Learning Goals Weather Report Flying has always been about safety and good planning. A good pilot is the one who takes the time to plan his flight and take into account all of the variables. One of the most importantt factors that need to be taken into considerationn is the weather. Pilots will therefore consult AIRMETS and SIGMETS Putting it simply, an AIRMET is weather that can have a significant impact on aviation operations and flight safety of small airplanes whereas a SIGMET is weather that can have a significant impact on all airplanes. AIRMETS and SIGMETS are non-scheduled reports (only issued when needed ) Let's go over the details AIRMETS: (Airman's Meteorological Information) Hazardous weather advisories of moderateintensity covering and area of at least 3000 square miles. Moderate Icing Moderate Turbulence Sustained surface winds of 30 knots or more Ceilings less than 1000ft and or visibility less than 3 miles affecting 50% of an areaa at one time. Extensive mountainn obscuration Convective SIGMETS:(Significant Meteorological Information) Hazardous weather advisories of severeintensity,covering and area of at least 3000 square miles. thunderstorms and related phenomena ( tornadoes, heavy precipitation, hail and high surface winds ) Valid for 2 hours only Non-Convective SIGMETS:(Significant Meteorological Information) Hazardous weather advisories of severe intensitycovering and area of at least 3000 square miles. Severe Icing not associated with thunderstorms Severe or extreme turnulencee or clear air turbulence (CAT) not associated with thunderstorms Widespread dust storms, sandstorms, or volcanicc ash lowering surface or in-flight visibilities to drop below 5km or 3 statute miles. Valid for up to 4 hours or in case of a hurricane 6 hours. Page 1 of 8
Since the Format of an AIRMET is practically the same as a SIGMET we are going to discuss how to read and interprett weather reports which have significant effect on airplane safety. 1. SIGMETS(Text format). 2. Significant Weather Charts(Graphical format) SIGMET reports Since convectivee SIGMETSS report about thunderstorms they will usually start with the abbreviation: WST "Weather SIGMET for Thunderstormss report". Note: Convection is the concentrated collective movement of ensembles of molecules within fluids. Discrete convective movement in the atmosphere can be seen as clouds. Stronger convection will result in thunderstorms. Non-convective SIGMETS which are issued for non-thunderstorm hazards will begin with the abbreviation: WS"Weather SIGMET report" The first time a report is issued it will be given the next available aplhabetic designator in the series as well as the first number. for instance: WS A 1 : weather sigmet report alpha number 1 if the weather phenomena continues for more than 4 hours another report is issued WS A 2 : weather sigmet report alpha number 2...etc... until the weather phenomena ends and the SIGMET report is officially removed. a new phenomena gets the next letter and starting again with nr 1 WS B 1...etc SIGMET reports can take letters from A (Alpha) to Y (Yankee) excluding S (Sierra), T (Tango) and Z (Zulu) S (Sierra), T (Tango) and Z (Zulu) are used for AIRMET reports only Page 2 of 8
SIGMETS are usually issued mostly for the continent of North America thus the following example is an example of a SIGMET in the United States. Example of a Non-Convective SIGMET Lots of codes isn t it? It is simple don t worry,,let s work it line by line. 1- SFO indicates that San Francisco weather Station is the one which originated this report. The letter R indicates the SIGMET phonetic series. UWS sayss Urgent Weather SIGMET. The 100130 means that the report is issued at day 10 of the month at time 0130Z. 2- This line explains the identity of the report. So it says the following report is a SIGMET report. Identifier Romeo. The number 1 indicated that this is the first report of the Romeo series and the report is valid until day 10 of the month at time 0530Z 3- The affected states are OR (Oregon) and WA (Washington) 4- Since we mentioned in the top that the SIGMET report covers a vast distance of over 3000 square miles. The fourth line indicates the boundaries of this area, so the report covers the area from SEA to PDT to EUG to SEA VORs. So if we take a map and draw a line between theses VORs the picture would look like the next picture below. So inside this yellow triangle is the affected area. Page 3 of 8
5- This line describes the Phenomena or what is happening. So this is how to read it: Occasional moderate or greater clear air turbulence between Flight Level 280 and Flight Level 350, expected due to jet stream. Conditions beginning after 0200Z continuing beyond 0530Z and spreading over central Idaho by 0400Z. That s it, we just fully decoded one of the hardest SIGMETs issued. Now you might be asking yourself a question. How did I get all of thesee symbols? Check the following link http:// /www.srh. noaa.gov/ /jetstream//append/acronyms_a.htm Once you open the link you will find all possible shortcuts that you can imagine. The first page that you open is for the acronyms starting with the letter A. If you want to find another acronym with a different letter of example the acronym ID that is found in the 5 th line of the SIGMET. Just click on the letter I on the left and scroll until you find ID which is equal to Idaho State. I guess you can now decodee any SIGMET you want. Want to look up a SIGMET for yourself? http:// /aviationweather.gov/adds/airmets/ Once you open this link. Tick the kind of SIGMET you want in the area requested. For example I want SIGMETs for icing issued by SFO weather station. So I will choose the Icing option and SFO from the list and click on retrieve. The result is going to be a huge text containing both AIRMET reports (For small airplanes) and SIGMET reports provided that there are any issued. Page 4 of 8
SIGNIFICANT WEATHER CHARTS Now we turn to a bit more interesting part of this document. The Significant Weather Charts. It is presented to the pilots in a graphical format making it quite easy to understand. Let s get some facts clear 1- Significant weather charts are issued 4 times a day At 0000Z, 0600Z, 1200Z, 1800Z 2- There are THREE types of Significant weather charts: Low level charts (Below FL100) Medium/High level charts (FL100-FL450) High Level Charts (FL250-FL630) SIGWX charts are issued for 7 areas of the world every day. They can be accessed from the following link: http://aviationweather.gov/products/swh/ Let s get to know some of the symbols that are usually found on this type of charts Page 5 of 8
These symbols may look complicated but we will look at an example of such a chart and explain it in some detail. Page 6 of 8
Page 7 of 8
1- The green arrows represent fast moving winds which are better known as JET STREAM.These are caused due to the earth rotation and sun rays heating the atmosphere. The triangles and dashes commonly knownn as Wind Barbs on the green line indicates the speed of the jet stream. The following is the legend (key) to decode it 2- As you can also notice the red areas are cloud boundaries with the type and top level of the clouds written inside the figure 3- The yellow lines indicate moderate to severe turbulence within the area enclosed by the yellow lines Additionally, you can notice the XXX written in some boxes, if the XX XX are found at the top of the box then is indicated the upper level of the chart which in this case is FL630. If the XXX were found at the bottom of the charts then it indicates the lower level of the chart which in this case is FL250 Page 8 of 8