Eagle Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Observatory clear sky chart from 2005-11-06 to 2024-04-25.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	83206
	Night	14% 9% 4 7% 5% 3 4 4 5% 6% 38%	85969
Transparency	Day	46% 5% 12% 23% 12% 1	82907
	Night	47% 5% 11% 23% 13% 2	85789
Seeing	Day	17% 9% 30% 26% 13% 5%	15024
	Night	18% 9% 30% 29% 12% 1	25067

By Month

Percentage Cloud Cover SE (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% 13% 9% 10% 6% 4 4 4 4 5% 28%	2527
	11th to 20th	Day	12% 13% 6% 14% 6% 3 4 9% 8% 6% 20%	2530
	21st to end	Day	17% 20% 10% 9% 5% 2 4 3 4 5% 21%	2844
February	1st to 10th	Day	12% 14% 5% 9% 7% 3 5% 5% 4 7% 29%	1719
	11th to 20th	Day	14% 11% 4 6% 5% 3 6% 4 4 6% 37%	1848
	21st to end	Day	12% 14% 5% 9% 5% 4 4 4 6% 6% 30%	1570
March	1st to 10th	Day	13% 10% 4 7% 5% 3 5% 4 5% 6% 39%	3120
	11th to 20th	Day	11% 7% 3 6% 6% 3 4 5% 6% 7% 42%	3273
	21st to end	Day	20% 12% 5% 10% 6% 4 4 4 5% 5% 24%	4165
April	1st to 10th	Day	18% 11% 5% 7% 6% 3 4 5% 4 6% 30%	2280
	11th to 20th	Day	17% 9% 3 6% 6% 4 5% 5% 5% 6% 35%	2254
	21st to end	Day	19% 8% 3 6% 6% 3 5% 5% 5% 6% 34%	2313
May	1st to 10th	Day	16% 9% 3 8% 6% 3 5% 5% 6% 7% 32%	2340
	11th to 20th	Day	18% 8% 3 7% 5% 3 5% 4 5% 7% 35%	2461
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	9% 5% 3 6% 5% 4 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	12% 5% 2 4 5% 3 5% 5% 5% 9% 45%	2520
	21st to end	Day	11% 6% 3 6% 6% 3 5% 6% 6% 9% 40%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 6% 7% 10% 47%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 5% 7% 10% 46%	2520
	21st to end	Day	7% 4 2 5% 5% 4 5% 6% 7% 9% 46%	2743
August	1st to 10th	Day	7% 5% 2 5% 5% 4 6% 7% 6% 9% 43%	2489
	11th to 20th	Day	9% 5% 2 6% 6% 4 6% 6% 6% 8% 41%	2147
	21st to end	Day	8% 4 2 5% 5% 3 5% 6% 7% 7% 47%	2376
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 5% 5% 7% 45%	2160
	11th to 20th	Day	13% 4 2 4 4 3 4 4 5% 8% 51%	2056
	21st to end	Day	11% 5% 2 6% 6% 4 4 4 6% 8% 43%	1980
October	1st to 10th	Day	13% 7% 3 5% 5% 3 4 4 5% 6% 45%	1913
	11th to 20th	Day	20% 8% 3 6% 6% 4 4 5% 5% 7% 33%	1787
	21st to end	Day	20% 9% 3 6% 5% 3 3 4 4 6% 37%	1782
November	1st to 10th	Day	11% 10% 3 6% 4 3 4 4 6% 6% 44%	1672
	11th to 20th	Day	13% 11% 3 9% 6% 4 5% 5% 5% 7% 32%	1710
	21st to end	Day	18% 11% 4 5% 4 3 3 3 5% 6% 37%	1601
December	1st to 10th	Day	15% 11% 5% 7% 7% 4 5% 4 6% 7% 29%	1520
	11th to 20th	Day	12% 14% 5% 7% 6% 3 6% 5% 6% 7% 29%	1918
	21st to end	Day	20% 21% 9% 11% 6% 3 4 3 4 4 15%	2783
January	1st to 10th	Night	14% 13% 8% 9% 6% 3 3 4 4 5% 31%	4428
	11th to 20th	Night	15% 15% 7% 12% 7% 4 4 8% 6% 4 19%	4440
	21st to end	Night	19% 17% 8% 9% 6% 2 4 4 3 6% 22%	4820
February	1st to 10th	Night	13% 13% 5% 8% 7% 4 5% 3 4 5% 33%	2460
	11th to 20th	Night	13% 9% 4 6% 5% 3 5% 5% 5% 6% 39%	2218
