Letter   4-92

Date of Issue:    August 31, 1992             Effective Date: September 1, 1992

In Reply Refer To:    W/OM23                 File With: B-24, C-73, F-21, F-22 , F-50 , and J-03

Subject: Interim Procedures for Manual Observations with the Implementation of Automated Surface Observing System (ASOS)

Purpose. The National Weather Service (NWS) Policy on Manual Observations with the Automated Surface Observing System (ASOS) (referred to as "the policy" in this letter) is given in Attachment 1. This policy supports NWS mission requirements and addresses requirements of the climate community. It recognizes the complementary nature of remote sensing systems, manually observed weather elements, and automated surface observations. This OML defines interim procedures for manual observations with ASOS based on this policy and on requirements of the Federal Aviation Administration (FAA).

Augmentation and Backup. While the policy identifies requirements for NWS-staffed sites to report certain manually observed weather elements separate from (supplementary to) the ASOS report, it does not identify any requirements to append (augment) manually observed weather elements to the ASOS report. Nor does it identify any requirements for manual backup to ASOS in the event of a system failure. In development of this policy, it was recognized that user communities, and in particular the aviation community, could identify further requirements for manual observations or backup that the NWS would need to address.

We have been actively supporting the FAA in its formulation of the aviation community's requirements for manual observations, as well as for backup. The FAA has provided a statement of its requirements for augmentation and backup for initial operations with ASOS. To support these requirements, NWS ASOS sites at airports are directed to:

Augment ASOS for thunderstorms, tornadoes, hail, virga, and volcanic ash as long as staff are available and trained in surface observing, and

Back up ASOS as long as staff are available and trained in surface observing.

In the near term, I expect that we should be able to provide this level of augmentation and backup for all of our early ASOS sites for their current observing times (i.e., part-time at current part-time offices) under this policy. We will continue to support the FAA as it refines its requirements based on early experiences with ASOS, introduction of new ASOS capabilities, and the availability of other complementary data sources. Also, we are advising the FAA of our site-specific modernization and associated restructuring schedule that impacts the availability of our staff to meet FAA's requirements. Transfer of these augmentation and backup responsibilities to the FAA will occur as the availability of our resources dictate.

One other area of augmentation needs to be addressed on an interim basis because of the delayed availability of the ASOS freezing rain sensor. NWS ASOS sites at airports are directed to:

Augment ASOS for freezing rain.

The Systems Program Office has advised us that this sensor will be available late this calendar year.

Specific procedures for augmentation and backup are described in the NWS Observing Handbook No. 7, Surface Observations.

Supplementary Data. Supplementary data reports that address requirements of the climate community are identified in Sections 2.5 and 2.8 of the policy. National standards for reporting these elements are under development and will be implemented later this year. In the interim, upon ASOS commissioning, regional and local procedures are encouraged to continue to maintain a record of these elements at future Weather Forecast Office locations that have a surface observing program.

Section 2.7 of the policy identifies weather elements to be reported at selected sites to support aviation forecast services. Attachment 2 identifies the sites from ASOS lots 1 through 2b that have requirements for reporting these weather elements. National standards for reporting these elements are under development and will be available prior to a commissioning of ASOS at these sites.

Elbert W. Friday, Jr.
Assistant Administrator
    for Weather Services

1. PURPOSE

The purpose of this policy is to provide guidance for the standardized implementation and operation of ASOS in support of NWS modernization and associated restructuring.

2. POLICY

2.1    Following ASOS commissioning, the ASOS observation will be the official observation from that site.

2.2    NWS forecast and warning services can be provided without ASOS augmentation. However, the NWS will work to support the augmentation requirements of other agencies.

2.3    The specified system availability meets NWS requirements. However, the NWS will work to support backup requirements of other agencies.

2.4    All NWS staffed field offices will report to cognizant NWS offices--for inclusion in weather warnings and statements--the existence of volcanic eruptions and volcanic ash when first noted and severe weather1 when first observed from the field offices.

