CAPE and lifted index (thunderstorms), Nokia N810

[gwicke]

Hello,

first of all thank you, Jaques, for a great application. I am using zyGrib on a Nokia N810 Internet tablet (using the Debian chroot), mainly for sailing on Tornado and A-Class sports catamarans. It is possible to check out the latest GFS forecast from the Trapeze

Pretty much the only feature I am missing is the capability to display GFS's CAPE and lifted index data. This would give good information about the likelihood of thunderstorms. Some indication can currently be had by looking at the 0º isotherm vs max temperature in connection with humidity, but CAPE should give better precision. An example of a nice display at Wetterzentrale: http://www.wzkarten.de/pics/Rmgfs036.gif, full list via http://www.wetterzentrale.de/topkarten/fsgfsmeur.html -> CAPE.

I can try to work on this on the client side, but would need extended output from the server side.

Thanks, and good sailing!

Gabriel

[jza]

Hello
Last news : there is CAPE visualization in 3.5.0 version.

[gwicke]

Wow, thanks a lot! I left for a sailing trip on the 22th, so I narrowly missed this It was my first trip with really good weather info, and it made a big difference. In addition to zyGrib, we used the German marine weather forecast in text form and checked CAPE from Wetterzentrale if that indicated the possibility of thunderstorms (as the image files are too big otherwise). The CAPE info proved quite accurate- we observed several big cells from a distance in the area where they were predicted (over Fyn island), while the german forecast just gave a general warning for the entire area between Jutland and Sweden. The threshold for likely thunderstorms seems to be around 600J/kg, with lifted index usually less than -2. There is sometimes minor lightning below 600J/kg, but the lightning maps mainly track the 600J/kg contour.

A small patch to stretch the color scheme slightly to show yellow from about 600J/kg:

Code: Select all

diff -r 446dbd831c64 src/GribPlot.cpp
--- a/src/GribPlot.cpp	Thu Aug 20 10:25:03 2009 +0200
+++ b/src/GribPlot.cpp	Thu Aug 20 10:41:34 2009 +0200
@@ -245,7 +245,7 @@
 {
 	double x = sqrt(v)*70.71;
 	double t0 = 0;  // valeur mini de l'échelle
-	double t1 = 3000;  // valeur maxi de l'échelle
+	double t1 = 4400;  // valeur maxi de l'échelle
 	double b0 = 0;    // min beauforts
 	double b1 = 12;   // max beauforts
 	double eqbeauf = b0 + (x-t0)*(b1-b0)/(t1-t0);

Thanks again

Gabriel