Eagle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle clear sky chart from 2005-11-06 to 2025-02-25.

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	8% 7% 2 5% 4 4 4 3 5% 6% 53%	112424
	Night	11% 8% 2 6% 4 4 4 3 5% 6% 47%	114966
Transparency	Day	30% 8% 12% 19% 18% 13%	112168
	Night	35% 8% 13% 19% 15% 10%	114811
Seeing	Day	10% 9% 22% 29% 23% 7%	14751
	Night	13% 5% 19% 38% 22% 3	24206

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	15% 18% 5% 10% 6% 6% 5% 5% 7% 6% 19%	3639
	11th to 20th	Day	12% 11% 4 9% 5% 4 4 4 6% 8% 34%	3640
	21st to end	Day	15% 11% 4 8% 5% 4 4 3 4 5% 38%	4004
February	1st to 10th	Day	14% 13% 4 8% 6% 4 5% 3 4 6% 33%	1760
	11th to 20th	Day	13% 13% 3 7% 5% 4 3 5% 6% 7% 35%	1950
	21st to end	Day	11% 12% 4 7% 7% 4 5% 3 6% 7% 34%	1611
March	1st to 10th	Day	10% 13% 4 9% 7% 6% 5% 4 6% 7% 28%	3138
	11th to 20th	Day	8% 8% 2 4 4 3 3 3 4 5% 56%	3352
	21st to end	Day	10% 11% 4 7% 6% 5% 6% 5% 7% 9% 31%	4010
April	1st to 10th	Day	11% 10% 2 6% 4 5% 4 4 6% 7% 41%	2280
	11th to 20th	Day	8% 8% 2 6% 5% 4 4 4 5% 8% 46%	2286
	21st to end	Day	9% 6% 2 6% 4 4 4 4 5% 7% 50%	2470
May	1st to 10th	Day	10% 8% 2 4 4 4 4 4 6% 6% 49%	4110
	11th to 20th	Day	6% 3 1 3 2 3 3 2 4 5% 68%	4219
	21st to end	Day	6% 5% 2 4 4 4 4 4 6% 8% 54%	4813
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 7% 8% 45%	2660
	11th to 20th	Day	7% 3 1 4 3 3 3 4 5% 7% 59%	2660
	21st to end	Day	3 3 1 2 2 2 3 3 4 5% 72%	2660
July	1st to 10th	Day	1 1 2 1 2 2 2 3 3 83%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	3 2 1 2 2 2 2 2 3 4 75%	4790
August	1st to 10th	Day	4 3 2 4 3 3 3 3 4 6% 64%	4247
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	4028
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4186
September	1st to 10th	Day	3 2 3 2 1 3 2 4 5% 75%	2280
	11th to 20th	Day	5% 4 1 3 3 3 3 3 4 6% 66%	2111
	21st to end	Day	6% 3 1 3 2 2 2 2 4 6% 67%	2090
October	1st to 10th	Day	5% 4 1 4 2 3 3 2 3 4 69%	3490
	11th to 20th	Day	8% 4 2 5% 4 3 4 4 5% 7% 55%	3028
	21st to end	Day	7% 7% 2 6% 4 4 4 3 5% 7% 49%	3101
November	1st to 10th	Day	15% 8% 2 6% 4 3 4 4 5% 7% 41%	1764
	11th to 20th	Day	17% 9% 3 6% 5% 5% 4 4 6% 7% 35%	1800
	21st to end	Day	12% 8% 4 8% 6% 6% 5% 3 6% 9% 34%	1755
December	1st to 10th	Day	10% 6% 2 7% 4 3 4 3 6% 9% 45%	2620
	11th to 20th	Day	17% 14% 5% 12% 6% 5% 5% 4 5% 7% 20%	3028
	21st to end	Day	18% 13% 4 11% 6% 5% 4 4 6% 8% 23%	4004
January	1st to 10th	Night	20% 15% 4 10% 5% 5% 4 4 5% 6% 21%	6306
	11th to 20th	Night	17% 12% 4 7% 4 4 3 2 5% 7% 34%	6320
	21st to end	Night	14% 9% 3 9% 4 3 3 3 4 6% 41%	6952
February	1st to 10th	Night	18% 11% 4 7% 5% 5% 4 4 4 6% 32%	2635
	11th to 20th	Night	14% 11% 3 6% 5% 5% 4 4 6% 7% 36%	2338
	21st to end	Night	15% 12% 4 7% 6% 5% 5% 4 5% 7% 32%	1937
March	1st to 10th	Night	12% 12% 3 8% 5% 5% 5% 4 5% 8% 34%	3736
