Xfce panel starting from v.4.9.0 supports multi-row/column layout and two plugin orientations in the vertical panels. Currently weather plugin scales its icon to the panel size, and doesn't rotate its labels vertically. This is OK for 4.8 but visually stands out among plugins following 4.9+ conventions. More details in https://wiki.xfce.org/dev/panel-deskbar-mode
Created attachment 4259 A patch implementing this feature
Fixed in http://git.xfce.org/panel-plugins/xfce4-weather-plugin/commit/?id=09c4ffec8b218d6851772dfcbeedf9804631e179, with a follow-up patch for the scrollbox scroll direction http://git.xfce.org/panel-plugins/xfce4-weather-plugin/commit/?id=5084944cbe03e7d8ef531b95d4e848759372b7d8. Thanks for reporting and for your patch.