Coast to Cactus Weather Examiner National Weather Service - S a n D i e g o Volume 28 Number 3 weather.gov/sandiego July 2021 The New Normal adapted from climate.gov Inside this issue: Climate normals are 30-year averages of key climate observa- tions made at weather stations and corrected for bad or missing val- The New Normal 1 ues and station changes over time. From the daily weather report to seasonal forecasts, the Normals are the basis for judging how tem- perature, rainfall, and other climate conditions compare to what’s The New Normal—SoCal 4 normal for a given location in today’s climate. For the past decade, the Normals have been based on weather observations from 1981 to 2010. In early May, climate experts at Aviation forecasting and 7 NOAA’s National Centers for Environmental Information (NCEI) re- support at nws san diego leased an updated collection—hourly, daily, monthly, and annual Normals for thousands of U.S. locations, states, regions—based on the Wildland Fire Support 10 weather experienced from 1991 to 2020. A warmer normal Spring-Summer Outlook 10 The U.S. Climate Normals collection has 10 versions: 1901- 1930, 1911-1940, and so on through 1991-2020. In the image below, we’ve compared the U.S. annual average temperature during each Quarterly Summary 11 Normals period to the 20th-century average (1901-2000). Places Annual U.S. temperature compared to the 20th-century average for each U.S. Climate Normals pe- riod from 1901-1930 (upper left) to 1991-2020 (lower right). Maps by NOAA Climate.gov, based on analysis by Jared Rennie, North Carolina Institute for Climate Studies/NCEI. The New Normal—continued where the annual temperature during a given Normals era was colder than the 20th-century aver- age are blue; places where the temperature was warmer than average are red. The influence of long-term global warming is obvious: the earliest map in the series has the most widespread and darkest blues, and the most recent map has the most widespread and dark- est reds. Today, the normal annual temperatures across the country are warmer than the 20th- century average virtually everywhere. From 1901-1930, the annual average temperature was mostly colder than the 20th-century average. What’s also obvious in these comparisons is that the influence of global warming on normal U.S. temperature isn’t the same everywhere or during every 30-year period on record. Otherwise, the maps would have transitioned gradually from dark blue everywhere to dark red everywhere. In fact, a few locations do exhibit that pattern of gradual, steady warming from one Normals era to the next. Southeastern Oregon. Southern Florida. You can probably spot others. But in many places, the pace of warming changes from decade to decade due to other climate influences, both natural and human (think the Dust Bowl and smokestack pollution before the Clean Air Act). For example, in much of the U.S. Gulf Coast re- gion, the maps show that normal annual temperatures were actual- ly warmer than the 20th-century average in the first four sets of Normals. Beginning with the 1941- 70 Normals, they reverted, with normal annual temperature grow- ing increasingly cooler over the next two periods. That cooling pattern began to weaken with the 1971-2000 Normals, and it has all but disappeared today. Annual mean temperature change from the old 1981-2010 normals to the new 1991-2020 normals. Map CISESS/NCEI. A wetter or drier normal? “It varies” is the main message of the maps showing how the normal annual precipitation across the country has changed. Precipitation—regardless of human-caused climate change—varies a lot from place to place across the United States. Few places exhibit a precipitation trend that is either steadily wetter or steadily drier than the 20th-century average. Instead, drier areas and wetter areas shift back and forth without an obvious pattern. For example, the Southwest was much wetter than the 20th-century average in the 1901-30 and 1911-40 Normals, and then mostly drier than the 20th-century average in the next four Nor- mals. The 1961-90 Normals were a mix, with few areas either very wet or dry relative to the 20th- century average. The next two Normals periods—1971-2000 and 1981-2010— were once again much wetter than the 20th-century average across much of the Southwest, but the pattern has reversed in the new Normals. That inconsistency isn’t surprising, despite the fact that human-caused climate change The New Normal—continued Normal annual U.S. precipitation as a percent of the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right). Maps by NOAA Climate.gov, based on analy- sis by Jared Rennie, North Carolina Institute for Climate Studies/NCEI. likely is influencing U.S. precipitation in