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M any technological advances and scientific break-throughs have allowed the National WeatherService (NWS) weather forecasts and warnings

to become much more specific and accurate. Betterways of communicating weather information to po-tential users have been devised. Partnerships withcommercial enterprises have been forged as a way formuch of the information to flow to the public andother users.

However, the production and dissemination ofroutine National Weather Service forecasts mustkeep pace with the need for such information in thisdigital age. A primary means of providing sensibleweather element forecasts (e.g., cloud cover, maxi-mum temperature) from NWS Weather ForecastOffices (WFOs) is still textual in form. The flagshipproduct of the NWS for years has been the zone

forecast: a brief, plain-English description of whatthe weather will be over the next few days for amulticounty area. Similar text, containing much ofthe same information, is produced to support marineand federal fire weather interests and emergencymanagers. Some of these products are voiced over theNational Oceanographic and Atmospheric Admin-istration (NOAA) Weather Radio. In the past,because such textual products have been composedon word-processing equipment, the output of theforecast staff has been essentially limited by typingspeed. The new Interactive Forecast Preparation Sys-tem (IFPS; Ruth 2002) circumvents this, providingnot only for familiar textual and voiced products, butalso providing in digital (i.e., numerical) form thedata from which these products are prepared. Thesedigital forecasts are being put into a National DigitalForecast Database (NDFD) and will be made widelyavailable to partners and customers.

Once a database of local forecasts exists at a WFO,today’s forecasters can produce textual, graphic, andvoiced products automatically by software. In es-sence, the forecaster now enters the forecast variablesin digital form instead of redundantly typing severalproducts containing largely the same information.But the real power of a digital database is that it opensthe door for providing much more forecast informa-tion and in more useful forms. The NDFD will con-

THE NEW DIGITAL FORECASTDATABASE OF THE NATIONAL

WEATHER SERVICEBY HARRY R. GLAHN AND DAVID P. RUTH

This new database capitalizes on the revolutionary way NWS forecasters are working

together to make their high-resolution, up-to-date forecasts available to the nation.

GLAHN AND RUTH—Meteorological DevelopmentLaboratory, Office of Science and Technology, National WeatherService, NOAA, Silver Spring, Maryland

Dr. Harry R. Glahn, NationalWeather Service, 1325 East–West Highway, Silver Spring, MD20910-3283E-mail: Harry.Glahn@noaa.govDOI: 10.1175/BAMS-84-2-195

In final form 18 October 2002

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tain much more data than the NWS was previouslyable to provide, at timescales as small as hourly andspace scales of a few kilometers. For instance, insteadof the textual zone forecast shown in Fig. 1, a digitalforecast for the same area is shown in Fig. 2. Whileeach of these forecasts has its use today, and bothwere produced from the local digital database atWFO Albany, New York, the product in Fig. 2 con-tains much more information.

The NDFD will be the first product of its kind inthe United States and, to our knowledge, in the world.The official forecasts of the sensible weather elementsare largely produced by WFOs; however, some offi-cial products will be provided by the National Cen-ters for Environmental Prediction (NCEP), such asmaximum expected winds from hurricanes, offshoremarine products, and climate forecasts.

NDFD will start in 2003 for the 50 states andPuerto Rico, and will eventually cover ocean areaswhere the United States has forecast responsibility. Itmay also grow to encompass digital descriptions ofmeteorological features such as frontal boundariesand areas of high risk weather.

INTERACTIVE FORECAST PREPARATIONSYSTEM. The creation of NDFD starts with the for-mulation of digital forecasts at each WFO. This, inturn, required the development and implementationof efficient methods whereby the results of the thought

processes of WFO forecasters could be put into digi-tal (or numerical) form. IFPS has been developed forthis purpose. It has been under development for anumber of years (Ruth et al. 1998; Peroutka et al.1998), but the processing power of the AdvancedWeather Interactive Processing System (AWIPS;Seguin 2002) was necessary to make it feasiblenationwide.

