Stoneham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stoneham clear sky chart from 2005-11-06 to 2026-04-17.

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	19% 11% 4 9% 5% 4 4 4 5% 6% 29%	131034
	Night	18% 12% 4 10% 5% 4 4 3 5% 5% 29%	131170
Transparency	Day	55% 6% 12% 17% 9% 1	134476
	Night	56% 5% 11% 17% 9% 1	135816
Seeing	Day	27% 17% 30% 18% 7% 1	16993
	Night	25% 12% 29% 26% 8% 1	25649

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	13% 16% 5% 13% 6% 4 4 3 5% 5% 26%	4661
	11th to 20th	Day	9% 18% 8% 19% 9% 6% 4 3 3 3 18%	4650
	21st to end	Day	6% 11% 7% 12% 7% 5% 4 5% 6% 6% 32%	5124
February	1st to 10th	Day	9% 15% 5% 13% 7% 6% 5% 3 4 5% 26%	1680
	11th to 20th	Day	13% 16% 7% 12% 6% 5% 4 3 4 5% 25%	2022
	21st to end	Day	13% 16% 5% 13% 6% 4 4 3 5% 5% 27%	1730
March	1st to 10th	Day	22% 16% 5% 11% 5% 4 3 3 3 4 25%	4576
	11th to 20th	Day	16% 16% 4 10% 4 4 4 3 5% 5% 28%	4848
	21st to end	Day	18% 16% 4 8% 4 3 3 3 3 4 33%	5954
April	1st to 10th	Day	22% 16% 4 8% 5% 3 4 3 4 5% 28%	2520
	11th to 20th	Day	23% 10% 3 6% 5% 4 4 3 4 5% 33%	2543
	21st to end	Day	24% 11% 3 8% 5% 4 4 3 4 5% 30%	2600
May	1st to 10th	Day	28% 9% 3 6% 4 4 4 3 5% 5% 29%	6060
	11th to 20th	Day	22% 8% 2 7% 5% 5% 5% 4 6% 7% 31%	6318
	21st to end	Day	22% 9% 3 8% 5% 5% 6% 4 5% 6% 28%	7038
June	1st to 10th	Day	23% 7% 3 7% 5% 6% 5% 5% 7% 7% 26%	3000
	11th to 20th	Day	22% 7% 3 6% 5% 5% 4 4 6% 7% 32%	3000
	21st to end	Day	26% 9% 3 7% 5% 5% 4 4 5% 7% 24%	3000
July	1st to 10th	Day	18% 8% 3 8% 5% 5% 6% 5% 7% 8% 25%	6462
	11th to 20th	Day	19% 7% 3 7% 5% 5% 5% 5% 7% 8% 29%	6360
	21st to end	Day	14% 5% 2 6% 5% 5% 6% 5% 7% 9% 37%	6926
August	1st to 10th	Day	17% 7% 3 7% 6% 5% 7% 5% 8% 9% 28%	4548
	11th to 20th	Day	22% 7% 2 7% 6% 5% 5% 5% 6% 8% 26%	4175
	21st to end	Day	22% 7% 2 6% 4 4 5% 4 5% 7% 33%	4477
September	1st to 10th	Day	21% 7% 2 6% 4 4 4 4 6% 7% 35%	2400
	11th to 20th	Day	18% 6% 2 5% 3 3 4 3 5% 6% 45%	2227
	21st to end	Day	24% 7% 2 5% 4 4 4 4 4 5% 36%	2200
October	1st to 10th	Day	22% 9% 3 7% 4 4 4 4 4 5% 34%	2190
	11th to 20th	Day	26% 10% 3 7% 4 5% 5% 3 5% 6% 25%	1830
	21st to end	Day	29% 12% 3 7% 4 4 5% 3 4 6% 24%	1980
November	1st to 10th	Day	21% 13% 5% 7% 5% 4 3 3 4 6% 28%	1851
	11th to 20th	Day	22% 15% 5% 11% 5% 4 3 3 4 4 24%	1879
	21st to end	Day	20% 20% 5% 9% 6% 4 4 2 4 4 21%	1501
December	1st to 10th	Day	19% 15% 6% 11% 6% 5% 5% 3 5% 5% 20%	2350
	11th to 20th	Day	20% 15% 7% 9% 5% 5% 3 3 3 3 27%	2688
	21st to end	Day	19% 17% 5% 10% 3 3 4 4 4 4 27%	3666
January	1st to 10th	Night	13% 18% 6% 14% 7% 4 4 3 4 4 22%	8234
	11th to 20th	Night	10% 21% 10% 18% 7% 5% 4 3 3 3 16%	8235
	21st to end	Night	5% 10% 6% 15% 8% 6% 6% 4 6% 7% 27%	9057
February	1st to 10th	Night	10% 13% 6% 12% 6% 5% 5% 4 4 5% 29%	2940
	11th to 20th	Night	12% 18% 5% 12% 6% 5% 4 3 5% 5% 26%	2478
