I had that cold a couple of weeks ago. The first three days were hell. On the fourth day I ran my last 20miler as a group run and ended up running in that hail. At one point I realised I had the onset of hypothermia but luckily the hail stopped an the sun came out. Could have been interesting, stuck out in the Hertfordshire countryside. I really should take a phone with me in the long ones.
By the 7th day I was back to normal. So good luck.