Roxbury Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roxbury Airport clear sky chart from 2005-11-06 to 2026-03-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	18% 7% 2 6% 4 4 4 4 5% 7% 38%	130816
	Night	18% 8% 2 6% 4 3 4 3 5% 6% 41%	130372
Transparency	Day	43% 6% 12% 22% 15% 3	134344
	Night	43% 5% 12% 22% 16% 3	134931
Seeing	Day	24% 18% 30% 19% 8% 2	16587
	Night	23% 16% 30% 23% 7% 1	25769

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	12% 9% 3 8% 4 5% 4 3 5% 5% 41%	4661
	11th to 20th	Day	15% 9% 3 7% 4 4 4 3 4 5% 42%	4650
	21st to end	Day	16% 9% 3 6% 3 3 4 3 5% 7% 42%	5341
February	1st to 10th	Day	16% 8% 2 7% 4 5% 5% 4 5% 6% 38%	1932
	11th to 20th	Day	15% 7% 3 7% 4 5% 4 4 5% 7% 39%	2048
	21st to end	Day	19% 10% 2 6% 4 3 4 3 4 6% 38%	1730
March	1st to 10th	Day	23% 9% 2 5% 3 3 4 3 4 5% 39%	4496
	11th to 20th	Day	15% 5% 2 7% 4 4 5% 4 6% 7% 42%	4687
	21st to end	Day	21% 7% 2 6% 4 4 4 4 6% 7% 36%	5970
April	1st to 10th	Day	19% 8% 3 6% 5% 4 4 3 5% 6% 36%	2400
	11th to 20th	Day	19% 6% 2 5% 4 4 4 3 5% 7% 40%	2374
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 5% 41%	2490
May	1st to 10th	Day	31% 8% 3 6% 3 4 4 3 5% 7% 26%	5886
	11th to 20th	Day	21% 8% 3 6% 5% 5% 4 3 5% 6% 34%	6216
	21st to end	Day	22% 7% 2 6% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	18% 6% 2 5% 5% 5% 5% 4 7% 8% 35%	2800
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 5% 7% 8% 36%	2800
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 37%	2800
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 4 6% 9% 34%	6360
	11th to 20th	Day	13% 7% 2 7% 4 5% 6% 5% 7% 10% 34%	6360
	21st to end	Day	16% 6% 3 6% 4 4 4 4 6% 7% 40%	6926
August	1st to 10th	Day	20% 7% 3 7% 5% 4 5% 4 7% 8% 32%	4415
	11th to 20th	Day	12% 6% 3 6% 5% 4 4 4 6% 9% 40%	3850
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 5% 4 4 5% 6% 44%	2400
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 5% 7% 50%	2280
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 6% 40%	2200
October	1st to 10th	Day	21% 7% 2 4 4 3 3 4 4 5% 43%	2140
	11th to 20th	Day	14% 6% 2 6% 4 3 4 4 5% 6% 46%	2000
	21st to end	Day	21% 6% 2 4 5% 4 4 3 5% 5% 41%	1981
November	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 5% 7% 49%	1851
	11th to 20th	Day	17% 6% 2 4 3 4 3 3 5% 6% 46%	1890
	21st to end	Day	18% 8% 2 6% 4 3 3 3 6% 6% 41%	1827
December	1st to 10th	Day	16% 8% 2 5% 4 3 3 3 4 7% 44%	2680
	11th to 20th	Day	21% 8% 2 4 2 3 3 3 4 6% 44%	3066
	21st to end	Day	19% 10% 3 6% 4 4 3 2 4 6% 37%	4048
January	1st to 10th	Night	15% 8% 2 7% 4 3 4 3 5% 6% 42%	8234
	11th to 20th	Night	15% 9% 3 7% 4 3 4 3 5% 6% 40%	8235
	21st to end	Night	15% 10% 3 6% 4 4 4 3 4 5% 42%	8835
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 4 5% 41%	2686
	11th to 20th	Night	16% 9% 3 6% 4 4 4 4 6% 6% 40%	2458
	21st to end	Night	19% 8% 2 6% 4 4 4 3 5% 5% 40%	2076
