Eagle Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Lake clear sky chart from 2005-11-06 to 2025-07-21.

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	3 6% 2 6% 4 4 4 3 5% 6% 58%	124192
	Night	3 7% 2 6% 4 4 4 3 5% 6% 56%	123758
Transparency	Day	26% 4 9% 20% 24% 18%	123939
	Night	27% 5% 11% 21% 23% 13%	123598
Seeing	Day	10% 14% 24% 28% 18% 6%	15836
	Night	8% 8% 18% 38% 24% 4	25053

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	2 10% 4 10% 7% 7% 7% 5% 7% 8% 34%	3639
	11th to 20th	Day	3 9% 4 9% 4 3 4 3 5% 6% 50%	3714
	21st to end	Day	4 11% 4 9% 5% 4 4 3 4 5% 46%	4510
February	1st to 10th	Day	5% 10% 4 7% 4 4 5% 4 7% 8% 42%	1800
	11th to 20th	Day	2 10% 3 8% 5% 5% 6% 3 6% 8% 44%	1862
	21st to end	Day	3 10% 4 8% 5% 5% 5% 3 6% 7% 44%	1650
March	1st to 10th	Day	4 15% 6% 11% 7% 5% 4 3 5% 7% 33%	4557
	11th to 20th	Day	3 8% 4 9% 5% 5% 5% 4 5% 7% 46%	5000
	21st to end	Day	3 14% 5% 10% 5% 6% 5% 4 5% 6% 36%	5747
April	1st to 10th	Day	5% 9% 4 9% 6% 4 4 4 6% 7% 42%	2400
	11th to 20th	Day	5% 9% 3 6% 4 4 4 4 6% 7% 48%	2369
	21st to end	Day	5% 9% 2 5% 4 4 4 3 6% 6% 53%	2400
May	1st to 10th	Day	3 4 2 4 3 3 2 2 3 6% 67%	5904
	11th to 20th	Day	3 4 2 4 3 3 3 3 5% 6% 65%	6277
	21st to end	Day	3 4 1 4 3 3 3 3 4 6% 67%	6902
June	1st to 10th	Day	5% 5% 2 5% 4 4 5% 5% 6% 8% 52%	2800
	11th to 20th	Day	2 3 2 4 2 3 3 3 4 6% 68%	2800
	21st to end	Day	2 2 1 3 2 2 3 3 3 4 75%	2800
July	1st to 10th	Day	1 1 1 1 1 2 2 3 3 85%	4560
	11th to 20th	Day	1 2 1 2 2 2 2 2 3 4 78%	4560
	21st to end	Day	1 1 1 2 2 2 3 2 4 5% 77%	4684
August	1st to 10th	Day	2 2 1 3 2 3 3 3 5% 5% 71%	4091
	11th to 20th	Day	1 1 1 1 2 3 2 3 4 82%	3821
	21st to end	Day	2 1 1 2 1 2 1 2 3 2 84%	4180
September	1st to 10th	Day	2 1 2 2 2 2 1 3 4 82%	2280
	11th to 20th	Day	2 2 1 4 3 3 3 3 4 6% 70%	2280
	21st to end	Day	3 3 1 3 2 2 2 2 4 5% 74%	2056
October	1st to 10th	Day	3 3 1 2 2 3 3 2 3 6% 71%	3180
	11th to 20th	Day	4 3 2 4 3 2 3 2 4 6% 66%	3161
	21st to end	Day	3 4 2 5% 4 4 4 4 5% 8% 57%	3391
November	1st to 10th	Day	7% 7% 2 6% 4 4 4 4 5% 7% 49%	1764
	11th to 20th	Day	5% 7% 2 6% 4 6% 6% 5% 7% 9% 44%	1800
	21st to end	Day	2 7% 2 7% 6% 5% 4 3 6% 7% 50%	1601
December	1st to 10th	Day	3 6% 2 6% 3 4 4 3 6% 9% 53%	2620
	11th to 20th	Day	7% 17% 5% 10% 5% 5% 6% 5% 7% 7% 24%	3028
	21st to end	Day	4 10% 4 11% 7% 5% 6% 5% 9% 9% 28%	4004
January	1st to 10th	Night	2 7% 3 9% 6% 7% 7% 6% 8% 10% 35%	6306
	11th to 20th	Night	2 10% 3 7% 6% 5% 4 3 5% 8% 47%	6232
	21st to end	Night	6% 13% 3 7% 4 4 4 3 4 6% 45%	6468
February	1st to 10th	Night	4 10% 3 8% 5% 4 4 5% 6% 8% 44%	2600
	11th to 20th	Night	3 9% 3 7% 5% 5% 5% 4 6% 8% 45%	2424
	21st to end	Night	3 8% 3 8% 5% 5% 5% 4 6% 8% 46%	1980
March	1st to 10th	Night	3 16% 5% 10% 5% 5% 4 3 5% 7% 36%	5332
	11th to 20th	Night	3 10% 3 8% 4 4 4 4 5% 7% 47%	5000
