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 2024-11-05.

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% 3 8% 5% 5% 4 4 6% 7% 37%	101366
	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 38%	97746
Transparency	Day	43% 6% 12% 24% 14% 1	104921
	Night	44% 5% 10% 23% 15% 2	102332
Seeing	Day	17% 9% 30% 26% 13% 5%	15860
	Night	18% 9% 30% 29% 13% 1	25700

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	12% 14% 8% 12% 5% 5% 4 3 4 5% 28%	2527
	11th to 20th	Day	11% 13% 6% 15% 4 4 4 8% 8% 6% 20%	2530
	21st to end	Day	17% 20% 10% 10% 5% 3 3 2 4 5% 21%	2844
February	1st to 10th	Day	12% 15% 5% 10% 5% 5% 5% 4 5% 7% 29%	1719
	11th to 20th	Day	13% 11% 4 7% 5% 5% 5% 3 4 6% 37%	1848
	21st to end	Day	12% 15% 5% 10% 5% 5% 4 3 6% 6% 30%	1570
March	1st to 10th	Day	13% 11% 3 7% 4 5% 4 3 5% 6% 39%	3120
	11th to 20th	Day	11% 7% 3 7% 5% 5% 4 4 6% 7% 42%	3273
	21st to end	Day	19% 13% 5% 11% 5% 4 4 4 4 5% 24%	4165
April	1st to 10th	Day	17% 12% 4 8% 6% 4 4 4 4 6% 30%	2280
	11th to 20th	Day	16% 9% 3 7% 5% 5% 4 5% 5% 6% 35%	2254
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 3 5% 6% 34%	2389
May	1st to 10th	Day	15% 7% 3 7% 4 4 5% 5% 6% 7% 37%	4082
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 5% 7% 43%	4367
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	4824
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	2660
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 45%	2660
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 5% 6% 8% 40%	2660
July	1st to 10th	Day	11% 8% 3 7% 5% 5% 6% 5% 8% 9% 33%	4440
	11th to 20th	Day	6% 4 1 6% 5% 5% 6% 4 7% 10% 47%	4440
	21st to end	Day	8% 6% 2 7% 5% 6% 5% 4 6% 8% 42%	4813
August	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 5% 7% 8% 42%	4391
	11th to 20th	Day	10% 5% 1 6% 4 5% 5% 4 6% 8% 44%	3764
	21st to end	Day	8% 5% 2 7% 4 4 4 4 6% 7% 47%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 5% 3 4 5% 7% 47%	2280
	11th to 20th	Day	12% 4 1 4 4 4 3 3 6% 8% 51%	2170
	21st to end	Day	11% 6% 2 7% 5% 5% 4 3 6% 8% 43%	2090
October	1st to 10th	Day	13% 7% 3 6% 4 4 4 2 5% 6% 47%	2019
	11th to 20th	Day	19% 8% 3 7% 5% 4 5% 3 5% 7% 34%	1886
	21st to end	Day	19% 10% 2 7% 4 3 4 3 4 6% 38%	1881
November	1st to 10th	Day	11% 11% 3 7% 3 4 3 3 6% 6% 44%	1708
	11th to 20th	Day	12% 13% 3 11% 5% 5% 4 4 5% 7% 32%	1710
	21st to end	Day	18% 12% 4 6% 4 4 3 2 5% 6% 37%	1601
December	1st to 10th	Day	15% 12% 5% 8% 6% 4 5% 3 6% 7% 29%	1520
	11th to 20th	Day	12% 14% 4 8% 6% 5% 5% 4 6% 7% 29%	1918
	21st to end	Day	19% 21% 9% 12% 5% 3 4 2 4 4 15%	2783
January	1st to 10th	Night	14% 14% 7% 10% 5% 4 3 3 4 5% 31%	4428
	11th to 20th	Night	14% 15% 6% 13% 6% 5% 4 7% 6% 4 19%	4440
	21st to end	Night	19% 18% 7% 10% 5% 4 3 3 3 5% 22%	4820
February	1st to 10th	Night	13% 14% 4 10% 6% 5% 4 3 4 5% 33%	2460
	11th to 20th	Night	13% 10% 3 7% 5% 4 5% 4 5% 6% 39%	2218
