Glossary — NWS Data Explorer

People & offices

SDM also: Senior Duty Meteorologist

Senior Duty Meteorologist — the national on-duty coordinator for NWS operations.

The Senior Duty Meteorologist sits at NWS Central Operations in College Park, Maryland, and acts as the national duty officer for the whole Weather Service. They coordinate across forecast offices and national centres, decide when to declare a Critical Weather Day, direct where the movable satellite sectors point, and issue the administrative messages this site translates.

NCO also: NWS Central Operations, NCEP Central Operations

NWS Central Operations — runs the computing behind the forecast models.

NCO operates the supercomputers and data systems that produce NWS model guidance and move products around. When a message talks about dataflow, ingest or the production suite, NCO is the organisation doing it.

NCEP

National Centers for Environmental Prediction.

The umbrella for NWS’s national-scale centres — including the Storm Prediction Center, Weather Prediction Center, National Hurricane Center and the Environmental Modeling Center. NCEP produces the guidance that local forecast offices build on.

WFO also: Weather Forecast Office

Weather Forecast Office — one of 122 local NWS offices.

Each WFO is responsible for forecasts and warnings in its own area, typically a few dozen counties. The three-letter office code (TOP for Topeka, OUN for Norman) shows up throughout the API, especially in grid coordinates and product identifiers.

Observations

RAOB also: rawinsonde, radiosonde, sounding, upper-air observation

Radiosonde observation — the data from a weather balloon flight.

Twice a day, at 00Z and 12Z, roughly 90 US sites release a balloon carrying a radiosonde: a small instrument package that radios back temperature, humidity, pressure and wind as it rises. A flight lasts about two hours and can reach 100,000 feet before the balloon bursts. These soundings are the only routine direct measurement of the whole depth of the atmosphere, and they anchor the models’ starting conditions.

TTAA

The mandatory-levels part of a coded sounding.

A balloon sounding is transmitted in parts. TTAA carries the mandatory pressure levels — 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150 and 100 mb — up to 100 mb. If TTAA is missing, the backbone of the sounding is missing.

TTBB

The significant-levels part of a coded sounding.

TTBB carries the “significant levels”: the extra points between the mandatory levels where temperature or humidity changes sharply. Losing TTBB means losing the fine structure — inversions, dry layers, the details that decide whether storms fire — even though the basic profile survived.

mb also: millibar, millibars, hPa

Millibars — the unit of atmospheric pressure, also used as a height coordinate.

Sea level averages about 1013 mb. Because pressure falls predictably with height, meteorologists use pressure as a stand-in for altitude: 850 mb is roughly 5,000 ft, 500 mb roughly 18,000 ft, 250 mb roughly 34,000 ft. So when a message says a balloon was “short to 577 mb”, it means the flight ended around 15,000 ft — the sounding covers the lower atmosphere but says nothing about the jet stream level above it.

METAR

A routine surface weather report from an airport.

The standard hourly observation format used worldwide: wind, visibility, cloud layers, temperature, dewpoint and pressure, in a dense code. Most “current conditions” you see anywhere trace back to a METAR.

PIREP

A pilot report of conditions actually encountered in flight.

Pilots radio in what they are experiencing — turbulence, icing, cloud tops, ride quality. PIREPs are one of the few direct observations of the mid-atmosphere between balloon launches.

Models

GFS

Global Forecast System — the main American global weather model.

The GFS simulates the entire planet’s atmosphere out to 16 days, four times a day. It is the model behind most free forecast apps and the starting point for a great deal of American forecasting.

NAM

North American Mesoscale model — higher resolution, smaller area.

The NAM covers North America at finer resolution than the GFS but runs out to only 84 hours. Because its domain is smaller it can resolve terrain and smaller-scale weather features better.

model production suite

The scheduled sequence of model runs NWS executes every cycle.

Models run on a strict timetable: gather observations, run the analysis, run the forecast, post the output. Each step has a target time. When SDM says the suite is “running on time”, downstream products — including the forecasts in your weather app — will land when expected.

ingest

Taking observations into a model’s starting conditions.

Before a model can forecast it must first work out what the atmosphere looks like right now, by blending millions of observations into a coherent picture. Data that arrives after the cut-off simply misses the run — which is why “stations available for ingest” is a number worth watching.

Time

Z also: UTC, Zulu

Coordinated Universal Time — the single clock all weather data uses.

Weather is global, so meteorology runs on one clock: UTC, written with a trailing Z and pronounced “Zulu”. 12Z is noon UTC, which is 8am Eastern Daylight Time or 5am Pacific Daylight Time. Every time on this site is shown in your local time with the original Z time kept alongside.

