Eagle Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Rock Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	7% 9% 3 6% 4 4 4 3 5% 6% 50%	105258
	Night	8% 10% 3 7% 4 4 4 3 5% 6% 46%	102421
Transparency	Day	36% 4 8% 22% 19% 11%	105007
	Night	39% 4 10% 21% 17% 9%	102260
Seeing	Day	13% 13% 27% 28% 16% 4	15305
	Night	14% 8% 23% 36% 17% 3	24907

By Month

Percentage Cloud Cover SW (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	10% 21% 8% 10% 5% 4 4 3 5% 6% 25%	2456
	11th to 20th	Day	12% 17% 7% 12% 5% 4 4 3 5% 4 28%	2643
	21st to end	Day	13% 21% 5% 11% 5% 4 3 3 4 4 27%	3146
February	1st to 10th	Day	11% 17% 6% 11% 6% 4 5% 4 5% 5% 26%	1710
	11th to 20th	Day	11% 15% 5% 10% 6% 4 5% 3 6% 6% 29%	1674
	21st to end	Day	7% 16% 5% 12% 7% 5% 4 3 5% 6% 29%	1570
March	1st to 10th	Day	7% 16% 6% 12% 5% 5% 4 4 4 6% 32%	3313
	11th to 20th	Day	6% 12% 3 5% 4 4 3 3 4 5% 50%	3490
	21st to end	Day	9% 17% 7% 12% 7% 6% 6% 4 7% 6% 20%	3825
April	1st to 10th	Day	10% 14% 3 8% 4 5% 5% 4 6% 7% 34%	2155
	11th to 20th	Day	7% 11% 3 8% 5% 4 4 4 5% 8% 41%	2437
	21st to end	Day	9% 11% 3 7% 5% 4 4 4 6% 7% 38%	2470
May	1st to 10th	Day	9% 11% 3 7% 4 4 5% 4 5% 6% 40%	4110
	11th to 20th	Day	4 5% 2 6% 4 4 5% 3 6% 8% 54%	4071
	21st to end	Day	8% 8% 2 7% 4 4 5% 4 5% 6% 46%	4783
June	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 7% 8% 48%	2767
	11th to 20th	Day	7% 6% 2 6% 4 4 4 4 4 7% 52%	2850
	21st to end	Day	2 2 1 3 2 3 2 3 5% 7% 70%	2850
July	1st to 10th	Day	2 1 1 2 2 2 2 2 4 5% 78%	4690
	11th to 20th	Day	1 2 1 3 3 3 3 3 5% 6% 71%	4368
	21st to end	Day	3 2 1 4 3 3 3 3 4 7% 67%	4454
August	1st to 10th	Day	4 4 1 5% 3 4 4 4 5% 8% 59%	4092
	11th to 20th	Day	2 2 1 3 3 3 4 3 4 7% 70%	4028
	21st to end	Day	2 2 1 3 2 2 3 3 4 6% 72%	4521
September	1st to 10th	Day	4 3 1 3 2 2 2 3 4 5% 70%	2205
	11th to 20th	Day	6% 4 1 4 3 3 3 3 5% 6% 61%	2090
	21st to end	Day	7% 4 2 3 2 2 3 2 4 7% 63%	2090
October	1st to 10th	Day	7% 4 1 5% 2 3 2 2 3 4 67%	3306
	11th to 20th	Day	5% 5% 2 6% 3 3 3 2 4 5% 61%	3150
	21st to end	Day	7% 9% 3 7% 4 4 5% 4 6% 6% 45%	3292
November	1st to 10th	Day	13% 13% 3 6% 4 3 4 3 5% 6% 40%	1701
	11th to 20th	Day	12% 12% 3 6% 4 4 4 4 6% 8% 38%	1587
	21st to end	Day	9% 14% 4 9% 4 4 3 3 4 5% 42%	1520
December	1st to 10th	Day	13% 14% 6% 11% 6% 4 3 3 5% 5% 31%	1520
	11th to 20th	Day	12% 14% 7% 12% 6% 6% 5% 4 4 6% 24%	1882
	21st to end	Day	8% 14% 4 10% 5% 3 4 4 5% 7% 34%	2442
January	1st to 10th	Night	9% 18% 7% 13% 5% 4 4 3 4 6% 28%	4505
	11th to 20th	Night	15% 20% 6% 11% 5% 3 3 3 4 6% 23%	4316
	21st to end	Night	13% 23% 5% 9% 5% 4 4 2 4 5% 26%	4521
February	1st to 10th	Night	12% 14% 5% 9% 6% 4 4 4 6% 6% 29%	2470
	11th to 20th	Night	12% 16% 5% 8% 4 4 3 3 5% 5% 35%	2388
	21st to end	Night	8% 14% 6% 11% 6% 6% 5% 4 6% 6% 28%	1884
March	1st to 10th	Night	8% 13% 5% 10% 5% 6% 5% 4 6% 7% 32%	3560
