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 2024-02-05.

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	10% 7% 3 5% 5% 3 4 4 5% 7% 49%	78184
	Night	13% 8% 3 5% 5% 3 4 4 5% 7% 44%	80688
Transparency	Day	34% 8% 13% 19% 17% 10%	77888
	Night	39% 8% 13% 18% 14% 8%	80505
Seeing	Day	10% 9% 23% 29% 22% 7%	13396
	Night	13% 5% 19% 37% 23% 3	22869

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% 17% 5% 8% 6% 3 6% 6% 6% 6% 21%	2539
	11th to 20th	Day	18% 15% 6% 10% 8% 4 5% 5% 5% 5% 19%	2540
	21st to end	Day	20% 13% 5% 10% 8% 4 5% 5% 4 7% 19%	2794
February	1st to 10th	Day	14% 12% 4 7% 6% 3 5% 4 4 6% 35%	1616
	11th to 20th	Day	12% 12% 3 6% 5% 3 4 5% 6% 7% 37%	1750
	21st to end	Day	11% 11% 5% 6% 8% 3 5% 4 6% 7% 34%	1480
March	1st to 10th	Day	13% 10% 4 6% 6% 4 5% 5% 5% 8% 34%	1800
	11th to 20th	Day	13% 10% 4 4 5% 3 5% 5% 6% 7% 38%	1894
	21st to end	Day	13% 11% 4 5% 6% 3 5% 5% 5% 8% 35%	2286
April	1st to 10th	Day	11% 8% 3 5% 5% 3 4 5% 6% 7% 41%	2160
	11th to 20th	Day	8% 7% 3 5% 5% 3 5% 5% 5% 8% 45%	2164
	21st to end	Day	10% 6% 3 5% 5% 3 4 4 5% 7% 50%	2340
May	1st to 10th	Day	7% 4 2 3 4 3 4 5% 6% 7% 54%	2340
	11th to 20th	Day	10% 5% 2 4 5% 3 4 5% 5% 8% 49%	2384
	21st to end	Day	8% 6% 3 5% 5% 4 5% 5% 7% 10% 44%	2723
June	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	8% 3 2 3 3 2 3 5% 5% 8% 58%	2520
	21st to end	Day	3 3 1 2 2 2 3 3 4 5% 72%	2520
July	1st to 10th	Day	2 2 1 2 2 2 3 4 4 5% 74%	2520
	11th to 20th	Day	2 1 1 1 2 1 2 2 3 4 81%	2520
	21st to end	Day	3 3 1 2 2 1 3 3 3 4 74%	2741
August	1st to 10th	Day	4 2 1 4 3 2 3 3 4 5% 68%	2419
	11th to 20th	Day	2 1 1 2 2 2 2 3 4 5% 77%	2299
	21st to end	Day	3 2 1 3 2 2 2 2 3 5% 75%	2382
September	1st to 10th	Day	3 2 2 2 1 2 2 4 4 76%	2160
	11th to 20th	Day	5% 3 1 3 3 2 3 3 4 6% 68%	2000
	21st to end	Day	7% 4 2 3 3 2 3 2 4 6% 65%	1980
October	1st to 10th	Day	9% 5% 2 4 4 3 4 3 4 6% 56%	1980
	11th to 20th	Day	9% 3 2 4 4 2 3 4 5% 7% 55%	1737
	21st to end	Day	9% 6% 2 6% 5% 3 3 4 6% 8% 48%	1782
November	1st to 10th	Day	15% 7% 3 5% 5% 2 4 5% 5% 8% 41%	1674
	11th to 20th	Day	17% 7% 3 5% 6% 4 5% 4 6% 7% 36%	1710
	21st to end	Day	12% 7% 4 7% 7% 4 5% 5% 6% 10% 33%	1668
December	1st to 10th	Day	18% 9% 3 8% 6% 3 4 5% 5% 7% 31%	1520
	11th to 20th	Day	17% 13% 5% 11% 8% 4 5% 5% 6% 7% 20%	1928
	21st to end	Day	14% 11% 4 9% 8% 4 5% 5% 6% 8% 27%	2794
January	1st to 10th	Night	18% 15% 5% 10% 6% 4 5% 5% 5% 7% 22%	4406
	11th to 20th	Night	24% 17% 5% 8% 6% 4 4 3 3 5% 21%	4420
	21st to end	Night	20% 12% 4 10% 6% 3 4 4 4 7% 25%	4862
February	1st to 10th	Night	18% 10% 5% 7% 5% 4 4 5% 4 6% 33%	2434
	11th to 20th	Night	14% 10% 3 4 5% 4 4 5% 5% 7% 38%	2098
	21st to end	Night	16% 10% 4 6% 7% 3 5% 5% 5% 6% 32%	1776
March	1st to 10th	Night	15% 10% 4 6% 6% 4 5% 5% 4 6% 35%	2160
	11th to 20th	Night	14% 9% 3 6% 5% 3 5% 5% 6% 8% 38%	2066
	21st to end	Night	14% 9% 3 7% 6% 4 5% 5% 5% 6% 36%	2066
April	1st to 10th	Night	13% 7% 3 5% 4 3 5% 4 6% 7% 44%	1800
	11th to 20th	Night	12% 7% 2 5% 5% 3 5% 5% 5% 6% 45%	1743
