PART 61KSNSGROUND SCHOOL
North Aero NORTH AERO

Phase 3 · Module 3-4

Weather Services at Checkride Depth

The Aviation Weather Center makes the products. Leidos Flight Service gives the briefings and the consultations. The apps on the tablet aggregate both. The Aviation Weather Handbook: "The website https://aviationweather.gov is operated by the NWS AWC in Kansas City, MO. It is a major aviation weather website for obtaining text and graphical preflight weather information and products," and the Flight Service site "allows pilots to review weather information, receive online preflight briefings, file flight plans, and receive automatic notifications and alerts" . A regulatory-compliant briefing does not require a phone call. The briefing checklist in AC 91-92 applies to the pilot who self-briefs from those sources , and a documented self-briefing complies.

The inflight sources today

Flight Watch and HIWAS no longer exist. Three inflight sources remain:

The AIM: "ARTCCs broadcast a Convective SIGMET, SIGMET, AIRMET (except in the contiguous U.S.), Urgent Pilot Report, or CWA alert once on all frequencies, except emergency frequencies, when any part of the area described is within 150 miles of the airspace under their jurisdiction. These broadcasts advise pilots of the availability of hazardous weather advisories and to contact the nearest flight service facility for additional details" . The center says the alert exists. The pilot asks the controller, or Flight Service, for the details.

The book

The current weather book is the Aviation Weather Handbook, FAA-H-8083-28B. The handbook: "This handbook describes the United States (U.S.) aviation weather program, products, and services. It also documents weather theory and its application to aviation," and it "is a consolidated source of weather information" . The FAA cancelled five weather advisory circulars in December 2022 when the handbook consolidated them:

A question that cites AC 00-45 cites a cancelled document.

A PIREP is the only direct observation of conditions aloft. All other products are surface observations, forecasts, or remote-sensor images. The handbook: "The two types of PIREPs are Urgent (UUA) and Routine (UA)" . UA marks routine and UUA marks urgent.

The slash codes

Slash codes mark the elements of a PIREP. The handbook: "Elements for all PIREPs are message type, location, time, altitude/FL, type aircraft, and at least one other element to describe the reported phenomena" . The codes are:

Each PIREP includes the airplane type, because turbulence and icing are relative to the airplane. The handbook: "Icing and turbulence reports always include aircraft type" . Turbulence that is moderate in a Boeing is more intense in a Warrior.

Volunteering

The AIM asks pilots to volunteer PIREPs. The AIM: "Pilots are urged to cooperate and promptly volunteer reports of these conditions and other atmospheric data such as: cloud bases, tops and layers; flight visibility; precipitation; visibility restrictions such as haze, smoke and dust; wind at altitude; and temperature aloft" . Reporting unforecast conditions helps the NWS fix the forecast: "The NWS uses the reports to verify or amend conditions contained in aviation forecast and advisories. In some cases, pilot reports of hazardous conditions are the triggering mechanism for the issuance of advisories" . The handbook adds that a forecast condition not encountered is worth reporting too: "If conditions were forecasted to occur but not encountered, a pilot can also report the observed condition" .

ATC solicits PIREPs when reported or forecast conditions reach the AIM's criteria. The AIM: "FAA air traffic facilities are required to solicit PIREPs when the following conditions are reported or forecast: ceilings at or below 5,000 feet; visibility at or below 5 miles (surface or aloft); thunderstorms and related phenomena; icing of light degree or greater; turbulence of moderate degree or greater; wind shear and reported or forecast volcanic ash clouds" . The absence of PIREPs is not the absence of hazard. Few pilots file. An empty PIREP list early in the morning can mean that no one has flown yet.

AIRMETs advise of widespread conditions hazardous especially to VFR pilots. The handbook: "AIRMETs are intended to inform all pilots, especially VFR pilots and operators of sensitive aircraft, of potentially hazardous weather phenomena" . The three categories:

G-AIRMETs

G-AIRMETs are graphical snapshots at three-hour steps out to twelve hours. The handbook: "AIRMETs over the CONUS are valid at discrete times no more than three hours apart for a period of up to 12 hours into the future (e.g., 00, 03, 06, 09, and 12 hours)" . The pilot assumes the hazard exists between the snapshots: "The user should assume the hazardous weather condition is occurring between the snapshots unless informed otherwise" .

