Cahas Mountain Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cahas Mountain Overlook clear sky chart from 2005-11-06 to 2025-12-03.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	126741
	Night	13% 6% 2 5% 4 4 4 4 6% 7% 45%	123874
Transparency	Day	40% 6% 11% 22% 16% 4	130347
	Night	37% 5% 11% 24% 18% 5%	128337
Seeing	Day	22% 15% 24% 22% 13% 5%	16662
	Night	19% 13% 23% 27% 16% 2	26833

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	12% 6% 2 5% 4 3 3 3 4 6% 50%	4056
	11th to 20th	Day	10% 6% 2 5% 4 3 4 3 4 5% 53%	4060
	21st to end	Day	14% 8% 3 8% 4 4 3 3 3 4 46%	4466
February	1st to 10th	Day	12% 9% 2 7% 5% 6% 6% 4 5% 6% 40%	1800
	11th to 20th	Day	18% 7% 3 6% 5% 4 5% 3 5% 6% 39%	1808
	21st to end	Day	17% 7% 3 6% 4 5% 4 3 5% 7% 40%	1727
March	1st to 10th	Day	17% 6% 2 6% 4 5% 4 4 6% 7% 39%	4935
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 5% 7% 52%	4980
	21st to end	Day	15% 8% 2 7% 4 4 5% 3 5% 6% 41%	5465
April	1st to 10th	Day	10% 6% 2 5% 4 5% 5% 4 6% 7% 47%	2267
	11th to 20th	Day	14% 6% 2 5% 5% 4 4 3 5% 8% 44%	2374
	21st to end	Day	16% 6% 2 6% 5% 4 5% 3 6% 6% 40%	2534
May	1st to 10th	Day	12% 6% 2 7% 6% 6% 7% 5% 8% 9% 32%	5862
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 7% 8% 28%	5861
	21st to end	Day	15% 5% 2 6% 5% 5% 5% 4 7% 9% 39%	6433
June	1st to 10th	Day	11% 4 2 6% 5% 6% 6% 5% 8% 9% 39%	2600
	11th to 20th	Day	9% 5% 2 6% 6% 6% 6% 6% 7% 11% 37%	2600
	21st to end	Day	9% 4 2 7% 5% 6% 7% 6% 7% 9% 39%	2600
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 6% 5% 9% 10% 37%	5900
	11th to 20th	Day	7% 5% 2 7% 6% 8% 8% 7% 9% 12% 29%	5900
	21st to end	Day	10% 7% 3 8% 7% 7% 7% 6% 9% 10% 26%	6424
August	1st to 10th	Day	16% 6% 2 6% 6% 5% 6% 5% 9% 10% 28%	4234
	11th to 20th	Day	9% 4 2 7% 6% 6% 8% 6% 9% 10% 34%	4174
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 46%	4351
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 6% 7% 45%	2354
	11th to 20th	Day	18% 7% 3 5% 5% 4 4 3 6% 7% 38%	2200
	21st to end	Day	25% 7% 2 6% 4 4 4 4 6% 5% 33%	2200
October	1st to 10th	Day	17% 5% 2 4 3 3 3 3 3 6% 50%	2017
	11th to 20th	Day	14% 6% 2 3 3 3 4 3 5% 6% 53%	2000
	21st to end	Day	13% 5% 2 6% 3 4 3 3 4 6% 51%	2200
November	1st to 10th	Day	12% 5% 2 5% 4 2 4 3 5% 6% 53%	2057
	11th to 20th	Day	14% 5% 1 4 3 3 3 3 5% 7% 50%	1936
	21st to end	Day	12% 5% 2 6% 5% 3 4 3 5% 7% 48%	1890
December	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 3 5% 6% 49%	2637
	11th to 20th	Day	15% 7% 2 5% 3 3 4 4 5% 8% 43%	3373
	21st to end	Day	18% 8% 3 6% 4 4 5% 4 6% 8% 34%	4466
January	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 6% 55%	5889
	11th to 20th	Night	11% 6% 2 6% 4 3 3 3 4 6% 52%	5900
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 5% 49%	6490
February	1st to 10th	Night	13% 8% 3 6% 3 4 4 4 5% 7% 44%	2600
	11th to 20th	Night	19% 7% 2 5% 5% 4 4 3 5% 6% 40%	2475
