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November 2019 discussion


weathafella
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Just now, OSUmetstud said:

Does anyone have information or some principles or criteria for how to determine if the water leftover on a road surface from rain or snowmelt with refreeze before it evaporates?  I can't seem to find much online for guidelines. 

I feel like that is such a concept with tons of variables. I'd say if you have generally 20+kts for 2 hrs after any precip ends and temps above 32, you are good except for random puddles. Even that may be conservative. I know Will used to do forecasts for DPW crews so he may know more.

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1 minute ago, OSUmetstud said:

Does anyone have information or some principles or criteria for how to determine if the water leftover on a road surface from rain or snowmelt with refreeze before it evaporates?  I can't seem to find much online for guidelines. 

So much in play, road temps at the surface and below, temp, wind, dewpoints and evaporation transpiration 

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1 minute ago, Ginx snewx said:

So much in play, road temps at the surface and below, temp, wind, dewpoints and evaporation transpiration 

Yeah, I know, I feel like it mostly a shot in the dark when forecasting. I mean I know generally speaking sharp temperature drops are one of things that really helps, but there's so much more to it. I was hoping someone did some modeling. I can't find anything on the aurora project website which is a collaborative effort on road weather forecasting that my company has contributed to. 

We had a sneaky re-freeze Tuesday morning where there was damp/wet ground and light winds and then pavement temperatures dropped to about 28F in the morning as it cleared out. Not a flash freeze per say, but still there a couple accidents around and light coating of ice in some areas. 

The re-freeze thought might have happened last night was mitigated by strong winds and drying dewpoints, so only a few icy puddles were left from yesterday's rain. 

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15 minutes ago, CoastalWx said:

I feel like that is such a concept with tons of variables. I'd say if you have generally 20+kts for 2 hrs after any precip ends and temps above 32, you are good except for random puddles. Even that may be conservative. I know Will used to do forecasts for DPW crews so he may know more.

don't forget about salt content. you know what i am talking about. the roads are over-salted, so when the puddle evaporates, it leaves a nice white ring around where the puddle was.

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1 minute ago, OSUmetstud said:

Yeah, I know, I feel like it mostly a shot in the dark when forecasting. I mean I know generally speaking sharp temperature drops are one of things that really helps, but there's so much more to it. I was hoping someone did some modeling. I can't find anything on the aurora project website which is a collaborative effort on road weather forecasting that my company has contributed to. 

We had a sneaky re-freeze Tuesday morning where there was damp/wet ground and light winds and then pavement temperatures dropped to about 28F in the morning as it cleared out. Not a flash freeze per say, but still there a couple accidents around and light coating of ice in some areas. 

The re-freeze thought might have happened last night was mitigated by strong winds and drying dewpoints, so only a few icy puddles were left from yesterday's rain. 

In my experience flash freeze occurs more often when antecedent ground conditions are primed. Meaning some deep cold in the ground before the rain allows for quicker refreeze. Last year we had a flash freeze when 33 degree rain ended as low 20 degree air took over, the dewpoint crashed but winds lagged. I was driving Tues night with temps in the 20s after our rain , roads were just wet, I kept tapping my breaks to see if the sheen was ice, it wasnt, the antecedent ground conditions kept the water from freezing despite what I would think were ideal conditions. Despite low temps low dews and wet roads nothing froze, on my return trip the road was dry. Lots to consider 

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1 minute ago, Ginx snewx said:

In my experience flash freeze occurs more often when antecedent ground conditions are primed. Meaning some deep cold in the ground before the rain allows for quicker refreeze. Last year we had a flash freeze when 33 degree rain ended as low 20 degree air took over, the dewpoint crashed but winds lagged. I was driving Tues night with temps in the 20s after our rain , roads were just wet, I kept tapping my breaks to see if the sheen was ice, it wasnt, the antecedent ground conditions kept the water from freezing despite what I would think were ideal conditions. Despite low temps low dews and wet roads nothing froze, on my return trip the road was dry. Lots to consider 

Yeah, thanks. I would think frozen ground and snowpack would help, doesn't allow absorption and the water can quickly freeze from both below and above. 

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