Methods and sources
Where every number on this site comes from, how it reaches the page you are reading, and what happens when a value cannot be confirmed. If you only read one reference page here, read this one.
All sources last checked October 10, 2026 3 entries are still waiting on a check
There are two kinds of authority on this site and they are kept apart. A climate record is measured data: an instrument recorded it, an agency published it, and the number either matches or it does not. An agency's guidance is a recommendation: a body responsible for public safety telling people what to do. The first is reproduced exactly. The second is repeated and linked, never extended, summarised away, or turned into a rule its author would not recognise.
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, monthly summaries, Phoenix Sky Harbor (USW00023183)
Monthly normal high, low and mean temperature, rainfall and day counts
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, daily summaries, Phoenix Sky Harbor (USW00023183)
Day-by-day normal high and low, used by the planting and pool calendars
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, hourly summaries, Phoenix Sky Harbor (USW00023183)
Typical temperature by hour of day, and dew point, for the Heat-Safe Hours Planner
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, annual and seasonal summaries, Phoenix Sky Harbor (USW00023183)
Annual totals quoted on the About and Methods pages
- NOAA Global Monitoring Laboratory: Solar Calculator and its published solar equations
Sunrise, sunset, solar noon and sun position, computed for Phoenix latitude and longitude
- NOAA National Centers for Environmental Information: Global Historical Climatology Network, Daily (GHCN-Daily), station USW00023183, Phoenix Sky Harbor
Actual daily observations back to 1933: how often a temperature has been reached on a given date, and how often the station has frozen
- CoCoRaHS: Community Collaborative Rain, Hail and Snow Network
What the volunteer network is (backyard observers, the largest source of daily precipitation observations in North America, more than 28,000 active observers) and its own figure that a daily reading takes five minutes
- U.S. Energy Information Administration: Arizona Electricity Profile
The average retail price of electricity across all sectors in Arizona, an all-sector average rather than a residential rate
- NOAA National Centers for Environmental Information: U.S. Climate Normals product page
The definition of the 1991–2020 normals window and what a climate normal is, so the frost and freeze explorer can say plainly what it is comparing the station record against. This is the landing page for the CSV files the other NCEI entries link to directly
- Maricopa County: "Protect Your Pet From the Heat", adapted from the Arizona Humane Society
The seven-second pavement test, and the county’s own figure for how hot a car gets at 100 °F outside
- Arizona Department of Transportation: "Pull Aside, Stay Alive" dust-storm guidance
What to do when a dust storm catches you on the road, in ADOT’s own four steps
- NOAA National Weather Service, Phoenix: Monsoon safety
The Phoenix office’s own vehicle figure for flood water, its barricade rule, and its guidance for dust storms, lightning, downbursts and downed power lines
- Arizona Department of Transportation: "Pull Aside, Stay Alive" dust-storm safety campaign (PDF hosted by the National Weather Service)
The campaign’s own lines about never driving into a dust storm and visibility falling to near zero in seconds. The document is dated 2014 and is flagged as such on the page
- City of Phoenix: Monsoon preparedness
The pre-season house work: roof drains and scuppers, thinning trees, clearing drywells, grading water away from the building, backing up data, and the after-the-storm steps
- City of Phoenix: Monsoon resources
The reusable self-activating flood barriers the city hands out, and the note that residents bring their own bags and shovels for sand
- City of Mesa: Severe weather, family preparedness guide
The city’s severe-weather steps, and its 20-foot downed-power-line distance, which is shorter than the 100 feet both utilities give, and is flagged on the site for that reason
- Ready.gov (FEMA): Floods
Flood preparation, evacuation and recovery: the insurance warning, moving valuables up, cleanup clothing, the warning about wet electrical equipment, and the instruction to run generators outdoors only
- Ready.gov (FEMA): Power outages
Food safety after an outage: four hours for a refrigerator, forty-eight for a full freezer, forty degrees as the discard line, and the instruction to discard refrigerated medication after a day without power
- Ready.gov (FEMA): Thunderstorms and lightning
Tree trimming before storm season, surge protectors and lightning protection, and the thirty-minute rule for going back outside
