There are people way more sophisticated that I am that trade more accurate weather maps and model than I do. I just like to keep track of the trends.
I look at this site every day for the updated forecast. It is important for NatGas, especially on Sunday nights. It will be important for grains during the growing season. You will see gaps at the Sunday open because of changes in these maps. The reason for the gaps it’s because more days have gone by since the last trading opportunity, so there is a piling in of information that the market hasn’t discounted, yet. During the weekend the weather models are run by computers and aren’t revised by meteorologists, as they are during the week.
The 8-14 day map is also help, but less impactful
I listen to other analysts comparing the Euro models and the US just to get a general idea.
Another important one is the drought map. I learned to pay attention to this one right at the start of my trading career in 2012, when a historic drought struck the US. Grain prices skyrocketed. Had I looked at these maps in the months ahead, I would have understood the size of the problem better.
For additional help, Allendale has a good list here: http://www.allendale-inc.com/ag-tools/weather-links/