	21st to end	Night	14% 16% 5% 10% 6% 5% 4 3 5% 5% 29%	2076
March	1st to 10th	Night	21% 14% 4 10% 6% 4 5% 3 4 5% 25%	5484
	11th to 20th	Night	15% 16% 4 9% 6% 6% 6% 4 5% 6% 24%	5330
	21st to end	Night	18% 15% 4 9% 5% 4 4 3 4 4 31%	5218
April	1st to 10th	Night	22% 15% 3 7% 4 3 4 3 4 5% 29%	2100
	11th to 20th	Night	21% 9% 3 6% 5% 4 4 3 5% 7% 32%	1938
	21st to end	Night	23% 10% 2 9% 3 3 3 2 4 6% 34%	1800
May	1st to 10th	Night	27% 8% 2 7% 4 4 4 3 4 5% 31%	3921
	11th to 20th	Night	25% 8% 2 6% 4 4 4 3 5% 6% 32%	3575
	21st to end	Night	19% 8% 2 6% 5% 4 4 4 5% 7% 35%	3838
June	1st to 10th	Night	21% 8% 3 6% 4 6% 6% 5% 6% 7% 29%	1400
	11th to 20th	Night	21% 6% 2 5% 5% 4 4 3 7% 8% 36%	1400
	21st to end	Night	26% 8% 3 7% 5% 4 3 4 4 7% 30%	1400
July	1st to 10th	Night	16% 7% 3 7% 5% 5% 6% 5% 7% 8% 31%	3485
	11th to 20th	Night	22% 7% 3 6% 5% 4 4 4 5% 8% 33%	3600
	21st to end	Night	13% 5% 2 7% 4 4 4 4 5% 7% 44%	3926
August	1st to 10th	Night	19% 7% 3 6% 4 5% 4 3 5% 7% 36%	2586
	11th to 20th	Night	21% 6% 3 6% 5% 5% 4 4 6% 7% 32%	2855
	21st to end	Night	21% 8% 3 7% 5% 5% 4 3 4 5% 34%	3419
September	1st to 10th	Night	20% 6% 3 6% 4 3 3 3 5% 6% 42%	2000
	11th to 20th	Night	19% 6% 2 5% 3 3 4 2 5% 6% 44%	2172
	21st to end	Night	22% 8% 2 6% 3 3 2 3 4 5% 42%	2200
October	1st to 10th	Night	21% 8% 3 6% 4 3 4 3 5% 5% 38%	2209
	11th to 20th	Night	26% 8% 3 6% 4 5% 4 3 5% 5% 32%	2569
	21st to end	Night	27% 11% 2 7% 3 4 4 4 5% 5% 28%	2860
November	1st to 10th	Night	21% 13% 4 8% 4 4 3 3 5% 7% 28%	2667
	11th to 20th	Night	20% 12% 4 9% 4 4 4 3 4 5% 30%	2737
	21st to end	Night	21% 17% 6% 10% 4 4 4 3 3 5% 22%	3116
December	1st to 10th	Night	16% 14% 7% 13% 8% 5% 4 3 5% 4 21%	5060
	11th to 20th	Night	22% 15% 5% 11% 7% 4 4 3 4 4 23%	5741
	21st to end	Night	20% 18% 5% 10% 4 3 3 2 3 3 28%	7544

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	59% 4 10% 17% 11%	4662
	11th to 20th	Day	70% 5% 6% 11% 6% 1	4680
	21st to end	Day	50% 5% 8% 20% 16% 1	5124
February	1st to 10th	Day	58% 6% 8% 15% 10% 2	1680
	11th to 20th	Day	61% 5% 10% 14% 10% 1	2031
	21st to end	Day	59% 4 9% 17% 9% 3	1730
March	1st to 10th	Day	63% 6% 7% 11% 9% 4	4579
	11th to 20th	Day	55% 7% 14% 14% 9% 1	4848
	21st to end	Day	56% 4 6% 15% 15% 4	5954
April	1st to 10th	Day	60% 4 10% 13% 10% 3	2520
	11th to 20th	Day	52% 5% 10% 20% 11% 2	2543
	21st to end	Day	55% 6% 11% 15% 11% 2	2600
May	1st to 10th	Day	55% 6% 12% 14% 13% 1	6071
	11th to 20th	Day	51% 9% 15% 17% 5% 3	6322
	21st to end	Day	55% 7% 10% 15% 11% 2	7038
June	1st to 10th	Day	53% 10% 12% 18% 6% 1	3000
	11th to 20th	Day	49% 7% 15% 17% 10% 1	3000
	21st to end	Day	59% 7% 12% 14% 8% 1	3000
July	1st to 10th	Day	54% 6% 16% 17% 6%	6392
	11th to 20th	Day	50% 7% 19% 21% 4	6285
	21st to end	Day	43% 6% 17% 26% 8%	6728
August	1st to 10th	Day	49% 9% 19% 17% 6%	4534
