Chechaquo Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chechaquo Ranch clear sky chart from 2005-11-06 to 2025-06-10.

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	6% 9% 3 7% 5% 5% 5% 4 6% 7% 43%	124230
	Night	6% 10% 3 7% 4 4 5% 4 6% 8% 43%	122707
Transparency	Day	36% 10% 16% 21% 14% 4	123995
	Night	36% 10% 17% 22% 12% 2	122585
Seeing	Day	14% 23% 34% 21% 7% 1	15412
	Night	12% 14% 38% 26% 9% 1	23964

By Month

Percentage Cloud Cover NW (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	7% 16% 7% 12% 6% 5% 5% 4 7% 7% 25%	3639
	11th to 20th	Day	5% 11% 3 8% 3 3 4 3 6% 7% 47%	3616
	21st to end	Day	9% 18% 4 7% 3 3 4 2 5% 7% 37%	4004
February	1st to 10th	Day	4 13% 5% 9% 6% 6% 6% 5% 8% 9% 28%	1720
	11th to 20th	Day	4 12% 5% 10% 5% 4 6% 5% 7% 10% 34%	1755
	21st to end	Day	3 12% 5% 13% 8% 6% 6% 4 8% 9% 25%	1617
March	1st to 10th	Day	3 11% 5% 8% 4 5% 6% 5% 7% 8% 37%	4518
	11th to 20th	Day	3 12% 4 8% 5% 5% 6% 5% 7% 7% 38%	4864
	21st to end	Day	7% 15% 5% 8% 5% 6% 6% 5% 7% 8% 28%	5834
April	1st to 10th	Day	7% 13% 3 8% 8% 7% 6% 5% 7% 9% 26%	2400
	11th to 20th	Day	5% 10% 4 9% 6% 6% 6% 5% 7% 9% 32%	2372
	21st to end	Day	5% 11% 3 7% 5% 7% 6% 6% 7% 9% 34%	2701
May	1st to 10th	Day	5% 6% 2 5% 4 5% 4 4 6% 8% 50%	6320
	11th to 20th	Day	6% 9% 3 7% 5% 5% 6% 5% 7% 9% 38%	6277
	21st to end	Day	9% 9% 3 7% 5% 5% 5% 4 6% 8% 40%	6903
June	1st to 10th	Day	11% 8% 2 7% 5% 6% 6% 5% 6% 7% 37%	2789
	11th to 20th	Day	8% 8% 3 8% 6% 6% 6% 5% 8% 8% 34%	2792
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 7% 7% 47%	2850
July	1st to 10th	Day	2 3 1 3 3 2 3 3 4 5% 71%	4677
	11th to 20th	Day	3 2 1 3 3 2 3 3 4 5% 72%	4420
	21st to end	Day	2 3 1 3 3 3 3 3 5% 6% 68%	4790
August	1st to 10th	Day	2 2 1 4 3 4 4 3 6% 7% 64%	4401
	11th to 20th	Day	3 3 2 5% 5% 5% 5% 4 7% 7% 55%	4179
	21st to end	Day	6% 5% 2 6% 4 4 4 4 6% 6% 53%	4242
September	1st to 10th	Day	5% 4 2 4 3 3 3 3 5% 8% 60%	2280
	11th to 20th	Day	6% 6% 2 6% 5% 5% 5% 4 5% 7% 48%	2280
	21st to end	Day	9% 8% 1 5% 4 4 4 3 6% 6% 49%	2042
October	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 8% 52%	3180
	11th to 20th	Day	9% 6% 3 8% 5% 5% 6% 5% 6% 7% 40%	3144
	21st to end	Day	9% 10% 2 6% 5% 4 6% 6% 6% 7% 40%	3101
November	1st to 10th	Day	10% 16% 3 7% 5% 4 5% 5% 7% 9% 28%	1674
	11th to 20th	Day	8% 17% 5% 8% 6% 5% 4 4 6% 7% 30%	1600
