Icing Forecasts: CIP, FIP, Freezing Level, and Icing Intensity

Structural icing adds weight and drag and takes away lift. The AIM says the result is "an increase in stall speed and a deterioration of aircraft performance" [2, para. 7-1-19]. This page explains the NWS icing products, the freezing level, and the intensity words pilots see in forecasts and reports. The Aviation Weather Center's icing web page was not available when this page was written, so the product descriptions come from the FAA Aviation Weather Handbook, with the AIM, the FAA's icing pilot guide (AC 91-74B), and NWS Instruction 10-811 [1][2][3][4].

Which products carry icing information?

The Handbook's Table 3-10 lists every product with in-flight icing information. The main ones [1, para. 3.4.2.7]:

Forecasters write the advisories. CIP and FIP are automated: the NWS produces them from model data, and observations for the CIP, "with no forecaster modifications" [1, para. 25.5]. The AIRMET and SIGMET rules are in the advisories guide.

What is the Current Icing Product (CIP)?

"The CIP combines weather satellite, weather radar, METAR, PIREPs and NWS model data to provide an hourly 3D diagnosis of the icing environment." Its graphics cover the contiguous U.S., much of Canada and Mexico, and their coastal waters [1, para. 25.5].

The CIP is generated for select altitudes from 1,000 ft MSL to FL300. You can view one altitude at a time or a composite of all of them, called the "maximum" or "max" [1, para. 25.5]. Icing PIREPs are plotted on a single-altitude chart if they are within 1,000 ft of that altitude and within 75 minutes of the chart's valid time; negative reports are left off to reduce clutter [1, para. 25.5].

Why the "C" doesn't mean now

The Handbook warns that "while the 'C' in CIP stands for 'current,' the product does not show the current conditions, rather it depicts the computer’s expected conditions at the valid time shown on the product." "This valid time can be an hour old or more depending on when it is received by the user." [1, para. 25.5] Check the valid time every time.

And the Handbook's usage rule: "The CIP should be used in conjunction with the report and forecast information contained in an AIRMET and SIGMET." [1, para. 25.5]

What is the Forecast Icing Product (FIP)?

The FIP is the CIP's forecast counterpart. "The FIP provides the same suite of products as the CIP (see Section 25.5), describing the icing environment in the future and being solely NWP model based." It is available at select forecast times through 18 hours, from 1,000 ft MSL to FL300, and it too should be used with AIRMETs and SIGMETs [1, para. 27.13]. The FAA's icing guide describes both products the same way: "This product is automatically produced with no human modification." [3, para. 1-3]

The three icing graphics

Both products come as a suite of graphics [1, paras. 25.5 and 27.13]:

The Severity plus SLD product "can help in determining the threat of SLD, which is particularly hazardous to some aircraft." [1, para. 25.5]

Source conflict, noted: the Handbook's CIP and FIP sections describe three graphics on the Aviation Weather Center website, while its Table 3-10 lists five, adding Icing Severity with probability over 25% and over 50% [1, paras. 3.4.2.7, 25.5, and 27.13]. The website version may change; this page describes the three core graphics.

What do icing intensity words mean?

Two different scales use similar words, and mixing them up is a real risk.

CIP and FIP severity: an accumulation rate

The FIP uses trace, light, moderate, and heavy [1, para. 27.13.2]. "Heavy icing is defined as the accretion of ¼ inch of ice on the airfoil in < 15 minutes." "This is a relative value and the use of which should take into account the airframe and the level of icing protection provided by the aircraft." [1, para. 27.13] The Handbook adds that because ice accumulation varies with wing shape, "the icing intensity categories depicted in CIPs and FIPs (e.g., none, light, moderate, heavy) is only a broad-brushed indication of ice accumulation rate, and not necessarily of aircraft performance." [1, para. 25.5]

AIM intensity: what happens to your airplane

"The icing terms used in SIGMETs and AIRMETs do refer to icing impact on aircraft." [1, para. 25.5] Those terms, and the ones pilots use in PIREPs, come from the AIM [2, para. 7-1-19]:

"Severe icing is aircraft dependent, as are the other categories of icing intensity." [2, para. 7-1-19] The full definitions, with ice types, are in the PIREP guide.

Source conflict, noted: the Handbook's CIP section lists the categories as none, light, moderate, and heavy, while its FIP section lists trace, light, moderate, and heavy [1, paras. 25.5 and 27.13.2]. This page follows the FIP section, the more detailed one. Either way, the top CIP and FIP category is "heavy," not "severe."

