more record warmth

Many of you will remember the string of 80s we had in March 2012. At the time it was called – with good reason – perhaps the most anomalous stretch of weather in Chicago history.

 

But what we’ve seen this past week is just as crazy.

 

• We’ve recorded four-straight record highs.
  • One of those records stood since 1880.
  • We broke each of the previous records by seven, eight, four, and six degrees, respectively.
  • We’re very likely to set another record tomorrow (Wednesday). Another record today (Monday) isn’t as likely but it is certainly possible.
  • We’re likely to have a string of six days with temps of at least 60 degrees, and three of them will likely have topped 70 degrees.
    • That string of six-straight days of at least 60F will set the all-time record for winter (Dec-Feb).
  • Our 70-degree high on 2/18/17 was the second-earliest 70 ever recorded here. (70 on 2/11/90 was the only one earlier.)
  • Our 66-degree high on 2/17/17 was the fourth-warmest day at that point in the year.
• Through Feb. 20^th, three of the top five warmest temps since 1871 were recorded this weekend (2/18 – 2/20).
• There are a total of 4,117 February days in Chicago’s recorded weather history, and five of them had temps in the 70s. That is a 0.12% (12 basis point) historical occurrence (and about 3 sigmas of standard deviation if you believe that the atmosphere’s temperatures are normally distributed, that 4,117 days is an appropriate sample, etc.). And of those five days, two of them were this weekend.
• The Friday-Sunday period saw several instances of Chicago temperatures that were higher than those in Los Angeles, Las Vegas, Phoenix, San Diego, etc. It appears that it is only the second time in recorder history that ORD had a higher February high temp than LAX.
• Our last 1-inch snowfall was on Dec. 17, 2016 -- we’re at 66 days and counting, breaking the previous record of 64 days.*
• And more broadly, we are going to set an all-time record for the only January-February period with less than 1” of snow. That’s never happened before and it is absolutely stunning. The previous record for the latest into a calendar year we’ve gone without at least 1” of snow was February 8^th. To make it through the entire January-February period is just crazy.
  • To contrast our current snow drought you only need to go back three years ago, when the January-February period of 2014 opened as the snowiest-ever with 53.2 inches.
• To give some further perspective, on Sunday we hit 70 degrees but exactly two years ago (2/19/15) the high temperature was 4 degrees. (We were on the way to tying the coldest-ever February in 2015. This year we’re likely to finish top-4 warmest.)

 

And it’s not over quite yet:

 

• Tomorrow (Wednesday) could see low- to mid-70s across the area. We need 75 to set the all-time record for the highest temp ever recorded in the month of February and in meteorological winter.
• But…we’re going to revert to something closer to normal by the end of the week. Friday could be a real soaker (1-2” of rain) ahead of a strong cold front that will drop us back into the 30s for the weekend.
• The first week of March could be cold (and by that I mean seasonable, with temps in the 30s) and potentially active with 1-2 storms passing near Chicago. We’ll likely be right on the rain-snow line for major storms so any snow will be especially hard to forecast more than 1-2 days in advance.
• Historically, snow is very likely from this point forward.
  • There is a >90% historical rate of occurrence of >1” of snow from this date forward.
  • March is our fourth-snowiest month, averaging 5-6”.
  • Historically, only ~15% of winters saw their last two-inch or greater snowfall occur before February 15^th, and the average for the last two-inch or greater snow was March 10^th.
  • March has produced big snows – two of the top 10 biggest snowstorms in Chicago history occurred in March.
  • On the flipside, there have only been nine years since 1958 – yes, an arbitrary cutoff – that saw more than 6” of snow after Feb. 20^th.
• To be clear, there is actually nothing in the models that shows a prolonged period of below-normal temps – even the colder periods ahead are projected to be 2-8 degrees above normal.
• The other good news is that sunlight is way up (solar radiation is two-thirds stronger than it was on Dec. 21^st solstice, and we’ve added almost two hours of daylight) and any snow that does fall is very unlikely to make it more than a couple of days before melting.

 

The usual caveat applies regarding the varying location of the official records in Chicago.

 

* There is some dispute about the winter of 1888-89 and a snow drought that year that may have lasted 83 days. Limiting ourselves to the more reliable measurements that were taken (mostly) away from the Loop and Lake Michigan during the 20^th century, the record is 64 days: Dec. 3-Feb. 4, 1905-06, and Dec. 23-Feb. 24, 1953-54

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