US

Analysis by Dr. Fry

US Cities Summer Highs Temperature Trends - Dr. Fry’s Research

The 26 places below have a slight negative urban heat island effect trend. But the 330 below those here have a slight postive one.

330 Cities, 41 Years

Recent temperature changes and trends for 330 places scattered around the contiguous (lower 48) US. Allocation of places among regions and states is based partly on area and partly on population. So is allocation of places within each state.

Above, US summer highs in general (averaged over 122 days each year from June 1 thru September 30) have risen a lot over the past 40 years, almost all in the last 20.

In contrast, the average of daily lows in winter does not show such a trend.
The winter lows trend is up for the 1st half of the period, and down for the 2nd half.
The 42-year trend for winter daily lows was slightly upward.

This map shows the 330 places + 18 more in Alaska and Hawaii.

The map below shows the 348 weather stations used in the analysis. These are most of American stations with continuous weather records and very little missing data. Only 1 or 2 of the most populous metrolitan areas are not represented here. 10 of the metro areas feature 2 or more weather stations, including NYC, LA, SF, Chicago, DC+, Miami+, Dallas+.

Below, 100% of states and 95% of places showed a warming trend for summer highs over the past 20 years (1995-2015). 100% of states and 92% of places showed one over the past 40 years (1975-2015).

Above, the faster warming areas, if they keep warming at their respective rates for the most recent 20 years, will have typical daily summer high temperatures before 2100 that are as hot as Las Vegas ones NOW, in various years.

64 of the places that woud get as hot as Las Vegas relatively soon are shown in the table above (also on the Home page). 51 would get that hot by 2100. Overall, 82 of the 330 (including, not shown, 10 more in Texas, 5 in California, 4 in Kansas, and 12 elsewhere) would get summers as hot as Las Vegas now by 2100 - IF 20-year trends continue.

See the US Temps data page for full data for the 330.

Above, if warming continues at the rate experienced over the past 20 years, 29 of the 49 states examined experience typical summers as hot as Las Vegas now before 2200. 8 of them become that hot by 2100, including Kansas.

Below are temperatures trends from a 2015-17 analysis, in °F per century, for the 119 places in the intermediate analysis. For the later 20 years, 1995-2015, they range from +26.9 in Hanford, California to -8.8 in Bartow, Florida. For the full 40 years, 1975-2015, they range from +20.0 in Twin Falls, Idaho to -4.6 in Bartow, Florida again.

119 places , as well as 7 in Alaska and 2 in Hawaii, are shown on the 2 maps above. The top map shows trends (°F / century) over the last 20 years, the bottom map over the last 40 years. More detail is available on the Data page.

The trends are almost identical (+5.8 and +10.5 or 10.4°F / century) for the 330 places and its subset of 119. The 330 includes most US weather stations that are largely free of missing data. New Haven CT, Stockton CA, Provo UT, Lancaster CA, Pensacola FL, and Visalia CA are the largest metro areas without a weather station included.

When will 2012 heat, the US record to date, become the new normal?

Years when 2012 (the hottest summer in US history) summer highs are expected to be the new normal, assuming warming continues at the rate for the last 20 years - in 48 states are shown on the Data page, in the States Warming Summary table.

2012 was cooler than normal in Florida, Louisiana, Washington, Oregon, Mississippi, Alabama, Georgia, South Carolina, Arizona, California, Tennessee, New England, and New Jersey. But 2012 heat could become the new normal in Nevada (2016), Virginia (2017), Texas (2018), Idaho (2019), Utah (2021), New York & Pennsylvania (2022), Kentucky (2025), Colorado & New Mexico (2026), Wyoming (2030), and Kansas (2032).

These are the summary graphs for 7 of the 8 major regions (excluding West Coast - see US Temps section), based on the 119 places.

Place and state graphs are on the US Temps Data page.

Consider other trends: Winter Highs, Summer Lows, and Winter Lows

US 26 Cities Other Temperature Trends - also Dr. Fry’s Research

Trends in daily winter highs are less pronounced in the last 22 years, but appreciably greater over the last 43 years.

While trends in summer and winter daily highs are quite pronounced, trends in daily summer lows are not. Trends in winter daily lows are not pronounced either over the 43 years. But there are strong and opposite trends in winter lows for the 1st and 2nd halves of the study period. See below.