National Weather Service; Automated Surface Observing System

As part of the NWS modernization, the NWS is undergoing a major shift in the methods used to observe and report surface weather information. The NWS has developed and is installing ASOS to automate certain observing functions, thereby taking advantage of advances in sensor and microprocessor technology. At approximately 900 airports in the United States during the 1990s, the U.S. Departments of Commerce, Transportation, and Defense are deploying ASOS to support aviation operations and weather forecasting and warnings, as well as general needs of the hydrometeorological, climatological, and meteorological research communities. ASOS will provide greatly expanded coverage (locations and observing hours), objective observations, a continuous weather watch, and improved operating efficiency. ASOS, when integrated with advances in remote sensing and weather information processing systems, is expected to contribute to improved warning and forecast services. ASOS will perform the basic observing functions necessary to generate a SAO. However, because some weather parameters observed manually today will not initially be observed by ASOS, the NWS is introducing two new classes of observations to the array of meteorological surface observations: the supplementary data observation (SDO) and the supplementary climate data (SCD). Supplementary observations are not appended to the ASOS observation; rather, they are disseminated as separate messages. The NWS will disseminate these reports to a variety of Federal and non- Federal users of NWS data. Supplementary data will be made available through NWS communication systems such as Family of Services, NOAA Weather Wire, and various computer and commercial vendor services. Surface observational data in the ASOS era will continue to come from many sources. ASOS, along with complementary data derived from remote sensing technologies, such as statellites, will form the backbone of the surface observing network (SAO) system. Surface data from over 20,000 automatic and manual hydrometerological sites, including cooperative and hydrologic networks, will continue to play an important role in NWS operational forecast programs. They comprise the climatological data bases and supply information to users who currently rely on surface observations from airports, as well as for non-aviation related information. The NWS Weather Forecast Offices (WFOs) will issue these new supplemtary data reports. The SDOs will provide significant, event- driven observations primarily intended to support weather forecasting and general hydrometeorological needs. Elements may be reported in SDOs on an ``as-observed'' basis and do not imply a continuous or basic weather watch. SDOs will not generally include elements that are in augmented ASOS observations from that location. The SCD reports may provide routinely scheduled observations useful for climatological applications, as well as hydrometeorological operations. SCDs are routinely issued at designated hours at about the same time as the recorded surface observation (note: the SDOs are issued on an event basis, which may fall ``on the hour'' only by chance). Most offices issuing SCDs and SDOs will not issue the full suite of SCD/SDO elements. There will be some variation among individual offices in the elements they report. Elements reported in SCDs will generally not be reported in SDOs. Exceptions are: (1) precipitation type and intensity reported in SCDs may also be reported in SDOs when considered significant by the on-site observer, and (2) volcanic ash reported in SCDs will also be reported in SDOs. Observations of volcanic eruptions and volcanic ash when first noted and severe weather (severe thunderstorms and tornadic

activity) when first observed may be included in weather warnings and statements issued by cognizant NWS offices rather than in supplementary data reports. The same elements may be reported in both SDO's and aviation observations from some sites (see enclosures). In the future, non-Federal observers (volunteers, Cooperative Observers, etc.) are expected to participate as members of the supplementary data network. Their reports will focus on snow depth, snowfall amount, hail and ice pellet occurrences. It is expected that a subset of volunteer observers will report water equivalent of snow on the ground. Susan F. Zevin, Deputy Assistant Administrator for Operations.

Report Format and Content

The information in supplementary data reports will follow the syntax and abbreviations used in Federal Meteorological Handbook Number 1 for Surface Observations (FMH-1). (FMH-2 for synoptic cloud reports) where practical. Supplementary data reports differ from surface aviation observations in the following ways: • Only a limited set of observed elements is included in supplementary data reports. A given supplementary report may contain one or several elements. • Supplementary data reports are not issued on an hourly basis. Time-scheduled SCDs are issued at main synoptic hours or at other designated hours of the day depending on the variable(s) being reported. Event-driven SDOs are issued when a significant phenomenon is first observed. A follow-up ``termination'' SDO will be issued after the cessation of certain events. • Some SDOs will contain a ``/'', solidus remarks separator. The purpose of the remarks separator is to help computer decoders differentiate between decodable (parsable) remarks and remarks not readily amendable to decoding. SCDs will not inclde the ``/'' remarks separator because all remarks in SCDs are decodable. Supplementary data reports are encoded as follows: SID--TYPE--(COR--)TIME--WX/--Decodable RMKS--/--Other RMKS (``--'' indicates a required space and ``/'' indicates a required solidus. The ``/'' will appear in an observation if and only if one or more ``WX'' elements are reported and are followed by remarks. The ``/'' remarks separator will appear in an SDO, only if, the SDO contains both decodable and noncodable remarks.

