I thought I understood about critical frequencies and MUFs and such, but
an event this evening has me puzzled.

I was on a military net on a frequency somewhat above the 75-meter band.
According to the "Near Real Time F2-Layer Critical Frequency Map" at
http://solar.spacew.com/www/fof2.html, the critical frequency in this area
at that time was below 3 MHz, which would have put it WELL below our
frequency of operation. Yet, I was able to communicate with another
station about 70 miles away, with weak-but-clear (Q5 copy) both ways. And
I'm only running 5 watts (he was running 100 watts I believe).

70 miles seems a bit far for groundwave, and the critical frequency seemed
much too low for NVIS, so how was I able to communicate reliably with this
other station?

My antenna is a half wave dipole for the frequency in use, at elevation 17
feet above ground. My ground elevation is about 250 feet above sea level.

Would that big solar storm of the last day or so, the one that made all
the news about how it might knock out satellites and power grids and such,
have anything to do with it? I would have thought that if anything, that
would have hurt not helped.

Seems very strange...