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.
Somewhere warmer.
You know how the northern US seems to have a week or two of arctic temperatures. Well it’s weather patterns forcing air from far north being pushed much further south than it usually does.
Air moves from areas of high pressure to areas of low pressure. so..the answer is that air in the high-pressure area is warmer than the air in the low pressure area. So…for example, if a dessert area that retains a lot of heat blows toward an area with canopy or near a cooling body of water the air that comes in at night may be warmer than the ambient temperature that it rushes towards.
It happens in Australia quite frequently. The centre of the country is a desert and heats up during the day. That heat rises and moves with the wind so it blows over the cooler areas of the country, meaning quite often we get 10C rises in the middle of the night. It is the hot air from the desert moving with wind across the rest of the country.
The same effect will happen to lesser extents all around the world for a variety of geographical reasons.
Additionally, there are established air currents that push hot air from the middle-east across northern europe (the gulf stream). That is what prevents the UK getting as cold as neighbouring scandinavia.
Sometimes the air temperature will warm up when rain starts due to the heat generated by the friction of the drops falling through the air. This can be a significant temperature increase.
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