Echo Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Echo Ridge Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	101461
	Night	12% 8% 3 7% 5% 4 5% 4 6% 8% 40%	98092
Transparency	Day	43% 7% 11% 20% 14% 4	105151
	Night	40% 7% 12% 22% 15% 5%	102541
Seeing	Day	23% 15% 24% 20% 13% 6%	15265
	Night	20% 13% 22% 26% 16% 2	25347

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% 8% 3 8% 5% 5% 5% 3 5% 7% 38%	2836
	11th to 20th	Day	11% 9% 4 9% 5% 6% 6% 4 5% 5% 36%	2840
	21st to end	Day	14% 12% 4 9% 5% 4 3 3 4 5% 36%	3124
February	1st to 10th	Day	11% 11% 3 9% 5% 5% 4 3 5% 5% 38%	1710
	11th to 20th	Day	14% 10% 4 8% 4 5% 5% 3 4 7% 36%	1796
	21st to end	Day	15% 9% 4 8% 6% 4 4 3 6% 6% 37%	1586
March	1st to 10th	Day	19% 8% 2 6% 4 4 4 4 5% 6% 37%	3435
	11th to 20th	Day	10% 7% 2 7% 4 4 4 3 5% 6% 47%	3480
	21st to end	Day	17% 8% 3 7% 4 4 4 3 5% 7% 39%	3815
April	1st to 10th	Day	10% 7% 3 6% 6% 5% 4 4 6% 8% 42%	2092
	11th to 20th	Day	14% 8% 2 7% 4 4 4 3 5% 7% 41%	2274
	21st to end	Day	15% 7% 2 7% 6% 5% 5% 4 5% 7% 37%	2470
May	1st to 10th	Day	12% 9% 4 10% 7% 7% 6% 4 7% 6% 28%	4082
	11th to 20th	Day	15% 9% 3 8% 6% 6% 7% 6% 6% 7% 27%	4081
	21st to end	Day	9% 5% 2 7% 6% 6% 7% 5% 9% 9% 34%	4476
June	1st to 10th	Day	11% 7% 2 6% 6% 6% 7% 6% 7% 9% 33%	2470
	11th to 20th	Day	8% 6% 3 7% 7% 6% 6% 5% 8% 10% 33%	2470
	21st to end	Day	9% 6% 2 8% 7% 6% 6% 7% 9% 10% 32%	2470
July	1st to 10th	Day	6% 5% 3 8% 7% 8% 7% 6% 8% 10% 32%	4120
	11th to 20th	Day	9% 6% 3 7% 6% 7% 7% 6% 8% 11% 29%	4120
	21st to end	Day	14% 10% 4 11% 8% 7% 7% 5% 7% 7% 18%	4466
August	1st to 10th	Day	13% 7% 3 8% 6% 6% 8% 6% 8% 11% 24%	4104
	11th to 20th	Day	9% 6% 2 9% 5% 6% 7% 7% 9% 11% 29%	4044
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 7% 11% 45%	4313
September	1st to 10th	Day	12% 7% 2 7% 5% 5% 6% 5% 6% 7% 38%	2128
	11th to 20th	Day	15% 8% 3 8% 4 5% 4 4 7% 9% 33%	2090
	21st to end	Day	21% 7% 3 6% 5% 4 4 4 5% 7% 33%	2090
October	1st to 10th	Day	16% 6% 2 5% 4 5% 3 3 4 6% 45%	1973
	11th to 20th	Day	13% 7% 3 6% 4 4 4 4 5% 6% 46%	1900
	21st to end	Day	12% 6% 2 7% 4 3 3 3 4 7% 48%	2090
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 4 7% 50%	1932
	11th to 20th	Day	10% 7% 2 6% 4 4 5% 4 5% 7% 46%	1800
	21st to end	Day	12% 7% 3 6% 6% 4 3 3 5% 7% 45%	1797
December	1st to 10th	Day	13% 11% 4 8% 6% 4 3 4 5% 8% 34%	1710
	11th to 20th	Day	13% 7% 3 7% 4 3 4 3 6% 7% 43%	2153
	21st to end	Day	15% 9% 4 7% 4 4 5% 5% 6% 7% 33%	3124
January	1st to 10th	Night	12% 11% 4 10% 6% 6% 5% 4 6% 6% 32%	4109
	11th to 20th	Night	10% 9% 3 9% 7% 4 4 3 5% 5% 41%	4120
	21st to end	Night	15% 12% 3 7% 4 5% 4 3 5% 5% 36%	4532
February	1st to 10th	Night	11% 8% 3 7% 5% 4 5% 4 6% 8% 39%	2470
	11th to 20th	Night	15% 9% 3 8% 5% 4 5% 4 6% 6% 35%	2266
	21st to end	Night	11% 8% 4 10% 4 5% 5% 4 6% 6% 36%	1866
March	1st to 10th	Night	18% 13% 4 8% 5% 4 4 3 5% 5% 31%	3418
