Bear Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bear Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	16% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	101419
	Night	16% 12% 4 9% 5% 5% 4 3 5% 5% 30%	97730
Transparency	Day	50% 8% 12% 19% 10% 1	104918
	Night	52% 8% 12% 18% 9% 1	102307
Seeing	Day	26% 19% 29% 16% 7% 2	14824
	Night	24% 18% 26% 23% 8% 1	23789

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% 17% 8% 11% 6% 4 4 3 3 5% 26%	2517
	11th to 20th	Day	12% 14% 7% 17% 10% 5% 4 3 4 4 21%	2520
	21st to end	Day	15% 19% 9% 13% 5% 4 4 3 4 4 20%	2772
February	1st to 10th	Day	13% 15% 5% 11% 7% 6% 4 4 6% 5% 24%	1694
	11th to 20th	Day	10% 15% 7% 15% 7% 5% 4 4 5% 5% 24%	1848
	21st to end	Day	15% 15% 6% 12% 6% 4 4 2 5% 5% 27%	1570
March	1st to 10th	Day	21% 15% 5% 10% 5% 5% 4 3 5% 5% 21%	3116
	11th to 20th	Day	14% 18% 7% 11% 4 4 4 3 4 5% 26%	3264
	21st to end	Day	18% 11% 5% 11% 6% 5% 4 3 4 4 31%	4166
April	1st to 10th	Day	18% 17% 3 8% 4 4 3 3 4 5% 31%	2280
	11th to 20th	Day	16% 13% 3 7% 5% 5% 4 3 4 6% 33%	2254
	21st to end	Day	21% 13% 4 8% 4 4 3 3 5% 5% 30%	2425
May	1st to 10th	Day	26% 11% 3 7% 5% 4 4 4 5% 6% 26%	4138
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	4398
	21st to end	Day	13% 7% 3 6% 4 4 5% 4 7% 8% 38%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 6% 5% 4 6% 7% 27%	2660
	11th to 20th	Day	20% 7% 2 6% 5% 4 5% 4 6% 9% 31%	2660
	21st to end	Day	20% 8% 3 7% 6% 6% 5% 5% 6% 6% 28%	2660
July	1st to 10th	Day	13% 7% 2 6% 5% 5% 5% 5% 8% 10% 35%	4440
	11th to 20th	Day	10% 6% 2 7% 6% 6% 5% 5% 9% 10% 34%	4440
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 6% 7% 36%	4814
August	1st to 10th	Day	15% 8% 2 8% 5% 5% 6% 4 7% 7% 32%	4372
	11th to 20th	Day	13% 8% 3 8% 5% 5% 6% 5% 6% 9% 33%	3858
	21st to end	Day	13% 6% 2 5% 4 4 5% 5% 6% 9% 39%	4180
September	1st to 10th	Day	15% 5% 2 5% 4 5% 4 4 5% 7% 42%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 3 4 5% 7% 48%	2161
	21st to end	Day	16% 8% 2 5% 4 4 5% 3 6% 7% 40%	2090
October	1st to 10th	Day	22% 9% 2 7% 5% 4 5% 3 6% 5% 32%	2030
	11th to 20th	Day	15% 12% 3 8% 5% 3 4 4 5% 7% 35%	1856
	21st to end	Day	23% 14% 3 7% 4 4 3 3 4 6% 28%	1881
November	1st to 10th	Day	13% 12% 4 8% 5% 4 4 4 6% 6% 35%	1752
	11th to 20th	Day	16% 14% 4 9% 5% 4 4 3 5% 6% 30%	1710
	21st to end	Day	16% 13% 5% 11% 5% 5% 5% 3 4 6% 27%	1578
December	1st to 10th	Day	18% 19% 5% 11% 5% 5% 4 3 5% 6% 21%	1520
	11th to 20th	Day	18% 17% 5% 11% 5% 4 4 3 3 5% 26%	1906
	21st to end	Day	18% 18% 6% 12% 6% 5% 4 2 3 4 21%	2772
January	1st to 10th	Night	13% 14% 7% 15% 5% 5% 4 4 4 4 26%	4429
	11th to 20th	Night	9% 15% 8% 17% 9% 6% 5% 4 4 5% 17%	4440
	21st to end	Night	19% 17% 6% 14% 6% 6% 3 3 4 3 20%	4884
February	1st to 10th	Night	13% 14% 6% 13% 9% 5% 5% 4 5% 5% 22%	2483
	11th to 20th	Night	10% 12% 6% 11% 8% 7% 6% 5% 6% 5% 23%	2218
