September is a month which continues the trend, begun back in the closing weeks of June, of very gradually decreasing daylight each day.
This happens the path the sun follows across the sky shifts very gradually farther and farther south each day.
It’s the southward shift in the sun’s trek across the sky which shortens the time we see it in the sky and is behind the decrease in sunlight we see each day.
There’s an accompanying decrease in solar energy which results across the northern hemisphere.
The effect on temperature is delayed–showing up in a decline in the normal day temps which first appears in August.
We’ll see 73 minutes less daylight by the end of the month and our normal Sept. temps will drop from 80 and 62 the first of the month to 70 and 51.
ON JUST COMPLETED CLIMATOLOGICAL SUMMER (June, July and August): DRY AND WARMER THAN NORMAL
The books closed on the 3-month climatological summer period and here are some observations:
–Summer 2022 finished 0.7 deg warmer than normal.
–The average temp of 74-deg over June, July and August place the just completed summer season among the 16% warmest in 151 years of official records–though modestly cooler than either last summer or the summer before
–My WGN meteorological colleague Mark Carroll notes this past summer was the coolest since 2019 and the 2nd driest of the past 10 years.
–Frank Wachowski notes summer 2022 produced 65% of its possible sun–a figure on par with other summer here, and our data on sunlight goes back to 1891.
REGARDING THE UPCOMING CLIMATOLOGICAL WINTER SEASON (Dec, Jan & Feb):
Seasonal forecasts attempt to identify general temp & precip patterns–and among the keys to this coming winter are expectations the current historically long running La Nina will continue into a third year.
La Nina’s have been known to produce weather volatility which can be beyond that of many other winters here. This swings from mild Pacific air to colder arctic blasts are common in such winters.
Our in-house examination of past La Nina winters in Chicago have shown a tendency toward the Dec through Feb period finishing with at least modestly ABOVE NORMAL TEMPS overall while precip (rain and snow) has often come in ABOVE NORMAL.
Whether the bulk of that will fall as liquid or as snow is far tougher to forecast and will ultimately depend on temp trends and winter storm tracks.
But an ABOVE NORMAL precip trend is not uncommon in Chicago in La Nina winters.