	11th to 20th	Night	10% 6% 2 7% 4 4 5% 3 6% 7% 45%	3480
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 7% 43%	3817
April	1st to 10th	Night	9% 6% 2 8% 5% 5% 5% 5% 5% 8% 41%	2085
	11th to 20th	Night	11% 7% 2 5% 5% 4 4 4 6% 8% 43%	1870
	21st to end	Night	13% 7% 2 7% 3 4 5% 3 6% 8% 43%	1710
May	1st to 10th	Night	12% 9% 3 7% 6% 4 5% 5% 7% 9% 34%	2813
	11th to 20th	Night	15% 8% 2 8% 4 4 6% 4 5% 7% 36%	2812
	21st to end	Night	9% 6% 2 6% 4 4 5% 5% 8% 11% 41%	3079
June	1st to 10th	Night	8% 5% 2 5% 6% 5% 6% 5% 8% 11% 40%	1710
	11th to 20th	Night	8% 5% 2 5% 4 5% 5% 4 8% 11% 43%	1710
	21st to end	Night	6% 5% 1 7% 5% 4 5% 4 8% 12% 43%	1710
July	1st to 10th	Night	5% 5% 2 7% 5% 5% 7% 5% 9% 12% 39%	2840
	11th to 20th	Night	7% 5% 1 5% 4 4 5% 5% 9% 12% 43%	2840
	21st to end	Night	9% 9% 3 10% 7% 5% 7% 5% 8% 10% 28%	3087
August	1st to 10th	Night	13% 8% 2 7% 5% 5% 5% 4 8% 12% 31%	2825
	11th to 20th	Night	8% 5% 2 6% 5% 6% 6% 5% 8% 11% 38%	2785
	21st to end	Night	5% 5% 1 5% 3 4 4 5% 6% 10% 52%	3311
September	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 6% 7% 46%	2047
	11th to 20th	Night	17% 6% 2 6% 3 4 4 3 6% 8% 42%	2090
	21st to end	Night	17% 7% 2 7% 5% 4 5% 4 4 5% 40%	2090
October	1st to 10th	Night	15% 7% 1 5% 4 3 3 3 4 7% 47%	2205
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 4 6% 49%	2280
	21st to end	Night	11% 6% 2 5% 4 4 3 3 4 7% 51%	2508
November	1st to 10th	Night	11% 7% 2 5% 4 3 4 4 5% 5% 49%	2364
	11th to 20th	Night	10% 7% 2 5% 5% 4 4 3 5% 7% 47%	2600
	21st to end	Night	10% 8% 2 6% 4 4 5% 3 6% 6% 45%	2599
December	1st to 10th	Night	13% 9% 4 8% 5% 5% 5% 4 6% 7% 34%	2470
	11th to 20th	Night	13% 8% 3 10% 5% 4 4 4 5% 6% 38%	3042
	21st to end	Night	16% 9% 4 8% 5% 5% 5% 4 6% 8% 29%	4532

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	43% 3 8% 21% 21% 4	2837
	11th to 20th	Day	48% 4 6% 18% 22% 3	2840
	21st to end	Day	49% 4 6% 19% 19% 3	3124
February	1st to 10th	Day	47% 4 9% 19% 18% 3	1710
	11th to 20th	Day	49% 4 8% 18% 16% 4	1806
	21st to end	Day	48% 4 11% 15% 16% 6%	1586
March	1st to 10th	Day	47% 5% 8% 19% 15% 6%	3435
	11th to 20th	Day	37% 5% 8% 23% 18% 9%	3480
	21st to end	Day	45% 5% 8% 23% 15% 4	3815
April	1st to 10th	Day	40% 5% 11% 22% 17% 5%	2092
	11th to 20th	Day	42% 6% 10% 20% 18% 5%	2274
	21st to end	Day	46% 6% 11% 22% 13% 2	2470
May	1st to 10th	Day	52% 8% 12% 18% 9% 1	4120
	11th to 20th	Day	52% 9% 10% 21% 7% 1	4085
	21st to end	Day	38% 11% 14% 20% 13% 3	4489
June	1st to 10th	Day	45% 10% 14% 20% 10% 1	2470
	11th to 20th	Day	43% 10% 14% 18% 13% 2	2470
	21st to end	Day	42% 10% 14% 19% 13% 1	2470
July	1st to 10th	Day	43% 11% 17% 18% 7% 4	4055
	11th to 20th	Day	45% 10% 19% 20% 5% 1	4051
	21st to end	Day	61% 8% 11% 14% 5%	4324
August	1st to 10th	Day	51% 9% 18% 19% 4	4091
	11th to 20th	Day	42% 11% 17% 20% 7% 2	4083
	21st to end	Day	34% 7% 18% 29% 11% 2	4313
