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 2026-10-14.

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% 8% 3 7% 4 4 5% 4 6% 8% 46%	154653
	Night	5% 9% 3 7% 4 4 4 4 6% 8% 46%	145832
Transparency	Day	32% 9% 15% 23% 15% 5%	154377
	Night	34% 10% 17% 24% 13% 3	145690
Seeing	Day	14% 23% 34% 21% 7% 1	17211
	Night	11% 14% 39% 26% 9% 1	25550

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	6% 14% 7% 14% 7% 5% 6% 4 7% 7% 24%	4723
	11th to 20th	Day	5% 10% 3 7% 3 3 3 3 5% 6% 52%	4716
	21st to end	Day	7% 15% 4 8% 4 4 5% 4 5% 7% 35%	5186
February	1st to 10th	Day	4 13% 5% 10% 6% 6% 6% 5% 8% 9% 28%	1806
	11th to 20th	Day	4 11% 5% 10% 5% 5% 6% 4 6% 9% 34%	1845
	21st to end	Day	3 13% 5% 12% 8% 6% 6% 4 8% 9% 26%	1696
March	1st to 10th	Day	3 11% 5% 8% 4 5% 6% 5% 7% 8% 37%	4618
	11th to 20th	Day	3 12% 4 8% 5% 5% 6% 5% 7% 7% 37%	4971
	21st to end	Day	7% 15% 5% 8% 5% 6% 6% 5% 7% 8% 28%	5963
April	1st to 10th	Day	7% 13% 3 8% 8% 6% 6% 5% 7% 9% 27%	2520
	11th to 20th	Day	5% 10% 4 9% 6% 6% 6% 5% 8% 9% 32%	2492
	21st to end	Day	4 10% 3 7% 5% 7% 6% 6% 7% 9% 35%	2836
May	1st to 10th	Day	4 6% 2 5% 4 5% 5% 4 6% 8% 52%	8195
	11th to 20th	Day	6% 8% 3 7% 5% 5% 6% 5% 8% 10% 39%	8160
	21st to end	Day	9% 9% 3 7% 5% 5% 5% 4 6% 9% 39%	8993
June	1st to 10th	Day	10% 8% 2 8% 6% 6% 6% 5% 6% 7% 37%	2940
	11th to 20th	Day	8% 7% 3 7% 6% 6% 6% 5% 8% 8% 37%	3086
	21st to end	Day	6% 6% 2 6% 5% 5% 5% 4 7% 7% 47%	3150
July	1st to 10th	Day	2 2 1 3 2 2 2 3 4 6% 74%	8701
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 5% 74%	8220
	21st to end	Day	2 2 1 4 3 3 3 3 5% 7% 66%	8916
August	1st to 10th	Day	1 2 1 3 2 3 3 3 5% 6% 71%	6441
	11th to 20th	Day	3 3 2 4 4 4 5% 4 7% 8% 55%	6146
	21st to end	Day	5% 5% 2 5% 4 4 4 4 6% 7% 55%	6166
September	1st to 10th	Day	5% 4 2 4 3 3 3 4 5% 9% 59%	2520
	11th to 20th	Day	6% 6% 2 6% 5% 5% 5% 4 5% 7% 50%	2520
	21st to end	Day	9% 8% 2 5% 4 4 4 3 5% 6% 50%	2256
October	1st to 10th	Day	6% 4 1 5% 5% 4 5% 4 6% 8% 52%	3380
	11th to 20th	Day	9% 6% 3 8% 5% 5% 5% 5% 6% 7% 40%	3275
	21st to end	Day	9% 10% 2 7% 5% 4 5% 6% 6% 7% 40%	3200
November	1st to 10th	Day	11% 16% 3 7% 5% 4 5% 5% 7% 9% 28%	1759
	11th to 20th	Day	8% 17% 5% 9% 6% 5% 5% 4 6% 7% 29%	1680
	21st to end	Day	5% 14% 4 11% 7% 7% 5% 4 5% 8% 30%	1680
December	1st to 10th	Day	4 9% 4 8% 6% 5% 5% 5% 7% 8% 41%	2700
	11th to 20th	Day	5% 18% 7% 10% 6% 6% 5% 3 6% 7% 27%	3105
	21st to end	Day	6% 17% 7% 13% 6% 5% 6% 4 6% 7% 23%	4092
January	1st to 10th	Night	5% 17% 7% 14% 7% 6% 5% 4 6% 7% 23%	8172
	11th to 20th	Night	4 10% 4 6% 3 3 3 4 6% 8% 49%	8182
	21st to end	Night	6% 16% 4 8% 4 4 4 3 6% 6% 38%	8994
February	1st to 10th	Night	7% 13% 4 9% 6% 6% 5% 4 7% 8% 30%	2809
	11th to 20th	Night	4 11% 4 8% 5% 4 5% 5% 7% 9% 39%	2662
	21st to end	Night	3 14% 4 10% 5% 6% 6% 6% 9% 9% 27%	2109
