Chicago Severe Weather Updates: November 2018

Sunday, November 25, 2018

Blizzard Warning

Sorry for one more email but this is really exceptional: NWS just added Cook and Dupage to a Blizzard Warning until 9:00 tomorrow morning.

The low continues to deepen and conditions are atrocious in Iowa. Many major roads are closed and impassable. The switch to snow is beginning across Chicago and the snow will intensify from west to east around 5-6pm. The worst conditions will arrive with heavy snow and winds over 40 mph (gusting to 50+) from 9pm through midnight. Snow totals are largely unchanged from prior models (see below; I'm taking the under by an inch or two, especially along the lake, but that doesn't change the fact that this is a big, nasty storm).

The very sharp line between rain/snow and light/heavy remains in place, running SW to NE right through the area. 10+ inches of heavy, wet snow will be separated by only 10-20 miles from a little slushy accumulation.

The airports are already a mess and by 8-9pm tonight the roads will be very tough. Hopefully crews can catch up by tomorrow morning but we'll see...

(Reminder: a blizzard is actually a specific term defined by three or more consecutive hours of 35+ mph sustained winds that cause blowing or falling snow to create visibility below 1/4 mile. There is no threshold for snowfall accumulation that pertains to a blizzard.)

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last storm update

This powerhouse storm is still barreling across the middle of the country, although the forward motion has slowed. Rain this morning will be later to transition to snow this afternoon. Best guess is rain or a rain-snow mix until 12-2 pm far NW, 2-4pm near suburbs, and after sunset in the city.

Best guess remains 8+ inches far NW -- Lake and McHenry counties remain in the bull's-eye -- with amounts tapering rapidly to the SE. 3-6+ inches for most suburbs toward O'Hare, and 1-2" right along the lakefront from Lincoln Park south to the Indiana border.

One moderate change is that the wind field is expanding and intensifying. Gusts of 45+ mph are likely across the whole area tonight. Airports will have a very tough time after sunset, and even driving will be a challenge tonight in many places.

The Winter Storm Warning is in effect from noon today until 9:00 tomorrow morning. The good news is that we should get a few more hours in the "good" travel window this afternoon on the roads and at the airports, but the morning commute could be somewhat of a problem tomorrow. The worst conditions will arrive well after sunset and be gone by sunrise, but lingering snow showers and the cleanup effort could make for slower travel times tomorrow.

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Saturday, November 24, 2018

Winter Storm Warning

Well, so much for the under – the entire area is under a Winter Storm Warning from late morning Sunday to pre-dawn Monday, and the snow totals are looking more impressive with each iteration. This is a serious storm.

Here is the best guess for now:

Temps in the 40s will support rain developing near dawn. Light, on/off rain will continue through the morning before the switch to snow begins some time after noon (beginning in the W/NW).
Areas to the far west and northwest will see snow first, near or shortly after noon, and even if snow melts at the onset the snowfall rates of 1+ inch/hour will quickly overwhelm road crews. Travel will be problematic by mid-afternoon. Flights – especially at O’Hare – are going to be a mess beyond 12:00 or so. Expect widespread cancellations and delays.
- Totals near O’Hare and the areas to the west and north – especially McHenry and Lake counties – could run to 8+ inches.
The city will see a later switch to snow, and the rain-snow line will be set up roughly parallel to I-55. Snow may be as late as 3-4pm in the city. Totals could range from 4-8” in the far NW sections to 1-2” in the Loop and southern areas.
Areas to the far SE, near the lake and Indiana border, will see the least snow and may not get much beyond a slushy inch or so
Snow will be very heavy and wet.
Winds will gust to 30-40+ mph. Power outages are a distinct risk.
Thundersnow is possible!

A quick note of caution is needed. If you wanted to create a difficult forecast, you’d want a powerful, developing low with a shifting track; early-season conditions, with an urban heat island and a warm lake; and a very sharp rain-snow line across a densely populated area. We have all of that with storm. The “bust potential” with the storm is low – there is a powerhouse coming, it’s just a matter of the precise location – but a tiny difference of 5-10 miles could mean the difference between one inch of snow and one foot of snow. Keep that in mind with everything for tomorrow.

Winter Storm Watch -- Sunday night

Snowvember rolls on after a brief shot of mild air yesterday and today, and we've just been upgraded to a Winter Storm Watch tomorrow (Sunday). This storm has been monitored for days, but it is really coming together and tracking south of its original projection.

With temps pushing 50 today it may not feel like winter, but our exceptionally cold November will return tomorrow after morning temps near 40 start to slide and rain changes to snow. Winds will also be an issue, gusting to 30-40+ and causing visibility issues (especially in open areas). Snow will be heaviest to the west, and totals will decrease rapidly from northwest to southeast. There is a good chance of 6+ inches far west toward DeKalb, while areas in Chicago -- especially near the lake -- will see far less accumulation. For now, I'd put the 50% probability total at 4-6 inches in far NW and N suburbs; 3-4 inches at O'Hare; 1-3 inches at Midway and Loop; and a trace to 1" far S and SE. Some projections are already up to 6-9" NW and 3-6" right through the city, but I'll take the under on that for now. It is still early, the track has been shifting, and as with all early-season storms the bust potential is significant. I will send an update tonight or tomorrow morning as details come together.

Especially at the onset of the rain-to-snow transition the snow will be heavy and wet. Warm surface temps should help it melt at first, but heavy snowfall rates will likely overwhelm road crews by mid-/late-afternoon, causing at least some problems on the roads. The timing in general is terrible given the busy travel schedule on the Sunday after Thanksgiving. Air travel will see delays given that heavy snow will be impacting areas from the central Rockies to the Upper Midwest. Chicago airports Driving west, especially through western Illinois, Iowa, and northern Missouri, is going to be problematic.

The good news is that the snow should end overnight, so hopefully roads will be clear and travel will be OK but the Monday morning rush. It will be cold, though, with near-record temperatures

Note: this is old and the Winter Storm Watch has been extended to the west and south to include Chicago.

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Thursday, November 8, 2018

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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