	21st to end	Day	5% 14% 4 11% 7% 7% 5% 3 5% 9% 30%	1600
December	1st to 10th	Day	4 9% 4 8% 6% 5% 5% 5% 7% 8% 41%	2620
	11th to 20th	Day	5% 18% 7% 10% 6% 6% 5% 3 6% 7% 27%	3025
	21st to end	Day	6% 17% 7% 13% 6% 6% 6% 4 6% 6% 23%	4004
January	1st to 10th	Night	6% 17% 7% 14% 7% 6% 5% 4 5% 7% 25%	6306
	11th to 20th	Night	4 12% 4 7% 4 3 3 4 6% 9% 44%	6282
	21st to end	Night	8% 19% 4 7% 4 4 4 3 5% 6% 37%	6952
February	1st to 10th	Night	7% 13% 4 9% 6% 6% 5% 4 7% 8% 29%	2675
	11th to 20th	Night	4 11% 3 7% 5% 4 5% 5% 7% 9% 39%	2532
	21st to end	Night	3 14% 5% 10% 5% 6% 6% 6% 9% 9% 27%	2012
March	1st to 10th	Night	2 10% 5% 8% 5% 5% 5% 4 6% 10% 39%	5376
	11th to 20th	Night	3 13% 4 7% 4 4 4 4 5% 7% 45%	5131
	21st to end	Night	7% 13% 4 10% 6% 7% 6% 4 6% 7% 30%	5140
April	1st to 10th	Night	5% 10% 3 7% 6% 5% 6% 5% 8% 10% 35%	2000
	11th to 20th	Night	4 8% 4 6% 6% 4 5% 5% 7% 8% 43%	1979
	21st to end	Night	5% 7% 2 5% 4 5% 6% 4 6% 10% 45%	1693
May	1st to 10th	Night	6% 4 1 4 3 3 4 3 6% 8% 57%	3640
	11th to 20th	Night	6% 7% 2 5% 5% 4 5% 4 6% 9% 47%	3616
	21st to end	Night	6% 5% 2 4 4 4 5% 4 8% 11% 47%	3972
June	1st to 10th	Night	7% 7% 2 5% 5% 6% 5% 5% 8% 9% 42%	1595
	11th to 20th	Night	5% 4 2 4 5% 5% 6% 5% 8% 10% 47%	1382
	21st to end	Night	4 3 1 3 4 4 5% 4 6% 9% 57%	1330
July	1st to 10th	Night	2 2 2 1 2 3 2 4 6% 77%	2279
	11th to 20th	Night	2 1 2 2 2 3 2 3 5% 78%	2540
	21st to end	Night	2 1 2 2 2 2 3 4 6% 75%	2762
August	1st to 10th	Night	1 2 1 3 4 3 4 3 4 6% 69%	2529
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 9% 67%	2650
	21st to end	Night	5% 3 1 3 3 4 5% 3 6% 7% 61%	3434
September	1st to 10th	Night	3 2 1 4 3 3 4 3 5% 6% 65%	1900
	11th to 20th	Night	6% 4 1 4 3 4 4 4 6% 7% 56%	1900
	21st to end	Night	7% 5% 2 5% 4 3 4 4 7% 10% 49%	2134
October	1st to 10th	Night	5% 4 1 4 3 3 4 4 6% 10% 55%	3800
	11th to 20th	Night	12% 7% 2 5% 5% 4 4 4 6% 8% 43%	3793
	21st to end	Night	10% 9% 2 5% 4 5% 4 4 6% 8% 43%	4457
November	1st to 10th	Night	12% 16% 3 7% 4 4 5% 4 7% 8% 30%	2624
	11th to 20th	Night	8% 15% 3 8% 6% 5% 6% 5% 6% 8% 31%	2800
	21st to end	Night	6% 16% 5% 9% 6% 5% 5% 5% 7% 8% 29%	2800
December	1st to 10th	Night	5% 9% 3 6% 4 4 4 3 6% 8% 48%	4560
	11th to 20th	Night	6% 17% 7% 11% 7% 6% 6% 5% 6% 7% 23%	5180
	21st to end	Night	8% 21% 6% 12% 5% 5% 5% 4 5% 6% 23%	6952

