Stony Creek Ranch Resort Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stony Creek Ranch Resort Observatory clear sky chart from 2005-11-06 to 2026-09-14.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	149328
	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	141746
Transparency	Day	47% 8% 13% 20% 11% 1	152807
	Night	47% 8% 13% 19% 12% 1	146355
Seeing	Day	23% 17% 30% 19% 8% 3	17114
	Night	20% 14% 30% 26% 9% 1	26075

By Month

Percentage Cloud Cover NE (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	9% 11% 5% 18% 7% 7% 6% 4 5% 5% 23%	4661
	11th to 20th	Day	11% 15% 7% 13% 8% 7% 5% 3 4 5% 22%	4650
	21st to end	Day	10% 11% 5% 10% 8% 7% 6% 4 5% 6% 28%	5243
February	1st to 10th	Day	11% 13% 4 11% 7% 6% 5% 5% 5% 6% 27%	1890
	11th to 20th	Day	11% 11% 5% 11% 7% 5% 6% 4 5% 5% 29%	1996
	21st to end	Day	17% 12% 5% 9% 6% 4 4 3 5% 5% 31%	1730
March	1st to 10th	Day	18% 13% 4 10% 5% 5% 4 3 4 5% 30%	4576
	11th to 20th	Day	15% 11% 4 7% 5% 4 4 3 5% 6% 34%	4826
	21st to end	Day	19% 11% 3 7% 5% 4 4 3 4 5% 34%	6091
April	1st to 10th	Day	19% 12% 3 7% 4 4 4 3 4 6% 34%	2520
	11th to 20th	Day	17% 10% 2 6% 5% 6% 4 4 5% 6% 35%	2494
	21st to end	Day	19% 10% 3 8% 5% 5% 5% 3 5% 6% 32%	2630
May	1st to 10th	Day	27% 10% 3 7% 5% 4 5% 4 6% 6% 23%	7894
	11th to 20th	Day	16% 8% 3 9% 5% 5% 6% 4 6% 7% 32%	8221
	21st to end	Day	19% 8% 3 6% 4 5% 5% 4 7% 8% 30%	9060
June	1st to 10th	Day	16% 7% 3 7% 6% 5% 5% 5% 7% 8% 31%	2940
	11th to 20th	Day	16% 5% 2 6% 6% 5% 6% 5% 8% 8% 32%	2940
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 4 7% 8% 31%	2940
July	1st to 10th	Day	12% 6% 2 6% 5% 6% 6% 5% 8% 10% 35%	8280
	11th to 20th	Day	8% 5% 2 5% 4 5% 6% 5% 9% 11% 40%	8280
	21st to end	Day	15% 6% 2 5% 4 5% 5% 5% 7% 7% 39%	8993
August	1st to 10th	Day	13% 6% 2 8% 6% 6% 6% 5% 7% 8% 33%	6483
	11th to 20th	Day	13% 6% 2 6% 4 6% 6% 5% 8% 10% 34%	5565
	21st to end	Day	12% 5% 2 6% 5% 5% 6% 5% 9% 10% 35%	6080
September	1st to 10th	Day	13% 4 2 6% 4 5% 5% 4 6% 8% 44%	2520
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 8% 48%	2350
	21st to end	Day	17% 5% 2 6% 4 4 4 4 6% 6% 40%	2200
October	1st to 10th	Day	20% 8% 3 8% 5% 4 5% 3 5% 6% 34%	2075
	11th to 20th	Day	15% 8% 3 7% 4 4 5% 4 6% 8% 36%	2000
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 5% 6% 30%	1980
November	1st to 10th	Day	12% 9% 3 8% 5% 4 5% 4 5% 7% 37%	1851
	11th to 20th	Day	14% 10% 3 6% 5% 5% 5% 4 5% 7% 35%	1890
	21st to end	Day	17% 11% 4 7% 6% 4 5% 4 5% 6% 32%	1685
December	1st to 10th	Day	16% 14% 7% 13% 6% 5% 5% 3 4 5% 21%	2680
	11th to 20th	Day	19% 12% 4 8% 5% 5% 4 4 4 5% 29%	3066
	21st to end	Day	19% 14% 5% 10% 5% 5% 3 3 4 6% 26%	4048
January	1st to 10th	Night	11% 12% 6% 12% 6% 5% 5% 4 5% 6% 27%	8234
