Roxbury Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roxbury Park clear sky chart from 2005-11-06 to 2024-11-01.

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	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	101104
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	97809
Transparency	Day	37% 9% 15% 19% 14% 5%	100917
	Night	38% 8% 13% 19% 16% 6%	97666
Seeing	Day	12% 9% 25% 27% 19% 7%	15501
	Night	13% 8% 24% 31% 21% 4	25577

By Month

Percentage Cloud Cover SE (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% 5% 2 6% 4 5% 5% 4 6% 8% 43%	2836
	11th to 20th	Day	12% 6% 2 6% 3 3 4 3 5% 8% 46%	2840
	21st to end	Day	14% 9% 3 6% 4 4 3 3 4 5% 45%	3124
February	1st to 10th	Day	14% 8% 2 6% 5% 3 5% 4 5% 7% 41%	1710
	11th to 20th	Day	18% 7% 2 4 3 4 3 4 5% 6% 45%	1844
	21st to end	Day	13% 6% 3 6% 4 3 4 3 4 6% 47%	1696
March	1st to 10th	Day	21% 9% 3 7% 4 4 3 3 5% 6% 35%	3435
	11th to 20th	Day	8% 4 1 4 4 4 4 4 6% 8% 54%	3480
	21st to end	Day	16% 5% 2 6% 4 4 4 3 5% 5% 45%	3815
April	1st to 10th	Day	8% 3 2 5% 4 4 4 4 6% 7% 53%	2090
	11th to 20th	Day	9% 5% 2 5% 4 3 5% 3 6% 7% 50%	2253
	21st to end	Day	6% 4 1 4 3 4 3 4 6% 10% 56%	2280
May	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 8% 11% 44%	4072
	11th to 20th	Day	14% 6% 3 7% 4 4 4 4 7% 8% 39%	4081
	21st to end	Day	6% 3 2 5% 4 4 5% 5% 7% 11% 49%	4476
June	1st to 10th	Day	8% 6% 3 7% 6% 6% 7% 5% 8% 10% 33%	2470
	11th to 20th	Day	7% 4 2 5% 5% 6% 6% 5% 9% 11% 38%	2470
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 6% 10% 13% 32%	2470
July	1st to 10th	Day	12% 6% 3 7% 6% 6% 7% 6% 9% 11% 28%	4120
	11th to 20th	Day	5% 4 2 7% 6% 7% 7% 7% 10% 14% 32%	4120
	21st to end	Day	6% 5% 2 8% 6% 8% 8% 6% 10% 14% 26%	4466
August	1st to 10th	Day	20% 6% 3 8% 5% 6% 6% 6% 9% 10% 23%	4104
	11th to 20th	Day	6% 5% 2 7% 5% 6% 7% 6% 10% 12% 34%	3957
	21st to end	Day	9% 6% 3 8% 5% 5% 6% 5% 8% 10% 35%	4180
September	1st to 10th	Day	11% 6% 2 7% 6% 5% 7% 5% 8% 8% 34%	2128
	11th to 20th	Day	12% 7% 3 7% 6% 5% 6% 4 8% 9% 32%	2090
	21st to end	Day	12% 7% 2 7% 5% 4 5% 4 6% 8% 39%	2090
October	1st to 10th	Day	11% 5% 2 6% 4 5% 4 3 6% 6% 47%	1953
	11th to 20th	Day	8% 4 1 4 3 3 3 3 5% 6% 60%	1900
	21st to end	Day	9% 5% 2 5% 3 4 4 3 5% 6% 55%	2090
November	1st to 10th	Day	10% 5% 1 4 3 4 4 3 5% 6% 54%	1857
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 5% 6% 50%	1900
	21st to end	Day	12% 6% 2 4 3 3 4 3 5% 6% 51%	1720
December	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 5% 7% 44%	1710
	11th to 20th	Day	16% 5% 2 4 3 2 2 2 5% 6% 53%	2153
	21st to end	Day	18% 8% 3 5% 4 3 4 3 4 6% 43%	3124
January	1st to 10th	Night	14% 6% 2 6% 4 5% 5% 4 5% 6% 43%	4109
	11th to 20th	Night	10% 7% 2 7% 5% 5% 5% 4 5% 8% 42%	4120
	21st to end	Night	13% 9% 3 7% 4 4 4 3 4 5% 43%	4532
February	1st to 10th	Night	15% 6% 2 6% 5% 4 4 4 5% 6% 43%	2470
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 3 5% 6% 43%	2218
