Eagle Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Ridge Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	5% 3 1 3 3 2 3 3 4 7% 64%	83495
	Night	6% 4 2 3 3 2 3 3 4 6% 63%	85372
Transparency	Day	20% 4 8% 20% 26% 22%	83218
	Night	22% 4 8% 18% 25% 23%	85171
Seeing	Day	7% 8% 27% 36% 17% 6%	14797
	Night	6% 3 14% 32% 35% 9%	24693

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	6% 3 1 2 3 2 2 3 4 6% 69%	2571
	11th to 20th	Day	9% 4 2 4 4 2 3 4 5% 9% 54%	2860
	21st to end	Day	13% 5% 2 3 3 2 3 4 5% 8% 52%	3315
February	1st to 10th	Day	10% 4 2 3 2 2 2 4 3 5% 62%	1900
	11th to 20th	Day	8% 3 2 2 3 1 4 3 5% 8% 61%	1850
	21st to end	Day	8% 3 2 4 4 3 3 3 4 6% 59%	1570
March	1st to 10th	Day	9% 6% 2 5% 4 3 4 4 5% 6% 52%	3138
	11th to 20th	Day	5% 3 1 3 3 2 3 4 5% 8% 64%	3354
	21st to end	Day	7% 4 2 3 4 3 5% 5% 7% 9% 51%	4134
April	1st to 10th	Day	6% 4 2 3 3 2 3 4 4 8% 60%	2270
	11th to 20th	Day	4 3 2 3 3 2 3 3 5% 7% 66%	2129
	21st to end	Day	5% 4 1 3 2 2 3 2 4 8% 68%	2160
May	1st to 10th	Day	5% 5% 1 3 3 1 3 4 5% 8% 62%	2160
	11th to 20th	Day	3 4 2 3 2 2 4 4 4 9% 63%	2291
	21st to end	Day	4 4 1 3 3 2 2 3 4 9% 64%	2530
June	1st to 10th	Day	4 6% 2 4 3 2 3 4 5% 8% 60%	2466
	11th to 20th	Day	3 4 2 3 3 2 3 3 5% 8% 66%	2520
	21st to end	Day	2 3 1 3 2 2 3 2 4 6% 73%	2520
July	1st to 10th	Day	2 3 1 2 3 2 3 3 4 7% 71%	2520
	11th to 20th	Day	2 2 1 2 2 2 3 3 3 6% 75%	2464
	21st to end	Day	2 2 1 2 3 2 4 3 6% 7% 70%	2420
August	1st to 10th	Day	2 3 1 2 2 2 2 3 3 6% 74%	2149
	11th to 20th	Day	1 2 1 1 1 1 2 3 4 6% 79%	2122
	21st to end	Day	1 1 1 2 2 1 3 3 4 5% 78%	2376
September	1st to 10th	Day	2 2 1 2 2 2 2 2 3 6% 76%	2160
	11th to 20th	Day	2 3 1 1 3 1 2 2 3 5% 78%	2070
	21st to end	Day	2 2 1 2 2 1 3 3 4 5% 77%	1980
October	1st to 10th	Day	3 3 1 2 2 1 2 3 4 6% 72%	1972
	11th to 20th	Day	4 3 1 3 3 2 2 2 3 4 74%	1800
	21st to end	Day	3 2 1 3 2 2 3 3 4 4 73%	1980
November	1st to 10th	Day	2 2 2 3 3 2 3 4 4 6% 70%	1692
	11th to 20th	Day	4 3 1 3 3 2 3 4 4 6% 69%	1710
	21st to end	Day	4 3 2 3 4 2 3 3 5% 7% 64%	1710
December	1st to 10th	Day	8% 4 2 4 3 2 4 4 5% 7% 57%	1710
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 3 5% 7% 45%	2128
	21st to end	Day	11% 5% 3 5% 5% 4 4 5% 5% 7% 45%	2794
January	1st to 10th	Night	7% 5% 2 3 3 2 3 3 4 6% 64%	4371
	11th to 20th	Night	9% 7% 2 4 4 2 3 4 5% 7% 54%	4110
	21st to end	Night	13% 7% 2 3 3 2 2 3 4 7% 54%	4353
February	1st to 10th	Night	8% 5% 2 4 4 2 3 3 4 4 62%	2280
	11th to 20th	Night	8% 3 2 4 3 2 3 3 4 6% 62%	2218
	21st to end	Night	11% 4 2 4 4 2 4 3 4 5% 58%	1884
March	1st to 10th	Night	8% 8% 2 4 3 2 4 5% 6% 8% 50%	3736
	11th to 20th	Night	4 6% 2 3 3 2 3 3 4 6% 63%	3622
	21st to end	Night	9% 5% 2 3 3 2 3 3 4 6% 59%	3506
