The Aviation Weather Center breaks down the weather product into three categories: observations, forecasts, and advisories, or, as I like to say, look, look out, and watch out! We must always keep in mind that these products are either history or a good guess-and realize the limitations. Current observations are old by the time they get to the web, often as much as 90 minutes in the case of the surface analysis chart and an hour in the case of a METAR. A clear understanding of the broader weather pattern will inform you of what is happening, why the winds and clouds are behaving that way, and when conditions might change and in what manner.
My goal of this series is to bridge the gap between weather theory and the weather products. I see many students who have their private pilot license and do a great job of reading a METAR, but they can’t tell me what the weather is and how it might be changing in a few hours.(Can you spot a frontal passage just by reading the previous 12 hours of METARS?) Why would a TAF have a line that predicts low ceilings and rain for a two-hour period and then quickly become VFR? (Hint: look at the radar picture in the area.) Can you reasonably detect a front just by looking at the station models? How about just looking at surface winds? Radar? Satellite images? Winds aloft? The clues are all there and each weather product reveals the story in its own language. The forecasts that we rely upon are built from many of the NOAA sites, not just the Aviation Weather Center. There is so much more valuable information that can be gleaned from the Weather Prediction Center, Storm Prediction Center, and other NOAA sources.
I will share with you some of the insights I gained from my 25-year career teaching at a university and 35 years as a CFII. I will include some homework (of course) and ways of combining weather sources that I find interesting. These lessons will be based on some basic assumptions: the student has had some previous lessons on weather theory and can read a simple METAR, TAF, and winds and temperatures aloft products. I will expand on each of these and show how combinations of these products and other, less used (and understood) features can create a comprehensive weather picture. I welcome you to join me and urge you to provide feedback so that we may all learn and share tricks and tips that have served us. We are all students of the art of flying. And weather is endlessly interesting and fun!
Weather Patterns
Weather theory states
that all weather is due to the uneven heating of the earth’s surface. It can be boiled down to simply temperature-in both the vertical and horizontal. Warm air masses have the ability to hold more moisture than cold air masses. Where the air mass originates, cold and dry, cold and moist, hot and dry, or hot and moist, is the first part of the weather story. Temperature also dictates air density and the type of clouds that might appear. The constant movement of air in its endless search for equilibrium on a spinning plant creates circulation patterns on both large and small scales. Temperature changes across air masses (fronts) and vertically (inversions, lapse rates) keep things interesting.
High pressure areas are areas of denser air and have a clockwise (anti-cyclonic) and outward rotation in the northern hemisphere while low pressure areas have counter-clockwise (cyclonic) and inward rotation. This is a standard FAA test question. The image of the surface analysis chart shows the current pressure centers and fronts. This static picture does not convey the air circulation patterns: we have to recall how the air moves around these pressure centers and it is difficult to see how the air moves along the frontal boundaries.
However, a moving image will quickly move yours student’s learning from rote level to correlation. This is beautifully demonstrated on a fantastic website, www.windy.com. If you have never visited this site, be prepared for a vivid demonstration of this effect. The wind patterns instantly comes to life and you can see how the surface winds move. You can watch the wind rotate dramatically around the low pressure off the east coast. The winds are moving outward from the high pressure in the upper Midwest and sweep down toward the central plains and circulate around the low in Iowa. You can understand how the Rocky mountains play a significant part in local wind patterns east of the mountain range- a very pronounced effect in the winter when strong high pressure slides down and that cold, continental dry air mass plants itself in the center of the country.
The circulation cells on the globe in the weather theory books jumps out from the screen. The strengths of the winds are color coded. From here you can zoom out and see circulation patterns across North America and the oceans. The north Atlantic is particularly interesting. Depending on the time of year, the intensity of low pressure systems and wind patterns reveal global circulation patterns such as the Bermuda High in the summer and nor’easters in the winter.
The neat trick is to have both of these websites open in different tabs and click between them or have both windows open at once. Circulation patterns become crystal clear.
Surface Analysis and Surface Prognostic Charts.
Let’s consider the surface prognostic (prog) chart as our salad bowl. It is updated 8 times each day starting at 0000Z. By the time it is analyzed and available on the AWC, it is usually about 90 minutes old. This is a “historical” document. It shows the frontal positions that were observed at the time listed on the chart in the top right-hand corner. As you click through the actual forecast charts, the first 4 images are 6-hour forecasts (the next 30 hours) followed by two 12-hour prog charts then three 24-hour prog charts. These surface prog charts are all updated every three hours. These charts all show the expected movement of surface fronts and the possibility of precipitation. The surface wind patterns on windy.com also has a forecast feature. By using both the AWC prog charts and windy.com, the broad weather picture becomes clear. Windy.com also has the excellent added feature of displaying airports and the most recent METAR pops up when you scroll over it.
Once your student understands weather patterns and sees how the air masses and frontal positions and winds flow, then teaching the different forecast products and how you can begin to predict the future weather based on those movements becomes easier. Fly safely out there (and often)!
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