Thinking about weather/#climate #records

People love sports analogies. Maybe that’s why talking about weather records – be it record lows, record snow, whatever – gets a lot of press and attention. Sometimes it’s warranted, a lot of times it is (Surprise!) exaggerated and, almost always, reported out of context. The series of winter storms causing so much disruption across the US right now are certainly severe … here’s the current snow cover map, and forecast additional snow over the next 48 hours …

Snow Cover (blue) as of this morning (16 Feb 2021)

But just how “record breaking” is it? Let’s take a quick look at one weather station in Texas and try to get some context. Since we’re talking about the US, we’ll use medieval measurement units related to the FFF system 😛 …

Here is an excerpt from the official daily climate report from the NWS office in Houston, for Houston International Airport yesterday (Monday the 15th):

000
 CDUS44 KHGX 160849
 CLIIAH
 CLIMATE REPORT
 NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
 249 AM CST TUE FEB 16 2021
 ……………………………..
 …THE HOUSTON INTERCONTINENTAL CLIMATE SUMMARY FOR FEBRUARY 15 2021…
 CLIMATE NORMAL PERIOD: 1981 TO 2010
 CLIMATE RECORD PERIOD: 1892 TO 2021
 WEATHER ITEM   OBSERVED TIME   RECORD YEAR NORMAL DEPARTURE LAST
                 VALUE   (LST)  VALUE       VALUE  FROM      YEAR
                                                   NORMAL
 ………………………………………………………….
 TEMPERATURE (F)
  YESTERDAY
   MAXIMUM         25   3:10 PM  83    1962  66    -41       67
                                       1990
                                       2000
   MINIMUM         16R  7:26 AM  18    1905  47    -31       40
   AVERAGE         21                        56    -35       54

That “R” next to the minimum means it is a new record. So … using the period 1892 to 2021 as the period of reference, the low temperature Monday set a new record for the 15th of February at 16 degrees. The old record was 18. In media headline terms, RECORD LOW IN HOUSTON!!! LOWEST TEMPERATURE IN OVER ONE HUNDRED YEARS!

But … if you read down a bit you will see the record for the 16th is 13 degrees, and if we check the 14th, the record was 10 degrees F (yes, ten!). So in that context, 16 is really cold but not so bad. Plus or minus a day in climate terms is no big deal, so for context you have to look at a couple of days either side of a record to see. In my global data archive I have daily records for thousands of stations since the mid 1970’s (that is the beginning of somewhat regular satellite data which is important in my research). Looking at Houston Intercontinental, we see that the twenty coldest temperatures since 1973 are:

     dtg         | lotempf 
 ---------------------+---------
  1989-12-24 00:00:00 |       7
  1989-12-23 00:00:00 |       7
  1983-12-25 00:00:00 |      11
  1989-12-25 00:00:00 |      11
  1983-12-26 00:00:00 |      11
  1982-01-11 00:00:00 |      12
  1985-01-22 00:00:00 |      16
  1985-01-21 00:00:00 |      16
  1989-12-22 00:00:00 |      16
  1979-01-03 00:00:00 |      17
  1979-01-02 00:00:00 |      17
  1983-12-27 00:00:00 |      18
  1983-12-31 00:00:00 |      18
  1977-01-20 00:00:00 |      18
  1977-01-11 00:00:00 |      18
  1977-01-10 00:00:00 |      18
  1983-12-24 00:00:00 |      18
  1977-01-19 00:00:00 |      18
  1983-12-30 00:00:00 |      19
  1976-11-30 00:00:00 |      19
 (20 rows)

So a low of sixteen is in fact pretty cold – now in the top 10 years since 1973, and the coldest mid February temperature since 1981 when there were a couple days that hit 20F.

In technical terms, this is the danger of looking at the tails of distributions, because of the way weather works with systems spanning several days, there is correlation between days, and gaps in the extremes.

So, yes, it’s cold. Yes, it’s disruptive (even though it shouldn’t be, but that’s a different rant). It’s hazardous or even dangerous if you don’t exercise some common sense and take some precautions. But while extreme, I think calling it “once in a lifetime” is probably a bit overblown, given the 1989 Christmas cold snap with a week of lows below 20F. As with most things, context is everything.

Final note – during these kinds of extreme weather events, especially with power outages, please keep an eye on your neighbors (especially the elderly and those with health issues or disabilities) to make sure they are safe. Bring animals in for sure, and consider helping with projects that try to shelter strays. Given icy roads, DON’T DRIVE ON THEM IF YOU DON’T KNOW WHAT YOU ARE DOING! And if you grew up in the south, be realistic: you don’t know what you are doing!!

Oh, and a reminder: WINTER STORMS DON’T HAVE NAMES!