Pilot Weather Chapters 18 and 19

SIGMET. To acquire it, you ATC may ask you whether you have the latest may have to request it Station. Some navigation aids also trans- via a Flight Service mit them on a continual basis. Or maybe you'll be lucky enough to have a datalink capability in the cockpit that die plays it for you.

HIWAS (Hazardous In-flight Weather Advisory Service) is a continuous broadcast of hazardous weather infor- mation transmitted over selected VOR navigation sta- tions in the U.S. Hazardous weather includes SIGMETS, convective SIGMETS, AIRMETS, Center Weather Advis- ories (CWAS), severe weather forecast alerts (AWW), and Urgent Pilot Weather Reports (PIREPS-UUA). On U.S. VFR sectional and IFR Enroute Aeronautical charts, the appropriate VOR station will have HIWAS listed just above the VOR identifier.

In the Contiguous United States (CONUS), non-convective SIGMETS are issued when the following phenomena occur or are expected to occur: A. Severe icing not associated with convection. B. Severe or extreme turbulence or clear air turbu- lence (CAT) not associated with convection. C. Widespread dust storms or sandstorms lowering surface visibilities to below 3 miles. D. Volcanic ash.

In Alaska and Hawaii, SIGMETS are also issued for: A. Tornadoes. B. Lines of thunderstorms. C. Embedded thunderstorms. D. Hail greater than or equal to 3/4 inch in diameter. SIGMETS describe designated hazardous weather condi- tions up to and including 45,000 feet MSL, regardless of the height of the phenomenon at its base.

SIGMET (SIGNIFICANT METEOROLOGICAL INFORMATION)

In a nutshell, it's an aviation weather warning for pilots, so take heed. A SIGMET (WS) bulletin provides a short-term warning of widespread weather phenomena considered potentially hazardous to all aircraft. SIGMETS are un- scheduled forecasts that are valid for 4 hours. However, SIGMETS associated with tropical cyclones and volcanic ash clouds are valid for 6 hours. According to the Avi- ation Weather Center's website, "These SIGMETS are considered to be widespread because they must be af- fecting or be forecast to affect an area of at least 3,000 square miles at any one time. However, if the total area to be affected during the forecast period is very large, it could be that only a small portion of this total area would be affected at any one time." Keep in mind that 3,000 square miles is about 60% of the size of the state of Connecticut.

There were very few sources for a cloud tops forecast. The FA was just about the only reliable source. Not to worry, the new GFA tool does provide a forecast for cloud tops, but as of this writing, it's not very effective or reliable when clouds are convectively driven. Often in locations where thunderstorms have formed or persisted, the GFA may show clear skies or high cirrus. So, buyer beware.

In addition to cloud tops, the tool allows you to View an hour by hour forecast over the next 15 hours for cloud coverage, ceiling, visibility, precipitation, thunder- storms, icing, turbulence and more. It is very compre- hensive. You can also overlay radar, satellite, SIGMETS, convective SIGMETS and G-AIRMETS.

The next G-AIRMET snapshot below is valid at 2100Z and shows further dissipation to the southwest. There- fore, to minimize your exposure to airframe icing on this particular flight, pushing the departure time an hour or two in the future may be a prudent decision.

In the end, G-AIRMETS were created to provide a higher temporal resolution than the legacy AIRMET. This makes them more useful for preflight planning decisions.

Issue Times and Valid Times GFAS are released four times a day, about 30 minutes prior to the forecast period. (Make sure you know the difference between issue time and valid time. The "valid times" are: 000oz, 0600Z, 120oZ and 1800Z, with their "issue times" approximately 30 minutes before: 2330Z, 0530Z, 1130Z, and 1730Z.

Issue times have an approximate 30-minute win- dow. GFAS can be sent out as early as 15 minutes past the hour or as late as 45 minutes past the hour. I re- member when I infringed on the deadline, I would see the "techie" entering the forecast room and walking to my desk with that look of urgency. Funny-scheduled pushback time at the airlines is just as stressful.

Example of a Convective SIGMET: WSUS32 KKCI 161855 SIGC CONVECTIVE SIGMET 86C VALID UNTIL 2055Z WI FROM 20ENE RHI-30NW DLL-20NNE ODI-50WSW RHI-20ENE RHI AREA TS MOV FROM 22035KT. TOPS TO FL430.

Translation: This convective SIGMET (WST) was issued on the 16th of the month at 1855Z. It is the 86th convective SIGMET to be issued in the central region since 0000Z. The convective SIGMET is valid for two hours or through 2055Z affecting the state of Wisconsin for an area of thunderstorms mov- ing from the southwest (220 degrees) at 35 knots. The maximum tops are to flight level 430 (43,000 feet MSL).

