Warning extended to 3pm

Our Winter Storm Warning has been extended to 3:00. So far the precip has tended to the heavy and frozen side, with many if not all locations reporting sleet, freezing rain or a mix. Accumulations are minor but meaningful, with many streets (even busy expressways) covered in a layer of ice/slush. Traffic is slow but volumes are light.

Thankfully the precip will trend toward all rain by late afternoon, with temps rising several degrees. But winds will pick up and that could result in power outages in places with ice accumulations.

Winter Storm Warning

NWS has just upgraded the whole area (except for far southern areas) to a Winter Storm Warning. This is a marginal storm but it may present some problems tomorrow morning.

Overnight toward dawn an area of snow and freezing rain will spread north. Snow totals will be light (1-3") in a few affected areas, but there could be an accumulation of ice. And is VERY tough to forecast freezing rain. A difference of just 1-2 degrees at the surface could lead to all snow, all freezing rain, or a mix. I think warm lake waters and ground in the city will lead to minimal snow and ice accumulations in the city and most of Cook County. But areas west and north could see meaningful ice as well as some snow. Pre up should switch to rain tomorrow morning into the afternoon, and by the evening commute things look better. Very high winds (40-50 mph) could lead to lakeshore flooding, isolated power outages, and flight delays.

Temps will be seasonal this week -- mostly 20s and 30s, sliding about 10 degrees into the first genuinely wintry air by New Year's Day.

Solstice + severe threat

In a truly unusual twist, we're talking about the winter solstice and the threat of severe thunderstorms at the same time. 

We celebrated (or not) the winter solstice last night at 10:48pm local time. We've already had the earliest sunset (Dec. 8th), and even though the sunrise times lag for a little bit (adding three more minutes until Jan. 10th), we'll start to add to each day's length from here. 

Tomorrow we're likely to have our 10th day of 50+ temps in Chicago this December, which is stunning (although the record is 16). Tomorrow could see see highs of 60+ in many locations, nearly 30 degrees above normal and threatening the record high for the day. 

Along with tomorrow's mild temps will come a flood of moisture -- dew points will be in the 50s, so it really will feel like March or April -- and a cold front behind the warm-up will threaten to spawn some strong or even severe thunderstorms. The primary threat is well to our south, and the mid-South could even see a tornado outbreak. Areas here or nearby could still see damaging winds in legitimately severe storms. In any case, high winds are likely along with the rain, so airport delays are possible.

Behind the storms skies will clear and temps will fall but remain ~10 degrees above normal. Both Christmas Eve and Christmas Day look partly to mostly sunny with highs in the low/mid 40s. 

There are no major cold-air outbreaks on the horizon for now. A few long-range models are trying to pick up some cold in the first week of January, but that's too far away to have much reliability. In general, there are no pending signs of a major pattern shift. 

snow for morning commute, then mild

A quick burst of snow looks likely late tonight and into the morning commute tomorrow. Accumulations should be fairly minor, but given the timing, during the height of the morning rush, even an inch of snow could have a significant impact on travel times. 

Beyond that, a very mild December pattern is shaping up. Temps are likely to break 50 later this week and into the weekend. No major intrusions of cold air are on the horizon and the month may actually get milder as we go. 

email/blog problems + storm recap + Thanksgiving + El Nino

Email updates and blog

I've heard from more than a few of you that these emails have gone missing, so I'm sending this twice. You should be getting it once from my email address and once from the blog ("Admin@....") if you've accepted the invitation to the Google Group. Since the emails got unwieldy I switched everything to the blog and the Google Group. You have to accept the invite from the Google Group to get the updates -- I'm not sending them from my email address anymore. (You can always go to the blog anytime if you think you've missed an email.) And please check your spam/junk folder because I imagine some of you are having that problem. If you still don't get them email me and I'll resend the invite from the Google Group. 

Storm recap

The Friday/Saturday storm was one for the record books (see below). Looking back at the forecasts, they were pretty good. Specifically, the core of Chicago got ~1" that melted quickly, right in line with the forecast. Many suburban areas got 4-6" so that also checks out. But things were definitely understated on the high side, as the high probabilities of >6" clearly did not point to the 8-16" that came down in some spots. It is hard to overstate how unusual that is -- especially in the third week of November -- but in any case, the forecast was clearly off in that regard. 