	21st to end	Night	13% 13% 4 13% 6% 5% 3 3 4 5% 29%	1884
March	1st to 10th	Night	20% 11% 4 10% 7% 4 4 4 4 5% 25%	3724
	11th to 20th	Night	12% 19% 6% 9% 6% 5% 4 3 4 5% 29%	3693
	21st to end	Night	17% 17% 4 11% 5% 4 3 3 3 3 31%	3466
April	1st to 10th	Night	18% 14% 5% 7% 5% 4 3 3 5% 5% 29%	1900
	11th to 20th	Night	18% 13% 3 8% 5% 3 4 3 6% 6% 31%	1875
	21st to end	Night	19% 14% 4 7% 4 3 4 3 5% 6% 31%	1753
May	1st to 10th	Night	27% 12% 3 8% 3 4 4 4 5% 6% 25%	2817
	11th to 20th	Night	17% 12% 4 9% 6% 6% 5% 4 5% 5% 29%	2495
	21st to end	Night	15% 8% 1 7% 5% 4 4 4 7% 8% 37%	2738
June	1st to 10th	Night	21% 8% 2 6% 5% 5% 4 4 6% 6% 33%	1520
	11th to 20th	Night	21% 6% 2 5% 4 4 4 4 6% 7% 36%	1520
	21st to end	Night	18% 7% 2 6% 6% 5% 5% 4 6% 6% 35%	1520
July	1st to 10th	Night	13% 6% 2 7% 6% 6% 7% 5% 6% 7% 35%	2520
	11th to 20th	Night	15% 8% 2 7% 5% 4 5% 5% 5% 8% 36%	2520
	21st to end	Night	14% 8% 2 6% 5% 5% 5% 4 5% 6% 39%	2739
August	1st to 10th	Night	22% 9% 4 7% 4 3 3 3 4 6% 34%	2525
	11th to 20th	Night	13% 6% 3 8% 5% 5% 5% 3 5% 9% 39%	2964
	21st to end	Night	11% 7% 2 5% 3 4 4 4 7% 9% 43%	3476
September	1st to 10th	Night	15% 7% 2 5% 3 4 4 3 4 6% 46%	1900
	11th to 20th	Night	17% 5% 2 5% 2 3 3 2 5% 6% 51%	2019
	21st to end	Night	16% 7% 2 5% 4 4 5% 3 5% 5% 44%	2090
October	1st to 10th	Night	22% 8% 3 7% 4 4 3 3 5% 6% 34%	2147
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 5% 35%	2323
	21st to end	Night	21% 13% 4 8% 4 5% 5% 3 4 5% 27%	2717
November	1st to 10th	Night	14% 14% 4 9% 5% 4 4 3 4 5% 35%	2531
	11th to 20th	Night	15% 14% 5% 9% 5% 4 3 4 4 6% 32%	2470
	21st to end	Night	14% 14% 5% 10% 6% 4 4 3 5% 6% 29%	2598
December	1st to 10th	Night	17% 19% 7% 11% 6% 4 5% 3 4 5% 19%	2660
	11th to 20th	Night	17% 17% 5% 10% 5% 5% 4 3 4 5% 24%	3288
	21st to end	Night	21% 16% 7% 13% 5% 4 3 3 4 4 20%	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	57% 9% 12% 18% 4	2518
	11th to 20th	Day	64% 9% 9% 13% 4 1	2520
	21st to end	Day	66% 7% 10% 11% 5% 1	2772
February	1st to 10th	Day	60% 7% 11% 14% 7% 1	1694
	11th to 20th	Day	60% 8% 9% 15% 8% 1	1857
	21st to end	Day	59% 5% 10% 14% 11% 1	1570
March	1st to 10th	Day	63% 7% 11% 10% 8% 1	3119
	11th to 20th	Day	57% 9% 11% 12% 8% 1	3264
	21st to end	Day	53% 8% 7% 13% 17% 2	4166
April	1st to 10th	Day	56% 5% 8% 19% 10% 2	2280
	11th to 20th	Day	51% 7% 9% 19% 13% 1	2254
	21st to end	Day	55% 6% 9% 16% 11% 2	2425
May	1st to 10th	Day	58% 7% 10% 18% 7% 1	4152
	11th to 20th	Day	50% 9% 16% 16% 8% 1	4402
	21st to end	Day	39% 10% 13% 26% 11% 1	4837
June	1st to 10th	Day	53% 8% 14% 16% 8%	2660
	11th to 20th	Day	49% 7% 12% 19% 12% 1	2660
	21st to end	Day	54% 8% 11% 17% 9% 1	2660
July	1st to 10th	Day	42% 8% 15% 23% 12%	4370
	11th to 20th	Day	40% 9% 17% 26% 8%	4365
	21st to end	Day	45% 8% 13% 24% 10%	4661
August	1st to 10th	Day	48% 9% 14% 19% 9%	4358
