Bradstreet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bradstreet Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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	15% 6% 2 5% 5% 3 5% 5% 5% 8% 41%	78730
	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 43%	81242
Transparency	Day	41% 7% 12% 23% 15% 2	78439
	Night	41% 6% 11% 23% 16% 3	81068
Seeing	Day	20% 14% 28% 22% 12% 4	14109
	Night	19% 11% 31% 28% 10% 1	23552

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	15% 6% 2 4 4 3 4 5% 4 5% 46%	2517
	11th to 20th	Day	14% 9% 3 7% 6% 3 4 5% 5% 6% 37%	2598
	21st to end	Day	21% 8% 3 5% 5% 3 4 4 4 6% 36%	3124
February	1st to 10th	Day	17% 7% 2 5% 6% 3 5% 5% 5% 7% 39%	1710
	11th to 20th	Day	16% 8% 3 5% 5% 3 4 5% 5% 6% 41%	1796
	21st to end	Day	19% 8% 3 5% 6% 2 4 4 4 6% 37%	1570
March	1st to 10th	Day	14% 6% 2 6% 5% 2 4 4 4 6% 46%	1905
	11th to 20th	Day	16% 6% 2 5% 5% 4 5% 6% 5% 7% 39%	2090
	21st to end	Day	21% 7% 3 5% 5% 3 4 4 4 7% 39%	2378
April	1st to 10th	Day	14% 8% 3 5% 5% 3 5% 4 5% 8% 41%	2160
	11th to 20th	Day	15% 6% 2 4 5% 3 5% 5% 4 7% 43%	2134
	21st to end	Day	17% 5% 3 5% 5% 3 5% 5% 6% 7% 38%	2160
May	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 5% 6% 6% 35%	2304
	11th to 20th	Day	20% 6% 3 5% 5% 3 5% 5% 5% 8% 35%	2478
	21st to end	Day	15% 6% 2 6% 4 3 4 5% 5% 10% 39%	2725
June	1st to 10th	Day	14% 5% 2 5% 5% 3 6% 5% 7% 10% 39%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 6% 7% 9% 36%	2520
	21st to end	Day	11% 4 2 4 6% 3 6% 6% 6% 10% 42%	2520
July	1st to 10th	Day	9% 6% 3 4 5% 4 6% 6% 8% 9% 39%	2520
	11th to 20th	Day	7% 4 2 4 5% 4 6% 7% 8% 10% 42%	2520
	21st to end	Day	10% 6% 3 6% 6% 3 6% 7% 7% 9% 37%	2690
August	1st to 10th	Day	10% 5% 2 6% 6% 4 6% 6% 7% 9% 39%	2327
	11th to 20th	Day	12% 5% 2 6% 6% 3 5% 6% 7% 10% 40%	2135
	21st to end	Day	13% 5% 2 4 5% 3 5% 6% 6% 8% 41%	2376
September	1st to 10th	Day	16% 5% 1 5% 5% 3 5% 4 5% 7% 43%	2160
	11th to 20th	Day	14% 4 2 4 3 3 3 4 5% 8% 50%	2138
	21st to end	Day	17% 7% 3 5% 5% 3 5% 4 6% 7% 39%	1973
October	1st to 10th	Day	19% 5% 2 4 4 2 4 4 5% 7% 42%	1800
	11th to 20th	Day	17% 5% 1 4 4 2 4 4 5% 8% 46%	1800
	21st to end	Day	19% 6% 3 4 4 2 4 4 5% 6% 43%	1924
November	1st to 10th	Day	14% 6% 2 4 3 3 3 3 4 7% 52%	1671
	11th to 20th	Day	17% 4 2 4 4 2 3 4 5% 7% 47%	1710
	21st to end	Day	16% 5% 2 5% 4 2 4 4 5% 8% 46%	1579
December	1st to 10th	Day	18% 7% 2 5% 5% 3 3 4 5% 8% 38%	1520
	11th to 20th	Day	20% 8% 3 3 3 2 3 4 5% 7% 43%	1906
	21st to end	Day	17% 6% 2 6% 5% 3 6% 7% 6% 7% 36%	2772
January	1st to 10th	Night	17% 6% 2 5% 5% 3 4 4 4 5% 45%	4429
	11th to 20th	Night	19% 8% 2 5% 4 2 4 3 4 5% 44%	4346
	21st to end	Night	24% 8% 2 5% 5% 2 4 4 4 5% 37%	4532
February	1st to 10th	Night	16% 8% 3 5% 4 3 4 5% 4 6% 41%	2470
	11th to 20th	Night	18% 7% 2 6% 5% 3 4 3 4 6% 41%	2268
	21st to end	Night	18% 7% 2 6% 4 3 4 3 4 6% 43%	1884