	11th to 20th	Night	9% 14% 7% 14% 8% 7% 6% 4 5% 6% 20%	8235
	21st to end	Night	12% 10% 4 9% 6% 7% 6% 5% 6% 7% 29%	8937
February	1st to 10th	Night	11% 11% 4 11% 8% 6% 6% 4 6% 6% 27%	2730
	11th to 20th	Night	10% 10% 4 10% 8% 4 5% 5% 6% 6% 32%	2510
	21st to end	Night	13% 10% 3 9% 6% 6% 5% 4 6% 7% 32%	2076
March	1st to 10th	Night	20% 10% 3 7% 5% 5% 5% 4 5% 6% 29%	5484
	11th to 20th	Night	14% 11% 3 7% 5% 4 4 4 5% 7% 37%	5336
	21st to end	Night	19% 11% 3 9% 5% 4 4 3 5% 6% 32%	5083
April	1st to 10th	Night	19% 8% 3 7% 5% 4 4 4 5% 5% 35%	2100
	11th to 20th	Night	18% 9% 3 7% 5% 3 5% 3 5% 7% 37%	2075
	21st to end	Night	18% 8% 2 7% 4 4 4 3 6% 6% 38%	1990
May	1st to 10th	Night	26% 10% 3 7% 5% 5% 5% 4 5% 6% 24%	5047
	11th to 20th	Night	15% 9% 4 10% 5% 4 4 3 5% 7% 33%	4639
	21st to end	Night	17% 6% 2 7% 5% 5% 5% 5% 6% 8% 33%	5114
June	1st to 10th	Night	17% 6% 1 5% 4 4 5% 4 6% 7% 40%	1680
	11th to 20th	Night	16% 7% 2 6% 4 4 5% 3 6% 9% 38%	1680
	21st to end	Night	15% 6% 2 6% 5% 4 6% 4 5% 7% 40%	1680
July	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 40%	4680
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	4680
	21st to end	Night	13% 5% 2 5% 4 4 4 4 6% 8% 46%	5084
August	1st to 10th	Night	16% 8% 3 7% 5% 5% 5% 3 5% 6% 37%	3666
	11th to 20th	Night	16% 5% 2 6% 4 4 4 4 6% 8% 41%	4417
	21st to end	Night	9% 5% 2 5% 4 5% 6% 5% 7% 9% 43%	5045
September	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 7% 7% 47%	2100
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 4 5% 53%	2116
	21st to end	Night	16% 6% 2 4 3 5% 5% 4 4 6% 46%	2200
October	1st to 10th	Night	19% 6% 3 8% 4 4 5% 4 5% 6% 36%	2321
	11th to 20th	Night	15% 6% 3 6% 5% 4 6% 3 5% 7% 40%	2400
	21st to end	Night	22% 8% 3 7% 4 4 4 5% 6% 7% 32%	2860
November	1st to 10th	Night	13% 8% 3 8% 5% 4 4 3 5% 6% 41%	2667
	11th to 20th	Night	17% 7% 3 8% 4 4 4 3 6% 7% 37%	2730
	21st to end	Night	15% 10% 3 8% 5% 4 5% 4 6% 7% 33%	2932
December	1st to 10th	Night	15% 13% 5% 10% 6% 7% 5% 4 6% 6% 24%	4720
	11th to 20th	Night	22% 11% 3 8% 5% 5% 4 3 4 5% 30%	5348
	21st to end	Night	20% 14% 5% 10% 5% 4 4 3 4 4 27%	7150

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	58% 8% 11% 16% 5% 1	4662
	11th to 20th	Day	61% 6% 10% 10% 10% 3	4680
	21st to end	Day	53% 6% 12% 18% 9% 2	5243
February	1st to 10th	Day	54% 10% 10% 17% 8% 2	1890
	11th to 20th	Day	55% 8% 11% 16% 10% 2	2005
	21st to end	Day	54% 6% 11% 16% 12% 1	1730
March	1st to 10th	Day	55% 6% 10% 12% 10% 7%	4579
	11th to 20th	Day	47% 9% 18% 14% 8% 4	4826
	21st to end	Day	51% 6% 7% 14% 18% 4	6091
April	1st to 10th	Day	51% 6% 9% 19% 12% 3	2520
	11th to 20th	Day	48% 7% 11% 18% 14% 2	2494
	21st to end	Day	52% 7% 10% 16% 12% 3	2630
