Tuesday, September 3, 2019

Smoking Hot Start to September

If you are one of the few readers of this blog who are into summer heat, you may have liked the start of September.  For the rest of us, it was an extreme continuation of meteorological summer.

The Salt Lake City International Airport observed record highs on Sunday (Sep 1, 100˚F) and Monday (Sep 2, 98˚F).  Sunday's 100 tied the all-time record for September, set on Sep 8, 1979.  To give an idea of the geographic breadth of the heat, Denver also set an all-time record for September on Sunday (98˚F), then broke it again on Monday, when they reached 100˚F for the first time ever in September. 

About the only positive thing I can say is that at least the sun angle is lower, the day shorter, and the night longer.  As a result, the sun rises later and sets earlier, leading to a later temperature rise in the morning and an earlier temperature fall in the evening.  For example, compare July 12th (top figure below) and September 1st (bottom figure below), both of which reached 100˚F at the airport.  The temperature rise on July 12th begins at about 7 AM, whereas it starts around 8 AM on September 1st.  At 8 PM, it's still about 96˚F on July 12th, but only 87˚F on September 1st. 

I've just cherry picked a couple of days there, but in general, extreme heat is not as difficult to tolerate in September due to the fact that we've already survived a hot summer, but also the day length is shorter. 

Of course, we have a saying in meteorology, All Generalizations are Wrong, and last night provided a great example.  Clouds overspread the area and although temperatures fell relatively early in the day compared to July, that cloud cover kept temperatures elevated all night long.  Note how through 8 AM most of the observations were above 80˚F. 

So far, the minimum for the calendar day is 79˚F.  If that were to hold, I think it would be the highest minimum ever observed at the Salt Lake City International Airport in September, and by a fairly wide margin.  The previous record if my inspection of prior observations is correct appears to be 76˚F, set on September 2, 2013.  The all time record high minimum at the airport is 81˚F set on July 18, 2016.

However, to be a record, that temperature needs to hold through midnight standard time.  Two things could happen to lower it.  One is that a shower or thunderstorm causes cooling.  The other is that we simply cool off radiatively to a lower temperature before midnight standard time. 

Time will tell if another record will fall.  Regardless, it has been a smoking hot start to September and meteorological fall.

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