	11th to 20th	Day	45% 9% 18% 23% 5%	3897
	21st to end	Day	37% 8% 17% 26% 10% 1	4180
September	1st to 10th	Day	40% 8% 11% 28% 12%	2280
	11th to 20th	Day	36% 7% 10% 29% 17% 1	2161
	21st to end	Day	41% 7% 13% 25% 11% 2	2090
October	1st to 10th	Day	47% 7% 9% 23% 13% 1	3368
	11th to 20th	Day	45% 4 13% 23% 13% 1	3059
	21st to end	Day	41% 6% 12% 28% 11% 2	3081
November	1st to 10th	Day	46% 8% 13% 20% 11%	1752
	11th to 20th	Day	54% 6% 11% 16% 12% 2	1710
	21st to end	Day	58% 6% 15% 15% 5% 1	1578
December	1st to 10th	Day	65% 7% 12% 10% 6% 1	1520
	11th to 20th	Day	60% 6% 12% 14% 6% 1	1906
	21st to end	Day	66% 5% 10% 12% 6%	2772
January	1st to 10th	Night	58% 8% 14% 13% 6%	4429
	11th to 20th	Night	63% 10% 11% 11% 5% 1	4440
	21st to end	Night	69% 6% 8% 11% 6% 1	4884
February	1st to 10th	Night	62% 8% 10% 12% 7% 1	2483
	11th to 20th	Night	57% 9% 10% 14% 9% 1	2220
	21st to end	Night	55% 7% 12% 17% 7% 2	1884
March	1st to 10th	Night	57% 6% 11% 17% 7% 1	3734
	11th to 20th	Night	52% 11% 12% 15% 9% 1	3694
	21st to end	Night	54% 8% 7% 12% 17% 3	3466
April	1st to 10th	Night	55% 6% 10% 17% 10% 1	1900
	11th to 20th	Night	51% 7% 10% 20% 12% 1	1875
	21st to end	Night	52% 7% 9% 17% 11% 3	1753
May	1st to 10th	Night	57% 9% 9% 15% 9% 1	2823
	11th to 20th	Night	54% 9% 12% 16% 7% 1	2496
	21st to end	Night	40% 11% 15% 19% 13% 2	2739
June	1st to 10th	Night	48% 9% 13% 17% 11% 1	1520
	11th to 20th	Night	46% 7% 16% 18% 12% 1	1520
	21st to end	Night	47% 9% 12% 22% 9% 1	1520
July	1st to 10th	Night	46% 8% 15% 19% 12% 1	2480
	11th to 20th	Night	43% 9% 14% 25% 9%	2472
	21st to end	Night	44% 7% 11% 26% 11% 1	2651
August	1st to 10th	Night	52% 7% 12% 20% 9%	2515
	11th to 20th	Night	42% 8% 20% 22% 8%	2991
	21st to end	Night	34% 8% 19% 27% 11% 1	3476
September	1st to 10th	Night	38% 7% 14% 27% 13%	1900
	11th to 20th	Night	34% 6% 12% 30% 17% 1	2019
	21st to end	Night	41% 7% 12% 24% 14% 2	2090
October	1st to 10th	Night	50% 7% 13% 20% 9% 1	3576
	11th to 20th	Night	44% 6% 12% 21% 15% 2	3859
	21st to end	Night	47% 7% 11% 27% 8% 1	4467
November	1st to 10th	Night	51% 6% 11% 18% 11% 2	2531
	11th to 20th	Night	52% 8% 11% 17% 11% 2	2470
	21st to end	Night	54% 8% 14% 17% 6%	2598
December	1st to 10th	Night	66% 8% 11% 12% 3	2660
	11th to 20th	Night	59% 10% 11% 11% 9%	3288
	21st to end	Night	66% 7% 10% 14% 3	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	31% 28% 25% 14% 2	180
	11th to 20th	Day	34% 24% 31% 9% 1 1	180
	21st to end	Day	23% 30% 32% 10% 5%	198
February	1st to 10th	Day	38% 35% 22% 4	263
	11th to 20th	Day	33% 28% 27% 9% 2	456
	21st to end	Day	34% 25% 27% 12% 2	382
March	1st to 10th	Day	32% 24% 30% 13% 2	460
	11th to 20th	Day	33% 25% 27% 11% 3 1	460
	21st to end	Day	32% 27% 22% 11% 5% 3	506
April	1st to 10th	Day	40% 20% 23% 12% 5% 1	460
	11th to 20th	Day	35% 25% 22% 11% 5% 2	452
	21st to end	Day	34% 22% 27% 11% 4 2	460
