Around Boston, rain falls on weekdays and weekends at almost exactly the same rate

Asked:

“what's the correlation between (weekday, non-weekday) and rainy weather in Boston, MA or surrounding areas?”

Ten years of daily Open-Meteo precipitation (2016–2025), 3,653 days per area across Boston and five neighbors — 2,609 weekdays and 1,044 weekend days each. A rainy day is one with at least 0.01 inch. Boston: rain on 44.54% of weekdays vs 43.87% of weekend days, a phi correlation of +0.0061 — effectively zero, and the same story everywhere nearby.

Weekday vs weekend rainy-day share, six areas

Share of days with ≥0.01 in precipitation, 2016–2025. Blue = weekday, orange = weekend. Axis runs 0–100% to show how tiny each gap is. Hover a dot for detail.

Boston year by year: the gap swings both ways

Weekday minus weekend rainy-day share, percentage points. Blue = weekdays rainier, orange = weekends rainier. The swings cancel out to a ten-year gap of +0.67 pp.

Phi correlations across all six areas range only from +0.0005 (Quincy) to +0.0094 (Lowell) — every one indistinguishable from zero. open-meteo.com

The widest weekday–weekend gap anywhere is Lowell’s +1.03 percentage points (43.85% vs 42.82%); Quincy’s is just +0.06 pp. open-meteo.com

Boston’s mean precipitation is nearly identical too: 0.1315 in per weekday vs 0.1221 in per weekend day. open-meteo.com

Annual Boston gaps swung from +7.75 pp in 2020 to −7.48 pp in 2021 — noise in both directions that averages out to +0.67 pp over ten years. open-meteo.com

Boston and Cambridge show identical numbers because Open-Meteo returned the same archive grid cell for both coordinate pairs. open-meteo.com

The rows behind the picture

Area	Day type	Days	Rainy days	Rainy %	Avg precip (in/day)	Source
Boston	Weekday	2609	1162	44.54%	0.1315	open-meteo.com
Boston	Weekend	1044	458	43.87%	0.1221	open-meteo.com
Cambridge	Weekday	2609	1162	44.54%	0.1315	open-meteo.com
Cambridge	Weekend	1044	458	43.87%	0.1221	open-meteo.com
Lowell	Weekday	2609	1144	43.85%	0.1328	open-meteo.com
Lowell	Weekend	1044	447	42.82%	0.1198	open-meteo.com
Quincy	Weekday	2609	1156	44.31%	0.1298	open-meteo.com
Quincy	Weekend	1044	462	44.25%	0.1227	open-meteo.com
Salem	Weekday	2609	1168	44.77%	0.1362	open-meteo.com
Salem	Weekend	1044	466	44.64%	0.1286	open-meteo.com
Waltham	Weekday	2609	1159	44.42%	0.1336	open-meteo.com
Waltham	Weekend	1044	462	44.25%	0.1216	open-meteo.com

Daily precipitation totals from the Open-Meteo historical archive, 2016-01-01 to 2025-12-31: 3,653 daily observations per area (2,609 weekdays Mon–Fri, 1,044 weekend days Sat–Sun) for six areas — 21,918 area-days summarized into 6 area rows, 10 Boston annual rows, and 12 area×day-type rows. A rainy day is daily precipitation ≥0.01 inch; precipitation is in inches; phi is the Pearson correlation of the binary weekday and rainy-day indicators. Open-Meteo returned identical grid-cell values for the nearby Boston and Cambridge coordinates, a grid-resolution artifact; both rows are kept. Descriptive correlation only — no causal claim.

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