	11th to 20th	Night	11% 9% 2 5% 3 3 3 3 4 5% 53%	3628
	21st to end	Night	12% 10% 3 7% 6% 5% 6% 4 6% 8% 32%	3626
April	1st to 10th	Night	13% 8% 2 5% 3 4 5% 3 6% 6% 45%	1900
	11th to 20th	Night	12% 8% 2 5% 5% 5% 4 4 5% 5% 46%	1840
	21st to end	Night	8% 5% 2 5% 4 4 3 4 6% 6% 52%	1710
May	1st to 10th	Night	13% 5% 1 4 3 3 4 4 6% 7% 49%	2860
	11th to 20th	Night	6% 3 1 3 3 3 3 3 4 6% 64%	2676
	21st to end	Night	7% 5% 2 5% 4 4 3 3 6% 6% 54%	2762
June	1st to 10th	Night	11% 6% 2 5% 5% 5% 3 3 7% 9% 45%	1520
	11th to 20th	Night	7% 4 1 4 3 3 4 3 5% 7% 59%	1520
	21st to end	Night	3 3 1 3 3 4 4 3 4 6% 68%	1520
July	1st to 10th	Night	1 1 1 2 2 2 2 2 4 4 80%	2540
	11th to 20th	Night	1 1 1 2 2 2 3 2 3 5% 79%	2540
	21st to end	Night	2 2 1 4 3 3 4 4 5% 5% 67%	2761
August	1st to 10th	Night	3 4 1 5% 3 4 4 3 5% 6% 61%	2684
	11th to 20th	Night	2 1 2 1 2 2 2 3 5% 78%	2811
	21st to end	Night	3 3 1 3 2 2 2 2 2 3 77%	3488
September	1st to 10th	Night	3 2 1 2 2 1 2 2 4 4 77%	1900
	11th to 20th	Night	6% 3 1 4 3 3 2 3 4 7% 64%	2067
	21st to end	Night	7% 3 1 3 2 3 3 2 4 6% 67%	2090
October	1st to 10th	Night	4 3 1 3 3 3 3 2 4 4 70%	3490
	11th to 20th	Night	7% 4 2 4 3 3 3 3 4 6% 61%	3889
	21st to end	Night	11% 6% 2 5% 3 4 4 4 6% 7% 47%	4457
November	1st to 10th	Night	15% 7% 3 6% 4 3 4 3 4 7% 44%	2535
	11th to 20th	Night	19% 7% 3 7% 4 4 3 4 5% 7% 38%	2600
	21st to end	Night	15% 9% 2 5% 4 4 4 3 5% 7% 42%	2640
December	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 6% 11% 46%	4560
	11th to 20th	Night	19% 14% 4 10% 6% 5% 5% 4 7% 6% 20%	5176
	21st to end	Night	17% 11% 4 10% 6% 5% 5% 4 6% 8% 24%	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	58% 16% 16% 10% 1	3639
	11th to 20th	Day	46% 12% 20% 18% 4	3640
	21st to end	Day	47% 10% 14% 22% 6% 1	4004
February	1st to 10th	Day	52% 11% 18% 15% 4 1	1760
	11th to 20th	Day	46% 12% 17% 19% 6%	1960
	21st to end	Day	47% 10% 18% 18% 8% 1	1611
March	1st to 10th	Day	43% 14% 18% 18% 6% 1	3138
	11th to 20th	Day	28% 8% 13% 39% 13% 1	3352
	21st to end	Day	41% 14% 20% 17% 7% 1	4010
April	1st to 10th	Day	39% 9% 17% 21% 12% 3	2280
	11th to 20th	Day	33% 9% 13% 24% 16% 4	2289
	21st to end	Day	32% 7% 15% 27% 17% 2	2470
May	1st to 10th	Day	30% 8% 11% 26% 21% 5%	4110
	11th to 20th	Day	18% 6% 8% 25% 31% 13%	4222
	21st to end	Day	23% 8% 16% 30% 19% 4	4814
June	1st to 10th	Day	33% 9% 13% 24% 19% 2	2660
	11th to 20th	Day	22% 5% 10% 24% 28% 11%	2660
	21st to end	Day	14% 4 8% 18% 32% 23%	2660
July	1st to 10th	Day	9% 2 4 9% 19% 57%	4351
	11th to 20th	Day	10% 2 3 6% 21% 58%	4345
	21st to end	Day	12% 2 3 8% 29% 45%	4639
August	1st to 10th	Day	20% 4 6% 11% 25% 34%	4231
	11th to 20th	Day	9% 2 4 16% 36% 33%	4067
	21st to end	Day	13% 3 4 18% 35% 27%	4185
September	1st to 10th	Day	12% 3 6% 17% 30% 32%	2280