	21st to end	Night	3 13% 4 10% 6% 6% 5% 4 5% 7% 36%	5226
April	1st to 10th	Night	3 8% 3 7% 6% 5% 5% 4 6% 9% 45%	2000
	11th to 20th	Night	5% 8% 3 5% 3 4 4 3 5% 7% 52%	1979
	21st to end	Night	4 6% 2 4 4 3 4 4 5% 7% 57%	2000
May	1st to 10th	Night	2 5% 2 5% 3 3 2 2 3 4 70%	4069
	11th to 20th	Night	2 4 1 5% 3 2 3 3 4 4 69%	3616
	21st to end	Night	3 4 1 3 2 2 2 2 3 4 73%	3972
June	1st to 10th	Night	4 5% 2 5% 5% 3 4 4 5% 7% 57%	1600
	11th to 20th	Night	3 2 1 3 3 2 3 3 4 5% 73%	1600
	21st to end	Night	2 3 1 3 3 2 2 2 3 4 76%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 2 3 89%	2620
	11th to 20th	Night	2 2 1 2 1 1 2 2 3 3 81%	2620
	21st to end	Night	1 1 2 2 2 2 1 2 4 83%	2854
August	1st to 10th	Night	2 3 1 2 2 1 2 2 5% 7% 72%	2848
	11th to 20th	Night	1 1 1 2 1 1 1 1 2 3 87%	3024
	21st to end	Night	2 2 1 2 1 1 1 1 2 2 85%	3498
September	1st to 10th	Night	2 1 1 1 1 2 2 2 3 84%	1900
	11th to 20th	Night	3 2 1 3 2 2 2 2 4 5% 74%	1900
	21st to end	Night	3 2 1 2 2 2 3 2 3 6% 75%	2119
October	1st to 10th	Night	3 2 1 4 3 2 2 2 2 3 76%	3800
	11th to 20th	Night	2 2 1 4 2 2 3 3 3 6% 71%	3777
	21st to end	Night	4 4 2 5% 3 3 5% 4 5% 6% 60%	4176
November	1st to 10th	Night	6% 6% 3 5% 5% 3 4 5% 7% 8% 49%	2535
	11th to 20th	Night	4 6% 2 6% 4 4 5% 4 8% 8% 49%	2600
	21st to end	Night	2 5% 3 6% 5% 4 5% 4 7% 8% 52%	2795
December	1st to 10th	Night	3 5% 2 5% 3 3 3 3 5% 8% 59%	4560
	11th to 20th	Night	6% 15% 4 10% 6% 5% 6% 5% 7% 9% 26%	5176
	21st to end	Night	7% 13% 4 10% 6% 6% 6% 5% 7% 8% 28%	6952

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	42% 11% 14% 22% 10%	3639
	11th to 20th	Day	35% 7% 11% 21% 22% 5%	3714
	21st to end	Day	41% 6% 9% 14% 23% 8%	4510
February	1st to 10th	Day	37% 7% 14% 25% 13% 4	1800
	11th to 20th	Day	36% 6% 15% 24% 16% 2	1871
	21st to end	Day	37% 7% 14% 24% 13% 5%	1650
March	1st to 10th	Day	49% 5% 8% 20% 14% 4	4557
	11th to 20th	Day	32% 6% 14% 29% 18% 1	5000
	21st to end	Day	44% 6% 14% 21% 13% 1	5747
April	1st to 10th	Day	39% 5% 14% 23% 15% 3	2400
	11th to 20th	Day	31% 6% 14% 26% 19% 4	2372
	21st to end	Day	32% 5% 14% 28% 19% 4	2400
May	1st to 10th	Day	19% 3 7% 27% 39% 6%	5904
	11th to 20th	Day	19% 4 9% 22% 36% 10%	6280
	21st to end	Day	17% 4 7% 28% 39% 5%	6904
June	1st to 10th	Day	27% 5% 10% 24% 29% 6%	2800
	11th to 20th	Day	17% 3 8% 21% 35% 16%	2800
	21st to end	Day	13% 2 4 17% 34% 30%	2800
July	1st to 10th	Day	7% 2 2 6% 15% 68%	4491
	11th to 20th	Day	12% 1 3 7% 15% 62%	4485
	21st to end	Day	10% 2 2 8% 25% 52%	4536
August	1st to 10th	Day	15% 2 3 9% 19% 53%	4076
	11th to 20th	Day	7% 1 2 8% 37% 45%	3859
	21st to end	Day	8% 1 2 13% 39% 37%	4179
September	1st to 10th	Day	9% 1 2 10% 30% 48%	2280
	11th to 20th	Day	16% 3 6% 18% 32% 24%	2280
	21st to end	Day	14% 2 5% 22% 32% 24%	2056
