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I know winter/cold weather fans will find little interest in this…but now that we are moving through Feb pretty fast, I’m starting to get a little excited about the coming of spring.
Based on just my personal thresholds…I really feel like the true mildness of early spring arrives when average highs are 60 F/16 C or higher. Admittedly, there are many stations in the far southern portions of the USA that never see average highs go below 60 F (San Diego, New Orleans, Savannah…etc)… however for much the rest of the mainland USA, I think the advance of the 60 F isotherm for daily highs is a fair line in the sand for when early spring warmth truly has arrived. Also, I think the 70 F/21 C isotherm is really more late spring, and anything above as the start of summer isotherms.
In just a few weeks the 60 F daily high isotherms will advance northward to cover much of California west of the Mt ranges, much of Arizona and southern New Mexico, through the Gulf States to the lower East Coast in March:
By early May...a large area of the USA has daily highs above 70 F...so I would consider this the start of late spring. Only a few areas of the far north and western Mts have ave daily highs below 70 F:
Is daily highs of 60 F a fair line for the start of early spring...and the 70 F isotherm the start of late spring? What would be the isotherm used to define early and late spring where you live? Do people in oceanic and southern hemisphere type climates have different thresholds?
70°F seems about right; maybe a few degrees less 67°F or 68°F; I'd call the threshold of late spring when it becomes warm enough one can usually leaves the windows open most of the time without worrying about cold. Earlier in the spring, I'd be uncomfortable having windows open the whole day.
Early spring I don't define by warmth, but it becoming noticeably warmer than winter. For where I live, that's highs above 45°F or so. At that point, snow is rare and if it does snow, it won't last long on the ground. If it's been a cold winter, snow will melt fast around this time. Obviously for warmer climates, the 45°F threshold doesn't make sense.
I'd define a separate part of spring, mid spring, which is roughly similar to your idea of "early spring". Weather is generally no longer chilly just sometimes cool. But more importantly, frosts have become rarer and plants, flowers are starting to bud out. My early spring feels like a warmer version of winter with the bare vegetation, but mid-spring should feel like an all together sudden change in season. 60°F is an ok threshold, but again I'd go slightly lower maybe 57 or 58°F, but if possible I'd use when flowers, plants start to pop out which is close to your 60°F thershold.
60F is about the average for September anyway, so feels about right. A few days in late winter feel like spring. The 70F mark isn't reached until the first month of summer, but that sounds about right. I think of summer as when the weather is settled, consistently "nice" and good for swimming, rather than by just the temps. Last summer seemed to start at about the start of November.
It's hard to place when exactly "spring" starts here but I'd say when average highs pass about 50F which is usually by the beginning of March. That's usually when the flowers start blooming. The trees start at about 55F which is several weeks to a month later. We don't hit the 70F isotherm until the height of summer here or in July, so it's more summer by Vancouver standards than spring.
I don't like the heat of Summer, but I love Spring! People start to get crazy when it gets to 50, I'll be outside but still with a jacket. People go with just shirt sleeves when it is 50 around here.
It will be interesting to see what happens as winter has been mild, less than 12" of snow, grass never turned completely brown, unless we get storms late Feb./Mar., we could have a very early Spring. Right now, I have no snow in my yard, last year would have been at least 2 feet.
60+F is summer here. Spring highs are 40-55F. April and May. I guess I'd call it early spring after the last major snowfall, when you start seeing serious melting. Late spring is when you start seeing green higher up on the mountains and the bears start coming out.
I've lived in too many different climates for me to have one spring temperature.
For example: Calgary - early spring means late March, early April, when snow no longer sticks and if it falls, it melts. Late spring means snow stops falling altogether and the end of frosts; things start becoming green, usually by mid-May.
Another example: Cairo - early spring means highs consistently in the 20sC, late spring sees highs consistently near 30C, and the cessation of all rain.
In Victoria the oceanic climate meant seasons were very blurry. 12C and light drizzle was normal weather in January and in June, what seemed to define the seasons were more the aberrations than the normals: the last outbreak of below 0C temperatures marked the ''last'' of winter, the first warm day above 20C the ''start'' of summer.
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