Cast your mind back to November……. I was banging on about the lack of choice in studded ice tyres in this country, yeah!? Well guess what!? I had a dance on the disco tarmac this morning! Nothing serious, pretty low speed on the cut through i use past the Navi road tram stop, so a road that doesn’t get gritted, nor driven very often being as it’s a dead end with only a handful of houses on it, and on top of that, it seems constantly in the shade, even in Winter when there are no leaves on the trees…… go figure!?
It was +2 degrees on my thermometer at home, and my ususal ic test, checking to see if any has formed on the BBQ cover suggested no ice, so i pulled the fixie out of the workshop, and layered up, +2 is still cold!!
So my question is, what did my front wheel part company with, was it ice? Was it oil or a patch of diesel? Difficult to see at 6:20 in the morning when it’s still pretty pitch black! I wasn’t completely alone, a lady at the side of the road stopped and asked if i was ok, and a car on the road i was turning onto stopped and wound the window down to check i was ok. I picked myself up and waved them, gingerley getting back on my bike whilst undergoing the slow personal check that everything was ok!
+2 and ice? On hearing this, my mate told me that he’d heard that the time after sunrise was the coldest, and it is this time when ice can form. I wasn’t sure, i’ve never heard this, so i Googled it, and he was right! “wiseGEEK” have a page dedicated to explaining the phenomenon;
Though some may believe the coldest time of the day is at midnight, or some time before the sun rises, this is generally not true. The coldest time of the day is usually just after the sun rises. However, there are a few times, especially in the winter, when the coldest time of the day may not be during this morning time period. Weather patterns can play a role in determining when low temperatures hit during the day.
To fully understand why the coldest time of the day is just after sunrise, it is important to understand how the Earth receives and loses heat. The planet is constantly receiving radiant heat from space and returning it to space. The vast majority of the heat the Earth receives comes from the sun. During the day, heat is gained and during the night it is lost. However, just because it is night at your location does not mean the entire Earth is losing heat. One side is losing heat, but the side facing the sun is gaining heat.
As the sun rises, the portion of the Earth that is just beginning to receive the sun’s rays is still in the process of losing heat. As with any property governed by inertia, it takes a little time to reverse this trend. Meteorologist David Cook at the Argonne National Laboratory explains “Because the sun is so low to the horizon at sunrise, most of the energy is absorbed by the distant atmosphere.”
However, weather changes from day to day and the coldest time of the day may not always be during the time right after dawn. In some cases, a cold front could pass through a location, leading to cold temperatures at any point during the day, if the front is powerful enough. If this happens, the coldest time of the day will likely be in the hours after the front passes through.
Generally speaking, this cold front scenario is very rare. It may only happen a few times a year at many locations. At lower latitudes, it may never happen. It is safe to say the coldest time of the day is usually just after the dawn.
So there you have it, he was right! It doesn’t explain to me though, why if my Thermometer says +2 degrees, ice is forming? There was no obvious ice anywhere else, save the reflection of crystals in the tarmac, but certainly not sheets of the stuff. Perhaps it was oil, who knows! It’s becoming my Nemesis though that short stretch of road there, is that the second or third time i have come off on it?!