	21st to end	Night	12% 7% 4 7% 5% 4 4 3 5% 6% 43%	1756
March	1st to 10th	Night	21% 11% 4 9% 4 3 3 2 4 5% 34%	3418
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 7% 49%	3480
	21st to end	Night	15% 5% 2 5% 4 3 3 3 5% 8% 45%	3817
April	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 5% 7% 51%	2090
	11th to 20th	Night	11% 4 2 5% 4 3 4 3 6% 7% 52%	1875
	21st to end	Night	7% 5% 2 4 4 3 4 4 6% 8% 54%	1900
May	1st to 10th	Night	6% 5% 2 4 4 4 4 4 7% 10% 49%	2850
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 6% 9% 44%	2812
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 8% 53%	3079
June	1st to 10th	Night	9% 5% 3 7% 5% 5% 5% 6% 9% 12% 34%	1710
	11th to 20th	Night	6% 5% 2 6% 6% 6% 5% 6% 10% 12% 38%	1710
	21st to end	Night	5% 5% 2 6% 6% 6% 7% 6% 9% 14% 34%	1710
July	1st to 10th	Night	10% 6% 3 8% 6% 5% 7% 6% 9% 12% 29%	2840
	11th to 20th	Night	6% 5% 3 8% 6% 6% 7% 7% 10% 13% 30%	2840
	21st to end	Night	8% 6% 3 8% 7% 7% 8% 6% 9% 13% 25%	3087
August	1st to 10th	Night	18% 7% 2 6% 4 5% 6% 6% 9% 13% 23%	2825
	11th to 20th	Night	7% 5% 3 6% 5% 5% 6% 6% 7% 13% 37%	2839
	21st to end	Night	7% 5% 2 7% 5% 5% 5% 4 6% 8% 45%	3476
September	1st to 10th	Night	9% 6% 3 7% 6% 5% 6% 5% 7% 9% 38%	2046
	11th to 20th	Night	10% 7% 3 6% 6% 5% 5% 5% 7% 8% 38%	2090
	21st to end	Night	13% 6% 3 7% 5% 5% 5% 3 6% 10% 38%	2090
October	1st to 10th	Night	12% 6% 3 6% 4 3 4 4 5% 6% 48%	2225
	11th to 20th	Night	9% 4 1 4 3 3 3 4 5% 7% 58%	2280
	21st to end	Night	8% 5% 2 6% 3 3 3 4 4 5% 57%	2508
November	1st to 10th	Night	9% 5% 2 4 3 4 3 4 5% 6% 54%	2228
	11th to 20th	Night	12% 7% 2 5% 4 4 3 3 5% 5% 50%	2280
	21st to end	Night	11% 6% 3 6% 4 4 4 3 6% 7% 46%	2455
December	1st to 10th	Night	13% 6% 2 7% 4 5% 5% 3 6% 8% 41%	2470
	11th to 20th	Night	16% 6% 2 5% 4 3 2 3 4 6% 49%	3042
	21st to end	Night	17% 9% 2 6% 4 4 4 3 5% 6% 40%	4532

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	36% 8% 8% 19% 19% 10%	2837
	11th to 20th	Day	35% 6% 7% 18% 25% 9%	2840
	21st to end	Day	42% 5% 6% 17% 22% 9%	3124
February	1st to 10th	Day	42% 6% 9% 19% 18% 6%	1710
	11th to 20th	Day	39% 5% 9% 16% 23% 8%	1854
	21st to end	Day	38% 5% 9% 18% 18% 11%	1696
March	1st to 10th	Day	49% 6% 11% 14% 13% 7%	3435
	11th to 20th	Day	26% 7% 13% 17% 23% 13%	3480
	21st to end	Day	40% 6% 8% 18% 20% 7%	3815
April	1st to 10th	Day	29% 7% 13% 21% 20% 10%	2090
	11th to 20th	Day	31% 6% 10% 23% 18% 10%	2253
	21st to end	Day	24% 7% 14% 29% 21% 5%	2280
May	1st to 10th	Day	30% 10% 19% 27% 11% 3	4110
	11th to 20th	Day	39% 8% 15% 25% 12% 1	4085
	21st to end	Day	26% 10% 20% 25% 18% 1	4489
June	1st to 10th	Day	41% 13% 18% 16% 10%	2470
	11th to 20th	Day	34% 12% 21% 26% 7%	2470
	21st to end	Day	37% 15% 23% 17% 7% 1	2470
July	1st to 10th	Day	45% 12% 20% 19% 3 1	4055
	11th to 20th	Day	38% 18% 31% 10% 3	4051
	21st to end	Day	42% 17% 26% 14% 2	4324
