How to Understand Aviation Weather Forecasts

Decoding Aviation TAFs and METARs, and Reading Synoptic Charts

Oct 5, 2009

Aviation Weather Can Seem to be a Black Art!, Ian Britton

Weather information is essential before going flying. But many pilots find meteorology to be a black art, and have trouble understanding aviation weather reports.

It is important to check the weather before going flying, particularly in the UK or some other country where weather can be very changeable. But many people find meteorology very complicated. Here is a simple guide.

First Steps to Checking the Weather Forecast

It is not always necessary to obtain an aviation weather report. Ordinary weather forecasts, on the TV, online, or in the newspapers, will give the pilot a good general guide. If they are forecasting heavy rain or high winds, then it not really necessary ti investigate further – the weather will not be flyable, particularly for the inexperienced pilot. In such circumstances the pilot does not need to check further…unless he or she just wants the practice in decoding aviation weather reports!

Understanding Aviation Weather Charts

If the weather looks like it might be alright, the next step is to check the aviation weather charts or synoptic charts. These will give a general picture of what the weather will be doing. It is not necessary to understand these in any great detail. Basically, if high pressure is being shown, the weather is likely to be stable and could be very good.

However, visibility might well be poor. If low pressure is shown, the weather is likely to be changeable and good be unsuitable for flying. Look for frontal systems too. If one of those is crossing the area where the pilot wants to fly, it is probably best to wait until it is past. Generally, warm fronts mean drizzle, low cloud, and poor visibility. Cold fronts signify heavy rain and wind, although the visibility may be good. But a simple rule is to avoid flying through any type of front.

Aviation TAFs and METARs

Many large airports give specific aviation weather reports for their area. TAFs are Terminal Area Forecasts, and predict the weather for the next few hours, or sometimes longer. A METAR is a Meteorological Airfield Report, and tells the pilot what the weather was like at the time the report was published. Both are updated every few hours.

TAF Decode

Here are examples of the codes the pilot is likely to see on a TAF…

EGSS – Station four-letter indicator, in this case London Stansted
130500Z – Date and time of the TAF, in this case the 13th at 05.00 Zulu time or GMT
1306/14/06 – Validity time of the TAF; this one is 6.00 am on the 13th to 6.00 am on the 14th
31015G25KT – Wind, in this instance from 310 degrees at 15 knots gusting to 25 knots
8000 – visibility in metres. 9999 means more than 10 kms visibility, and is the maximum given
-SHRA – type of weather, in this case light rain showers
FEW 0500, SCT010 – cloud cover, in this case a few at 500 feet and scattered at 1000 feet

The TAF may then show any significant changes occurring during the validity period.

METAR Decode

The METAR codes are very similar but will also include the QNH or atmospheric pressure, eg Q995. They will also give the temperature and dew point, eg 10/03.

The above should give pilots a reasonable idea of how to understand aviation weather services and forecasts. However, if in doubt it is a good idea to ask someone who can interpret them in more detail There is no shame in not knowing!

Source

“Get Met 2009”, published by the Met office, UK

The copyright of the article How to Understand Aviation Weather Forecasts in Aviation is owned by Helen Krasner. Permission to republish How to Understand Aviation Weather Forecasts in print or online must be granted by the author in writing.