The whole weather notification text is a bit of a hack. I had to create an image for every possible temperature, because Android does not have an API for showing text in the title bar. So what I am saying is that there is no way to make the notification temperature text perfect, and believe me, I tried. With the space that is available that is pretty much the best I can do... sorry. I put an option to simply show an icon rather than the temperature if it is annoying you.
Can you create the images one the widget is started for the first time.
You can use the current font and just blit to the image instead of the screen. Then use those images for showing as notification temperature.