a fair-weather friend= a friend who doesn't support you in bad times： "I'm a bit disappointed in John and David. It turned out they were only fair-weather friends."
a snowball's chance= very little chance (as much chance as a snowball has in hell)： "We don't have a snowball's chance of winning that contract!"
a storm in a teacup= a lot of fuss over something small： "Don't worry about those two arguing. it's just a storm in a teacup."
be a breeze= to be easy： "The exam was a breeze."
be snowed under= to be very busy： "We're snowed under at work."
blow hot and cold= to keep changing your attitude： "They're blowing hot and cold over this issue. It's impossible to know what they want!"
brass-monkey weather= very cold weather： "It's brass-monkey weather today. You'd better wrap up warm!"
come rain or shine= whatever happens： "He's always working in his garden – come rain or shine."
the lull before the storm= a quiet time before a busy or difficult time： "It's going to get very busy on Thursday. Today and tomorrow are just the lull before the storm."
save up for a rainy day= put money aside for when you might need it later： "I don't want to spend this extra money. I'll save it up for a rainy day."
see which way the wind blows= to analyse a situation before doing something： "I'm going to see which way the wind blows before asking her about a raise."
steal someone's thunder= do what someone else was going to do and get all the praise： "You'll steal her thunder if you wear that dress tonight!"
take a rain check= postpone something： "I don't really want to go the cinema tonight. Can we take a rain-check on it?"
under the weather= not feel very well： "I'm feeling a bit under the weather at the moment."
weather the storm= to survive a difficult situation： "This recession is quite serious and it's becoming difficult to weather the storm."