October	1st to 10th	Day	17% 2 5% 15% 32% 31%	3180
	11th to 20th	Day	19% 3 6% 29% 35% 9%	3161
	21st to end	Day	23% 4 10% 32% 23% 8%	3391
November	1st to 10th	Day	33% 5% 13% 21% 23% 5%	1764
	11th to 20th	Day	32% 8% 16% 25% 18% 1	1800
	21st to end	Day	33% 5% 14% 23% 21% 4	1601
December	1st to 10th	Day	28% 4 9% 24% 28% 7%	2620
	11th to 20th	Day	54% 8% 12% 17% 8%	3028
	21st to end	Day	45% 11% 19% 18% 7% 1	4004
January	1st to 10th	Night	38% 10% 19% 23% 10%	6306
	11th to 20th	Night	34% 7% 12% 20% 20% 7%	6232
	21st to end	Night	40% 4 9% 14% 25% 8%	6468
February	1st to 10th	Night	35% 5% 15% 24% 16% 5%	2600
	11th to 20th	Night	34% 6% 15% 27% 17% 1	2426
	21st to end	Night	34% 7% 16% 24% 15% 5%	1980
March	1st to 10th	Night	44% 6% 12% 22% 13% 4	5332
	11th to 20th	Night	32% 6% 13% 29% 19% 1	5000
	21st to end	Night	43% 8% 19% 21% 9% 1	5226
April	1st to 10th	Night	32% 8% 16% 27% 13% 3	2000
	11th to 20th	Night	29% 7% 16% 24% 19% 5%	1979
	21st to end	Night	24% 7% 17% 31% 18% 3	2000
May	1st to 10th	Night	19% 4 8% 28% 33% 8%	4066
	11th to 20th	Night	20% 3 7% 28% 31% 10%	3616
	21st to end	Night	15% 4 10% 30% 38% 3	3972
June	1st to 10th	Night	26% 7% 13% 27% 24% 4	1600
	11th to 20th	Night	15% 4 8% 23% 39% 11%	1600
	21st to end	Night	14% 3 5% 18% 33% 28%	1600
July	1st to 10th	Night	5% 1 2 8% 18% 65%	2580
	11th to 20th	Night	11% 1 3 8% 16% 62%	2572
	21st to end	Night	9% 1 2 7% 36% 45%	2764
August	1st to 10th	Night	13% 2 3 10% 22% 50%	2839
	11th to 20th	Night	7% 1 1 10% 40% 41%	3052
	21st to end	Night	9% 2 2 15% 41% 31%	3498
September	1st to 10th	Night	8% 2 2 10% 29% 49%	1900
	11th to 20th	Night	14% 3 6% 21% 30% 26%	1900
	21st to end	Night	12% 2 5% 22% 34% 24%	2119
October	1st to 10th	Night	15% 2 5% 12% 33% 33%	3800
	11th to 20th	Night	14% 4 8% 30% 34% 10%	3777
	21st to end	Night	21% 5% 10% 27% 27% 10%	4176
November	1st to 10th	Night	30% 7% 15% 22% 19% 7%	2535
	11th to 20th	Night	28% 8% 18% 24% 21% 2	2600
	21st to end	Night	28% 5% 16% 25% 20% 6%	2795
December	1st to 10th	Night	24% 5% 10% 24% 28% 10%	4560
	11th to 20th	Night	49% 9% 10% 19% 12%	5176
	21st to end	Night	47% 9% 17% 18% 9% 1	6952

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	17% 20% 34% 22% 7% 1	200
	11th to 20th	Day	15% 15% 29% 25% 13% 3	235
	21st to end	Day	12% 13% 29% 29% 14% 3	440
February	1st to 10th	Day	16% 18% 25% 26% 14% 2	400
	11th to 20th	Day	14% 22% 28% 25% 11%	450
	21st to end	Day	13% 18% 24% 35% 10% 1	414
March	1st to 10th	Day	17% 23% 30% 20% 9% 1	500
	11th to 20th	Day	16% 21% 25% 24% 13% 1	500
	21st to end	Day	17% 22% 26% 23% 11% 2	550
April	1st to 10th	Day	15% 20% 27% 26% 10% 3	500
	11th to 20th	Day	16% 21% 25% 21% 13% 3	492
	21st to end	Day	12% 20% 25% 23% 16% 4	500
May	1st to 10th	Day	11% 17% 32% 24% 12% 4	503
	11th to 20th	Day	17% 18% 24% 21% 15% 6%	528