March	1st to 10th	Night	2 10% 5% 8% 5% 5% 5% 4 7% 10% 39%	5496
	11th to 20th	Night	3 12% 4 8% 4 4 4 4 5% 7% 45%	5244
	21st to end	Night	7% 13% 4 10% 6% 7% 6% 4 6% 7% 30%	5253
April	1st to 10th	Night	5% 10% 3 7% 5% 5% 5% 5% 8% 10% 36%	2100
	11th to 20th	Night	4 8% 3 6% 6% 4 5% 5% 7% 8% 44%	2079
	21st to end	Night	5% 7% 2 5% 4 5% 5% 4 6% 9% 47%	1778
May	1st to 10th	Night	4 3 1 4 3 3 4 4 7% 9% 59%	4724
	11th to 20th	Night	5% 6% 2 5% 4 4 5% 4 7% 11% 48%	4700
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 8% 12% 45%	5178
June	1st to 10th	Night	7% 7% 2 4 5% 6% 5% 5% 8% 9% 42%	1680
	11th to 20th	Night	5% 4 2 4 5% 4 5% 5% 7% 9% 50%	1527
	21st to end	Night	4 3 1 3 4 4 5% 4 6% 9% 56%	1470
July	1st to 10th	Night	1 2 1 3 1 2 2 2 4 5% 76%	4255
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 5% 77%	4740
	21st to end	Night	2 2 1 2 2 2 3 3 5% 6% 73%	5152
August	1st to 10th	Night	1 1 1 2 3 2 3 2 4 5% 75%	3709
	11th to 20th	Night	2 2 1 3 3 3 4 3 5% 8% 67%	3905
	21st to end	Night	4 2 1 3 2 3 4 3 5% 7% 65%	5000
September	1st to 10th	Night	4 2 1 5% 3 3 4 3 5% 6% 63%	2100
	11th to 20th	Night	6% 4 1 4 3 4 4 4 6% 7% 57%	2100
	21st to end	Night	7% 5% 2 4 4 3 4 4 7% 9% 49%	2360
October	1st to 10th	Night	5% 4 1 4 3 3 4 4 6% 10% 55%	4040
	11th to 20th	Night	11% 7% 2 5% 4 4 4 4 6% 8% 44%	3949
	21st to end	Night	10% 9% 2 5% 4 4 4 4 6% 8% 43%	4600
November	1st to 10th	Night	12% 16% 4 7% 4 4 5% 4 7% 8% 30%	2759
	11th to 20th	Night	8% 15% 3 8% 6% 4 6% 4 6% 8% 31%	2940
	21st to end	Night	5% 16% 5% 10% 6% 5% 5% 5% 7% 8% 29%	2940
December	1st to 10th	Night	5% 9% 3 6% 4 4 4 4 6% 8% 47%	4700
	11th to 20th	Night	6% 17% 7% 11% 7% 6% 6% 5% 6% 7% 23%	5320
	21st to end	Night	8% 21% 6% 12% 5% 5% 5% 4 5% 6% 23%	7106

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% 16% 16% 6%	4723
	11th to 20th	Day	33% 6% 16% 28% 13% 3	4740
	21st to end	Day	47% 8% 13% 18% 13%	5187
February	1st to 10th	Day	48% 14% 17% 14% 6% 2	1806
	11th to 20th	Day	43% 14% 17% 16% 8% 1	1854
	21st to end	Day	49% 15% 15% 15% 7%	1696
March	1st to 10th	Day	38% 14% 14% 13% 17% 4	4618
	11th to 20th	Day	38% 11% 16% 28% 6% 1	4971
	21st to end	Day	48% 14% 17% 13% 7% 1	5963
April	1st to 10th	Day	48% 13% 19% 15% 5%	2520
	11th to 20th	Day	43% 13% 17% 16% 9% 2	2492
	21st to end	Day	40% 13% 17% 19% 10% 1	2836
May	1st to 10th	Day	27% 9% 13% 34% 15% 1	8195
	11th to 20th	Day	31% 9% 25% 25% 9%	8163
	21st to end	Day	38% 11% 20% 27% 5%	8994
June	1st to 10th	Day	43% 10% 14% 17% 13% 3	2940
	11th to 20th	Day	38% 13% 17% 18% 13% 2	3086
	21st to end	Day	31% 10% 17% 25% 14% 2	3150
July	1st to 10th	Day	12% 5% 11% 26% 29% 18%	8628
	11th to 20th	Day	12% 4 8% 23% 29% 25%	8145
	21st to end	Day	14% 5% 10% 30% 31% 10%	8723
August	1st to 10th	Day	12% 6% 8% 24% 34% 16%	6424
	11th to 20th	Day	20% 9% 20% 35% 14% 2	6188
	21st to end	Day	25% 7% 18% 30% 17% 3	6165
