Subzero temps but no frost

[qwertyK]

So I generally use weather.com and accuweather to look back for past weather, although the latter seems to underestimate the maxima (any experience with best one to check for past weather?) and for the first 3 or 4 days of March in my area its shown minima of 0C twice, and -1C once. Yet on those mornings I never even saw frost. Surely the skies would have been clear enough for such cold temps in the first place? I've seen frost on mornings back in late October November when temps were higher at around 3C. 

[feb1991blizzard]

24 minutes ago, qwertyK said:

So I generally use weather.com and accuweather to look back for past weather, although the latter seems to underestimate the maxima (any experience with best one to check for past weather?) and for the first 3 or 4 days of March in my area its shown minima of 0C twice, and -1C once. Yet on those mornings I never even saw frost. Surely the skies would have been clear enough for such cold temps in the first place? I've seen frost on mornings back in late October November when temps were higher at around 3C. 

You don't always see frost, you can touch a thermometer on the ground sometimes and see significantly below freezing temps and not see frost, its because there is low humidity.

[Summer of 95]

What time did you look in the mornings? 9am is 2-3 hours after sunrise in March, less than an hour in December, more time for the sun to melt a slight frost. When it's just frosty due to clear skies at night rather than actual cold airmasses (when it can persist all day in March e.g. in 2018) it's noticeable how much earlier it can melt. Last Friday it got down to -4 here, it was very frosty at 7am but hardly any sign of it by 10.

[qwertyK]

22 minutes ago, Summer of 95 said:

What time did you look in the mornings? 9am is 2-3 hours after sunrise in March, less than an hour in December, more time for the sun to melt a slight frost. When it's just frosty due to clear skies at night rather than actual cold airmasses (when it can persist all day in March e.g. in 2018) it's noticeable how much earlier it can melt. Last Friday it got down to -4 here, it was very frosty at 7am but hardly any sign of it by 10.

Around 7/8ish

[Mike Poole]

2 hours ago, qwertyK said:

So I generally use weather.com and accuweather to look back for past weather, although the latter seems to underestimate the maxima (any experience with best one to check for past weather?) and for the first 3 or 4 days of March in my area its shown minima of 0C twice, and -1C once. Yet on those mornings I never even saw frost. Surely the skies would have been clear enough for such cold temps in the first place? I've seen frost on mornings back in late October November when temps were higher at around 3C. 

First I would question the source of temperature info, some of these sites it is just raw GFS data.  But it is true that there can be no frost even if the temperature is well below freezing.  How dry the air is is key.  This was brought home during the Beast From the East in 2018.  We got our decent snow here in the second phase, but the first phase was probably more interesting from a meteorological point of view.  it snowed, yes, and it sublimated.  Changed from solid to gas.  Just disappeared, as I was watching, never seen it before like that.  

[damianslaw]

Yes when the air is very dry with little moisture, low humidity takes place and this can inhibit visible frost, sometimes producing a 'black frost'. This happened in early Feb 2012, when maxima let alone minima were often only just above freezing, and nights consistently below freezing yet no frost visible - this was also when glaze took place, and everything was coated in a 'white' non-visible ice, due to freezing rain. I think there was a notable inversion, with very cold dense air just above the surface, and milder uppers higher up.

[qwertyK]

20 minutes ago, Mike Poole said:

First I would question the source of temperature info, some of these sites it is just raw GFS data.  But it is true that there can be no frost even if the temperature is well below freezing.  How dry the air is is key.  This was brought home during the Beast From the East in 2018.  We got our decent snow here in the second phase, but the first phase was probably more interesting from a meteorological point of view.  it snowed, yes, and it sublimated.  Changed from solid to gas.  Just disappeared, as I was watching, never seen it before like that.  

Any reliable data for past weather? AccuWeather is almost never accurate for predicting weather, always overestimating and underestimating Maxima. I don't like BBC weather either and weather.com not sure where the data comes from.

[Mike Poole]

3 minutes ago, qwertyK said:

Any reliable data for past weather? AccuWeather is almost never accurate for predicting weather, always overestimating and underestimating Maxima. I don't like BBC weather either and weather.com not sure where the data comes from.

With weather websites or phone apps, I'd look at how often the forecast changes dramatically, if it is every 6 hours, they are probably just regurgitating the latest GFS run.  What you get from the Met Office is much better because they are analysing the many runs of many models and making predictions based on that ensemble of model runs. 

[qwertyK]

3 minutes ago, Mike Poole said:

With weather websites or phone apps, I'd look at how often the forecast changes dramatically, if it is every 6 hours, they are probably just regurgitating the latest GFS run.  What you get from the Met Office is much better because they are analysing the many runs of many models and making predictions based on that ensemble of model runs. 

Weather.com can change every ten minutes but never drastixallt. AccuWeather never changes. TWO is the only one that changes drastically. My annoyance with the weather channel is that I've noticed at around mid day most days . It'll say about eg 9C in the morning then at mid day it will suddenly claim to be 12c, yet it never reaches that temp and that's reflected when you look at the past weather and it's 9C. I was more interested in Apps or services to check past weather conditions and temps, I don't believe the met provide that ?