Surface Weather Observations Comparison of Various Observing Systems Scott Landolt & Matthias Steiner National Center for Atmospheric Research [email protected] USHST Infrastructure Summit 12 – 13 March 2020 in Washington, DC © 2020 University Corporation for Atmospheric Research 1 Surface Stations & Reporting Frequency Station Type Frequency of Reports Automated Surface 5 minutes Observing System (ASOS) (limited access to 1 minute data) Automated Weather 20 minutes Observing System (AWOS) 15 minutes (standard), can be Road Weather Information more frequent but varies state to System (RWIS) state and even site to site 5 – 15 minutes, can vary from Mesonet station to station Iowa station network © 2020 University Corporation for Atmospheric Research 2 Reporting Variables Weather Variable ASOS AWOS RWIS Mesonet Temperature X X X X Relative X X X X Humidity/Dewpoint Wind Speed/Direction X X X X Barometric Pressure X X X X Ceiling Height X X X X Visibility X X X X Present Weather X X X X Precipitation X X X X Accumulation Road Condition X X X X X – All Stations Report X – Some Stations Report X – No Stations Report © 2020 University Corporation for Atmospheric Research 3 Station Siting Requirements Station Type Siting Areal Representativeness Automated Surface Miles (varies depending on Airport grounds, unobstructed Observing System (ASOS) local conditions & weather) Automated Weather Miles (varies depending on Airport grounds, unobstructed Observing System (AWOS) local conditions & weather) Next to roadways, can be in canyons, valleys, mountain 500 feet to miles (varies Road Weather Information sides, near rivers/lakes, on depending on local System (RWIS) bridges, etc. Terrain and local conditions & weather) features can play significant role in observations Farmland/ranchland, generally Miles (varies depending on Mesonet outside of city influences local conditions & weather) © 2020 University Corporation for Atmospheric Research 4 Scale Comparison • Surface stations cover synoptic scale • Satellite covers meso scale • Radar covers storm scale • Combined they capture processes at 10s of minutes & 100s of meters - except in complex terrain Radar & urban environments Satellite ASOS ASOS, AWOS & MesoWest station separation distances Networks • Network availability, type of sensors, & station density varies notably among locations © 2020 University Corporation for Atmospheric Research 5 Sensor Standardization Station Type Sensors Nearly all sensors standardized Automated Surface from site to site; FAA/NWS Observing System (ASOS) owned and maintained Four different companies authorized to install/maintain; Automated Weather sensors standardized within Observing System (AWOS) companies but not between companies Limited to no standardization, Road Weather Information even within individual state System (RWIS) sites Sensors typically standardized Mesonet within each network but not between networks The four vendors for AWOS are: 1) All Weather Inc. (AWI) 2) Optical Scientific Inc. (OSI), formerly Belfort Instrument Co. 3) Mesotech International 4) DBT Transportation Services LLC, formerly Vaisala © 2020 University Corporation for Atmospheric Research 6 Maintenance Requirements ASOS • All sensors checked twice per year (unless a sensor is flagged as needing maintenance) AWOS • All sensors checked twice per year (unless a sensor is flagged as needing maintenance) RWIS • Variable, may be sensor dependent • Could be weekly to yearly maintenance intervals Mesonet • Variable, typically six months to one year. © 2020 University Corporation for Atmospheric Research 7 Sensor Intercomparison Previous Studies ASOS Visibility Sensor • Prior studies conducted utilizing non-collocated sensors - several RWIS sites surrounding ASOS site - terrain/altitude differences can have significant impacts AWOS Visibility Sensors (two examples of four) on non-collocated sites - lack of standardized sensors means prior study results may only be valid for subset of RWIS stations Future Studies RWIS Visibility Sensors (two examples of many) • Need co-located sensors • Need to understand data quality issues as well - both at sensor & network levels © 2020 University Corporation for Atmospheric Research 8 Supporting Documents Links to Key Documents • https://ops.fhwa.dot.gov/publications/ess05/ess05.pdf • https://www.ncdc.noaa.gov/data-access/land-based-station-data/ land-based-datasets/automated-weather-observing-system-awos • https://www.ofcm.gov/meetings/atd/gmu2016/pdf/8%20Joseph.pdf Scientific Publications • Several conference & some peer-reviewed comparison studies • Some technical reports • Few textbooks on atmospheric measurements Other Relevant Websites • https://madis.ncep.noaa.gov • https://wxde.fhwa.dot.gov • https://mesowest.utah.edu • http://mesonet.agron.iastate.edu/info/nni.phtml © 2020 University Corporation for Atmospheric Research 9.