I was mulling this over and it could be colorful. As have we all, I have run in wicked electrical storms, sick as dog, blinding hail and rain, mud, icy roads, snow.
But for me the worst weather and overall run was on the way back to Boulder in January, 2000, right after a debauchery-filled New Year's mosh-pit-themed weekend in Las Vegas. I made my non-running friend stop in Santa Fe where I had to, HAD to go for a run--he's usually cool about it, normally liked to catch a nap.
Still, it was sooo cold and though winter had started I was poorly prepared for it to be record cold. I was wearing long underwear under a thick sweatshit and Levis. I just said f*** it, tied a bandana around my face, dug out some down North Face mittens, pulled out the long-eared fleece cap, threw on the shoes, and went for a 10-miler along the dirt strip beside the Old Taos highway north of Santa Fe. There was a 30-40 MPH wind (unusual when it's that frigid) and it was unbearably cold so I ran hard the whole way, mainly so I didn't turn into a popsicle, even though I could barely even sweat. New Year's hangover didn't help either.
I get back to the truck and Joe has it running and the windows are frosted over. He's a big Mexican dude, and pissed as hell I'm gone for over 70 minutes. Apparently he froze his butt off the whole time and probably considered leaving my ass in New Mexico. We stopped in nearby Espanola for dinner, almost 2,000 feet in elevation lower than Santa Fe and the temperature on the bank was -3. Probably was -10-15 and being windy in Santa Fe. Probably not as bad as running in North Dakota but it was the harshest run I had ever done and it almost cost me a drinking buddy to boot.