SID--Station identifier (3 to 5 alphanumeric characters). TYPE--Type of observation (either SCD or SDO). If the observation is a correction to a previously disseminated SCD or SDO, the contraction COR will follow the type of observation (in which case the time (TIME) will be the time of the observation being corrected). TIME--Time of observation in hours and minutes UTC [0000 * * * 2359]. WX--Weather and/or obstructions to vision. This field will be from 1 to 15 characters in length including the precipitation intensity symbol (-,+). The elements to be reported in the ``WX'' field are given in Table 1 of this guide. Contractions for precipitation types are given in Table 2; contractions for obstructions to vision are in Table 3.

Decodable RMKS, Other RMKS--Remarks are separated from the ``WX'' group with a solidus and a space. If no ``WX'' is reported, the remarks are preceded with a space after the time (TIME) element. SCD remarks are encoded in the following order:

8NNhCLhCMCH--Total cloud cover and synoptic cloud types 931nnn--Depth of new snow (snowfall) 933RRR--Water equivalent of snow on the ground 4/sss--Depth of snow on ground 98xxx--Duration of sunshine 7R24R24R24R24--Calendar day total precipitation (from designated sites) 4snTxTxTxsnTnTnTn--Calendar day maximum and minimum temperature (from designated sites) NIL--Nothing to report

SDO remarks are encoded in the following order: Temination reports for ``WX'' elements (e.g., END IP) SNOINCR x/x--Snow increasing rapidly HLSTO x--Size of largest hailstone observed `` / '' remarks separator

Other SDO remarks when considered significant by the on-site staff:

Local variation in visibility (e.g., VSBY N2; F BANK N-E2) (designated stations) Virga--Precipitation evaporating before reaching ground (designated stations) Precipitation not at station (e.g., RWU SW; SU OVR MTNS N) (designated stations) Clouds above 12,000 feet (types and/or layers) (designated stations) Distant clouds obscuring mountains (designated stations) Other meteorological information considered significant, such as blowing volcanic ash

The SDO ``WX'' group, remarks of snow increasing rapidly (SNOINCR), hailstorms (HLSTO), and termination reports for ``WX'' elements are considered decodable. Initiation and termination reports will be issued for selected ``WX'' elements (those listed in Table 2 of this guide). An exception is hail, for which only an initiation report will be issued. Termination reports will be issued for any weather and/or obstructions to vision previously reported in the ``WX'' field of an SDO when the event is determined to have ended. Termination reports are not required for information reported in SDO remarks unless designated by NWS regional headquarters. • The initiation report for a ``WX'' element is implicit in the ``WX'' field (e.g., ``MCI SDO 1325 BS'' is an initiation report for blowing snow). The initiation report for other significant events carries the information in the SDO remarks section (e.g., ``MCI SDO 1325 BD/ RWU SW'' may be an initiation report for distant rain showers. The blowing dust, previously reported, continues). • Termination reports contain the key word ``END'' followed by a space and a description of the event which ended. All termination information, even for a ``WX'' element, is considered to be in the remarks category. Termination information for ``WX'' elements precedes any `` / '' remarks separator (e.g., ``MCI SDO 1445 END BD / END RWU SW''). • Termination reports for items listed under ``other SDO remarks when considered significant by the on-site staff'' can have several meanings: (1) the event ended, (2) the event is no longer considered significant, but it may still exist, or (3) because of darkness, it is not possible to determine if the event still exists. Plain language remarks may at times be necessary to clarify changing local conditions. For example, if a fog bank previously reported to the north (e.g., ``ANC SDO 1205 F BANK N2'') moves over the airport, ``ANC SDO 1330 F BANK MOVD OVR ARPT'' might be subsequently reported. Location of phenomena within 10 miles of the station will be reported as ``VCNTY STN,'' followed by the direction from the station. Phenomena between 10 and 30 miles of the station will be located by direction from the station. Phenomena beyond 30 miles will be reported as ``DSNT,'' followed by the direction from the station. If there are no coded remarks or weather to report in a scheduled SCD,