What does it mean to “make digital forecasts?” Allinformation in a digital computer is digital. Putting afew forecasts into AWIPS is no trick; they can be sim-ply typed in. But it is no small task to enter the largenumber of values needed to represent forecast con-ditions at the needed space and timescales for evensome relatively small area such as a county-sized zonefrom the present out to a few days. Further, a WFOis responsible for making forecasts for areas muchlarger than a single county.

IFPS incorporates three methods for entering digi-tal forecasts into the database (Ruth 2000): matrixentry, graphical entry, and model interpretation.

• Matrix entry. The Interactive Computer WordedForecast (ICWF); (Ruth and Peroutka 1993) em-ployed this method, making interactive earliertechnology for producing text from digital fore-

FIG. 1. Textual zone forecast from Albany, NY.

FIG. 2. Digital forecast for the same zone and timeas shown in Fig. 1.

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casts (Glahn 1970, 1979), and has been integratedinto IFPS. While this method was successful(Rezek 2002; Dickman 2002) and still provides amethod for “fine tuning” data entered by othermethods to specific times and locations, it has beenlargely replaced by the graphical method.

• Graphical entry can insert forecasts into a griddeddatabase at a spatial resolution essentially boundedonly by computer power (Wier et al. 1998). Thegraphics depict an underlying grid of values. Theforecaster works with the graphics until he or sheis satisfied them. Then, the underlying grid be-comes the “forecast.”

• Model interpretation involves working directlywith numerical model output (Ruth 1998) or its in-terpretation (e.g., Model Output Statistics; MOS)to forecast sensible weather elements. Model in-terpretation, through IFPS, requires a higher levelof understanding and training and is not yet be-ing used at most WFOs. As weather predictionmodels improve, direct interaction with the mod-els through this interface will probably becomemore prevalent.

Each of these interfaces provides a viable way ofentering data into the digital database. The forecast-ers at WFOs choose the interfaces they use. The fore-casts can have a time resolution of 1 h at short rangesand 3 or 6 h at longer ranges. Spatial resolution isexpected to be at least as fine as 5 km with full imple-mentation of IFPS in 2003. These digital forecastsautomatically result in the routine textual (Peroutkaet al. 1998) and voiced (Calkins et al. 1998) forecasts,and also experimental graphic products (LeFebvreet al. 1996; Dickman 2002).

The WFO digital forecasts are updated as the needarises; they become official at a designated “effective”time when entered into the NDFD. It is expected thatthe NDFD can be updated hourly. This does not meanthat all forecasts in the NDFD will be updated hourly,but usually only a small portion affecting limited ar-eas and/or periods.

The digital database makes the updating of fore-casts easier. For minor or only moderate changes, theforecaster at a WFO can change a few numbers orgrids, and a whole suite of textual, voiced, and graphicproducts can be generated automatically. No longerdoes each product have to be updated individually.This illustrates the concept of “nudging” the forecastdatabase that is in vogue now; once the decision ismade that a change is needed, the current database isnudged to make the new forecast. Time saved in creat-ing products will allow forecasters time to apply science

in their analysis. However, sometimes numericalmodel results will make wholesale changes necessary.

COMPOSITION OF THE NDFD. For eachweather element and each time projection, the indi-vidual grids from the WFOs are entered into theNDFD. The grids sent by the WFOs do not overlapeach other except for a narrow boundary. The NDFDalways contains a current set of forecasts, as providedby the WFOs. Time and spatial resolution varies byweather element and projection as appropriate foruser needs, forecast skill, and forecaster work load.The national grids are mosaics of these individualgrids. The NDFD will also contain watch and warn-ing information and weather elements from NCEPcenters such as marine and climate products.

It is a challenge to insure the mosaicked grids are“seamless” at the boundaries between WFO areas.Discontinuities are much more apparent whenfinescale grids are abutted than with the current setof NWS products. Thus, collaboration among NCEPand WFOs to ensure consistent forecasts is critical.Collaboration is carried out at three levels—amongNCEP and WFOs, between adjacent WFOs, and a fi-nal quality control check at the NDFD central serverand at NCEP.

