Basically, what Trump is insinuating is that "good old global warming" couldn't possibly be a real threat because it's cold outside. You can see his logic.
The problem is, weather and climate aren't the same thing. As Nasa explains:
The difference between weather and climate is a measure of time. Weather is what conditions of the atmosphere are over a short period of time, and climate is how the atmosphere 'behaves' over relatively long periods of time.
In fact, 2016 was the third consecutive hottest-year-on-record - and the World Meteorological Organisations says that 2017 is easily going to top it.
But as with most of Donald Trump tweets, there was a counter-tweet already in place to show how wrong the 45th president of the United States really is. And this one comes from the Washington Post's weather reporters, the Capital Weather Gang, who tweeted nearly two days prior to Trump:
U.S. to be coldest region in world relative to normal over next week. Please note rest of world will be much warme… https://t.co/WH0guiFedn
— Capital Weather Gang (@Capital Weather Gang)