On Tuesday, November 1, 2016 at 4:25:28 PM UTC-7, Casey wrote:
On Sunday, October 30, 2016 at 6:22:26 PM UTC-4, WaltWX wrote:
I am interested in hear U.S. glider pilot comments on the pros/cons of all these sites for soaring forecasts. I have used them all at one time or another and find them generally comparable. But, some like RASP and DrJack do a much better job of locating convergence zones/shear lines. Geo-referencing data and ease of use varies a lot. The biggest difficulty is that archive and looking at past forecasts makes it difficult to do inter comparisons.

Your inputs will valuable to me as I am in the process of writing an article for Soaring magazine discussing the basic of Numerical Weather Prediction and how it relates to these soaring web sites.

Walt Rogers WX

I started using XC skies around 2010-2011 and thought it was easy to use and felt like I did not have to decipher much. I liked the XC Potential and other bar graphs. Very easy to use. I also liked being able to save My Map Profile for different areas. I'm still learning Dr Jacks and have been hesitant to use much due to XC skies was so easy. I stopped using XC skies for I thought it was not being updated. The copyright is from 2005-2012, and the future development was last updated April 18, 2009. The owner of XC skies is supposably in Salt Lake City, UT. I don't think that I am the only one that seems to think its no longer updated by looking at the XC skies discussion board.

Casey

I used Topmeteo and Blipmaps this last summer at Ely, Nv. I also did my own analysis using skew-T diagrams. What I really like about Topmeteo was:
1. The predicted cross country distance
2. The hourly forecasts
3. The detailed cloud types
4. Wind predictions
What I didn't like was the near total lack of geographic references (towns, roads, etc.), making it more difficult to get a frame of reference. Blipmaps has the Univiewer that is much more detailed.

Generally, I thought the accuracy of Topmeteo was good, but missed overdevelopment at times. The accuracy of the predicted cross country distance was all over the map, and I couldn't rely on it. At best, it could be used as an upper limit. Sometimes it predicted Cu and it never appeared, and other times it was vice versa. At least it was better than nothing.

My most insightful observation is the inherent error in atmospheric models. If you compare model soundings to actual balloon soundings there is a significant loss of vertical resolution. This means that inversion layers are washed out dramatically. This can impact predicted thermal heights by 3,000 ft, which is not an insignificant difference (actual thermal heights were generally higher than predicted. In fact it means you can fly much further distances than predicted. This happens because model heat from higher altitudes gets moved down to lower altitudes, limiting usable thermal height, and is unavoidable due to the vertical resolution of the models. Examining the skew-Ts also gives me a better idea of thunder storm probability (if you know how to read them). This is a real issue flying in out west in the high mountain deserts.

Tom