Automated Surface Observing System (ASOS)

1 Automated Surface Observing System ( asos )User s GuideNational Oceanic and Atmospheric AdministrationDepartment of DefenseFederal Aviation AdministrationUnited States NavyMarch 1998 ForewardThe 1990s have witnessed a carefully planned and executed modernization of the nation sweather services . The Automated Surface Observing System ( asos ) is the first System to beoperationally deployed as part of theis modernization. asos is therefore in the forefront of systemdeployments and associated service improvements that will require most of this decade tocomplete. In this sense, asos is the harbinger of 21st century weather the end state, asos will be operational at about 1,000 airports across the United States.

2 This System is the primary Surface weather Observing System in the United States, which supportsthe essential aviation observation programs of the national weather Service (NWS), the FederalAviation Administration (FAA), and the Department of Defense (DOD).The implementation of asos brings with it many opportunities and challenges. Theopportunities include the unprecedented availability of timely, continuous and objectiveobservations from many more locations. The challenges generally related to institutional learningneeded to fully understand and adjust operation to take the greatest advantage of this newtechnological resource. The potential applications of the asos data go beyond that of providingbasic weather information for aviation and forecasting; asos also will provide enhanced support tovital national programs such as public safety, hydrology, climatology, agriculture, andenvironmental protection, just to name a few.

3 The asos User s Guide is intended as basicreference and introduction to asos for a broad range of of this writing (March 1998), there are about 500 commissioned asos s nationwide. Anadditional 500 are coming on-line in the next few years. This deployment fulfills the commitmentof the Government made over a decade ago to provide the nation a highly cost-effective, capableand reliable Automated weather Observing System for safe, efficient aviation operations and otherapplications. This achievement is made possible by the dedicated effort of many people throughoutthe government and private industry working together as a team to conceive, plan, develop, testand evaluate, implement, commission, monitor, maintain and operate a asos User s Guide is gratefully dedicated to all who have worked so hard to makeASOS a reality.

4 Special thanks are extended to Dr. Jim Bradley for mentoring this program fromthe very beginning. Finally I wish to thank Dave Mannarano for coordinating the writing andproduction of this asos User s L. NadolskiASOS Program ManageriExecutive SummarySince the last Automated Surface Observing System ( asos ) User s Guide was publishedin June 1992, numerous changes have occurred. These changes have, to the maximum practicalextent, been incorporated into this updated version of the asos User s Guide. These changesinclude the transition of Observing code format from the Surface Aviation Observation (SAO)code to the Aviation Routine weather Report (METAR) code in 1996; the implementation of newsoftware loads into asos up to and including software Version ; the incorporation of varioussensor enhancements and improvements, including modification to the Heated Tipping Bucketprecipitation accumulation gauge, the hygrothermometer, and anemometer; and incorporation ofthe Freezing Rain and Lightning Sensors into the asos sensor suite.

5 Additional product improve-ment efforts are underway to further expand and improve the capabilities of asos . These effortsare also described in the asos User s of this writing (March 1998), there are about 500 commissioned asos s nationwide. Anadditional 400 + are coming on-line in the next few years. This deployment fulfills the commitmentthe Government made over a decade ago to provide the nation a highly cost-effective, capableand reliable Automated weather Observing System for safe, efficient aviation operations and otherapplications. This achievement is made possible by the dedicated efforts of many people through-out the government and private industry working together as a team to conceive, plan, develop,test and evaluate, implement, commission, monitor, maintain and operate the asos User s Guide is gratefully dedicated to all who have worked so hard to makeASOS a reality.

6 Special thanks are extended to Dr. Jim Bradley for mentoring this program fromthe very beginning. Finally I wish to thank Dave Mannarano for coordinating the writing andproduction of this asos User s L. NadolskiASOS Program ManageriiTable of ContentsCHAPTER Purpose and Scope .. Background .. Total Surface Observation Concept .. Quality General Conventions .. 3 CHAPTER TWO .. System Description .. System Components .. asos Sensor Groups .. Control Operator Interface Device .. asos Data Outlets .. asos Data Types .. METAR Elements .. Automated METAR vs. Manual METAR .. 10 CHAPTER Automating the Objective weather Elements.

7 Ambient and Dew Point Temperature .. Ambient/Dew Point Temperature Sensor .. Ambient Temperature/Dew Point Temperature Algorithm .. Ambient Temperature/Dew Point Temperature Strengths and Limitations .. Wind .. Wind Sensor .. Wind Direction and Speed .. Character .. Gusts .. Variable Wind .. Remarks .. Wind Peak Wind .. Wind Strengths and Limitations .. Pressure Sensor .. Pressure Algorithm .. Pressure Strengths and Limitations .. Precipitation Accumulation .. Heated Tipping Bucket Precipitation Gauge .. Precipitation Accumulation Algorithm .. Precipitation Accumulation Strengths and Limitations.

8 22 CHAPTER 2 Automating the Subjective weather Elements .. Automating Sky Cloud Height Indicator Sensor .. Condition Discontinuity Sensors .. Sensors .. Sky Condition Strengths and Limitations .. Automating Surface Visibility .. in Visibility Forward Scatter Sensor .. Visibility Discontinuity Visibility Back-Up Visibility Sensor .. Visibility Strengths and Automating Present weather and Obscurations .. Single Site Lightning Sensor .. Single Site Lightning Sensor Algorithm .. Automated Lightning Detection and Reporting System (ALDARS) .. asos Lightning Sensor Strengths and Limitations.

9 Precipitation Identification Sensor .. PI Algorithm .. PI Strengths and Limitations .. Freezing Rain Sensor .. FZRA Algorithm .. FZRA Strengths and Limitations .. Obscuration Obscuration Algorithm Strengths and Limitations .. 39 CHAPTER FIVE .. 4 Explanations/Examples of asos Observations .. 5-Second Wind Updates .. One-Minute Observations .. asos Aviation Routine weather Reports .. Backup and Augmentation .. Missing vs. Non-Event Data .. Estimated Data .. Examples of METAR/SPECI Reports .. 43 Table of ContentsivAppendicesAppendix A: asos Video Screens ..A1-11 Appendix B: asos Initial Operation Capabilities.

10 B1-2 Appendix C: Content of asos -Generated METAR: A Quick Reference Guide .. C1-2 Appendix D: asos Voice Vocabulary .. D1 Appendix E: Acronyms .. Auxiliary Data .. Standard Hydrometeorological Exchange Format (SHEF) Messages .. SHEF 15-Minute Precipitation Criteria Message .. SHEF Hourly Routine Precipitation Message .. Daily and Monthly Summaries .. Daily Summary Message .. Monthly Summary Message .. asos High-Resolution Sensor Data .. 50 CHAPTER SIX .. 5 asos Data Outlets .. Interactive Video Screen Displays .. Non-Interactive Screen Displays .. asos Printer .. Long-Line Dissemination .. Computer-Generated Voice Messages.