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 2024-09-29.

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%	100966
	Night	11% 8% 2 6% 4 4 4 3 5% 6% 47%	97418
Transparency	Day	30% 8% 12% 19% 18% 15%	100710
	Night	35% 8% 12% 18% 16% 11%	97263
Seeing	Day	10% 9% 23% 29% 23% 7%	14340
	Night	13% 5% 19% 37% 23% 3	23612

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	14% 18% 5% 9% 5% 5% 6% 5% 6% 6% 21%	2539
	11th to 20th	Day	17% 15% 5% 11% 6% 5% 5% 4 5% 5% 19%	2540
	21st to end	Day	20% 14% 5% 11% 6% 5% 5% 4 5% 6% 18%	2794
February	1st to 10th	Day	14% 13% 4 8% 6% 4 5% 3 4 6% 34%	1671
	11th to 20th	Day	12% 13% 2 7% 5% 4 3 5% 6% 7% 35%	1850
	21st to end	Day	11% 12% 4 7% 7% 5% 5% 3 6% 6% 34%	1570
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% 4 1 3 2 2 3 1 4 6% 67%	2069
October	1st to 10th	Day	9% 5% 2 5% 3 4 4 3 5% 6% 56%	1980
	11th to 20th	Day	9% 4 2 5% 4 3 4 3 6% 7% 55%	1737
	21st to end	Day	9% 6% 2 7% 4 4 3 3 6% 8% 48%	1782
November	1st to 10th	Day	15% 8% 3 6% 4 3 4 4 5% 7% 40%	1674
	11th to 20th	Day	17% 8% 2 6% 5% 5% 5% 4 6% 7% 36%	1710
	21st to end	Day	12% 8% 4 8% 6% 6% 5% 4 6% 9% 33%	1668
December	1st to 10th	Day	18% 10% 3 10% 5% 4 5% 4 5% 7% 31%	1520
	11th to 20th	Day	16% 13% 5% 13% 6% 5% 5% 4 6% 8% 20%	1928
	21st to end	Day	14% 11% 4 11% 6% 5% 4 4 6% 8% 26%	2794
January	1st to 10th	Night	17% 16% 5% 11% 5% 5% 5% 4 5% 7% 22%	4406
	11th to 20th	Night	24% 17% 5% 9% 5% 5% 4 2 3 5% 21%	4420
	21st to end	Night	20% 12% 4 11% 5% 4 4 3 4 7% 25%	4862
February	1st to 10th	Night	18% 11% 4 7% 4 5% 4 4 4 6% 33%	2504
	11th to 20th	Night	14% 11% 3 5% 5% 5% 4 4 6% 6% 37%	2218
	21st to end	Night	14% 12% 4 7% 6% 5% 5% 4 5% 7% 32%	1884
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%	2079
October	1st to 10th	Night	7% 5% 2 4 3 3 3 2 5% 5% 60%	1980
	11th to 20th	Night	9% 4 2 3 3 3 4 3 5% 6% 57%	2221
	21st to end	Night	11% 5% 2 5% 4 4 3 4 6% 8% 48%	2574
November	1st to 10th	Night	16% 7% 2 6% 4 3 4 3 4 7% 44%	2405
	11th to 20th	Night	19% 7% 3 7% 4 4 3 4 5% 7% 38%	2470
	21st to end	Night	15% 9% 2 5% 4 4 4 3 5% 6% 42%	2508
December	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 5% 8% 32%	2660
	11th to 20th	Night	18% 11% 4 10% 6% 5% 5% 3 5% 6% 26%	3276
	21st to end	Night	16% 9% 4 9% 5% 5% 4 4 5% 9% 30%	4862