some places and seasons. It’s just that what controls precipitation varies so much from place to place and month to month that the influence of global warming also varies a lot. Some parts of the country are projected to see increases in annual aver- age precipitation, and others may see decreases. Some may see wetter winters but drier sum- mers, with little net change in annual average precipitation—but big impacts on natural ecosys- tems and agriculture that depend on a certain seasonal cycle. Some will see a shift in the type or intensity of precipitation without seeing a change in their annual total. More rain, less snow. More downpours, with longer dry spells between. With all this nuance, it’s not surprising that precipitation maps don’t show the same unmis- takable fingerprint of climate change that the temperature maps do. And yet, it’s probably not a coincidence that the last four maps in the series—the 1961- 1990, 1971-2000, 1981-2010, and 1991-2020 Normals—are nationally the four wettest-looking maps in the collection. At least some of that wetness relative to the 20th- century average is linked to the overall warming and “wetting” of the atmosphere that’s occurred as rising temperatures enhance Annual mean precipitation change from the old 1981-2010 normals evaporation of water from the to the new 1991-2020 normals. Map CISESS/NCEI. ocean and land surface. The New Normal—continued What used to be normal The 1991-2020 Normals tell us what is normal in today’s climate. NOAA does other analyses that tell us about what used to be normal. For its monthly and annual climate monitoring, tem- perature averages and precipitation totals are ranked since 1895, with many states ranking to- wards warm extremes recently. Also, U.S. and global climate conditions are compared to the 20th -century average. Average annual temperatures for the contiguous United States from 1895 to 2020 (orange line), along with the warming trend of 0.16˚Fahrenheit per decade (red line). Graph by NOAA Climate.gov, based on data from NCEI Climate at a Glance. Having the entire 20th century included for comparison means the baseline captures more of the range of natural variability that’s possible in U.S. and global climate. It also provides a rea- sonable—but conservative—indication of the influence of long-term warming on temperatures. The Normals are shifting, but NOAA isn’t losing track of climate change. The New Normal—SoCal Edition by Miguel Miller When the new normals were released in early May 2021, Southern California forecasters and climate lovers were eager to see 1) how much warmer the new normals would be compared to the previous normals, and 2) what changes to precipitation there would be. The no-brainer is that the new normals would reflect a warmer climate for all stations in Southern California. And that has been confirmed for most of the region. The new normal precipi- tation ended up drier than the old normals for all stations. Temperature Monthly average temperatures in the 1991-2020 normals increased most months for San Die- go, Santa Ana, Riverside, Big Bear Lake and Indio. Surprisingly, monthly average temperatures ac- tually fell slightly in Victorville. The charts on the following page illustrate that average temperatures (average of maxi- mum and minimum temperatures of each day) for the month made a small increase near the coast (San Diego and Santa Ana) and in the valleys (Riverside). They decreased slightly in the high desert (Victorville). A very small increase was found in the low desert (Indio) and in the mountains (Big Bear Lake). The New Normal—SoCal Edition—cont’d Santa Average Temp Average Temp Vic- Average Temp Average Temp Ana 1981-2010 1991-2020 change torville 1981-2010 1991-2020 change Jan 58.4 59.0 0.6 Jan 46.1 45.8 -0.3 Feb 59.1 59.4 0.3 Feb 49.0 48.4 -0.6 Mar 60.8 61.5 0.7 Mar 53.9 53.4 -0.5 Apr 63.3 63.7 0.4 Apr 59.4 58.6 -0.8 May 66.1 66.4 0.3 May 67.4 66.2 -1.2 Jun 69.0 69.5 0.5 Jun 74.9 74.7 -0.2 Jul 73.1 73.6 0.5 Jul 81.0 80.9 -0.1 Aug 74.3 75.0 0.7 Aug 80.5 80.1 -0.4 Sep 73.1 73.8 0.7 Sep 74.5 74.4 -0.1 Oct 68.7 69.4 0.7 Oct 63.6 63.3 -0.3 Nov 62.7 63.4 0.7 Nov 52.8 52.3 -0.5 Dec 57.7 58.2 0.5 Dec 45.2 44.7 -0.5 Annual 65.6 66.1 0.5 Annual 62.4 61.9 -0.5 River- Average Temp Average Temp Big Bear Average Temp Average Temp change change side 1981-2010 1991-2020 Lake 1981-2010 1991-2020 Jan 56.0 56.4 0.4 Jan 34.1 34.8 0.7 Feb 57.2 56.9 -0.3 Feb 34.6 34.7 0.1 Mar 59.7 59.6 -0.1 Mar 38.6 39.1 0.5 Apr 63.8 63.9 0.1 Apr 43.9 44.2 0.3 May 68.9 68.0 -0.9 May 51.9 51.5 -0.4 Jun 73.9 74.1 0.2 Jun 59.0 59.3 0.3 Jul 79.5 79.5 0.0 Jul 64.7 65.1 0.4 Aug 80.3 80.7 0.4 Aug 63.6 64.1 0.5 Sep 76.8 77.4 0.6 Sep 57.9 58.5 0.6 Oct 69.0 69.4 0.4 Oct 48.5 49.2 0.7 Nov 60.7 61.4 0.7 Nov