April	1st to 10th	Night	6% 4 2 4 3 2 3 3 5% 7% 61%	1900
	11th to 20th	Night	4 4 2 3 3 1 3 3 4 6% 67%	1779
	21st to end	Night	4 4 1 2 2 2 3 2 5% 7% 68%	1800
May	1st to 10th	Night	4 5% 1 3 3 2 3 3 6% 7% 63%	1800
	11th to 20th	Night	3 5% 2 4 3 2 3 3 5% 7% 64%	1600
	21st to end	Night	2 3 2 2 3 1 2 2 5% 5% 72%	1746
June	1st to 10th	Night	2 4 2 3 3 2 3 5% 5% 8% 63%	1488
	11th to 20th	Night	2 2 1 2 2 2 2 2 5% 8% 70%	1440
	21st to end	Night	1 4 1 2 2 2 2 2 3 7% 74%	1440
July	1st to 10th	Night	2 2 1 1 2 1 2 3 4 8% 74%	1440
	11th to 20th	Night	1 2 1 3 2 2 3 3 4 7% 73%	1491
	21st to end	Night	2 1 1 2 2 2 2 5% 5% 9% 68%	1894
August	1st to 10th	Night	2 2 1 1 3 2 3 3 5% 9% 70%	1790
	11th to 20th	Night	1 2 1 1 2 1 2 4 6% 7% 73%	1780
	21st to end	Night	1 1 1 2 2 1 3 2 4 7% 76%	1980
September	1st to 10th	Night	2 3 2 3 2 2 2 3 4 7% 72%	1800
	11th to 20th	Night	2 2 1 2 2 1 2 2 4 6% 76%	1890
	21st to end	Night	1 1 1 2 2 1 2 3 4 5% 77%	1980
October	1st to 10th	Night	3 2 1 3 2 2 3 3 4 4 72%	1985
	11th to 20th	Night	4 3 1 3 3 2 2 2 3 6% 71%	2160
	21st to end	Night	3 4 1 3 2 1 2 3 3 5% 74%	2376
November	1st to 10th	Night	3 3 1 2 2 2 2 3 5% 6% 70%	2385
	11th to 20th	Night	4 4 2 3 3 1 2 3 4 6% 69%	2470
	21st to end	Night	5% 3 2 3 4 3 4 3 4 7% 63%	2470
December	1st to 10th	Night	7% 5% 2 4 4 2 3 4 4 6% 59%	2470
	11th to 20th	Night	17% 6% 2 5% 4 2 3 3 5% 6% 46%	3076
	21st to end	Night	12% 7% 2 5% 5% 3 5% 4 4 6% 46%	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	18% 3 6% 26% 32% 15%	2571
	11th to 20th	Day	27% 6% 14% 19% 19% 15%	2860
	21st to end	Day	29% 4 6% 22% 24% 14%	3315
February	1st to 10th	Day	25% 3 5% 15% 24% 27%	1900
	11th to 20th	Day	22% 4 7% 18% 28% 21%	1860
	21st to end	Day	26% 4 8% 21% 23% 18%	1570
March	1st to 10th	Day	31% 5% 9% 24% 14% 16%	3138
	11th to 20th	Day	18% 5% 14% 34% 15% 16%	3354
	21st to end	Day	25% 7% 16% 28% 16% 7%	4134
April	1st to 10th	Day	22% 5% 13% 24% 24% 12%	2270
	11th to 20th	Day	18% 4 10% 25% 28% 16%	2132
	21st to end	Day	18% 4 9% 25% 32% 11%	2160
May	1st to 10th	Day	21% 5% 11% 24% 26% 14%	2160
	11th to 20th	Day	19% 5% 10% 25% 30% 11%	2294
	21st to end	Day	19% 6% 11% 30% 27% 7%	2530
June	1st to 10th	Day	25% 4 11% 19% 30% 11%	2466
	11th to 20th	Day	18% 5% 7% 15% 33% 23%	2520
	21st to end	Day	13% 4 4 10% 35% 33%	2520
July	1st to 10th	Day	13% 3 5% 11% 26% 41%	2451
	11th to 20th	Day	12% 4 6% 18% 32% 28%	2389
	21st to end	Day	14% 5% 8% 22% 31% 20%	2286
August	1st to 10th	Day	14% 3 4 12% 34% 33%	2135
	11th to 20th	Day	9% 3 3 14% 37% 34%	2122
	21st to end	Day	9% 4 4 11% 37% 35%	2376
September	1st to 10th	Day	11% 3 5% 10% 31% 40%	2160
	11th to 20th	Day	11% 3 5% 14% 30% 37%	2070
	21st to end	Day	12% 3 3 17% 35% 30%	1980
October	1st to 10th	Day	14% 3 7% 21% 23% 32%	1972
