Hi Pauline,

In general precipitation will be a few degrees Celsius colder than the air temperature near the ground.

1) Precipitation develops typically several kilometers above the ground, where the air is colder (~5 to 10 deg/km colder as you rise). As it falls, warming of the precipitation particle will lag behind that of the environment air.

2) It warms and melts when falling below the freezing level. It will stay at 0°C in melting condition as energy is consumed for transitioning from ice to water phase.

3) Assuming the air is not saturated, evaporation takes energy from the particle and  cools it towards the wet-bulb temperature: http://www.srh.noaa.gov/epz/?n=wxcalc_rh

The main exception would be the case when there is an inversion of temperature near the ground (cold layer).

I hope someone can provide you a reference for measured precipitation temperatures.

Thanks Oscar, this helps!

Hello Pauline from a fellow teacher at the University of Bologna. I teach cloud physics at  UNIBO/Dept. of Physics. See:

https://www.unibo.it/sitoweb/vincenzo.levizzani

http://www.scienze.unibo.it/it/corsi/insegnamenti/insegnamento/2014/384495

Having said so, what Oscar wrote is correct and it all depends on the vertical temperature structure of the atmosphere in and out the cloud. It is all basic cloud physics and thermodynamics. To my knowledge there aren't specific papers on the temperature of hydrometeors because what mostly matters is the air temperature and the humidity conditions.

You may want to go first to 

http://www.meted.ucar.edu/norlat/snow/preciptype/

MetEd from UCAR is a set of lectures that are very useful and of notable level. You have to register and then will have full access to everything. The rest is available in cloud physics books. Should you be interested, I am available to discuss with you.

Cheers,

Vincenzo

Thanks Vincenzo, I'll let you know if I have more questions!