I got lucky.
I had expected it to be a day of 20mph winds and freezing temperatures. What I got was a balmy 11°C (52°F) and just a gentle breeze. All for the good as I planned to spend several hours hanging off the weather mast installing wiring to improve the new dew point sensor. A cold wind can quickly turn the roof of the observatory into a miserable place.
The original sensor housing had proved to be vulnerable to heavy icing. The new housing should be more resilient, as well as providing better daytime temperature readings. This is due to changing to a different shelter design that uses a fan to move air through the housing past the sensor. I also modified the housing with the addition of a heating element to allow de-icing.
To make the heating element I needed heavy nichrome wire. Not having any on hand I took a trip to the thrift shop. There I bought a used toaster for a couple dollars and spent an hour dismantling the toaster to remove the heating elements. I took the wire and wrapped it through the interior of the instrument housing, creating a heating element that should work quite nicely with a 12V supply, gently warming the housing and melting any ice.
A beautiful day on the summit, nice to spend a few hours atop the roof, hanging in a safety harness from the weather mast. I even remembered to put on some sunscreen to avoid frying in the high altitude sunlight. A new cable pulled through the conduit, the instrument shelter replaced, a little further wiring inside and the job was done. I will have to await another round of bad weather to see if the changes work, but given the trend this winter, I will not have to wait long.