Like several towns and cities in the midwest and northeast USA, Wooster, OH broke its daily high temperature record for January 11 last Saturday. Below is a graph of some of the data (made a little prettier in powerpoint) from the weather station I run at my house.
The outdoor air temperature is the black curve, and the two vertical shaded regions show a period of rapid warming (red) midday Thursday and a period of rapid cooling (blue) on Sunday morning. I’m about to teach a unit about weather and climate to start this semester in ESCI 275, and this weekend was a great example of how an extratropical cyclone (a.k.a. a “winter storm”) can impact the temperature you feel outside. There wasn’t much rain in this storm, but the winds and temperatures show the impact. Courtesy of the Weather Channel, here’s what the situation looked like Thursday:
See that big red “L” on the border of Nebraska and Iowa? That’s what’s responsible for the crazy swing in temperatures. The red line extending east from it represents a warm front — south of that front, the air was much warmer than north of that front. The white contours are isobars (lines of constant pressure), and those show that behind that warm front, southerly winds were bringing warm air northward. The arrows on the graph at the top show the same thing. If you’d watched a flag flapping in the wind all morning Thursday, you’d watch it twist around from the turning — northerly wind then easterly wind then southerly wind by midday. The temperature rose by more than 20°F over a few hours Thursday as that warm front passed over Ohio.
Anybody who looks at weather maps obsessively knows that behind most red warm fronts is a blue cold front; and a cold front was beginning to form with this Low (a.k.a. cyclone (a.k.a. storm)), extending from Nebraska to Texas…. it was just delayed. By noon Friday, the Low in Nebraska shot all the way up to Canada, moving around that big area of stalwart high pressure (the blue “H”) to its east. (That’s often called a “blocking high”, by the way.) The cold front extending from the Low on this second map is not a pure cold front, either. Notice the alternating red and blue from Michigan down to Oklahoma? That’s a sign that this front was actually “stationary” — it wasn’t moving. This stalling of the front led to a delay in the cooling down part of an extratropical cyclone, so places like Wooster and Pittsburgh continued to see southerly winds all day Friday and most of Saturday. This led to a few oddities: 1) The daily high on Thursday was at 11:59 PM. 2) The daily high on Friday was also 11:59 P. 3) The temperature on Saturday peaked at a whopping 67.6°F at 2:15 PM local time in Wooster. That’s like May weather in January.
The fun did not last forever, though. The stalled section of the cold front re-formed a secondary Low, and by late Saturday, the cold front was on the move over the USA again. This last map is from 10:15 PM Saturday night, less than two hours before that secondary Low passed almost directly over Wooster. Temperatures dropped almost 30°F overnight, and Sunday felt a little more like winter.
That 67.6°F wasn’t just warm, by the way; it was higher than any temperature ever recorded on a January 11at the OARDC station in Wooster from 1900 to 2019. This last graph shows the same temperature curve as before, but it also shows box plots for the daily high temperature 1900-2019 for each day January 9 through January 13. A normal highest temperature of the day is between about 22°F and 42°F for this four-day period. (The red boxes show the “interquartile range”, meaning that the coldest 30 years are below the red box, the middle 60 years are inside the red box, and the warmest 30 years are above the red box.) That 67.6°F would have been a record for any of these four days. (The “whisker” ends show the maximum and minimum.) Moreover, those box plots are showing the daily high, not the average temperature for the whole day… so the fact that even Sunday remained above the median daily high the entire day when it’s the cold day is a further sign of how impressive that warm snap was.
And again, this happened because a Low pressure system started moving east, got stuck, and reformed into two separate lows — first a Canadian Low, then a Michigan Low. While it stalled and reformed, southerly winds kept pumping warmth into Ohio, and that’s what set the record on Saturday — we had nearly 60 hours of consistent southerly winds.