	11th to 20th	Day	20% 5% 10% 23% 28% 15%	2111
	21st to end	Day	21% 3 8% 25% 33% 10%	2090
October	1st to 10th	Day	21% 4 7% 18% 40% 10%	3490
	11th to 20th	Day	28% 5% 12% 28% 24% 4	3028
	21st to end	Day	33% 6% 13% 29% 18% 1	3101
November	1st to 10th	Day	40% 9% 17% 24% 10%	1764
	11th to 20th	Day	46% 9% 20% 21% 4	1800
	21st to end	Day	45% 12% 21% 17% 5%	1755
December	1st to 10th	Day	35% 13% 24% 26% 3	2620
	11th to 20th	Day	59% 13% 19% 8% 1	3028
	21st to end	Day	55% 12% 17% 13% 2	4004
January	1st to 10th	Night	59% 13% 17% 10% 1	6306
	11th to 20th	Night	48% 11% 16% 18% 6%	6320
	21st to end	Night	43% 10% 13% 21% 10% 2	6952
February	1st to 10th	Night	51% 9% 17% 18% 3 1	2635
	11th to 20th	Night	44% 10% 17% 20% 8% 1	2339
	21st to end	Night	47% 10% 15% 18% 9% 1	1937
March	1st to 10th	Night	41% 11% 15% 21% 10% 1	3736
	11th to 20th	Night	33% 5% 9% 30% 22% 1	3628
	21st to end	Night	39% 15% 18% 21% 7%	3626
April	1st to 10th	Night	37% 7% 13% 24% 16% 3	1900
	11th to 20th	Night	36% 8% 11% 23% 19% 3	1840
	21st to end	Night	29% 6% 13% 26% 23% 3	1710
May	1st to 10th	Night	28% 8% 11% 24% 23% 5%	2860
	11th to 20th	Night	19% 5% 8% 22% 37% 9%	2676
	21st to end	Night	27% 8% 13% 26% 23% 3	2762
June	1st to 10th	Night	35% 8% 12% 24% 20% 2	1520
	11th to 20th	Night	25% 5% 9% 21% 31% 9%	1520
	21st to end	Night	16% 5% 7% 17% 30% 24%	1520
July	1st to 10th	Night	9% 2 4 9% 18% 59%	2500
	11th to 20th	Night	9% 2 3 7% 17% 61%	2492
	21st to end	Night	17% 4 4 6% 26% 43%	2674
August	1st to 10th	Night	22% 4 5% 11% 21% 38%	2676
	11th to 20th	Night	9% 3 4 11% 27% 46%	2838
	21st to end	Night	14% 2 3 12% 32% 36%	3488
September	1st to 10th	Night	13% 3 5% 13% 29% 37%	1900
	11th to 20th	Night	21% 4 7% 19% 25% 24%	2067
	21st to end	Night	20% 3 6% 20% 32% 18%	2090
October	1st to 10th	Night	18% 4 5% 19% 30% 24%	3490
	11th to 20th	Night	24% 4 11% 27% 29% 6%	3889
	21st to end	Night	34% 5% 12% 28% 20% 2	4457
November	1st to 10th	Night	39% 7% 13% 22% 17% 1	2535
	11th to 20th	Night	45% 7% 14% 25% 9%	2600
	21st to end	Night	41% 7% 19% 24% 8%	2640
December	1st to 10th	Night	33% 12% 28% 23% 4	4560
	11th to 20th	Night	60% 12% 17% 10% 2	5176
	21st to end	Night	52% 13% 18% 13% 4	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	23% 12% 20% 26% 17% 4	200
	11th to 20th	Day	15% 12% 19% 33% 16% 7%	200
	21st to end	Day	15% 7% 18% 34% 19% 7%	220
February	1st to 10th	Day	20% 9% 30% 22% 16% 3	312
	11th to 20th	Day	18% 13% 28% 26% 14% 2	495
	21st to end	Day	18% 15% 26% 27% 13% 2	399
March	1st to 10th	Day	15% 16% 31% 26% 11%	460
	11th to 20th	Day	12% 12% 30% 28% 16% 3	460
	21st to end	Day	13% 16% 30% 25% 15% 2	506
April	1st to 10th	Day	14% 18% 23% 22% 18% 5%	460
	11th to 20th	Day	10% 17% 31% 24% 15% 4	452
	21st to end	Day	9% 16% 32% 25% 15% 4	460
May	1st to 10th	Day	5% 16% 31% 27% 15% 5%	463