	21st to end	Night	14% 6% 2 6% 5% 4 5% 3 5% 7% 43%	1901
March	1st to 10th	Night	18% 6% 2 5% 3 4 4 3 4 6% 45%	4918
	11th to 20th	Night	10% 3 1 4 3 3 4 4 6% 7% 55%	4980
	21st to end	Night	14% 6% 2 6% 5% 4 5% 4 5% 6% 43%	5467
April	1st to 10th	Night	13% 8% 2 5% 5% 4 3 3 6% 8% 44%	2131
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 7% 49%	1975
	21st to end	Night	14% 5% 2 4 4 3 4 4 6% 6% 47%	1882
May	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 6% 9% 40%	4033
	11th to 20th	Night	21% 8% 2 7% 4 4 4 3 5% 7% 34%	4032
	21st to end	Night	16% 5% 2 5% 3 4 4 4 7% 10% 41%	4421
June	1st to 10th	Night	10% 4 1 5% 5% 5% 5% 5% 8% 10% 42%	1800
	11th to 20th	Night	10% 5% 2 6% 4 4 3 4 7% 10% 46%	1800
	21st to end	Night	7% 4 2 4 5% 5% 5% 4 8% 12% 45%	1800
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 5% 8% 10% 41%	4058
	11th to 20th	Night	8% 6% 2 6% 5% 5% 6% 6% 9% 12% 34%	4057
	21st to end	Night	9% 7% 3 7% 5% 6% 7% 5% 8% 10% 35%	4427
August	1st to 10th	Night	18% 6% 2 7% 4 4 5% 4 7% 11% 32%	2915
	11th to 20th	Night	8% 4 2 5% 4 4 5% 5% 7% 10% 45%	2875
	21st to end	Night	8% 4 2 5% 4 4 4 3 5% 8% 54%	3512
September	1st to 10th	Night	12% 5% 3 6% 3 4 4 3 5% 7% 48%	2041
	11th to 20th	Night	17% 5% 2 5% 4 4 4 4 5% 6% 44%	2200
	21st to end	Night	22% 7% 2 6% 4 4 3 3 4 5% 38%	2200
October	1st to 10th	Night	17% 6% 1 5% 3 3 3 2 4 6% 48%	2381
	11th to 20th	Night	14% 5% 2 4 3 3 4 2 5% 5% 53%	2400
	21st to end	Night	14% 4 2 4 3 2 3 3 4 6% 55%	2640
November	1st to 10th	Night	14% 6% 2 5% 3 4 3 3 4 5% 52%	2461
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 4 5% 53%	2682
	21st to end	Night	12% 5% 2 5% 4 4 4 3 5% 7% 49%	2730
December	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	4489
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 7% 39%	4822
	21st to end	Night	18% 5% 1 5% 3 4 4 4 6% 8% 42%	6490

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	34% 3 7% 22% 29% 5%	4057
	11th to 20th	Day	34% 3 6% 20% 30% 7%	4060
	21st to end	Day	43% 3 5% 24% 21% 4	4466
February	1st to 10th	Day	45% 4 10% 21% 18% 3	1800
	11th to 20th	Day	46% 3 7% 22% 16% 5%	1817
	21st to end	Day	46% 3 10% 17% 18% 6%	1727
March	1st to 10th	Day	43% 4 7% 19% 17% 10%	4935
	11th to 20th	Day	32% 3 7% 24% 22% 11%	4980
	21st to end	Day	44% 4 8% 21% 18% 5%	5465
April	1st to 10th	Day	36% 5% 10% 23% 19% 7%	2267
	11th to 20th	Day	38% 4 11% 24% 18% 5%	2374
	21st to end	Day	44% 4 11% 25% 13% 3	2534
May	1st to 10th	Day	46% 7% 15% 22% 10% 1	5897
	11th to 20th	Day	53% 6% 11% 21% 9% 1	5865
	21st to end	Day	41% 6% 14% 20% 16% 3	6447
June	1st to 10th	Day	38% 8% 16% 25% 13% 1	2600
	11th to 20th	Day	39% 8% 17% 21% 14% 2	2600
	21st to end	Day	38% 9% 14% 25% 13% 2	2600
July	1st to 10th	Day	38% 11% 17% 21% 9% 3	5835
	11th to 20th	Day	41% 14% 20% 18% 6%	5831
	21st to end	Day	48% 12% 14% 19% 7%	6240
August	1st to 10th	Day	48% 8% 17% 22% 5%	4221