May	1st to 10th	Day	57% 8% 9% 15% 9% 1	7906
	11th to 20th	Day	48% 10% 14% 19% 9% 1	8225
	21st to end	Day	48% 8% 13% 22% 9%	9061
June	1st to 10th	Day	46% 11% 13% 18% 11% 1	2940
	11th to 20th	Day	45% 9% 14% 18% 12% 1	2940
	21st to end	Day	47% 9% 14% 19% 10% 1	2940
July	1st to 10th	Day	40% 8% 17% 24% 11%	8210
	11th to 20th	Day	34% 8% 16% 31% 12%	8205
	21st to end	Day	41% 7% 14% 28% 11%	8795
August	1st to 10th	Day	46% 9% 15% 16% 12% 1	6469
	11th to 20th	Day	40% 9% 19% 26% 6%	5602
	21st to end	Day	39% 9% 17% 26% 9%	6080
September	1st to 10th	Day	36% 9% 13% 30% 12% 1	2520
	11th to 20th	Day	34% 7% 12% 28% 19% 1	2350
	21st to end	Day	41% 8% 15% 22% 13% 1	2200
October	1st to 10th	Day	45% 6% 9% 23% 16% 1	3374
	11th to 20th	Day	39% 6% 14% 24% 15% 2	3240
	21st to end	Day	38% 7% 14% 28% 13% 1	3180
November	1st to 10th	Day	43% 10% 16% 20% 12%	1851
	11th to 20th	Day	46% 8% 13% 16% 15% 2	1890
	21st to end	Day	51% 9% 15% 16% 7% 1	1685
December	1st to 10th	Day	64% 6% 10% 15% 4	2680
	11th to 20th	Day	55% 7% 12% 16% 10% 1	3066
	21st to end	Day	59% 6% 8% 13% 13% 1	4048
January	1st to 10th	Night	54% 8% 13% 14% 10% 1	8234
	11th to 20th	Night	61% 8% 11% 9% 9% 2	8280
	21st to end	Night	51% 6% 12% 14% 14% 3	8937
February	1st to 10th	Night	54% 8% 11% 17% 8% 1	2730
	11th to 20th	Night	49% 8% 13% 18% 11% 2	2512
	21st to end	Night	48% 8% 13% 19% 9% 2	2076
March	1st to 10th	Night	52% 7% 11% 13% 14% 3	5494
	11th to 20th	Night	45% 8% 17% 17% 10% 2	5337
	21st to end	Night	52% 5% 7% 16% 17% 2	5083
April	1st to 10th	Night	50% 6% 11% 18% 14% 1	2100
	11th to 20th	Night	46% 8% 11% 20% 14% 1	2075
	21st to end	Night	44% 8% 11% 19% 15% 3	1990
May	1st to 10th	Night	56% 9% 11% 12% 11% 1	5053
	11th to 20th	Night	48% 10% 13% 20% 9% 1	4640
	21st to end	Night	45% 8% 14% 22% 10% 1	5115
June	1st to 10th	Night	42% 8% 14% 21% 13% 1	1680
	11th to 20th	Night	42% 8% 16% 21% 13% 1	1680
	21st to end	Night	41% 9% 14% 24% 12% 1	1680
July	1st to 10th	Night	39% 8% 19% 21% 13%	4640
	11th to 20th	Night	35% 7% 14% 25% 18% 1	4632
	21st to end	Night	35% 7% 16% 30% 12% 1	4967
August	1st to 10th	Night	45% 8% 16% 19% 10% 2	3656
	11th to 20th	Night	39% 7% 18% 28% 7%	4445
	21st to end	Night	34% 8% 18% 30% 11%	5045
September	1st to 10th	Night	34% 9% 15% 29% 13% 1	2100
	11th to 20th	Night	33% 6% 13% 28% 19% 1	2116
	21st to end	Night	38% 8% 13% 23% 15% 2	2200
October	1st to 10th	Night	45% 8% 11% 21% 14% 1	3802
	11th to 20th	Night	35% 6% 14% 25% 17% 4	3899
	21st to end	Night	42% 7% 13% 28% 9% 1	4610
November	1st to 10th	Night	43% 7% 14% 21% 13% 2	2667
	11th to 20th	Night	44% 8% 12% 21% 12% 2	2730
	21st to end	Night	48% 9% 16% 18% 9% 1	2932
December	1st to 10th	Night	55% 8% 15% 17% 4	4720
	11th to 20th	Night	55% 7% 10% 14% 13% 1	5348
