Photo: Fir0002/Flagstaffotos (http://en.wikipedia.org/wiki/GNU_Free_Documentation_License GFDL licence )
Mainly for Johannesburg - Dunnottar area |
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Laura's forecast Today, Sunday, 11 April 2010: 7h30am: Yesterday turned out OK, although it was quite gusty and rough in the middle of the day. Today is likely to be fairly similar (my opinion). The weather bureau says that there was a very strong wind this morning (could not see it myself but must believe them) but it is going away. Low cloud (mist) until 9am or there abouts. The wind is going from NE to NW on the ground and maybe even W and SW in the upper air. Again, no rain expected. The radar seems to have the correct picture today. How am I ever going to trust the radar again after yesterday's fiasco when it showed huge storms over us during an amazingly bright and clear day? Someone was playing silly buggers in their IT department, I guess. On the other hand, one of the pilots put a picture of a rainy or misty Hartebeespoort Dam @9h45 yesterday morning on one of the lists ...... Ah, well, these things happen, I suppose, to challenge us. And to show that even with all our fancy gadgets, we perhaps do not always know the truth! Will be @ Dunnottar field by 10am. With my bakkie with a non-functional alternator (again). We have worked out that I can continue winching as long as I recharge the battery with jumper cables every now and again. :-) Maybe it will be our last day at Dunnottar, maybe it won't! (Remember that you will not be getting the sms info unless you have subscribed or are a Fun Ventures student. If you have paid but are not receiving the sms info, please remind me where and when you have done so.) |
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Ulf's Forecast Today, Thursday, 8 April 2010: Ulf says: Due to high cloud , overcast, ... no decent thermals for the next few days. Weekend should be nice for training.
08 14 NE 08km/h +2.3m/s 0900m Cu to 1300m 08 17 NE 06km/h +1.4m/s 0500m 09 11 NW 13km/h +1.9m/s 0400m Cu to 0700m 09 14 NW 15km/h +1.8m/s 0400m Cu to 0600m 09 17 NW 11km/h +1.4m/s 0200m 10 11 SW 14km/h +2.2m/s 1000m Cu to 1100m 10 14 SW 17km/h +2.6m/s 1300m Cu to 1700m 10 17 SW 11km/h +1.4m/s 0900m 11 11 NE 14km/h +1.8m/s 0500m Cu to 0600m 11 14 NW 11km/h +2.2m/s 0700m Cu to 1100m 11 17 NW 10km/h +1.4m/s 0500m Code available from https://sourceforge.net/projects/t3d2/files/ in the NOAA-READY-ANALYZE Folder Instructions at http://t3d2.sourceforge.net/NOAA_html_Doc/NOAA.html |
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Factors that Influence Laura's Forecast The factors that influence the sms and info that I put out:
The difficult one is when the wind is marginally strong, especially in the upper air - do we or don't we go out? That decision will likely be influenced by what the windspeed is doing from 7000'asl up to 10,000'asl, according to the aircraft sounding. There is a serious possibility that stronger winds will make their way towards the ground with time during the day. Similarly, lighter winds will usually eventually make their way downwards. The other difficult decision is the prediction on when the rain will start, if it is going to rain? I hope the Met will be right, but often they are not. It may rain or not at all, or it may rain earlier or later than predicted! But one can very often fly before or after the rain at Dunnottar and other sites, so it is not necessarily a deterrent. One's mindset must remain positive!The radar is a big help in this situation. Another awkward situation is when the aircraft data is not available, the clouds are scuttling across the sky with speed, and the Met has given a flyable forecast! It's a toss up - do I believe the Met or not?! Long term forecasts hold no charm for me, especially not when we are going away for a weekend. Apart from the problem that one has to book and pay a deposit for accommodation that is often difficult to cancel, long term forecasts often turn out to be incorrect. We have proven that it could be flyable - though the window may be short - on most days. We should be flexible enough to enjoy our time away with doing other things as well - paradriving (looking at other sites), cycling, hiking, investigating the local attractions, talking with other pilots, and just generally having fun and relaxing. If we "lose" a day, so what? We are living in a too hectic world, and occasionally it is good to step back and really do very little, get in touch with nature and/or human nature. It helps us deal better with the "real" world - if what we are doing is really the "real" world - when we return. |
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Factors that Influence Ulf's Forecast Ulf likes NOAA, and also looks at a number of other websites. He will often give a long term forecast, although he will usually not say much when a bad forecast is expected! He says:
Weather page, or Sounding info, or NOAA Sounding. Thermal strength is not related to the cloud size. In Sept/Oct we have dry air, before the rains start, and we have very turbulent thermals, with no clouds. The lapse rate determines the thermal strength. And how long the air had a chance to warm up before it got triggered. My thermal strength calculations work on the US East Coast soaring formula that I found some while ago. As trigger temperature I use the sounding temperature on the ground. Comparing what I forecast and the max climbs I had, one can 2x to 3x the values that I post for your maximum climb in a thermal. But for an average climb the values are close. Wind wise I take the lowest and the next higher expected windspeed and average it. A good day forecast shows the same 10kt windspeed lower and higher up. For this weekend we got 10kt for the ground, and the next layers higher up are 20kt or more, what is not a good sign. The NOAA data is using GFS (Global Forecast System). Windguru does their forecast on GFS. XCSkies uses GFS,... so they all use the same data and if they all agree then one can assume it might really turn out this way. Windguru specializes on windspeed on the ground (what they tend to have far too low) and cloudcover or rain. My code focuses on expected climb rate, thermal height, wind on the ground (if we can takeoff and land without too much trouble), and the GUI shows cloudbase and OD possibility. None of the code can predict if you will experience a nice flight or have some rock'n roll. If you are a low airtime pilot or have not flown for some time, I would recommend that you plan to come out in the afternoons. Mornings have small, rough, punchy little thermals. 12-14 is small core thermal time, and you might not like it. From 14.00 onwards thermals get bigger, smoother and by 15.00 you should have the best thermic conditions. Also phone your buddies upfront before you come out in the afternoon. If you get hold of them, ask them why they are not flying. If they do not answer, assume they are having a good time and you might still get some smooth afternoon flight. |
Photo: Dietmar Neumann
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