Phoenix Weather History (2000–2025): Is It Getting Hotter?

The work behind this dashboard is what I do for companies.

This Phoenix weather dashboard is a personal project, but the skill behind it is exactly what I do professionally: turning raw, scattered data into clear, interactive reporting a team can actually trust, for organizations up to $800M.

Project Details

The Technical Challenge: Building the Gantt Chart

The Gantt chart became the centerpiece of this dashboard, and the most technically demanding piece to build.

The concept was simple: show the heat season for each year as a horizontal bar, starting on the first day that hit 100°F and ending on the last. Bar length represents season duration. Stacked vertically by year, the chart should immediately show whether the season is getting longer. It does.

Getting there required Level of Detail (LOD) expressions, one of Tableau's more powerful but less intuitive features. Two fixed LOD calculations find the first and last 100°F day for each calendar year:

• First 100°F day: FIXED YEAR(DATE) : MIN(IF High >= 100 THEN DATE END)
• Last 100°F day: FIXED YEAR(DATE) : MAX(IF High >= 100 THEN DATE END)

A third calculation derives the season length in days from those two anchors. The Gantt chart plots the start date on a normalized timeline (so every year's bar begins from the same left-side reference point) and extends rightward by the season length value.

Adding readable date labels directly onto each bar, showing the exact first and last day of each year's heat season, turned out to be a Tableau limitation. Gantt charts use a bar mark type that doesn't support text marks in the same view. The workaround would require a dual-axis setup with a calculated reference line per year, which added more complexity than the visual payoff justified. The start and end dates are visible on hover via tooltip instead.

The visual result still tells the story cleanly: bars starting earlier in late April instead of mid-May, ending later in mid-October instead of late September, and measurably longer across the 2020s compared to the early 2000s.

The Four-Chart Dashboard

The final dashboard uses four complementary visualizations:

1. 100°F Days Timeline (Bar Chart): The headline story, dramatic increase in extreme heat days, especially 2020+
2. Heat Season Extension (Gantt Chart): Shows when the heat starts and ends each year, revealing the season's expansion
3. Monthly Temperature Heatmap: A 26-year × 12-month grid showing exactly when and where the warming is occurring
4. Temperature Distribution (Stacked Area): Shows the underlying shift, cool days (blue) shrinking, hot days (red) expanding

The Validation

After analyzing 9,497 days of weather data spanning 25 years, the answer is clear:

It's not you. Phoenix really is getting hotter.

The data validates what residents have been feeling:

• More 100°F days (up to 188 vs. historical ~117)
• More 110°F days
• Heat season starting earlier and ending later
• The "nice season" shrinking
• December warmer by ~7°F
• Summer peak temperatures 5-6°F higher

Who This Dashboard Is For

This project serves two audiences:

1. Phoenix residents and prospective residents: Make informed decisions about living in (or moving to) a rapidly warming city
2. Climate-conscious individuals: See localized climate change data, not global models or projections, but actual observed temperatures from one city over 25 years

The Takeaway

After analyzing 9,497 days of weather data across 25 years, the answer to the original question is straightforward: yes, Phoenix is getting hotter, and the data shows exactly where and when.

The signal isn't in summer. July has always been brutal and it's incrementally worse, up about 1.5°F over two decades, which matters at those temperatures but isn't the headline. The signal is in the shoulder seasons. October is 2.5°F hotter. November is 2.1°F hotter. December is 3.5°F hotter. The months that used to make Phoenix livable year-round are warming faster than the peak summer months. That's the part that changes how the city actually functions as a place to live.

The 2020 inflection shows up clearly in the data: years before it fluctuate around a range, years after it track in a consistent direction. Whether 2020 itself was the cause or the marker of an underlying trend isn't something a single-city temperature dataset can answer. What it can say is that the Phoenix that existed between 2000 and 2019 and the Phoenix that has existed from 2020 forward are measurably different, and the gap has kept widening.

For data professionals: the project is also a case study in AI-assisted data workflows. Google Gemini pulled 25 years of NOAA records into a clean Excel file with no cleaning required. Claude assisted with calculated field design and chart recommendations. The analysis itself was done in Tableau, but neither the data acquisition nor the LOD expression development would have moved as quickly without AI tools at each step. That workflow, AI for data gathering and formula logic and Tableau for the visualization layer, is repeatable on any project with a similar structure.

Tools Used: Google Gemini AI, Excel, Tableau Public, Claude AI

Last Updated: February 2026

Frequently Asked Questions

How many days over 100°F does Phoenix have per year?

Based on 25 years of NOAA data (2000 to 2025), the average across the full dataset is roughly 145 to 150 days per year. But that average obscures a clear shift: years before 2020 averaged around 117 days above 100°F, while years from 2020 onward have consistently exceeded that baseline. 2023 reached 174 days; 2024 hit 188. The number is still rising.

What does Phoenix weather history show about temperature trends?

Phoenix weather history from 2000 to 2025 shows a clear and measurable warming trend. Analyzing 9,497 days of daily temperature records, the signal is strongest in the fall and winter months: December highs are up 3.5°F, October highs are up 2.5°F, November highs are up 2.1°F compared to the 2000s decade. The summer peak months are warmer too, but the shoulder season warming is the larger shift in terms of how Phoenix actually functions as a place to live year-round.

When does it cool down in Phoenix?

The data puts this in concrete terms. October average highs are now 91°F (up from 88.5°F in the 2000s). November averages 78.7°F. Consistent highs below 80°F don't arrive until December, and December itself is warmer than it used to be (69.5°F average high, up from 65.9°F). In practice, the weather that most people would describe as "cool" doesn't appear until November at the earliest.

How long is Phoenix's heat season?

Defined as the period between the first and last 100°F day of the year: the 2000s average was roughly 140 to 150 days. Recent years are approaching and exceeding 180 days. The season now typically starts in late April (previously mid-May) and ends in mid-October (previously late September). That's roughly a month of extension on each end.

What is the average Phoenix temperature by month?

Phoenix temperature peaks in July: 108.6°F average daily high across the recent decade (2016 to 2025). In 2023, July averaged 114°F. June averages 106°F, August 105°F. The shoulder months run: April 88.2°F, May 98.1°F, September 100.3°F, October 91°F. December is the coolest month at 69.5°F average high, though that's 3.5°F warmer than it was in the 2000s. July nights average 86.5°F low, meaning the Phoenix temperature rarely drops below 85°F even overnight.

What months are mild in Phoenix?

January (67.5°F avg high), February (72.2°F), March (78.1°F), and December (69.5°F) are the coolest months based on the 25-year dataset. April (88.2°F) and November (78.7°F) round out the transition months. The November through March window is when Phoenix's weather is most comparable to other Sun Belt cities in spring or fall.

What year was the hottest in Phoenix over the last 25 years?

By annual average high temperature, 2024 was the hottest year in the dataset at 90.5°F. 2025 was second at 89.8°F. The five hottest years in the 25-year record are all from 2020 onward.

Where does the data come from?

NOAA's daily summaries for the Phoenix area, covering 2000 to 2025. Google Gemini AI was used to access and export the data directly into Excel, 25 years of daily records pulled cleanly with no manual data entry or cleaning required. The dataset includes daily high temperature, daily low temperature, and precipitation for each of the 9,497 days in the analysis period.