	11th to 20th	Night	4 8% 3 6% 4 3 4 3 6% 8% 50%	3490
	21st to end	Night	7% 11% 4 9% 6% 5% 5% 5% 7% 8% 33%	3828
April	1st to 10th	Night	9% 11% 4 8% 5% 4 4 4 6% 7% 38%	2021
	11th to 20th	Night	8% 11% 3 7% 5% 5% 4 4 5% 7% 41%	1691
	21st to end	Night	9% 8% 2 6% 4 4 4 3 6% 6% 46%	1710
May	1st to 10th	Night	8% 13% 4 7% 4 4 4 3 5% 6% 41%	2860
	11th to 20th	Night	5% 4 2 5% 4 4 4 3 6% 8% 53%	2834
	21st to end	Night	7% 6% 2 6% 4 4 4 4 6% 9% 46%	2802
June	1st to 10th	Night	6% 5% 2 5% 4 4 5% 5% 7% 9% 48%	1407
	11th to 20th	Night	8% 5% 2 4 4 4 4 3 6% 7% 53%	1330
	21st to end	Night	2 3 1 4 2 3 2 2 5% 7% 68%	1330
July	1st to 10th	Night	3 1 1 3 2 2 3 3 4 7% 71%	2252
	11th to 20th	Night	1 1 1 2 3 3 4 3 5% 8% 69%	2590
	21st to end	Night	1 2 1 3 3 4 4 4 6% 7% 66%	3109
August	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 8% 61%	2847
	11th to 20th	Night	2 2 1 3 3 3 4 4 5% 7% 65%	2811
	21st to end	Night	3 3 1 3 2 2 3 2 3 4 73%	3146
September	1st to 10th	Night	4 3 1 4 2 3 3 3 4 5% 69%	1971
	11th to 20th	Night	6% 4 1 4 4 3 4 4 5% 7% 59%	2090
	21st to end	Night	7% 4 1 3 2 3 3 3 4 5% 64%	2090
October	1st to 10th	Night	6% 3 1 3 2 2 2 2 4 5% 69%	3667
	11th to 20th	Night	9% 7% 2 6% 3 3 4 3 4 5% 55%	3778
	21st to end	Night	7% 9% 3 7% 4 4 4 5% 5% 7% 46%	4262
November	1st to 10th	Night	12% 9% 3 6% 4 4 4 3 5% 6% 44%	2450
	11th to 20th	Night	10% 13% 4 7% 5% 4 4 3 5% 6% 40%	2571
	21st to end	Night	9% 12% 4 8% 5% 4 4 3 5% 6% 40%	2660
December	1st to 10th	Night	12% 15% 5% 10% 5% 4 3 3 5% 6% 32%	2660
	11th to 20th	Night	12% 16% 5% 10% 5% 5% 4 3 5% 6% 29%	3306
	21st to end	Night	10% 14% 5% 11% 6% 5% 5% 3 4 5% 34%	5214

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% 3 13% 18% 3 1	2456
	11th to 20th	Day	61% 3 13% 16% 7% 1	2643
	21st to end	Day	62% 4 13% 15% 6% 1	3146
February	1st to 10th	Day	61% 5% 12% 18% 5% 1	1710
	11th to 20th	Day	56% 4 13% 19% 7% 1	1683
	21st to end	Day	56% 7% 11% 18% 8% 1	1570
March	1st to 10th	Day	54% 4 8% 24% 8% 1	3313
	11th to 20th	Day	38% 3 9% 34% 14% 1	3490
	21st to end	Day	64% 3 13% 15% 4	3825
April	1st to 10th	Day	48% 5% 13% 18% 13% 2	2155
	11th to 20th	Day	42% 5% 9% 27% 14% 3	2440
	21st to end	Day	44% 5% 10% 27% 14% 1	2470
May	1st to 10th	Day	42% 5% 5% 25% 19% 3	4110
	11th to 20th	Day	27% 5% 5% 34% 21% 7%	4074
	21st to end	Day	38% 5% 7% 34% 14% 1	4783
June	1st to 10th	Day	34% 4 12% 32% 18% 1	2767
	11th to 20th	Day	31% 4 8% 23% 23% 11%	2850
	21st to end	Day	16% 3 3 24% 37% 17%	2850
July	1st to 10th	Day	11% 2 3 11% 29% 44%	4617
	11th to 20th	Day	14% 3 3 10% 26% 45%	4293
	21st to end	Day	19% 3 3 12% 33% 30%	4314
August	1st to 10th	Day	24% 3 3 15% 29% 25%	4078
	11th to 20th	Day	16% 3 3 20% 38% 21%	4067
	21st to end	Day	14% 3 4 21% 30% 28%	4520
September	1st to 10th	Day	18% 3 5% 18% 33% 23%	2205