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	51% 11% 14% 19% 5% 1	3639
	11th to 20th	Day	37% 7% 18% 24% 12% 2	3640
	21st to end	Day	46% 8% 14% 18% 14%	4004
February	1st to 10th	Day	48% 14% 17% 13% 6% 2	1720
	11th to 20th	Day	43% 14% 18% 16% 8% 1	1764
	21st to end	Day	50% 15% 14% 15% 7%	1617
March	1st to 10th	Day	39% 14% 14% 13% 17% 4	4518
	11th to 20th	Day	37% 11% 16% 29% 6% 1	4864
	21st to end	Day	48% 14% 17% 13% 7% 1	5834
April	1st to 10th	Day	49% 14% 18% 14% 5%	2400
	11th to 20th	Day	44% 14% 15% 16% 9% 2	2372
	21st to end	Day	41% 14% 17% 19% 8% 1	2701
May	1st to 10th	Day	28% 10% 13% 30% 17% 2	6320
	11th to 20th	Day	35% 10% 24% 23% 8%	6280
	21st to end	Day	38% 11% 21% 24% 6% 1	6904
June	1st to 10th	Day	43% 10% 14% 18% 12% 3	2789
	11th to 20th	Day	41% 13% 19% 17% 9% 1	2792
	21st to end	Day	31% 11% 17% 24% 15% 2	2850
July	1st to 10th	Day	16% 6% 9% 16% 29% 24%	4604
	11th to 20th	Day	15% 4 7% 14% 27% 32%	4345
	21st to end	Day	15% 4 11% 26% 29% 14%	4639
August	1st to 10th	Day	16% 7% 10% 25% 32% 10%	4384
	11th to 20th	Day	20% 9% 19% 31% 16% 3	4221
	21st to end	Day	28% 8% 16% 24% 20% 4	4241
September	1st to 10th	Day	22% 7% 14% 29% 22% 5%	2280
	11th to 20th	Day	32% 9% 12% 21% 21% 5%	2280
	21st to end	Day	33% 8% 18% 21% 16% 3	2042
October	1st to 10th	Day	26% 8% 19% 32% 13% 1	3180
	11th to 20th	Day	38% 11% 13% 21% 16% 1	3144
	21st to end	Day	37% 12% 14% 22% 15% 1	3101
November	1st to 10th	Day	48% 13% 15% 15% 8% 1	1674
	11th to 20th	Day	52% 12% 14% 13% 7% 1	1600
	21st to end	Day	50% 11% 16% 13% 7% 3	1600
December	1st to 10th	Day	36% 12% 18% 24% 10%	2620
	11th to 20th	Day	54% 10% 17% 12% 7%	3028
	21st to end	Day	57% 11% 14% 12% 6%	4004
January	1st to 10th	Night	58% 10% 12% 16% 4 1	6306
	11th to 20th	Night	35% 9% 18% 22% 14% 2	6320
	21st to end	Night	49% 7% 15% 17% 11% 1	6952
February	1st to 10th	Night	48% 13% 16% 14% 7% 2	2675
	11th to 20th	Night	40% 13% 18% 19% 9% 2	2534
	21st to end	Night	46% 16% 15% 15% 8%	2012
March	1st to 10th	Night	35% 12% 16% 20% 15% 3	5376
	11th to 20th	Night	34% 10% 17% 27% 12%	5132
	21st to end	Night	50% 14% 16% 14% 5%	5140
April	1st to 10th	Night	38% 14% 22% 20% 6%	2000
	11th to 20th	Night	34% 12% 19% 21% 12% 1	1979
	21st to end	Night	32% 12% 20% 26% 10%	1693
May	1st to 10th	Night	22% 8% 16% 33% 21%	3637
	11th to 20th	Night	27% 10% 25% 29% 7% 1	3616
	21st to end	Night	24% 15% 28% 28% 4 1	3972
June	1st to 10th	Night	34% 11% 18% 22% 14% 2	1595
	11th to 20th	Night	28% 12% 22% 24% 12% 1	1382
	21st to end	Night	21% 11% 22% 30% 15% 2	1330
July	1st to 10th	Night	11% 5% 9% 24% 29% 21%	2243
	11th to 20th	Night	10% 4 9% 20% 32% 25%	2492
	21st to end	Night	10% 5% 13% 27% 29% 16%	2674
August	1st to 10th	Night	14% 7% 12% 27% 31% 9%	2521
	11th to 20th	Night	13% 7% 24% 38% 15% 3	2674
	21st to end	Night	19% 8% 18% 32% 20% 2	3434
September	1st to 10th	Night	18% 7% 15% 33% 23% 4	1900
	11th to 20th	Night	25% 8% 13% 29% 22% 3	1900
	21st to end	Night	29% 9% 19% 27% 14% 4	2134
October	1st to 10th	Night	25% 8% 19% 34% 14% 1	3800
	11th to 20th	Night	37% 9% 16% 25% 14%	3793
	21st to end	Night	37% 9% 17% 25% 12% 1	4457
November	1st to 10th	Night	47% 13% 17% 14% 8% 2	2624
	11th to 20th	Night	48% 13% 14% 16% 7% 2	2800
	21st to end	Night	49% 13% 15% 14% 7% 2	2800
December	1st to 10th	Night	34% 10% 19% 26% 10%	4560
	11th to 20th	Night	56% 11% 16% 12% 5%	5176
	21st to end	Night	57% 11% 13% 14% 5% 1	6952

