Author Topic: Ice forecasting... (Read 2820 times)

andyoxon · « **on:** 04 January, 2018, 11:30:51 am »

What weather indicators do people normally use to try and predict the risk of ice on road? Simply temps less than say 2C (i.e. close to freezing)? Something else? At what point might you ride on non-major roads with care?

Whitedown Man · « **Reply #1 on:** 04 January, 2018, 12:55:59 pm »

My threshold is a forecast of 3 degrees or below - can offer no science for this, but experience suggests that when the forecast says 3 there may be isolated / localised patches of road that are likely to have iced.

Mr Larrington · « **Reply #2 on:** 04 January, 2018, 02:19:01 pm »

My motor-car bongs at me and displays an appropriate symbol on the dash when it thinks it's 4 degrees or lower outside.

Kim · « **Reply #3 on:** 04 January, 2018, 02:32:25 pm »

Depends on what the temperature's been doing previously. 3C will likely be fine if it's been 8-10C for the previous three days. Not so much if it's been freezing for a week and there's still snow on the ground.

If it's 5C or lower I tend to have asthma issues, so I'm already thinking about what I'm doing on a bike vis whether it's worthwhile, potential bailout options and so on. Considering studs or three wheels is a logical extension of that.

Torslanda · « **Reply #4 on:** 04 January, 2018, 05:00:04 pm »

Looking out of the bedroom window in the morning at the windows on the car.

Sorry, not much help i know . . .

Ben T · « **Reply #5 on:** 04 January, 2018, 07:23:38 pm »

Avoid cycling early in the morning.

Cudzoziemiec · « **Reply #6 on:** 04 January, 2018, 07:55:11 pm »

I think BenT's advice is sound. Black ice forms on the ground, sometimes when rain freezes on hitting the ground but more commonly when an already wet surface freezes. So if it's been above zero and raining then the temperature drops overnight, surface water freezes and black ice forms. Or snow gets compressed and/or slushed by car tyres then freezes. But you probably knew all that already. Nevertheless, I generally reckon freezing evenings are okay but take extra care (like stay at home!) the following morning.

Peter · « **Reply #7 on:** 04 January, 2018, 08:14:07 pm »

Whichever method(s) you try, you need to bear in mind that even when the temerature seems to suggest safety there may be areas in the shade of hedges on e.g. Cheshire lanes that may never have seen the low winter sun for weeks. "Run-off" (aka water) can stay frozen for days in such circumstances. Please, if you have the slightest suspicion that there might be ice, just don't go!

telstarbox · « **Reply #8 on:** 04 January, 2018, 08:37:08 pm »

If it's likely that vehicles have been over a frozen road before you ride it (eg after morning rush hour), does this help or hinder?

LittleWheelsandBig · « **Reply #9 on:** 04 January, 2018, 08:40:47 pm »

Helps. Friction and pressure creates heat. Heavily used roads stay ice-free much longer than bikeways and it isn't just because of gritting.

Bridges, particularly lightweight bridges, cool down quicker and to a greater degree than roads on the ground.

Kim · « **Reply #10 on:** 04 January, 2018, 08:50:54 pm »

The exception is snow, where virgin snow of reasonable depth can be tackled with a normal MTB tyre, but once vehicles have been over it you get ruts of unpredictable levels of compactedness, frozenness and shear strength.

But you can at least see that.

Cudzoziemiec · « **Reply #11 on:** 04 January, 2018, 08:53:04 pm »

...except when it's hidden under further snow fall.

Moleman76 · « **Reply #12 on:** 05 January, 2018, 06:44:27 am »

Quote from: Mr Larrington on 04 January, 2018, 02:19:01 pm

My motor-car bongs at me and displays an appropriate symbol on the dash when it thinks it's 4 degrees or lower outside.

Mine does too, but in the Fahrenheit equivalent.

Bear in mind that the air temp isn't identical to the surface temp. If it has been clear overnight, the cooling-to-sky effect can yield black ice on roads even when the air temp is above freezing.

andyoxon · « **Reply #13 on:** 05 January, 2018, 03:51:27 pm »

Thanks all. Difficult to predict ice with any certainty I guess. I notice some weather websites have 'freezing altitute', but this doesn't seem very useful really.

Kim · « **Reply #14 on:** 05 January, 2018, 07:02:47 pm »

"Clear sky at night, cyclist's in for a fright."

Basil · « **Reply #15 on:** 05 January, 2018, 07:36:53 pm »

Clear in the morning., cyclists' warning.

mattc · « **Reply #16 on:** 05 January, 2018, 07:51:41 pm »

Quote from: andyoxon on 05 January, 2018, 03:51:27 pm

Thanks all. Difficult to predict ice with any certainty I guess.

Indeed - but you woldn't have asked if it was easy!

One thing that helps is the council/highways gritting plans (i think they tweet in our area? There is certainly a map online, although that is more use for finding out WHICH roads are gritted!).

Internet winter is full of people claiming the power of ice prediction, and the ability to see ice soon enough to avoid a crash by simply slowing down; thus making cold weather entirely safe for these people. they claim. I think this thread demonstrates how much bollox that usually is!

mattc · « **Reply #17 on:** 05 January, 2018, 07:55:11 pm »

carp - me and my big mouth

I;ve just checked the forecast, and tomorrow's dawn start has now been revised - temp-wise - downwards. Sub-zero start. Bah!

Luckily I think I can main-road the early route ... please noone point and laugh at my imminent broken collar-bone photos ...

'ere ya go Andy:

Oxfordshire County‏ @OxfordshireCC Following Following @OxfordshireCC More Our gritters will hit the roads just after 7pm. It's a cold Friday night ahead so if you're out for a drink don't sit in the beer garden!! If any of you have plans for driving tomorrow morning please take care on the roads. Gritting helps - but it's still Winter conditions.

https://twitter.com/OxfordshireCC/status/949353304739459072

Mr Larrington · « **Reply #18 on:** 06 January, 2018, 12:39:36 pm »

After Oxfordshire CC assured Nik Windle that there was no flooding anywhere in the whole county the day before the 2007 Cheddar Gorge 300 I'm not sure I'd trust their opinion

Pickled Onion · « **Reply #19 on:** 06 January, 2018, 03:12:40 pm »

It's very difficult, often before the temperature drops the humidity drops too and the roads will dry out so there's no ice even though it's several degrees below freezing. Other times there is precipitation then the skies clear overnight and there are frozen patches but the air temperature is a few degrees positive. I tend to go on a combination of "are the cars frosted up" plus "is the road wet". You have to look at an untreated road, as the salt attracts moisture, so a treated road will be wet when the untreated ones are dry.

Jon P · « **Reply #20 on:** 12 January, 2018, 03:33:27 pm »

Surely you'll be fine once you get onto the main roads? Though my Dahon folder's wheels slide at the slightest opportunity, so it takes a lot less than ice to make me ultra careful on it. I remember a January audax from Oxford a while ago where the country lanes were frozen solid - I started it with another 'bent rider who ditched after he came off, dragging me down with him! - thereafter, roads were fine. But stalwart blokes on uprights were tackling it nonetheless, a battlefield with regular instances of the fallen lying along the roads, but most made it through unscathed.

Author Topic: Ice forecasting... (Read 2820 times)

Ben T