Severe weather updates and forecasts for the Chicago area. Updated as needed for severe or disruptive weather conditions.
Saturday, December 17, 2016
One more weather update
A couple of inches of snow last night has moved on and today through sunset should be mostly dry. There could be some freezing drizzle and there have been reports of icy roads so exercise caution. And snow reemerges in the 4-7pm range. Another 2-4" is likely tonight (less south of I-80, more toward Wisconsin line)) along with howling winds that will cause blowing and drifting. Visibility could be briefly below 1/4 of a mile with poor road conditions. Officially we're under a winter weather advisory for snow and blowing snow as well as a wind chill advisory.
And temps are going to plummet. The high tomorrow (Sunday) will be at 12:01 AM and by daybreak we'll be near zero and still falling. Daytime temps are unlikely to break zero. Overnight into Sunday night and Monday morning we could hit -10 to -15F which could set a record (see below). And these are all actual air temps. The wind will be blowing 5-15 mph so it will feel colder, but wind chill is bogus and please don't confuse the too. If you'd like my full rant as to why wind chill is bogus please email me.
To show the fluky but powerful nature of these arctic outbreaks, here are the record low temps for each date. 1983 was a barbarically cold month so these comparisons are impressive.
Dec. 17: -1 (1951)
Dec. 18: -11 (1983)
Dec. 19: -14 (1983)
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Thursday, December 15, 2016
Cold, then snow/sleet, then cold, then pattern flip?
We bottomed out officially at O’Hare at -2F this morning. We didn’t set a record (-12F in 1901) but yesterday was the earliest high temp <10F in 21 years. So this is very unusual even if not actually record-breaking.
Temps are going to be stuck in the single digits today, but after sunset the winds will swing around to the south in advance of our storm and temps will actually rise throughout the night. Tomorrow (Friday) will see temps climbing toward the low/mid 20s, but snow moves in during the afternoon. Despite some absurd numbers I’ve seen floating around, there is not much threat for more than a few inches of snow tomorrow. But the timing (afternoon/evening rush on a Friday in December) combined with very cold temps/pavement could make for a traffic and airport nightmare. We’ve seen this before and it usually doesn’t end well.
Light snow is likely overnight Friday into Saturday as temps continue to climb. The storm total through Saturday looks to be about 3-4” but I would put at least a 2” margin of error on that. We are right on the edge of a big winter storm with very heavy snow likely just to our north in southern Wisconsin and freezing rain or sleet likely just to our south. It doesn’t take much of a shift to have a dramatic impact on the result.
By Saturday noon we could well top 32F for the first time in days, but the cost will be a threat of some freezing rain and/or sleet. Again, keep an eye on travel problems. Hopefully roads will be well treated, but any ice accumulations could obviously pose a big problem.
Temps will then plunge again on Saturday night, approaching or falling below 0F by daybreak Sunday. The daytime high on Sunday might struggle to break zero, and there is some chance we’ll set the record for the coldest Bears home game on record.
Beyond that, things look much milder in the 10-14 day range. We should get back to season normal toward the middle of next week and there don’t appear to be any more arctic outbreaks through Christmas and the week leading up to New Year’s Day. We could even average just above normal for that period.
Monday, December 12, 2016
Light snow, then bitter cold, then more snow?
We’re not breaking any records but we are certainly locked in to an unusually cold and snowy winter pattern.
· A cold front is approaching the area tonight and it will bring a dose of severe cold.
o First, we could see a brief burst of snow tonight that might accumulate an inch or so in some places (see below for one model’s projection). Don’t be shocked to wake up to a covering on untreated surfaces tomorrow morning.
· Temps will peak in the teens tomorrow and fall through the afternoon. We’ll be in the single-digits to near zero tomorrow night and likely at or below zero Wednesday morning and Thursday morning. Thursday’s high will struggle to make it out of single-digits.
· Friday and Saturday will “warm up” to the 20s, but the price will be a chance of another significant snow. Stay tuned for details but the Friday/Saturday period looks very promising for significant accumulating snow across the Chicago area.
· A second cold surge arrives Sunday. It doesn’t look quite as cold in Chicago as the Wednesday-Thursday variety, but we’ll see.