September	1st to 10th	Day	21% 7% 15% 29% 22% 5%	2520
	11th to 20th	Day	31% 8% 13% 23% 21% 4	2520
	21st to end	Day	33% 9% 17% 23% 16% 3	2256
October	1st to 10th	Day	26% 8% 20% 32% 13% 1	3380
	11th to 20th	Day	37% 11% 13% 21% 16% 1	3275
	21st to end	Day	37% 12% 14% 21% 14% 1	3200
November	1st to 10th	Day	48% 13% 16% 15% 8% 1	1759
	11th to 20th	Day	53% 12% 14% 12% 7% 1	1680
	21st to end	Day	50% 11% 16% 14% 7% 2	1680
December	1st to 10th	Day	37% 12% 18% 24% 10%	2700
	11th to 20th	Day	54% 10% 17% 12% 7%	3108
	21st to end	Day	56% 11% 14% 12% 6%	4092
January	1st to 10th	Night	57% 10% 13% 15% 5%	8172
	11th to 20th	Night	31% 9% 16% 27% 14% 3	8220
	21st to end	Night	46% 7% 16% 18% 13% 1	8994
February	1st to 10th	Night	47% 14% 16% 14% 7% 2	2809
	11th to 20th	Night	40% 13% 17% 19% 9% 2	2664
	21st to end	Night	46% 16% 15% 15% 8%	2109
March	1st to 10th	Night	34% 12% 16% 20% 15% 3	5496
	11th to 20th	Night	35% 10% 17% 26% 12%	5245
	21st to end	Night	50% 13% 16% 15% 5%	5253
April	1st to 10th	Night	37% 14% 22% 21% 5%	2100
	11th to 20th	Night	34% 12% 20% 21% 12% 1	2079
	21st to end	Night	31% 12% 20% 26% 11%	1778
May	1st to 10th	Night	19% 7% 16% 40% 17%	4721
	11th to 20th	Night	24% 9% 27% 30% 9% 1	4700
	21st to end	Night	25% 14% 26% 29% 6%	5182
June	1st to 10th	Night	33% 11% 18% 21% 14% 2	1680
	11th to 20th	Night	27% 12% 20% 25% 15% 1	1527
	21st to end	Night	21% 11% 22% 30% 14% 2	1470
July	1st to 10th	Night	11% 4 13% 32% 25% 15%	4219
	11th to 20th	Night	9% 4 11% 24% 29% 21%	4692
	21st to end	Night	11% 5% 10% 36% 27% 11%	5040
August	1st to 10th	Night	10% 5% 9% 27% 36% 12%	3701
	11th to 20th	Night	14% 6% 27% 39% 12% 2	3929
	21st to end	Night	17% 7% 18% 38% 19% 1	5000
September	1st to 10th	Night	19% 7% 15% 32% 22% 4	2100
	11th to 20th	Night	25% 8% 13% 30% 22% 3	2100
	21st to end	Night	28% 9% 18% 29% 13% 3	2360
October	1st to 10th	Night	24% 8% 19% 34% 14% 1	4040
	11th to 20th	Night	36% 9% 15% 25% 14%	3949
	21st to end	Night	36% 9% 17% 25% 12% 1	4600
November	1st to 10th	Night	48% 13% 17% 14% 8% 2	2759
	11th to 20th	Night	48% 13% 14% 16% 6% 2	2940
	21st to end	Night	49% 14% 14% 14% 7% 2	2940
December	1st to 10th	Night	34% 10% 19% 26% 10%	4700
	11th to 20th	Night	56% 11% 16% 11% 5%	5316
	21st to end	Night	57% 11% 13% 14% 6% 1	7106

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	20% 21% 29% 19% 9% 3	220
	11th to 20th	Day	14% 20% 30% 24% 10% 3	220
	21st to end	Day	17% 16% 36% 20% 10%	242
February	1st to 10th	Day	16% 27% 38% 13% 6%	346
	11th to 20th	Day	18% 22% 37% 17% 4 1	425
	21st to end	Day	13% 29% 38% 17% 3	430
March	1st to 10th	Day	16% 30% 32% 17% 4 1	540
	11th to 20th	Day	17% 29% 30% 17% 7% 1	540
	21st to end	Day	21% 27% 34% 15% 2	594
April	1st to 10th	Day	20% 28% 31% 15% 6% 1	540
	11th to 20th	Day	18% 31% 28% 17% 6% 1	532
	21st to end	Day	14% 28% 32% 17% 8% 2	540