	21st to end	Night	19% 10% 4 8% 5% 3 4 3 4 6% 35%	1884
March	1st to 10th	Night	16% 11% 2 7% 4 4 4 3 4 6% 40%	3733
	11th to 20th	Night	9% 7% 3 5% 4 5% 4 4 5% 8% 46%	3716
	21st to end	Night	22% 12% 5% 9% 4 4 4 3 4 4 29%	3466
April	1st to 10th	Night	16% 9% 3 7% 5% 6% 4 4 4 5% 38%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 4 3 3 3 7% 37%	1875
	21st to end	Night	18% 7% 2 7% 5% 3 4 3 5% 7% 39%	1791
May	1st to 10th	Night	15% 7% 2 7% 4 4 4 4 6% 8% 37%	2813
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 6% 8% 40%	2520
	21st to end	Night	12% 8% 3 7% 5% 4 4 4 4 7% 44%	2743
June	1st to 10th	Night	8% 5% 2 5% 4 4 6% 5% 5% 8% 48%	1520
	11th to 20th	Night	10% 6% 1 6% 3 3 4 4 6% 9% 46%	1520
	21st to end	Night	8% 8% 3 5% 5% 5% 4 4 6% 8% 44%	1520
July	1st to 10th	Night	14% 6% 2 7% 5% 5% 4 5% 7% 7% 40%	2530
	11th to 20th	Night	5% 4 2 4 4 4 4 4 8% 9% 53%	2530
	21st to end	Night	6% 4 2 5% 5% 5% 6% 4 7% 8% 48%	2750
August	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 6% 9% 51%	2547
	11th to 20th	Night	9% 5% 2 6% 3 4 4 3 6% 8% 49%	3062
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 9% 51%	3476
September	1st to 10th	Night	8% 6% 2 6% 4 3 3 3 4 5% 55%	1900
	11th to 20th	Night	10% 5% 1 5% 4 3 4 4 4 6% 55%	1990
	21st to end	Night	12% 5% 2 6% 5% 4 4 3 4 7% 48%	2090
October	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 4 6% 51%	2156
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 6% 44%	2294
	21st to end	Night	19% 8% 3 6% 4 4 3 4 5% 6% 38%	2717
November	1st to 10th	Night	12% 8% 2 6% 4 3 4 3 5% 5% 47%	2470
	11th to 20th	Night	13% 12% 4 7% 5% 5% 4 3 5% 6% 36%	2470
	21st to end	Night	17% 10% 3 7% 5% 4 3 3 6% 6% 37%	2574
December	1st to 10th	Night	15% 12% 4 9% 5% 4 5% 4 4 7% 31%	2660
	11th to 20th	Night	15% 13% 4 8% 6% 4 4 4 5% 6% 30%	3279
	21st to end	Night	22% 17% 6% 10% 5% 5% 4 3 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	51% 5% 12% 18% 13% 1	2389
May	1st to 10th	Day	44% 7% 11% 23% 15%	4120
	11th to 20th	Day	39% 6% 11% 28% 15%	4371
	21st to end	Day	38% 7% 13% 22% 17% 4	4837
June	1st to 10th	Day	36% 5% 13% 27% 17% 2	2660
	11th to 20th	Day	34% 6% 13% 24% 20% 2	2660
	21st to end	Day	40% 6% 14% 23% 15% 2	2660
July	1st to 10th	Day	42% 7% 13% 25% 11% 2	4371
	11th to 20th	Day	29% 7% 16% 29% 18% 1	4365
	21st to end	Day	37% 8% 15% 19% 19% 2	4662
August	1st to 10th	Day	36% 7% 14% 29% 12% 1	4376
	11th to 20th	Day	34% 7% 12% 33% 13% 1	3801
	21st to end	Day	34% 7% 12% 24% 22% 2	4179
September	1st to 10th	Day	36% 5% 12% 28% 17% 2	2280
	11th to 20th	Day	31% 5% 11% 32% 18% 2	2170
	21st to end	Day	39% 4 10% 30% 16% 1	2090
October	1st to 10th	Day	25% 3 7% 40% 24% 1	3357
	11th to 20th	Day	34% 4 11% 29% 22% 1	3114
	21st to end	Day	43% 3 8% 29% 13% 4	3081
November	1st to 10th	Day	40% 5% 13% 24% 16% 2	1708
	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 11% 22% 16% 2	1791
May	1st to 10th	Night	44% 6% 12% 19% 16% 2	2840