August	1st to 10th	Day	52% 13% 22% 11% 2	4091
	11th to 20th	Day	37% 14% 20% 21% 8%	3996
	21st to end	Day	41% 10% 16% 30% 3	4180
September	1st to 10th	Day	42% 13% 16% 15% 11% 3	2128
	11th to 20th	Day	44% 12% 14% 17% 11% 3	2090
	21st to end	Day	42% 8% 14% 19% 14% 4	2090
October	1st to 10th	Day	36% 7% 11% 17% 21% 8%	1953
	11th to 20th	Day	25% 6% 10% 21% 27% 11%	1900
	21st to end	Day	29% 6% 7% 17% 28% 12%	2090
November	1st to 10th	Day	31% 5% 10% 17% 24% 13%	1857
	11th to 20th	Day	35% 5% 8% 17% 22% 12%	1900
	21st to end	Day	34% 4 9% 23% 21% 8%	1720
December	1st to 10th	Day	38% 7% 13% 19% 15% 8%	1710
	11th to 20th	Day	34% 4 8% 21% 27% 7%	2150
	21st to end	Day	42% 5% 7% 19% 23% 4	3124
January	1st to 10th	Night	38% 6% 8% 15% 22% 11%	4109
	11th to 20th	Night	39% 6% 8% 17% 25% 6%	4120
	21st to end	Night	43% 5% 7% 12% 22% 11%	4532
February	1st to 10th	Night	41% 5% 8% 19% 19% 8%	2470
	11th to 20th	Night	42% 5% 9% 14% 20% 10%	2219
	21st to end	Night	41% 5% 10% 18% 15% 12%	1756
March	1st to 10th	Night	53% 5% 11% 12% 12% 7%	3418
	11th to 20th	Night	32% 6% 11% 17% 22% 13%	3480
	21st to end	Night	37% 6% 12% 19% 18% 8%	3817
April	1st to 10th	Night	32% 7% 13% 20% 20% 9%	2090
	11th to 20th	Night	31% 6% 9% 23% 20% 11%	1875
	21st to end	Night	26% 7% 13% 26% 22% 5%	1900
May	1st to 10th	Night	27% 9% 20% 29% 13% 3	2877
	11th to 20th	Night	35% 11% 13% 26% 14% 1	2813
	21st to end	Night	26% 9% 16% 30% 18% 1	3087
June	1st to 10th	Night	38% 13% 21% 19% 8%	1710
	11th to 20th	Night	35% 13% 21% 25% 7%	1710
	21st to end	Night	35% 15% 25% 20% 5% 1	1710
July	1st to 10th	Night	44% 13% 20% 20% 3 1	2795
	11th to 20th	Night	39% 17% 30% 11% 3	2786
	21st to end	Night	46% 14% 24% 14% 2	2988
August	1st to 10th	Night	48% 15% 24% 11% 2	2814
	11th to 20th	Night	35% 13% 24% 21% 6%	2866
	21st to end	Night	35% 10% 18% 33% 4	3476
September	1st to 10th	Night	39% 12% 18% 18% 10% 2	2046
	11th to 20th	Night	41% 10% 16% 19% 12% 2	2090
	21st to end	Night	41% 8% 14% 19% 14% 2	2090
October	1st to 10th	Night	35% 7% 10% 20% 21% 7%	2225
	11th to 20th	Night	26% 5% 10% 21% 25% 13%	2280
	21st to end	Night	29% 5% 8% 18% 27% 14%	2508
November	1st to 10th	Night	30% 5% 9% 18% 25% 13%	2228
	11th to 20th	Night	36% 5% 7% 18% 23% 12%	2280
	21st to end	Night	37% 5% 9% 18% 22% 9%	2455
December	1st to 10th	Night	40% 7% 14% 16% 16% 6%	2470
	11th to 20th	Night	38% 4 8% 17% 27% 6%	3044
	21st to end	Night	44% 5% 7% 18% 21% 4	4532

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	13% 20% 50% 15% 3	270
	11th to 20th	Day	12% 18% 41% 20% 8% 1	270
	21st to end	Day	22% 25% 38% 13% 2	297
February	1st to 10th	Day	17% 21% 39% 18% 6%	270
	11th to 20th	Day	26% 17% 38% 16% 3	270
	21st to end	Day	16% 21% 43% 16% 4	351
March	1st to 10th	Day	15% 18% 36% 23% 9%	460
	11th to 20th	Day	14% 16% 43% 19% 7% 1	460
	21st to end	Day	15% 19% 37% 21% 8% 1	506
April	1st to 10th	Day	15% 17% 35% 23% 9% 1	460