	11th to 20th	Day	17% 3 5% 14% 27% 35%	1800
	21st to end	Day	15% 4 5% 14% 24% 39%	1980
November	1st to 10th	Day	15% 5% 5% 18% 25% 33%	1692
	11th to 20th	Day	17% 4 7% 13% 21% 38%	1710
	21st to end	Day	20% 3 7% 15% 22% 33%	1710
December	1st to 10th	Day	25% 5% 6% 18% 22% 24%	1710
	11th to 20th	Day	39% 3 7% 16% 21% 14%	2127
	21st to end	Day	36% 6% 8% 24% 15% 12%	2794
January	1st to 10th	Night	23% 3 6% 14% 35% 19%	4371
	11th to 20th	Night	29% 5% 9% 23% 16% 17%	4110
	21st to end	Night	31% 3 6% 17% 25% 17%	4353
February	1st to 10th	Night	26% 3 5% 14% 24% 29%	2280
	11th to 20th	Night	25% 3 5% 17% 24% 25%	2219
	21st to end	Night	29% 4 6% 16% 23% 21%	1884
March	1st to 10th	Night	28% 6% 10% 22% 23% 11%	3736
	11th to 20th	Night	20% 6% 13% 27% 19% 15%	3622
	21st to end	Night	26% 6% 11% 28% 21% 8%	3506
April	1st to 10th	Night	23% 5% 12% 25% 22% 13%	1900
	11th to 20th	Night	18% 6% 8% 24% 27% 17%	1779
	21st to end	Night	17% 4 9% 24% 32% 13%	1800
May	1st to 10th	Night	22% 6% 10% 23% 26% 13%	1800
	11th to 20th	Night	21% 5% 8% 26% 27% 12%	1601
	21st to end	Night	16% 5% 12% 31% 29% 8%	1746
June	1st to 10th	Night	20% 5% 14% 21% 27% 12%	1488
	11th to 20th	Night	14% 5% 9% 18% 35% 20%	1440
	21st to end	Night	13% 6% 5% 12% 32% 33%	1440
July	1st to 10th	Night	11% 3 8% 13% 23% 44%	1400
	11th to 20th	Night	12% 5% 7% 19% 29% 28%	1443
	21st to end	Night	13% 5% 10% 24% 29% 20%	1789
August	1st to 10th	Night	12% 5% 5% 12% 32% 34%	1780
	11th to 20th	Night	10% 7% 6% 11% 36% 31%	1780
	21st to end	Night	10% 4 5% 11% 34% 36%	1980
September	1st to 10th	Night	14% 3 7% 9% 27% 41%	1800
	11th to 20th	Night	11% 4 5% 12% 31% 36%	1890
	21st to end	Night	10% 6% 3 12% 34% 35%	1980
October	1st to 10th	Night	14% 3 5% 19% 24% 34%	1985
	11th to 20th	Night	16% 4 6% 14% 24% 36%	2160
	21st to end	Night	16% 3 4 12% 21% 45%	2376
November	1st to 10th	Night	15% 3 6% 15% 25% 35%	2385
	11th to 20th	Night	17% 4 7% 12% 21% 39%	2470
	21st to end	Night	22% 3 5% 18% 19% 33%	2470
December	1st to 10th	Night	25% 4 5% 15% 20% 30%	2470
	11th to 20th	Night	38% 5% 7% 13% 21% 17%	3076
	21st to end	Night	38% 4 8% 21% 16% 12%	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	14% 11% 36% 28% 11%	199
	11th to 20th	Day	14% 13% 36% 28% 8% 1	370
	21st to end	Day	13% 16% 39% 24% 7% 1	456
February	1st to 10th	Day	13% 13% 39% 23% 8% 3	460
	11th to 20th	Day	10% 15% 36% 31% 5% 2	455
	21st to end	Day	12% 17% 38% 25% 8% 1	382
March	1st to 10th	Day	14% 18% 38% 22% 7% 1	460
	11th to 20th	Day	13% 14% 38% 24% 9% 2	460
	21st to end	Day	11% 17% 36% 29% 7% 1	506
April	1st to 10th	Day	9% 13% 34% 30% 12% 3	457
	11th to 20th	Day	7% 17% 34% 29% 9% 3	412
	21st to end	Day	4 13% 33% 31% 14% 5%	420
May	1st to 10th	Day	10% 11% 30% 35% 11% 4	423