	11th to 20th	Day	24% 3 7% 25% 27% 13%	2090
	21st to end	Day	23% 3 7% 28% 30% 9%	2090
October	1st to 10th	Day	25% 2 6% 22% 33% 13%	3306
	11th to 20th	Day	27% 3 9% 37% 18% 6%	3150
	21st to end	Day	38% 5% 13% 27% 17% 1	3292
November	1st to 10th	Day	46% 4 14% 23% 11% 2	1701
	11th to 20th	Day	45% 4 17% 24% 8% 2	1587
	21st to end	Day	46% 3 18% 22% 10% 2	1520
December	1st to 10th	Day	56% 5% 13% 17% 6% 3	1520
	11th to 20th	Day	63% 4 12% 19% 3	1880
	21st to end	Day	51% 3 14% 22% 10% 1	2442
January	1st to 10th	Night	59% 3 10% 21% 6%	4505
	11th to 20th	Night	64% 4 11% 15% 4 1	4316
	21st to end	Night	62% 2 16% 14% 4 1	4521
February	1st to 10th	Night	56% 5% 14% 18% 6% 1	2470
	11th to 20th	Night	52% 4 14% 21% 9% 1	2389
	21st to end	Night	57% 5% 11% 19% 6% 2	1884
March	1st to 10th	Night	49% 5% 9% 25% 11% 1	3560
	11th to 20th	Night	33% 3 13% 31% 19% 1	3490
	21st to end	Night	48% 3 15% 28% 4 1	3828
April	1st to 10th	Night	45% 5% 12% 21% 14% 3	2021
	11th to 20th	Night	42% 4 12% 25% 15% 2	1691
	21st to end	Night	39% 4 10% 28% 18% 1	1710
May	1st to 10th	Night	43% 5% 6% 25% 18% 3	2860
	11th to 20th	Night	27% 5% 7% 32% 22% 7%	2835
	21st to end	Night	33% 4 7% 31% 21% 3	2802
June	1st to 10th	Night	31% 5% 13% 25% 24% 2	1407
	11th to 20th	Night	29% 4 8% 20% 27% 11%	1330
	21st to end	Night	18% 2 4 19% 33% 24%	1330
July	1st to 10th	Night	14% 3 3 11% 24% 45%	2216
	11th to 20th	Night	13% 3 2 11% 22% 49%	2542
	21st to end	Night	16% 3 4 13% 31% 33%	3011
August	1st to 10th	Night	21% 3 4 13% 28% 32%	2838
	11th to 20th	Night	19% 3 3 18% 34% 23%	2838
	21st to end	Night	16% 3 4 16% 29% 32%	3146
September	1st to 10th	Night	20% 2 4 13% 32% 29%	1971
	11th to 20th	Night	25% 3 6% 23% 26% 17%	2090
	21st to end	Night	24% 3 4 26% 32% 11%	2090
October	1st to 10th	Night	20% 1 6% 20% 36% 16%	3667
	11th to 20th	Night	33% 2 7% 32% 17% 8%	3778
	21st to end	Night	37% 4 11% 28% 18% 2	4262
November	1st to 10th	Night	42% 4 13% 26% 13% 2	2450
	11th to 20th	Night	46% 4 14% 24% 10% 2	2571
	21st to end	Night	45% 4 15% 23% 11% 2	2660
December	1st to 10th	Night	54% 5% 16% 16% 7% 3	2660
	11th to 20th	Night	57% 4 15% 19% 5%	3307
	21st to end	Night	55% 2 11% 20% 11% 1	5214

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	27% 18% 13% 24% 12% 4	180
	11th to 20th	Day	20% 10% 27% 23% 18% 2	211
	21st to end	Day	20% 10% 27% 30% 11% 2	297
February	1st to 10th	Day	20% 20% 31% 22% 6% 1	270
	11th to 20th	Day	20% 17% 33% 19% 9% 1	279
	21st to end	Day	17% 21% 31% 22% 8% 1	382
March	1st to 10th	Day	18% 23% 31% 22% 6% 1	460
	11th to 20th	Day	13% 19% 28% 28% 10% 1	460
	21st to end	Day	20% 22% 33% 19% 7%	506
April	1st to 10th	Day	20% 19% 27% 24% 8% 2	460
	11th to 20th	Day	17% 19% 34% 21% 8% 1	452
	21st to end	Day	17% 15% 27% 25% 12% 3	460
May	1st to 10th	Day	12% 16% 29% 29% 11% 3	463