	21st to end	Night	19% 9% 5% 6% 6% 2 4 3 4 6% 36%	1884
March	1st to 10th	Night	17% 11% 2 6% 5% 3 4 4 4 6% 40%	3733
	11th to 20th	Night	9% 6% 3 5% 5% 4 5% 5% 5% 8% 46%	3716
	21st to end	Night	22% 11% 5% 8% 6% 3 5% 3 4 4 29%	3466
April	1st to 10th	Night	16% 8% 3 6% 6% 4 5% 5% 4 6% 38%	1900
	11th to 20th	Night	19% 8% 3 6% 5% 2 4 3 3 7% 37%	1875
	21st to end	Night	18% 7% 3 6% 5% 3 4 4 5% 7% 39%	1746
May	1st to 10th	Night	15% 7% 3 7% 6% 4 4 5% 7% 8% 35%	1620
	11th to 20th	Night	17% 7% 3 6% 4 2 3 4 6% 8% 39%	1430
	21st to end	Night	12% 6% 3 5% 6% 4 5% 4 4 8% 42%	1551
June	1st to 10th	Night	8% 3 2 4 5% 3 6% 5% 5% 8% 49%	1440
	11th to 20th	Night	11% 6% 2 5% 4 3 3 5% 6% 9% 46%	1440
	21st to end	Night	8% 6% 4 4 5% 4 4 5% 6% 9% 46%	1440
July	1st to 10th	Night	7% 3 2 4 5% 2 5% 6% 7% 9% 51%	1440
	11th to 20th	Night	8% 5% 2 3 4 3 4 5% 6% 8% 52%	1440
	21st to end	Night	6% 3 2 3 4 3 4 5% 8% 9% 53%	1575
August	1st to 10th	Night	5% 4 2 5% 4 3 4 6% 6% 10% 51%	1449
	11th to 20th	Night	8% 3 3 4 4 3 3 5% 6% 9% 52%	1751
	21st to end	Night	7% 4 2 4 5% 3 4 5% 5% 7% 53%	1980
September	1st to 10th	Night	9% 6% 2 5% 5% 3 4 4 4 5% 53%	1800
	11th to 20th	Night	11% 4 1 4 5% 2 4 4 3 6% 55%	1885
	21st to end	Night	12% 5% 2 5% 6% 2 4 4 4 7% 48%	1980
October	1st to 10th	Night	12% 6% 2 4 4 3 4 4 4 6% 50%	2042
	11th to 20th	Night	18% 7% 2 5% 4 2 4 3 5% 6% 43%	2173
	21st to end	Night	20% 8% 3 5% 5% 3 3 5% 5% 7% 38%	2574
November	1st to 10th	Night	12% 7% 3 5% 5% 3 4 4 4 6% 48%	2406
	11th to 20th	Night	13% 11% 4 6% 6% 3 5% 4 5% 6% 37%	2470
	21st to end	Night	17% 9% 4 6% 5% 3 4 4 6% 6% 37%	2574
December	1st to 10th	Night	15% 11% 4 8% 6% 4 5% 5% 4 7% 31%	2660
	11th to 20th	Night	15% 12% 5% 7% 6% 3 5% 4 5% 6% 30%	3279
	21st to end	Night	23% 16% 6% 9% 6% 4 4 4 4 5% 19%	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	59% 5% 12% 17% 7%	2528
	11th to 20th	Day	60% 5% 12% 16% 7%	2530
	21st to end	Day	68% 3 7% 17% 6%	2844
February	1st to 10th	Day	55% 4 12% 18% 10% 1	1719
	11th to 20th	Day	48% 5% 10% 24% 11% 2	1858
	21st to end	Day	54% 5% 8% 21% 10% 2	1570
March	1st to 10th	Day	46% 6% 10% 24% 12% 3	3120
	11th to 20th	Day	41% 6% 9% 31% 12% 1	3273
	21st to end	Day	61% 6% 12% 16% 5% 1	4165
April	1st to 10th	Day	54% 5% 10% 20% 10%	2280
	11th to 20th	Day	49% 6% 8% 21% 13% 3	2254
	21st to end	Day	50% 5% 12% 18% 13% 1	2313
May	1st to 10th	Day	50% 6% 14% 23% 8%	2340
	11th to 20th	Day	48% 6% 12% 22% 12% 1	2465
	21st to end	Day	42% 7% 13% 22% 14% 2	2725
June	1st to 10th	Day	36% 5% 13% 27% 17% 2	2520
	11th to 20th	Day	35% 6% 13% 24% 20% 2	2520
	21st to end	Day	40% 6% 14% 23% 15% 2	2520
July	1st to 10th	Day	30% 6% 15% 31% 15% 3	2451
	11th to 20th	Day	32% 7% 14% 26% 19% 2	2445
	21st to end	Day	31% 7% 16% 27% 15% 3	2591
August	1st to 10th	Day	34% 7% 15% 30% 13% 2	2474
	11th to 20th	Day	38% 7% 15% 26% 13% 1	2147
