Local Weather Conditions
On the chart that the link above will take you to, *TI* is the thermal index.
The elevation to the left of *TI* -3.0 is the approximate maximum altitude that can be acheived in a glider.
The elevation to the left of *TI* 0.0 usually indicates the approximate base of the clouds.
This data can be used to forecast the suitability of the coming day for glider operations.
This page explains all the data in detail.