SIGMET

Operations Duty Managers

Current SIGMET information is provided at the start of each weather briefing to ATC unit supervisors.

Operations Duty Managers will check in with unit supervisors and ATC when a SIGMET is active in their airspace. This is done to maintain awareness and coordinate with neighboring ATC or the NTMU if needed. Potential impacts are also communicated directly to customers on the NOC call to facilitate planning and discuss any required actions from an ATFM perspective.

• ATC will relay messages to Operations Duty Managers from crews indicating a smooth ride within a SIGMET, which would be useful PIREP information if it could be passed along to forecasters, especially when issued SIGMETs cover large swaths of airspace. 

Forecast charts are also consulted and heads-up given to potential areas of interest for the shift. This includes analysis of GFAs, TAFs, HLT charts, TCF panels, and CoSPA. Analysis of these products support discussions:

• With the NTMU regarding the possibility of taking or refusing additional traffic via CAN Routes, or the implementation of possible SWAP Routes (for TSRA).
• Of staffing levels within sub-units. If significant weather is planned, the Operations Duty Managers will work with the unit to upstaff if possible.
• Of potential TMIs in events that will impact major airport operations.

Current observations are discussed and supplemented by current satellite/radar imagery and any PIREPs using the HubWX weather map.

• A strong weather and continuous watch throughout the shift is essential to proper strategic and tactical planning, especially at the four majors where capacity constraints arise from significant weather events.

NTMU will treat a SIGMET similarly to a forecast in taking appropriate actions for sectors involved, evaluating staffing and routes and making recommendations as deemed required.

ATC (Major Tower)

SIGMETs within terminal airspace and impacting the airfield provide crucial information of significant weather phenomena. Individual impacts vary based on the SIGMET: thunderstorms, severe icing, severe turbulence, etc. However, overall a SIGMET can increase communications with crews and can cause congestion on frequency. A controller’s workload will be increased.

• For example, in CYUL, SIGMETs are put on the ATIS if they affect an area within 100NM of the tower.

ATC (Regional Tower)

SIGMET along the planned route of flight for departing aircraft are passed on them before departing and can be published on the ATIS for pilot info.

FIC

In the FIC, a SIGMET gets immediate attention, regardless of if based on Forecast or Observed conditions. The FISE Specialist will broadcast the SIGMET on all relevant frequencies and may call ATC to request relevant PIREPS to confirm the data. Each Specialist conducting briefings will take note of the geographical and altitude parameters of the SIGMET, to decide if it is relevant to each customer’s particular requirements (ie. A student pilot performing circuits at a small airport is not concerned with overhead CAT based at FL200). 

AAS

Advisory Specialists are required to Broadcast on the MF any SIGMET within 20SM of the edge of the MF Area, up to 10000’ASL (or further as may be required). Specialists will always issue an updated ATIS with the new SIGMET information and solicit PIREPs more often to verify Observed conditions and confirm Forecasted ones to improve the data set for forecasters and briefing specialists.

• Depending on the type and severity of the phenomena described in the SIGMET it is possible that route changes or vectoring may be requested by customers. The workload can be slightly increased.
• In the terminal environment, we deal more with observed weather rather than forecasted. Our airspace is so small and limited, we can’t just stop using a quadrant of it if some bad weather is forecasted. Usually, unless an area is extremely obviously bad (such as intense thunderstorms), aircraft will still at least try to use their usual route to exit the terminal. In this case the impact would be that during the time in which aircraft are “trying” their usual routes, we have to be ready for them to suddenly tell us “we need to deviate”, so we must plan accordingly and make sure we have option B or option C if the aircraft decides it has to go somewhere else. Once an aircraft has deviated around an area, we will pass along the info to the next aircraft so they can decide if they want to deviate straight away or try to go through it. But this is all mostly done with observed phenomena, we will almost never “force” deviations around an area that only has forecasted bad weather.

At major airports, SIGMETs are included on the ATIS. Controllers will ensure that all arriving aircraft have the most current information. The most up to date conditions are generally passed from the terminal controller to the en-route controller and relayed to the pilots.

En-route controllers ensure that all pilots in their airspace are aware of a SIGMET, be it forecast or observed.

• Generally, a controller will simply confirm the pilot has access to the SIGMET information by asking if they are aware of it. For example, ‘confirm you have SIGMET ALPHA-TWO’. If the pilot has the SIGMET and there is nothing more to add, the controller’s job is complete.
• If the pilot does not have the information, the controller will read the SIGMET on the frequency. A controller will always pass the observed and most current information to the pilots. This can increase workload.
• If a SIGMET forecasts severe turbulence between FL180 and FL230, for example, but the only turbulence in the region at that moment is moderate between FL190 and FL210, the controller will pass that information along to all pilots when confirming they have the forecast.

High level FL290 and +: SIGMET impacts can vary greatly depending on the type and the volume of traffic at that time. 

SIGMETs impact the decisions on whether we open sectors or not, acceptance of SWAP routes, mileage in trail, etc. In some high level ATC units, SIGMETs within 100NM of their airspace must be passed along to crews. This is where situational awareness and receiving SIGMET information from forecast offices is imperative.

Generally speaking, we will focus on the location of the SIGMET and its consequences. For high level, the most important conditions to target are thunderstorms and CAT.