	21st to end	Day	10% 14% 19% 29% 21% 7%	573
June	1st to 10th	Day	8% 14% 22% 25% 21% 10%	530
	11th to 20th	Day	10% 15% 28% 25% 17% 5%	530
	21st to end	Day	3 9% 21% 32% 25% 11%	530
July	1st to 10th	Day	2 5% 22% 37% 24% 10%	526
	11th to 20th	Day	1 4 21% 38% 23% 12%	524
	21st to end	Day	2 5% 20% 37% 25% 12%	532
August	1st to 10th	Day	3 5% 22% 31% 27% 12%	487
	11th to 20th	Day	3 5% 20% 31% 24% 16%	477
	21st to end	Day	3 5% 24% 33% 27% 9%	539
September	1st to 10th	Day	4 4 26% 32% 27% 7%	490
	11th to 20th	Day	6% 9% 22% 30% 25% 8%	490
	21st to end	Day	5% 11% 22% 33% 25% 4	490
October	1st to 10th	Day	8% 10% 26% 27% 22% 6%	490
	11th to 20th	Day	10% 13% 18% 32% 23% 4	490
	21st to end	Day	10% 15% 25% 30% 17% 3	506
November	1st to 10th	Day	16% 12% 19% 27% 23% 3	300
	11th to 20th	Day	9% 13% 26% 28% 19% 5%	300
	21st to end	Day	13% 13% 25% 28% 18% 5%	200
December	1st to 10th	Day	12% 16% 25% 24% 19% 6%	200
	11th to 20th	Day	14% 14% 28% 26% 15% 5%	200
	21st to end	Day	13% 20% 28% 23% 16% 1	220
January	1st to 10th	Night	12% 10% 23% 35% 15% 5%	800
	11th to 20th	Night	8% 10% 22% 38% 19% 4	800
	21st to end	Night	10% 6% 23% 37% 20% 4	880
February	1st to 10th	Night	13% 9% 21% 38% 17% 2	800
	11th to 20th	Night	9% 12% 22% 37% 17% 3	784
	21st to end	Night	8% 15% 20% 39% 17% 2	660
March	1st to 10th	Night	13% 12% 24% 32% 16% 3	800
	11th to 20th	Night	13% 12% 20% 31% 22% 3	800
	21st to end	Night	12% 15% 24% 32% 15% 1	880
April	1st to 10th	Night	9% 12% 24% 38% 16% 2	800
	11th to 20th	Night	12% 13% 20% 33% 19% 3	791
	21st to end	Night	8% 11% 22% 34% 22% 3	800
May	1st to 10th	Night	7% 9% 27% 35% 19% 3	595
	11th to 20th	Night	6% 7% 21% 39% 24% 4	394
	21st to end	Night	9% 7% 20% 33% 29% 2	433
June	1st to 10th	Night	6% 6% 17% 43% 27% 3	400
	11th to 20th	Night	5% 5% 21% 44% 24% 2	400
	21st to end	Night	2 3 13% 49% 32% 2	400
July	1st to 10th	Night	2 1 9% 51% 37% 1	390
	11th to 20th	Night	2 1 8% 58% 30% 2	388
	21st to end	Night	2 1 4 48% 41% 4	473
August	1st to 10th	Night	3 4 46% 42% 5%	567
	11th to 20th	Night	2 1 10% 44% 37% 5%	686
	21st to end	Night	3 1 10% 45% 38% 4	836
September	1st to 10th	Night	3 1 13% 43% 36% 4	760
	11th to 20th	Night	4 3 13% 36% 38% 7%	760
	21st to end	Night	4 4 15% 35% 35% 8%	760
October	1st to 10th	Night	6% 4 16% 39% 28% 6%	760
	11th to 20th	Night	5% 7% 13% 36% 35% 4	760
	21st to end	Night	7% 7% 17% 35% 24% 8%	836
November	1st to 10th	Night	9% 10% 17% 35% 25% 4	780
	11th to 20th	Night	9% 9% 22% 37% 20% 3	800
	21st to end	Night	7% 10% 22% 35% 23% 4	800
December	1st to 10th	Night	11% 9% 20% 36% 21% 3	800
	11th to 20th	Night	15% 9% 20% 35% 19% 3	800
	21st to end	Night	14% 15% 23% 34% 12% 1	880

Page generated at 2025-07-17 22:10:03. Version ac07

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