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 2024-12-24.

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	20% 11% 4 8% 5% 4 4 4 5% 6% 29%	101768
	Night	19% 12% 4 9% 5% 4 4 3 5% 5% 30%	98366
Transparency	Day	54% 7% 13% 17% 8% 1	105228
	Night	55% 6% 12% 17% 8% 1	102996
Seeing	Day	26% 17% 30% 19% 7% 1	15346
	Night	25% 12% 28% 26% 8% 1	23922

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	14% 16% 6% 13% 7% 5% 5% 3 4 5% 21%	2517
	11th to 20th	Day	10% 15% 7% 18% 8% 5% 4 3 3 4 25%	2520
	21st to end	Day	10% 13% 6% 10% 6% 4 4 4 4 5% 33%	2772
February	1st to 10th	Day	10% 16% 5% 14% 7% 6% 5% 4 4 5% 24%	1520
	11th to 20th	Day	13% 15% 7% 13% 6% 5% 4 3 4 5% 24%	1822
	21st to end	Day	14% 16% 5% 12% 6% 4 3 3 5% 6% 26%	1570
March	1st to 10th	Day	21% 13% 4 10% 5% 4 3 3 4 4 29%	3116
	11th to 20th	Day	17% 20% 5% 10% 4 4 4 3 4 4 25%	3313
	21st to end	Day	15% 15% 4 8% 5% 4 3 3 3 4 35%	4063
April	1st to 10th	Day	22% 16% 4 8% 5% 3 4 3 4 5% 28%	2280
	11th to 20th	Day	22% 10% 3 6% 5% 4 4 3 4 5% 34%	2345
	21st to end	Day	24% 12% 3 8% 5% 4 4 3 4 5% 30%	2470
May	1st to 10th	Day	22% 9% 3 6% 4 4 4 3 5% 5% 34%	4224
	11th to 20th	Day	19% 8% 2 7% 5% 4 5% 4 6% 8% 32%	4398
	21st to end	Day	21% 7% 2 7% 5% 5% 6% 4 6% 7% 31%	4898
June	1st to 10th	Day	23% 7% 3 7% 5% 6% 5% 5% 7% 7% 26%	2850
	11th to 20th	Day	22% 7% 3 6% 5% 4 4 4 6% 7% 32%	2850
	21st to end	Day	26% 9% 4 7% 5% 5% 4 4 5% 7% 24%	2850
July	1st to 10th	Day	17% 8% 3 8% 6% 5% 6% 5% 7% 8% 27%	4514
	11th to 20th	Day	19% 7% 3 8% 6% 5% 5% 6% 7% 8% 26%	4440
	21st to end	Day	17% 6% 2 6% 5% 5% 5% 5% 7% 7% 36%	4814
August	1st to 10th	Day	17% 7% 3 7% 6% 5% 7% 5% 8% 9% 27%	4408
	11th to 20th	Day	23% 7% 2 7% 6% 5% 5% 5% 6% 9% 25%	4045
	21st to end	Day	22% 6% 2 6% 4 4 5% 4 5% 7% 34%	4340
September	1st to 10th	Day	21% 7% 2 6% 4 4 4 4 6% 7% 34%	2280
	11th to 20th	Day	19% 6% 2 5% 3 3 4 3 5% 6% 43%	2116
	21st to end	Day	25% 7% 2 5% 4 4 4 4 4 5% 35%	2090
October	1st to 10th	Day	23% 9% 3 8% 4 4 4 4 5% 5% 32%	2081
	11th to 20th	Day	27% 10% 3 8% 4 5% 4 3 5% 5% 24%	1739
	21st to end	Day	29% 12% 3 6% 4 4 5% 3 4 6% 24%	1881
November	1st to 10th	Day	21% 13% 5% 7% 5% 4 3 3 4 6% 29%	1761
	11th to 20th	Day	22% 15% 4 10% 5% 4 3 3 4 5% 25%	1790
	21st to end	Day	21% 19% 5% 9% 6% 4 4 2 4 4 21%	1430
December	1st to 10th	Day	24% 17% 5% 10% 5% 4 3 3 3 4 22%	1400
	11th to 20th	Day	21% 15% 4 10% 5% 5% 3 3 4 3 27%	1738
	21st to end	Day	20% 19% 5% 9% 4 3 3 3 4 4 26%	2523
January	1st to 10th	Night	13% 19% 7% 13% 8% 4 3 3 3 4 22%	4429
	11th to 20th	Night	12% 16% 6% 14% 8% 6% 4 3 4 4 23%	4440
	21st to end	Night	9% 14% 6% 12% 7% 5% 6% 4 5% 5% 26%	4884
February	1st to 10th	Night	11% 14% 5% 12% 6% 5% 5% 4 5% 6% 28%	2660
	11th to 20th	Night	12% 18% 5% 12% 6% 5% 5% 3 5% 5% 26%	2238
	21st to end	Night	14% 15% 5% 10% 6% 4 4 3 5% 5% 29%	1884