• NCEP–WFO collaboration. The role that NCEP’sHydrometeorological Prediction Center (HPC)plays in the production of guidance for WFOs ischanging dramatically with the introduction of theNDFD. Rather than distributing general guidancein graphical and textual form to WFOs as in the tra-ditional process (see Fig. 3), HPC provides digitalguidance more specific in space and time. Forecast-ers at HPC, as usual, judge the strengths and weak-nesses of output from NCEP’s numerical modelsas well as model output from other countries. Inaddition, in this new paradigm, HPC critically ana-lyzes the NDFD to see what areas or forecast pro-jection may need updating. HPC initiates collabo-ration with WFOs in the affected areas, and togetherthey judge the evolution of meteorological events(see Fig. 4). In this process, HPC issues digital guid-ance targeted for the affected areas. Collaborationcan also be initiated by any of the WFOs.

This change in HPC operations is critical to thesuccess of the NDFD and truly makes NCEP andthe WFOs a team in producing official products.While the WFOs have responsibility for the produc-tion and accuracy of their gridded products, NCEPis playing a much larger role than in the past in fore-cast preparation, especially at longer time ranges.

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• WFO–WFO collaboration. Once the NCEP–WFOcollaboration is under way or complete, the WFOsproduce their grids via IFPS. Subsets of these gridsare sent to the neighboring WFOs; software allowssimultaneous viewing of grids from both WFOs,and provides chat capability to facilitate boundaryconsistency. Thus, after NCEP–WFO collaborationsets the stage, the WFOsrefine and tailor to ter-rain, etc.

• Central quality control.When the forecast gridsfrom the WFOs arrive atthe NDFD central server,they are automaticallychecked by softwarefor consistency at theboundaries. If a discon-tinuity greater than theagreed upon thresholdis detected, the submit-ting WFOs are auto-matically notified of apotential problem. TheWFOs have the oppor-tunity to modify theirsubmissions to makethem more compatiblewith their surroundings.NCEP will also have the

opportunity to view themosaic and offer sugges-tions to the WFOs. As a lastresort, a consensus forecastmay be calculated at WFOboundaries.

This three-pronged col-laboration toward produc-ing a “consistent” mosaicshould, with practice, per-severance, and dedicationyield the desired results. Thecollaboration among NCEPand the WFOs, and the in-creased emphasis on consis-tency, should also producemore accurate forecasts.

Forecasters at NCEPwill be relieved of produc-ing those national productsthat can be produced auto-matically from the NDFD,

such as temperature and probability of precipitation.At the same time, this assures that these national prod-ucts are consistent with any locally produced prod-ucts; consistency is achieved because the locally pro-duced products, generated from the local digitaldatabases, will be reflected in the NDFD, which iscomposed of the local databases (see Fig. 4).

FIG. 3. Traditional process for NCEP distributing guidance to WFOs and prod-ucts being prepared.

FIG. 4. New paradigm of collaboratively preparing forecast products.

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AVAILABILITY OF NDFD. The NDFD shouldbe a boon to the commercial meteorology, broadcast,and risk management industries that rely on readyand efficient access to NWS data. The NWS intendsto make the entire NDFD available to customers andpartners. This will be done in a multistep process, assoftware, techniques, and work patterns at NCEP andthe WFOs are established. The dissemination of thisdatabase will be largely “pull” rather than “push” asis currently done with most official NWS forecastproducts. By the end of 2003, the NWS plans to makeavailable those grids produced by WFOs. These willbe in “mosaic” format, although work will still be inprogress to assure consistency at WFO boundaries. Afew national graphics produced from these grids willbe available, such as temperature and probability ofprecipitation. The NWS already produces suchgraphic products, but not from a digital database;graphics will be prepared this way for efficiency and toensure consistency of those products with the NDFD.