September	1st to 10th	Day	44% 7% 11% 18% 15% 5%	2128
	11th to 20th	Day	47% 7% 8% 20% 16% 1	2090
	21st to end	Day	50% 5% 9% 18% 15% 2	2090
October	1st to 10th	Day	31% 5% 7% 19% 28% 9%	3272
	11th to 20th	Day	27% 3 6% 27% 16% 21%	3140
	21st to end	Day	27% 3 8% 31% 16% 17%	3428
November	1st to 10th	Day	34% 4 9% 21% 25% 7%	1932
	11th to 20th	Day	36% 4 8% 20% 26% 6%	1800
	21st to end	Day	40% 4 8% 21% 23% 4	1797
December	1st to 10th	Day	49% 5% 10% 18% 15% 4	1710
	11th to 20th	Day	39% 4 9% 19% 24% 6%	2150
	21st to end	Day	47% 5% 8% 20% 17% 3	3124
January	1st to 10th	Night	47% 5% 10% 17% 15% 6%	4109
	11th to 20th	Night	45% 5% 6% 17% 20% 7%	4120
	21st to end	Night	49% 4 8% 16% 20% 4	4532
February	1st to 10th	Night	43% 4 10% 23% 17% 2	2470
	11th to 20th	Night	47% 4 9% 19% 16% 5%	2267
	21st to end	Night	46% 7% 9% 21% 12% 5%	1866
March	1st to 10th	Night	54% 7% 6% 16% 14% 3	3418
	11th to 20th	Night	37% 5% 7% 25% 17% 9%	3480
	21st to end	Night	38% 6% 11% 25% 15% 5%	3817
April	1st to 10th	Night	39% 6% 13% 22% 16% 4	2085
	11th to 20th	Night	36% 6% 12% 22% 19% 5%	1870
	21st to end	Night	39% 5% 15% 27% 13% 2	1710
May	1st to 10th	Night	44% 10% 15% 23% 8% 1	2840
	11th to 20th	Night	45% 10% 14% 26% 5%	2813
	21st to end	Night	32% 12% 18% 27% 9% 2	3087
June	1st to 10th	Night	36% 10% 19% 22% 12% 1	1710
	11th to 20th	Night	32% 11% 19% 25% 11% 1	1710
	21st to end	Night	33% 10% 18% 24% 13% 2	1710
July	1st to 10th	Night	36% 12% 20% 22% 8% 1	2795
	11th to 20th	Night	32% 11% 26% 24% 6% 2	2786
	21st to end	Night	50% 10% 16% 18% 5%	2988
August	1st to 10th	Night	44% 8% 23% 18% 6%	2814
	11th to 20th	Night	36% 11% 21% 23% 8% 1	2812
	21st to end	Night	27% 8% 17% 36% 10% 1	3311
September	1st to 10th	Night	37% 8% 15% 20% 17% 4	2047
	11th to 20th	Night	41% 6% 12% 23% 18% 1	2090
	21st to end	Night	45% 7% 9% 23% 14% 2	2090
October	1st to 10th	Night	31% 5% 9% 22% 24% 8%	3686
	11th to 20th	Night	26% 4 8% 22% 20% 19%	3779
	21st to end	Night	25% 2 8% 28% 20% 16%	4120
November	1st to 10th	Night	36% 5% 10% 19% 23% 6%	2364
	11th to 20th	Night	35% 4 8% 21% 24% 8%	2600
	21st to end	Night	38% 4 8% 24% 22% 5%	2599
December	1st to 10th	Night	47% 5% 9% 20% 15% 4	2470
	11th to 20th	Night	46% 5% 7% 16% 22% 4	3044
	21st to end	Night	50% 6% 10% 17% 16% 2	4532

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	40% 26% 22% 9% 3 1	270
	11th to 20th	Day	43% 23% 28% 6% 1	270
	21st to end	Day	40% 27% 24% 7% 2	297
February	1st to 10th	Day	37% 28% 24% 9% 3	270
	11th to 20th	Day	50% 24% 21% 5%	270
	21st to end	Day	43% 29% 22% 5%	241
March	1st to 10th	Day	32% 22% 25% 17% 5%	460
	11th to 20th	Day	36% 25% 24% 10% 4 1	460
	21st to end	Day	30% 27% 24% 14% 5% 1	506
April	1st to 10th	Day	30% 22% 25% 14% 7% 1	460
	11th to 20th	Day	27% 19% 26% 15% 10% 3	452
	21st to end	Day	25% 20% 27% 16% 10% 3	460
