are looking for a reference point, then make amendments on this forecast depending on where you intend visiting. For example; If you are visiting Yes Tor, which is another 200m higher then you will most probably need to subtract a few degrees from the suggested temperature at Princetown and add a few miles per hour to the wind speed.
There are several webcams available that can give an indication to the weather on Dartmoor. The most reliable being the DartCam (location: 50.57°N, 3.94°W – SX 628770 – facing North, 369m a.s.l. and updated every 10 minutes. The close proximity of the vegetation in the webcam helpfully allows you to predict visibility and surface snow/frost conditions. If you can see snow here then you know that the upper tors are bound to be laiden.