What is the freezing level, and where do you find it?

"The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0°C." [1, para. 25.4] Temperature inversions aloft can change the normal relationship between altitude and temperature [3, para. 4-1c], and where the surface is below freezing with warmer air above, the graphics show multiple freezing levels [1, para. 25.4].

Freezing level graphics

The analysis and forecast graphics are updated hourly from NWS computer models. Colors show the height of the lowest freezing level in hundreds of feet MSL. "Regions with white indicate the surface and the entire depth of the atmosphere are below freezing." Hatched or spotted areas show a below-freezing surface with multiple freezing levels aloft [1, paras. 25.4 and 27.12]. The forecasts "supplement the forecast freezing level information contained in the icing AIRMETs." [1, para. 27.12]

Other sources

• AIRMETs. NWS Instruction 10-811 says freezing level information is included: multiple freezing levels, where the lowest is the declared one; areas with multiple freezing levels; and "Range of freezing levels over the area is included." [4, sec. 7.1]
• Winds aloft. "Freezing levels can be determined from the winds aloft forecast." [3, para. 4-1g] Look where the temperature changes sign between levels (winds aloft guide).
• PIREPs. Outside air temperature at a known altitude is a direct check. The FAA's icing guide calls PIREPs "generally the most useful as they are factual weather reports for specific times and places." [3, para. 4-1]
• Radar. "Bright band is a distinct feature observed by radar that denotes the freezing (melting) level." [1, para. 15.2.15.1.5] See the radar guide.

Source conflict, noted: the FAA Aviation Weather Handbook and NWS Instruction 10-811 give different height intervals for the lowest freezing levels in AIRMETs [1, para. 3.4.2.8][4, sec. 7.1]. This page states no interval. Read the heights in the current AIRMET or G-AIRMET itself.

Why the freezing level matters

"It is critically important for pilots to obtain the freezing levels for the areas in which they will be flying to be able to make educated decisions on how to exit icing conditions if they are encountered." [3, para. 4-1c] The AIM agrees: "Proper preflight action includes obtaining information on the freezing level and the above freezing levels in precipitation areas." It also warns that the escape altitude is not always down: "This 'warmer' altitude may not always be a lower altitude." [2, para. 7-1-19] Freezing rain means warm air above you.

What are supercooled large drops (SLD)?

The Handbook: "SLD is defined as supercooled water droplets larger than 50 micrometers in diameter." They include freezing drizzle and freezing rain aloft [1, para. 27.13.3]. The AIM gives the same size as 0.05 mm [2, para. 7-1-20]. They matter because "SLD ice tends to form aft, beyond the reach of deicing equipment." [1, para. 20.3.2.1] That is why the CIP and FIP mark SLD threat areas separately.

Where are the official icing product descriptions?

Official icing product descriptions

• Start here: FAA Aviation Weather Handbook, Sections 25.4 and 25.5 (freezing level analysis and CIP, PDF pages 365 to 366) and Sections 27.12 and 27.13 (freezing level forecasts and FIP, PDF pages 454 to 455) [1, paras. 25.4 to 27.13.3].
• AIM 7-1-19, PIREPs Relating to Airframe Icing, and 7-1-20, Definitions of Inflight Icing Terms [2].
• AC 91-74B, Pilot Guide: Flight in Icing Conditions [3].
• NWS Instruction 10-811, Section 7.1, for AIRMET icing and freezing level content [4, sec. 7.1].

Links checked September 29, 2026: all returned HTTP 200.

Where do icing forecasts mislead pilots?

• The valid time is older than you think. A CIP can be an hour old or more when you see it [1, para. 25.5].
• Broad brush. CIP and FIP intensity is an accumulation rate, not a statement about your wing [1, para. 25.5].
• No forecaster in the loop. CIP and FIP are automated [1, paras. 25.5 and 27.13]. AIRMETs and SIGMETs carry a forecaster's judgment.
• Absence of reports. "nor can a report of no icing assure the absence of icing conditions at a later time" [2, para. 7-1-20].
• The human factor. The Handbook ends its FIP section plainly: "The ultimate safety factor is the vigilance demonstrated by the pilot in potential icing situations." [1, para. 27.13]

How do you use icing forecasts in a go/no-go decision?

