When Tmax and Tmin Are Poor at Describing Weather

Last Sunday was a miserable day in Rockhampton- overcast with drizzling rain and cold all day.  Mean maximum for October is 29.7 degrees, so the maximum reported by the Bureau of 20.4 was 9.5 degrees below average, as expected.  However, that does not tell you anything like the whole story.

Here is the temperature graph from the Bureau for the period midday Saturday to midday Tuesday.  The solid horizontal line shows the duration of Sunday 23rd, and the thin black vertical lines show 9.00 a.m., which is the time when the daily minimum and the previous day’s maximum are recorded.   Temperatures at recording times are circled.


On fine, clear days, minima usually occur around sunrise and maxima in the early afternoon: you can see this on the 22nd, 24th, and (almost) on the 25th.  Sunday 23rd was wet.  As you can see the temperature was falling fairly steadily from Saturday afternoon until Monday morning.   The maximum for Sunday was 22.7 at midnight, and the coldest temperature on Sunday was 14.3 from 7.30 p.m. to 9.00 p.m. on Sunday night- not the 17.6 at 9.00 a.m.   The official maximum for Sunday of 20.4 degrees was actually the temperature at 9.00 a.m. on Monday!

So what was the Diurnal Temperature Range?  Was 20.6 (or 22.7) a good representation of how high the temperature “rose”?  The temperature in the early afternoon varied between 15 and 16.4, and this was about 14 degrees below normal for this time of the year (and two to three degrees below the official lowest maximum of 18.1 on 10th October 1982).

Which is one reason I don’t take a lot of notice of claims of hottest or coldest extremes.

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4 Responses to “When Tmax and Tmin Are Poor at Describing Weather”

  1. ngard2016 Says:

    Ken, what do you think of Werner Brozek’s monthly update for the various temp data-sets. He uses Nick Stokes’ software to calculate the trends. The two satellite data-sets show no stat. significant warming for 23 years 1 mth and 22 years 3 mths. Also the older HAD 3 surface data shows no stat sig warming for 19 years and 8 months. Here are the results in his words.

    “On several different data sets, there has been no statistically significant warming for between 0 and 23 years according to Nick’s criteria. Cl stands for the confidence limits at the 95% level.

    The details for several sets are below.

    For UAH6.0: Since September 1993: Cl from -0.002 to 1.801
    This is 23 years and 1 month.
    For RSS: Since July 1994: Cl from -0.033 to 1.800 This is 22 years and 3 months.
    For Hadcrut4.4: The warming is statistically significant for all periods above three years.
    For Hadsst3: Since February 1997: Cl from -0.029 to 2.124 This is 19 years and 8 months.
    For GISS: The warming is statistically significant for all periods above three years”

    Here’s the link. https://wattsupwiththat.com/2016/10/26/hadcrut-adjustments-and-the-1-5c-tipping-point-now-includes-september-data-except-for-hadcrut/

  2. ngard2016 Says:

    Ken what do you make of the USCRN data? This is supposed to avoid any problems of the UHIE. But it only started in 2005. But how does it compare with GISS for USA since that time, so far as temp and trend etc?


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