SIGMETs

A SIGMET warns of non-convective conditions severe for all airplanes. The handbook lists them: "Severe or greater turbulence (SEV TURB). Severe icing (SEV ICE). Widespread dust storm (WDSPR DS). Widespread sandstorm (WDSPR SS). Volcanic ash (VA)" . A SIGMET is valid for up to four hours: "A SIGMET can have a valid period up to, but not exceeding, four hours" .

A Convective SIGMET covers severe thunderstorms, embedded thunderstorms, and lines of storms. The handbook's criteria:

The AWC issues Convective SIGMETs hourly at 55 past, valid up to two hours. The handbook: "Convective SIGMET bulletins for the eastern, central, and western regions of the CONUS (see Figure 26-5) are issued on a scheduled basis, hourly at 55 minutes past the hour," and "Convective SIGMETs are valid for two hours or until superseded by the next hourly issuance" . The polygon is a snapshot at 55 past, and the storms move out of it.

Any Convective SIGMET implies three hazards. The handbook's rule: "Any Convective SIGMET implies severe or greater turbulence, severe icing, and LLWS" .

The Center Weather Advisory

A Center Weather Advisory is a nowcast for airplanes already en route. The handbook: "A CWA is a concise description of the occurrence or expected occurrence of specified weather phenomena that meet or approach in-flight advisory (e.g., AIRMET, SIGMET, or Convective SIGMET) criteria. A CWA is issued for hazardous weather when there is no existing in-flight advisory from the AWC or the AAWU," and "CWAs are valid for up to two hours" . It is not a flight planning product. It reaches the pilot through the center's broadcast.

The Convective Outlook

The Storm Prediction Center's Convective Outlook grades storm risk. The handbook: "The Convective Outlook defines areas of marginal risk (MRGL), slight risk (SLGT), enhanced risk (ENH), moderate risk (MDT), or high risk (HIGH) of severe weather based on a percentage probability," and the day one to three outlooks "also depict areas of general thunderstorms (TSTM)" . The categories are probabilities of severe weather within 25 miles of a point. The SPC: "The probabilities that you see on the graphics represent the probability of one or more events occurring within 25 miles of a point during the outlook period" . A marginal risk is not zero risk. The SPC's definition: "Marginal risk - An area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity" .

The Graphical Forecasts for Aviation is the interactive replacement for the old text Area Forecast over the continental United States. The handbook: "The GFA Tool is a set of web-based displays intended to provide the necessary aviation weather information to give users a complete picture of the weather that may impact their flight operations. It is a one-stop shop for multiple data fields" . Text Area Forecasts still exist for Alaska and for the Gulf and Caribbean. The handbook's table lists the "Alaska Area Forecast" and the "Gulf and Caribbean Area Forecast," each "A description of significant clouds and weather that includes freezing levels" . The GFA hides a hazard when the user turns an overlay off: "Users can turn on and turn off certain functions (e.g., AIRMET and SIGMET overlays for a given geographical area). This can lead to hidden areas of hazardous weather for a given flightpath" .

The surface analysis

The Surface Analysis Chart shows observed pressure systems and front positions. It is what is, not what will be. The handbook: "A surface chart (also called surface map or sea level pressure chart) is an analyzed chart of surface weather observations," showing "the positions of highs, lows, ridges, and troughs, and the location and character of fronts and various boundaries, such as drylines, outflow boundaries, and sea breeze fronts" . The Weather Prediction Center issues it "eight times daily, valid at 00, 03, 06, 09, 12, 15, 18, and 21 UTC" .

The ceiling and visibility picture

The ceiling-and-visibility picture the ACS calls "CVA" is today a gridded real-time analysis on aviationweather.gov. It is an analysis of now, not a forecast. The product's name has changed, and the examiner might use the old one. The answer is the same: the current ceiling and visibility over the country, drawn from the observations, and it says nothing about the next hour.

Prog charts

Prog charts show forecast front and pressure positions at future times. The handbook: "The NWS WPC provides Short-Range Surface Prog Charts (see Figure 27-24) of surface pressure systems, fronts, and precipitation for a multiday period," and "Each chart depicts a 'snapshot' of weather elements expected at the specified valid time" . The surface analysis is the observation. The prog is the forecast of the same map.

The winds and temperatures aloft forecast, the FB, gives direction in tens of degrees true, speed in knots, and temperature in Celsius. The handbook: "Wind direction is indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits)," and "Temperature is indicated in degrees Celsius (two digits)" .

