In ERA-Interim the Convective Available Potential Energy (CAPE) values are all zero for 03:00 and 15:00.
This is a data error, caused by an error in how ERA-Interim is calculated.
In ERA-Interim CAPE is available as forecasted parameter in 3 hourly time steps initialized at 00Z and 12Z, so data is available for these times:
03:00 (00:00 + 03h) - erroneous values!
06:00 (00:00 + 06h)
09:00 (00:00 + 09h)
12:00 (00:00 + 12h)
15:00 (12:00 + 03h) - erroneous values!
18:00 (12:00 + 06h)
21:00 (12:00 + 09h)
24:00 (12:00 + 12h)
In ERA-Interim there is an error in how CAPE is calculated at step 3 (+03 hours forecast). The error does not affect other steps.
There is no workaround for this issue. ECMWF do not have alternative CAPE data for +03 hours.