Cold weather conditions usually present challenges for most types of automotive vehicle.  Some of these are listed below:

• Diesel vehicles require the fuel to be pre-heated before ignition
• Petrol vehicles require a higher petrol -to-air concentration at startup
• Battery vehicles can suffer from a faster power drain

So what are the challenges facing a hydrogen vehicle? Well that really depends on what type of vehicle you have – Hydrogen Internal Combustion Engine Vehicles (HICE) work much in the same way as a traditional car engine and present less of a challenge. However, Hydrogen Fuel Cell Vehicles present a slightly different challenge because water is produced in the cell as one of the outputs and freezes at 0°C. If no countermeasures are taken then some water typically gets left in the fuel cell when it powers down.

The end result can be water getting stuck in the fuel cell before start up because it has frozen. This can both cause damage to the components of the fuel cell as well as failure to start. Manufacturers such as GM and Honda are believed to have worked around this issue by extracting all water from the membranes during shutdown: http://www.nytimes.com/2004/12/12/automobiles/12CELL.html

It is worth noting that once the fuel cell is running, heat is a by-product and maintains an operational temperature within the cell.
Most manufacturers have now achieved operability down to temperatures as low as -20°C, although the technology behind this is still very secretive.