March	1st to 10th	Night	15% 6% 2 4 4 3 4 4 5% 7% 45%	2259
	11th to 20th	Night	16% 7% 3 5% 5% 3 4 3 4 4 45%	2089
	21st to end	Night	16% 8% 3 6% 5% 2 3 3 4 6% 44%	2132
April	1st to 10th	Night	17% 6% 2 5% 5% 3 5% 5% 5% 7% 41%	1800
	11th to 20th	Night	15% 6% 2 6% 5% 3 4 5% 5% 7% 42%	1775
	21st to end	Night	19% 5% 2 4 4 3 4 5% 5% 7% 43%	1800
May	1st to 10th	Night	19% 8% 3 6% 6% 3 4 4 5% 7% 35%	1670
	11th to 20th	Night	18% 5% 4 5% 5% 3 4 4 6% 6% 39%	1415
	21st to end	Night	15% 6% 3 5% 5% 2 4 4 5% 8% 41%	1550
June	1st to 10th	Night	16% 6% 3 5% 4 2 4 3 6% 8% 42%	1440
	11th to 20th	Night	11% 5% 2 5% 6% 4 6% 6% 6% 10% 39%	1440
	21st to end	Night	10% 4 1 4 5% 3 5% 6% 8% 11% 42%	1440
July	1st to 10th	Night	10% 5% 3 5% 6% 3 7% 5% 8% 9% 38%	1440
	11th to 20th	Night	7% 4 2 6% 5% 4 4 8% 7% 10% 43%	1440
	21st to end	Night	8% 7% 2 6% 4 2 5% 6% 9% 9% 43%	1623
August	1st to 10th	Night	9% 6% 3 5% 5% 3 5% 6% 7% 9% 42%	1611
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 6% 6% 8% 39%	1746
	21st to end	Night	14% 4 2 5% 5% 3 4 5% 6% 10% 42%	1980
September	1st to 10th	Night	15% 7% 2 5% 5% 2 3 4 4 6% 46%	1800
	11th to 20th	Night	14% 5% 2 3 4 2 3 4 5% 6% 53%	1822
	21st to end	Night	17% 5% 2 5% 5% 2 4 5% 5% 7% 41%	1984
October	1st to 10th	Night	19% 6% 3 5% 4 3 4 3 4 6% 43%	2160
	11th to 20th	Night	16% 5% 1 4 4 2 3 4 4 6% 49%	2160
	21st to end	Night	18% 7% 2 5% 3 2 3 3 4 5% 48%	2430
November	1st to 10th	Night	12% 5% 2 4 4 2 3 4 5% 6% 54%	2407
	11th to 20th	Night	18% 6% 2 5% 4 2 3 4 3 5% 48%	2470
	21st to end	Night	14% 5% 2 4 5% 3 5% 4 6% 7% 46%	2598
December	1st to 10th	Night	19% 7% 3 4 5% 3 5% 4 5% 6% 39%	2660
	11th to 20th	Night	17% 5% 2 6% 5% 3 4 3 5% 7% 43%	3288
	21st to end	Night	17% 7% 3 6% 5% 3 4 4 5% 7% 38%	4884

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	38% 5% 13% 27% 13% 3	2518
	11th to 20th	Day	45% 7% 11% 22% 13% 2	2598
	21st to end	Day	49% 7% 12% 22% 10% 1	3124
February	1st to 10th	Day	43% 7% 14% 24% 11% 2	1710
	11th to 20th	Day	43% 5% 10% 24% 15% 2	1805
	21st to end	Day	47% 5% 11% 22% 12% 4	1570
March	1st to 10th	Day	39% 5% 12% 27% 14% 3	1908
	11th to 20th	Day	42% 6% 12% 22% 15% 4	2090
	21st to end	Day	46% 5% 9% 20% 17% 3	2378
April	1st to 10th	Day	41% 6% 11% 22% 16% 5%	2160
	11th to 20th	Day	39% 6% 13% 22% 16% 4	2134
	21st to end	Day	43% 7% 11% 19% 17% 4	2160
May	1st to 10th	Day	46% 7% 10% 18% 15% 3	2304
	11th to 20th	Day	47% 7% 10% 20% 14% 2	2482
	21st to end	Day	41% 8% 13% 23% 13% 2	2725
June	1st to 10th	Day	40% 8% 14% 23% 14% 1	2520
	11th to 20th	Day	42% 9% 14% 22% 11% 2	2520
	21st to end	Day	36% 9% 13% 24% 16% 1	2520
July	1st to 10th	Day	38% 10% 14% 21% 14% 3	2450
	11th to 20th	Day	33% 10% 14% 25% 15% 3	2445
	21st to end	Day	40% 9% 13% 21% 16% 2	2540
August	1st to 10th	Day	38% 9% 15% 23% 14% 1	2314
	11th to 20th	Day	38% 9% 14% 23% 15% 2	2135
