There is a user that works for NOAA's National Weather Service (NWS) Joshua Kastman, that has the following idea:
He would like the ability to draw cold fronts on ArcGIS Online. He has noticed that in ArcMAP you can change the line style to cold fronts by referencing the "Weather" style in the symbol selection gui.
This is his justification:
This enhancement would be beneficial to the Weather Prediction Centers's (WPC) Hydrometeorology Testbed (HMT). We have three separate experiments with collaborators throughout the nation with dozens of participants for each experiment. We currently exploring ways to enhance collaboration and visualization of experiential products and will be increasing our use of ArcGIS Online to further that goal . Access to the custom symbol libraries would certainly enhance HMT's ability to effectively communicate experimental forecast in a GIS environment.
Note: ESRI has created Enh-000087498 that is similar to this issue.