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 2026-02-16.

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% 7% 3 8% 5% 5% 5% 4 6% 8% 36%	131206
	Night	11% 7% 3 7% 5% 4 5% 4 6% 8% 41%	129648
Transparency	Day	43% 7% 11% 20% 15% 4	134852
	Night	39% 7% 12% 22% 16% 5%	134072
Seeing	Day	24% 15% 24% 19% 12% 6%	16847
	Night	21% 13% 22% 26% 16% 2	26989

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% 7% 3 7% 4 4 4 3 5% 6% 43%	5258
	11th to 20th	Day	7% 8% 4 8% 4 5% 4 3 4 5% 47%	5280
	21st to end	Day	11% 10% 4 8% 5% 4 3 3 4 5% 43%	5780
February	1st to 10th	Day	10% 11% 3 9% 5% 5% 5% 3 5% 6% 38%	1890
	11th to 20th	Day	15% 10% 4 8% 4 5% 5% 3 4 6% 36%	1941
	21st to end	Day	14% 8% 4 8% 6% 4 4 3 5% 6% 38%	1667
March	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 4 5% 6% 37%	4935
	11th to 20th	Day	10% 7% 3 7% 4 3 3 3 5% 6% 49%	4980
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 7% 41%	5465
April	1st to 10th	Day	11% 7% 3 6% 6% 5% 4 4 6% 8% 41%	2202
	11th to 20th	Day	14% 7% 2 7% 4 4 4 3 5% 7% 41%	2395
	21st to end	Day	14% 7% 2 7% 6% 5% 6% 4 5% 7% 37%	2600
May	1st to 10th	Day	10% 8% 3 10% 7% 7% 7% 5% 8% 8% 26%	5862
	11th to 20th	Day	17% 8% 3 9% 6% 6% 7% 5% 7% 8% 25%	5861
	21st to end	Day	14% 6% 2 7% 6% 5% 7% 5% 8% 9% 31%	6433
June	1st to 10th	Day	11% 6% 2 6% 6% 6% 7% 5% 7% 9% 34%	2600
	11th to 20th	Day	8% 6% 2 7% 7% 6% 6% 6% 8% 11% 33%	2600
	21st to end	Day	8% 6% 2 7% 7% 5% 5% 7% 9% 10% 33%	2600
July	1st to 10th	Day	7% 6% 2 8% 6% 7% 7% 6% 8% 10% 34%	5900
	11th to 20th	Day	8% 6% 3 8% 7% 7% 8% 7% 9% 12% 26%	5900
	21st to end	Day	11% 9% 4 10% 7% 7% 8% 6% 8% 10% 20%	6424
August	1st to 10th	Day	14% 8% 3 8% 6% 6% 8% 6% 8% 11% 23%	4234
	11th to 20th	Day	9% 6% 2 9% 5% 6% 7% 7% 9% 11% 29%	4174
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 7% 11% 44%	4449
September	1st to 10th	Day	12% 7% 2 7% 5% 5% 6% 4 6% 7% 39%	2240
	11th to 20th	Day	14% 8% 3 8% 4 5% 4 4 7% 8% 34%	2200
	21st to end	Day	21% 7% 3 6% 6% 4 4 4 6% 7% 32%	2200
October	1st to 10th	Day	15% 6% 2 5% 4 5% 3 3 4 6% 46%	2077
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 5% 6% 47%	2000
	21st to end	Day	13% 7% 2 7% 4 3 3 3 4 7% 48%	2200
November	1st to 10th	Day	10% 7% 2 5% 4 3 4 3 4 7% 50%	2031
	11th to 20th	Day	10% 6% 1 6% 4 4 5% 4 5% 8% 46%	1890
	21st to end	Day	12% 7% 3 6% 5% 4 3 3 5% 7% 45%	1890
December	1st to 10th	Day	8% 9% 3 7% 5% 4 3 4 5% 6% 44%	3020
	11th to 20th	Day	14% 7% 2 8% 5% 5% 5% 4 5% 7% 38%	3463
	21st to end	Day	15% 9% 4 7% 4 4 5% 4 7% 8% 33%	4565
January	1st to 10th	Night	11% 9% 3 9% 5% 4 4 3 5% 6% 41%	7635
	11th to 20th	Night	8% 7% 3 8% 6% 4 4 3 4 5% 48%	7680
	21st to end	Night	12% 9% 3 6% 4 4 4 3 5% 6% 43%	8401
February	1st to 10th	Night	11% 8% 3 7% 5% 5% 5% 4 6% 7% 40%	2730
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 4 6% 6% 35%	2451
	21st to end	Night	11% 8% 4 10% 4 5% 5% 4 6% 6% 37%	1961
