Where are the temperatures measured on the quick jump menu?

They are always colder than my temperatures in Ajijic.
Where are they measured in Chapala?

At least 10 years ago there was a weather channel in Mexico. And they had an automated weather station/site in Chapala. When the TV station closed down (Didn't show a profit) the weather station was also closed down and data that was fed for Chapala started being copies of the data from the GDL Airport.

Even today often the weather data reported about Chapala is a copy of the airport data.

We have several new weather stations lakeside located between Chapala and Ajijic. Shown below is one of them, which is located at Riberas Del Pilar. The link is shown below.  Check out the site closely and you will see that it has links to the other local weather station.

Why are the temperatures to different on this side of the small mountain separating us from Guad so different? It's the large "Heat Sink" created by the lake.

http://chapalaweather.net/

Temps can be very different in lower Ajijic versus upper Ajijic near the mountain. As Pete says its the lake.