Understanding Measurements & Data Follow

There is often an explanation for readings that seem only a little off. Observations from nearby weather stations and other data sources may not match exactly. Weather stations can be sited differently and some areas subject to microclimate conditions. Instrumentation also varies between weather stations; different sensor manufacturers and styles of instruments have different accuracy spec.'s and limitations. The ultrasonic wind sensing used in the Tempest device is a different style of equipment and measurement technique compared to a mechanical cup and vane anemometer. The haptic rain sensor is also a different style of instrument with a different measuring technique compared to a tipping bucket or even a conventional rain collection gauge.

Microclimates are localized atmospheric conditions that differ from those in the surrounding area. For example, most airport weather stations read higher temperatures and lower humidity as they are sited over a tarmac surface where the material of the ground is better at radiating into the air above it. These microclimates can be created from ground vegetation and trees, bodies of water, urban areas or terrain influences, etc.

Siting differences can result in different readings too. Some personal, home weather stations may be poorly sited or just experiencing the environment as it is around them. Anemometers can be obstructed from certain directions and subject to turbulent flow around any obstacle in the wind. Temperature and humidity sensors can be affected by moisture in wood decks, dryer vents, radiation from nearby surfaces.

If possible, try moving your Tempest device around and analyze the data - you might be surprised at the varying microclimates around you and how careful siting makes for accurate data.

Temperature

• Temperature is reading high: Your device might too close to a surface radiating heat, or another heat source like a dryer vent. Be careful comparing other weather station data to yours because equipment may not be sited the same way.
  While other thermometers may need to be properly sited in radiation shields, the thermometer used in the Tempest device is shielded from direct solar radiation and the heat energy absorbed by the device is accounted for; Tempest utilizes temperature correction software that provides a very accurate ambient temperature reading according to a properly sited, fan aspirated thermometer.
  

• Temperature is reading low: Temperature discrepancies are often explained by siting and location differences. Other weather station equipment could be sited close to heat sources, or something radiating heat such as a roof or the side of a house. The Tempest software adjusts the raw temperature reading to an ambient temperature simulating a fan aspirated environment.
  If other equipment (that is being used for comparison) is using a fan aspirated thermometer, there could be cobwebs, leaves, or other debris, which might be restricting air flow. Some weather station equipment uses batteries that need to be changed, or fans with motors that need to be replaced. If other equipment is not fan aspirated, then that could explain why the Tempest is giving a cooler temperature reading.

Relative Humidity

• RH is high: Higher humidity readings are typically caused by nearby sources of moisture. Check surrounding environment around your Tempest device for any potential moisture sources, soaking wood, standing water, etc. Try moving the Tempest device to a drier location if the humidity remains high for long. See Siting & Installation for Tempest.

Pressure

• Pressure is incorrect: Check the Tempest’s "height above ground" setting in the app. This should be set as the height of the unit above the ground surface - not the elevation of your location above sea level. Open the app, go to Settings > Stations > choose your station > Manage Devices > select an Tempest > edit the height above ground.

Wind Speed

• Wind speed is incorrect: Make sure that nothing is in between the transducers and the reflective plate, such as snow, leaves, bird droppings or other debris.
• Wind speed is too low: Observe the surrounding area, 360° around your Tempest device; make note of any obstructions that might influence the wind flow. Winds are typically faster at higher altitudes because of surface turbulence. Note how high above ground your Tempest device is mounted.
  
  
  
  
  Tempest uses an ultra sonic anemometer to sample an instantaneous wind speed, there is no inertia involved with the measurement. A spinning cup anemometer or any mechanical sensor relies on the momentum of moving air to rotate the bearings. An inertia-less method of wind speed measurement has inherent differences compared to a mechanical anemometer and the data provided is not going to look exactly the same.
  

  Tempest has a lower cut-in speed compared to most consumer anemometers; it is capable of measuring very light winds. Take note of any low lull readings which lower the average wind speed. Low lulls or near 0 speeds are an indicator of turbulent flow around the device. Try locating the Tempest device further away from any obstacles which could create turbulent flow. You may find that wind speed readings are more in line with expectations.

• Unreal wind gust: Erroneously high gust readings are typically caused by water droplets or other debris on the bottom reflector plate. In the winter time, ice accretion can also cause incorrect readings. Anything that obstructs the ultrasonic signals within the wind gap can cause issues with readings. Check to see if the super hydrophobic coating is still intact, look for signs of peeling which could allow water or debris to accumulate.

Wind Direction

• Direction incorrect: Make sure the arrow marked on the exterior of the Tempest unit is pointed towards true North (not magnetic North) if you are in the northern hemisphere, or true South (not magnetic South) if you are in the southern hemisphere. Also ensure the mast and Tempest is level. See info on proper orientation for Tempest.
  Take a look at the transducers under the roof of the gap - if you notice anything off with any of the transducers, please contact us.
• Direction is not displayed: Direction will not be displayed when wind speed is measured to be 0.
  Sometimes direction cannot be determined during precipitation events. Check the Tempest's sensor status in the Tempest app: go to settings > station > choose your station > tap Status > scroll down to Tempest's Sensor Status. If you read a "Wind Failed" message, please contact us.

Rain

• False rain readings: Most false rain readings can result from strong winds on unstable mounts which cause the Tempest to sway or shake leading to vibrations detected by the haptic rain sensor. Check your mounting situation and see if you might be able to mitigate any unwanted vibrations. Sturdy masts and added cushioning on the mount can help improve structural stability and reduce wind driven vibrations.
  Birds can be another common cause of false rain. If birds become a problem, consider installing a higher perch for them to land on or use shiny, reflective stickers on the Tempest and/or the mast to deter avian visitors.
• Over-reporting rain accumulation: Excess rain accumulation is inevitable on wobbly, unstable mounts, especially in in strong winds. The haptic rain sensor in Tempest is a precision instrument that is very sensitive to vibrations. It is essential to install the Tempest unit on a sturdy mast with secure mount. Check your mounting situation and see if you might be able to mitigate any unwanted vibrations.
  
• Under-reporting rain accumulation: If your sensor is consistently under-reporting rain accumulation, please see the Rain Accumulation help page.
  
• Inaccurate rain accumulation: Please see the Rain Accumulation help page.
• Not registering rain: Tempest will pick up on light rain but trace amounts of precipitation are unlikely to be detected. If the rain was heavy enough to make an impact on the device, but no rain was reported, first check the device's battery level in the app. The haptic rain sensor will be disabled under 2.36v to conserve power.
  If the battery level is above 2.36v, check the Tempest's sensor status in the Tempest app to see if there has been a failure, go to settings > station > choose your station > tap Status > scroll down to Tempest's "sensor" status. Try power cycling the Tempest unit first, twist the device off its mounting attachment and flip the power switch off and back on. If you still see any failed sensor message, please contact us.
• No accumulation after rain start: If rain has started, but you are not seeing an accumulation value, simply wait for the accumulation to build. The rain is probably very light and if so, there will not be an accumulation above 0.01" immediately.

UV

• Low UV readings: Check that nothing is obstructing the UV sensor at the top of the Tempest device; leaves, ice, debris, shadows, etc.
• Inaccurate Calibration: It can take many days of clear skies to properly calibrate the UV/solar radiation sensor as many cloudless days of measurement are needed to perform calibration routines. Be careful when comparing UV index readings from different equipment. If you find any abnormalities with the sensor readings or notice your UV readings do not improve after a month or so, please contact us.