Weather & Decoding
Decode GRF SNOWTAM runway condition reports and ICAO NOTAM notices into clear operational language. Identify RWYCC braking action codes, contaminant type and depth, runway thirds, and NOTAM Q-line qualifier codes — everything a pilot needs to assess runway usability and airspace restrictions before departure.
Select the type, paste the raw text, and decode — hover each token for its ICAO definition
Usage Guide
Four steps from raw coded text to a complete operational picture.
Click SNOWTAM or NOTAM to switch between the two decoders. Paste the raw text from your briefing source. The SNOWTAM decoder handles GRF format (post-November 2021). The NOTAM decoder handles ICAO standard format with Q-line qualifiers.
The raw text is displayed with every token as a grey hoverable chip. Hover any token to see a tooltip with the field name, its ICAO definition, and what it means operationally. No aviation knowledge is required — every code is explained in plain language.
Each field appears as an individual box with the raw code in bold at the top. For SNOWTAMs: RWYCC per third with braking action descriptor, contaminant type, depth, and coverage. For NOTAMs: Q-line breakdown, validity window, and operational description.
The decoder highlights RWYCC 0–2 conditions with a warning flag — these require specific aircraft approval and operator authorisation. For NOTAMs, facility outages affecting your planned approach or route are highlighted. Cross-reference with your aircraft performance manual for contaminated runway distances.
Foundational Knowledge
NOTAMs and SNOWTAMs are the two primary channels through which aviation authorities communicate time-sensitive operational changes that affect the safety of flight. Neither can be treated as optional.
A SNOWTAM is issued by the aerodrome authority after each physical inspection of the runway surface and provides the current state of each runway affected by precipitation or surface contamination. Under the GRF introduced in November 2021, every SNOWTAM uses RWYCC codes (0–6) to describe the braking action expected in each third of the runway — touchdown zone, mid-runway, and rollout zone.
SNOWTAMs are operationally critical because published landing distances in the AFM are based on dry runway performance. A RWYCC 1 or 2 surface can require 60–100% more landing distance than the published dry figure. Maximum validity is 8 hours — always check the B and C times to confirm the SNOWTAM covers your planned arrival window.
A NOTAM is a notice distributed via official channels containing information about the establishment, condition, or change in any aeronautical facility, service, procedure, or hazard. NOTAMs cover runway closures, navigation aid outages (ILS, VOR, NDB), approach procedure amendments, airspace restrictions (TFRs, prohibited areas, danger areas), construction and crane activity, laser activity, parachute operations, and unmanned aircraft activity.
ICAO Doc 8126 and ICAO Annex 15 govern NOTAM issuance and distribution. NOTAMs are distributed via the AFTN (Aeronautical Fixed Telecommunication Network) and are available through national AIS offices, briefing services such as 1800wxbrief.com (US), and EUROCONTROL NOTAM services (Europe).
RWYCC Reference
The RWYCC scale is the universal language of runway surface conditions under the Global Reporting Format. Each code maps to a specific braking action descriptor, typical surface condition, and operational implication.
RWYCC 0 operations: Operations on a RWYCC 0 (Nil braking action) surface require specific aircraft type certification and explicit operator approval. Most commercial operators prohibit operations on RWYCC 0 surfaces. Pilots encountering RWYCC 0 conditions not anticipated in the SNOWTAM should issue a PIREP immediately and consider diverting.
SNOWTAM Format Reference
The Global Reporting Format (GRF) SNOWTAM has been the ICAO standard since 4 November 2021. It replaced all previous national formats with a single universal structure.
NOTAM Format Reference
Every ICAO NOTAM follows the same structure. Understanding each section allows rapid operational assessment without reading every word of free text.
Operational Knowledge
The ability to decode a SNOWTAM or NOTAM is only half the competency. The other half is knowing the operational implication of what you are reading.
A SNOWTAM is only valid for 8 hours from the observation time. If your planned arrival is beyond the SNOWTAM expiry, you cannot use it for performance planning. Request a new SNOWTAM from the destination or plan conservatively. Conditions can change significantly — a RWYCC 4 runway can deteriorate to RWYCC 1 within an hour if temperature drops.
The RWYCC is reported per runway third: touchdown zone / mid-runway / rollout. For landing distance calculation, the touchdown zone code is the governing value because braking begins immediately on touchdown. A touchdown zone RWYCC of 2 with a RWYCC 4 mid-runway still requires RWYCC 2 landing distance corrections — the worst third determines required performance.
Slush depth is uniquely critical for takeoff performance. Slush creates substantial aerodynamic and rolling drag during the takeoff roll — more than snow or ice. A slush depth >15mm can prevent an aircraft from accelerating to rotation speed within the available runway length. Always cross-reference slush depth in the SNOWTAM with your aircraft's contaminated runway takeoff performance data in the AFM or operations manual.