	11th to 20th	Day	5% 10% 27% 38% 16% 5%	448
	21st to end	Day	7% 9% 32% 32% 15% 5%	485
June	1st to 10th	Day	7% 7% 23% 35% 22% 7%	450
	11th to 20th	Day	5% 3 19% 41% 25% 7%	450
	21st to end	Day	4 3 16% 42% 26% 10%	450
July	1st to 10th	Day	2 10% 47% 30% 11%	446
	11th to 20th	Day	2 5% 44% 32% 16%	444
	21st to end	Day	1 8% 45% 30% 16%	487
August	1st to 10th	Day	2 1 12% 49% 24% 12%	447
	11th to 20th	Day	2 1 8% 45% 29% 15%	437
	21st to end	Day	1 1 12% 48% 26% 12%	495
September	1st to 10th	Day	3 2 19% 46% 23% 8%	450
	11th to 20th	Day	3 3 25% 45% 18% 5%	450
	21st to end	Day	2 5% 23% 41% 24% 6%	450
October	1st to 10th	Day	2 6% 31% 41% 17% 3	450
	11th to 20th	Day	3 5% 34% 40% 15% 3	450
	21st to end	Day	4 7% 33% 34% 18% 4	495
November	1st to 10th	Day	6% 7% 25% 36% 19% 7%	288
	11th to 20th	Day	4 10% 35% 34% 14% 3	270
	21st to end	Day	9% 10% 35% 28% 16% 3	270
December	1st to 10th	Day	14% 8% 31% 32% 14% 2	270
	11th to 20th	Day	7% 12% 33% 34% 13% 2	257
	21st to end	Day	15% 12% 36% 26% 10% 1	198
January	1st to 10th	Night	11% 5% 24% 39% 16% 5%	760
	11th to 20th	Night	8% 5% 28% 39% 17% 2	760
	21st to end	Night	14% 8% 24% 36% 16% 3	836
February	1st to 10th	Night	11% 6% 22% 35% 21% 5%	760
	11th to 20th	Night	9% 3 23% 39% 20% 6%	744
	21st to end	Night	13% 5% 23% 37% 20% 3	628
March	1st to 10th	Night	9% 6% 21% 43% 19% 2	760
	11th to 20th	Night	8% 4 15% 40% 26% 6%	760
	21st to end	Night	9% 4 16% 42% 25% 3	836
April	1st to 10th	Night	7% 4 13% 42% 29% 5%	760
	11th to 20th	Night	4 5% 16% 39% 32% 5%	711
	21st to end	Night	5% 4 11% 39% 33% 9%	720
May	1st to 10th	Night	7% 3 11% 38% 35% 7%	720
	11th to 20th	Night	3 2 12% 32% 44% 7%	537
	21st to end	Night	2 2 14% 34% 42% 7%	584
June	1st to 10th	Night	2 1 7% 32% 47% 12%	408
	11th to 20th	Night	2 2 2 23% 60% 11%	360
	21st to end	Night	2 1 23% 61% 12%	360
July	1st to 10th	Night	3 1 6% 69% 21%	350
	11th to 20th	Night	2 2 5% 59% 32%	399
	21st to end	Night	2 1 2 9% 59% 28%	712
August	1st to 10th	Night	2 1 1 19% 57% 20%	716
	11th to 20th	Night	2 1 2 10% 60% 25%	712
	21st to end	Night	1 1 14% 59% 25%	792
September	1st to 10th	Night	3 1 3 20% 53% 20%	720
	11th to 20th	Night	2 1 3 26% 54% 15%	720
	21st to end	Night	2 5% 28% 51% 14%	720
October	1st to 10th	Night	3 1 8% 39% 44% 5%	720
	11th to 20th	Night	4 1 11% 38% 38% 8%	720
	21st to end	Night	4 2 17% 34% 32% 10%	792
November	1st to 10th	Night	4 4 15% 40% 28% 9%	740
	11th to 20th	Night	4 3 19% 39% 28% 6%	760
	21st to end	Night	6% 4 24% 38% 24% 4	760
December	1st to 10th	Night	9% 6% 26% 35% 19% 5%	760
	11th to 20th	Night	14% 6% 24% 36% 18% 3	760
	21st to end	Night	12% 6% 22% 39% 18% 4	836

Page generated at 2024-04-07 06:28:11. Version ac07

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