Updated: May 17, 2019
Some terminal aerodrome forecasts (TAFs) are of a higher quality than others. That is, some forecasters describe the expected weather better than other forecasters while still adhering to the strict NWS guidelines for TAFs.
Forecasters at the local weather forecast offices (WFOs) issue these point forecasts four times a day (more frequently at airports in New York City, Chicago and Atlanta). TAFs are perhaps one of the most difficult forecasts any meteorologist must make. Their primary goal, however, is to construct the forecast in a way that is simple and easy for the pilot to understand. It also must provide guidance that is representative of the expected weather event. In other words, can a pilot clearly envision what the weather will look like strictly based on the terminal forecast?
Let's look at an example of a TAF that could have been much better. Take a look at the following terminal forecast for Lake Charles, Louisiana (KLCH). This TAF was issued by the Lake Charles WFO on April 17 at 1143 UTC.
KLCH 171143Z 1712/1812 VRB03KT 5SM BR SCT010
TEMPO 1712/1714 1/2SM FG VV010
FM171500 13010G18KT P6SM VCSH SCT035 BKN150=
This is a forecast that describes a marginal VFR (MVFR) condition (5SM BR SCT010) that is temporarily interrupted by a low IFR (LIFR) weather event (1/2SM FG VV010). Keep in mind