Spectacular tropo conditions on US east coast

For two days now, a spectacular tropospheric ducting event's been happening on the northeastern US coast. I noticed this yesterday morning on FM, as very uncommon FMs from Philadelphia, New Jersey, Maryland's eastern shore, Charlottesville, Richmond, and Hampton Roads were all coming in. At around 10am a Cape Cod FM came in for 30 minutes.

Today (Wednesday September 9) the event is continuing. At 10:30am, WGBH 89.7 Boston suddenly overpowered the semi-local WTMD Baltimore and was strong and steady for over 40 minutes.

daily predictions: [www.dxinfocentre.com]

Map for 9/9 showing the event: