Monday PM commute + winter recap + historic Feb. 2018

After several nice spring-like days in a row, Monday and Tuesday are going to flip back to a taste of winter. NWS has put out a sneaky Winter Weather Advisory for tomorrow, and the outlook there calls for 2-4” of wet, heavy snow in the late afternoon and evening. That looks overdone according to almost everyone/everything else, and I’d take the under. 2-4” might be a good range for the far northern suburbs while 1-2” looks like a good possibility for most of the area north of I-80. And it could come down at a heavy clip during a brief window near/during the PM commute after starting as all rain earlier in the day. Temps will be mild (near 40 early in the day to low/mid-30s later) so the roads should be decent.

 

Another shot at some minor snow comes through on Tuesday, but beyond that the week looks quiet if a little on the chilly side.

 

Also, there is another major Nor’Easter that looks likely to develop mid-week and impact most/all of the big cities along the East Coast. Just a heads up for anyone with travel plans because the airports could be backed up for a day or two. (There could even be a third major Nor’Easter about a week from now, but that’s pretty far away and needs to be monitored.)

 

 

******

 

Much like the man who drowned in the river that was one foot deep on average, the winter of 2017-18 was average…with some incredible swings along the way.

 

Figures are for meteorological winter (Dec.-Feb.) data at O’Hare.

 

• The average temp (a simple/dumb average of daily highs and lows) was 26.9 degrees, warmer than the 30-year average of 26.4 degrees.
• The warmest (66 on 2/20/18) and coldest (-9 on 1/2/18) temps were typical.
• 37 of the 90 days failed to break 32F for a high.
• 30.2 inches of snow fell, compared to the average of 28.1.
• We recorded three days with thunderstorms, 7 days with rain, and 33 days with snowfall.

 

Not mentioned in those summary figures was the epic cold snap that ran from late December into the second week of January. As mentioned previously, that was – by subjective but reasonable standards – among the coldest three or four two-week spells in Chicago history. January then went on to record five days with temps >50F for only the second time ever. And February…

 

***********

 

I recently wrote to the Tribune/WGN team asking about the historical significance of our February 2018 precipitation. My hunch was that we had never before had a month with both 20+ inches of snow and 4+ inches of rain. And by rain I meant “pure rain,” not just liquid equivalent. (For official measurement purposes, NWS records precipitation as the sum of rainfall and all frozen precipitation melted down to water.)

 

Here’s the question and their response:

 

Dear Tom,
How many months in Chicago’s weather history have recorded 20-plus inches of snow and 4-plus inches of rain? I would think that February 2018 is very rare, if not one of a kind!
— Phil Ordway
Dear Phil,
We had Chicago climatologist Frank Wachowski check concurrent monthly snowfall and liquid equivalent precipitation totals, which date to the winter of 1884-85, and while not unique February 2018 is just the seventh month to record 20-plus inches of snow and 4-plus inches of liquid equivalent. Keep in mind that the melted snowfall water content is included in the monthly precipitation total, so to date, this February’s 20.3 inches of snow contributed 1.73 inches of liquid-equivalent precipitation. The other six months that fit the bill are Januaries of 1918, 1999 and 2005 and Decembers of 1973, 1978 and 2008.
February 2018 is just the seventh month to record 20-plus inches of snow and 4-plus inches of liquid equivalent.

 

http://wgntv.com/2018/02/25/months-in-chicago-with-20inches-of-snow-and-4-inches-of-rain/

 

So as you can see, they kinda missed the point – everything in that response refers to liquid precipitation, not just rainfall. My idea was that the combination of massive snowfall and “pure” rain within the same month is exceedingly rare. It takes a lot of moisture and massive swings in temperature to get that much snow and that much rain in the span of just a few weeks.

 

The reason I asked them is that (a) it’s a lot of work to comb through the data, and (b) Frank Wachowski has access to continuous data (including actual rain as well as liquid equivalent) at Midway Airport dating to 1928, and unfortunately that data is not available to the public.

 

As a consolation prize we did confirm that February 2018 was unique among all Februarys in recorded Chicago history, but the other six events in December and January beg the question. So using their seven months of 20+ inches of snow and 4+ inches of liquid equivalent, we have the following list of months with >20” of snow, ranked by liquid equivalent:

 

Rank			Snowfall (in.)	Liquid Equivalent (in.)
1	December	2008	21.9	5.77
2a	February**	2018	21.8	5.46
2b	February*	2018	20.3	4.64
3	January	1999	29.6	4.47
4	December	1973	26.0	4.32
5	January	1918	42.5	4.12
6	December	1978	31.4	4.11
7	January	2005	27.8	4.00
	* Full month February 2018 at O'Hare Airport
	** Month-to-date as of February 25, 2018 at Midway Airport, according to Wachowski. The last three days of the month didn’t much much/any rain.

 

So the only month that compares is December 2008. The snowfall total was pretty close to what we had in February 2018, but the total liquid-equivalent precipitation was a good bit higher at O’Hare in December 2008. To my point, though, December 2008 saw more of its precip fall as snow – it was just a wetter variety of snow than we saw  in February 2018. Unfortunately we don’t have the rain and snow components of liquid-equivalent in 2008, but if we eliminate the snow-only and rain-snow-mix events to focus just on the all-rain storms, December 2018 had just 1.94 inches of “pure” rain.

 

As with all things – especially with regards to the weather – questions of measurement and accuracy render many compares to the realm of the arbitrary. But if we use 20 inches of snow as the cutoff for a snowy month – fewer than 8% of all snow-producing months hit that threshold – we can see that February 2018 was truly unique for February and second only to December 2008 overall.

 

 

 

Climatological Data for Chicago Area, IL (ThreadEx) - December 2008
Date	Temperature				HDD	CDD	Precipitation	New Snow	Snow Depth
	Maximum	Minimum	Average	Departure						All rain
12/1/2008	33	21	27	-5.7	38	0	0.42	2.7	3	no
12/2/2008	35	21	28	-4.3	37	0	T	T	2	no
12/3/2008	38	20	29	-2.8	36	0	0.09	1	2	no
12/4/2008	22	12	17	-14.4	48	0	T	T	2	no
12/5/2008	23	7	15	-16	50	0	T	T	2	no
12/6/2008	32	13	22.5	-8.1	42	0	0.02	2.1	2	no
12/7/2008	20	4	12	-18.2	53	0	T	T	2	no
12/8/2008	38	16	27	-2.8	38	0	0.02	0	2	0.02
12/9/2008	38	25	31.5	2.1	33	0	1.47	2.6	4	no
12/10/2008	29	18	23.5	-5.6	41	0	0	0	3	0
12/11/2008	32	17	24.5	-4.2	40	0	0	0	3	0
12/12/2008	21	11	16	-12.4	49	0	0	0	3	0
12/13/2008	39	19	29	0.9	36	0	0.19	T	0	no
12/14/2008	50	31	40.5	12.7	24	0	0.18	0	0	0.18
12/15/2008	31	5	18	-9.5	47	0	0.07	0.1	0	no
12/16/2008	22	6	14	-13.3	51	0	0.31	4.8	0	no
12/17/2008	20	6	13	-14	52	0	T	T	4	no
12/18/2008	23	3	13	-13.7	52	0	0.06	0.3	3	no
12/19/2008	32	22	27	0.5	38	0	0.59	2.4	4	no
12/20/2008	31	17	24	-2.3	41	0	0.05	1.4	4	no
12/21/2008	16	-6	5	-21.1	60	0	T	0.1	6	no
12/22/2008	7	-4	1.5	-24.4	63	0	0	0	4	0
12/23/2008	34	7	20.5	-5.2	44	0	0.27	3.8	4	no
12/24/2008	34	6	20	-5.5	45	0	0.18	0.4	7	no
12/25/2008	24	0	12	-13.4	53	0	0	0	6	0
12/26/2008	52	24	38	12.8	27	0	0.09	T	6	no
12/27/2008	61	32	46.5	21.5	18	0	1.74	0	0	1.74
12/28/2008	32	24	28	3.1	37	0	T	T	0	no
12/29/2008	43	29	36	11.2	29	0	0	0	0	0
12/30/2008	40	24	32	7.4	33	0	0.02	0.2	0	no
12/31/2008	24	11	17.5	-7	47	0	T	T	0	no
Sum	976	441	-	-	1302	0	5.77	21.9	-	1.94
Average	31.5	14.2	22.9	-4.8	-	-	-	-	2.5
Normal	34.8	20.7	27.7	-	1155	0	2.25	8.2	-

 

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.