- FEMA: Flood insurance
The national thirty-day waiting period for an NFIP policy to take effect
- Maricopa County: Flood insurance
The county’s own thirty-day warning, and its figure that one in four flood insurance claims comes from outside a mapped floodplain
- Maricopa County Public Health: Fight the Bite
Mosquito control after rain: the four Rs, repairing screens, and the instruction to tip and toss even the smallest amounts of standing water
- Arizona Public Service: preparing for monsoon season
Securing outdoor objects that blow into power lines, learning to open an automatic garage door by hand, and the hundred-foot distance from a downed line
- Salt River Project: staying prepared during monsoons
The emergency supply list, one gallon of water per person per day, surge protectors, knowing where the utility shut-offs are, and what to switch off during an outage
- Maricopa County: Monsoon flooding and preparedness, Flood Control District
The county’s own water depths, the rule against driving around a barricade, sandbag construction, the three-day emergency kit, and the order to do things in after a flood
- NOAA National Weather Service: "Turn Around, Don’t Drown" flood safety campaign
The national flood-water depths, and how many flood deaths happen in vehicles
- CDC National Institute for Occupational Safety and Health: "Heat-related Illnesses"
The symptom list and first-aid steps for heat stroke, heat exhaustion, heat syncope, heat cramps and heat rash
- CDC National Institute for Occupational Safety and Health: Rhabdomyolysis (rhabdo)
The signs of rhabdomyolysis, what to do about it, and the CDC’s own warning that symptoms alone cannot tell you whether you have it
- CDC: sunburn symptoms and treatment, Division of Cancer Prevention and Control
How to treat a sunburn, and the list of reasons to see a doctor about one
- CDC: Heat and Health Index and heat risk factor guidance
Who the CDC names as at higher risk from heat
- NOAA National Weather Service, Phoenix: heat safety and heat-illness first aid
The symptom wording this site quotes, and the cooling steps NWS Phoenix tells people to take
- NOAA National Weather Service: HeatRisk, the five-level heat risk forecast used to trigger heat alerts
The current names and levels of NWS heat alerts, which replaced Excessive Heat Warning in March 2025
- Arizona Revised Statutes § 28-910: "Liability for emergency responses in flood areas; definitions"
The statute commonly called the Stupid Motorist Law: who is liable for the cost of a flood rescue, the $2,000 cap per incident, and the fact that the section creates no offence of its own
- Arizona Revised Statutes § 28-693: "Reckless driving; violation; classification; license; surrender; aiding and abetting"
The offence § 28-910 subsection B hangs its second route to liability on: reckless driving, defined as driving in reckless disregard for the safety of persons or property
- City of Phoenix Parks and Recreation: Trail Heat Safety Program
The restricted trail segments and the 8 a.m. to 5 p.m. hours, what stays open, the program’s own history, and the city’s 2024 closure and rescue counts
- City of Phoenix Parks and Recreation: "Take a Hike. Do it Right."
The eight-item hiking checklist, in the city’s own wording
- Yuma County Sheriff’s Office Search and Rescue: "Desert Safety"
The only government water figure this site could open: a litre per hour, rising sharply above 85 °F. Yuma County, not Maricopa, and labelled as such
- American Society for the Prevention of Cruelty to Animals: Toxic and Non-Toxic Plant List
Which desert plants are listed as toxic to dogs, cats or horses, and which are not
- Arizona Humane Society: hot weather pet safety
Local pet heat guidance cited alongside the county’s own pet page
- American Kennel Club: veterinary guidance on hot pavement and dog paws
The ten-second version of the hand test, and why paws burn before a person notices
- NOAA National Weather Service, Phoenix: Monsoon Awareness Week and Arizona flood facts
Arizona flash-flood figures, the low-water crossings, and how many deaths happen in vehicles
- University of Arizona Cooperative Extension
The plant categories used for low-desert landscapes, and the guidance to select for the site rather than for the plant
- University of Arizona Cooperative Extension, "Frost Protection" (az1002)
The Maricopa County first- and last-frost ranges, the protection limits of frost cloth, the instruction to drape cloth to the ground and remove it in the morning, the three-night limit on running water, and the list of measures testing has not supported
- University of Arizona Cooperative Extension, "Protecting a Citrus Tree from Cold" (az1222)
That citrus is not cold hardy, and that site selection is the first and largest part of protecting a tree
