The Major League Baseball season started last week, and it's not uncommon that cold weather and snow causes problems in some of the more northern cities, as happened last night in Pittsburgh. There could be the same kind of fun for tonight's game in Pittsburgh, and again on Friday night. For Friday night's game between the Pirates and Reds, there may be rain and then windy conditions and temperatures dropping into the 30's, and maybe some snow before the end of the game, if it's not postponed. Let's predict Friday's low temperature for Pittsburgh, which may come at the end of the day instead of in the morning.
On most days, the daily minimum temperature happens in the early morning hours, near the time of sunrise. Why is it usually colder then than at the end of the day, near midnight?
There was rain and a little snow during Friday night's game in Pittsburgh and the low temperature dropped to 29 F at the very end of the contest day (2 am EDT, which is 0600 UTC).
Answer: On most days, the minimum temperature occurs after a full night of radiative cooling, just before the sun has an opportunity to start warming again. But that normal cycle can be easily overwhelmed by the timing of cloud cover and precipitation, or by the advection of warmer or colder air by fronts. In this case, it was the advection of colder air after a cold frontal passage that caused the 2 am temperature to be less than the previous morning.
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