	21st to end	Day	38% 9% 12% 20% 17% 3	2376
September	1st to 10th	Day	40% 7% 11% 19% 21% 3	2160
	11th to 20th	Day	32% 5% 10% 25% 23% 4	2138
	21st to end	Day	45% 6% 9% 18% 21% 2	1973
October	1st to 10th	Day	41% 5% 13% 23% 18% 1	1800
	11th to 20th	Day	35% 7% 11% 24% 21% 2	1800
	21st to end	Day	41% 6% 10% 25% 17% 2	1924
November	1st to 10th	Day	34% 4 13% 25% 20% 3	1671
	11th to 20th	Day	37% 5% 11% 25% 20% 3	1710
	21st to end	Day	37% 4 13% 31% 12% 2	1579
December	1st to 10th	Day	44% 5% 16% 21% 13%	1520
	11th to 20th	Day	42% 5% 13% 28% 10% 2	1906
	21st to end	Day	44% 8% 14% 23% 11% 1	2772
January	1st to 10th	Night	40% 5% 9% 28% 13% 3	4429
	11th to 20th	Night	43% 5% 11% 25% 13% 3	4346
	21st to end	Night	49% 5% 8% 25% 11% 2	4532
February	1st to 10th	Night	43% 6% 12% 25% 12% 2	2470
	11th to 20th	Night	45% 4 9% 20% 18% 4	2270
	21st to end	Night	43% 5% 8% 22% 16% 5%	1884
March	1st to 10th	Night	38% 6% 12% 24% 17% 4	2269
	11th to 20th	Night	41% 6% 9% 23% 17% 4	2090
	21st to end	Night	43% 5% 9% 18% 20% 6%	2132
April	1st to 10th	Night	42% 6% 11% 21% 17% 4	1800
	11th to 20th	Night	41% 6% 10% 20% 20% 3	1775
	21st to end	Night	40% 6% 11% 20% 19% 5%	1800
May	1st to 10th	Night	48% 7% 9% 17% 16% 3	1670
	11th to 20th	Night	45% 6% 13% 16% 17% 3	1416
	21st to end	Night	40% 9% 16% 17% 15% 2	1551
June	1st to 10th	Night	39% 7% 11% 22% 19% 2	1440
	11th to 20th	Night	39% 9% 13% 23% 14% 1	1440
	21st to end	Night	33% 11% 15% 26% 14% 2	1440
July	1st to 10th	Night	39% 14% 14% 18% 13% 2	1400
	11th to 20th	Night	31% 12% 16% 24% 14% 2	1392
	21st to end	Night	32% 10% 17% 24% 15% 2	1533
August	1st to 10th	Night	35% 10% 16% 22% 15% 1	1600
	11th to 20th	Night	40% 9% 15% 18% 16% 2	1746
	21st to end	Night	37% 9% 13% 20% 18% 3	1980
September	1st to 10th	Night	38% 7% 11% 20% 20% 3	1800
	11th to 20th	Night	33% 5% 9% 22% 27% 4	1822
	21st to end	Night	41% 6% 8% 21% 22% 2	1984
October	1st to 10th	Night	42% 5% 13% 22% 16% 2	2160
	11th to 20th	Night	35% 6% 11% 27% 18% 3	2160
	21st to end	Night	40% 4 9% 26% 18% 2	2430
November	1st to 10th	Night	33% 6% 12% 25% 19% 6%	2407
	11th to 20th	Night	40% 5% 9% 22% 20% 5%	2470
	21st to end	Night	37% 5% 13% 28% 15% 2	2598
December	1st to 10th	Night	45% 6% 11% 23% 14% 1	2660
	11th to 20th	Night	41% 6% 12% 20% 17% 4	3288
	21st to end	Night	44% 7% 14% 24% 11% 1	4884

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	22% 28% 33% 13% 2 2	180
	11th to 20th	Day	21% 37% 28% 10% 3	204
	21st to end	Day	24% 30% 26% 14% 5%	297
February	1st to 10th	Day	26% 26% 33% 12% 4	270
	11th to 20th	Day	28% 24% 35% 12% 2	404
	21st to end	Day	28% 22% 32% 15% 3	382
March	1st to 10th	Day	22% 24% 31% 19% 4	460
	11th to 20th	Day	22% 25% 33% 15% 3 2	460
	21st to end	Day	28% 21% 29% 16% 5% 1	490
April	1st to 10th	Day	24% 22% 33% 13% 7% 1	420
	11th to 20th	Day	20% 20% 33% 18% 7% 2	412