The decision is yours as pilot in command, and it starts with what your airplane is approved for. A few habits:

• Find the freezing level and the tops. Together they tell you whether a climb or descent gets you out. In stratiform clouds, icing is often "confined to a relatively thin layer, either climbing or descending may be effective in exiting the icing conditions within the clouds." [3, para. 4-1h]
• Layer the products. AIRMET Zulu and SIGMETs first, then CIP and FIP for detail, then PIREPs to check them (PIREP guide).
• Treat SLD as its own hazard. Freezing drizzle or freezing rain aloft changes the plan [1, para. 20.3.2.1].
• Write down your out. A FRAT records the hazard and the escape plan [5, ch. 3].

Where do icing forecasts fit in a disciplined decision?

PlaneWX is decision support for general aviation pilots, built around one idea: "Fly like it's your job." Treat the weather decision the way a professional crew would, with the same process every time. That process is a loop: Brief, then FRAT, then Fly or Stay, then Debrief, with a Mentor if you want one. Icing products feed the Brief. Here's how PlaneWX handles them, as described in the help center [6]:

• Brief: which icing data. On CONUS flights within 18 hours of departure, PlaneWX layers the FAA/NWS CIP nowcast and the DAFS Icing Forecast Integration forecast over icing soundings from several weather models (Icing Analysis).
• Brief: no cloud, no ice. When model soundings show cloud tops at or below the freezing level, PlaneWX zeros that waypoint's icing severity even if the icing product still paints it, and the briefing explains why (Icing Analysis).
• Brief: severe is severe. "PlaneWX always marks severe icing as unfavorable regardless of aircraft equipment." (Icing Analysis)
• FRAT. The flight risk assessment opens within 4 hours of departure, and your own ratings drive it (FRAT).
• Fly or Stay. "PlaneWX never recommends GO or NO-GO. You make the call as PIC." (The Risk Loop)
• Debrief. If you picked up ice, the debrief is the moment to file the PIREP. Self Debrief is a PlaneWX Labs feature for Pro Plus (The Risk Loop).

The help center is plain about the limits: "PlaneWX is not a substitute for a complete, independent pre-flight weather briefing. Pull one from a source you already trust before you fly." (The Risk Loop)

See the icing picture along your next route in a PlaneWX briefing, or read how PlaneWX analyzes icing. Related: the PlaneWX guide to icing forecasts for small aircraft.

Frequently asked questions

What is the difference between CIP and FIP?

The CIP is an hourly diagnosis of icing built from satellite, radar, METARs, PIREPs, and model data. The FIP is its forecast counterpart, based on computer models, out to 18 hours. Both are automated, with no forecaster changes [1, paras. 25.5 and 27.13].

Does the CIP show current icing?

Not exactly. Despite the name, the Handbook says it shows the computer's expected conditions at the product's valid time, and "This valid time can be an hour old or more depending on when it is received by the user." [1, para. 25.5]

What does heavy icing mean on the FIP?

"Heavy icing is defined as the accretion of ¼ inch of ice on the airfoil in < 15 minutes." The Handbook calls it a relative value that depends on the airframe and its ice protection [1, para. 27.13].

Is FIP heavy icing the same as severe icing?

No. CIP and FIP categories are a broad indication of ice accumulation rate, not of aircraft performance [1, para. 25.5]. The AIM's severe icing is defined by what happens to the aircraft: ice protection can't keep up and immediate exit is required [2, para. 7-1-19].

What is the freezing level?

"The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0°C." There can be more than one [1, para. 25.4].

Where do I find the freezing level?

The freezing level analysis and forecast graphics, updated hourly [1, paras. 25.4 and 27.12]; AIRMET Zulu [4, sec. 7.1]; and PIREP temperatures and the temperatures in the winds aloft forecast [3, para. 4-1].

What are supercooled large drops?

Liquid drops larger than 50 micrometers, 0.05 mm, below 0°C, such as freezing drizzle and freezing rain [1, para. 27.13.3][2, para. 7-1-20]. They can freeze behind the protected areas [1, para. 20.3.2.1].

Can a report of no icing be trusted?

Only for that time and place. The AIM notes that a report of no icing can't assure the absence of icing later [2, para. 7-1-20]. Negative icing PIREPs still help forecasters [3, para. 4-3].

How does PlaneWX use CIP and FIP?

On CONUS flights within 18 hours, the help center says PlaneWX layers the CIP nowcast and the DAFS Icing Forecast Integration, which it describes as the successor to FIP, over multi-model icing soundings. PlaneWX never recommends GO or NO-GO; you make the call as PIC [6].