	11th to 20th	Day	54% 7% 19% 15% 4	4214
	21st to end	Day	49% 7% 16% 16% 12%	4477
September	1st to 10th	Day	46% 7% 16% 22% 9%	2400
	11th to 20th	Day	39% 6% 18% 27% 10%	2227
	21st to end	Day	49% 7% 12% 22% 9%	2200
October	1st to 10th	Day	55% 7% 11% 21% 6%	3567
	11th to 20th	Day	55% 6% 15% 22% 2	2955
	21st to end	Day	58% 6% 15% 14% 7%	3180
November	1st to 10th	Day	58% 7% 12% 18% 6%	1851
	11th to 20th	Day	63% 4 10% 16% 6% 1	1879
	21st to end	Day	67% 6% 10% 11% 5% 1	1501
December	1st to 10th	Day	67% 4 11% 11% 7%	2350
	11th to 20th	Day	63% 4 6% 16% 11%	2688
	21st to end	Day	60% 5% 8% 13% 12% 2	3666
January	1st to 10th	Night	65% 4 9% 13% 8%	8234
	11th to 20th	Night	72% 5% 6% 12% 4 1	8280
	21st to end	Night	55% 5% 9% 16% 15% 1	9057
February	1st to 10th	Night	56% 6% 8% 19% 10% 1	2940
	11th to 20th	Night	59% 5% 11% 13% 11% 1	2480
	21st to end	Night	56% 5% 8% 15% 13% 2	2076
March	1st to 10th	Night	62% 5% 9% 11% 12% 1	5494
	11th to 20th	Night	59% 7% 12% 13% 8% 2	5331
	21st to end	Night	57% 4 6% 20% 11% 2	5218
April	1st to 10th	Night	57% 5% 9% 13% 14% 3	2100
	11th to 20th	Night	50% 6% 10% 20% 12% 2	1938
	21st to end	Night	53% 6% 9% 17% 14% 2	1800
May	1st to 10th	Night	54% 6% 9% 17% 13% 1	3927
	11th to 20th	Night	50% 9% 13% 19% 9% 1	3576
	21st to end	Night	48% 6% 13% 17% 15% 2	3839
June	1st to 10th	Night	51% 9% 12% 19% 8% 1	1400
	11th to 20th	Night	45% 8% 13% 20% 11% 3	1400
	21st to end	Night	55% 7% 11% 16% 12%	1400
July	1st to 10th	Night	49% 6% 21% 19% 5%	3445
	11th to 20th	Night	50% 5% 20% 22% 3	3552
	21st to end	Night	40% 5% 20% 26% 8%	3809
August	1st to 10th	Night	47% 6% 17% 22% 7%	2576
	11th to 20th	Night	49% 10% 19% 16% 6% 1	2882
	21st to end	Night	51% 6% 13% 22% 9%	3419
September	1st to 10th	Night	42% 8% 14% 24% 11% 1	2000
	11th to 20th	Night	41% 8% 15% 28% 7% 1	2172
	21st to end	Night	45% 5% 13% 25% 12%	2200
October	1st to 10th	Night	50% 4 12% 26% 8%	3612
	11th to 20th	Night	51% 5% 14% 26% 4	4183
	21st to end	Night	53% 5% 17% 15% 9%	4610
November	1st to 10th	Night	56% 6% 13% 19% 6% 1	2667
	11th to 20th	Night	56% 6% 11% 17% 10%	2737
	21st to end	Night	65% 5% 10% 13% 6% 1	3116
December	1st to 10th	Night	66% 4 12% 13% 4	5060
	11th to 20th	Night	66% 3 7% 16% 8%	5742
	21st to end	Night	62% 4 7% 14% 11% 2	7544

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	26% 19% 36% 15% 4	220
	11th to 20th	Day	24% 25% 32% 14% 5%	220
	21st to end	Day	17% 22% 41% 15% 4 1	242
February	1st to 10th	Day	27% 26% 35% 10% 2 1	220
	11th to 20th	Day	23% 26% 34% 14% 3	518
	21st to end	Day	24% 23% 32% 17% 3	446
March	1st to 10th	Day	26% 24% 30% 16% 4	540
	11th to 20th	Day	29% 20% 31% 15% 5% 1	540
	21st to end	Day	28% 23% 26% 16% 6% 1	594
April	1st to 10th	Day	32% 20% 28% 16% 4	540
	11th to 20th	Day	31% 19% 29% 15% 4 2	516
	21st to end	Day	32% 18% 33% 12% 4 1	500