In the U.S., what are the hotspots for convective SIGMETS? Florida is probably high on your list of guesses. How about the famed Tornado Alley in the Midwest? You'd be right about Florida, but throughout most of the year, Tornado Alley isn't a significant hotspot for convective SIG- METS. Tornado Alley remains tranquil in the months of July and August for convective SIGMETS. While Tornado Alley has no clearly defined peaks throughout the year, June seems to carry most of the weight.

What three months throughout the year does the Aviation Weather Center issue the most convec- tive SIGMETS? No surprises here; the months of June, July and August keep the convective SIGMET desk at the AWC the busiest.

The best way to understand the value of G-AIRMETS is to look at a specific example. Shown below in the North- east is the original legacy AIRMET graphic as it was de- picted on the AWC website.

When reading the text of this AIRMET below, it fore- casts the potential for widespread moderate ice from 4.000 feet to 8,000 feet MSL. The AIRMET is valid over a 6-hour period from 1500Z to 2100Z. The pilot must assume that moderate icing is possible anywhere within the bounds of this AIRMET during the time and alti- tudes specified. G-AIRMETS, however, describe a different story. Let's assume you are departing at 1600Z under in- strument flight rules out of Teterboro Airport in north- ern New Jersey (west of NYC) heading northwest to Buf- falo, New York (between Lakes Ontario and Erie). It's a two-hour flight with an expected arrival time in Buffalo at 1800Z. Will airframe icing be a factor assuming an en route altitude of 10,000 feet?

GFA Versus GAF

You are probably asking, "Why isn't it called GAF?" Years ago-in 2000, to be exact-the GFA was introduced to as a graphic replacement for the wordy and confusing FA (Area Forecast). After all, a picture is a worth a thousand words, especially when a lot of those words are abbrevia- tions or acronyms. Many pilots could not decipher the codes in the FA nor assemble the "big picture" in their heads. Doug used to write those forecasts, and even so, now and again he had to consult a book called MANABS-a manual on abbreviations! Sure, the ab- breviations and acronyms are still there, but many are now much easier to decipher, since there is an associated pictorial. Coming back to the 'GFA' versus 'GAF' issue: well, back in the pre-graphic days, the term FA was used to mean (Forecast-Area). So why didn't they switch things around when they went to the GFA? That answer perhaps no one knows.

Clouds and Weather Forecast Chart This chart will include the main large-scale (synoptic) weather-makers, like fronts, lows, troughs, highs, etc, along with their speed and direction. The direction of motion is depicted with an arrow and a speed value in

knots. If the speed is less than five knots, QS (quasi-sta- tionary) is used. Organized areas of clouds, areas of pre- cipitation, and obstruction to vision will also be indicat- ed in the package. Isobars separated every 4 millibars, are included, as are strong just like a surface analysis, winds of 20 knots or more.

CWAS are issued by forecasters as a textual product. They often cover a smaller region of airspace than most AIRMETS or SIGMETS and typically consist of an area, line or radius from a specific point. CWAS can be de- picted graphically from the AWC's website. Some flight planning apps can also display the geographic area de- scribed in the CWA's text. Unlike their AIRMET counterpart, CWAS are not routinely issued and have no defined schedule. So it's possible there may be a day and time where no CWAS have been issued. Moreover, they have a very short lead time since they are issued on an as-needed basis. So it's not unusual to see a CWA issued at 50 minutes past the hour to describe adverse weather that is evolving very rapidly. Once issued, CWAS are valid two hours or sometimes less. If conditions are anticipated to improve

or persist through the forecast period, it will be indicated in the last line of the CWA text. As mentioned earlier, CWAS are not as valuable of a preflight planning tool be- cause of its short lead time and duration. While CWAS can be issued at any time, they are generally coordinated with other agencies within NOAA to ensure meteoro- logical consistency between products. This includes me- teorologists at the AWC who are responsible for issuing AIRMETS, SIGMETS and convective SIGMETS. It's typ- ical for the meteorologist at the CWSU to have a brief phone conversation with the appropriate meteorologist at the AWC before issuing a new CWA. the end, CWAS often augment or in some cases fill in the gaps where adverse weather conditions may not meet national AlR- MET or SIGMET criteria. A good example of its complementary nature is a CWA for low IFR conditions. An AIRMET for IFR condi- tions is primarily directed at pilots flying under visual flight rules (VFR). It describes an area that may experi- ence a ceiling and/or visibility below VFR minimums. However, what if a portion of the AIRMET region is also plagued with persistent low IFR conditions? This is critic- al information for all pilots including those flying under instrument flight rules (IFR). As shown in Figure 19-12 using a flight planning app called ForeFlight Mobile, given the number of stations reporting low 1IFR condi- tions (magenta markers) within the AlIRMET region (dark grey polygons), the Denver CWSU issued a CWA for ceilings at or below 500 feet and visibility at or below 1/2 statute miles.

conditions Warranting an AIRMET:

* AIRMET Sierra is an advisory to VFR pilots for a widespread area with ceilings less than 1,000 feet and/or visibility less than 3 miles (IFR con- ditions) or the potential for extensive mountain obscuration. B. AIRMET Tango warns all pilots about the po- tential for moderate non-convective turbulence aloft, sustained winds of 30 knots or more at the surface or a forecast for non-convective low level wind shear (LLWS). C. AIRMET Zulu is an advisory to all pilots for the potential of moderate non-convective icing and offers a forecast for the freezing level. Each AIRMET also includes a six-hour outlook.