	11th to 20th	Day	15% 8% 24% 27% 19% 7%	488
	21st to end	Day	9% 10% 16% 31% 23% 11%	529
June	1st to 10th	Day	8% 9% 22% 28% 23% 10%	490
	11th to 20th	Day	7% 11% 27% 32% 18% 5%	490
	21st to end	Day	5% 5% 24% 33% 27% 7%	490
July	1st to 10th	Day	2 4 18% 39% 29% 8%	486
	11th to 20th	Day	1 2 22% 40% 28% 6%	484
	21st to end	Day	3 1 15% 37% 35% 8%	531
August	1st to 10th	Day	4 3 18% 37% 31% 7%	487
	11th to 20th	Day	3 1 16% 32% 36% 12%	477
	21st to end	Day	3 4 17% 32% 30% 14%	539
September	1st to 10th	Day	5% 3 13% 30% 34% 16%	490
	11th to 20th	Day	6% 4 16% 30% 29% 13%	490
	21st to end	Day	5% 5% 19% 30% 32% 9%	490
October	1st to 10th	Day	7% 8% 17% 23% 31% 13%	490
	11th to 20th	Day	10% 5% 23% 25% 26% 11%	386
	21st to end	Day	12% 10% 24% 28% 22% 4	330
November	1st to 10th	Day	15% 8% 23% 29% 20% 4	300
	11th to 20th	Day	16% 9% 21% 31% 19% 5%	300
	21st to end	Day	13% 6% 19% 32% 24% 5%	277
December	1st to 10th	Day	21% 5% 18% 26% 19% 13%	200
	11th to 20th	Day	21% 10% 24% 29% 13% 4	200
	21st to end	Day	20% 10% 25% 28% 14% 3	220
January	1st to 10th	Night	22% 8% 21% 28% 19% 3	800
	11th to 20th	Night	19% 6% 19% 31% 22% 3	800
	21st to end	Night	18% 4 17% 35% 24% 3	880
February	1st to 10th	Night	22% 6% 21% 33% 16% 2	800
	11th to 20th	Night	16% 4 24% 36% 17% 2	784
	21st to end	Night	17% 8% 25% 35% 14% 2	646
March	1st to 10th	Night	16% 9% 27% 33% 14% 2	760
	11th to 20th	Night	15% 8% 21% 38% 17% 2	760
	21st to end	Night	15% 9% 25% 37% 11% 2	836
April	1st to 10th	Night	14% 8% 21% 38% 17% 2	760
	11th to 20th	Night	11% 9% 28% 33% 16% 2	712
	21st to end	Night	9% 10% 23% 40% 15% 2	570
May	1st to 10th	Night	9% 9% 24% 38% 19% 2	570
	11th to 20th	Night	11% 6% 20% 33% 26% 4	469
	21st to end	Night	9% 6% 18% 34% 28% 5%	411
June	1st to 10th	Night	12% 4 17% 39% 24% 3	380
	11th to 20th	Night	8% 6% 24% 36% 24% 2	380
	21st to end	Night	3 1 19% 45% 30% 2	380
July	1st to 10th	Night	2 1 14% 49% 32% 2	370
	11th to 20th	Night	1 1 15% 57% 27%	368
	21st to end	Night	3 1 13% 48% 34% 1	416
August	1st to 10th	Night	4 1 13% 49% 32% 1	468
	11th to 20th	Night	1 2 10% 49% 36% 2	564
	21st to end	Night	4 2 13% 45% 31% 5%	826
September	1st to 10th	Night	3 1 11% 43% 37% 5%	760
	11th to 20th	Night	6% 2 11% 36% 39% 6%	760
	21st to end	Night	8% 3 15% 37% 29% 9%	760
October	1st to 10th	Night	8% 3 17% 40% 28% 4	760
	11th to 20th	Night	9% 4 16% 38% 28% 6%	760
	21st to end	Night	12% 4 19% 39% 23% 4	836
November	1st to 10th	Night	16% 5% 19% 34% 24% 2	780
	11th to 20th	Night	20% 6% 20% 37% 16% 3	800
	21st to end	Night	18% 4 17% 36% 21% 5%	800
December	1st to 10th	Night	20% 5% 17% 36% 19% 4	800
	11th to 20th	Night	24% 7% 16% 37% 15% 3	800
	21st to end	Night	26% 7% 23% 32% 11% 2	880

Page generated at 2025-02-22 04:51:38. Version ac07

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