Glossary

Every term below links to the FAA, NWS, or NOAA document that defines it. The same definitions appear when you hover, focus, or tap a dotted term on this page.

AIRMET Zulu

The AIRMET series for moderate icing; it also gives freezing level heights. Source: FAA Aviation Weather Handbook, 26.3.1.2

CIP (Current Icing Product)

An hourly, automated 3D diagnosis of icing probability, severity, and supercooled large drop threat, built from satellite, radar, METARs, PIREPs, and model data. Source: FAA Aviation Weather Handbook, 25.5

Convective SIGMET

The SIGMET issued for thunderstorms over the contiguous U.S. It implies severe or greater turbulence, severe icing, and low-level wind shear. Source: FAA Aviation Weather Handbook, 26.2.4.2

CWA (Center Weather Advisory)

A short-term advisory from a Center Weather Service Unit for weather that meets or approaches AIRMET or SIGMET criteria, valid for up to 2 hours. Source: FAA Aviation Weather Handbook, 26.4

FIP (Forecast Icing Product)

The automated forecast counterpart of the CIP: icing probability, severity, and supercooled large drop threat out to 18 hours, from computer model output. Source: FAA Aviation Weather Handbook, 27.13

FRAT (Flight Risk Assessment Tool)

A form or checklist for recording flight hazards and the risk they add up to before you fly. Source: FAA Risk Management Handbook, Chapter 3, Using a Flight Risk Assessment Tool (FRAT)

Freezing level

The lowest altitude over a place where the air temperature reaches 0°C. There can be more than one. Source: FAA Aviation Weather Handbook, 25.4

PIREP (Pilot Weather Report)

A report of weather a pilot actually encountered in flight, shared to help other pilots and forecasters. Source: FAA Aviation Weather Handbook, 24.5.1

SIGMET (Significant Meteorological Information)

An unscheduled warning of en route weather that may affect the safety of aircraft operations, such as severe icing, severe turbulence, widespread dust storms or sandstorms, and volcanic ash. Source: FAA Aviation Weather Handbook, 26.2

SLD (Supercooled large drops)

Liquid water drops larger than 50 micrometers, such as freezing drizzle and freezing rain, that stay unfrozen below 0°C and can freeze behind ice protection. Source: FAA Aviation Weather Handbook, 27.13.3

This page explains published FAA and NWS guidance. It is not a substitute for your aircraft's flight manual limits on flight in icing. Always get a current briefing before you fly.

References

1. FAA-H-8083-28B, "Aviation Weather Handbook." Federal Aviation Administration, Flight Standards Service. April 2, 2026. Paragraphs cited: 3.4.2.7 (Table 3-10), 3.4.2.8 (Table 3-11), 15.2.15.1.5, 20.3.2.1, 25.4, 25.5, 27.12, 27.13, 27.13.1 to 27.13.3. https://www.faa.gov/regulationspolicies/handbooksmanuals/aviation/faa-h-8083-28b-aviation-weather-handbook. PDF: https://www.faa.gov/sites/faa.gov/files/FAA-H-8083-28B.pdf
2. "7-1-19. PIREPs Relating to Airframe Icing" and "7-1-20. Definitions of Inflight Icing Terms." Aeronautical Information Manual (AIM), Chapter 7, Section 1. Federal Aviation Administration. Effective July 9, 2026 (Change 3). https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap7_section_1.html
3. AC 91-74B, "Pilot Guide: Flight in Icing Conditions." Federal Aviation Administration. October 8, 2015. Paragraphs cited: 1-3, 4-1, 4-1c, 4-1g, 4-1h, 4-3. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-74B.pdf
4. NWS Instruction 10-811, "En Route Forecasts and Advisories." National Weather Service. September 2, 2025. Section 7.1. https://www.weather.gov/media/directives/010_pdfs/pd01008011curr.pdf
5. FAA-H-8083-2A, "Risk Management Handbook." Federal Aviation Administration. 2022. Chapter 3, "Using a Flight Risk Assessment Tool (FRAT)." https://www.faa.gov/regulationspolicies/handbooksmanuals/risk-management-handbook-faa-h-8083-2a
6. PlaneWX Help Center: "Icing Analysis," "FRAT," "The Risk Loop." PlaneWX. Accessed September 29, 2026. Icing Analysis · FRAT · The Risk Loop