Happy Solstice Eve! The solstice occurs tomorrow (Dec. 21st) at 10:28 AM local when the sun’s most direct rays reach their southern nadir and the North Pole is titled away from the sun at its greatest angle. Tomorrow is the “shortest” day of the year (even though we’ve already passed our earliest sunset about two weeks ago, and our latest sunrise is still to come). In the meantime, here is a quick update since I know this quiet and mild weather has given everyone withdrawal symptoms. And don’t worry! It looks like the pattern is about to flip so you’ll probably be able to count on a few more updates as we close 2017.
Speaking of 2017, it has been a remarkable weather year in Chicago in several ways. We opened the year with a record-breaking snow drought: after a snowy start to the season the snow shut off around this time in December 2016 and the January-February 2017 period was the first in recorded history to receive less than 1” of snowfall. The calendar-year-to-date total is officially <11” so last year’s snow drought has carried over into this season (at least so far).* 2017 also saw a long string of above-average-temperature months (10, in most locations) and severe flooding in July (northern burbs) and October (western and southern burbs).
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This week will remain mild for at least another day or two – highs will be well into the upper 30s with lows near or even above 32F.
But by Friday a storm will be approaching Chicago. For now it looks like we will remain in the warm sector, with rain or a rain/snow mix here – ice and significant snow is likely to our west and north. Stay tuned for details, but expect travel delays given the busy holiday travel season and the wide-ranging impact on airports everywhere east of the Rockies as a potential powerhouse develops toward the East Coast by Christmas Eve and Christmas Day. There is a lot of uncertainty about the track of this weekend storm so anyone with travel plans so keep an eye on it.
Behind that storm a very cold airmass will arrive by Monday and likely set up for at least a week or two. It is not going to be record breaking, or even close, but it will be cold compared to what we’ve had so far. With the cold will come repeated chances for snow, starting on Sunday. It is far too early to pin down details, but even if we stay on the warm side on Friday it looks like we could see a little bit of snow . The historical odds for a White Christmas are just under ~40% and at this point it’s not looking much more likely than that.**
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* The average annual/seasonal snowfall in Chicago is about 37”, with some variation depending on location (especially pertaining to proximity to the lake). But calendar-year snowfall is even more arbitrary since it covers parts of two distinct snow season. And given the variation in official reporting sites (various in the Loop from the 1870s, then Hyde Park, then Midway Airport until 1980 and O’Hare Airport since then) it is possible that <1” was recorded at another site in the area.
** If a White Christmas is defined as ≥1” of snow cover at 7am on Christmas morning, O’Hare’s historical occurrence since 1980 is 37%.
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