Couple of thoughts about this past event. These are my own casual observations, feel free to add/subtract/disagree.
1.) Severe weather events are messy here 9.9 times out of 10. We usually bust on the low side of things. No matter how animated the meso models are leading up to an event, always remain skeptical and rely on the nowcasting stuff the morning of to determine where everything is lining up.
2.) The warm front will struggle to push north of I-66 the night before the event. It seems that no matter what happens, warm fronts tend to settle out between I-66 and the Potomac and not make much progress until around late morning or lunch. The longer northward progression is delayed, the lower the chances of a middle to high end event.
3.) Big dynamics with okay instability beats great instability over meh dynamics. The February event and this past event on April 13th show that it doesn't take much surface based instability to get things going if upstairs is rocking.
4.) Sub 1000mb lows just to our NW don't go quietly into the night (Credit: @Rainshadow). The June, 2013 event, the Feb 2020 event and the April 13th event reinforce my thoughts on #3.