· To skip ahead, I’d reiterate two points.
o The reliability of long-range forecasts (beyond 10-14 days) is very, very low. The best indicators we have are the correlations to El Niño/La Niña conditions, and this year we essentially have neither.
o Really strong, persistent patters -- like the mild, sunny and dry pattern most of eastern CONUS had in the fall and the cold, snowy one now underway – are prone to sharp “flips.” Yes, there are short- and medium-range feedback loops, but there is nothing ensuring a cold winter just as there is nothing preventing us from a mild January/February.
Now for the fun facts everyone has been waiting for.
· Fun fact! Our season-to-date snow total officially at ORD is already over 14 inches and the highest since the barbaric winter of 1978-79.
· Fun fact! Our snow totals officially at ORD (6.4” last week and 7.8” this weekend) make this only the fourth time on record that Chicago has had two storms of >6” in the first two weeks of December. The most recent occasion was 2000 -- a month that saw a crazy total of 41.3” at MDW and 30.9” at ORD -- and the other two were 1978 and 1934. And no, none of those years are good analogs if you like mild winters!
· Fun fact! About 1 in 8 Americans will more than likely experience a subzero temp this week.
· Fun fact! The broadly-defined area around Chicago has about a 40% chance of a White Christmas (at least 1” of snow cover at 6am on the 25th) based on historical experience. (I’d put our odds this year a little higher.)
· Fun fact! Most people know that the solstice (December 21st at 4:44 AM CST this year) is the shortest day of the year (i.e., the day with the least amount of possible daylight, with the sun’s least direct rays in the northern hemisphere and the most direct rays over the Tropic of Capricorn). But because of the oddities of the earth’s elliptical orbit and the difference between solar noon and the time we keep on our clocks, the earliest sunset of the year has already passed (last week on December 8th, to be specific). We’ve already pushed the sunset back by a minute or so, and from here until June the sunset will get later each day. (For related reasons the sunrise will get later even beyond the solstice. This season the latest sunrise will be January 3, 2017.)
Saturday, December 10, 2016
Re: Winter Storm Warning
This email is confidential and intended only for the recipient(s). If you have received this message in error, please notify the sender at compliance@anabaticllc.com and delete this message and any attachments. This message is provided for informational purposes only and should not be construed as a solicitation or offer to buy any financial instruments. Please see the full disclaimer at www.anabaticllc.com.A little odd -- NWS took down the Watch overnight in favor of just a Winter Weather Advisory. But now we're back to a full Warning, and the snow totals haven't changed much. Best guess for totals through tomorrow night is 8-12" northern suburbs, 6-10" western burbs, and 3-6" southern burbs and Loop. There could be a brief break in the snowfall tomorrow which would drop totals by an inch or two.
Snow will start very late afternoon into early evening. It should be light until after midnight. The heaviest snowfall rates are likely tomorrow morning. After a potential break there could be more heavy snow tomorrow afternoon. Road conditions could be dicey at various points and airport delays will be substantial.
And if we get more than 6" officially at ORD that would be only the fourth time since official records began in 1884 that we've had two snowfalls of at least 6" in the first two weeks of December. The most recent occurrence was in 2000.
The arctic outbreak also looks on track for next week. After a relatively tranquil Monday and Tuesday temps will plunge on Wednesday and Thursday. Daytime highs will struggle into the teens and overnight lows will likely be subzero in many locations.
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N/a · N/A · Chicago, IL 60606 · USA
Winter Storm Warning
Snow will start very late afternoon into early evening. It should be light until after midnight. The heaviest snowfall rates are likely tomorrow morning. After a potential break there could be more heavy snow tomorrow afternoon. Road conditions could be dicey at various points and airport delays will be substantial.
And if we get more than 6" officially at ORD that would be only the fourth time since official records began in 1884 that we've had two snowfalls of at least 6" in the first two weeks of December. The most recent occurrence was in 2000.
The arctic outbreak also looks on track for next week. After a relatively tranquil Monday and Tuesday temps will plunge on Wednesday and Thursday. Daytime highs will struggle into the teens and overnight lows will likely be subzero in many locations.