Many pilots believe that the symbol for moderate turbulence indicates light turbulence. I have heard very seasoned pilots make the same error. The fact that tur- bulence is not mentioned does not mean you won't encounter light turbulence. Environment Canada does not use a symbol for light turbulence, but many aviation weather websites do.

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On June 19, 2014, the FAA finally issued a notice to dis- continue the aviation area forecast (FA) in favor of developing digital and graphical alternatives. It took nearly three years, but the National Weather Service's project to replace the area forecast with a digital-age interactive forecasting tool moved from experimental to operational status on April 13, 2017. This status now means pilots can legitimately use the new tool to make operational decisions. In fact, on July 24, 2017, Flight Service started using this for standard pilot weather briefings.

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Clouds and Weather Chart (Some of the GFA's Features)

1. Main synoptic features such as fronts, highs. and lows (troughs). 2. Speed and direction of the main synoptic fea- tures. 3. Organized areas of cloud (ceilings). 4. Organized areas of precipitation and obstruc- tions to vision. 5. Isobars spaced four hPa (mb) apart. 6. Winds 20 knots or greater with wind barbs and speeds. 7. IFR Outlook for an additional 12 hours found on the T +12 Clouds and Weather chart. Only areas of organized IFR are mentioned in the IFR outlook. Any local IFR is not included. 1FR means ceilings are less than 1.000 feet and/or visibility is less than 3 statute miles.

Icing/Turbulence/Freezing Level chart

1. Main synoptic features. 2. Speed and direction of features, if possible. 3. Areas of turbulence (moderate or severe). 4. Areas of icing (moderate or severe). 5. Freezing level height to the nearest multiple of 2,500 feet.

Freezing Level Contours:

A dashed black line indicates where the freezing layer is at the SFC (surface) and at 2,500-foot intervals in feet ASL, The GFA is a great tool for general VFR and low-level IFR. Remember, both aviation centers welcome feedback, so try submitting PIREPS.

AIRMET- WA (AIRMEN'S METEOROLOGICAL INFORMATION)

AIRMETS are advisories to pilots flying small aircraft of potentially hazardous weather that does not meet SIG- MET criteria. They warn pilots about the potential of hazardous en route weather that is considered wide- spread. Similar to SIGMETS, widespread is defined as an area greater than 3,000 square miles. There are three AIRMETS bulletins issued by the AWC, namely AlRMET Sierra, AIRMET Tango and AIRMET Zulu. All AIRMETS are valid for 6-hour period and are ISsued at 0245Z, 0845Z, 1445Z, 2045Z.

Once these snapshots are finalized, the AIRMET text is then automatically generated from the first three snap- shots, namely, 1500Z, 1800Z and 2100Z. Moreover, the last three snapshots are commensurate with the legacy AIRMET outlook that extends beyond the 6-hour peried to 12 hours.

Back in August 2006, the NWS and FAA aimed to standardize the text in the AIRMET. Standardiza- tion was necessary to remove ambiguity, become more com- pliant with international standards and, most importantly, to allow text to be automatically generated from G-AIRMET graphics. Some of the changes to the legacy AIRMET text included the removal of: OCNL or FRQ (for occasional or fre- quent), trend remarks such as CONDS SPRDG EWD (condi- tions spreading eastward), changes in intensity such as INTSF or WKN (Intensifying or weakening), reasons for amendment or cancellation of the AIRMET, causes of turbu- Tence, strong surface winds and Jow-level wind-shear poten- tlal, type of icing and location of icing with respect to clodes and precipitation. While these don't appear in the legacy non-convective SIG- AIRMET text, they can still appear in any METS since those advisories remain untouched.

Based on the legacy AlIRMET alone, yes, airframe icing will certainly be a factor given that will need to you eventually descend through the forecast icing layer fore- cast from 4,000 to 8,000 feet. G-AIRMETS, on the other hand, provide a much higher temporal resolution than the legacy AlIRMET. The first G-AIRMET snapshot below is valid at 1500Z and covers a good portion of the proposed route as well as covering the entire region shown in the legacy AIRMET.

But the next G-AIRMET snapshot below valid three hours later at 1800Z shows no widespread moderate icing risk along the entire route. Essentially the icing is being forecast to dissipate on the southwestern side of the AIRMET.