March	1st to 10th	Night	20% 10% 2 6% 3 3 4 3 5% 6% 40%	5389
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 41%	5267
	21st to end	Night	21% 10% 3 6% 4 3 3 2 4 5% 38%	4962
April	1st to 10th	Night	19% 8% 3 5% 4 4 5% 4 5% 7% 35%	2000
	11th to 20th	Night	20% 6% 2 5% 5% 4 4 4 5% 6% 39%	1975
	21st to end	Night	20% 7% 2 6% 5% 3 3 3 4 5% 42%	1909
May	1st to 10th	Night	31% 10% 2 6% 4 3 3 3 4 6% 27%	4054
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 5% 7% 33%	3719
	21st to end	Night	23% 8% 3 6% 3 3 4 3 6% 6% 35%	3926
June	1st to 10th	Night	18% 6% 3 6% 5% 4 4 4 4 7% 40%	1600
	11th to 20th	Night	17% 7% 2 5% 4 3 4 4 5% 10% 39%	1600
	21st to end	Night	15% 6% 2 5% 3 5% 4 4 5% 10% 42%	1600
July	1st to 10th	Night	16% 6% 2 6% 4 4 5% 4 7% 8% 39%	3600
	11th to 20th	Night	19% 9% 2 7% 5% 4 4 4 6% 8% 33%	3600
	21st to end	Night	14% 7% 2 6% 4 3 4 4 6% 5% 45%	3926
August	1st to 10th	Night	23% 8% 2 7% 5% 4 4 4 5% 6% 32%	2698
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 3 5% 7% 41%	3197
	21st to end	Night	12% 4 1 4 3 3 3 3 5% 8% 53%	3586
September	1st to 10th	Night	16% 7% 2 5% 4 4 4 3 4 6% 46%	2000
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 6% 54%	2120
	21st to end	Night	18% 7% 2 4 3 3 5% 3 4 4 45%	2200
October	1st to 10th	Night	19% 7% 2 5% 4 3 3 2 4 7% 43%	2256
	11th to 20th	Night	16% 5% 2 5% 5% 4 3 3 4 6% 47%	2400
	21st to end	Night	22% 6% 2 5% 4 3 4 3 5% 6% 41%	2857
November	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 5% 6% 48%	2667
	11th to 20th	Night	18% 7% 2 4 4 3 4 3 5% 5% 46%	2730
	21st to end	Night	15% 7% 2 5% 4 3 4 3 4 7% 45%	2792
December	1st to 10th	Night	17% 8% 2 5% 3 3 3 3 4 5% 47%	4720
	11th to 20th	Night	24% 8% 2 4 3 3 3 3 4 4 41%	5348
	21st to end	Night	21% 9% 3 7% 4 3 3 3 4 4 39%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	42% 5% 10% 25% 15% 3	4662
	11th to 20th	Day	44% 4 10% 20% 14% 8%	4680
	21st to end	Day	42% 4 10% 25% 18% 1	5341
February	1st to 10th	Day	46% 5% 12% 20% 15% 2	1932
	11th to 20th	Day	43% 5% 11% 22% 16% 3	2057
	21st to end	Day	48% 4 11% 22% 13% 2	1730
March	1st to 10th	Day	47% 4 11% 16% 13% 10%	4499
	11th to 20th	Day	38% 6% 15% 28% 10% 3	4687
	21st to end	Day	47% 4 9% 14% 20% 6%	5970
April	1st to 10th	Day	47% 5% 10% 20% 14% 3	2400
	11th to 20th	Day	43% 6% 11% 21% 17% 2	2374
	21st to end	Day	44% 6% 10% 21% 16% 3	2490
May	1st to 10th	Day	57% 6% 14% 13% 9% 1	5897
	11th to 20th	Day	50% 7% 10% 18% 13% 1	6220
	21st to end	Day	46% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	44% 7% 14% 22% 12% 1	2800
	11th to 20th	Day	44% 8% 14% 22% 11% 1	2800
	21st to end	Day	41% 8% 15% 22% 13% 1	2800
July	1st to 10th	Day	45% 8% 11% 20% 15% 1	6290
	11th to 20th	Day	42% 8% 16% 21% 11% 1	6285
	21st to end	Day	42% 6% 11% 22% 18% 1	6728
August	1st to 10th	Day	49% 7% 14% 21% 8% 1	4401