March	1st to 10th	Night	23% 13% 3 7% 5% 3 6% 3 4 5% 28%	3724
	11th to 20th	Night	16% 20% 4 9% 5% 5% 5% 3 4 5% 23%	3645
	21st to end	Night	16% 13% 4 9% 5% 4 4 3 4 4 33%	3567
April	1st to 10th	Night	22% 15% 3 7% 4 3 4 3 4 5% 29%	1900
	11th to 20th	Night	21% 9% 3 7% 4 3 4 3 5% 7% 33%	1783
	21st to end	Night	23% 10% 3 9% 3 4 3 2 4 6% 34%	1710
May	1st to 10th	Night	23% 7% 2 6% 4 4 4 3 4 6% 35%	2743
	11th to 20th	Night	23% 8% 2 6% 4 4 4 4 5% 6% 35%	2495
	21st to end	Night	21% 5% 2 5% 4 5% 4 4 5% 8% 36%	2676
June	1st to 10th	Night	21% 9% 3 6% 4 6% 6% 5% 6% 7% 28%	1330
	11th to 20th	Night	20% 6% 2 5% 5% 4 4 3 7% 8% 37%	1330
	21st to end	Night	26% 8% 3 7% 5% 4 3 3 4 7% 29%	1330
July	1st to 10th	Night	16% 7% 3 7% 6% 5% 6% 5% 6% 8% 31%	2444
	11th to 20th	Night	21% 8% 3 7% 5% 4 4 4 5% 8% 32%	2520
	21st to end	Night	15% 5% 2 6% 4 3 4 4 5% 7% 44%	2739
August	1st to 10th	Night	19% 7% 3 7% 4 5% 4 4 5% 7% 35%	2506
	11th to 20th	Night	22% 6% 3 6% 5% 5% 5% 4 6% 7% 31%	2766
	21st to end	Night	20% 7% 3 7% 4 5% 4 3 4 5% 35%	3314
September	1st to 10th	Night	20% 6% 3 6% 4 3 3 3 5% 6% 41%	1900
	11th to 20th	Night	20% 6% 2 5% 3 3 4 2 5% 6% 44%	2063
	21st to end	Night	22% 8% 2 6% 4 3 2 3 4 5% 41%	2090
October	1st to 10th	Night	22% 9% 3 6% 4 4 4 3 5% 5% 36%	2098
	11th to 20th	Night	27% 9% 3 6% 4 5% 4 3 5% 5% 31%	2440
	21st to end	Night	27% 11% 2 7% 3 3 4 4 5% 6% 28%	2717
November	1st to 10th	Night	20% 13% 4 7% 4 4 3 3 6% 7% 29%	2537
	11th to 20th	Night	21% 12% 4 9% 4 4 4 3 4 5% 31%	2606
	21st to end	Night	21% 17% 6% 10% 4 4 4 3 3 5% 23%	2967
December	1st to 10th	Night	21% 17% 5% 11% 7% 4 3 3 4 5% 20%	3000
	11th to 20th	Night	21% 15% 4 11% 5% 4 4 3 4 4 24%	3681
	21st to end	Night	21% 20% 6% 9% 4 3 2 2 3 3 26%	5210

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	62% 7% 12% 13% 4 1	2518
	11th to 20th	Day	61% 8% 9% 14% 7% 1	2520
	21st to end	Day	50% 8% 11% 20% 11% 1	2772
February	1st to 10th	Day	60% 7% 9% 13% 9% 2	1520
	11th to 20th	Day	61% 5% 10% 12% 10% 1	1831
	21st to end	Day	60% 4 9% 17% 8% 3	1570
March	1st to 10th	Day	56% 9% 9% 15% 9% 3	3119
	11th to 20th	Day	58% 8% 11% 14% 7% 1	3313
	21st to end	Day	52% 5% 8% 16% 14% 5%	4063
April	1st to 10th	Day	60% 5% 11% 12% 10% 4	2280
	11th to 20th	Day	51% 6% 10% 20% 11% 2	2345
	21st to end	Day	55% 6% 10% 15% 11% 2	2470
May	1st to 10th	Day	48% 7% 15% 15% 14% 1	4238
	11th to 20th	Day	47% 10% 17% 19% 6% 1	4402
	21st to end	Day	49% 9% 11% 17% 13% 1	4898
June	1st to 10th	Day	53% 10% 12% 17% 6% 1	2850
	11th to 20th	Day	49% 7% 16% 17% 10% 1	2850
	21st to end	Day	59% 7% 11% 14% 8%	2850
July	1st to 10th	Day	52% 7% 16% 17% 7%	4444
	11th to 20th	Day	52% 8% 18% 18% 4	4365
	21st to end	Day	45% 8% 18% 23% 7%	4661
August	1st to 10th	Day	51% 9% 18% 17% 5%	4394
	11th to 20th	Day	55% 7% 19% 15% 4	4084