Convective SIGMETS Some pilots rarely venture more than a few hundred miles from their home airport. When they do plan a Jong cross country flight, even before they look at a sin- ole weather map, it is common for them to be curious about what weather to expect in the area outside of their comfort zone, especially regarding thunderstorms. We're not talking about just any thunderstorm, but those that are deemed to be significant to aviation. While a single thunderstorm may interrupt your day at the beach or amusement park it may not be considered a significant hazard to aviation as long as you don't fly through it or under it. However, thunderstorms that are embedded, severe or form a solid brick wall forcing large deviations (read, carry extra fuel) are those potentially problematic for pilots. Defining the location of these sig- nificant thunderstorms is the primary job of the convec- tive SIGMET (WST). WST breaks down to W (Warning) S (SIGMET) and T for (Thunderstorm).

Convective SIGMETS are routinely issued at 55 minutes past each hour by a single forecaster on duty at the Avi- ation Weather Center (AWC). They are en route advis- ories warning pilots of a widespread area or line of thunderstorms as well as embedded or severe thunder- storms. While a convective SIGMET is valid for two hours or until superseded by the next hourly issuance, they represent more of a NOWcast rather than a fore- Cast. In other words, they warn pilots of active thunder- storms that meet specific criteria. According to the AWC,

Since the GFA is totally automated, it will be issued hourly and is largely based on guidance from the Rapid Refresh (RAP) weather prediction model. Therefore, each forecast hour represents a single snapshot valid at some time in the near future. Unlike the forecaster-generated FA, you won't see the GFA amended even if it is way off base since there's no amendment criteria defined for the GFA-a disadvantage over a forecast like the FA and G-AIRMETS (discussed in the next chapter) that are issued by highly trained meteorologists.

Each GFA forecast hour is a snapshot that delineates adverse weather elements precisely in time and space. Consequently, the AIRMET must emphasize the most conservative weather condition during that six-hour fore- cast window and provides no precise guidance where the adverse weather is occurring at any given time. Unlike the AIRMET, the GFA snapshots allow you to see the ad- verse weather element move or grow with time and space including the growth and decay of these areas.

CENTER WEATHER ADVISORIES (CWAS) Center Weather Advisories or CWAS provide aviation with the "front lines" of adverse weather within the US This includes advisories for low IFR conditions, thunder- storms, icing, and turbulence, just to name a few. When they exist along or near your proposed route, a standard briefing from Flight Service will include these advisories. While they smell a lot like an AIRMET or SIGMET, they represent more of an in-flight advisory telling a pilot about current adverse weather than a forecast used dur- ing preflight planning. Therefore, it's critical to look for these advisories just before you depart and while en route to your destination CWAS are issued by highly trained meteorologists at the Center Weather Service Units (CWSUS) located at the various Air Route Traffic Control Centers (ARTCCS). They can be issued for in-flight weather hazards to in- clude, conditions meeting or expecting to meet convec- tive SIGMET criteria, moderate or greater airframe icing, moderate or greater turbulence, heavy precipitation, freezing precipitation, conditions at or approaching low

JER (ceilings at or below 500 feet and/or visibilities at or helow 1 statute mile), sustained surface winds and gusts greater than 30 knots, non-convective low level wind shear below 2,000 feet AGL and volcanic ash, dust storms or sandstorms.

Areas of Icing:

Moderate icing symbols are shown by stippling (blue dots) enclosed by a blue line. Severe icing is indicated using a denser stippling. The denominator is the base and the numerator is the top of the icing layer in hundreds of feet ASL. Three icing types are forecast: rime, clear and mixed (RIME, CLR and MXD). Light The icing icing is only mentioned in the comment box. intensity "trace" is not forecast.

Areas of Turbulence:

Moderate turbulence is depicted with hatching enclosed by a solid red line. Severe turbu- lance is shown as denser red hatching. The bases and as of the turbulence are indicated the same way as ieing and cloud layers. The forecast types of turbulence ve: Clear Air Turbulence (CAT), Mechanical (MECH), Low Level Wind Shear (LLWS), Lee Waves (LEEWV) (Mountain Waves) and Low Level Jet (LLJ). When turbu- lence is expected to be light, it is indicated in the com- ment box.

a convective SIGMET is issued when thunderstorm(s) meet one or more of the following criteria: 1. A line of thunderstorms of significant radar echoes at least 60 nautical miles long with at least 40 percent coverage along the line. 2. An area of thunderstorms producing precipitation of significant radar echoes affecting 40 percent or more of an area at least 3,000 square miles. 3. Embedded thunderstorm(s) independent of the size, number or area of coverage. 4. Thunderstorm(s) that the local Weather Forecast Office (WFO) has labeled as severe also independ- ent of the size, number or area of coverage.