The blanks and the codes

Blanks near the ground are deliberate. The handbook: "Wind forecasts are not issued for altitudes within 1,500 ft of a location's elevation. Temperature forecasts are not issued for altitudes within 2,500 ft of a location's elevation" . The code 9900 means light and variable: "Light and variable wind or wind speeds of less than 5 kt are expressed by 9900" .

Direction digits of 51 to 86 mean 100 knots or more. The handbook: "Forecast wind speeds of 100 through 199 kt are indicated by adding 50 to the first two digits of the wind direction and subtracting 100 from the speed. For example, a forecast of 250°, 145 kt, is encoded as 7545" . The pilot subtracts 50 from the direction and adds 100 to the speed. Temperatures above 24,000 feet print without a sign: "Above 24,000 ft, the sign is omitted since temperatures are always negative at those altitudes" .

The handbook calls the FB archaic: "Although FB winds are still produced today, they are archaic compared with model output available to the pilot and flight planner" . The app's model winds update hourly. The FB is the form on the written test.

A METAR is a point observation. The handbook: "A METAR includes the airport identifier, time of observation, wind, visibility, Runway Visual Range (RVR), present weather phenomena, sky conditions, temperature, dewpoint, and altimeter setting," and METARs "are routinely produced near the top of the hour" . It describes the sensor's spot at one moment. The far end of the field can differ, and the next hour can differ more.

True and magnetic

Coded winds reference true north. Voice winds and runway numbers reference magnetic north. The handbook's table gives the reference for each product . METAR, TAF, and FB are coded and true. ATIS, the tower, and the AWOS voice are spoken and magnetic.

The runway number is magnetic. The pilot computes the crosswind from the voice wind or from a corrected coded wind, never from the raw METAR against the runway.

The TAF's schedule and the amendment

NWS offices issue scheduled TAFs four times daily, at six-hour intervals. The handbook: "Scheduled TAFs prepared by NWS offices are issued at least four times a day, every six hours" . An amended TAF supersedes and cancels the previous one: "Whenever an amended TAF (TAF AMD) is issued, it supersedes and cancels the previous TAF. That is, users should not wait until the start of the valid period indicated within the TAF AMD to begin using it" . The pilot who briefed at breakfast checks for the amendment before engine start.

Military TAFs

Military TAFs read differently. The handbook's list for joint-use airports: "Visibility is in meters instead of statute miles," and the forecast "Includes a forecast of the lowest barometric altimeter setting (QNH) during the forecast period in inches of mercury" . Military TAFs also carry turbulence groups that begin with 5 and icing groups that begin with 6. A 5-group or a 6-group is turbulence or icing in a military TAF, and pressure tendency or precipitation in a METAR's remarks. The pilot reads which product the group is in before reading the group.

The forecaster's discussion

The NWS Area Forecast Discussion, read beside the TAF, names the hazards the TAF left out and says how confident the forecaster is. The NWS guideline for its aviation section: "Forecasters may use the AFD to discuss details not permitted in the Terminal Aerodrome Forecast (TAF) (i.e. confidence factors, areal coverage and probabilities)," with the first rule "Cover your biggest concern. Where might the TAF go wrong?" and "Confidence level described as a percentage" . The TAF is the forecast. The discussion states the forecaster's doubt in plain words.

The flight of N3079M

On September 27, 2023, at 10:49 at night, a Piper Warrior broke apart in flight in a thunderstorm near Whitesville, Kentucky. The NTSB: "The flight instructor and student pilot were fatally injured" . The instructor was 22, with 447 hours, a flight instructor certificate five months old, 20 hours at night, and 6.6 hours in actual instrument conditions . The student had 37 hours. The flight was a night cross-country "to satisfy the student pilot's night flight training requirements before completing a private pilot practical examination," and it was "the student pilot and accident flight instructor's first time flying together" .

The briefing was complete. "The flight instructor had obtained a weather briefing for the accident flight from an online commercial source. The briefing included a convective SIGMET that was active for the accident location and time. It warned of an area of severe thunderstorms with cloud tops to 42,000 ft, hail of up to 1.25 inches in diameter, and wind gusts of up to 50 knots (kts)" . The SIGMET area "was moving from 280° at 15 knots. Convective SIGMETs implied severe or greater turbulence, severe icing, and low-level wind shear" .