	21st to end	Day	32% 8% 11% 25% 20% 3	2376
September	1st to 10th	Day	37% 6% 12% 26% 17% 2	2160
	11th to 20th	Day	32% 5% 12% 33% 16% 2	2056
	21st to end	Day	40% 4 10% 31% 14% 1	1980
October	1st to 10th	Day	40% 4 10% 29% 15% 1	1913
	11th to 20th	Day	51% 4 11% 21% 12% 1	1787
	21st to end	Day	50% 4 10% 24% 11% 2	1782
November	1st to 10th	Day	40% 5% 13% 24% 17% 2	1672
	11th to 20th	Day	51% 5% 12% 21% 10% 1	1710
	21st to end	Day	50% 3 12% 25% 9%	1601
December	1st to 10th	Day	53% 4 15% 19% 8% 1	1520
	11th to 20th	Day	53% 5% 15% 17% 8% 2	1915
	21st to end	Day	74% 3 8% 11% 4	2783
January	1st to 10th	Night	57% 4 9% 20% 9% 1	4428
	11th to 20th	Night	65% 4 9% 14% 8%	4440
	21st to end	Night	65% 3 10% 15% 6% 1	4820
February	1st to 10th	Night	54% 4 9% 19% 13% 2	2460
	11th to 20th	Night	46% 4 11% 23% 14% 2	2219
	21st to end	Night	51% 4 8% 21% 11% 4	1884
March	1st to 10th	Night	47% 5% 12% 24% 9% 3	3733
	11th to 20th	Night	35% 6% 11% 27% 18% 3	3716
	21st to end	Night	60% 5% 8% 17% 10% 1	3466
April	1st to 10th	Night	47% 5% 9% 23% 14% 2	1900
	11th to 20th	Night	49% 4 6% 20% 17% 4	1875
	21st to end	Night	45% 4 12% 21% 15% 2	1746
May	1st to 10th	Night	46% 6% 14% 22% 12%	1620
	11th to 20th	Night	43% 6% 11% 25% 14% 2	1431
	21st to end	Night	42% 5% 12% 22% 16% 2	1552
June	1st to 10th	Night	31% 6% 13% 28% 19% 3	1440
	11th to 20th	Night	34% 7% 8% 26% 22% 2	1440
	21st to end	Night	34% 6% 16% 25% 16% 2	1440
July	1st to 10th	Night	28% 8% 13% 30% 17% 4	1400
	11th to 20th	Night	28% 5% 13% 32% 18% 4	1392
	21st to end	Night	25% 7% 15% 29% 19% 5%	1487
August	1st to 10th	Night	26% 8% 17% 30% 16% 3	1440
	11th to 20th	Night	28% 7% 16% 31% 17% 1	1751
	21st to end	Night	28% 6% 11% 30% 20% 4	1980
September	1st to 10th	Night	34% 5% 10% 25% 24% 3	1800
	11th to 20th	Night	32% 4 9% 34% 20% 2	1885
	21st to end	Night	37% 5% 9% 33% 16% 1	1980
October	1st to 10th	Night	36% 4 10% 30% 19% 2	2042
	11th to 20th	Night	42% 4 10% 24% 18% 1	2173
	21st to end	Night	47% 5% 11% 24% 12% 1	2574
November	1st to 10th	Night	38% 4 9% 27% 19% 3	2406
	11th to 20th	Night	49% 4 11% 22% 12% 1	2470
	21st to end	Night	47% 5% 13% 23% 11% 1	2574
December	1st to 10th	Night	53% 5% 11% 20% 10% 1	2660
	11th to 20th	Night	54% 5% 12% 19% 10% 1	3281
	21st to end	Night	67% 4 9% 14% 5%	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	19% 15% 34% 26% 6%	270
	11th to 20th	Day	20% 14% 38% 24% 4 1	270
	21st to end	Day	23% 11% 39% 18% 8% 1	297
February	1st to 10th	Day	14% 21% 41% 19% 4 1	270
	11th to 20th	Day	20% 23% 36% 16% 5%	270
	21st to end	Day	22% 18% 46% 12% 2 1	225
March	1st to 10th	Day	16% 23% 44% 14% 3	270
	11th to 20th	Day	24% 17% 33% 20% 5% 2	286
	21st to end	Day	27% 10% 30% 22% 8% 2	506
April	1st to 10th	Day	25% 11% 34% 24% 6%	460
	11th to 20th	Day	21% 19% 27% 21% 8% 3	452
	21st to end	Day	23% 11% 28% 23% 12% 3	437
