Where's the temperature gauge sensor?

[Thackeray]

Does anyone know where the sensor for the dashboard outside temperature gauge is located? 

I washed my car recently and when I drove off afterwards the temperature display seemed to be stuck on 20 degrees. The actual temperature must have been around 25. It didn't really move for around 20 minutes but later in the day on a different trip it began to creep up to a more realistic number.

I wondered if some water had accumulated around the sensor and kept it at a constant temperature. Seems unlikely I know as this would probably happen whenever it rained.

Anyway, does anyone know the location of the sensor? And if it's not prone to water pooling around it, is there something else that might have caused it to stick for a while? 

[Shada]

it sits behind the front bumper between the number plate and radiator. It would be easy for it to get wet with a hosing and cool the plastic sensor, taking it some time to warm up again.