The D-line of a NOTAM contains a schedule — the NOTAM only applies during specified hours or days. A runway closure NOTAM with D) 0600-1400 MON-FRI does not apply on weekends or outside those hours. Many pilots miss D-line restrictions, incorrectly treating a scheduled NOTAM as applicable 24/7. Always check the D-line when planning operations outside normal business hours at maintenance-intensive airports.
Pilot reports (PIREPs) of braking action are an independent data source that must be cross-referenced with the SNOWTAM. If a pilot reports braking action significantly worse than the current SNOWTAM indicates — for example, POOR braking on a runway reported as MEDIUM — the aerodrome should issue an updated SNOWTAM. When PIREPs and SNOWTAMs conflict, always use the most conservative (worse) value for performance planning.
A NOTAM indicating an ILS component is unserviceable directly affects your legal approach minima. An ILS with a glidepath (GP) component unserviceable reverts to a localiser-only approach with significantly higher decision altitude and lower probability of visual contact. A NOTAM for ILS unusable requires the pilot to plan an alternative approach or, if no suitable alternative exists, to treat the airport as non-usable and plan to an alternate. Always check ILS NOTAMs for destination and alternate before filing.
Common Questions
A SNOWTAM is a special series NOTAM issued by the aerodrome authority to notify pilots, airlines, and ground handlers about runway surface conditions caused by snow, ice, slush, standing water, or other contaminants. It is issued after each inspection of the runway surface and is valid for a maximum of 8 hours from the observation time, or until a new SNOWTAM supersedes it. Since November 2021, the global standard for runway condition reporting is the GRF (Global Reporting Format), which replaced the older SNOWTAM format with a standardised RWYCC (Runway Condition Code) system. SNOWTAMs are part of the broader NOTAM system and must be reviewed as part of every preflight briefing during winter or after precipitation.
RWYCC (Runway Condition Codes) are standardised numerical codes from 0 to 6 used in the Global Reporting Format (GRF) to describe the surface friction and braking action expected on each third of a runway. RWYCC 6 represents a dry runway — full braking effectiveness. RWYCC 5 represents a wet runway. RWYCC 4 is wet snow over compacted snow or dry snow on a wet runway. RWYCC 3 is ice with frost. RWYCC 2 is compacted snow or ice. RWYCC 1 is ice with very poor braking. RWYCC 0 represents nil braking action — essentially no directional control or stopping ability on the runway. Aircraft operators must cross-reference the RWYCC against performance data in their Aircraft Flight Manual or Airplane Performance Manual before operating on contaminated runways. Operations on RWYCC 0 surfaces require specific aircraft certification and operator approval.
A NOTAM (Notice to Air Missions / Notice to Airmen) is the general system for distributing time-sensitive operational information about any aeronautical facility, service, procedure, or hazard. It covers runway closures, navigation aid outages, airspace restrictions, laser activity, parachute operations, construction, approach procedure changes, and thousands of other subjects. A SNOWTAM is a specific sub-type of NOTAM — a special series NOTAM that is exclusively used to report aerodrome runway surface conditions due to precipitation or surface contamination. Every SNOWTAM is a NOTAM, but not every NOTAM is a SNOWTAM. NOTAMs are encoded in a standardised ICAO format with a Q-line qualifier and lettered sections (A through G). SNOWTAMs use the same delivery mechanism but have a specific coded format for runway condition data defined by ICAO Doc 9981 (PANS-Aerodromes).
The Global Reporting Format (GRF) is the ICAO-standardised system for reporting and using runway surface condition information. It was mandated by ICAO and introduced globally on 4 November 2021, replacing the previous SNOWTAM format and the various national formats (including the US RCAM, the European FAA-equivalent, and others) that had created inconsistency in how runway conditions were communicated. The GRF introduced the RWYCC (Runway Condition Code) scale from 0 to 6 as the universal language for surface friction, replacing descriptive terms like "good," "medium," "poor" that were inconsistently applied. Under GRF, each runway is assessed in thirds (touchdown zone, mid-point, and rollout/stopend), and each third receives its own RWYCC code. The GRF was developed following a joint ICAO/industry task force established after multiple serious runway excursion accidents were linked to inconsistent winter operations procedures.
The NOTAM Q-line is the qualifier line that provides structured information for automated NOTAM filtering and briefing systems. It has the format: Q) FIR/NOTAM-CODE/TRAFFIC/PURPOSE/SCOPE/LOWER-LIMIT/UPPER-LIMIT/COORDINATES-RADIUS. FIR is the Flight Information Region (e.g. EGTT = London FIR). The NOTAM code is a 5-letter code beginning with Q: the first two letters after Q identify the subject (e.g. MR = runway, IL = ILS, LG = lighting), and the last two identify the condition or status (e.g. LC = closed, CO = operational, XX = plain language). Traffic identifies who the NOTAM applies to: IV = IFR and VFR, I = IFR only, V = VFR only. Purpose codes: N = immediate, B = briefing, O = operations, M = misc. Scope: A = aerodrome, E = en-route, W = warning area. Lower/upper limits are in flight levels. Coordinates-radius give the geographic centre and radius in nautical miles.
