How can the outdoor temperature ever increase in the middle of the night? Where is this warmth coming from?
In: Physics
There are several ways, but the primary method is through **advection** of an air mass. That is, some weather feature is delivering warm air to a colder region; this can easily cancel out any cooling that might normally happen overnight.
[Here](https://i.imgur.com/pwsMlaf.png) is a plot of current winds and temperature (shaded) for the surface [this is only a model but it’s a good enough estimate and smooths out raw observations for us]. Here we see a low centred around Lake Superior, with the usual clockwise flow around it. In this example, areas south and east in the warm sector should expect to either increase in temperature or, in this case, remain relatively stable as warm air advection cancels any cooling from lack of sunlight.
[Plotting](https://i.imgur.com/LIVnl3o.png) a time-series for tonight in central New York (the sweet spot in our nocturnal warm sector), we indeed see slightly increasing temperature as this warm air wins the fight against any cooling that the absence of sun can provide.
The opposite is true for daytime; just south and west of this low there is cold air invading from the Prairies, which in theory should bring either drop or at least lack of noticeable increase in temperature tomorrow for, say, the [Northern Peninsula of Michigan](https://i.imgur.com/E0YDZXR.png) despite a fair amount of sunlight pouring in.
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