Highs and Lows

The National Centers for Environmental Information (part of the National Oceanic and Atmospheric Administration(NOAA)) has a dataset of historical climate observations from thousands of stations around the world. Over 25,000 stations are active and their data is updated regularly. Historical data, at times going back over 100 years, is available for active stations as well as those no longer in service.

I decided to focus just on stations in the US. Specifically, stations (active or not) with at least 40 years worth of daily temperature (high/low) measurements. There are 5706 weather stations in the country that meet this criteria. A little more than half are still in use; some have reported data for nearly 150 years. Where are these stations? Glad you asked:

(Yeah, you’ll have to zoom in to see anything useful. Lots of stations!)

First I’ll look at the extremes. Let’s start with high temperatures – what are the warmest places? Well, first you have to define what you mean by “warmest”. There are several possibilities:

• “Average daily high temperature”. Calculate the average daily temperature for each of the 365 days of the year.¹Leap year days only occur one quarter as frequently as the other dates, so they complicate the calculations and thus are ignored Average these values. This provides the overall ‘warmness’ of the area, year-round.
• “Average temperature of the warmest day”. Calculate the average daily temperature for each of the 365 days of the year. Find the day that has the highest value, and use that temperature.
• “Average highest temperature”. For each year, find the hottest day. Average those temperatures.

I’ll use the first two of these (the last one seems kind of like cherry-picking, since you’re using the hottest day of the year no matter when it occurs).

As an example, let’s look at Santa Cruz, where I currently live. The Santa Cruz weather station has data going back over 125 years, to the 1890s. Looking at all of the reports, the average high temperature on January 1 is 59.4. On January 2 it is 59.2; January 3 is 59.8. Later in the year, on July 1 it is 74.6, and so on. Summing up each of the 365 days of the year and dividing by 365 gives an average daily high temperature of 69.06.

On the other hand, looking through those 365 averages shows that September 21 has the highest average temperature (77.3) so the average high temperature of the warmest day is 77.3 F (September 21st).

Using both techniques, here are the hottest places in the United States:

	Average Daily High (year-round)			Warmest Day	Average High
Death Valley SP, CA	91.3		Death Valley SP, CA	July 29	117.7
Gila Bend, AZ	89.5		Gila Bend, AZ	July 5	110.5
El Centro 2 SSW, CA	89.0		Overton, NV	July 14	110.4
Indio Fire Stn, CA	88.9		Needles AP, CA	July 14	110.1
Desert Resorts Airport, CA	88.8		Quartzite, AZ	July 13	110.0

No surprise that Death Valley is #1. After that, there are a lot of desert locations in California, Arizona, and Nevada. Here are the top few. Hovering over the marker gives you some details about the station.

What about daily highs in cold places? There are places in Alaska where the year-round Average Daily High is well below freezing (e.g., Barrow Post, 16.5 F). Excluding Alaska, Mt. Washington in New Hampshire has an Average Daily High of 34.1. Imagine, the hottest part of a typical day is just above freezing. Ooof. Mt. Washington also holds the mainland record for the coldest warmest day of the year: July 17 averages 56.3 degrees, and that’s as hot as it gets.

Now, let’s look at daily lows. Alaska dominates, of course. At the top of the lists: Barter Island WSO AP has the year-round average low of 5 F, and Allakaket’s coldest day (January 14th) is -34.9. Ignoring Alaska again (sorry, Alaska), here are the top 5s:

	Average Daily Low (year-round)			Coldest Day	Average Low
Fraser, CO	14.8		Taylor Park, CO	January 2	-14.2
Darwin Ranch, WY	15.0		Thief River Falls, MN	January 25	-13.6
Hermit 8 SE, CO	16.6		Hannah 2 N, ND	January 27	-13.5
Bondurant, WY	16.8		Tower 2S, MN	January 26	-13.2
Taylor Park, CO	16.9		Eckman, ND	January 22	-12.8

Overnight lows in Fraser, Colorado are below freezing about 10 months of the year. Whew.

Here’s where those places are:

At the other end of the spectrum are the daily low temperatures in places that never really cool off. In other words, the highest Average Daily Low, and the hottest Coldest Day. Florida and Hawaii dominate these lists. Topping the two categories: 1) Key West has a year-round average low of 73.3 degrees; 2) the coldest overnight lows in Honolulu happen on February 8th, when it gets down to 65 degrees. Almost sweater weather!