March	1st to 10th	Night	16% 9% 3 7% 5% 4 4 3 5% 5% 40%	4918
	11th to 20th	Night	11% 6% 2 6% 3 3 4 3 5% 7% 50%	4980
	21st to end	Night	11% 8% 3 7% 4 5% 4 4 6% 7% 41%	5467
April	1st to 10th	Night	10% 7% 3 8% 5% 5% 5% 4 5% 8% 41%	2195
	11th to 20th	Night	11% 7% 2 5% 5% 4 4 4 5% 8% 44%	1970
	21st to end	Night	12% 7% 2 7% 4 5% 5% 4 6% 8% 42%	1800
May	1st to 10th	Night	12% 8% 3 6% 5% 4 5% 4 7% 11% 34%	4033
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	4032
	21st to end	Night	16% 7% 2 7% 4 4 5% 5% 7% 9% 34%	4421
June	1st to 10th	Night	8% 5% 2 5% 5% 5% 6% 6% 8% 10% 40%	1800
	11th to 20th	Night	8% 5% 2 6% 4 5% 5% 4 8% 11% 42%	1800
	21st to end	Night	6% 5% 1 7% 5% 4 5% 4 8% 11% 44%	1800
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 7% 5% 8% 11% 40%	4058
	11th to 20th	Night	6% 6% 2 7% 5% 5% 7% 6% 9% 13% 35%	4057
	21st to end	Night	8% 9% 3 9% 6% 5% 7% 5% 8% 10% 29%	4427
August	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 4 8% 11% 31%	2915
	11th to 20th	Night	8% 5% 2 6% 5% 6% 6% 5% 9% 11% 38%	2875
	21st to end	Night	6% 5% 2 5% 3 4 4 4 6% 10% 52%	3416
September	1st to 10th	Night	10% 6% 2 5% 4 5% 5% 4 6% 7% 47%	2155
	11th to 20th	Night	16% 6% 2 6% 3 4 4 3 6% 8% 43%	2200
	21st to end	Night	17% 8% 2 7% 4 5% 5% 4 4 5% 39%	2200
October	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 4 7% 48%	2321
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 4 6% 49%	2400
	21st to end	Night	12% 6% 2 5% 4 3 3 3 4 7% 50%	2640
November	1st to 10th	Night	11% 8% 2 5% 4 3 4 4 5% 5% 49%	2485
	11th to 20th	Night	10% 7% 2 6% 5% 4 4 3 5% 7% 48%	2730
	21st to end	Night	10% 8% 2 6% 4 4 5% 3 6% 6% 45%	2730
December	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 4 5% 7% 45%	4380
	11th to 20th	Night	14% 11% 4 10% 5% 5% 4 4 5% 5% 32%	4952
	21st to end	Night	15% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	6633

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	40% 4 11% 17% 25% 3	5259
	11th to 20th	Day	37% 4 5% 16% 30% 9%	5280
	21st to end	Day	43% 4 6% 22% 19% 6%	5780
February	1st to 10th	Day	47% 4 9% 19% 18% 3	1890
	11th to 20th	Day	49% 4 8% 19% 16% 4	1951
	21st to end	Day	47% 4 11% 16% 17% 6%	1667
March	1st to 10th	Day	44% 5% 6% 16% 17% 11%	4935
	11th to 20th	Day	35% 5% 6% 20% 20% 13%	4980
	21st to end	Day	42% 5% 8% 24% 17% 4	5465
April	1st to 10th	Day	41% 5% 11% 22% 17% 4	2202
	11th to 20th	Day	41% 5% 10% 21% 17% 5%	2395
	21st to end	Day	46% 6% 11% 23% 12% 2	2600
May	1st to 10th	Day	50% 9% 13% 18% 9% 1	5897
	11th to 20th	Day	54% 8% 12% 19% 6% 1	5865
	21st to end	Day	43% 9% 12% 18% 13% 4	6447
June	1st to 10th	Day	44% 10% 14% 21% 11% 1	2600
	11th to 20th	Day	43% 11% 14% 18% 13% 1	2600
	21st to end	Day	41% 10% 14% 20% 13% 1	2600
July	1st to 10th	Day	42% 10% 16% 21% 8% 2	5835
	11th to 20th	Day	46% 13% 21% 16% 4 1	5831
	21st to end	Day	55% 10% 14% 15% 6%	6240
August	1st to 10th	Day	51% 9% 17% 19% 4	4221
