Even with the recent snowstorms, fuel providers are wondering whether they'll be looking at half full inventories come spring.    A combination of persistently high prices compared to just a few years ago and warmer than what was previously considered normal weather has contributed to more than adequate supplies of propane and natural gas this year.   Although the worst is yet to come in terms of expected low temperatures, for those who are holding these btu's on their balance sheets it can't come soon enough!    Already forecasters are looking forward to the spring "shoulder months" and the possibility of $2 gas.   Could it happen again?  Stay tuned.