2.5    At offices scheduled to be Weather Forecast Offices (WFOs), while the information remains climatologically important, operationally useful, or until it can be provided by complementary technologies, supplemental networks, or other means, the following will be reported:

¹Severe weather in the context of this policy encompasses tornadic activity (tornados, funnel clouds, and waterspouts) and severe thunderstorms (thunderstorms accompanied by wind gusts > 50 knots and/or hail > 3/4 inch diameter). The availability of official wind measuring equipment or a wind recorder is not a prerequisite for reporting severe thunderstorms at NWS staffed sites. At such sites without official wind equipment, the primary low-level wind shear alert sensor, other on-site wind equipment, other available observing systems information, or visual estimates (e.g., observations of damage compatible with winds of 50 kts or greater) will suffice for resolving thunderstorm severity.

. Total cloud cover
. Low cloud base height (at WFOs without collocated ASOS)
. Low cloud amount (at WFOs without collocated ASOS)
. Low, middle, and high cloud types|
. Precipitation type and intensity2 (at WFOs without collocated ASOS)
. Snowfall amount and snow depth.
. Volcanic ash when observed.

- SNOINCR remarks - hourly when snowfall rate equals or exceeds 0.5"/hr.

- Hail of any size - when first observed.
- Ice pellets - when first observed and when the event ends.

These data will be communicated as messages separate from the ASOS report and will not be appended to the ASOS observation.

2.6    Supplementary networks (comprised of utilities, air quality agencies, transportation departments, cooperative observers, etc.) will continue to supplement the surface observation database with operationally useful information. NWS staffed sites which are not destined to become WFO's may function as members of these supplementary data networks while staff are available at the sites. The observational information provided by supplementary networks will not be appended to ASOS observations.

The role of Data Collection Offices (DCO's) as providers of supplementary data will be examined.

²It is recognized that the intensity reported for snow and drizzle are related to visibility and that visibility will be particularly difficult to assess at some WFOs. Lacking suitable visibility reference points, the best available means will be used to estimate the visibility restriction.

2.7    At specific, currently staffed NWS observing sites which are determined to be especially problematic with respect to terrain, one or more of the following will be reported as needed to support aviation forecast services:

    - Virga and distant precipitation, on occurrence, in mountainous areas lacking radar coverage.

    - Operationally significant clouds above 12,000 ft in mountainous areas.

    - Distant clouds obscuring mountains.

    - Operationally significant local variations in visibility (e.g., fog banks), where multiple visibility sensors are not available or do not suffice.

These data will be manually reported while they are needed or until they can be provided by complementary technologies or other means. They will be communicated as messages separate from the ASOS report and will not be appended to the ASOS observation.

2.8    At existing official NWS sunshine duration reporting sites until an ASOS sunshine sensor is fielded, the following will be reported:

- Daily total sunshine duration.

These data will be communicated as messages separate from the ASOS report and will not be appended to the ASOS observation.

2.9    At selected NWS staffed ASOS sites, for a period of at least one year, the following will be reported:

- Comparative observations (ASOS vs manual):
. Calendar day liquid precipitation accumulation.
. Calendar day max/min temperatures.

- 6-hourly supplemental observations:
.Temperature and dew point.
.Total cloud cover and cloud types.
.Visibility and obstructions to vision.
.Present weather.
. Snowfall amount and snow depth.

These data will be made available for comparative analysis to support a climate data continuity study sponsored by the NWS. They will not be appended to the ASOS observation.

Station	Site Identifier
Anchorage, Ak	ANC
Annette, AK	ANN
Astoria, OR	AST
Bakersfield, CA	BFL
Cold Bay, AK	CDB
Fairbanks, AK	FAI
Helena, CA	HLN
Homer, AK	HOM
Kalispell, MT	FCA
King Salmon, AK	ARN
Kodiak, AK	ADQ
Lewiston, ID	LWS
McGrath, AK	MCG
Olympia, WA	OLM
Phoenix, AZ	PHX
St. Paul Island, AD	SNP
Santa Maria, CA	SMX
Stampede Pass, WA	SMP
Talkeetna, AK	TKA
Yakima, WA	YKM
Yakutat, AK	YAK