Thirty-four minutes before the accident the instructor posted a screenshot of the tablet, the route, and the radar, with the storms circled. The NTSB compared it to the record: "the weather radar image was from internet sources and not Flight Information Services – Broadcast," and "Based on the airplane's position at the time of the screen capture, the weather radar information depicted was about 10 minutes old. Given this information, it is likely that the flight instructor was aware that convective weather was in the vicinity of the planned route of flight but was not aware of the latency of the weather radar information and continued on-course in an attempt to fly past the approaching convective weather" .

Five minutes before the accident, "the pilot contacted ATC at 2244 and the controller advised the flight of heavy to extreme precipitation at the airplane's nine o'clock position. ADS-B data showed that the airplane continued its northwesterly course; about 2 minutes later, the flight instructor requested an instrument flight rules clearance. The controller issued the clearance and provided an easterly radar vector to assist the flight in getting out of the weather. The flight instructor stated to the controller that the airplane was 'getting blown around like crazy,' and the airplane's flight track showed a turn to the northwest followed by a right circling turn. The controller reiterated the heading of 090º, and the flight instructor responded that they were in 'pretty extreme turbulence'" . "Overall, the distribution of the wreckage was consistent with an in-flight breakup" . The probable cause: "The flight instructor's improper decision to continue flight into a known area of thunderstorms, which resulted in an in-flight breakup" .

Where the instructor could have prevented the accident

An instructor with a complete briefing flew a student into a Convective SIGMET area at night, using a radar picture ten minutes old. Each decision below carries the PAVE category that applied to it.

E

The briefing carried a Convective SIGMET for the route and the time: tops to 42,000 feet, hail to 1.25 inches, gusts to 50 knots. The flight departed into that area at night.

The safe decision: a pilot cancels a VFR night cross-country in a Warrior when a Convective SIGMET covers the route. Each one implies severe turbulence, severe icing, and low-level wind shear, and this one gave tops above the 35,000-foot threshold for extremely hazardous thunderstorms. The instructor read the briefing. He did not make the decision it called for. The student flies the night hours another night.

V

The radar on the tablet showed the storms beside the route, and the instructor planned to fly past them. The picture was about ten minutes old. The storms moved at 15 knots.

The safe decision: datalink and internet radar are for broad strategic avoidance, never for tactical maneuvering around cells. AC 00-63B sets the minimum at 7 to 8 minutes older than the time stamp. The handbook says the mosaic can be 15 to 20 minutes older than the age it displays. A cell moving 15 knots moves 2 miles in 8 minutes and 5 miles in 20. A developing cell was not on the picture at all. The picture on the tablet showed where the weather had been. The safe route was the one that kept the airplane clear of the whole SIGMET area, chosen on the ground.

P

The controller reported heavy to extreme precipitation at nine o'clock. The airplane held its course for two minutes, then the instructor asked for an IFR clearance.

The safe decision: a controller's report of heavy to extreme precipitation is a live observation, minutes old at most. It outranks any picture on the tablet. The pilot turns away at once, to the side the controller offers. The climb, descent, or 180-degree turn that keeps the airplane in visual conditions comes before any clearance. An IFR clearance into a severe thunderstorm is not an escape.

✕

"Getting blown around like crazy," then "pretty extreme turbulence," then a right descending turn and a debris field of 25 acres. Two dead.

Each product in this Module was available to the instructor, and he read most of them. The SIGMET was the reason to stay on the ground. The radar showed where the storms had been. The controller said where they were. The airplane flew into the area that all three sources identified.

Weather radar shows precipitation, not clouds. The handbook: "Weather radar observations and their resultant images are graphical displays of precipitation and non-precipitation targets detected by weather radars" . An empty radar picture is not proof of visual conditions. A solid stratus deck at 800 feet with no rain in it produces no radar return.

Satellite imagery shows clouds. The handbook: "Four types of satellite imagery are commonly used: GeoColor, visible, infrared (IR), and water vapor. Visible imagery is only useful during daylight hours. IR and water vapor imagery are useful day or night" . Radar and satellite show two different things.

Latency

Datalink radar is always at least 7 to 8 minutes older than its time stamp. AC 00-63B: "since initial processing and transmission of Next Generation Weather Radar (NEXRAD) data can take several minutes, pilots must assume that data link weather information will always be a minimum of 7 to 8 minutes older than shown on the time stamp. Thus, pilots should only use data link weather radar images for broad strategic avoidance of adverse weather" . The mosaic can be older still. The handbook: "Datalinked mosaic radar imagery shows where the precipitation was, not where the precipitation is occurring. The displayed radar precipitation may be 15 to 20 minutes older than the age indicated on the display" .