May	1st to 10th	Day	24% 18% 31% 14% 9% 4	463
	11th to 20th	Day	20% 14% 26% 22% 10% 7%	487
	21st to end	Day	19% 10% 24% 21% 16% 10%	529
June	1st to 10th	Day	13% 9% 31% 24% 15% 8%	490
	11th to 20th	Day	10% 10% 27% 26% 18% 9%	490
	21st to end	Day	15% 10% 31% 23% 14% 8%	490
July	1st to 10th	Day	11% 5% 22% 27% 23% 13%	485
	11th to 20th	Day	8% 5% 16% 35% 24% 12%	484
	21st to end	Day	12% 5% 20% 28% 21% 14%	532
August	1st to 10th	Day	16% 6% 24% 22% 19% 13%	486
	11th to 20th	Day	11% 5% 24% 22% 23% 15%	479
	21st to end	Day	12% 4 17% 26% 22% 19%	539
September	1st to 10th	Day	13% 6% 19% 25% 24% 13%	490
	11th to 20th	Day	17% 5% 17% 25% 23% 13%	490
	21st to end	Day	28% 9% 20% 23% 16% 4	490
October	1st to 10th	Day	20% 11% 20% 24% 21% 5%	490
	11th to 20th	Day	20% 16% 23% 23% 15% 3	490
	21st to end	Day	21% 15% 27% 23% 11% 3	539
November	1st to 10th	Day	20% 16% 27% 24% 10% 3	470
	11th to 20th	Day	28% 21% 29% 17% 4 1	300
	21st to end	Day	27% 23% 28% 16% 5% 1	299
December	1st to 10th	Day	34% 22% 32% 9% 3	270
	11th to 20th	Day	31% 22% 28% 15% 3 1	270
	21st to end	Day	33% 22% 28% 11% 5% 1	297
January	1st to 10th	Night	28% 24% 27% 17% 4 1	760
	11th to 20th	Night	29% 22% 26% 21% 2	760
	21st to end	Night	28% 23% 29% 19% 2	836
February	1st to 10th	Night	26% 20% 27% 25% 2	760
	11th to 20th	Night	35% 27% 24% 13% 1	743
	21st to end	Night	27% 25% 33% 13% 2	628
March	1st to 10th	Night	25% 20% 32% 20% 3	760
	11th to 20th	Night	29% 20% 26% 18% 6% 1	760
	21st to end	Night	23% 18% 32% 21% 7%	836
April	1st to 10th	Night	25% 18% 28% 23% 6%	760
	11th to 20th	Night	20% 19% 26% 25% 9% 1	746
	21st to end	Night	18% 13% 26% 34% 8% 1	570
May	1st to 10th	Night	18% 12% 26% 27% 14% 2	570
	11th to 20th	Night	16% 10% 21% 31% 18% 3	561
	21st to end	Night	17% 4 19% 27% 28% 6%	617
June	1st to 10th	Night	11% 4 19% 38% 26% 4	570
	11th to 20th	Night	9% 4 19% 31% 33% 4	570
	21st to end	Night	8% 4 18% 33% 33% 4	570
July	1st to 10th	Night	10% 2 14% 28% 40% 6%	555
	11th to 20th	Night	6% 1 10% 35% 42% 6%	552
	21st to end	Night	7% 2 11% 36% 37% 7%	624
August	1st to 10th	Night	13% 4 11% 29% 38% 5%	567
	11th to 20th	Night	14% 1 11% 33% 34% 7%	564
	21st to end	Night	11% 2 10% 29% 40% 9%	736
September	1st to 10th	Night	13% 4 14% 28% 36% 7%	760
	11th to 20th	Night	18% 3 15% 27% 31% 6%	760
	21st to end	Night	22% 6% 17% 29% 24% 2	760
October	1st to 10th	Night	17% 9% 19% 25% 24% 5%	760
	11th to 20th	Night	20% 11% 22% 28% 15% 3	760
	21st to end	Night	20% 13% 22% 31% 12% 2	836
November	1st to 10th	Night	18% 13% 23% 30% 14% 2	780
	11th to 20th	Night	24% 13% 24% 30% 9% 1	800
	21st to end	Night	25% 17% 23% 26% 9% 1	800
December	1st to 10th	Night	26% 22% 25% 22% 5%	760
	11th to 20th	Night	24% 18% 27% 25% 5% 1	760
	21st to end	Night	28% 18% 26% 24% 5%	836

Page generated at 2024-11-27 17:30:49. Version ac07

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