My latest hobby – the weather and my home weather station

Well, not really my latest, but the one I’ve been working on more than others.

At one point in time I did some chasing and was a trained spotter.  I’ve let the spotter certification lapse, but it still doesn’t cease my interest and wonder in Mother Nature and her wonderful crazy weather in Oklahoma.

I got heavy into PWS (that’s Personal Weather Stations for the acronym-challenged) when my uncle had a LaCrosse 2310.  In 2006 I purchased a LaCrosse 2310 as well that lasted two years, then I purchased a Honeywell TE923W.  I also bought software to monitor, and post stats and charts to a website.

The intricacies of siting weather instruments is definitely something that most of you will roll your eyes at.  Do you often wonder what the term “60 degrees in the shade” means?  It has to do with the standard of measuring air temperature by the weather agencies.  They have precise criteria where they place their instruments.  For one, it has to be in an aspirated shield, and in most cases, it’s in a louvered cabinet that is called a Stevenson Shield.  Otherwise, if you place an instrument out in the open sunlight with no protection, what the weather office says is 60 degrees, winds up being 75 degrees because the case or enclosure you have the thermometer situated in is in direct contact with the daytime sun.

1. Now, a Stevenson Shield for most PWS hobbyists is a bit much.  I happen to have the CAD files for the certified NOAA Stevenson Screen, but after looking at it with my brother who is actually pretty good on AutoCAD, he informs me that it’s likely going to cost around $400 (do-it-yourself) to construct this screen.

The alternative is what is called a SRS (Solar Radiation Shield).  I purchased this for $34 US from Ambient Weather.

Here is the difference:

This is an SRS (Solar Radiation Shield)

This is a Stevenson Screen/Shield

The Stevenson is typically a ‘passive’ aspirated shield.  What that means is that the ambient air temperature (the real one you want to measure) is maintained using existing air circulation (just a fancy way for me to say wind, which I emit a lot of, I’ll freely admit to).

In most cases, where airport weather stations are sited, this will suffice, since it’s typically out in the middle of a field with little or no obstructions for several hundred meters in radius.  i.e. no wind breaks.

But, where this gets tricky with the personal weather stations is that, especially in an urban environment (in which I reside), there are MANY wind breaks and opportunities for what are called ‘microclimates’.  This could be as menial as road concrete or asphalt, patio concrete, heat radiating from out-buildings and utility sheds, or emanating from your house.  This can change the temperature in comparison to your closest official NOAA weather reporting station (which is likely the local airport..in my case, I have two).  Especially if that weather station sits’ at an elevation of 65 to 70 feet higher when only two miles away.  Yes, I live in a microclimate in the city, which does the following:

1. Wind deceleration.  This reduces the wind speed in comparison to the reported speed at the airport.  Caused by multiple buildings and trees.
2. Topography.  The valley tends to get cooler in the evenings quicker.  As I write this, my PWS is reporting a temperature nearly 4 degrees cooler than the nearest airport reporting station.
3. Buildings and drainage affect how the temperature and humidity is reported.

The main problem is locating the shield in a decent place.  Out in the middle of my back yard, about 4 feet above the grass.  Problem is, with all the windbreaks, the shield won’t aspirate properly, and in direct sunlight, a temperature bias (higher than the ambient air temperature due to radiational heating) of up to 10 degrees above the ambient occurs.

My solution was to artificially aspirate the shield.

How I managed this:

1. My SRS was used (first picture above, Ambient Weather’s SRS100LX
2. Since we know the problem manifests itself during the direct sunlight, I purchased a solar cell, rated at 12 volts.
3. Using an old PC fan (50mm, rated at 12v and 0.17a), I crafted a mount to place in the shields sensor chamber (if you look at the above photo, imagine the center of the shield having an oval cut out starting at the third plate down and ending at the 2nd plate up).  The thermo/hygro sensors gets suspended in this chamber with a graphite post that the sensor is strapped to.  I placed this mount at the bottom of the chamber, so it draws air out of the chamber.  This removes any built up heat in the shield, but the fan only runs if the sun is out.  The fan runs based on solar strength.  It needs at the very least 0.2 a to start, this usually converts into about 13v.  In full sunlight the panel generates over 20v.

Here are some photos of my setup:

Here’s the station console itself

The anemometer/directional

This is the rain gauge and UV sensor.  You’ll see more detailed images of the radiation shield below.

 

Here’s the finished product with the solar fan and radiation shield; some detailed photos are provided.  I have yet to fashion a permanent mount for the solar panel; that is something I am still working on.

 

 

Here’s a close-up of the shield.  You can clearly see the fan above the second plate.

Here’s a little closer shot of the fan.

An even better shot of the fan.

And here’s the finished (well, almost) product.  Still need to fashion a mount for the solar panel to put atop the post.

Advertisement