inktomi Posted June 16, 2013 Report Posted June 16, 2013 Hello - I was looking at DUATs weather today preparing for my IFR test tomorrow, and ran across a new chart (a colorful one at that!) which I hadn't seen before. This is what CSC DUATs is calling a Constant Pressure chart, and I see the areas of constant pressure. What I'm curious about is DPD and the numbers at the various stations. What do they mean? I'm in Las Vegas, and I'm quite certain that we don't have a moderate icing potential.. does it mean that if I were flying in clouds there would be a moderate icing potential? Looking north of Las Vegas, the "21" at the Reno station is the temperature, correct? Looking at the white tags, 10400, 10300, 10200.. that's the altitude where the pressure is 700 mb, correct? Sorry for this being the first post of mine.. long time lurker, first time poster.
carusoam Posted June 16, 2013 Report Posted June 16, 2013 Ice requires two things, moisture and near freezing temps... I believe the chart is giving information about the moisture level and has also mentioned temps. So there is moisture enough to be an icing issue if it gets cold. Look at the greens and the temps. You have to get to the northern states to have both moisture and temps, according to this chart. There is a chart that specifically points out freezing levels. Look that one up as well. Moisture is most often combined with clouds, so a satellite picture is good at predicting where clouds are. Finding cloud heights is another good chart to have a feeling for. This time of year, the thunderstorms are very important to know where they are and how to go around them. Two weather issues that are important to Mooney drivers...freezing/icing and convection, followed by T/O performance at the given density altitude. Let me know what you see. I am only a private pilot with an IR, not an expert by any means. Welcome to the site, hope that helped. -a-
inktomi Posted June 16, 2013 Author Report Posted June 16, 2013 Thanks! Truth be told I've always liked the look of Mooneys.. which brought me here. I've enjoyed lurking and reading what people have to offer. I learn so much about aircraft just reading the issues that other people have had with them. My flight school just got a rental 1987 M20J which I'm very excited to try out after my IFR rating is complete. Hopefully soon! I thought that the numbers near the circles may mean temperature because 21 Celsius matches up with the temperature in Reno, but the numbers in the white boxes being the altitude at which 700 mb pressure actually existed was basically a guess. I couldn't find a legend online.. Attached is the matching freezing level chart. Visually the gradients seem to match up, but I'm not sure if that's just a coincidence. I see that around Las Vegas the freezing level is about 11-15 thousand feet. I do know that to have icing you need visible moisture, something that Las Vegas doesn't have right now... which is why I was curious about the Moderate Icing Potential. Then I looked up DPD and really couldn't find anything relevant at all. Sooo much stuff that I'm trying to review, and then I run into little things that I just haven't seen before.. like a new way to display a constant pressure chart!
carusoam Posted June 16, 2013 Report Posted June 16, 2013 I updated my post above. You seem to have a grasp of the charts. They do have there limitations... Best regards, -a-
N201MKTurbo Posted June 16, 2013 Report Posted June 16, 2013 The DPD is just the temperature dew point spread. The red areas have a large spread meaning it is very dry at the 700 MB level.
PTK Posted June 16, 2013 Report Posted June 16, 2013 I'm not an expert on weather either but I believe the DPD chart gives a lot of useful info. It shows an approximation of the actual height of the 700mb pressure above msl. The DPD values are taken along approx. corresponding 700mb points. The lower the DPDs the more moisture in the air. Also what the chart depicts is airflow info. This is good to have because air movement at the 700mb level is a good indicator of how systems at the surface will move.
inktomi Posted June 16, 2013 Author Report Posted June 16, 2013 Thank you for all the replies. I think I feel good enough about this chart now to include it in my weather packet for my test today. It seems like no matter how much I think that I know, as soon as I go to look up the details of something that I'm unsure of there's a whole bunch of stuff that I never even knew I didn't know. I guess I'll do the best I can today, and then resolve to never stop learning about this sort of stuff!
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