May	1st to 10th	Day	23% 10% 32% 23% 9% 2	423
	11th to 20th	Day	22% 9% 31% 26% 8% 4	607
	21st to end	Day	17% 7% 30% 23% 17% 7%	679
June	1st to 10th	Day	9% 7% 33% 30% 16% 6%	630
	11th to 20th	Day	14% 6% 28% 31% 15% 6%	630
	21st to end	Day	14% 6% 29% 30% 16% 5%	630
July	1st to 10th	Day	8% 2 21% 31% 25% 13%	621
	11th to 20th	Day	9% 3 28% 33% 17% 10%	618
	21st to end	Day	8% 3 26% 37% 19% 7%	684
August	1st to 10th	Day	10% 3 19% 34% 23% 11%	608
	11th to 20th	Day	11% 3 20% 25% 27% 15%	439
	21st to end	Day	10% 3 18% 33% 25% 11%	495
September	1st to 10th	Day	16% 6% 23% 25% 23% 9%	450
	11th to 20th	Day	12% 2 19% 31% 24% 11%	450
	21st to end	Day	14% 9% 24% 26% 18% 8%	450
October	1st to 10th	Day	17% 7% 25% 28% 17% 6%	383
	11th to 20th	Day	26% 18% 29% 20% 7% 1	270
	21st to end	Day	31% 12% 34% 16% 6%	297
November	1st to 10th	Day	16% 15% 34% 25% 8% 2	270
	11th to 20th	Day	20% 16% 40% 13% 10%	270
	21st to end	Day	26% 8% 42% 19% 4	270
December	1st to 10th	Day	19% 17% 39% 19% 5% 1	270
	11th to 20th	Day	20% 16% 36% 21% 6% 1	270
	21st to end	Day	26% 21% 33% 19% 2	297
January	1st to 10th	Night	19% 16% 36% 24% 5%	950
	11th to 20th	Night	22% 15% 35% 22% 6% 1	950
	21st to end	Night	22% 10% 38% 25% 6%	1045
February	1st to 10th	Night	21% 13% 36% 24% 6%	940
	11th to 20th	Night	20% 15% 35% 25% 4	743
	21st to end	Night	25% 13% 38% 20% 4	628
March	1st to 10th	Night	20% 11% 37% 24% 8% 1	760
	11th to 20th	Night	17% 12% 37% 26% 8% 1	732
	21st to end	Night	23% 8% 30% 29% 9% 1	627
April	1st to 10th	Night	19% 10% 36% 27% 6%	570
	11th to 20th	Night	24% 10% 33% 25% 7% 2	563
	21st to end	Night	21% 5% 31% 32% 10% 1	555
May	1st to 10th	Night	19% 7% 32% 33% 8% 1	540
	11th to 20th	Night	19% 5% 27% 34% 14% 1	531
	21st to end	Night	15% 4 24% 33% 21% 2	584
June	1st to 10th	Night	10% 3 24% 44% 18% 1	540
	11th to 20th	Night	15% 3 28% 38% 16% 1	540
	21st to end	Night	10% 3 26% 42% 18% 1	540
July	1st to 10th	Night	9% 1 15% 39% 32% 3	525
	11th to 20th	Night	9% 2 20% 40% 25% 4	522
	21st to end	Night	6% 2 17% 48% 25% 2	591
August	1st to 10th	Night	6% 2 13% 47% 28% 4	537
	11th to 20th	Night	10% 2 13% 38% 31% 6%	534
	21st to end	Night	9% 2 15% 39% 32% 3	594
September	1st to 10th	Night	11% 3 21% 35% 26% 6%	540
	11th to 20th	Night	13% 3 19% 33% 28% 5%	625
	21st to end	Night	15% 7% 22% 30% 22% 4	720
October	1st to 10th	Night	15% 6% 26% 30% 20% 2	720
	11th to 20th	Night	23% 9% 32% 27% 9%	720
	21st to end	Night	24% 9% 33% 25% 8% 1	792
November	1st to 10th	Night	15% 11% 36% 25% 11% 1	740
	11th to 20th	Night	19% 15% 34% 25% 6% 1	760
	21st to end	Night	21% 12% 36% 23% 7%	864
December	1st to 10th	Night	21% 14% 37% 23% 5%	950
	11th to 20th	Night	23% 12% 36% 24% 5%	950
	21st to end	Night	28% 12% 37% 19% 3	1045

Page generated at 2024-04-22 08:25:44. Version ac07

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