	11th to 20th	Day	39% 7% 15% 29% 10% 1	3886
	21st to end	Day	35% 6% 13% 30% 16% 1	4312
September	1st to 10th	Day	40% 7% 10% 22% 19% 2	2400
	11th to 20th	Day	34% 6% 10% 24% 25% 2	2280
	21st to end	Day	43% 7% 10% 20% 16% 3	2200
October	1st to 10th	Day	38% 5% 9% 19% 25% 4	3491
	11th to 20th	Day	29% 4 9% 25% 28% 5%	3240
	21st to end	Day	32% 4 15% 24% 22% 3	3181
November	1st to 10th	Day	36% 4 13% 25% 19% 2	1851
	11th to 20th	Day	38% 4 12% 24% 19% 3	1890
	21st to end	Day	43% 4 13% 27% 11% 2	1827
December	1st to 10th	Day	41% 4 16% 27% 11% 1	2680
	11th to 20th	Day	42% 4 14% 20% 17% 3	3066
	21st to end	Day	49% 4 8% 21% 14% 4	4048
January	1st to 10th	Night	42% 4 12% 24% 16% 2	8234
	11th to 20th	Night	45% 4 13% 19% 14% 6%	8280
	21st to end	Night	44% 3 10% 20% 19% 4	8835
February	1st to 10th	Night	46% 5% 12% 23% 13% 2	2686
	11th to 20th	Night	45% 5% 10% 20% 17% 4	2460
	21st to end	Night	46% 4 9% 23% 14% 4	2076
March	1st to 10th	Night	45% 4 12% 18% 15% 6%	5399
	11th to 20th	Night	42% 6% 15% 22% 11% 3	5268
	21st to end	Night	48% 4 6% 14% 23% 5%	4962
April	1st to 10th	Night	46% 6% 10% 20% 14% 3	2000
	11th to 20th	Night	45% 6% 11% 19% 19% 1	1975
	21st to end	Night	44% 6% 9% 22% 16% 4	1909
May	1st to 10th	Night	58% 6% 13% 12% 9% 1	4060
	11th to 20th	Night	50% 9% 11% 16% 12% 3	3720
	21st to end	Night	48% 6% 13% 22% 10% 1	3927
June	1st to 10th	Night	45% 6% 9% 21% 17% 1	1600
	11th to 20th	Night	41% 9% 15% 24% 10% 1	1600
	21st to end	Night	37% 9% 14% 25% 15% 1	1600
July	1st to 10th	Night	42% 8% 14% 20% 14% 1	3560
	11th to 20th	Night	47% 8% 15% 19% 10% 1	3552
	21st to end	Night	39% 5% 12% 24% 18% 1	3809
August	1st to 10th	Night	52% 8% 13% 18% 9% 1	2688
	11th to 20th	Night	42% 7% 14% 29% 8% 1	3227
	21st to end	Night	29% 6% 12% 35% 16% 1	3586
September	1st to 10th	Night	40% 5% 9% 26% 18% 1	2000
	11th to 20th	Night	32% 6% 11% 24% 26% 2	2120
	21st to end	Night	42% 6% 9% 22% 20% 2	2200
October	1st to 10th	Night	39% 5% 12% 22% 20% 2	3685
	11th to 20th	Night	28% 4 9% 27% 27% 4	3899
	21st to end	Night	34% 4 13% 29% 18% 2	4607
November	1st to 10th	Night	36% 5% 11% 23% 20% 4	2667
	11th to 20th	Night	40% 4 10% 23% 19% 4	2730
	21st to end	Night	40% 4 13% 29% 12% 1	2792
December	1st to 10th	Night	40% 4 12% 31% 11% 1	4720
	11th to 20th	Night	47% 4 12% 17% 17% 3	5348
	21st to end	Night	48% 4 10% 18% 16% 4	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	34% 25% 27% 13% 1	220
	11th to 20th	Day	35% 31% 24% 10% 1	220
	21st to end	Day	30% 30% 29% 7% 4	281
February	1st to 10th	Day	32% 28% 29% 10% 1	372
	11th to 20th	Day	32% 25% 32% 9% 1	536
	21st to end	Day	33% 25% 30% 9% 3	446
March	1st to 10th	Day	31% 23% 32% 12% 2	508
	11th to 20th	Day	29% 26% 31% 11% 2 1	500
	21st to end	Day	32% 24% 30% 10% 3 1	550
April	1st to 10th	Day	34% 26% 23% 10% 6% 1	500
	11th to 20th	Day	33% 21% 28% 12% 4 1	492