To highlight another aspect of this storm, downtown Chicago saw about an inch of snow while areas within the same county saw more than a foot. That is a massive dispersion even by Chicago standards. The heavy bands of snow targeting the N/NW suburbs were understated, but overall this was an impressively accurate forecast for such a complex, messy, and unusual storm.  

Officially, ORD recorded a storm total of 11.2" which is very impressive and #2 all-time for November (with the usual caveat about shifting record locations over the years). Chicago normally sees a storm with that much snow once every 3-4 years, and in November it is almost unprecedented. Other official tallies included 5.8" at Midway and 4.7" at NWS in Romeoville.

New records established, from NWS:

• A record maximum daily snowfall was set for November 20th for Chicago as 4.2 inches fell.  The previous record was 2.8 inches set in 1996.
  
• A record maximum daily snowfall was set for November 21st for Chicago as 7.0 inches fell.  The previous record was 3.0 inches set way back in 1893. (The 7" also makes it the third-snowiest calendar day ever recorded.)
  
• There had been zero flakes of snow recorded in Chicago before this major storm, and it goes down as the biggest-ever first snow of the season. 

• 
  

To give a little more perspective, the 11.2" just recorded at ORD is nearly one-third of the average for a full year of snow and it was higher than the average snow in any given month. Along those lines, and especially with December setting up mild at least from this distance, there is a chance that November will go down as the snowiest month of the 2015-16 winter. That has only happened once, in 1940. 

Thanksgiving

Temps today and tomorrow will stay in the 30s, although the sunshine will help melt some snow. Clouds will gather on Wednesday as temps warm into the 40s. Thursday looks wet with temps in the mid 50s. Details are tough at the point, but we could see quite a bit of rain, which would obviously create a lot of messy runoff. Email me if you have travel plans or need more specifics as the time approaches. The good news is that major travel delays look unlikely -- there are no large systems hitting any of the major airports on Wednesday/Thursday. 

El Nino

El Nino remains at record levels for now, and while mid-range forecasts are notoriously unreliable this is worth noting. The numbers are almost literally off the chart and in strong agreement regarding extreme December warming across much of North America, especially the northern tier of states. Nothing is written in stone, of course, but this is stunning:

Snow update

As of 12:30 snow totals are already toward the high end of the range from yesterday. And now a strong plume of lake-effect is sliding through the area. See the image below -- the darker green and yellow radar returns indicate near white-out conditions. Expect treacherous conditions for the next few hours in the affected areas. Snow should taper by mid/late afternoon.

Totals so far are near a foot far NW to 1-2" (since melted to bare ground) in the city along the lake. Officially:

@NWSChicago: Snowfall totals so far from the Airports as of Noon....
O'Hare... 7.1"
3 SW Midway... 3.5"
Rockford... 8.6"
Romeoville... 3.3"



KLOT - SuperRes Reflectivity Tilt 1 12:30 PM

snow update

A quick update as this storm comes together -- it's actually pretty impressive. 

No significant change to the outlook for the city and especially downtown. A couple of inches would be toward the high end. Warm pavement and the warming effect of the lake could keep precip more to the liquid side and/or limit accumulations. Rain will eventually shift to snow and it might look impressive at times, but it's not likely to pile up.

To the west, however, conditions look like to deteriorate more than previously expected. The center of the low continues to intensify and drive south. The axis of heaviest snow -- which has laid down more than a foot in Sioux Falls, SD and across portions of Iowa -- may now target northern Will County, DuPage, portions of Kane, and far W/NW Cook County. The same NEward gradient exists, as snow rates will fall as you travel to the SE (especially in areas within a few miles of the lake). Warm surface temps (near or just above 32F) also give me pause.  But there is growing confidence that very strong snowfall rates (well above 1" per hour) will overcome other factors. Many suburban areas could see 4-6" of snow. Some of the probabilistic models (see below) really like the odds for >6" in the darker oranger and reddish areas. 

No major change to timing. The rain will commence after sunset, with a transition to snow near midnight. The heaviest snow will fall between midnight and mid-morning, with the snow tapering after noon.