	21st to end	Day	48% 7% 16% 16% 13%	4340
September	1st to 10th	Day	47% 7% 15% 21% 9%	2280
	11th to 20th	Day	40% 6% 18% 26% 9%	2116
	21st to end	Day	50% 7% 12% 22% 9%	2090
October	1st to 10th	Day	57% 7% 11% 20% 5%	3458
	11th to 20th	Day	55% 6% 15% 22% 2	2864
	21st to end	Day	57% 6% 16% 13% 7%	3081
November	1st to 10th	Day	57% 7% 11% 18% 6%	1761
	11th to 20th	Day	61% 5% 10% 16% 6% 1	1790
	21st to end	Day	67% 7% 11% 11% 5% 1	1430
December	1st to 10th	Day	67% 5% 10% 12% 6%	1400
	11th to 20th	Day	61% 6% 7% 17% 9%	1738
	21st to end	Day	62% 6% 10% 14% 7% 2	2523
January	1st to 10th	Night	65% 6% 10% 12% 6% 1	4429
	11th to 20th	Night	61% 7% 9% 16% 5% 1	4440
	21st to end	Night	55% 9% 10% 14% 11% 1	4884
February	1st to 10th	Night	57% 6% 8% 18% 10% 1	2660
	11th to 20th	Night	60% 5% 11% 12% 11% 1	2240
	21st to end	Night	57% 5% 9% 15% 12% 2	1884
March	1st to 10th	Night	57% 7% 12% 13% 8% 2	3734
	11th to 20th	Night	61% 7% 11% 13% 6% 1	3646
	21st to end	Night	55% 5% 8% 20% 10% 2	3567
April	1st to 10th	Night	57% 5% 9% 13% 13% 3	1900
	11th to 20th	Night	49% 7% 9% 21% 12% 2	1783
	21st to end	Night	53% 6% 8% 17% 14% 2	1710
May	1st to 10th	Night	49% 8% 11% 20% 11% 1	2749
	11th to 20th	Night	46% 11% 14% 18% 10% 1	2496
	21st to end	Night	45% 7% 13% 18% 15% 1	2677
June	1st to 10th	Night	52% 10% 12% 18% 8% 1	1330
	11th to 20th	Night	44% 8% 13% 20% 11% 3	1330
	21st to end	Night	55% 7% 11% 16% 11%	1330
July	1st to 10th	Night	49% 7% 20% 18% 5%	2404
	11th to 20th	Night	51% 6% 19% 20% 4	2472
	21st to end	Night	39% 6% 24% 22% 9%	2651
August	1st to 10th	Night	48% 6% 17% 22% 6%	2496
	11th to 20th	Night	50% 10% 20% 15% 5%	2793
	21st to end	Night	51% 6% 13% 22% 9%	3314
September	1st to 10th	Night	43% 8% 14% 23% 12% 1	1900
	11th to 20th	Night	42% 8% 15% 27% 7% 1	2063
	21st to end	Night	45% 6% 14% 24% 11%	2090
October	1st to 10th	Night	51% 4 12% 25% 8%	3501
	11th to 20th	Night	52% 6% 14% 26% 4	4054
	21st to end	Night	53% 6% 17% 15% 9%	4467
November	1st to 10th	Night	55% 6% 14% 19% 6% 1	2537
	11th to 20th	Night	55% 6% 11% 17% 10%	2606
	21st to end	Night	64% 5% 10% 13% 6% 1	2967
December	1st to 10th	Night	68% 5% 10% 12% 5%	3000
	11th to 20th	Night	62% 5% 9% 14% 9%	3682
	21st to end	Night	64% 5% 8% 14% 7% 2	5210

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	24% 18% 36% 18% 4	180
	11th to 20th	Day	23% 25% 34% 14% 3	180
	21st to end	Day	16% 19% 43% 16% 5% 1	198
February	1st to 10th	Day	28% 26% 37% 7% 2 1	180
	11th to 20th	Day	21% 26% 36% 14% 3	438
	21st to end	Day	25% 25% 29% 18% 4	382
March	1st to 10th	Day	24% 22% 32% 18% 4	460
	11th to 20th	Day	26% 20% 31% 16% 6% 1	460
	21st to end	Day	25% 24% 26% 17% 7% 1	506
April	1st to 10th	Day	30% 19% 29% 17% 5%	460
	11th to 20th	Day	29% 20% 27% 17% 5% 2	452
	21st to end	Day	31% 19% 33% 12% 4 1	460