Strategic, never tactical

Datalink weather is for broad strategic avoidance. It is never for tactical storm penetration. The pilot uses the picture on the ground and in cruise to pick a route around a whole area. The pilot does not use it to thread between cells, because the cells are not where the picture shows them.

Pilots have died maneuvering around storms with a mosaic they believed was live. The NTSB wrote its safety alert after two such accidents: "The National Transportation Safety Board (NTSB) has recently investigated two fatal accidents where in-cockpit NEXRAD mosaic imagery was available to pilots operating near quickly developing and fast-moving convective weather" . The alert's finding: "The age indicator associated with the mosaic image on the cockpit display does not show the age of the actual weather conditions as detected by the NEXRAD network," and "Weather conditions depicted on the mosaic image will ALWAYS be older than the age indicated on the display" .

FIS-B is free over the 978 MHz UAT link to an ADS-B In receiver. AC 00-63B: "A ground-based broadcast service provided through the UAT network. The service provides users with a 978 MHz data link capability when operating within range" . The products include METARs, TAFs, NEXRAD, AIRMETs, SIGMETs, NOTAMs, and more.

FIS-B does not replace a preflight briefing. AC 00-63B: "FIS-B METI and AI do not include all the weather products or Notices to Air Missions (NOTAM). As a result, FIS-B METI and AI may not include all the weather products or NOTAMs that a preflight briefing includes," and "FIS-B does not replace a thorough preflight briefing" .

NEXRAD coverage has real gaps. AC 00-63B: "ground-based systems that require a line of sight may have relatively limited coverage below 5,000 feet above ground level (AGL)," and "NWS NEXRAD coverage has gaps, especially in the western states" . A blank area on the mosaic in the mountains can be a gap, not clear air.

An outlook briefing is for planning only. AC 91-92: "An outlook briefing should be obtained when the proposed departure is 6 hours or more from the time of the briefing. This type of briefing is provided for planning purposes only" . The pilot gets a standard briefing closer to departure, and refreshes it when it ages. AC 91-92: "Obtain an abbreviated briefing just before takeoff if your standard briefing is 1 hour or more old or if the weather is questionable" .

VFR not recommended

"VFR flight not recommended" is advisory. The AIM: the briefer uses the phrase when conditions "would make flight under VFR doubtful," and "This recommendation is advisory in nature. The final decision as to whether the flight can be conducted safely rests solely with the pilot" . The decision is the pilot's alone, so the pilot considers the advisory and does not delegate the decision. The briefer has seen the weather products and given the recommendation. The pilot who overrides it is responsible for the outcome.

The trend outranks the snapshot

A current METAR with good conditions does not override a worsening TAF. The METAR describes the sensor's spot at one moment. The TAF is the forecaster's judgment of the next 24 hours. When they disagree in the direction of deterioration, the trend outranks the snapshot. The pilot reads improving versus deteriorating from four places:

The divert point, before launch

A pilot with onboard weather is more likely to continue into deteriorating weather. The picture on the tablet shows an apparent gap. The pilot picks the divert point before launch, before any pressure to continue exists. AC 00-63B limits the datalink to "broad strategic avoidance of adverse weather" . The pilot makes the strategic decision on the ground: a named place and a named condition. At that place the airplane turns if the condition holds.

Issue time and valid time

Each weather product has a valid time and an issue time. The AIM asks the pilot to know "the currency of the product (that is, product issue and valid times), and the relevance of the product" . A product read without its times can describe weather that no longer exists. A TAF issued at 1720 and read at 0600 the next morning is a forecast written before the front arrived. A Convective SIGMET from 1455 is a snapshot from 1455. The pilot reads the time before the weather.

Sources for this module

You are not asked to read these end to end. Have them, and know where in them this module lives. On the checkride you may open the handbook and you may not open this site. Each one links to where you get it. Reading a full chapter is worth it, and it is not required to pass this module.

Your study guide and quiz

The facts to remember are:

Study guide — Module 3-4 (PDF)

Write the quiz answers in full. Task C on the checkride is the examiner handing you the products for a real day and asking what they say. The answer names the product, its time, and what it means for the flight.