Limitations
There are many limitations of the hardware and software that make the data presented by this weather station far from perfect. Most of the siting limitations are dictated by the instruments being located in a suburban neighborhood. In addition, quality siting was sometimes sacrificed to keep the instruments away from children's play areas where they weren't likely to fare well. Some of these limitations are spelled out below and crude estimates are made of their effects on the accuracy of the results.
Temperature
More effort was made toward producing accurate temperatures than was spent on any other aspect of this endeavor. The calibration data shows the instrument was capable of producing temperature readings within approximately 0.5 deg F of the actual value. Note that is 0.5 deg F of the temperature of the sensor which is not necessarily the temperature of the surrounding air. The sensor is located approximately 10 feet off the ground, a bit higher than the standard of 5 feet. The largest contributors to inaccurace readings are:
1. Solar heating of the enclosure. This has been greatly reduced by painting the enclosure white and installing a fan to continously move air through the system. In addition, the portion of the enclosure containing the sensor is below the slats making up the patio cover so sunlight usually cannot hit this part of the structure. This system appears to be quite effective. When initially installed, results over a few cloudless days showed maximum temperatures within 1-2 degrees F of the closest airport. Other nearby instruments listed in Weather Undeground often show jumps in the temperature that probably occur when the sun starts hitting the sensor. No such jumps have been seen with this setup.
2. Injestion of air heated by objects close to the sensor. The three main sources of this error are the patio cover the unit is installed in, the small concrete patio beneath the cover and the house that lies only about 10 feet away. Noise of 2-3 degrees F has been seen on a cloudless day which may be due to warm air from these sources blowing across the unit as the wind changes. Any error due to this source would result in reported temperatures higher than the actual temperatures.
3. Radiative cooling at night. This should be minimized by the fan in the same way that it reduces the effects of solar heating.
The location is not near the house's air conditioner so there should be no error from that source. It is, unfortunately, located almost directly above a portable outdoor barbecue grille which will probably result in some wild readings for a short time when something's cooking.
The Citizens Weather Observer Project (CWOP) has published guidelines for the installation of amateur weather instruments. Based on these guidlines, the current installation would probably get a rating of approximately 6 out of 10 (10 being best). Data suggests the readings are within 3 deg F of the actual air temperature in this neighborhood and are probably closer most of the time.
Humidity/Dew Point
Rules for siting a humidity sensor are essentially the same as for the temperature sensor. Since relative humidity is a function of temperature, any temperature errors will be reflected in the relative humidity values through and inverse relationship. Dew point, however, shouldn't show any effect of temperature errors. One additional requirement for the humidity sensor is that it not be placed under large trees or bushes that could raise the humidity locally. The current installation is not close to any such plants so this shouldn't be a problem. Since the requirements are assentially the same the current installation would rate about a 6 out of 10 based on the CWOP guidlines. The calibration data shows uncertainty in the humidity readings of up to 4%. Limited comparisons with data from a local airport imply the results are probably accurate to within 5%.
Barometric Pressure
The pressure transducer is located on the base station which remains inside the house. One possible source of error is momentary pressure spikes when doors are closed. Since the data is presented as an average of 30 points over 5 minutes, any such spikes will have little effect on the reported values. Another source of error comes about in how the data is reduced. Normally pressure readings are adjusted to sea level altitude. League City averages about 15 feet above sea level so this correction is of little concern. In addition, since there was no reasonable way to calibrate the instrument its values were adjusted to match the local airport which lies less than 10 miles away and maybe 20 feet higher. This "calibration" essentially accounts for instrument errors as well as elevation effects. Over a reasonable range of ambient pressures the difference in the two stations was seen to be almost a constant 1.9 mbar so this is used as an offset in the data presented.
Wind speed and direction
As described in the hardware section, the anemometer is sited worse than the other instruments. The approximate 30' installation height is very close to the ideal of 33' for an open area. Since this instrument is located in a residential neighborhood, however, it should be at least 7' higher than the surroundings. The installation places the anemometer roughly even with the peak of the house it is installed on so the 7' rule is violated. As a consequence, the local wind speed and direction will be strongly affected by the presence of the house. The most likely effect will be an increase in local wind velocity when the wind is blowing from the north, south or west. When the wind is blowing from the east the anememeter will be in the wake of the roof peak resulting in underpredicted wind velocities and a larger scatter in velocity and direction. The data polling interval for the wind speed and direction is also not ideal. The CWOP standard is 2 minute averages instead of 5 and a rate of at least 1 sample every 5 seconds instead of 1 sample every 10 seconds as done here. It would be relatively easy to change the averaging interval to 2 minutes but due to the poor siting the extra effort seemed pointless. Since the hardware is limited to update the data no more often than once every 8 seconds there was no way to meet the second requirement either. The longer averaging interval shouldn't have much effect on the reported wind speeds and should have essentially no effect on the reported wind gust speeds. The slower sampling interval will result in some wind gusts being missed. This siting would probably rank 4 out of 10 by CWOP standards.
Precipitation
The accuracy of the rain gauge setup also leaves something to be desired. The first problem is the rain gauge shape and size are substandard. A standard rain gauge has a circular opening 8 inches in diameter. A 4" diameter opening is considered the smallest that is acceptable. In windy conditions the wind accelerating over the top of the rain gauge deflects some of the droplets away from the opening. This is true even for an 8" gauge but the larger size reduces the effect. The small size of the WS-2310 rain gauge means it will be more susceptible to this effect. The rectangular shape means the effect will be stronger when the wind is blowing normal to the long side than when it blows normal to the short side. At any rate, the rainfall will be underpredicted when the wind is blowing relatively hard at the level of the gauge. The effect of the wind is made even greater by the height of the gauge above the ground. The standard is 2 feet since the wind velocity near the ground is lower. The installed height of roughly 10 feet puts it above some of the surroundings such as fences that would reduce the local wind velocity. Fortunately the "canyon" created by the surrounding houses and trees will reduce the local velocity somewhat counteracting this effect.
Another siting problem is the presence of the slats making up the roof of the patio cover the gauge is attached to. Normally gauges are installed 2 feet above grass so splashed from the ground will not find their way into the gauge resulting in overprediction of rainfall. The short height of the gauge walls, approximately 6", means splashing from the pation cover is possible. The effect will be cut in half since the cover is about 50% open space. By CWOP standards the installation would probably rate about a 4 out of 10.