May	1st to 10th	Day	30% 19% 31% 14% 5% 1	463
	11th to 20th	Day	23% 17% 32% 21% 6% 1	487
	21st to end	Day	28% 21% 29% 16% 5%	564
June	1st to 10th	Day	25% 16% 30% 22% 8%	680
	11th to 20th	Day	25% 15% 28% 23% 9% 1	680
	21st to end	Day	29% 12% 29% 20% 9% 1	680
July	1st to 10th	Day	21% 15% 33% 21% 9%	533
	11th to 20th	Day	21% 12% 35% 23% 7% 1	484
	21st to end	Day	21% 12% 32% 24% 9% 1	532
August	1st to 10th	Day	24% 10% 31% 23% 10% 2	486
	11th to 20th	Day	23% 9% 25% 30% 11% 2	479
	21st to end	Day	24% 14% 24% 20% 12% 5%	539
September	1st to 10th	Day	24% 13% 28% 21% 10% 3	490
	11th to 20th	Day	22% 11% 28% 23% 14% 2	490
	21st to end	Day	25% 13% 27% 20% 10% 5%	490
October	1st to 10th	Day	27% 14% 28% 20% 10% 1	490
	11th to 20th	Day	34% 15% 24% 18% 8% 1	405
	21st to end	Day	37% 18% 25% 16% 4	429
November	1st to 10th	Day	36% 15% 26% 18% 4 1	395
	11th to 20th	Day	29% 19% 28% 17% 7% 1	390
	21st to end	Day	34% 22% 30% 14% 1	200
December	1st to 10th	Day	32% 15% 29% 17% 8% 1	200
	11th to 20th	Day	35% 21% 27% 14% 4 1	200
	21st to end	Day	30% 21% 32% 13% 3	204
January	1st to 10th	Night	23% 17% 33% 23% 4	760
	11th to 20th	Night	25% 18% 31% 22% 6%	760
	21st to end	Night	16% 13% 36% 30% 6%	836
February	1st to 10th	Night	18% 16% 35% 26% 5%	760
	11th to 20th	Night	22% 16% 40% 17% 4	743
	21st to end	Night	22% 15% 34% 24% 5%	628
March	1st to 10th	Night	21% 14% 37% 24% 4	760
	11th to 20th	Night	23% 19% 32% 20% 5% 1	760
	21st to end	Night	21% 17% 31% 24% 6% 1	836
April	1st to 10th	Night	29% 16% 27% 21% 6%	760
	11th to 20th	Night	26% 12% 32% 25% 5%	659
	21st to end	Night	29% 16% 29% 20% 6%	570
May	1st to 10th	Night	27% 11% 31% 26% 5%	518
	11th to 20th	Night	23% 10% 28% 31% 7% 1	374
	21st to end	Night	28% 7% 32% 24% 8%	411
June	1st to 10th	Night	23% 8% 28% 33% 7%	380
	11th to 20th	Night	21% 6% 24% 37% 12%	380
	21st to end	Night	27% 4 23% 37% 9% 1	380
July	1st to 10th	Night	20% 4 28% 36% 12% 1	370
	11th to 20th	Night	20% 3 23% 39% 14% 1	368
	21st to end	Night	18% 5% 20% 41% 15% 1	416
August	1st to 10th	Night	19% 4 16% 43% 19%	378
	11th to 20th	Night	19% 5% 21% 38% 16% 1	546
	21st to end	Night	20% 7% 24% 31% 16% 2	739
September	1st to 10th	Night	21% 6% 27% 32% 13% 1	760
	11th to 20th	Night	21% 8% 24% 29% 17% 2	760
	21st to end	Night	24% 9% 24% 28% 14% 1	760
October	1st to 10th	Night	26% 9% 26% 28% 10% 1	760
	11th to 20th	Night	30% 10% 26% 25% 9%	760
	21st to end	Night	33% 13% 27% 22% 5%	836
November	1st to 10th	Night	28% 14% 27% 24% 6% 1	780
	11th to 20th	Night	27% 16% 25% 24% 8% 1	800
	21st to end	Night	30% 17% 28% 19% 5% 1	885
December	1st to 10th	Night	31% 13% 25% 23% 7%	900
	11th to 20th	Night	26% 19% 27% 22% 5% 1	900
	21st to end	Night	30% 18% 29% 19% 4	929

Page generated at 2024-12-21 04:13:53. Version ac07

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