Notice that lightning or precipitation intensity isn't a re- quirement. Moreover, convective SIGMETS always imply severe or extreme turbulence, severe icing and IFR con- ditions near the surface. Even though convective SIG- METS are valid for two hours when issued, the following hour the forecaster will once again evaluate the convec- tive threat and issue a new round of convective SIG- METS. Each new issuance at 55 minutes past the hour will supersede the previous set of convective SIGMETS. Therefore, no convective SIGMET will ever exist for two either be obsolesced or allowed to expire (can- hours; it'll issued at 55 celled) after one hour. Even though they are minutes past each hour, a "special" can be issued at any time when, in the forecaster's judgement, an area of con- vection has evolved into a significant threat and is not covered under any other advisory (see CWAS later in this chapter). Convective SIGMETs are issued and numbered by regions that include west (W), central (C) and east (E). Beginning at 0000Z each day, they are numbered start- ing with 1. So the 23rd convective SIGMET issued for the central region will be number 23C.

300 means "isolated" (25% or less spatial coverage) cumulonimbus topped at 30,000 feet." If multiple layers are expected, the acronym LYRS is used. Cirrus (high) clouds are not included. Remember: this is a three-dimensional forecast, and unlike a METAR and TAF, cloud layers are NOT summed. You can't have two overcast layers in a METAR or a TAF, but in a GFA you could have two or more. For example, you might run into a situation here. CYYZ's METAR is reporting OVC020 and its TAF is predicting OVC020(both at 2,000' overcast AGL), but the GFA will state OVC 60/25 OVC 160/100 (one layer based at 2,500' ASL topped at 6,000' and the second layer based at 10,000' topped at 16,000').

Prevailing visibility on a GFA is listed in statute miles, NOT nautical miles. (A statute mile is 5,280 feet, whereas a nautical mile is 6,076 feet). The associated ob- structing weather phenomena are included when visibil- ity is six statute miles or less. If visibility is greater than six statute miles (unlimited for a GFA), it is shown as P6SM-similar to a TAF. Do not confuse GFA unlimited visibility with METAR unlimited visibility, which is de- fined at 15 SM (statute miles). Vertical visibility (VV) is how far up into a surface-based layer (OBSCD-ob- scured) a pilot will see; this measurement is listed in hundreds of feet. Wind speed is listed in knots (nautical miles per hour) and NOT MPH (statute miles per hour). Surface winds are included when they are blowing at 20 knots or more, or when gusts to 30 knots or more are forecast. They are indicated with wind barbs accompanied by the letter "G" denoting gusts. Remember: GFAS should jibe with the public and marine forecasts. Additionally, the areas along the borders of GFAS should agree. If the Prairie GFA mentions a fast eastward-moving cold front crossing into Ontario, then the Ontario/Quebec GFA had better mention it too!

Example of an AIRMET: WAUS45 KKCI 161445 SLCT WA 161445 AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL 162100 AIRMET TURB...ID NV UT WA OR CA AND CSTL WTRS AOM YDC TO 20WNW PIH TO HEC TO 20WSW

RZS TO 140WSW FOT TO 140W TOU TO YDC MOD TURB BLW FL180, CONDS CONTG BYD 21Z THRU 03Z. OTLK VALID 2100-0300Z...TURB ID NV WA OR CA AND CSTL WTRS BOUNDED BY 30W HUH-20ONW YKM-LKT-20S TWF- OAL-SNS-130WSW SNS- 140WSW FOT-130W FOT-15OWNW FOT-140W TOU- 30W HUH MOD TURB BTN FL180 AND FL410. CONDS CONTG THRU 03Z. Translation: This AIRMET (WA) Tango for turbulence was issued on California and coastal (SLC) forecaster at the the 16th of the month at 1445Z by the western region AWC. The AIRMET will affect the states of ldaho, Nevada, Utah, Washington, Oregon, waters and is valid until 2100Z. Widespread moderate nonconvective turbulence should be anticipated below flight level 180 (18,000 feet MSL). The outlook is valid from 2100Z to 0300Z (on the 17th of the month) for moderate non-convective tween flight level 180 (18,000 feet MSL) and flight level turbulence be- 410 (41,000 feet MSL). These conditions are expected to continue through 0300Z.

Structure of the SIGMET (WS) Bulletin:

SIGMETS are identified by an alphabetic designator from November through Yankee excluding Sierra and Tango. (Sierra, Tango, and Zulu are reserved for AIR- MET text (WA) products. Note that G-AIIRMETS (de- scribed later) do not use the Sierra, Tango, or Zulu desig- nators. Issuance for the same phenomenon is sequentially numbered, using the original designator until the phenomenon ends. For example, the first issu- ance in the Chicago (CHI) FA area for phenomenon moving from the Salt Lake City (SLC) FA area will be SIGMET Papa 3, if the previous two issuances, Papa 1 and Papa 2, had been in the SLC FA area. Note that no two different phenomena across the country can have the same alphabetic designator at any one time.

