Sources, products and the go/no-go decision

Knowing what each product is FOR is most of the skill. The rest is knowing what it is not allowed to tell you.

Weather Information — FI.III.C · CA.I.C · PA.I.C

The sources

Flight Service on 122.2 is the number every applicant is expected to have, along with 1-800-WX-BRIEF and the official web sources. Around them sit the automated products, the graphical tools and, in the air, ATC and datalink.

The distinction worth holding onto is between official sources — the ones that constitute a legal briefing and that you can point to afterwards — and supplemental ones that are often more convenient and sometimes better, but are not the record.

Observations and forecasts

METAR is an observation: what the weather actually is, in a standard international format. Read one here.

TAF is a forecast, and its scope is narrower than most people assume: it covers roughly a 5 statute mile radius around the airport, is issued four times a day at 0000, 0600, 1200 and 1800Z, and is valid for 24 hours at most sites (30 at some larger ones). It is not an area forecast, and using it as one is a common error. Read one here.

GFA — the Graphical Forecasts for Aviation — replaced the old textual Area Forecast. It covers the US, the Gulf, the Caribbean and parts of the Atlantic and Pacific, and it is the tool for the gap the TAF leaves: everything between the airports. Observations, forecasts, thunderstorms, cloud, precipitation, icing, turbulence and wind, on one interactive map.

MOS, and its limitations

Model Output Statistics takes raw model output and applies statistics from historical observations to produce a specific point forecast — temperature, chance and type of precipitation, cloud cover and height, wind. It is completely automated, and it is genuinely useful for planning because it gives you numbers where a TAF gives you none.

It is not required by the ACS. It is also the kind of thing an examiner may ask about if you bring it up, so know the limits:

Every one of those gaps is a case where the honest answer is "MOS has nothing to say here" rather than "MOS says no". The EFB carries LAMP MOS beside the TAF for exactly this reason: side by side, the disagreements are the interesting part.

The charts

The surface analysis chart covers the contiguous 48 states, is computer-prepared and transmitted every three hours, and carries pressure, fronts, temperatures, dewpoints, wind, and station plots showing local weather and obstructions to visibility. It is the chart that answers "what is the pattern", which no amount of individual station reports will tell you. See what is on it right now.

Alongside it sit the ceiling and visibility analysis, the winds and temperatures aloft forecast — see the live one — and the convective outlook, which is a planning product for thunderstorm risk over the coming days rather than an in-flight one.

In-flight advisories

AIRMET Sierra for IFR conditions and mountain obscuration, Tango for turbulence, strong surface winds and low-level wind shear, Zulu for icing and the freezing level. SIGMETs for the severe end, and convective SIGMETs for thunderstorms. Full treatment in PIREPs, AIRMETs, SIGMETs and TFRs, with live examples under thunderstorms, icing and turbulence.

The go/no-go decision

The ACS frames this as risk management, and the frame it uses is PAVE: Pilot, Aircraft, enVironment, External pressures. Weather is only the third letter. A forecast that is fine for a current, well-rested pilot in a known-ice-approved aircraft is not fine for the same weather, a rusty pilot and a trainer.

Recent experience belongs in the same conversation. Being legally current is not the same as being ready, and the ACS expects an instructor to be able to separate those.

It does not stop at the hangar door

The most important idea here is that a go/no-go decision is continuous. It is made again at every point where new information arrives, and the outcome can be to divert or discontinue:

• Reduced visibility — watch the temperature and dewpoint converging rather than waiting for the ceiling to drop.
• Hazardous weather ahead: storms, icing, turbulence.
• PIREPs, SIGMETs, updated METARs, LLWAS, and what ATC tells you.
• Conditions falling below your personal minimums, which are lower than the regulatory ones for a reason.
• What you can see: cloud forms, vertical development, blowing dust, a rain shaft.

Visual indications belong on that list deliberately. Every product here has latency — the surface analysis is up to three hours old, a TAF was written hours ago — and the window is the only source with none.

Uses and limitations, in one line

Every product on this page is a model of the atmosphere made at a moment in the past for a place that is not exactly where you are. Treat each one as evidence rather than as truth, prefer the most recent and most local, and let a PIREP from someone who was actually there outweigh a forecast that says otherwise.

Where you meet it next

• Reading a METAR, with a live report to practise on
• Reading a TAF
• The surface analysis, right now
• Live visualizations — every station reporting, mapped

Sources

Product descriptions and issuance are from the FAA Aviation Weather Handbook (FAA‑H‑8083‑28) and the AIM, chapter 7; risk management follows the ACS and the Pilot's Handbook of Aeronautical Knowledge.