the SCD will be transmitted with ``NIL'' (e.g., ``PHL SC 1758 NIL''). Table 1 gives the type of supplementary information reported, the category of the supplementary data report, criteria for reporting, and type of site making the report. It also gives the syntax of the element and one or more examples. Examples of complete supplementary data reports are given in the back of this guide. Except where explicitly stated otherwise, the ``WFO'' column refers to all WFOs, whether or not they have a collocated ASOS. The ``Other NWS Office'' column refers to NWS staffed or manual observing sites with responsibility for supplementary data reporting. This table represents the initial supplementary data reporting configuration by office type (augmented elements are excluded).

Table 1.--Description of Elements Reported as Supplementary Data -------------------------------------------------------------------------------------------------------------------------------------------------------- Type of report Reported by Element ---------------------------------------- When reported -------------------------------------- Format, example, SDO SCD WFO Other NWS offices comments -------------------------------------------------------------------------------------------------------------------------------------------------------- WX--Weather and/or obstructions .................. X................. at 6-hrly X................ Designated Format: Table 2 gives to vision. Volcanic ash will synoptic times Stations. contractions for --All precipitation types and not be included (00, 06, 12, and precipitation types; intensities. in SCDs from 18 UTC) and Table 3 gives --Volcanic ash................. sites with a staff is contractions for collocated ASOS. available. obstructions to vision. Where: ``WX'' refers to weather and obstructions to vision. Weather refers to precipitation and tornadoes. Obstructions to vision refer to phenomena that reduce visibility but are not precipitation. Weather and obstruction to vision elements included in SCDs and SDOs are given in the ``Element'' column to the left. Examples: VOLCANIC ASH; IF; HLSTO \1/4\; IP-: END VOLCANIC ASH; END IF Comments: Visibility specified by FMH-1 for qualifying intensity of snow and drizzle may not be well resolved at certain WFOs without a collocated ASOS. Consequently, snow and drizzle intensities reported by non-ASOS WFOs must be considered to be estimates. A follow- up ``termination'' SDO will be issued upon termination of the event (with the exception of hail). The termination SDO will give the event preceded by the key world ``END.'' Volcanic ash will not be reported in supplementary data originating from sites which have collocated ASOS. Volcanic ash is appended directly to the ASOS observations at those sites. Visibility will not be a factor in reporting ``VOLCANIC ASH'' as present weather (WX) in an SDO. Any observed ``VOLCANIC ASH'' will be reported.

WX--Weather and/or obstructions X................. .................. when observed and X................ Designated ...................... to vision. Volcanic ash will staff is stations. --Ice pellets.................. not be included available. --Volcanic ash................. in SDOs from --Other nonaugmented elements sites with a when considered significant by collocated ASOS. the on-site staff (ice crystals, ice fog, smoke, blowing snow, blowing sand, blowing dust, and blowing spray). Daily total sunshine duration.. .................. X................. Once daily at 08 Reported at ................. Format: 98xxx. UTC. If the official NWS Where: ``98'' is the station is sunshine- code group indicator closed at 08 duration and ``xxx'' gives the UTC, the reporting sites. total minutes of ``98xxx'' group These sites may sunshine for the will be reported be moved as previous calendar in the first 6- required. day. ``xxx'' is hrly observation encoded in hundreds, after opening. tens, and units. Equipment must Example: 98096; 98000. be available. Interpretation: 96 minutes of sunshine; 0 minutes of sunshine. Missing data indicator: 98///. Calendar day total prescription .................. X................. 24-hour value Only reported by ................. Format: 7R24R24R24R24. accumulation (water once daily at 00 WFOs which do Where: ``7'' is the equivalent). LST and staff is not have a code group indicator; available. collocated ASOS. R24R24R24R24 gives precipitation amount encoded in tens, units, tenths, and hundredths of inches. Example: 70125. Interpretation: 1.25 inches of precipitation (water equivalent) in the preceding 24 hours. Missing data indicator: 7////. Comment: Note that in the SCD the ``7'' group refers to a 24- hr precip total ending at midnight LST whereas the ``7'' group in the remarks of an ASOS observation or a manual surface observation refers to a 24-hr precip total ending at 12 UTC. Calendar day maximum and .................. X................. 24-hour value Only reported by ................. Format: minimum temperatures. once daily at 00 WFOs which do 4s,TxTxTxsnTnTnTn. LST and staff is not have a Where: ``4'' is the available. collocated ASOS. code group indicator; sn gives sign of the data (``1'' for temperatures below 0 deg.F, ``0'' for temperatures 0 deg.F or higher); TxTxTx is the maximum temperature in whole degrees F; TnTnTn is the minimum temperature in whole degrees F. Example: 400700045. Interpretation: 24-hr max temperature of 70 deg.F, 24-hr min temperature of 45 deg.F. Missing data indicator: 4////////.