	21st to end	Day	27% 18% 31% 18% 5% 1	420
May	1st to 10th	Day	29% 17% 28% 15% 9% 2	423
	11th to 20th	Day	23% 12% 31% 24% 9% 2	447
	21st to end	Day	21% 6% 23% 27% 18% 5%	485
June	1st to 10th	Day	13% 14% 28% 26% 15% 3	450
	11th to 20th	Day	16% 10% 28% 27% 15% 3	450
	21st to end	Day	13% 10% 27% 30% 14% 5%	450
July	1st to 10th	Day	14% 3 19% 32% 24% 8%	445
	11th to 20th	Day	8% 2 21% 35% 27% 6%	444
	21st to end	Day	14% 4 24% 34% 19% 5%	488
August	1st to 10th	Day	10% 4 25% 33% 22% 7%	446
	11th to 20th	Day	14% 3 17% 35% 22% 8%	439
	21st to end	Day	13% 7% 24% 28% 18% 10%	495
September	1st to 10th	Day	18% 9% 21% 26% 18% 8%	450
	11th to 20th	Day	16% 5% 26% 26% 17% 10%	450
	21st to end	Day	22% 13% 21% 25% 13% 5%	450
October	1st to 10th	Day	26% 7% 24% 22% 14% 8%	450
	11th to 20th	Day	16% 14% 29% 25% 14% 2	450
	21st to end	Day	23% 14% 33% 18% 10% 3	466
November	1st to 10th	Day	18% 12% 31% 24% 12% 3	365
	11th to 20th	Day	20% 19% 32% 22% 6% 1	370
	21st to end	Day	18% 19% 36% 20% 6% 1	239
December	1st to 10th	Day	24% 25% 34% 9% 7%	180
	11th to 20th	Day	31% 22% 32% 11% 4	180
	21st to end	Day	27% 21% 32% 11% 9% 1	198
January	1st to 10th	Night	19% 18% 38% 21% 4	760
	11th to 20th	Night	24% 16% 31% 24% 4	760
	21st to end	Night	19% 18% 38% 23% 2	836
February	1st to 10th	Night	22% 15% 38% 24% 1	760
	11th to 20th	Night	24% 20% 38% 17% 1	743
	21st to end	Night	22% 19% 38% 18% 3	628
March	1st to 10th	Night	20% 18% 35% 23% 3	760
	11th to 20th	Night	21% 19% 36% 19% 5% 1	760
	21st to end	Night	20% 12% 40% 22% 6%	821
April	1st to 10th	Night	20% 19% 38% 18% 5%	720
	11th to 20th	Night	18% 13% 36% 27% 6%	711
	21st to end	Night	22% 11% 33% 29% 6%	720
May	1st to 10th	Night	24% 10% 31% 28% 6%	590
	11th to 20th	Night	20% 10% 34% 30% 6%	354
	21st to end	Night	19% 5% 20% 41% 14% 2	389
June	1st to 10th	Night	18% 5% 26% 37% 12% 1	360
	11th to 20th	Night	12% 6% 29% 41% 11% 1	360
	21st to end	Night	10% 2 26% 47% 15%	360
July	1st to 10th	Night	13% 4 21% 41% 19% 2	350
	11th to 20th	Night	7% 2 20% 45% 23% 2	348
	21st to end	Night	9% 4 24% 40% 20% 2	443
August	1st to 10th	Night	12% 2 16% 44% 23% 2	537
	11th to 20th	Night	15% 2 17% 38% 26% 2	682
	21st to end	Night	14% 4 17% 39% 23% 2	792
September	1st to 10th	Night	17% 4 24% 34% 18% 3	720
	11th to 20th	Night	15% 4 20% 35% 22% 4	720
	21st to end	Night	22% 4 22% 33% 19% 1	720
October	1st to 10th	Night	23% 7% 22% 26% 17% 4	720
	11th to 20th	Night	18% 9% 27% 33% 13%	720
	21st to end	Night	22% 10% 32% 26% 9%	792
November	1st to 10th	Night	15% 8% 36% 28% 11% 1	740
	11th to 20th	Night	21% 14% 30% 27% 8% 1	760
	21st to end	Night	16% 16% 34% 26% 7% 1	760
December	1st to 10th	Night	25% 15% 33% 21% 6% 1	760
	11th to 20th	Night	19% 15% 36% 24% 6%	760
	21st to end	Night	22% 14% 35% 26% 3	836

Page generated at 2024-03-24 23:37:02. Version ac07

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