Later, mosaicked grids will be available in “pack-ages” small enough to be dealt with by a variety ofusers. A single grid at 5 km or finer resolution overthe United States is quite large. To get a picture ofthe weather over even a small time period of a dayor two will require a large transfer of data. A user maynot be able to deal with this quantity of data and mayonly be interested in, say, the southeastern seaboard.Also, the full spatial resolution available may not al-ways be needed. Packages of data small enough tomeet the user’s needs willbe provided, probably inlate 2004, by either reduc-ing the area covered or bydecreasing the resolutionor both. Note that this isjust the basic NWS databeing furnished in a modethat the user can accom-modate, and is consistentwith today’s practice ofproviding data in modesthat the user can handle.These packages are not spe-cially tailored, value-addedproducts for a specific cli-entele; such products areleft for the commercial en-terprises to provide, and theNDFD opens the door toan essentially unboundedarray of such specializedproducts.

Dissemination of highly time-critical forecasts andwarning such as severe thunderstorm and tornadowarnings will not rely solely on the NDFD; NWS willissue these life-saving forecasts in the usual manner;however, this information will also be part of theNDFD.

BENEFITS OF THE NDFD. Benefits of a digitaldatabase are both external to the NWS and internal.Partners in the production and dissemination ofweather forecast products should find the NDFD agold mine of information. It will be up to date, withthe exception of time-critical warnings that are dis-seminated within seconds by other means, and willbe national in scope. It will eventually contain essen-tially all the basic information from which forecastsare produced by NWS. Businesses will be able to pro-duce a plethora of products, either general informa-tion for radio and television broadcast, or tailoredproducts for specific customers. For instance, fore-casts for a drive across country with projectionsmatched to user itinerary can be provided. Teamingthis database with geographic information systems(GIS) will provide very powerful capabilities. TheNDFD will give customers what they want when theyneed it (see Fig. 5).

Commercial products available today that providepoint forecasts or large-scale graphics sometimes relyon direct model output or the algorithmetic interpre-tation of model output (e.g., MOS). The NDFD will

FIG. 5. The new forecast and distribution process will be more responsive tothe needs of customers and partners.

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be the source of more accurate official NWS forecastsproduced by forecasters at WFOs and NCEP; previ-ously such digital forecasts were not available.

Any individual user with a computer and access tothe Internet will be able to download informationfrom the NDFD to suit his or her needs. No longerwill this customer have to wait for the timed broad-cast of weather information, but can time the receiptof specific information needed to his or her schedule.The NDFD will provide a veritable data mine for ev-ery person in the United States with a computer; assuch, it will be a one-stop shopping center for NWSforecasts and underlying data. Where commercialenterprises have in the past had to rely on directmodel output or postprocessed products such asMOS, they will now be able to use the official NWSforecasts because they will be in digital form and beavailable from a single source.

It is also expected that through the much enhancedcollaboration among NCEP and WFOs and betweenthe adjacent WFOs, the resulting forecasts will bemore accurate than in the past. The NDFD and itsassociated IFPS will usher in a new paradigm for pro-ducing and disseminating forecasts and a new plateaufor the NWS in providing service in the nation.

STATUS OF THE NDFD. IFPS is currently be-ing implemented nationwide with a target completionof 30 September 2003 for the conterminous states and31 December 2003 for Alaska, Hawaii, and Guam.Many WFOs are already using IFPS to produce thefull range of routine products (Dickman 2002). ThreeNDFD prototype areas have been established, and theWFOs in those areas are sending their grids to theNDFD central server on which the NDFD softwareis being developed and the NDFD prototyped. HPCis providing guidance specifically for the 17 WFOs inthe prototype areas, and its full responsibilities willbe dispatched when the NDFD is in full test mode inthe summer of 2003. It is planned that the data fromthe NDFD will be provided in GRIB, edition 2 (seeWMO 2001), for which decoding software is availableonline at www.nws.noaa.gov/mdl/iwt (see Glahn andLawrence 2002).

Test data will be made available before full imple-mentation. Current information on IFPS and NDFDcan be found online at www.weather.gov/ndfd.

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Glahn, H. R., 1970: Computer-produced worded fore-casts. Bull. Amer. Meteor. Soc., 51, 1126–1131.

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