Snow increasing rapidly........ X................. X................. Hourly when snow Designated Designated Format: SNOINCR x/x. depth increase stations. stations. Reference: FMH-1 Table equals or A3-88, 2.e modified exceeds 0.5''/hr to exclude the depth and staff is increase since the available. last 6-hrly report. Where: ``SNOINCR'' is the code group indicator. ``x/x'' gives the snow depth increase in the past hour/total depth of snow on the ground at time of observation, both of which are reported in whole inches. Example: SNOINCR 1/6. Interpretation: One inch depth increase in the past hour with 6 inches on the ground at time of observation. Size of largest hailstone X................. .................. when first Designated Designated Format: HLSTOx. observed. observed and stations. stations. Where: ``HLSTO'' is staff is the group indicator. available. ``x'' gives the diameter (in inches) of the largest hailstone observed. Hailstone size is reported in \1/4\ inch increments. If the hailstone size is less than \1/8\ inch, it will be encoded as h CL hCM cloud types (low cloud base synoptic times stations. CH. height; low cloud amount; low, (00, 06, 12, and Reference: FMH-2 middle, and high cloud types). 18 UTC) unless paragraph 4.2.7 the sky is clear. modified to include ``N'' (total cloud cover) as described in FHM-2 paragraph 4.2.2.1 and ``h'' (height of lowest cloud) as described in FMH-2 paragraph 4.2.1.3. Where: ``8'' is the code group indicator. ``N'' is total fraction of oktas (eighths) of the celestial dome covered by clouds, where ``9'' represents sky obscured by fog and/ or other meteorological phenomena and ``/'' in the ``N'' position means cloud cover is indiscernible for reasons other than fog or other meteorological phenomena, or the observation was not made. Nh gives the total amount (oktas) of all CL clouds. If there are no CL clouds, Nh gives the total amount of all CM clouds. Otherwise Nh=0. Nh=9 for sky obscured by fog and/ or other meteorological phenomena. Nh=/ for cloud cover indiscernible for reasons other than fog or other meteorological phenomena, or if the observation is not made. CL, CM, and CH are types of low, middle, and high clouds respectively. ``0'' is coded for clouds absent, except that ``/'' is coded in the cloud layer subfield(s) above on overcast layer if the types are not determinable. ``h'' gives the height with respect to the surface of the base of the lowest cloud seen. It is a single digit coded in accordance with FMH- 2. Table 3-3. ``h'' and CL CM CH are coded with ``/'' if there is a total surface based obscuration which prevents an observation of the clouds. Example: 8220850. Interpretation: N=2 oktas total cloud cover. Scattered middle clouds (Nh=2 oktas cloud coverage and CL=0) with bases between 7,000 and 8,000 ft AGL (h=8); no low clouds; middle clouds are altocumulus progressively invading the sky; no high clouds. Missing data indicator: The ``8'' group is not reported for clear skies. --------------------------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------- Precipitation types ----------------------------------------------------------------------------------------------------------------- Weather Contraction Weather Contraction ---------------------------------------------------------------------------------------------------------------- Rain................................. R...................... Snow................... S Rain Showers......................... RW..................... Snow Showers........... SW Drizzle.............................. L...................... Snow Pellets........... SP Freezing Rain........................ ZR..................... Snow Grains............ SG Freezing Drizzle..................... ZL..................... Ice Crystals........... IC Ice Pellets.......................... IP..................... Hail................... A Ice Pellet Showers................... IPW.................... ....................... ....................... ----------------------------------------------------------------------------------------------------------------

