March 24th, 2018
Session with DE
PDT: 17:00 to 18:30
Zulu: 00:00 to 01:30
With time comes change. Over my past 9 months I have learned a lot more than I wanted to about weather, aviation weather, and most importantly weather forecasting. Now that I am back I hope to pass off some of this information to my fellow VATSIM pilots and controllers who grace the SW CONUS (Continental US). The new products that are available on the Current Weather page all play an important role in aviation. All sections of the previous weather page have been updated and some new products are now available. This document will cover how these products can be utilized to enhance your virtual aviation endeavors.
Ill start off going left to right on the menu of the new weather site. METARs, most of us know how to decode them, which is the important part. For the most part, thats all VATSIM pilots know, and wish to know to enjoy their flight. Something new on the METAR page is a Local Area Work Chart (LAWC). The LAWC is used by meteorologist, dispatchers, as well as pilots to get a visual image of how the atmosphere is flowing over a geographic area. The LAWC will give the customer the ability to have a quick look of the conditions over a region, allowing the customer to find a quick alternate if one has not been planned for in pre-flight. Using the LAWC controllers can look upstream of their area of responsibiliy to see if a wind shift can be expected, which allows for early planning for when it comes time to turn the field around. The various meteorological symbols used on the LAWC will be supplied at the bottom of this text. Feel free to check it out and familiarize yourself with the new product available to ZLA customers and staff. In the soon future Terminal Aerodrome Forecasts (TAF) will be available on the METAR page, which will facilitate a tittle change to METAR & TAFs. TAFs are utilized by all customers of aviation weather products as a text forecast for an area. TAFs are written for 5sm around an airport. So the TAF you see for LAX will only be for a 5sm radius around the field. Utilizing the TAF will allow a pilot, controller, or other customer the chance to find their arrival or departure time, read the line, and see what conditions are forecasted to be occurring during one's arrival or departure.
Next I will cover the significance of NEXRAD, some misconceptions, as well as how to use it. First off, NEXRAD, known widely as the WSR-88D (Weather Surveillance Radar 1988 D). The D really is not significant, but Im sure many of you have heard your local meteorologist tack on the term "Doppler Radar." This is where it comes from. In the aviation sector we use the WSR88D for two primary purposes. The first being the detection of water droplets that are perceptible. All the echoes from the radar that are 18.5dbz or greater are considered preciptible echoes. Meaning the obvious, that if you see an echo of 18.5dbz or greater, it is raining in that area, or at least the possible for rain to affect the area is high. Once echoes of roughly 50dbz start to show up hail is apparent. How does this work you ask? Im going to cover this in a very basic way, if you want more information feel free to check the resource links at the bottom. The WSR88D sends out a pulse, that pulse hits an object, and due to back scattering energy which returns to the radar site, an echo appears. The greator the echo, the thicker the object, or more dense an object. One thing to remember out of this is that key 18.5dbz level, the precipitable echo. The second use of the WSR88D system is the location, and tracking of severe storm systems. You remember that 50dbz level? Hail only forms within thunderstorms, so what that means is also once you see echoes in the low 40's start to transition into the 50, get ready for one heck of a time as some convective severe weather is about ready to open shop. There are a wide variety of products the WSR88D system produces, the one available on the site is the base reflectivity. You may also notice the Composite Radar Summary for the SW CONUS? This is used as a quick glance of what all the radar sites in the area are showing. Start with the big picture, then move down to the smaller sites available to us.
Moving on to the new and improved Satellite section of the site. You will now notice there are 3 images, one visible, one enhanced infrared, and the water vapor shot. The visible image has one big limitation. It can only be used during daylight hours, as well, the name implies it is a visual image, pretty much what the human eye would see from space. The visible shot is used to identify low clouds. One thing we will benefit from this is being able to view the fog banks that form off the SoCal coasts. This image will allow controllers a quick and true view of the weather situation outside. Next is the Enhanced Infrared, there is nothing really enhanced about it with the exceptions that it uses colors to indicate temperature. Infrared is used to view mid to high etage clouds. At the bottom of the image you will see a scale, going from left to right temperature wise. Left most side is warm, right most side is coldest. What that means is that when you see colors that lie to the very right of the scale, you can bet your money that there are some cloud tops that are very cold, hence higher in the atmosphere. Infrared is great for viewing thunderstorms, and various other convective activity. Now to the water vapor. Water Vapor is used to show the amount of water vapor in the higher parts of the atmosphere (higher than 300mb or 30,000ft). So don't use the Water Vapor as a tool to view fog, or low to high level clouds, cause it will not help. Use the Water Vapor as a tool to find the different jetstream (Polar Front, Sub-Tropical, and Arctic jets). Dark areas indicate areas of low moisture content, indicating displacement of water vapor. With this large displacement, one can visually see the jet streams. To better understand how this works, think of a small tub of water. Now run your finger, or any object through it. The displacement of the water to the left and right of the object is the same principle that applies to our atmosphere in all levels.
Only two more sections to go, first is the Upper Air and Surface chart section. Upper Air soundings (weather balloons) play a vital role in aviation. The data is real, live upper air information. Starting from the highest level down, the 300mb (roughly FL300) provides a CONUS size picture of the long wave pattern. As well as the location of the predominant jet features. Winds over 50kts constitute a Jet. With that said, we can move on down to the 500 (FL180) and 700mb (10,000ft) levels. Now it is possible to pick out synoptic features, such as troughs (associated with Low pressure / unstable) and ridges (associated with High pressure / stable). Troughs are created due to rising air associated with low pressure systems. Ridges are created due to the sinking of air associated with high pressure systems. With each bring their own share of weather. Troughs are normally associated with poor weather, while ridges are associated with fair weather. Troughs that are deep enough stack all the way down to the surface. Which we call a cold front, the ridges also can indicate an area of warm air advection, indicating a warm front at the surface. Just a quick note, ridges are not always associated with warm fronts though. Also being provided on the 500 and 700mb levels is wind data, just like the 300mb. Now available is mid level wind information. The 850mb (5000ft) is very similar to the 500 and 700mb levels. Providing a closer to earth view of synoptic features, as well as low level jet / wind data. The surface chart available from us through UNISYS provides us fronts (cold, warm, occluded, stationary.) As well as a CONUS Radar Composite summary overlay. Allowing customers a quick glance of weather associated with the various surface features.
Finally the SIGMET page, basically a SIGMET is a text output that is converted to an image to provide customers a visual representation of areas of IFR conditions, MTN obstructions, Convection (Thunderstorms), Icing, and Turbulence. For information on how to read the Icing and Turbulence images and the symbols used, follow the link at the bottom of this document. The Convection image shows a forecasted area of thunderstorm activity, and will usually list the top of such activity in three digit format. IFR conditions and MTN obstructions is very simple, just shows areas where each is forecasted to occur. Very simple, and useful product to use as an aviator. But remember to check the TAF of the field your departing from, or arriving to for a more precise forecast.
Lastly this is a very basic introduction to some of the products available. There are many more products available to assist you in making your flight as real as it gets. Feel free to send questions, comments, and suggestions my way. If you would like a certain subject related to weather explained feel free to suggest it. Enjoy!
Following are standard weather depiction symbols, as well as surface / upper air station plots. For SIGMET Icing and Turbulence symbol help click here
For more information, questions, or comments contact Josh Hjemvick