snow/cold and winter outlook

Yes, there is some (very light) snow on the way tonight. Normally this would not merit any attention, but given that it’s early in the season and this is the first real snow, it is getting a lot of attention.

 

• Snow arrives near or after midnight and exists tomorrow morning after rush hour.
• A dusting to maybe an inch of snow could accumulate in some locations.
• Given the date and warm surface temps I would not expect much if any accumulation on the roads, especially in the city and near the lake.
• Visibility should be decent, so even though there could be some minor traffic delays on the roads and the airports tomorrow morning it shouldn’t be terrible.
• This is going to be a wet/slushy snow and a lot of leaves are still on the trees, but amounts will be so light that I don’t think there will be any issue with power lines.

 

 

Beyond the next seven days, which look very cold for the season, the outlook is mixed. There are no major warm-ups showing up just yet, but I would bet more to the mild side toward Thanksgiving. Beyond that there isn’t much to say. The various prognosticators/soothsayers probably have some strong and useless forecasts, but I would ignore them all. We do know that a weak/moderate El Niño is somewhat likely this winter (see below), and we do know that El Niño winters are correlated with mild-ish winters in Chicago.* Beyond that it is safe to pay attention to details within a day or two, broad trends and outliers to 10-14 days, and ignore the rest.

 

* Here is the evergreen reminder that the atmosphere is endlessly complex and we cannot prove causation, let alone model it with precision in the future, when it comes to El Niño or any other specific event. El Niño winters may come with better-than-average odds for a mild winter, but no two events are alike. In any case, an El Niño winters doesn’t mean we will be free of (big) snowstorms or occasional cold snaps. And even if we get an El Niño, and even if the correlation holds up over time, please don’t confuse a winter that turns out to be cold/snowy with what “should” or was “supposed” to have happened. We had a moderate/strong El Niño in 2015-16, and that was a very mild winter in Chicago. But 2009-10 was a moderate El Niño and Chicago actually had a slightly colder than average winter.

 

So maybe the most important thing to remember about El Niño is this analysis from The Weather Channel’s “WeatherScope” segment:

 

http://www.nbc.com/saturday-night-live/video/el-nino/2861308

 

 

 

EL NIÑO/SOUTHERN OSCILLATION (ENSO)

DIAGNOSTIC DISCUSSION

issued by CLIMATE PREDICTION CENTER/NCEP/NWS and the International Research Institute for Climate and Society

8 November 2018

ENSO Alert System Status: El Niño Watch

Synopsis:  El Niño is expected to form and continue through the Northern Hemisphere winter 2018-19 (~80% chance) and into spring (55-60% chance). ENSO-neutral continued during October, despite widespread above-average sea surface temperatures (SSTs) across the equatorial Pacific Ocean [Fig. 1]. All four Niño regions showed increased SST anomalies in October, with the latest weekly values near +1.0°C in the Niño-4, Niño-3.4 and Niño3 regions, and +0.2°C in the Niño-1+2 region [Fig. 2]. Positive subsurface temperature anomalies (averaged across 180°-100°W) also continued [Fig. 3], due to the persistence of above-average temperatures at depth across the eastern half of the equatorial Pacific Ocean [Fig. 4]. However, atmospheric convection remained slightly suppressed near the Date Line and over Indonesia [Fig. 5]. Low-level westerly wind anomalies were observed over the eastern Pacific during October, while weak upper-level westerly wind anomalies were present over the far western Pacific. The traditional and equatorial Southern Oscillation indices were near zero. Despite the above-average ocean temperatures across the equatorial Pacific Ocean, the overall coupled ocean-atmosphere system continued to reflect ENSO-neutral. The majority of models in the IRI/CPC plume predict a Niño3.4 index of +0.5°C or greater to continue through the rest of the fall and winter and into spring [Fig. 6]. The official forecast favors the formation of a weak El Niño, with the expectation that the atmospheric circulation will eventually couple to the anomalous equatorial Pacific warmth. In summary, El Niño is expected to form and continue through the Northern Hemisphere winter 2018-19 (~80% chance) and into spring (55-60% chance; click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

 

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