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. 

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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. 

Winter Storm Warning

Late yesterday the track of the storm did turn south, and last night we were upgraded to a Winter Storm Warning. There are a lot of caveats here, but the potential for sticking snow has increased dramatically. The Warning is in effect from 9pm tonight (Friday) through 3pm Saturday for the entire area north of I-80. (Thankfully the evening commute should have no effects.)

For starters, do not fall victim to the "OMG we're going to get a foot of snow" hysteria some people will undoubtedly start spewing. The 7-11" totals referenced in some forecasts, including from NWS, are both somewhat unlikely (in my opinion) and not applicable to the vast majority of people in the forecast area. 

What is clear is that there will be a sharp gradient from the NW to SE along which snow totals will decrease rapidly. Areas near DeKalb or even as close as Kane and McHenry counties have a decent shot at 6+ inches of snow. For the vast majority of the area's population it gets trickier and snow totals will almost certainly be well below that. 

Clouds will thicken this afternoon and precip will start as rain before potentially switching to snow tonight as we approach midnight. The best bet for now:

• 6+ inches of snow for far western and northern suburbs (Kane, McHenry, Lake)
• 3-6" for Dupage and far NW Cook, decreasing rapidly to the SE
• Trace to 2" for areas in Cook and Lake that are within 10 miles of Lake Michigan, including the entire city of Chicago. (I think for the core of the city-- within 2-3 miles of the lake -- there is a 30-40% chance that the snow never really piles up. It is hard to see much more than a couple of inches even if it does accumulate. )

For context, the difficulties with this type of storm are worth noting.

• An earlier or later shift from rain to snow -- a transition that is very hard to pinpoint -- can dramatically alter snowfall totals.
• The ground is still warm after a very mild fall. Even getting the atmospherics right might not be enough to get the snowfall totals right if the snow melts before accumulating. 
• The warm ground effect is amplified in the city. 
• The surface water of Lake Michigan is still near or above 50 degrees (10-12 degrees warmer than at this point last year), and winds initially blowing off the lake could well keep the precip in liquid form over much of the city. 

Miscellaneous:

• Should a 6" snow be recorded officially at ORD, it would be very rare -- it's only happened twice in Chicago (and four times in Rockford) since the late 19th century. 
• It has been 238 days since our last measurable snowfall in Chicago, which is slightly above average. 
• Temps will rebound into the 40s and 50s next week, so any snow won't last long. 
• No major storms are on the horizon here for holiday travel next week. 

snow possible

A storm lifting out of the Plains could impact the area beginning tomorrow (Friday) night through Saturday afternoon. A Winter Storm Watch has been posted for areas well west and north of Chicago, where 5-8" of snow could fall. I think far less than that is likely in and around Chicago, and I'll generally take the under on everything I've seen so far. A wind off the 50-degree lake water is likely to keep the precip as mostly or all rain in Cook County and south of I-80. Additionally, the ground is still warm which won't help accumulations. Western and northern suburbs could see a dusting to maybe 1-2" if things come together, with the switch to snow only happening on the backside of the storm Saturday morning/afternoon. A slight shift to the south or an unexpected intensification could change things, but for now the accumulations and impact look very modest for the city of Chicago, moderate at worst for most suburbs, but potentially substantial for areas well west and north (e.g., Rockford). I will only send an update if something changes and significant accumulations become likely for the Chicago area. 

And to pre-answer the question, this potential snow is behind schedule. The average date of first flakes is November 1st, and the average date of measurable snow is November 15th -- we've had zero snow so far this year. The season overall has been very mild, and beyond this cold over the weekend things look seasonal (although not as balmy as they have been). And for comparison, last year on this date the high temperature was 19, with a low of 9. 

Heavy rain possible

After a glorious day, clouds will fill in tomorrow (Monday) and rain will develop by Monday night or Tuesday morning. Some projections are pointing to 3" of rain, with more than that possible under some isolated thunderstorms. There is a chance that we'll need to back off those totals, but it's still a good idea to check gutters and downspouts for leaf blockages. Tuesday is likely to be a washout. By late week we'll be back toward more seasonal highs in the 40s.

In other news, enjoy these 50s and 60s -- a year ago right now we were going into one of the coldest ever weeks in November history with highs were in the 20s and low 30s. On Wednesday we have a good chance to crack 60; that date last year saw a high of 19.

Severe storms

We are under a severe thunderstorm watch until 11pm and a line of severe-warned storms is approaching rapidly from the west. Warnings may be issued for our area between 8:30 and 10:00, give or take. The main threat is winds gusting 60-70. These storms have a history of tornadoes and wind damage but they are weakening and not very impressive overall.

High winds 30-45 mph will continue on the back side of this massive system through tomorrow. Temps will fall into the 40s but the weekend should be nice with daytime temps in the 50s to near 60 and lots of sun.