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Friday, December 9, 2016
Winter Storm Watch -- heavy snow
NWS just issued a Winter Storm Watch for the entire area beginning tomorrow (Saturday) evening and running through Sunday night. It looks increasingly likely that we’re going to have an extended period of nearly continuous snow, and the totals could get pretty impressive. As we saw last weekend there is no such thing as certainty, but as things stand right now I wouldn’t be surprised to see widespread storm totals in the 4-12” range across the entire area (including the Loop and lakefront). As shown below the northern suburbs are favored for heavier amounts, with a mix possible south of I-80 and generally lighter amounts as you go south.
Expect significant travel disruptions, especially at the airports. The good news is that most or all of Saturday should be OK before the core of the snow moves in after sunset.
I would also expect an upgrade to a full Winter Storm Warning later today or early tomorrow morning. As the models refine their guidance for snowfall totals and timing I will also send at least one update.
Thursday, December 8, 2016
early look at snowy, cold pattern
So yes, last weekend’s snow in the western suburbs was a surprise.* That said, the coming 7-10 days have a much more pronounced pattern. The details are sketchy at this distance but it is going to be snowy and it is going to be cold.
Some flurries or light snow today will give way to slightly better conditions tomorrow, but temps will struggle to get out of the 20s or low 30s at any point. Outdoor hockey rinks will have ideal conditions to get established for the season.
On Saturday afternoon/evening we’ll have the first of several chances at snow. Again, details are tough at this point, but a few inches of snow is certainly possible through Sunday morning.
On Sunday night and potentially into Monday morning it gets even more interesting. One model (and the good one, no less) has picked up a potentially major snow storm. That model is an outlier and it is very early, but we’ll have to watch this one closely.
Either way, the odds strongly favor at least a few inches of weekend snow followed by a blast of bitterly cold air in the middle of next week. It looks likely that we’ll go near or below zero at night on one or two occasions next week, with some marginal relief after that. The good news is that the mid-range forecast (i.e., 2-3 weeks) shows a milder pattern coming back into control. But for now winter is really locked in for at least the next 10-14 days.
TSkillz/WGN:
* The snow that fell on Sunday was a surprise to me and most forecasters/models. The available moisture looked limited to 0.10-0.20 inches but in reality the storm pulled in 0.5 to as much as 0.7 inches in a few spots. That is a massive difference for a storm like that, although the point should not be lost that a third to a half an inch of rain really isn’t a lot and would have gone unnoticed had it fallen as rain. It’s also worth noting that the first snow system of any season often produces a perceived “bust” because the warm ground limits accumulations even if everything else verifies in the atmosphere. In any case, the storm’s lift was also more impressive than expected, enabling snowfall rates that overwhelmed the very warm ground and relatively mild surface temps that were at or above freezing. The precip also persisted for several hours longer than anticipated, allowing the snow to really pile up in a few place. And this was also one for the record books – we had had only a trace of snow coming into this storm, and the 6.4” at ORD and 5.5” at MDW set the record for the biggest-ever first measurable snowfall of the year. So this was a unique storm to say the least. The snow did not, however, accumulate meaningfully in the city near Lake Michigan. So while people in the western suburbs probably see this is as blown forecast, that’s only partially accurate. The forecast did fail to project the moisture content, but that happens – nothing is certain. Given the other variables involved (and the verified result in the city/lakeshore areas), I would view this as a moderate disappointment. If the odds – across the whole area -- called for an 80% chance of little/no accumulation, that means that 20% of the time (or over 20% of the area) there would in fact be meaningful snow. So even though I wish the forecast had been better and more helpful than it was, that is life – situations like this are going to happen.
Sunday, December 4, 2016
Snow
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Saturday, December 3, 2016
First snow
Tomorrow (Sunday) morning and area of snow will arrive and persist through the early to middle part of the afternoon. Air temps at the surface and the ground itself will be well above freezing so snow should melt quickly if not on contact. Official accumulations may reach a half inch to an inch in western areas but the roads will likely just be wet. Areas in the city will likely see no accumulations except on a few grassy spots.
So this is the definition of a non-event but since it is the first snow of the season and since I've seen some breathless "we're going to get 2 inches of snow!" comments, I thought I would send something.
Also, a warmup on Monday into the mid/upper 40s will he short lived. On Wednesday we'll sink below normal for the first time in a long, long time. Most of the following week will be cold. Nothing unusual for December but a big change from what we've had lately.
Two more chances for light snow will have to be watched midweek and next weekend.
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