	11th to 20th	Day	13% 14% 28% 25% 17% 3	488
	21st to end	Day	15% 9% 22% 30% 18% 7%	705
June	1st to 10th	Day	9% 13% 25% 27% 19% 7%	680
	11th to 20th	Day	14% 13% 28% 30% 13% 2	680
	21st to end	Day	5% 6% 28% 34% 20% 6%	680
July	1st to 10th	Day	4 7% 22% 37% 25% 4	648
	11th to 20th	Day	3 7% 26% 40% 20% 4	484
	21st to end	Day	4 3 21% 34% 30% 8%	531
August	1st to 10th	Day	6% 5% 28% 32% 23% 6%	487
	11th to 20th	Day	5% 5% 25% 34% 24% 7%	477
	21st to end	Day	5% 11% 25% 29% 22% 8%	539
September	1st to 10th	Day	4 7% 25% 29% 27% 7%	490
	11th to 20th	Day	9% 12% 26% 29% 19% 5%	490
	21st to end	Day	10% 9% 26% 26% 23% 6%	490
October	1st to 10th	Day	12% 11% 18% 29% 25% 6%	384
	11th to 20th	Day	11% 17% 19% 22% 20% 10%	300
	21st to end	Day	16% 15% 26% 29% 11% 3	330
November	1st to 10th	Day	24% 11% 27% 23% 9% 6%	279
	11th to 20th	Day	15% 14% 29% 26% 13% 3	270
	21st to end	Day	16% 12% 27% 30% 13% 2	270
December	1st to 10th	Day	23% 12% 24% 26% 11% 4	270
	11th to 20th	Day	24% 10% 33% 21% 11% 1	255
	21st to end	Day	25% 14% 26% 21% 11% 4	198
January	1st to 10th	Night	22% 9% 19% 31% 17% 1	820
	11th to 20th	Night	23% 8% 23% 28% 16% 3	760
	21st to end	Night	22% 6% 20% 36% 14% 2	836
February	1st to 10th	Night	20% 11% 28% 28% 12% 1	760
	11th to 20th	Night	21% 10% 26% 31% 11% 3	744
	21st to end	Night	14% 13% 28% 31% 11% 3	628
March	1st to 10th	Night	15% 12% 27% 32% 12% 2	760
	11th to 20th	Night	11% 8% 29% 34% 16% 2	760
	21st to end	Night	13% 10% 28% 36% 11% 1	836
April	1st to 10th	Night	16% 10% 25% 35% 13% 1	713
	11th to 20th	Night	15% 11% 30% 35% 8% 2	563
	21st to end	Night	13% 8% 24% 37% 17% 2	570
May	1st to 10th	Night	12% 9% 24% 35% 19% 1	570
	11th to 20th	Night	11% 6% 20% 35% 23% 4	561
	21st to end	Night	13% 7% 20% 38% 18% 3	617
June	1st to 10th	Night	9% 8% 22% 34% 24% 4	457
	11th to 20th	Night	11% 7% 30% 33% 18% 1	380
	21st to end	Night	4 2 21% 42% 25% 6%	380
July	1st to 10th	Night	3 1 20% 44% 26% 6%	370
	11th to 20th	Night	2 1 22% 49% 25% 1	392
	21st to end	Night	3 3 16% 46% 29% 4	624
August	1st to 10th	Night	6% 2 16% 47% 26% 2	567
	11th to 20th	Night	3 2 18% 46% 28% 3	564
	21st to end	Night	5% 4 21% 41% 26% 3	627
September	1st to 10th	Night	5% 3 20% 42% 25% 5%	662
	11th to 20th	Night	7% 4 21% 37% 26% 6%	760
	21st to end	Night	10% 3 21% 38% 21% 7%	760
October	1st to 10th	Night	12% 5% 19% 39% 23% 2	760
	11th to 20th	Night	12% 8% 20% 36% 20% 4	760
	21st to end	Night	12% 9% 22% 40% 13% 4	836
November	1st to 10th	Night	16% 11% 24% 31% 16% 3	754
	11th to 20th	Night	17% 10% 27% 32% 13% 1	861
	21st to end	Night	15% 9% 22% 34% 17% 2	950
December	1st to 10th	Night	20% 9% 25% 35% 11% 1	950
	11th to 20th	Night	24% 9% 23% 30% 12% 1	950
	21st to end	Night	27% 11% 22% 28% 10% 2	1045

Page generated at 2024-11-01 20:47:42. Version ac07

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