	11th to 20th	Day	43% 10% 17% 20% 7% 2	4213
	21st to end	Day	34% 7% 18% 29% 11% 2	4449
September	1st to 10th	Day	43% 7% 11% 18% 16% 5%	2240
	11th to 20th	Day	46% 7% 8% 21% 16% 1	2200
	21st to end	Day	51% 5% 9% 18% 14% 2	2200
October	1st to 10th	Day	31% 5% 7% 20% 28% 9%	3376
	11th to 20th	Day	27% 3 6% 26% 17% 21%	3240
	21st to end	Day	27% 3 8% 30% 16% 16%	3538
November	1st to 10th	Day	33% 4 10% 20% 25% 6%	2031
	11th to 20th	Day	35% 4 9% 21% 26% 5%	1890
	21st to end	Day	40% 4 8% 22% 23% 4	1890
December	1st to 10th	Day	38% 6% 8% 20% 24% 4	3020
	11th to 20th	Day	45% 4 9% 17% 20% 4	3460
	21st to end	Day	46% 6% 11% 20% 14% 3	4565
January	1st to 10th	Night	41% 5% 11% 21% 15% 7%	7636
	11th to 20th	Night	38% 5% 5% 19% 25% 9%	7680
	21st to end	Night	41% 5% 8% 20% 22% 5%	8401
February	1st to 10th	Night	43% 4 11% 23% 17% 2	2730
	11th to 20th	Night	48% 4 9% 19% 16% 5%	2452
	21st to end	Night	45% 7% 9% 21% 13% 5%	1961
March	1st to 10th	Night	45% 6% 5% 19% 16% 8%	4918
	11th to 20th	Night	34% 4 6% 22% 22% 12%	4980
	21st to end	Night	42% 6% 11% 24% 14% 4	5467
April	1st to 10th	Night	40% 6% 13% 22% 15% 4	2195
	11th to 20th	Night	36% 6% 12% 22% 19% 5%	1970
	21st to end	Night	40% 5% 15% 26% 13% 1	1800
May	1st to 10th	Night	43% 11% 15% 21% 9%	4060
	11th to 20th	Night	48% 9% 16% 21% 5%	4033
	21st to end	Night	43% 10% 16% 23% 7% 1	4429
June	1st to 10th	Night	36% 10% 19% 22% 12% 1	1800
	11th to 20th	Night	33% 12% 19% 25% 11% 1	1800
	21st to end	Night	32% 10% 18% 25% 13% 2	1800
July	1st to 10th	Night	36% 12% 18% 26% 8% 1	4015
	11th to 20th	Night	38% 13% 26% 18% 4 1	4006
	21st to end	Night	47% 11% 18% 17% 7%	4297
August	1st to 10th	Night	45% 8% 23% 18% 5%	2904
	11th to 20th	Night	36% 11% 21% 23% 8% 1	2902
	21st to end	Night	28% 8% 17% 36% 10% 1	3416
September	1st to 10th	Night	36% 8% 16% 19% 17% 3	2155
	11th to 20th	Night	40% 6% 13% 23% 18% 1	2200
	21st to end	Night	46% 7% 9% 22% 14% 2	2200
October	1st to 10th	Night	31% 5% 9% 23% 25% 8%	3802
	11th to 20th	Night	26% 4 8% 22% 20% 19%	3899
	21st to end	Night	26% 2 8% 28% 21% 15%	4252
November	1st to 10th	Night	35% 6% 10% 20% 23% 6%	2485
	11th to 20th	Night	35% 4 9% 21% 24% 7%	2730
	21st to end	Night	38% 4 8% 24% 22% 5%	2730
December	1st to 10th	Night	36% 6% 9% 25% 22% 2	4380
	11th to 20th	Night	51% 5% 9% 16% 15% 4	4954
	21st to end	Night	45% 6% 13% 20% 14% 2	6633

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	44% 25% 21% 8% 2 1	330
	11th to 20th	Day	47% 21% 26% 5% 1	330
	21st to end	Day	42% 27% 23% 6% 2	363
February	1st to 10th	Day	37% 29% 24% 8% 2	330
	11th to 20th	Day	53% 23% 19% 4	315
	21st to end	Day	42% 29% 23% 5% 1	266
March	1st to 10th	Day	33% 22% 24% 16% 4	500
	11th to 20th	Day	35% 25% 25% 10% 4 1	500
	21st to end	Day	31% 27% 23% 14% 5% 1	550
April	1st to 10th	Day	31% 22% 25% 14% 7% 1	500
	11th to 20th	Day	27% 21% 26% 15% 9% 2	492