May	1st to 10th	Day	11% 24% 37% 22% 6% 1	543
	11th to 20th	Day	21% 19% 29% 22% 8% 1	568
	21st to end	Day	17% 23% 31% 21% 7% 1	617
June	1st to 10th	Day	16% 23% 35% 19% 6% 1	570
	11th to 20th	Day	17% 27% 35% 17% 4 1	716
	21st to end	Day	10% 22% 38% 22% 7% 1	780
July	1st to 10th	Day	7% 23% 37% 27% 6% 1	731
	11th to 20th	Day	8% 19% 36% 29% 7% 2	564
	21st to end	Day	5% 17% 36% 30% 11% 2	619
August	1st to 10th	Day	7% 14% 38% 28% 12% 2	567
	11th to 20th	Day	5% 14% 32% 35% 13% 2	557
	21st to end	Day	8% 21% 35% 25% 10% 2	627
September	1st to 10th	Day	8% 20% 36% 23% 12% 2	570
	11th to 20th	Day	11% 19% 32% 25% 11% 1	570
	21st to end	Day	16% 22% 35% 21% 6% 1	570
October	1st to 10th	Day	12% 22% 35% 23% 8% 1	570
	11th to 20th	Day	15% 26% 29% 21% 8% 2	538
	21st to end	Day	19% 22% 35% 17% 6% 1	363
November	1st to 10th	Day	18% 28% 33% 17% 5%	280
	11th to 20th	Day	17% 25% 29% 17% 9% 3	220
	21st to end	Day	21% 12% 35% 20% 10% 3	220
December	1st to 10th	Day	15% 15% 29% 20% 16% 5%	220
	11th to 20th	Day	14% 22% 36% 22% 5%	220
	21st to end	Day	10% 18% 38% 24% 10%	242
January	1st to 10th	Night	17% 18% 37% 21% 7% 1	840
	11th to 20th	Night	15% 15% 42% 20% 8% 1	840
	21st to end	Night	14% 13% 38% 26% 9%	924
February	1st to 10th	Night	13% 18% 42% 22% 5%	840
	11th to 20th	Night	10% 16% 40% 27% 7%	824
	21st to end	Night	15% 17% 38% 21% 9%	692
March	1st to 10th	Night	10% 17% 39% 26% 7% 1	840
	11th to 20th	Night	13% 16% 41% 22% 9%	840
	21st to end	Night	13% 16% 43% 23% 4 1	924
April	1st to 10th	Night	9% 15% 41% 26% 7% 1	840
	11th to 20th	Night	8% 20% 40% 24% 6% 1	831
	21st to end	Night	9% 18% 44% 22% 7% 1	518
May	1st to 10th	Night	9% 15% 41% 30% 5%	420
	11th to 20th	Night	11% 14% 34% 31% 10%	414
	21st to end	Night	11% 12% 39% 29% 9%	455
June	1st to 10th	Night	11% 15% 38% 29% 7%	420
	11th to 20th	Night	7% 18% 42% 28% 4	420
	21st to end	Night	6% 10% 40% 34% 10%	420
July	1st to 10th	Night	3 10% 42% 35% 9%	410
	11th to 20th	Night	3 12% 43% 34% 7%	408
	21st to end	Night	2 10% 36% 41% 11%	460
August	1st to 10th	Night	4 7% 32% 41% 16%	418
	11th to 20th	Night	3 7% 34% 38% 17% 1	514
	21st to end	Night	5% 12% 33% 36% 13% 1	882
September	1st to 10th	Night	5% 10% 37% 30% 16% 2	840
	11th to 20th	Night	7% 11% 27% 32% 18% 4	840
	21st to end	Night	11% 12% 34% 29% 12% 2	840
October	1st to 10th	Night	11% 12% 35% 30% 11% 1	840
	11th to 20th	Night	13% 14% 39% 22% 11% 1	812
	21st to end	Night	17% 17% 35% 22% 7% 2	880
November	1st to 10th	Night	20% 17% 40% 20% 4	820
	11th to 20th	Night	21% 15% 38% 18% 7% 1	840
	21st to end	Night	15% 14% 40% 20% 8% 2	840
December	1st to 10th	Night	14% 13% 39% 25% 8% 1	840
	11th to 20th	Night	16% 15% 44% 22% 3 1	840
	21st to end	Night	15% 16% 44% 21% 4	924

Page generated at 2026-10-11 02:06:32. Version ac07

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