Since this was meant to replace the FA, the weather forecasts stop at the U.S. border. While the FAA wants this to be a wholesale replacement, it doesn't make logic- al sense to terminate the forecast due to a geopolitical border. It's hard to assess the big picture including This is certainly may trends that be hiding upstream. true for the model-based forecasts such as icing and tur- bulence which cover much of North America.

THE CANADIAN GFA-WHEN YOU VENTURE NORTH OF THE BORDER The GFA (Graphic Area Forecast) describes the most probable meteorological conditions expected from the surface to FL240 (24,000 feet ASL) at a forecast time over a given area. This product is geared toward general aviation. Airline pilots may consult these forecasts for takeoff and landing, but generally not en route-at that point, they are more concerned about high altitude charts starting at 25,000 feet. There are seven GFA areas, called domains, across Canada. Starting from GFACN31 in the Pacific region, they work east across the country to GFACN34 and north to the Arctic region at GFACN37. The Canadian GFA coverage also stops at the border just like the U.S GFAS.

Meteorologists for decades issued forecasts by sitting at a keyboard and typing a bunch of text. The same was true of the legacy AIRMET. In January 2006, the FAA and NWS embarked on a mission to take aviation me- teorologists out of the teletype age into the digital age using graphics-The GFA (Internet era) has replaced the antiquated FA (teletype era). As you might imagine, this wasn't a simple and straightforward process.

The FA was an overview of weather conditions that could impact aviation operations. The domestic FA was issued three times a day by three highly skilled meteor- ologists on any particular shift at the Aviation Weather Center (AWC) and contained a 12-hour forecast of VFR clouds and weather conditions. Additionally, a 6-hour categorical outlook for VFR, MVFR or IFR conditions followed the 12-hour forecast. The FA together with AIRMET Sierra was used by pilots to determine forecast en route weather and to interpolate conditions at air- ports which do not have a Terminal Aerodrome Forecast (TAF) issued.

THINGS YOU SHOULD KNOW...

The GFA (Internet era) has replaced the anti- quated FA (teletype era). • The GFA includes "observations and forecasts valid for the Contiguous United States provid- ing data critical for aviation safety. • Cloud heights are above sea level, unless noted, unlike the METAR and TAF.

Any product that shifts away from the traditional text- based paradigm is a good decision. The GFA is primarily a graphical product or tool that may ultimately have a textual sidekick called the GAMET-for now, there's no official GAMET like you might see when flying abroad. You can find the GFA tool and tutorials online at www. aviationweather.gov/gfa. (Under Tools click GFA Tool).

The GFA provides the necessary aviation weather give a complete picture of the weather that may impact flight in the Contiguous United States (CONUS). Viewed from 14 hours in the past to 15 hours in the future, the GFA includes observational data, forecasts, warnings in- cluding thunderstorms, clouds, flight category (VFR, MVFR, IFR, LIFR), PIREPS, precipitation, icing, turbu- lence and wind. Wind, icing and turbulence forecasts are available in 3,000 foot increments from the surface up to 30,000 feet MSL, and in 6,000 foot increments from 30,000 MSL to 48,000 feet MSL.

Canadian GFA

The Graphical Area Forecast (GFA) is a three- dimensional aviation forecast for a defined area (domain) in graphic format covering a 12-hour period. It consists of two charts: 1. Clouds and Weather; 2. Icing, Turbulence and Freezing Level; over the same area and time. There are three panels in each chart (six in total) spaced six hours apart (TO, T+6 and T+12) which up- date the charts every six hours. • There are seven Canadian domains with forecast periods from: 00-12Z, 06-18Z, 12-24Z, 18-06Z. Visibility is listed in statute miles, distance in nautical miles, wind speed in true direction and in knots. • The Clouds and Weather T+12 panel includes a 12-hour outlook, but only where IFR condi- tions are expected.

IFR Comment Box

The comment box on the T +12hr Clouds and Weather chart includes an IFR outlook for the next 12 hours. (At one time, the outlook included either VFR, MVFR, or IFR. If it was MVFR or IFR, then the reason why would need to be provided).

G-AIRMETS are constructed by the same forecast- ers as the legacy AIRMET. Moreover, the G-AIRMET is a forecast for the same hazardous weather conditions in- cluding moderate icing, moderate turbulence, IFR condi- tions, mountain obscuration, etc. The G-AIRMET con- sists of five individual snapshots where each snapshot is valid at a specific time in the future instead of being valid over a range of time like the legacy AIRMET. For example, let's assume that it's 1445Z. The fore- caster has just issued his/her G-AIRMET forecast. From the G-AIRMET perspective, this will include a snapshot valid at 1500Z, referred to as the 0-hour or initial snap- shot. It will also include a snapshot valid at 1800Z that represents a 3-hour forecast; a snapshot valid at 2100z that represents a 6-hour forecast; a snapshot valid at 0000Z that represents a 9-hour forecast and the last snapshot is valid at 0300Z that represents a 12-hour forecast.