	21st to end	Day	24% 20% 28% 16% 10% 2	500
May	1st to 10th	Day	24% 18% 32% 14% 9% 4	503
	11th to 20th	Day	21% 15% 27% 21% 10% 6%	527
	21st to end	Day	22% 11% 23% 20% 15% 9%	573
June	1st to 10th	Day	13% 10% 32% 23% 15% 8%	530
	11th to 20th	Day	9% 9% 28% 27% 17% 9%	530
	21st to end	Day	14% 9% 29% 25% 16% 7%	530
July	1st to 10th	Day	10% 5% 22% 28% 23% 12%	525
	11th to 20th	Day	8% 5% 15% 35% 26% 11%	524
	21st to end	Day	11% 6% 20% 28% 22% 13%	576
August	1st to 10th	Day	18% 6% 23% 23% 18% 12%	526
	11th to 20th	Day	11% 6% 22% 24% 23% 15%	519
	21st to end	Day	12% 5% 19% 26% 21% 17%	583
September	1st to 10th	Day	13% 5% 20% 26% 23% 13%	530
	11th to 20th	Day	16% 5% 17% 26% 23% 13%	530
	21st to end	Day	27% 9% 21% 23% 16% 4	530
October	1st to 10th	Day	19% 11% 19% 24% 22% 5%	530
	11th to 20th	Day	19% 16% 25% 22% 14% 3	530
	21st to end	Day	24% 15% 26% 22% 10% 3	583
November	1st to 10th	Day	21% 17% 28% 22% 9% 3	509
	11th to 20th	Day	28% 23% 28% 16% 4 1	330
	21st to end	Day	30% 22% 28% 15% 4 1	330
December	1st to 10th	Day	36% 24% 31% 7% 3	330
	11th to 20th	Day	32% 22% 29% 13% 3 1	330
	21st to end	Day	33% 22% 28% 11% 4 1	363
January	1st to 10th	Night	30% 23% 26% 16% 4	840
	11th to 20th	Night	32% 22% 26% 19% 2	840
	21st to end	Night	28% 24% 29% 17% 2	924
February	1st to 10th	Night	27% 20% 28% 24% 2	840
	11th to 20th	Night	36% 27% 24% 12% 1	804
	21st to end	Night	26% 25% 34% 13% 2	660
March	1st to 10th	Night	26% 20% 31% 20% 3	800
	11th to 20th	Night	29% 20% 26% 18% 6% 1	800
	21st to end	Night	24% 18% 32% 20% 6%	880
April	1st to 10th	Night	26% 19% 28% 23% 5%	800
	11th to 20th	Night	20% 18% 27% 25% 8% 1	786
	21st to end	Night	18% 14% 26% 34% 8% 1	600
May	1st to 10th	Night	18% 12% 28% 27% 14% 2	600
	11th to 20th	Night	18% 10% 21% 31% 18% 3	591
	21st to end	Night	19% 4 19% 26% 26% 6%	650
June	1st to 10th	Night	10% 4 20% 37% 26% 3	600
	11th to 20th	Night	9% 5% 19% 32% 33% 4	600
	21st to end	Night	8% 3 18% 33% 35% 4	600
July	1st to 10th	Night	10% 2 13% 29% 41% 6%	585
	11th to 20th	Night	6% 2 9% 36% 42% 6%	582
	21st to end	Night	8% 3 11% 35% 37% 7%	657
August	1st to 10th	Night	15% 4 11% 28% 38% 4	597
	11th to 20th	Night	14% 2 11% 33% 34% 6%	594
	21st to end	Night	11% 3 11% 28% 38% 8%	775
September	1st to 10th	Night	13% 3 14% 29% 35% 7%	800
	11th to 20th	Night	17% 3 14% 27% 32% 6%	800
	21st to end	Night	22% 6% 17% 30% 23% 2	800
October	1st to 10th	Night	16% 9% 19% 26% 25% 5%	800
	11th to 20th	Night	21% 11% 22% 28% 15% 3	800
	21st to end	Night	22% 12% 21% 31% 11% 2	880
November	1st to 10th	Night	18% 13% 23% 30% 13% 2	820
	11th to 20th	Night	24% 14% 24% 28% 9% 1	840
	21st to end	Night	25% 17% 23% 26% 9% 1	840
December	1st to 10th	Night	26% 23% 27% 20% 4	840
	11th to 20th	Night	25% 18% 28% 24% 5%	840
	21st to end	Night	28% 18% 25% 24% 4	924

Page generated at 2026-02-13 01:42:18. Version ac07

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