Halloween, by region
Late October normals, from daily records for 1991 to 2020. Daytime high first, overnight low second — and the overnight low is the one that matters for an evening event.
| City | Normal high | Normal low |
|---|---|---|
| Phoenix | 32 °C (89 °F) | 16 °C (62 °F) |
| Los Angeles | 28 °C (82 °F) | 14 °C (57 °F) |
| Atlanta | 22 °C (72 °F) | 13 °C (55 °F) |
| Denver | 18 °C (65 °F) | 3 °C (37 °F) |
| New York | 18 °C (64 °F) | 10 °C (50 °F) |
| Chicago | 16 °C (60 °F) | 10 °C (49 °F) |
| Seattle | 15 °C (59 °F) | 8 °C (46 °F) |
| Minneapolis | 14 °C (58 °F) | 6 °C (43 °F) |
Two things to read off it. Denver's spread is the striking one — an 18 °C day with a 3 °C night, a fifteen-degree swing that comes from altitude and dry air, where coastal Los Angeles manages half that. And the low is what an evening event meets, because after sunset the temperature is heading for the overnight figure rather than holding at the afternoon one.
Thanksgiving, by region
Late November, same sources, and the change over four weeks is larger than most people anticipate.
| City | Normal high | Normal low | Change from October |
|---|---|---|---|
| Phoenix | 24 °C (76 °F) | 10 °C (49 °F) | −7 °C |
| Los Angeles | 23 °C (74 °F) | 10 °C (50 °F) | −4 °C |
| Atlanta | 17 °C (62 °F) | 7 °C (44 °F) | −6 °C |
| New York | 12 °C (53 °F) | 4 °C (39 °F) | −6 °C |
| Denver | 11 °C (51 °F) | −4 °C (25 °F) | −8 °C |
| Seattle | 10 °C (50 °F) | 4 °C (40 °F) | −5 °C |
| Chicago | 8 °C (47 °F) | 3 °C (37 °F) | −7 °C |
| Minneapolis | 5 °C (41 °F) | −2 °C (29 °F) | −9 °C |
The last column is the useful one. Four weeks costs the continental interior eight or nine degrees, and coastal California four. That is the ocean's thermal mass slowing the seasonal decline, and it is the same effect that makes coastal winters milder and coastal summers cooler.
By Thanksgiving, Denver and Minneapolis have overnight lows below freezing as their normal condition — which puts them into frost and, on the colder years, pipe territory.
Why the average is a poor prediction
A normal is the middle of thirty years. The individual years scatter widely either side, and on a single calendar date in autumn the scatter is enormous — a swing of twenty degrees between the warmest and coldest instance of the same date is entirely ordinary in the continental interior.
Late October in the northern tier has produced genuine snowstorms and genuine shirtsleeve afternoons. Both are inside the normal range; the average is simply the point that has the same amount of history either side of it.
Which is why memory disagrees with the average so reliably. You remember the Halloween it snowed and the one that was unseasonably warm, and you do not remember the eleven unremarkable ones that set the number.
Both of these are evening events, and an afternoon high is the wrong figure for an evening. The temperature at 7pm is usually several degrees below the day's peak and falling, so the number worth checking is the hourly forecast for the hours you will actually be outside.
Planning either one
Six weeks out, use the normals above. That is what they are for: buying costumes, deciding whether the meal can spill outdoors, judging whether a coat has to fit over the outfit.
A week out, switch to the forecast. Temperature at that range is one of the more reliable things a forecast does — see is Apple Weather accurate.
On the day, use the hourly. For trick-or-treating, that means the 6pm to 9pm window, which in Chicago or Minneapolis is a very different proposition from the afternoon.
Whatever the number, remember your own garden runs its own offset from the regional figure, sometimes by several degrees on a clear calm evening — hyperlocal weather explains why. Normals for any city and month are in the average temperature tool.