Highway 2331 runs into Phu Rin Rong Kla national park which is a little northwest of Lom Sak or southeast of Dan Sai. The video of the climb up to the park entrance can be found here. Initially the road in the park was unsealed but soon comes good and the road is OK past the end of the video.
As can be seen from the elevation graph and the photo you are high up and fog is most likely in the mornings but should clear up as the day advances. Temperature drops off so good to have an extra layer to hand during the cool season.
Map of the route:
Ride carefully and always within your ability. The video shows speed (it is not completely accurate and has some inconsistencies), elevation graph, longitude and latitude, time and date, distance along the route and a squiggly line representing the road with a dot showing the current location. This video was shot in December 2014 and roads in Thailand do change over the years, a once pristine section of tarmac can degrade and likewise a bad section can be resurfaced and become as smooth as silk!
Leave a comment if you have an up to date report.
You can find excellent bike reports and information of northland Thailand over at Golden Triangle Riders