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	21% 21% 28% 19% 9% 3	200
	11th to 20th	Day	16% 19% 32% 21% 10% 3	200
	21st to end	Day	19% 17% 36% 17% 10%	220
February	1st to 10th	Day	17% 28% 38% 12% 5%	320
	11th to 20th	Day	19% 23% 37% 15% 4 1	395
	21st to end	Day	13% 27% 39% 18% 3	399
March	1st to 10th	Day	17% 29% 33% 16% 4 1	500
	11th to 20th	Day	17% 28% 30% 18% 7% 1	500
	21st to end	Day	22% 28% 32% 16% 2	550
April	1st to 10th	Day	21% 28% 32% 14% 4 1	500
	11th to 20th	Day	17% 32% 28% 17% 5% 1	492
	21st to end	Day	14% 28% 32% 16% 8% 2	500
May	1st to 10th	Day	12% 24% 36% 22% 5% 1	503
	11th to 20th	Day	20% 19% 29% 22% 8% 2	528
	21st to end	Day	17% 23% 30% 21% 7% 1	573
June	1st to 10th	Day	16% 23% 36% 18% 7%	527
	11th to 20th	Day	17% 27% 35% 16% 4 1	622
	21st to end	Day	10% 24% 37% 21% 7% 1	680
July	1st to 10th	Day	7% 23% 36% 27% 6%	635
	11th to 20th	Day	8% 17% 36% 29% 8% 2	484
	21st to end	Day	5% 17% 37% 30% 10% 2	531
August	1st to 10th	Day	7% 14% 38% 28% 11% 2	487
	11th to 20th	Day	4 14% 34% 34% 13% 2	477
	21st to end	Day	7% 22% 36% 25% 7% 1	539
September	1st to 10th	Day	9% 21% 39% 22% 9% 2	490
	11th to 20th	Day	12% 21% 34% 23% 9% 1	490
	21st to end	Day	16% 24% 33% 20% 6% 1	490
October	1st to 10th	Day	13% 23% 34% 21% 9% 1	490
	11th to 20th	Day	16% 27% 27% 20% 8% 2	485
	21st to end	Day	20% 22% 35% 15% 6% 2	330
November	1st to 10th	Day	17% 27% 34% 16% 5%	255
	11th to 20th	Day	18% 26% 30% 16% 9% 3	200
	21st to end	Day	21% 11% 36% 19% 11% 4	200
December	1st to 10th	Day	16% 14% 28% 21% 17% 5%	200
	11th to 20th	Day	12% 23% 37% 23% 6% 1	200
	21st to end	Day	10% 19% 39% 22% 10%	220
January	1st to 10th	Night	17% 18% 37% 21% 8% 1	800
	11th to 20th	Night	15% 15% 42% 19% 8% 1	800
	21st to end	Night	15% 13% 38% 26% 8%	880
February	1st to 10th	Night	14% 19% 42% 20% 5% 1	800
	11th to 20th	Night	11% 16% 41% 26% 7%	784
	21st to end	Night	15% 15% 38% 22% 9%	660
March	1st to 10th	Night	10% 16% 39% 27% 8% 1	800
	11th to 20th	Night	12% 15% 40% 23% 10%	800
	21st to end	Night	13% 15% 43% 24% 4 1	880
April	1st to 10th	Night	9% 16% 41% 26% 8% 1	800
	11th to 20th	Night	8% 20% 41% 23% 6% 2	791
	21st to end	Night	9% 17% 43% 23% 7% 1	493
May	1st to 10th	Night	9% 15% 40% 30% 6%	400
	11th to 20th	Night	11% 13% 32% 32% 11%	394
	21st to end	Night	12% 12% 38% 29% 9%	433
June	1st to 10th	Night	11% 14% 38% 28% 8%	399
	11th to 20th	Night	8% 18% 40% 29% 5%	380
	21st to end	Night	6% 10% 39% 34% 11%	380
July	1st to 10th	Night	4 10% 40% 36% 10%	370
	11th to 20th	Night	3 11% 42% 36% 8%	368
	21st to end	Night	1 10% 34% 42% 13%	416
August	1st to 10th	Night	4 7% 30% 41% 17%	378
	11th to 20th	Night	2 7% 33% 38% 18% 2	464
	21st to end	Night	5% 13% 33% 34% 14% 1	798
September	1st to 10th	Night	5% 11% 37% 29% 16% 2	760
	11th to 20th	Night	7% 12% 27% 30% 20% 5%	760
	21st to end	Night	11% 11% 32% 29% 14% 3	760
October	1st to 10th	Night	12% 12% 33% 31% 12% 1	760
	11th to 20th	Night	14% 14% 37% 23% 12% 1	760
	21st to end	Night	18% 18% 34% 22% 7% 2	836
November	1st to 10th	Night	20% 16% 40% 20% 4	780
	11th to 20th	Night	20% 15% 38% 18% 8% 1	800
	21st to end	Night	16% 14% 39% 20% 9% 3	800
December	1st to 10th	Night	14% 12% 39% 25% 9% 2	800
	11th to 20th	Night	16% 15% 43% 23% 3 1	800
	21st to end	Night	15% 17% 44% 21% 4	880

Page generated at 2025-06-07 07:28:12. Version ac07

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