	21st to end	Night	8% 5% 1 4 5% 3 4 4 6% 6% 53%	1620
May	1st to 10th	Night	8% 5% 1 4 3 2 3 5% 6% 7% 56%	1620
	11th to 20th	Night	10% 5% 2 5% 5% 3 5% 4 6% 8% 47%	1506
	21st to end	Night	8% 6% 3 5% 5% 4 5% 5% 8% 8% 43%	1552
June	1st to 10th	Night	11% 5% 2 5% 5% 3 4 4 6% 8% 46%	1440
	11th to 20th	Night	7% 4 1 4 4 2 3 4 5% 7% 58%	1440
	21st to end	Night	3 3 1 2 3 3 4 4 4 5% 68%	1440
July	1st to 10th	Night	2 2 1 2 3 2 3 3 6% 7% 69%	1440
	11th to 20th	Night	1 1 1 2 2 2 3 2 3 5% 79%	1440
	21st to end	Night	3 2 1 3 3 1 4 5% 5% 4 70%	1576
August	1st to 10th	Night	4 3 1 4 3 2 3 3 4 6% 66%	1517
	11th to 20th	Night	2 1 2 2 2 2 4 3 6% 76%	1602
	21st to end	Night	3 2 1 2 2 2 3 3 3 5% 74%	1970
September	1st to 10th	Night	4 2 1 2 3 1 2 2 3 4 77%	1800
	11th to 20th	Night	5% 3 2 3 3 2 3 3 4 7% 66%	1958
	21st to end	Night	7% 3 1 3 3 2 3 3 4 6% 66%	1980
October	1st to 10th	Night	7% 4 2 4 4 2 4 3 4 5% 60%	1980
	11th to 20th	Night	9% 4 2 3 3 3 4 4 5% 7% 57%	2221
	21st to end	Night	11% 5% 2 4 4 3 4 5% 6% 8% 48%	2574
November	1st to 10th	Night	16% 6% 3 5% 5% 2 4 4 4 7% 44%	2405
	11th to 20th	Night	19% 6% 3 6% 5% 3 4 5% 4 7% 39%	2470
	21st to end	Night	15% 8% 2 5% 5% 3 4 4 5% 7% 42%	2508
December	1st to 10th	Night	18% 10% 3 7% 5% 3 4 4 5% 9% 33%	2660
	11th to 20th	Night	18% 11% 4 9% 8% 4 6% 5% 5% 6% 26%	3276
	21st to end	Night	17% 9% 4 8% 6% 3 4 5% 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	1616
	11th to 20th	Day	45% 12% 17% 19% 6%	1760
	21st to end	Day	48% 9% 17% 18% 8% 1	1480
March	1st to 10th	Day	47% 10% 16% 20% 7% 1	1800
	11th to 20th	Day	42% 10% 16% 23% 9% 1	1894
	21st to end	Day	45% 9% 19% 17% 8% 1	2286
April	1st to 10th	Day	39% 8% 17% 20% 13% 3	2160
	11th to 20th	Day	34% 9% 13% 24% 16% 4	2167
	21st to end	Day	33% 7% 14% 27% 17% 2	2340
May	1st to 10th	Day	26% 7% 13% 27% 23% 4	2340
	11th to 20th	Day	31% 9% 12% 27% 17% 4	2387
	21st to end	Day	32% 9% 18% 22% 16% 3	2724
June	1st to 10th	Day	33% 9% 13% 24% 18% 2	2520
	11th to 20th	Day	23% 6% 10% 24% 27% 10%	2520
	21st to end	Day	14% 4 9% 18% 32% 23%	2520
July	1st to 10th	Day	14% 4 7% 15% 29% 33%	2451
	11th to 20th	Day	9% 2 4 9% 28% 47%	2445
	21st to end	Day	13% 3 4 9% 26% 44%	2589
August	1st to 10th	Day	19% 4 8% 15% 26% 28%	2402
	11th to 20th	Day	11% 3 5% 17% 33% 30%	2299
	21st to end	Day	13% 3 6% 17% 35% 26%	2382
September	1st to 10th	Day	13% 3 6% 17% 29% 32%	2160
	11th to 20th	Day	18% 5% 10% 22% 29% 16%	2000
	21st to end	Day	22% 3 8% 26% 31% 10%	1980
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	2434
	11th to 20th	Night	44% 10% 17% 21% 8% 1	2099
	21st to end	Night	48% 9% 15% 17% 9% 1	1776
March	1st to 10th	Night	48% 8% 13% 20% 10% 2	2160
	11th to 20th	Night	42% 8% 12% 25% 12%	2066
	21st to end	Night	45% 9% 16% 21% 9%	2066
April	1st to 10th	Night	37% 7% 13% 24% 16% 3	1800
	11th to 20th	Night	37% 8% 11% 23% 19% 3	1743
	21st to end	Night	30% 6% 13% 26% 23% 3	1620
May	1st to 10th	Night	25% 7% 11% 24% 30% 3	1620
	11th to 20th	Night	33% 7% 11% 24% 20% 5%	1506
