I have the Smartthings Hub in my home automation system. Among other things, I use it to monitor temps in certain areas. It is pretty easy to set up a sensor to trigger a notification or email if a certain threshold is crossed. Here are the 'caveats'-  You need the  Samsung Smartthings (or  similar) hub. You need internet/wifi & the sensor needs to be in range of the hub. Many sensors are battery only and, depending on the sensor, may only last 3 months up to a couple years. For just one 'thing' it may be a fair amount of work.

Do you have a sensor in mind? There aren't a lot of 'outdoor' rated sensors. Finding the 'right' sensor is going to be half the battle.

good luck- jim