Braking action is a pilot-reported or aerodrome-measured assessment of the effectiveness of braking on a runway. Under the GRF, braking action descriptors are directly linked to RWYCC codes: RWYCC 6 = Dry (full effectiveness). RWYCC 5 = Good (wet surface). RWYCC 4 = Good to Medium. RWYCC 3 = Medium. RWYCC 2 = Medium to Poor. RWYCC 1 = Poor. RWYCC 0 = Nil (no braking effectiveness). These descriptors are used in pilot reports (PIREPs) using the same terminology, allowing cross-checking between the aerodrome assessment and actual pilot experience. If a pilot reports braking action significantly worse than the current SNOWTAM indicates, the aerodrome authority should reassess conditions and issue a new SNOWTAM. Airlines and operators use the RWYCC to look up landing distance correction factors in their performance manuals — a runway with RWYCC 1 may require landing distances 60–80% longer than on a dry surface.
A runway closure NOTAM follows the standard ICAO NOTAM format. The Q-line will contain the code QMRLC (MR = runway, LC = closed). The A-line identifies the aerodrome. The B-line gives the start time in UTC (YYMMDDHHmm). The C-line gives the end time (or PERM for permanent, or EST if estimated). The E-line contains the plain-language description, typically specifying the runway designator(s), the reason for closure, and any relevant operational information such as a divert recommendation. Example: A) EGLL B) 2301270600 C) 2301270900 E) RWY 09L/27R CLSD FOR SNOW CLEARING. Pilots receiving a runway closure NOTAM for their intended destination must verify the closure window against their planned arrival time and confirm an alternate approach is available or file an alternate.
A NOTAM validity period is defined by the B (start) and C (end) times in UTC. Short-duration NOTAMs (runway closures for maintenance, parachute activity, air shows) may be valid for hours. Long-duration NOTAMs (approach procedure changes, navigation aid outages) may be valid for weeks or months. SNOWTAMs have a maximum validity of 8 hours. A NOTAM with C) PERM indicates a permanent change — typically for procedure or airspace changes — and will eventually be incorporated into the AIP. A NOTAM with C) EST indicates the end time is estimated and the NOTAM may be extended or cancelled. NOTAMs are cancelled by issuing a NOTAMR (replace) or NOTAMC (cancel) with reference to the original NOTAM number.
The GRF SNOWTAM reports the contaminant type covering each third of the runway using standardised descriptors: Dry snow (precipitation that will blow into drifts), Wet snow (will not blow into drifts, higher water content), Compacted snow (mechanically compressed by traffic, appears smooth), Slush (saturated snow with significant water content, causes aquaplaning risk), Ice (clear or opaque frozen water), Dry snow on top of compacted snow, Wet snow on top of compacted snow, Ice on top of compacted snow, Compacted snow on top of ice, Dry snow on top of ice, Water on top of ice, and Frost. Each contaminant has different implications for aircraft performance. Slush is particularly hazardous because it creates significant drag during the takeoff roll, reducing acceleration and potentially preventing rotation before the end of the runway. ICAO Doc 9981 provides the complete contaminant classification matrix.
These suffixes identify the type of NOTAM action. NOTAMN means New — a new NOTAM being issued for the first time. NOTAMR means Replace — a new NOTAM that supersedes and cancels a previously issued NOTAM; the replaced NOTAM number is referenced in the text. NOTAMC means Cancel — a NOTAM that cancels a previously issued NOTAM without replacing it with new information (e.g. the condition has ended or the situation has been resolved). When reviewing NOTAMs for a flight, any NOTAMR or NOTAMC for a NOTAM in your briefing means the original information is no longer valid and must be replaced or removed from your planning.
NOTAMs must be checked for every IFR and VFR flight as part of the preflight planning process. For each airport — departure, destination, and alternates — pilots should check for runway closures or restrictions, navigation aid outages, approach procedure changes or NOTAMs to instrument approach plates, lighting outages, construction activity near runways or taxiways, TFRs or restricted airspace along the route, and any special activity (parachuting, UAV operations, military exercises). In winter, SNOWTAMs for all relevant airports must be included. For flights to remote or unfamiliar airports, all NOTAMs affecting the airport should be read in full — not just the headline — as the E-line may contain operational detail that changes the feasibility of the planned approach. A Pre-Flight Information Bulletin (PIB) aggregates NOTAMs by route or airport area and is the standard format used in IFR filing packages.