	11th to 20th	Day	39% 10% 16% 24% 9% 2	4213
	21st to end	Day	33% 8% 15% 30% 12% 2	4351
September	1st to 10th	Day	38% 6% 13% 21% 19% 4	2354
	11th to 20th	Day	44% 6% 8% 24% 17% 2	2200
	21st to end	Day	51% 5% 8% 18% 15% 2	2200
October	1st to 10th	Day	32% 4 8% 19% 29% 8%	3277
	11th to 20th	Day	25% 2 6% 25% 24% 17%	3240
	21st to end	Day	25% 3 10% 26% 21% 14%	3538
November	1st to 10th	Day	32% 4 9% 22% 27% 5%	2057
	11th to 20th	Day	34% 3 8% 25% 24% 6%	1936
	21st to end	Day	36% 4 8% 24% 25% 3	1890
December	1st to 10th	Day	35% 6% 9% 19% 25% 5%	2637
	11th to 20th	Day	40% 5% 11% 20% 19% 5%	3370
	21st to end	Day	47% 5% 9% 22% 15% 2	4466
January	1st to 10th	Night	30% 2 7% 23% 28% 9%	5889
	11th to 20th	Night	33% 3 8% 20% 28% 8%	5900
	21st to end	Night	39% 2 7% 26% 22% 5%	6490
February	1st to 10th	Night	40% 4 11% 23% 20% 2	2600
	11th to 20th	Night	45% 4 9% 20% 17% 6%	2477
	21st to end	Night	41% 4 10% 24% 15% 6%	1901
March	1st to 10th	Night	40% 4 6% 24% 18% 9%	4918
	11th to 20th	Night	28% 3 7% 23% 28% 11%	4980
	21st to end	Night	41% 4 10% 22% 18% 4	5467
April	1st to 10th	Night	39% 5% 11% 21% 20% 4	2131
	11th to 20th	Night	35% 4 11% 23% 22% 5%	1975
	21st to end	Night	37% 4 12% 28% 17% 2	1882
May	1st to 10th	Night	42% 7% 17% 22% 11% 1	4060
	11th to 20th	Night	50% 6% 11% 23% 9% 1	4033
	21st to end	Night	38% 7% 17% 26% 9% 3	4429
June	1st to 10th	Night	34% 10% 17% 25% 14% 1	1800
	11th to 20th	Night	34% 8% 18% 25% 14% 2	1800
	21st to end	Night	31% 9% 17% 26% 15% 3	1800
July	1st to 10th	Night	36% 11% 19% 22% 10% 2	4015
	11th to 20th	Night	39% 13% 23% 19% 5% 1	4006
	21st to end	Night	43% 10% 17% 21% 9%	4297
August	1st to 10th	Night	45% 7% 21% 21% 6%	2904
	11th to 20th	Night	33% 8% 19% 29% 11% 1	2902
	21st to end	Night	30% 5% 15% 37% 11% 2	3512
September	1st to 10th	Night	37% 6% 14% 21% 17% 6%	2041
	11th to 20th	Night	41% 5% 9% 24% 19% 2	2200
	21st to end	Night	49% 5% 8% 20% 15% 3	2200
October	1st to 10th	Night	36% 4 8% 20% 26% 7%	3901
	11th to 20th	Night	24% 2 8% 24% 26% 16%	3899
	21st to end	Night	20% 3 8% 31% 24% 15%	4252
November	1st to 10th	Night	36% 3 8% 22% 24% 6%	2461
	11th to 20th	Night	34% 3 7% 23% 25% 8%	2682
	21st to end	Night	34% 4 8% 26% 22% 5%	2730
December	1st to 10th	Night	30% 4 10% 29% 24% 2	4489
	11th to 20th	Night	44% 5% 11% 17% 17% 7%	4824
	21st to end	Night	40% 4 11% 25% 18% 2	6490

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	37% 26% 22% 11% 3	300
	11th to 20th	Day	38% 25% 27% 9%	300
	21st to end	Day	30% 32% 28% 8% 2	330
February	1st to 10th	Day	29% 26% 32% 11% 2	300
	11th to 20th	Day	46% 25% 23% 3 2	300
	21st to end	Day	34% 28% 25% 12% 2	326
March	1st to 10th	Day	27% 25% 28% 15% 4	500
	11th to 20th	Day	31% 24% 26% 14% 4 1	500
	21st to end	Day	28% 23% 28% 16% 4 1	550
April	1st to 10th	Day	25% 27% 24% 17% 7% 1	500
	11th to 20th	Day	23% 18% 28% 18% 10% 3	492
	21st to end	Day	23% 17% 29% 17% 11% 3	500
