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 specifications and limitations.
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.
Instrumentation can differ between weather observing equipment. The ultrasonic wind sensor 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 conventional rain collection gauge.
- Temperature is reading high:
Your device might be 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.
- 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 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.
UV & Solar Radiation
- Low UV readings:
Check that nothing is obstructing the UV sensor at the top of the Tempest device; leaves, ice, debris, shadows, etc.
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.
- Lightning Disturber Status:
The lightning disturber status is a benign status of the lightning sensor. It indicates the lightning sensor is detecting EMG signals in the vicinity, but these signals are not being qualified as a lightning strike. It is actually very common for EMG signals to be present at many locations and the sensor can easily detect these non-lightning signals if they are strong enough or if the device is close enough to the source. If you'd like you could relocate the Tempest device to be farther away from the signals but the sensor is doing it's job filtering out the false positives.
- False Positive Lightning Strikes:
If your Tempest is receiving false positive lightning strikes you may want to relocate the Tempest device to be farther away from false positive sources. These could be from other electromagnetic sources including boilers/furnaces, motors, microwaves, monitors, speakers, and even motion detectors and other EMG sources that may not be so obvious. Software will help to mitigate occurrences of false positive strikes.
- Missed Lightning Strikes:
A missed lightning strike may stem from another issue, such as an offline device, a Hub that's disconnected from WiFi, etc. The Tempest's lightning sensor is not going to detect every single lightning strike that occurs in a 40km radius; some strikes may go undetected. Software will help to mitigate incidences of missed strikes.
Wind Speed & Direction
When comparing data from your Tempest to another anemometer, remember that any individual device can only offer an indication of winds at that specific location. Keep in mind that wind speed typically increases with height, and stations in WeatherFlow’s industrial grade network and in NOAA’s observing network generally measure winds at a height of 10 meters or higher above ground level. Winds can also be slowed by obstructions several hundred yards upstream. Professional anemometers are only sited in ideally suited locations with large expanses of clean fetch for winds to accelerate to their full potential (like an airport). Understand that most homes do not have a location suitable for measuring prevailing mesoscale winds. Wind readings from home weather stations will not be comparable to those from professionally sited and installed equipment.
- Wind speed is low:
It is common and normal for home weather stations to observe lighter wind speeds in comparison to professionally installed weather stations. This is mainly due to siting and location differences. Most weather apps and news channels report data from weather stations at nearby major airports. These professional installations are mounted at standardized heights 10m (~33ft) above ground, with no obstructions (houses, trees, fences, etc.) in the area to slow or influence the winds. Winds are slower closer to ground due to frictional forces, especially in residential neighborhoods where obstacles create turbulence and disrupt the wind field.
Observe the surrounding area, 360° around your device; make note of any obstructions that might influence the winds to slow them down.
- Incorrect wind speed or direction, high wind gusts, or erroneous wind measurements:
Erroneous wind gusts and direction readings are typically caused by something blocking the signal path of the ultrasonic anemometer. Anything that obstructs the ultrasonic signals can cause issues with a wind sample, e.g. water droplets, ice accretion, or other debris like pollen, dirt, detritus, spider webs, etc.
Calm wind conditions may allow water droplets to remain present in the signal path. There are filters in place that prevent incorrect readings from being accepted as valid data; while rare, it's possible some afflicted samples can sneak through the filters. If and when erroneous measurements occur, it should only be temporary. The sensor should automatically correct itself and readings will return to normal after some time.
Check for debris in the gap of the device between the top and main body. There is a super-hydrophobic coating that covers the important areas for wind sampling. It is relatively coarse in texture compared to the body of the device. Look for signs of peeling of this coating which could allow water or debris to accumulate and lead to reduced wind sample integrity.
- Wind readings are different from another instrument
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.
- Wind direction is incorrect:
Keep in mind wind direction reports are based on where the wind is blowing from. Wind direction is displayed in degree format or cardinal direction. Conventional wind barbs point into the wind but you can also treat the wind as a vector using an arrow that points in the direction of the flow.
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 Accumulation values are calculated over a 24 hour period from midnight to midnight using the station's local time. Be cautious when comparing rain accumulation readings to other sources as collection times may differ and rain does not fall evenly across regions, towns or even neighborhoods.
- 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.
When judging accuracy and troubleshooting potential data issues, the following factors should be considered...
- Microclimate Variances
When comparing data from your Tempest to another rain gauge, remember that any individual device can only offer an indication of rain accumulation at that gauge’s specific location. Professional rain gauges co-located just a few feet from each other often show substantial differences in accumulation levels, as rainfall accumulation from a given event may differ greatly across even small distances. Mesoscale variability can make it especially difficult to compare data from gauges located larger distances apart, such as on the other side of town.
- Wind Effects on Rain Accuracy
The primary negative effect on accuracy for any all-in-one weather station is the effect of wind on rain detected by the sensor. This is due to deformations of the wind field caused by the device itself and changes to the angle of incidence of rain drops onto or into the device. The Tempest system minimizes these effects more than other all-in-one stations. Nonetheless, most professional weather networks (including WeatherFlow Networks’ industrial grade weather network) install wind instruments at 33 feet (10 m) and rain gauges at only 2 feet above ground level to mitigate this issue. For Tempest owners looking to optimize rain accumulation accuracy, we recommend placing the Tempest 2 to 5 ft above ground level, sheltered from wind while still ensuring clear exposure to the sky and sufficient horizontal distance from nearby obstacles (generally more than twice the obstacle's height).
- Optimizing Siting
No all-in-one station placed at a height optimized for capturing clean wind will measure rainfall as accurately as one placed closer to the ground where it is sheltered from the strongest winds. The optimal height for the overall functionality of a Tempest for most users is typically 6 to 8 feet above ground. This compromise height allows good rain accumulation accuracy, while still capturing wind gusts needed for Tempest’s derived parameters and keeps your Tempest safe from accidental contact. Most homes do not have a location suitable for measuring prevailing mesoscale winds but for those that do we recommend mounting your Tempest at height above all surrounding obstacles. The neighborhood rain value reported by the Tempest System will take this into account.
The Tempest rain sensor receives an initial factory calibration and, like all automated rain gauges, will benefit from additional calibration once installed by the user. This additional calibration is recommended for optimal performance due to the natural variability in hardware as well as differences in siting, installation methods and materials. Unlike other rain sensors, the Tempest can receive an unattended (over the air) field calibration any time our continuous learning system determines one is necessary. Manual (user-performed) field calibration will result in the most accurate values but most users will not find any gains in accuracy functionally useful. We stand behind the accuracy of the device and in the rare circumstances where necessary we will gladly recalibrate/repair your device or replace it.
See more details on adjusting the Haptic Rain Sensor Calibration.
- False Rain
The haptic rain sensor measures rain accumulation by detecting and quantifying the force of vibration caused by rain impacting hitting the device. This technology means that your Tempest can report false rain readings if something else causes vibration. This is most often due to siting & installation issues. It is important to follow the guidelines in our siting guide to make sure your device is not affected by non-rain sources of vibration. Because a small amount of false rain is expected, Tempest also utilizes several false-rain mitigation techniques. First, there are filters on the hardware to limit more obvious non-rain signals. Second, the Tempest System employs software that considers forecast & observation data along with data (from your Tempest and others) to make a decision about whether a given signal is likely "real" or "false". It gets better over time as more data is collected, reducing if not eliminating the incidence of false rain readings in your Tempest data.
If you are unable to totally prevent your Tempest from experiencing vibration and the false rain prevention measures do not appear to be working, please contact our support team. We guarantee accurate rain data or your money back.