Satellite

MDS also: mesoscale sector, mesoscale domain sector, meso sector

Mesoscale Domain Sector — a small, movable, rapid-scan satellite window.

Each GOES satellite scans a fixed full-disk view and a continental view on a set schedule, plus two small “mesoscale” boxes about 1,000 km across that can be aimed anywhere in view and are photographed roughly every 60 seconds. Forecasters point them at the day’s highest-stakes weather — a developing tornado outbreak, a hurricane’s eye, a fast-moving wildfire.

GOES also: GOES-East, GOES-West

The American geostationary weather satellites.

GOES satellites sit 22,236 miles above the equator, orbiting at exactly the speed the Earth turns, so each one stares at the same face of the planet forever. GOES-East watches the Americas and the Atlantic; GOES-West watches the western US and the Pacific.

Operations

Critical Weather Day also: CWD

An internal NWS posture that freezes non-essential system changes.

When NWS expects high-impact weather, the Senior Duty Meteorologist can declare a Critical Weather Day. Scheduled software, hardware and network changes at the affected offices are postponed so nothing is disturbed while forecasters work. Emergency changes still happen, with senior approval. It says something about how NWS is protecting its own systems — not about the forecast where you live.

NWSTG

NWS Telecommunication Gateway — the hub that routes NWS products.

Nearly every NWS product passes through the Gateway on its way to the public, the FAA, broadcasters and international partners. When the Gateway has trouble, products can be delayed or missing across many systems at once.

EMWIN

Emergency Managers Weather Information Network.

A low-cost satellite and internet broadcast of NWS warnings and products, designed so emergency managers can keep receiving data even when normal internet is unavailable.

NOAAPort

The satellite broadcast that pushes NWS data to bulk users.

NOAAPort delivers a firehose of NWS data by satellite to universities, broadcasters, private weather companies and emergency managers — the pipe most large weather data consumers actually drink from.

IDSS

Impact-based Decision Support Services.

NWS’s term for working directly with emergency managers and other officials — briefings, phone calls, on-site support — rather than only publishing forecasts and warnings.

IMET

Incident Meteorologist — a forecaster deployed to a wildfire.

IMETs deploy to the field with a mobile weather station and provide forecasts directly to fire incident commanders. When an SDM message mentions IMETs, there is a significant fire being actively worked.

Products

ADM

Administrative Message — the routine SDM status product.

The product code for the Senior Duty Meteorologist’s regular operational messages: model production status, balloon reports, satellite sector moves and Critical Weather Day status.

ADA

Alert Administrative Message — the higher-urgency SDM product.

Used for outages, dataflow problems and Critical Weather Day declarations. Worth noting: the message header, not the product code, is what actually tells you whether a message is an alert — ADM-coded products sometimes carry an ALERT header.

AFD

Area Forecast Discussion — the forecaster’s reasoning, in their own words.

Several times a day each forecast office publishes an unvarnished explanation of how they read the situation, which models they trust today and what they are unsure about. It is written for other meteorologists but is readable and often fascinating.

API concepts

gridpoint also: forecast grid

One square of a forecast office’s editing grid, roughly 2.5 km across.

Modern NWS forecasts are not written as text first. Forecasters edit a grid of numbers covering their area, and the text forecast is generated from it. The API exposes both: the grid itself, and the readable forecast built from it.

zone also: forecast zone, fire weather zone

A named area that forecasts and warnings are written for.

NWS divides the country several different ways at once: public forecast zones, county zones, fire weather zones and marine zones. They overlap and are not the same shapes, which is why a warning sometimes covers a different area than the forecast for the same town.

GeoJSON

The default format api.weather.gov returns.

A JSON format for geographic data, where each item carries both its data and its shape on the map. The NWS API returns GeoJSON by default; you can ask for JSON-LD instead with an Accept header.

Radiosonde status codes

RAOB recaps often report a bare five-digit code next to a station — 10142, 10159 and so on. These are internal NWS codes and, as far as we can find, NWS does not publish a legend for them anywhere public. We checked the NWS upper-air program pages, the NCO radiosonde quality-control reports and the message archive itself.

So we only define a code when the messages themselves define it, and we show every other code as a raw code with an honest label. Guessing would be worse than useless here: it would be believed.

10142

Ground equipment failure — the station’s tracking/receiving equipment was down, so no usable sounding was produced.

How we know: The SDM messages themselves print this code alongside the text "Ground equipment failure", so the meaning comes straight from the source.

10145, 10158, 10159 and others

Meaning not published.

These appear regularly and clearly indicate some problem with the launch or the data, but we have no verifiable source for what each one specifically means. They are shown on message cards as unrecognised codes rather than translated.