	11th to 20th	Night	39% 8% 12% 29% 12% 1	2521
	21st to end	Night	41% 6% 9% 18% 18% 8%	2751
June	1st to 10th	Night	32% 6% 12% 28% 19% 3	1520
	11th to 20th	Night	34% 7% 8% 26% 23% 3	1520
	21st to end	Night	35% 6% 15% 24% 17% 2	1520
July	1st to 10th	Night	42% 7% 13% 22% 12% 4	2490
	11th to 20th	Night	24% 6% 16% 37% 15% 2	2482
	21st to end	Night	31% 8% 14% 21% 23% 3	2662
August	1st to 10th	Night	29% 6% 15% 28% 20% 1	2538
	11th to 20th	Night	31% 7% 13% 33% 16% 1	3091
	21st to end	Night	28% 6% 13% 30% 19% 4	3476
September	1st to 10th	Night	32% 5% 10% 26% 24% 3	1900
	11th to 20th	Night	31% 4 9% 33% 21% 2	1990
	21st to end	Night	37% 5% 8% 32% 17% 1	2090
October	1st to 10th	Night	24% 3 7% 39% 26% 1	3598
	11th to 20th	Night	34% 5% 9% 26% 24% 2	3805
	21st to end	Night	42% 4 9% 26% 18% 2	4467
November	1st to 10th	Night	39% 5% 9% 27% 18% 3	2470
	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% 22% 12% 3	460
May	1st to 10th	Day	22% 10% 32% 24% 9% 2	463
	11th to 20th	Day	21% 9% 31% 27% 8% 4	656
	21st to end	Day	16% 7% 31% 23% 16% 6%	734
June	1st to 10th	Day	10% 8% 32% 29% 15% 6%	680
	11th to 20th	Day	14% 6% 30% 30% 15% 5%	680
	21st to end	Day	14% 6% 31% 30% 15% 5%	680
July	1st to 10th	Day	8% 2 23% 31% 24% 12%	671
	11th to 20th	Day	9% 3 28% 33% 17% 10%	668
	21st to end	Day	8% 3 24% 39% 19% 7%	739
August	1st to 10th	Day	10% 4 21% 33% 22% 11%	657
	11th to 20th	Day	11% 3 21% 26% 26% 14%	479
	21st to end	Day	9% 3 17% 32% 27% 11%	539
September	1st to 10th	Day	14% 5% 24% 26% 22% 9%	490
	11th to 20th	Day	11% 1 19% 32% 25% 12%	490
	21st to end	Day	15% 9% 26% 27% 16% 8%	490
October	1st to 10th	Day	16% 7% 26% 27% 18% 5%	419
	11th to 20th	Day	24% 18% 29% 21% 8% 1	300
	21st to end	Day	29% 12% 34% 18% 5% 1	330
November	1st to 10th	Day	17% 14% 35% 24% 7% 2	282
	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% 6% 31% 31% 9% 1	570
May	1st to 10th	Night	19% 7% 32% 34% 8% 1	570
	11th to 20th	Night	19% 5% 27% 34% 14% 1	561
	21st to end	Night	15% 4 24% 34% 21% 2	617
June	1st to 10th	Night	11% 4 24% 44% 17% 1	570
	11th to 20th	Night	14% 3 30% 38% 15% 1	570
	21st to end	Night	10% 4 26% 41% 18% 1	570
July	1st to 10th	Night	10% 1 16% 39% 30% 3	555
	11th to 20th	Night	9% 2 20% 40% 25% 4	552
	21st to end	Night	6% 2 16% 49% 25% 3	624
August	1st to 10th	Night	6% 2 14% 46% 27% 4	567
	11th to 20th	Night	11% 2 13% 39% 30% 5%	564
	21st to end	Night	9% 2 15% 40% 32% 2	627
September	1st to 10th	Night	10% 2 21% 34% 26% 6%	570
	11th to 20th	Night	12% 3 18% 34% 29% 5%	660
	21st to end	Night	14% 8% 22% 31% 21% 4	760
October	1st to 10th	Night	15% 6% 26% 32% 20% 2	760
	11th to 20th	Night	22% 8% 32% 27% 10%	760
	21st to end	Night	24% 9% 33% 26% 8%	836
November	1st to 10th	Night	16% 11% 35% 25% 11% 1	760
	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 2024-11-03 01:11:11. Version ac07

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