The Terminal Aerodrome Forecast (TAF) is a very useful tool when understood and applied correctly!
TAFs are found at airports where they make sense… Obviously, right? What I mean is there are TAFs at various airports over a large area. TAFs are commonly found at airport where arriving flights will be departing many hours before arriving, making an accurate pin point forecast a desirable thing for the pilots to have while they plan their flight, especially long lasting long distance flights. TAFs are also published for airports based on geographical need for a more detailed forecast than the “Area Forecast” produced for pilots.
It was not uncommon for me to “check the TAFs” in the morning as a full-time flight instructor to see if I could sleep in a little or if I needed to get up and get going in the morning. Even though there was no TAF at the airport where I was teaching, I had a system. I understood the simple fact that an airport’s TAF only covers an area of five miles from the airport. Not a very large area. Though, occasionally, with the proper modifier a TAF can provide pilots information about a slightly larger area, up to 10 miles from the airport, but only for certain weather phenomenon. More on that later…
TAFs at larger airports with a greater number of long distance/duration arriving flights have TAFs that provide a 30-hour forecast, whereas most TAFs provide a 24-hour forecast. Previously, all TAFs were for 24 hours, but a change a number of years ago added an additional 6 hours to some that “required it,” these TAFs can be found at airports with international flights as an example.
Let’s take a look at a couple TAFs and the forecast format. If you can read a METAR (see our last “Back to Basics” post) a TAF will be easy! Of course, ForeFlight and many other apps/websites provide decoded information for the novices out there too…
Let’s take a look at the TAF for KLAF (Purdue University Airport):
KLAF 202327Z 2100/2124 26010KT P6SM VCTS SCT045CB BKN080
The first line includes the station identifier, the date (20) and time (2327 Zulu) of issuance, the period of forecast validity (0000 Zulu on the 21st to 2400 Zulu on the 21st, said another way, this is a 24-hour forecast lasting the duration of the 21st in Zulu time).
Following the introductory/identifier information are the four pieces of information provided in a TAF. The wind information is formatted the same way the wind information is presented in a METAR, the wind is presented in knots and the wind direction is displayed based on True North. In this report the wind is 10 knots from 260-degrees.
Following the wind information is visibility. Since TAFs are used to provide pilots an exact forecast for flight planning purposes, the visibility is forecast with a maximum of Plus 6 Statue Miles as is shown here with “P6SM”. Lower visibilities will be displayed as 3SM or 5SM, depending on the desired value. Visibility greater than six miles guarantors visual meteorological consitions (VMC).
Next is VCTS which stands for Vicinity Thundershowers. This “VC” prefix means that the condition (thundershowers) will not pass within the 5-mile area covered by the TAF, but they will pass within an area 5 miles beyond that area. Another way to think of this as a donut, the thundershowers will pass through that area between 5 and 10 miles from the airport.
The final piece of the forecast is cloud information in the same format as METAR. Here the clouds are projected to be scattered at 4,500′ above ground level (these clouds will be cumulonimbus in type as highlighted with the “CB” modifier), there will also be a broken layer of clouds at 8,000′ above ground level. Cloud information related to the possibility of convective activities (thunderstorms) is the only cloud-specific information provided in TAFs (or METARs).
TEMPO 2100/2101 2SM TSRA BKN025 OVC045CB
This next time indicated that temporarily between 0000 Zulu and 0100 Zulu the conditions will worsen/change with visibility of 2 miles, thunder and rain showers and broken closed at 2,500′ and overcast cumulonimbus clouds at 4,500′.
FM210200 32006KT P6SM SCT080 BKN250
The next time shows that from 0200 Zulu the conditions will again change, within an hour, with conditions improving as the storms pass.
FM211500 30012KT P6SM FEW250 AMD LTD TO CLD VIS AND WIND 2101/2113
The final line indicates that an amendment is limited to clouds, visibility and wind between 0100 Zulu and 1300 Zulu on the 21st.
TAFs can be great forecast tools, after flying int he same area for a period of time you’ll see that for the most part TAFs are pretty accurate, not always, but pretty often they are very close. It is best to develop a system, maybe you’re lucky and you’re based at an airport that is served by a TAF forecast, but more likely than not you’re flying from an airport that does not have a public Terminal Aerodrome Forecast.
Earlier in the post I mentioned that I had a method of utilized TAFs at local airports, as they provide more detail than the non-aviation forecast and even the aviation Area Forecast. I was flying from the Mansfield Municipal Airport (1B9), an airport conveniently located between four aiports that were served with TAFs. As can be seen below my airport was nicely placed between Boston, MA and Providence, RI. Most days these two locations were enough, but just incase there was Worcester, MA to the northwest and Falmouth, MA to the southeast. If the TAFs agreed, it was highly unlikely (but not impossible) that the conditions at Mansfield would be pretty similar.
Take a look around, maybe you can come up with a way to leverage the terminal forecasts located close to your airport…
-Fly Safe, @MTElia1B9