Generally, you can anticipate the weather in Istanbul during December is 6. Highs are around 10 degrees and a low of 6 celsius. The table below includes more detail:
| Month | Degrees Celsius |
|---|---|
| Temperature | 6 |
| High Temperature | 10 |
| Low Temperature | 6 |
| Sunshine Per Day | 4 |
Useful Links: Istanbul Weather: Average Weather & Yearly Climate