- University of Arizona Cooperative Extension: citrus educational materials
The extension publications the citrus calendar follows by name (irrigating citrus, the citrus fertilisation chart for Arizona, pruning citrus, and diagnosing home citrus problems)
- University of Arizona Cooperative Extension: December monthly gardening guide for Pima County
What the extension expects a desert gardener to be doing in December, and its own caution that the month is the coldest of the year
- NOAA National Weather Service: glossary
The glossary's own PDS and PDS Watch entries, including its note that the wording may also accompany severe thunderstorm watches
- NOAA National Weather Service: heat index
The shaded heat-index chart the site reads its bands from. The page shows the chart without printing the numeric edges, which is why the band boundaries are attributed to the planner instead
- NOAA National Weather Service, Weather Prediction Center: "The Heat Index Equation"
The Rothfusz regression and the two standard adjustments the site computes its derived heat index with, including the rule that the index is only calculated above 80 °F
- NOAA National Weather Service: "Flood Warning VS. Watch"
The distinction the flash-flood article is built on: a watch means conditions are possible, a warning means it is happening or imminent
- NOAA National Weather Service, Jackson Mississippi forecast office: hydrologic product guide
The definition of a Flash Flood Emergency. It is the only NWS page this site could open that states the tier (no Phoenix page does) and the article says so
- NOAA National Weather Service, JetStream: lightning safety
The thunderstorm-development and lightning-behaviour material behind the lightning article
- NOAA National Weather Service: lightning safety, national overview
The national lightning-safety guidance the article follows (when to be indoors, and what counts as shelter)
- Maricopa County
The county as the authority the site defers to on heat, flooding and pool water, where a specific county page is not the one being cited
- Maricopa County: heat relief and heat safety
The county's heat-safety and heat-relief material, and the landing page to cite if the department's news-item links move
- Maricopa County Department of Public Health: "2024 Shows First Decline in Heat Deaths in a Decade"
The county's figure of 113 consecutive days at or above 100 °F, 27 May to 16 September 2024, used as the example of how far a single year can sit from the normal. These are preliminary county figures, and the articles say so
- Flood Control District of Maricopa County
The district as the authority on washes, retention basins and flood risk in the county
- Ready.gov (FEMA): alerts
How a Wireless Emergency Alert behaves: a unique sound and vibration repeated twice, no subscription and no charge, and no loss from network congestion
- Arizona Municipal Water Users Association
The guidance to reset an irrigation clock with the change of season, and the association's landscape and watering material for Valley residents
- Arizona Municipal Water Users Association: Plants for the Arizona Desert
The mature height and width, water-use rating, growth rate, sun exposure and cold-hardiness figures the plant tool and the tree comparison draw on
- Arizona Public Service: residential pricing pages
That APS publishes more than one residential pricing option and that some price a kilowatt-hour differently at different hours. No APS rate or window is reproduced on this site. The residential pricing pages could not be opened from this environment and the host did not answer at all, so no date is claimed
- Salt River Project: residential pricing pages
The fact that both Valley utilities publish time-of-use plans with their own on-peak windows. The site states the hours differ by plan and does not print any of them. SRP returned HTTP 403 to every attempt to open it from this environment, so no date is claimed
- Arizona Department of Water Resources
The department as the state authority on groundwater, active management areas and assured water supply. The department's newer site would not open from this environment, so the article cites this root and says that is what it did
- ASPCA Animal Poison Control Center
The 24-hour Poison Control hotline number and the standing instruction to contact a veterinarian or the hotline when an animal may have eaten something poisonous
- Centers for Disease Control and Prevention: drowning prevention
The CDC as the authority on drowning risk and prevention, and the landing page for the material the pool-safety article follows
- Centers for Disease Control and Prevention: drowning prevention, data and research
The CDC's own published drowning figures, quoted as the source states them
- Centers for Disease Control and Prevention: drowning prevention, prevention
