I think this waiver is a good call based on the currently forecasted atmospheric conditions on the 17th, and I can see why the DL Meteorologists issued one.
During the day, a low pressure system will be moving east through the Ohio valley into the Northeast. Storms in the Ohio valley can cause issues for the flight tracks into the Northeast. In the morning, most of the storms would occur in central PA/NY and points west with the "first round".
Then, later in the day (afternoon), storms may form closer to, and eventually directly impact, the NYC airports.
I agree with ethernal that it doesn't seem like you should worry about your PDX-JFK flight. Storms shouldn't be too widespread at that time.