Rain Hitting the Hills

Our new (ok, not so new any more) office is in the 7th floor. We've got a wide view. Some days just watching the weather unroll is a spectacle.
Today there was a lot of rain and lightning. Not a drop fell on our building, but the hills that surround Athens took some beating. Large quantities of water coming down. Black clouds moving to and from.
I stuck my little Pentax against the window, hoping to catch a lightning. But no such luck. Obviously calculating the reaction time of me and then the camera, it's useless to see a lightning and hit the button... and expect to have it on the picture. The proper way to do it is make a long exposure (about a minute maybe) and be lucky. To do so, one uses ND (for "neutral density") filters, to prolong the exposure time without overexposing the picture.
Silly me, I had not brought my ND filter to work. In fact, I don't even own an ND filter. Maybe I should buy one. Still, I liked one or two of the pictures I took.