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	56% 17% 17% 10% 1	2539
	11th to 20th	Day	62% 13% 15% 9% 1	2540
	21st to end	Day	62% 14% 15% 8% 1	2794
February	1st to 10th	Day	51% 11% 19% 15% 3 1	1671
	11th to 20th	Day	46% 12% 17% 19% 6%	1860
	21st to end	Day	47% 10% 17% 18% 8% 1	1570
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% 32% 10%	2069
October	1st to 10th	Day	29% 6% 12% 24% 24% 4	1980
	11th to 20th	Day	27% 6% 12% 32% 21% 3	1737
	21st to end	Day	33% 9% 16% 27% 14% 1	1782
November	1st to 10th	Day	40% 9% 17% 23% 10%	1674
	11th to 20th	Day	45% 9% 20% 20% 5%	1710
	21st to end	Day	46% 12% 21% 17% 5%	1668
December	1st to 10th	Day	51% 13% 20% 13% 5%	1520
	11th to 20th	Day	58% 16% 17% 8% 2	1928
	21st to end	Day	50% 13% 19% 14% 4	2794
January	1st to 10th	Night	57% 14% 19% 8% 1	4406
	11th to 20th	Night	65% 11% 12% 10% 2	4420
	21st to end	Night	56% 14% 16% 12% 2	4862
February	1st to 10th	Night	50% 9% 18% 19% 3 1	2504
	11th to 20th	Night	44% 10% 17% 20% 8% 1	2219
	21st to end	Night	47% 9% 15% 18% 9% 1	1884
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	21% 3 6% 20% 32% 18%	2079
October	1st to 10th	Night	26% 6% 9% 25% 25% 10%	1980
	11th to 20th	Night	27% 5% 11% 27% 24% 5%	2221
	21st to end	Night	32% 6% 14% 24% 21% 3	2574
November	1st to 10th	Night	39% 7% 13% 22% 17% 1	2405
	11th to 20th	Night	44% 7% 14% 26% 9%	2470
	21st to end	Night	41% 8% 18% 24% 9% 1	2508
December	1st to 10th	Night	50% 10% 19% 15% 7%	2660
	11th to 20th	Night	55% 11% 17% 14% 2	3276
	21st to end	Night	47% 13% 21% 15% 4	4862

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	24% 12% 19% 23% 18% 4	180
	11th to 20th	Day	17% 13% 18% 32% 15% 6%	180
	21st to end	Day	16% 8% 20% 35% 16% 6%	198
February	1st to 10th	Day	20% 10% 30% 21% 16% 4	283
	11th to 20th	Day	18% 13% 29% 25% 14% 2	455
	21st to end	Day	17% 15% 26% 26% 14% 2	382
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%	483
October	1st to 10th	Day	8% 9% 18% 23% 30% 12%	450
	11th to 20th	Day	11% 5% 23% 26% 26% 9%	352
	21st to end	Day	12% 10% 24% 26% 23% 5%	297
November	1st to 10th	Day	16% 9% 23% 29% 21% 3	270
	11th to 20th	Day	14% 9% 19% 32% 20% 6%	270
	21st to end	Day	12% 5% 20% 33% 26% 4	250
December	1st to 10th	Day	23% 5% 19% 27% 17% 9%	180
	11th to 20th	Day	21% 10% 26% 28% 12% 4	180
	21st to end	Day	18% 10% 26% 27% 15% 4	198
January	1st to 10th	Night	21% 8% 21% 28% 20% 3	760
	11th to 20th	Night	20% 6% 19% 29% 23% 3	760
	21st to end	Night	19% 4 17% 33% 24% 3	836
February	1st to 10th	Night	21% 6% 21% 33% 16% 2	760
	11th to 20th	Night	17% 4 24% 36% 18% 2	744
	21st to end	Night	16% 8% 25% 35% 14% 2	628
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 14% 37% 29% 9%	756
October	1st to 10th	Night	8% 3 17% 40% 27% 5%	720
	11th to 20th	Night	9% 4 17% 38% 27% 6%	720
	21st to end	Night	12% 4 19% 38% 23% 4	792
November	1st to 10th	Night	16% 5% 18% 35% 23% 2	740
	11th to 20th	Night	19% 6% 19% 37% 17% 3	760
	21st to end	Night	18% 3 17% 36% 21% 5%	760
December	1st to 10th	Night	21% 5% 17% 37% 18% 3	760
	11th to 20th	Night	23% 6% 16% 37% 15% 3	760
	21st to end	Night	26% 7% 22% 32% 11% 2	836

Page generated at 2024-09-26 07:52:25. Version ac07

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