Table 2.--Precipitation Types and their Contractions ---------------------------------------------------------------------------------------------------------------- Obstructions to vision ----------------------------------------------------------------------------------------------------------------- Obstruction Contraction Obstruction Contraction ---------------------------------------------------------------------------------------------------------------- Volcanic ash......................... VOLCANIC ASH........... Blowing Sand........... BN Ice Fog.............................. IF..................... Blowing Dust........... BD Smoke................................ K...................... Blowing Spray.......... BY Blowing Snow......................... BS..................... Fog.................... F Ground Fog........................... GF..................... Dust................... D Haze................................. H...................... ....................... ....................... ----------------------------------------------------------------------------------------------------------------

Table 3.--Obstructions to Vision and their Contractions Examples of Supplementary Data Reports CAESCDCHS TTAA00 KCHS DDHHMM CHS SCD 1758 IP-/ 8872// 931024 933009 4/009

This SCD shows the occurrence of weather (ice pellets) along with coded remarks. 8872// indicates overcast low clouds (ragged shreds of stratus or cumulus associated with precipitation) with low cloud base height of 400-600 ft. 931024 represents a 6 hour snowfall amount of 2.4 inches. The water equivalent of snow on the ground was 0.9''. The snow depth (4/009) at time of observation was 9 inches.

PHLSCDPHL TTAA00 KPHL DDHHMM PHL SCD 0455 70050 400700045

This SCD, issued at midnight EST, is from a WFO which does not have a collocated ASOS. The 24-hour precipitation total (70050) was 0.50 inches water equivalent. The 24-hour maximum and minimum temperatures were 70 deg.F and 45 deg.F respectively.

BISSCDBIS TTAA00 KBIS DDHHMM BIS SCD 0755 98096

This SCD from a network sunshine duration station reports 96 minutes of sunshine for the previous calendar day.

STLSDOMCI TTAA00 KMCI DDHHMM MCI SDO 0642 IP-

This SDO reports the onset of light ice pellets.

STLSDOMCI TTAA00 KMCI DDHHMM MCI SDO 0729 END IP

This SDO reports the cessation of ice pellets.

PHLSDOACY TTAA00 KACY DDHHMM ACY SDO 0759 SNOINCR \1/2\

This SDO indicates snow depth increase at a rate of more than 0.5 inches/hour. The snow depth increased 1 inch during the past hour. Two inches of snow were on the ground at observation time.

PHLSDOACY TTAA00 KACY DDHHMM ACY SDO 2036 HLSTO \3/4\

This SDO reports a hail occurrence with the largest observed hailstone size of \3/4\ inch.

SEASDOSMP TTAA00 KSMP DDHHMM SMP SDO 1756 END IP / RWU CAD LYR 140 OVC

This SDO was reported from a mountainous site where terrain is problematic. Ice pellets ended. Rain showers of unknown intensity were observed to the southwest. There was a significant overcast cloud layer based at 14,000 feet above the observer's ground level. The ``/ '' remarks separator separates decodable and nondecodable remarks.

DENSDODEN TTAA00 KDEN DDHHMM DEN SDO 1056 CLD BASES OBSCG MTNS W

This SDO was also reported from a mountainous site where terrain is problematic. Clouds were observed obscuring mountains to the west.

/D ANC SDO HHMM ANC SDO 1310 IF=

This SDO shows the initiation of ice fog. Notice that a different communications header and message ending code (=) are used in Alaska.

/D ANC SDO HHMM ANC SDO 1645 END IF=

This SDO terminates the ice fog event.

[FR Doc. 95-30246 Filed 12-12-95; 8:45 am] BILLING CODE 3510--12-M