	21st to end	Day	30% 19% 32% 13% 4 1	500
May	1st to 10th	Day	35% 19% 29% 11% 5% 1	503
	11th to 20th	Day	25% 19% 34% 17% 5% 1	527
	21st to end	Day	23% 11% 32% 22% 9% 2	573
June	1st to 10th	Day	22% 12% 32% 23% 9% 2	530
	11th to 20th	Day	20% 15% 33% 21% 10% 1	530
	21st to end	Day	17% 14% 31% 27% 10% 1	530
July	1st to 10th	Day	16% 8% 33% 27% 14% 2	525
	11th to 20th	Day	11% 10% 33% 28% 15% 2	524
	21st to end	Day	13% 11% 36% 28% 11% 1	576
August	1st to 10th	Day	15% 9% 29% 31% 12% 4	526
	11th to 20th	Day	15% 7% 28% 31% 13% 5%	519
	21st to end	Day	11% 12% 32% 25% 14% 6%	583
September	1st to 10th	Day	20% 12% 27% 21% 15% 5%	530
	11th to 20th	Day	14% 11% 28% 27% 12% 8%	530
	21st to end	Day	22% 13% 30% 22% 9% 4	530
October	1st to 10th	Day	28% 10% 27% 15% 14% 5%	530
	11th to 20th	Day	18% 23% 28% 21% 8% 2	530
	21st to end	Day	29% 15% 30% 18% 7% 1	462
November	1st to 10th	Day	22% 18% 28% 23% 8% 2	425
	11th to 20th	Day	27% 23% 27% 17% 4 1	430
	21st to end	Day	30% 22% 28% 16% 4	367
December	1st to 10th	Day	32% 21% 30% 13% 5%	220
	11th to 20th	Day	40% 24% 24% 11% 1	220
	21st to end	Day	30% 25% 26% 14% 3 1	242
January	1st to 10th	Night	26% 20% 37% 15% 3	840
	11th to 20th	Night	29% 22% 30% 18% 2	840
	21st to end	Night	23% 23% 35% 16% 2	924
February	1st to 10th	Night	24% 20% 35% 18% 2	840
	11th to 20th	Night	27% 22% 36% 13% 1	823
	21st to end	Night	28% 22% 32% 16% 2	692
March	1st to 10th	Night	27% 20% 34% 17% 2	809
	11th to 20th	Night	23% 24% 33% 16% 3 1	800
	21st to end	Night	25% 22% 33% 16% 4	880
April	1st to 10th	Night	27% 21% 32% 17% 2	800
	11th to 20th	Night	25% 21% 32% 19% 3	791
	21st to end	Night	24% 21% 34% 17% 4 1	709
May	1st to 10th	Night	29% 15% 32% 20% 5%	600
	11th to 20th	Night	22% 18% 34% 23% 3	460
	21st to end	Night	21% 9% 30% 32% 7% 1	433
June	1st to 10th	Night	20% 8% 32% 30% 10% 1	400
	11th to 20th	Night	18% 8% 30% 33% 11%	400
	21st to end	Night	17% 5% 27% 41% 10%	400
July	1st to 10th	Night	15% 5% 22% 38% 20%	390
	11th to 20th	Night	13% 5% 25% 40% 14% 2	388
	21st to end	Night	14% 4 28% 39% 15%	438
August	1st to 10th	Night	12% 4 27% 40% 16% 1	458
	11th to 20th	Night	16% 7% 22% 36% 19% 2	790
	21st to end	Night	15% 6% 22% 37% 18% 2	880
September	1st to 10th	Night	17% 7% 30% 32% 13% 2	800
	11th to 20th	Night	15% 8% 24% 33% 18% 3	800
	21st to end	Night	23% 8% 25% 28% 15% 2	800
October	1st to 10th	Night	22% 11% 27% 26% 13% 1	800
	11th to 20th	Night	19% 15% 31% 25% 8% 1	800
	21st to end	Night	27% 14% 32% 21% 7%	880
November	1st to 10th	Night	18% 15% 32% 25% 8% 1	820
	11th to 20th	Night	23% 19% 33% 19% 6% 1	840
	21st to end	Night	24% 18% 30% 23% 5% 1	840
December	1st to 10th	Night	28% 17% 31% 19% 4 1	840
	11th to 20th	Night	27% 21% 29% 20% 3	840
	21st to end	Night	29% 19% 33% 17% 2	924

Page generated at 2026-02-28 01:40:19. Version ac07

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