The key point to understand is that all of these snapshots are valid at a single time in the future. This answers the question of where will the adverse weather be located at that time. It therefore represents a forecast for coverage of that adverse weather element.

Example of a SIGMET: BOSR WS 050600 SIGMET ROMEO 2 VALID UNTIL 051000 ME NH VT FROM CAR TO YSJ TO CON TO MPV TO CAD OCNL SEV TURB BLW 080 EXP DUE TO STG NWLY FLOW. CONDS CONTG BYD 1000Z.

Translated: This SIGMET (WS) was issued by the eastern region forecaster (BOS) at the AWC. This was issued on the 5th of the month at 0600Z and is valid for four hours until 1000Z on the 5th of the month. It will affect (in part) the states of Maine, New Hampshire and Vermont. This SIGMET is a warning for occasional severe turbulence below 8,000 feet MSL (the base of the turbulence is the surface in this case) and is due to strong north-westerly flow. Conditions are expected to continue beyond 1000Z (so you should expect another SIGMET to be issued be- fore the current one expires). You could plot this area by using the points listed in the "VOR line" just below the list of states. However, some websites, apps and cockpit avionics will plot these SIGMETS automatically.

Graphical AIRMETS (G-AIRMETS) As of March 16, 2010, AIRMETS were operationally re- placed with a new product called the Graphical AIRMET or more simply G-AIRMET. The legacy six hour AlR- MET continues to exist (and will be retired soon), but it's not the product that's now generated by forecasters at the AWC. As will be explained later, the legacy AlIRMET is actually a by-product of the G-AIRMET. One of the biggest complaints from pilots is AIR- METS seem to cover such large areas at times. That's be- cause AIRMETS are a "time-smeared" forecast. Since they are valid for a six hour period, the forecast area must be large enough to encompass the entire region that may be affected during this six hour period. So, the perception from pilots is that they tend to be much larger than necessary which creates doubt of their accuracy. This is especially true for icing AIRMETS that seem to

cover most of the northern tier of states throughout the entire winter even though at any single time icing condi- tions may not exist at all locations covered by these AlR- METS. In comes G-AIRMETS to the rescue. While you may be able to see a graphical depiction of the AlIRMET within many flight planning apps and websites, the G-AIRMET takes the AlIRMET concept a bit further. The G-AIRMET consists of multiple graph- ical snapshots that are valid at a specific time and not over a range of time like the legacy AIRMET. These snapshots better define hazardous weather in both time and space. As mentioned earlier, AIRMETS are issued four times a day and are valid for 6 hours. It wasn't all that long ago these AIRMETS were prepared by forecasters at the AWC simply using weather charts and a keyboard. And that's because the legacy AIRMET is really a textual product and the graphic we see within various flight planning apps and websites is really a by-product of the text. Of course, this "text" is what makes the AlIRMET a time-smeared forecast. The FAA and NWS are trying to move away from a textual system that's been around for many decades and build the forecasts graphically. The G-AIRMET was the first big step in this direction. Let's look at what makes this G-AlIRMET so special.

When teaching SIGMETS, I ask the class to list types of weather that are inclement for a pilot. Many think widespread fog should be one. It certainly applies to VFR pilots, as it could be catastrophic if you are unable to land due to fog. But for an IFR-rated pilot, fog is just part of doing business, so you won't see it on the list even though fog has been the cause of many aviation fatalities. The worst aviation disaster of all time, the collision of two Boeing 747s in Tenerife, Canary Islands, involved fog. The captain of the departing aircraft and the control tower could not see that the landing B747 was still on the runway, leading to the crash that killed 583 people. There is also the role that fog plays

in the high number of runway incursion accidents. (However, will see it listed in the AIRMET section, discussed later you in this chapter).