May	1st to 10th	Day	23% 20% 32% 15% 7% 3	503
	11th to 20th	Day	20% 15% 24% 23% 12% 6%	527
	21st to end	Day	21% 10% 22% 23% 18% 6%	573
June	1st to 10th	Day	15% 9% 28% 28% 15% 5%	530
	11th to 20th	Day	12% 8% 24% 31% 19% 7%	530
	21st to end	Day	11% 8% 27% 29% 17% 8%	530
July	1st to 10th	Day	11% 4 16% 32% 26% 10%	525
	11th to 20th	Day	6% 5% 17% 33% 29% 9%	524
	21st to end	Day	13% 6% 17% 31% 23% 10%	576
August	1st to 10th	Day	18% 6% 21% 24% 19% 12%	526
	11th to 20th	Day	12% 5% 18% 30% 21% 14%	519
	21st to end	Day	12% 4 16% 32% 19% 16%	583
September	1st to 10th	Day	15% 5% 18% 27% 23% 12%	530
	11th to 20th	Day	20% 4 16% 28% 23% 10%	530
	21st to end	Day	28% 11% 18% 26% 12% 4	530
October	1st to 10th	Day	22% 8% 20% 27% 18% 6%	530
	11th to 20th	Day	18% 16% 25% 24% 15% 3	530
	21st to end	Day	20% 16% 29% 23% 9% 2	583
November	1st to 10th	Day	20% 16% 30% 22% 10% 2	535
	11th to 20th	Day	26% 23% 28% 15% 7% 1	376
	21st to end	Day	30% 21% 28% 16% 4 1	330
December	1st to 10th	Day	27% 31% 26% 13% 2 1	214
	11th to 20th	Day	24% 25% 32% 14% 4	300
	21st to end	Day	29% 22% 30% 15% 5%	330
January	1st to 10th	Night	25% 24% 30% 18% 3	800
	11th to 20th	Night	25% 21% 30% 22% 3	800
	21st to end	Night	21% 23% 34% 20% 1	880
February	1st to 10th	Night	20% 23% 32% 23% 3	800
	11th to 20th	Night	30% 25% 29% 16% 1	783
	21st to end	Night	22% 23% 32% 19% 3	660
March	1st to 10th	Night	21% 20% 32% 23% 4	800
	11th to 20th	Night	25% 19% 30% 19% 6% 1	800
	21st to end	Night	21% 18% 32% 23% 5%	880
April	1st to 10th	Night	23% 20% 29% 22% 6%	800
	11th to 20th	Night	19% 16% 29% 25% 11% 1	791
	21st to end	Night	18% 12% 28% 31% 10%	682
May	1st to 10th	Night	19% 10% 29% 27% 14% 1	600
	11th to 20th	Night	22% 7% 21% 30% 18% 2	591
	21st to end	Night	18% 4 16% 30% 28% 4	650
June	1st to 10th	Night	11% 3 18% 40% 27% 2	600
	11th to 20th	Night	12% 5% 13% 34% 32% 5%	600
	21st to end	Night	10% 3 15% 37% 29% 5%	600
July	1st to 10th	Night	11% 4 9% 38% 32% 5%	585
	11th to 20th	Night	8% 10% 33% 42% 6%	582
	21st to end	Night	7% 3 11% 39% 35% 5%	657
August	1st to 10th	Night	18% 2 12% 30% 32% 5%	597
	11th to 20th	Night	14% 2 11% 31% 38% 4	594
	21st to end	Night	12% 3 11% 31% 35% 8%	832
September	1st to 10th	Night	14% 4 12% 32% 32% 7%	800
	11th to 20th	Night	19% 3 11% 30% 30% 7%	800
	21st to end	Night	26% 7% 17% 27% 21% 3	800
October	1st to 10th	Night	19% 8% 19% 23% 26% 6%	800
	11th to 20th	Night	20% 12% 23% 28% 16% 2	800
	21st to end	Night	19% 11% 24% 33% 12% 2	880
November	1st to 10th	Night	19% 12% 25% 29% 14% 2	820
	11th to 20th	Night	20% 17% 25% 27% 9% 1	840
	21st to end	Night	18% 19% 26% 25% 11%	840
December	1st to 10th	Night	23% 22% 27% 22% 6%	809
	11th to 20th	Night	19% 21% 29% 26% 6%	800
	21st to end	Night	23% 18% 25% 28% 5%	880

Page generated at 2025-11-30 01:00:54. Version ac07

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