	21st to end	Night	34% 10% 14% 23% 14% 4	1552
June	1st to 10th	Night	35% 8% 12% 23% 20% 2	1440
	11th to 20th	Night	25% 5% 10% 21% 30% 8%	1440
	21st to end	Night	17% 5% 7% 18% 30% 23%	1440
July	1st to 10th	Night	13% 3 6% 15% 26% 36%	1400
	11th to 20th	Night	10% 2 5% 10% 26% 47%	1392
	21st to end	Night	15% 3 5% 7% 22% 47%	1488
August	1st to 10th	Night	19% 4 8% 13% 23% 33%	1509
	11th to 20th	Night	10% 4 6% 13% 29% 39%	1602
	21st to end	Night	14% 4 5% 13% 29% 34%	1970
September	1st to 10th	Night	13% 3 5% 14% 28% 38%	1800
	11th to 20th	Night	20% 4 7% 18% 26% 26%	1958
	21st to end	Night	21% 3 6% 19% 32% 18%	1980
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	21% 9% 30% 21% 16% 4	264
	11th to 20th	Day	18% 12% 28% 25% 14% 3	415
	21st to end	Day	17% 16% 27% 26% 13% 2	346
March	1st to 10th	Day	15% 15% 32% 26% 11%	420
	11th to 20th	Day	13% 12% 31% 29% 15% 1	420
	21st to end	Day	13% 16% 31% 24% 13% 2	462
April	1st to 10th	Day	14% 19% 23% 22% 18% 5%	420
	11th to 20th	Day	11% 17% 31% 24% 14% 4	412
	21st to end	Day	10% 16% 32% 24% 14% 4	420
May	1st to 10th	Day	5% 15% 31% 27% 16% 5%	423
	11th to 20th	Day	16% 8% 23% 27% 19% 7%	448
	21st to end	Day	9% 10% 16% 31% 22% 12%	485
June	1st to 10th	Day	8% 9% 23% 27% 23% 10%	450
	11th to 20th	Day	8% 10% 28% 32% 17% 5%	450
	21st to end	Day	5% 5% 24% 33% 26% 7%	450
July	1st to 10th	Day	2 3 19% 39% 29% 7%	446
	11th to 20th	Day	1 3 23% 41% 27% 6%	444
	21st to end	Day	3 1 16% 38% 34% 8%	487
August	1st to 10th	Day	4 3 18% 36% 31% 7%	447
	11th to 20th	Day	3 1 16% 31% 38% 13%	437
	21st to end	Day	3 4 16% 33% 31% 13%	495
September	1st to 10th	Day	5% 4 12% 31% 34% 14%	450
	11th to 20th	Day	6% 5% 16% 30% 30% 13%	450
	21st to end	Day	6% 6% 20% 31% 32% 7%	450
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% 20% 34% 16% 2	738
	11th to 20th	Night	16% 4 23% 36% 18% 2	704
	21st to end	Night	17% 8% 26% 33% 14% 2	592
March	1st to 10th	Night	16% 8% 26% 33% 15% 2	720
	11th to 20th	Night	15% 8% 20% 38% 16% 2	720
	21st to end	Night	16% 9% 25% 36% 11% 2	792
April	1st to 10th	Night	14% 7% 21% 38% 18% 2	720
	11th to 20th	Night	12% 9% 27% 33% 17% 2	675
	21st to end	Night	10% 10% 23% 39% 16% 2	540
May	1st to 10th	Night	8% 8% 23% 39% 20% 2	540
	11th to 20th	Night	11% 6% 19% 34% 26% 4	444
	21st to end	Night	9% 6% 17% 33% 30% 5%	389
June	1st to 10th	Night	12% 5% 16% 38% 26% 3	360
	11th to 20th	Night	8% 6% 24% 34% 26% 2	360
	21st to end	Night	3 1 18% 44% 31% 2	360
July	1st to 10th	Night	2 1 14% 47% 33% 2	350
	11th to 20th	Night	1 1 16% 57% 26%	348
	21st to end	Night	3 1 13% 48% 35% 1	394
August	1st to 10th	Night	4 1 12% 49% 32% 2	443
	11th to 20th	Night	1 2 9% 49% 38% 2	534
	21st to end	Night	4 2 13% 45% 32% 5%	782
September	1st to 10th	Night	3 1 11% 43% 36% 5%	720
	11th to 20th	Night	6% 2 11% 36% 39% 6%	720
	21st to end	Night	8% 2 15% 37% 29% 9%	720
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 2024-02-02 03:20:33. Version ac07

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