Each GFA has two charts with three panels each: two panels each at time markers TO T+6 and T+12 (short range, 6-hour and 12-hour forecast). The first set of two (TO, also called near term) includes a depiction of Clouds and Weather on one panel and Icing, Turbulence, and freezing Level on a separate panel. The next two sets (T +6 and T+12) are valid six hours and twelve hours later. Thereafter, an additional 12-hour IFR "outlook" is in- cluded in the Clouds and Weather T+ 12 panel. A GFA is

issued at 2330, 0530, 1130 and 1730Z and are valid e 0000, 0600,1200 and 1800Z. Each GFA covers a period of 12 hours with an IFR outlook for the next 12 hours AIRMETS (Aviation Weather Advisory) and SIG- METS (Significant Meteorological Information) may be issued as amendments to the GFA. If a GFA needs to be corrected, a correction code CCA (first correction), CCB (second correction) or CCC (third correction)] is added in the title box. So, who writes/creates these forecasts? In Canada, this job is performed by the same two centers that write the TAFS: CMAC-E (Montreal) and CMAC-W (Edmonton). At the two CMAC centers, meteorologists write Canadian aviation forecasts, tucked away in secur- ity-enhanced offices. These dedicated people do a fan- tastic job, but sadly lack direct contact with the general user-YOU! Sure, they might get a call from an airline dispatcher querying the forecast or from a flight service specialist, but a private pilot will rarely meet the writer of aviation forecasts.

Units The GFA uses codes and units similar to the TAF and METARS. For example, SCT/BKN/OVC is used for Scat- tered/Broken/Overcast; -SHRA/TSRA is used for light rain showers and moderate rain in thunderstorms. All cloud heights are in hundreds of feet Above Sea Level (ASL) unless otherwise noted. Heck, they even remind you of this in the legend (HGTS ASL UNLESS NOTED),

so do not get the answer wrong on exams when you are asked whether the GFA includes this information AGL or ASL. So: if the heights are listed above sea level "un- less noted," when are they "noted"? Well, that happens whenever AGL (Above Ground Level), ABV GND or CIGS (ceilings) is mentioned. Example: CIGS 7 AGL means ceilings 700 feet above ground (or bodies of water). This is restricted to the range between 0 and 1,500 AGL-i.e., you will never see CIGS 20 AGL. Organized cloud bases and tops (broken or overcast) are enclosed in a scalloped border and constitute a ceil- ing. Scattered (SCT) or (FEW) clouds are mentioned if they occur outside the scalloped area. If convective clouds (TCU, ACC, CB) are forecast, the cloud tops are mentioned even if they exceed 24,000 feet. ISOLD CB

The Aviation Weather Center (AWC) in Kansas City has three forecasters on each shift that issue all

the AIRMETS, SIGMETS and Area Forecasts (FAS) for the CON- US. There is one forecaster for the eastern region (BOS and MIA), one forecaster for the central region (CHI and DFW) and one forecaster for the western region (SFO and SLC).

Convective Outlooks Convective outlooks are perhaps one of the most under- utilized weather products provided by the AWC. These outlooks are issued hourly by the same meteorologist that issues the convective SIGMETS. As mentioned ear- lier, convective SIGMETS define regions of airspace with active areas of thunderstorms that meet specific criteria. On the other hand, convective outlooks are not sio METS at all. Convective outlooks are truly forecastes there isn't a requirement that active thunderstorms evist when they are issued. Instead, they define larger regions of airspace that are expected to contain thunderstorms that meet convective SIGMET criteria in the next two to six hours after the outlook was issued. These may in- clude ongoing areas or lines of convection covered by a convective SIGMET or they may include new areas or lines of thunderstorms that are expected to develop and reach convective SIGMET criteria in the two to six-hour valid period. That window is a perfect "sweet spot" for many pi- lots just about to depart on a flight. There may nót be any thunderstorms as you taxi to the runway, but if your proposed route takes you through one of these convec-

tive outlook areas in the range of time specified, you may likely see one or more convective SIGMETS issued within this outlook area during your flight.

Remember: only areas of moderate or severe icing are mentioned in the forecast. By definition, this sort of icing is serious! On the other hand, you will run the risk of light icing whenever you are above the freezing level and in cloud. You may be IFR certified, but as soon as you fly into potentially icy cloud with an aircraft not certifled for flight into icing conditions, you are flying illegally! Even

with deicing boots it won't be legal unless the airplane has all the required equipment.

THINGS YOU SHOULD KNOW...

• SIGMETS (WS) are forecasts for hazardous weather for pilots flying any aircraft regardless of size. • AIRMETS (WA) are advisories to pilots flying small aircraft for widespread hazardous weather. • Most SIGMETS are valid for four hours. • Volcanic Ash (WVNT) and Tropical Cyclone (WTNT) SIGMETS are valid for six hours. • SIGMETS are issued for severe turbulence or icing, widespread sand or dust storms and vol- canic ash. • Convective SIGMETS (WST) are issued for active areas of convection (thunderstorms) significant to aviation and valid for 2 hours. G-AIRMETS (and AlIRMETS) are issued four times a day by forecasters at the AWC. The G-AIRMET operationally replaced the lega- cy AIRMET in 2010 and is an advisory consisting of five snapshots valid at a specific time. G-AIRMETS have a better temporal resolution than their legacy counterpart. • Center Weather Advisories (CWAS) are issued to augment AlIRMETs and SIGMETS or fill in the ad verse weather gaps not covered by any advisory.