	11th to 20th	Day	10% 15% 31% 25% 14% 5%	452
	21st to end	Day	6% 10% 33% 30% 15% 6%	460
May	1st to 10th	Day	5% 16% 33% 28% 13% 6%	463
	11th to 20th	Day	10% 6% 27% 32% 19% 5%	487
	21st to end	Day	10% 5% 19% 34% 24% 8%	529
June	1st to 10th	Day	11% 4 21% 34% 23% 7%	490
	11th to 20th	Day	8% 3 20% 30% 27% 13%	490
	21st to end	Day	7% 2 17% 32% 31% 11%	490
July	1st to 10th	Day	7% 2 9% 31% 35% 16%	485
	11th to 20th	Day	8% 8% 31% 36% 17%	484
	21st to end	Day	5% 2 11% 38% 33% 10%	532
August	1st to 10th	Day	13% 2 11% 28% 33% 13%	486
	11th to 20th	Day	6% 4 8% 28% 38% 16%	479
	21st to end	Day	15% 3 11% 26% 31% 15%	539
September	1st to 10th	Day	14% 3 11% 30% 32% 10%	490
	11th to 20th	Day	16% 3 16% 33% 24% 8%	490
	21st to end	Day	15% 2 16% 32% 25% 10%	490
October	1st to 10th	Day	16% 6% 23% 30% 16% 9%	490
	11th to 20th	Day	9% 6% 26% 32% 20% 7%	490
	21st to end	Day	12% 6% 24% 35% 18% 5%	539
November	1st to 10th	Day	14% 6% 31% 28% 18% 4	455
	11th to 20th	Day	17% 9% 38% 25% 10% 2	460
	21st to end	Day	12% 14% 33% 31% 9% 1	280
December	1st to 10th	Day	18% 13% 36% 24% 8% 1	270
	11th to 20th	Day	20% 14% 35% 21% 10% 1	270
	21st to end	Day	25% 12% 31% 23% 9% 1	297
January	1st to 10th	Night	14% 15% 34% 29% 7%	760
	11th to 20th	Night	14% 17% 30% 29% 10%	760
	21st to end	Night	18% 15% 38% 24% 4	836
February	1st to 10th	Night	17% 12% 34% 30% 7%	760
	11th to 20th	Night	20% 15% 34% 28% 4	743
	21st to end	Night	16% 13% 36% 29% 6%	628
March	1st to 10th	Night	13% 10% 35% 34% 7%	760
	11th to 20th	Night	15% 12% 32% 32% 9%	760
	21st to end	Night	11% 15% 34% 29% 11% 1	836
April	1st to 10th	Night	11% 13% 33% 31% 11% 1	760
	11th to 20th	Night	12% 11% 29% 30% 16% 2	751
	21st to end	Night	10% 7% 29% 36% 17% 1	760
May	1st to 10th	Night	6% 8% 27% 37% 21% 2	594
	11th to 20th	Night	9% 5% 25% 33% 23% 5%	561
	21st to end	Night	8% 3 16% 32% 34% 7%	617
June	1st to 10th	Night	11% 3 11% 43% 26% 6%	570
	11th to 20th	Night	7% 2 11% 32% 35% 12%	570
	21st to end	Night	7% 1 12% 37% 34% 9%	570
July	1st to 10th	Night	7% 2 10% 35% 36% 11%	555
	11th to 20th	Night	9% 1 7% 26% 45% 12%	552
	21st to end	Night	7% 1 7% 39% 38% 8%	624
August	1st to 10th	Night	10% 2 7% 31% 40% 10%	567
	11th to 20th	Night	6% 3 7% 31% 41% 12%	592
	21st to end	Night	12% 3 9% 26% 36% 14%	836
September	1st to 10th	Night	10% 3 11% 28% 39% 8%	760
	11th to 20th	Night	13% 3 12% 31% 34% 6%	760
	21st to end	Night	16% 3 13% 29% 32% 7%	760
October	1st to 10th	Night	14% 3 20% 32% 24% 6%	760
	11th to 20th	Night	11% 5% 23% 32% 25% 4	760
	21st to end	Night	10% 6% 24% 32% 23% 3	836
November	1st to 10th	Night	13% 6% 24% 34% 19% 3	743
	11th to 20th	Night	15% 11% 28% 31% 15% 1	760
	21st to end	Night	14% 10% 29% 29% 17% 2	760
December	1st to 10th	Night	16% 12% 28% 31% 11% 1	760
	11th to 20th	Night	19% 10% 29% 26% 15% 1	760
	21st to end	Night	21% 11% 31% 27% 11%	836

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