• Convection that can be observed on radar imagery supports a SIGMET and reduces the associated workload. Convective SIGMETs over areas with no radar coverage (ex: the Atlantic and across Northern Canada) provide valuable additional information to ATC when gauging sector impacts and passing information to crews.
• SIGMETs associated with turbulence, especially when very large, often have levels of smooth flight within them. ATC workload increases as all information must be transmitted to crews transiting that airspace and can result in route or altitude change requests. Being able to pass along smooth ride reports in the form of PIREPs outside of a sub-unit, if it allowed for redefinition of the associated SIGMET, would be a huge benefit to ATC.
• Forecasted SIGMETs are not as bad. In these cases, aircrafts can decide to fly through the SIGMET and thereafter PIREPS could be made to either confirm the SIGMET or not. Observed SIGMETs signify that the weather phenomena is actually present. Aircraft react differently to Forecasted vs. Observed.

• SIGMETs conditions at major airports will likely disrupt operations. Holding, diversions, ground delay programs and flight cancellations are all possible.
• A forecast SIGMET condition provides awareness of a possible threat and should be validated by pilot reports, METAR, weather radar, runway surface condition reports, etc. Fuel planning should include an alternate airport and possible contingency fuel.
• Observed SIGMET reports require flight planning to provide mitigations for the hazard. Updates of the condition through pilot reports, METAR, radar, RSC, etc. help manage the risk.
• Let's focus on the three main categories of SIGMETs (CAT, icing, convection). From a perspective of a medium to heavy airline jet operating medium to long-haul flights, the icing SIGMET will not significantly change the planning of the flight. If it is observed, we will try to seek more information about the occurrence, evaluate which type of aircraft reported and if any other traffic has flown in the area. A severe icing SIGMET will be active for freezing rain sectors. If the METAR reports freezing rain, we expect that there is a potential for significant icing accretion. For reasons listed in the freezing rain and freezing drizzle discussions (temperature inversion and total air temperature), the layer's depth of effective ice accretion is typically shallow. On an IFR approach, we transition through the area quickly, in a matter of one or two minutes.
• For a line of thunderstorms, the emission of a SIGMET will attract our attention to the area in question. In-flight, we have access to ground weather radar data as well as our airborne weather radar. We can make our own assessment of the size of the line of thunderstorms, the maximum height, and how scattered the line is. Until we get to about 150nm from the line, ground radar data will be our primary source of information. If we expect our route to be a problem, we can initiate a deviation or request a reroute from ATC earlier. The earliest will make that decision, the less time and fuel will be needed to deviate around the line. Thunderstorms being a very dynamic phenomenon, deviating too early can also result in a useless deviation. Inside 150nm, our primary source of information will be our weather radar. We can supplement our decision making with ground weather data, but tactical thunderstorm avoidance must be done with our onboard radar. This category of SIGMET will attract our attention to a problematic area, although our decision making will be made with more granular data, like both radars.
• Out of the three listed categories of SIGMET, a turbulence SIGMET will be the most likely type that would result in an avoidance route during flight planning stages. As discussed during the topic of Clear Air Turbulence, we will use multiple sources to evaluate the likelihood of the significant turbulence. Government SIGMETs will typically not be the sole exclusive source of decision-making.
• If the hazard is observed, or reported, versus forecasted, we do differentiate in between the two. Our flight operations manual restricts flight through known severe icing or severe turbulence. If it is forecasted, we will use all available information to assess the likelihood of the SIGMET. The severe occurrences can be very local phenomena. If the condition is reported or observed, our dispatcher will try to seek more information from aircrafts operating in the area, to get a validation of the initial report.
• Keeping in mind medium to long haul flights, dispatchers will work on the flight plan about 3 hours before departure. The flight crew will do their flight planning one to two hours before the flight. Considering departure and the flight time to the SIGMET area, the SIGMET validity will not cover the time at which the aircraft will fly that area. Thus, SIGMETs are typically of limited value during flight planning because we need a longer forecast or outlook. Using all sources of information, we can determine if a line of thunderstorm can be present along the route. Similar assessment can be made for turbulence. The dispatcher can decide to plan around the area if it is determined that the impact is minimal on flight time and fuel. The other most common mitigation strategy is boarding more fuel. By adding more contingency fuel, the pilots can use that fuel for deviating around a line of weather, significantly changing cruise altitude to find smoother air.

Most weather associated with a SIGMET constitutes a severe hazard for a General Aviation (GA) pilot. It is recommended to check this along with other pre-flight weather information gathering.

• Unfortunately, many GA pilots skip this step (relying primarily on METAR/TAF/GFA/RADAR). To mitigate this, it's recommended that pilots use an easily adaptable technology that visually displays the majority of pertinent weather information and products.

Using and being aware of the SIGMET before flight can greatly reduce the risk associated with encountering that type of weather.

• If forecasted it will usually be best to avoid those areas by a large margin.
• When observed, it can provide a more accurate description of the conditions to occur and the location or path of the disturbance, allowing the pilot to make an informed decision of how their planned route will be affected.

Some weather criteria currently used in Canada do not always align with the risks related to light GA aircraft. Something that would be considered a moderate risk for a B737 could present a severe risk for a C172. For example, wind shear of 30 kts may be considered moderate, however could lead to severe turbulence in a light GA aircraft and/or easily lead to a loss of control. Therefore, it is very important to understand the limitations of weather reporting related to certain phenomena and how the relative risks can be different - both as a pilot decoding this information and as an air traffic service professional providing this information.

When a SIGMET is issued in flight, it is often noticed on a digital device (GPS, tablet, etc). If tuned to the correct frequency, pilots may also hear it as an FIC broadcast.

• The FIC broadcast has the advantage of being more immediate in the dispersal of information.
• However, when specific coordinates are involved, a digital device can provide a more useful visual reference as to the location.
• Of course, being aware of the weather products available and the technology the pilot has at their disposal should be part of the pre-flight planning and decision making, especially if planning a flight with variable conditions.