How to determine whether steep rock will “sweat” based on weather data?

We’ve been shut down by condensation three times in five days here at the RRG. Is there a way to calculate the conditions based off of temperature, dew point, etc. to find out if there’s a good chance your steep and sheltered project will be soaked?

I’m curious because I’m certain there’s a science behind it all. And approaching half-hour to the crag to find out myself is depleting our supply of dry socks.

If the humidity exceeds 90 percent and it’s been raining recently;
You are probably not gonna climb

I haven’t found a perfect way to predict it. But in general terms, colder weather, followed up with warmer front and rain is a recipe for condensation. (The rock is still cold, the air is warmer/humid, therefore beads of sweat on the rock)

I usually combine that with a look at humidity in the forecast. Anytime the humidity drops below 50% for several hours, RRG is likely to be good

There is a good way to predict it.  Too much to write on a post though.  

Is this effect an issue on vertical rock that has some sun exposure, or just in more "cave-like" situations? 

For an easy visualization, here's a forecast plot from NOAA for Slade, KY. You can look at these graphs by going to weather.gov, plugging in your desired location, and then once you're in the forecast find the "Hourly Weather Forecast" link.

Dewpoint is the temperature at which water will condense out of the atmosphere. The temperature at which this can occur will vary over time. Anytime the red and blue lines in the graph get close to the green line, you might have condensation. Anytime the red and blue lines are well above the green line, standing water will tend to evaporate.

What complicates things is that the red and blue lines are only a prediction of air temperature. You are also concerned with the temperature of the rock,. Lots of other factors influence that (e.g. sun exposure, ground temperature). But if you have a general idea of what temperature the rock will be, then you can make a good guess how that will match up to the dewpoint.

From the graph above you can see that tomorrow the dewpoint should be way low. So things should dry out pretty nicely then.

Optimistic wrote: Is this effect an issue on vertical rock that has some sun exposure, or just in more "cave-like" situations? 

It affects all rock, but in OP's situation the practical consideration is for overhanging areas. The vertical rock with some sun and wind exposure would, of course, dry faster. But on a day like today, the vertical rock is wet from the rain, there is no sun, and the overhanging rock, normally perfectly climbable in the rain, is condensed. 

Another thing I forgot to mention is that the dewpoint given in these forecasts is a prediction for Slade in general. If you're in a hollow with a bunch of wet vegetation, then the humidity (and therefore the green dewpoint line) may end up being higher where you are.

Like a climbing friend of mine said once, "I have a microclimate in my pants!"

According to some dude I heard on a podcast a while back, the RRG "Sendex" is 2x dewpoint + humidity -- temp; 100 or less is bueno.

Jon Rust wrote: According to some dude I heard on a podcast a while back, the RRG "Sendex" is 2x dewpoint + humidity -- temp; 100 or less is bueno.

That is the Sendex but doesn't factor risk of condensation.  It is an easy science for those in the know.

I appreciate the responses. Even having a ballpark idea of what condition the crags may be in is helpful. Apparently somebody has created a webpage that calculates the short term “sendex” in the rrg??

Eric Carlos wrote:

That is the Sendex but doesn't factor risk of condensation.  It is an easy science for those in the know.

I know it's not specifically for condensation, but it seems to me that the measures of dewpoint, temp and humidity will give you a pretty good idea of the potential for it.

Dylan Randall wrote: We’ve been shut down by condensation three times in five days here at the RRG. Is there a way to calculate the conditions based off of temperature, dew point, etc. to find out if there’s a good chance your steep and sheltered project will be soaked?

Basically, if the temperature of the rock is at or lower than the dew point and the air temperature is above the dew point water will condense on the rock.  Last Saturday, Oct. 26th, this was the case and most of the rock was covered in condensation (plus it was raining). You can check the weekend hourly weather data for Slade, KY and get a good idea if there will be an issue.

This is also a problem on the random warm winter day in the Red.  Let's say the low was in the 30's but the temperature gets up to mid 50's.  If the dew point is in the 40's the rock would be covered with condensation because it would take a long time for the rock to warm above the dew point.  If you run into this problem, the best bet is to find the highest, sunniest, most exposed cliff face (think windy) and hope the rock warms up.

J. R. wrote:

Basically, if the temperature of the rock is at or lower than the dew point and the air temperature is above the dew point water will condense on the rock. 

^This is it in a nutshell. 

Rule of thumb: When warm weather changes to cooler weather you will generally be in good shape, as the rock will be warmer than the atmosphere. And of course the inverse is also true.

A little more, conceptually: The key is the tiny area of air immediately above the surface of the rock. The temp of the rock influences this. If this layer is cool (think layer of air immediately surrounding an ice cube), as the warm and moist air layer above mixes with the cooler layer, water vapor cannot be sustained and will condense onto the rock.