The prevention steps the pool-safety article is organised around (barriers, supervision, and learning to swim)
- Occupational Safety and Health Administration: heat
The workplace heat guidance behind the outdoor-work article: water, rest and shade, and the acclimatisation principle. No employer-specific obligation is stated as advice to a reader
- U.S. Department of Energy: Energy Saver
The maintenance guidance the cooling checklist follows: filter condition and airflow, coil cleaning, condensate drainage, duct sealing and thermostat scheduling. No efficiency figure or saving is quoted from it
- U.S. Environmental Protection Agency: WaterSense
The outdoor water-use guidance behind the pool cover and evaporation point, which treats a cover as a way to cut both evaporation and heat loss. No figure is quoted from it here
- U.S. Consumer Product Safety Commission: Pool Safely
The Water Watcher, the requirement for compliant drain covers, the four-foot barrier and self-closing self-latching gate, and the reference to the Virginia Graeme Baker Pool and Spa Safety Act
- University of Arizona Cooperative Extension: Bulletin #41, "Irrigating Native Southwest Trees and Shrubs"
Every irrigation duration and frequency in the hydrozone planner: the two-hour minimum drip run, the 8-to-10-hour leaching run every fifth irrigation, the twice-a-week watering for one-gallon plants above 100 °F, the daily or alternate-day case above 105 °F, the first one-to-two-year establishment rule, and the soil water-holding figures quoted in the section on where the numbers stop
- Arizona Municipal Water Users Association: Tools for successful landscapes
The association's own statement of what it publishes for a home landscape, used to keep the wording about what AMWUA does and does not rate tied to the association's own site
- Centers for Disease Control and Prevention: Home Pool and Hot Tub Water Treatment and Testing
The chemistry routine: pH 7.0–7.8, free chlorine of at least 1 ppm and 2 ppm where a stabilised product is used, and the instruction to test chlorine and pH at least twice a day in season and more often when the pool is busy
- Centers for Disease Control and Prevention: Model Aquatic Health Code
The water-temperature bands, by kind of swimmer: the lap and swim-team range, the recreational and multi-use range, and the instructional and therapeutic ranges above them that a Phoenix pool reaches on its own in high summer
- Maricopa County Environmental Services: Swimming Pools Management, Environmental Health Code Chapter VI, Section 2
The county's enforceable ranges for public pools and spas (free chlorine 1–5 ppm, pH 7.2–7.8, total alkalinity 60–180 ppm), the daily testing and twelve-month log, and the equipment and filter guidance the household tasks are modelled on. These are public-pool requirements, not rules for a backyard pool, and the tool says so
- ENERGY STAR (U.S. Environmental Protection Agency): "Heat & Cool Efficiently"
The filter routine in the federal programme's own terms (a check every month through the season, a change when it looks dirty, and a change at least every three months) and the cooling-side habits behind the pre-cooling point, including that the air conditioner holding its setpoint is the load a Phoenix household cannot switch off
- U.S. Environmental Protection Agency: Stationary Refrigeration and Air Conditioning (Section 608)
The refrigerant rule: that handling refrigerant requires Section 608 certification and that knowingly venting it is prohibited, which is why the refrigerant item in the cooling schedule is written as a technician's job rather than a top-up
- University of Arizona Cooperative Extension, WaterWise: "Swamp Cooler Maintenance"
Every evaporative-cooler task in the cooling schedule: the spring start-up, the pads, the belt tension, the water level about an inch below the tray top, the 85 °F running point, the descaling with vinegar, and the winterising that drains the line before the freezing nights
- McLaren C, Null J, Quinn J. "Heat Stress From Enclosed Vehicles." Pediatrics, July 2005; 116(1):e109–e112
The measured rate a parked car heats: 3.2 °F every five minutes, 80% of it in the first half hour
- Jan Null, CCM, San José State University: "Vehicle Interior Temperature Rise vs. Elapsed Time", calculated from the 2005 Pediatrics study
The interior temperature at every five-minute step from 70 to 110 °F, which is what the Parked-Car Heat Timeline draws
- Berens JJ. "Thermal contact burns from streets and highways." JAMA 1970;214(11):2025–2027
The earliest measured asphalt temperatures against air temperature
- Arizona State University, Arizona State Climate Office: urban heat island surface temperature measurements, Mesa, Arizona
The Phoenix-area surface measurements: 155 °F asphalt, 140 °F concrete in sun, 93 °F concrete in shade
- University of Georgia Cooperative Extension: "How Hot Does Pavement Get?"