May	1st to 10th	Day	32% 18% 30% 14% 5% 1	503
	11th to 20th	Day	25% 17% 31% 21% 6% 1	527
	21st to end	Day	28% 20% 29% 17% 5%	610
June	1st to 10th	Day	25% 16% 30% 22% 8%	730
	11th to 20th	Day	26% 15% 28% 22% 8% 1	730
	21st to end	Day	29% 14% 29% 19% 8% 1	730
July	1st to 10th	Day	22% 15% 33% 21% 8% 1	575
	11th to 20th	Day	22% 13% 34% 23% 7% 1	524
	21st to end	Day	21% 14% 33% 23% 8% 1	576
August	1st to 10th	Day	22% 10% 32% 23% 11% 3	526
	11th to 20th	Day	21% 9% 27% 29% 12% 2	519
	21st to end	Day	25% 14% 25% 19% 12% 5%	583
September	1st to 10th	Day	24% 13% 28% 21% 11% 3	530
	11th to 20th	Day	21% 12% 28% 23% 14% 2	530
	21st to end	Day	25% 13% 28% 20% 10% 5%	530
October	1st to 10th	Day	26% 15% 29% 20% 10% 1	530
	11th to 20th	Day	33% 15% 25% 18% 8% 1	436
	21st to end	Day	37% 18% 24% 16% 5%	462
November	1st to 10th	Day	37% 16% 26% 17% 4 1	425
	11th to 20th	Day	29% 20% 28% 16% 7% 1	419
	21st to end	Day	34% 22% 30% 13% 1	220
December	1st to 10th	Day	30% 17% 29% 16% 7%	220
	11th to 20th	Day	35% 21% 27% 13% 3	220
	21st to end	Day	30% 22% 30% 15% 3	242
January	1st to 10th	Night	24% 17% 33% 22% 4	840
	11th to 20th	Night	25% 17% 30% 22% 6%	840
	21st to end	Night	15% 13% 36% 29% 6%	924
February	1st to 10th	Night	17% 16% 35% 26% 6%	840
	11th to 20th	Night	23% 16% 39% 18% 4	823
	21st to end	Night	22% 15% 34% 24% 4	692
March	1st to 10th	Night	23% 15% 37% 23% 3	840
	11th to 20th	Night	24% 18% 33% 20% 5% 1	840
	21st to end	Night	22% 17% 32% 23% 5% 1	924
April	1st to 10th	Night	30% 16% 28% 20% 5%	840
	11th to 20th	Night	27% 11% 34% 23% 5%	718
	21st to end	Night	30% 16% 30% 19% 5%	600
May	1st to 10th	Night	28% 11% 31% 25% 5%	545
	11th to 20th	Night	23% 10% 29% 31% 7% 1	394
	21st to end	Night	28% 7% 32% 25% 8%	433
June	1st to 10th	Night	24% 8% 28% 33% 7%	400
	11th to 20th	Night	22% 6% 24% 37% 12%	400
	21st to end	Night	27% 5% 24% 36% 9% 1	400
July	1st to 10th	Night	20% 4 28% 36% 11% 1	390
	11th to 20th	Night	21% 3 22% 39% 14% 1	388
	21st to end	Night	18% 6% 21% 41% 14% 1	438
August	1st to 10th	Night	18% 4 16% 43% 19%	398
	11th to 20th	Night	18% 5% 22% 38% 16% 1	575
	21st to end	Night	21% 6% 24% 31% 16% 2	778
September	1st to 10th	Night	21% 6% 27% 33% 13% 1	800
	11th to 20th	Night	20% 8% 24% 30% 16% 2	800
	21st to end	Night	24% 9% 25% 28% 13% 1	800
October	1st to 10th	Night	26% 9% 27% 29% 10% 1	800
	11th to 20th	Night	29% 10% 26% 26% 9%	800
	21st to end	Night	33% 13% 27% 22% 5%	880
November	1st to 10th	Night	29% 14% 27% 23% 6% 1	820
	11th to 20th	Night	27% 15% 25% 24% 8% 1	840
	21st to end	Night	29% 17% 28% 19% 5% 1	934
December	1st to 10th	Night	30% 13% 26% 23% 7%	950
	11th to 20th	Night	26% 20% 28% 21% 5% 1	950
	21st to end	Night	29% 17% 29% 20% 4	1015

Page generated at 2026-04-14 02:44:24. Version ac07

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