Chicago Severe Weather Updates

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 25^th) based on historical experience. (I’d put our odds this year a little higher.)

· Fun fact! Most people know that the solstice (December 21^st 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 8^th, 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.)

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Saturday, December 10, 2016

Re: Winter Storm Warning

Last update as the storm arrives and snow is overspreading the region. It arrived a little ahead of schedule and roads are already covered in the western and some northern burbs. The models continue to take totals up and this storm looks more impressive by the hour. Snowfall will be more or less continuous for the next 24 hours with only a short break or two. I would take the over on 6" at both airports and it would not be a surprise to see a few spots hit 12".

On Dec 10, 2016, at 11:51 AM, Philip C. Ordway <pordway@anabaticllc.com> wrote:

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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Winter Storm Warning

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.
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.

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

We are in the heaviest snow bands now. Biggest problem is low visibility -- below 1/4 mile in many places. Airport delays will pile up. Side roads may have a covering but main roads will remain wet and slushy. Ground is covered in many suburbs with 1/2" to 1" but I noticed it is barely sticking at Soldier Field. In any case the snow will move out by sunset. Expect another 1/2" to 1" in "hardest hit" areas. (Exception would be way out in Dekalb where snow is legit and NWS upgraded to WSW.)
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Saturday, December 3, 2016

First snow

We have only had a trace of snow so far this season but that looks likely to change. It has also been exceptionally mild but that is also in the rear view mirror.

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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