The
National Weather Service called for 74 degrees as the high on Friday. But
when I looked at Dr. Jack's RUC
miniBLIPSPOT forecast and noticed the forecasted surface temperature was
much lower:

Instead of 74 it was 67.7. This would make a big difference in lift value,
height of lift, and cloud base.
Here
is the overall RUC surface temperature forecast from Dr. Jack, calling for 67-68
degrees.

Well, instead of 3,900', cloud base was 6,000'. And like the weather service
forecast for the surface temperature did indeed get to 74 (at Leesburg airport)
. From here.

Dr. Jack's
NAM forecast for the day:

Notice that the
NAM
forecast for the surface temperature was higher than the RUC forecast.

This map and the previous one was for 4 PM. Notice that the NAM miniBLIPSPOT
gets the cloud base much better.