Surface temperatures for blacktop, cement, brick and both grass surfaces at the same hour
- Williams CF, Pulley GE. "Synthetic Surface Heat Studies." Brigham Young University, 2002
How much hotter artificial turf runs than asphalt and natural grass, and how fast it heats back after water
- Harrington WZ et al. "Pavement Temperature and Burns: Streets of Fire." Annals of Emergency Medicine 1995;26(5):563–568
Measured in Phoenix: the hours asphalt was hot enough to burn, and to burn within 35 seconds
- Air Conditioning Contractors of America
The trade standards behind the division of work, the load calculation a contractor performs before sizing or replacing equipment. No numeric tolerance is quoted from it
- Central Arizona Project
What the canal system is and where its water comes from, as background to the Colorado River figures in the water-law article
- American Red Cross: training and certification
Named only as a place to find CPR and first-aid training. No figure on this site comes from the Red Cross
- Arizona Revised Statutes § 45-401: Groundwater code; declaration of policy (Arizona Legislature)
The groundwater code's declaration of policy, including the findings that withdrawals exceed the safe annual yield and that groundwater should be allocated to its most beneficial uses
- Arizona Revised Statutes § 45-562: Management goals for the active management areas (Arizona Legislature)
The Phoenix active management area's statutory management goal, safe-yield, and the different goals set for the other areas
- Arizona Revised Statutes § 45-576: Assured water supply; certificate; designation (Arizona Legislature)
The assured-water-supply requirement a subdivision must meet before it can be built in an active management area. The article states the rule and does not advise on it
- NOAA Global Monitoring Laboratory: Solar Calculation Equations
The published equations behind every sun angle on the site: the fractional-year term, the declination, the equation of time, the hour angle, the altitude and the azimuth. The 90.833° sunrise zenith these use (which folds in atmospheric refraction and the sun's own radius) is what makes every sunrise and sunset about three minutes later than a flat 90° would give. The site runs the arithmetic itself for 33.4278° N, 112.0039° W rather than looking a time up
No figure on this site is typed into a page. Each one travels the same route, and each step is visible in the repository:
- The source file is downloaded from the agency that publishes it, in its original format, and kept. Nothing is transcribed by hand at this stage.
- A build script reads it and writes a dataset into the site's data directory. The script parses the file by its real column headings, checks that the row count and date range are what they should be, and fails the build if they are not.
- Every value carries its provenance. A dataset records the value, the name of the source, a link to that exact file, and the date it was checked, together, in the same record. A number cannot be separated from where it came from.
- The page reads the dataset. A tool or an article imports the value rather than restating it, so correcting the dataset corrects every page that uses it, in one step.
Several pages run a check on themselves as they build. The Season Clock, for example, refuses to build if its compact daily series is not exactly 366 days long, because a series that is one day short would put every date after the gap on the wrong day of the year, and it would do so quietly.
No guessed numbers, ever
If a figure cannot be confirmed against a primary source, it is not estimated, not taken from a secondary summary, and not softened into "approximately". It is marked as needing verification in the dataset and listed in the site's data notes, and the page that would have shown it either says the figure is still being checked or shows nothing there.
The same rule applies to whole tools. If a tool could not be built on a verifiable dataset, it was changed to something that could be: the tool was replaced, not the number invented. Numbers that look plausible and are wrong are worse than no number at all, because they are believed.
Two things follow from that, and both are visible on the site. First, some pages are narrower than they could be: the frost and freeze explorer reports how often Phoenix has actually reached freezing rather than pretending the normal year has a frost season, because the normal overnight low here never reaches 32 °F even though individual winters do. Second, unverified items are listed openly rather than hidden: a page carrying one says so at the point where it matters.
The site uses the units people in Phoenix actually use: degrees Fahrenheit, inches of rain, miles, and a 12-hour clock. Metric equivalents are given where a source publishes in metric and a conversion would otherwise be a surprise, and are rounded to the same number of significant figures as the original, not to a false precision.
All times are Mountain Standard Time, all year. Arizona does not observe daylight saving time, so there is no seasonal shift anywhere on this site. Sunrise, sunset, solar noon, sunrise bearing, the hour of peak normal heat and every hour printed by a tool are in MST. A calculator that applied daylight saving would place the hottest hour an hour early for half the year, and it would look entirely reasonable while doing it.
Climate figures are the 1991–2020 normals, the current thirty-year period published by NOAA NCEI. A normal is an average of thirty years, not a prediction, and every tool says so.
If a figure here is wrong, the fastest way to get it fixed is to open the source yourself and send the link. Corrections are made to the dataset, which updates every page that reads it, and where a change alters what a page claims the page notes the change rather than quietly rewriting itself. Silent corrections make a reference uncitable, which defeats the point of it.