May	1st to 10th	Day	34% 23% 26% 10% 5% 2	463
	11th to 20th	Day	23% 18% 35% 18% 4 2	487
	21st to end	Day	19% 18% 34% 20% 7% 2	529
June	1st to 10th	Day	24% 20% 32% 16% 7% 1	490
	11th to 20th	Day	23% 16% 32% 19% 9% 1	490
	21st to end	Day	26% 17% 33% 16% 8% 1	490
July	1st to 10th	Day	20% 11% 33% 23% 11% 2	485
	11th to 20th	Day	14% 11% 40% 25% 9% 2	484
	21st to end	Day	17% 11% 39% 23% 9% 2	532
August	1st to 10th	Day	17% 13% 30% 25% 13% 3	486
	11th to 20th	Day	19% 13% 30% 21% 12% 6%	479
	21st to end	Day	17% 14% 27% 25% 10% 6%	539
September	1st to 10th	Day	16% 16% 28% 22% 13% 6%	490
	11th to 20th	Day	17% 14% 23% 19% 17% 9%	490
	21st to end	Day	20% 15% 29% 20% 12% 5%	490
October	1st to 10th	Day	28% 15% 27% 16% 13% 2	490
	11th to 20th	Day	26% 18% 26% 19% 10% 1	466
	21st to end	Day	35% 18% 26% 17% 3 1	429
November	1st to 10th	Day	27% 23% 23% 18% 9% 1	392
	11th to 20th	Day	29% 26% 24% 15% 5% 1	370
	21st to end	Day	33% 20% 34% 11% 3	238
December	1st to 10th	Day	33% 28% 24% 13% 1 1	180
	11th to 20th	Day	38% 32% 22% 7% 2	180
	21st to end	Day	37% 23% 27% 10% 3	198
January	1st to 10th	Night	25% 24% 33% 15% 3	760
	11th to 20th	Night	28% 24% 28% 18% 2 1	760
	21st to end	Night	20% 23% 32% 20% 3	836
February	1st to 10th	Night	24% 25% 35% 15% 1	760
	11th to 20th	Night	23% 28% 30% 17% 2	743
	21st to end	Night	25% 25% 30% 18% 2	628
March	1st to 10th	Night	26% 21% 31% 18% 3	760
	11th to 20th	Night	28% 24% 28% 17% 4	760
	21st to end	Night	29% 22% 23% 19% 7%	836
April	1st to 10th	Night	28% 23% 26% 19% 4	760
	11th to 20th	Night	25% 26% 23% 17% 8%	751
	21st to end	Night	30% 19% 24% 21% 5% 1	613
May	1st to 10th	Night	32% 14% 26% 20% 8%	566
	11th to 20th	Night	21% 15% 28% 29% 6%	374
	21st to end	Night	20% 11% 26% 31% 11% 1	411
June	1st to 10th	Night	20% 12% 28% 27% 12% 1	380
	11th to 20th	Night	21% 11% 20% 36% 12% 1	380
	21st to end	Night	17% 11% 27% 33% 11% 1	380
July	1st to 10th	Night	16% 5% 23% 42% 13% 1	370
	11th to 20th	Night	16% 5% 23% 39% 16% 2	368
	21st to end	Night	15% 5% 25% 37% 18%	416
August	1st to 10th	Night	15% 6% 20% 39% 20% 1	384
	11th to 20th	Night	16% 7% 24% 33% 17% 4	666
	21st to end	Night	17% 8% 19% 33% 21% 1	836
September	1st to 10th	Night	18% 9% 23% 31% 16% 2	760
	11th to 20th	Night	18% 8% 19% 29% 21% 4	760
	21st to end	Night	20% 11% 23% 27% 15% 2	760
October	1st to 10th	Night	28% 12% 19% 26% 14% 2	760
	11th to 20th	Night	24% 16% 24% 25% 11% 1	760
	21st to end	Night	30% 21% 24% 20% 6%	836
November	1st to 10th	Night	25% 21% 26% 22% 7% 1	779
	11th to 20th	Night	25% 22% 26% 19% 7% 2	760
	21st to end	Night	25% 26% 26% 17% 6% 1	760
December	1st to 10th	Night	29% 28% 24% 15% 4	760
	11th to 20th	Night	30% 25% 23% 18% 3	760
	21st to end	Night	30% 24% 28% 15% 2	836

Page generated at 2024-11-07 06:55:45. Version ac07

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