	21st to end	Night	58% 8% 8% 12% 11% 2	7150

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	23% 22% 32% 15% 7%	220
	11th to 20th	Day	26% 30% 29% 13% 2 1	220
	21st to end	Day	22% 27% 34% 13% 4 1	264
February	1st to 10th	Day	25% 33% 32% 7% 2	330
	11th to 20th	Day	24% 31% 32% 11% 1	484
	21st to end	Day	30% 24% 29% 14% 2	446
March	1st to 10th	Day	29% 17% 34% 16% 3	540
	11th to 20th	Day	29% 25% 28% 14% 4 1	540
	21st to end	Day	31% 25% 24% 13% 6% 2	594
April	1st to 10th	Day	36% 22% 24% 12% 6% 1	540
	11th to 20th	Day	32% 23% 24% 13% 6% 2	532
	21st to end	Day	29% 22% 29% 14% 5% 2	540
May	1st to 10th	Day	34% 18% 28% 11% 6% 2	543
	11th to 20th	Day	19% 19% 35% 19% 5% 2	567
	21st to end	Day	21% 15% 32% 21% 9% 2	617
June	1st to 10th	Day	19% 16% 32% 23% 9% 2	570
	11th to 20th	Day	18% 16% 32% 23% 9% 1	570
	21st to end	Day	19% 14% 34% 21% 8% 2	570
July	1st to 10th	Day	14% 10% 32% 27% 13% 3	565
	11th to 20th	Day	16% 9% 31% 28% 13% 3	564
	21st to end	Day	15% 10% 35% 26% 10% 3	620
August	1st to 10th	Day	12% 9% 27% 30% 16% 5%	566
	11th to 20th	Day	17% 9% 26% 27% 14% 7%	559
	21st to end	Day	12% 12% 32% 25% 14% 5%	627
September	1st to 10th	Day	15% 10% 28% 25% 14% 8%	570
	11th to 20th	Day	13% 9% 26% 23% 18% 11%	542
	21st to end	Day	19% 10% 31% 22% 11% 7%	530
October	1st to 10th	Day	25% 15% 25% 17% 14% 4	530
	11th to 20th	Day	21% 18% 29% 22% 8% 2	530
	21st to end	Day	29% 15% 30% 19% 6% 1	462
November	1st to 10th	Day	27% 18% 25% 19% 11%	425
	11th to 20th	Day	23% 23% 27% 19% 7% 1	430
	21st to end	Day	33% 20% 31% 14% 2	225
December	1st to 10th	Day	27% 25% 30% 14% 4 1	220
	11th to 20th	Day	32% 25% 30% 11% 3	220
	21st to end	Day	26% 22% 33% 15% 3	242
January	1st to 10th	Night	19% 19% 37% 23% 3	840
	11th to 20th	Night	23% 19% 33% 22% 3	840
	21st to end	Night	15% 20% 37% 24% 4	924
February	1st to 10th	Night	17% 19% 40% 22% 2	840
	11th to 20th	Night	19% 21% 40% 19% 2	823
	21st to end	Night	21% 19% 38% 19% 2	692
March	1st to 10th	Night	25% 18% 33% 22% 2	840
	11th to 20th	Night	25% 19% 32% 21% 3	840
	21st to end	Night	23% 19% 32% 20% 6%	924
April	1st to 10th	Night	26% 19% 30% 22% 3	840
	11th to 20th	Night	23% 20% 31% 19% 6%	831
	21st to end	Night	25% 17% 29% 23% 6%	730
May	1st to 10th	Night	26% 15% 29% 22% 8%	560
	11th to 20th	Night	18% 17% 32% 26% 7%	414
	21st to end	Night	16% 9% 28% 34% 12% 1	455
June	1st to 10th	Night	20% 6% 26% 35% 12% 1	420
	11th to 20th	Night	18% 8% 26% 35% 12%	420
	21st to end	Night	17% 5% 28% 38% 11%	420
July	1st to 10th	Night	12% 5% 24% 42% 17% 1	410
	11th to 20th	Night	13% 3 25% 41% 18%	408
	21st to end	Night	11% 4 25% 43% 16% 1	460
August	1st to 10th	Night	10% 1 24% 44% 19% 1	418
	11th to 20th	Night	14% 5% 21% 36% 21% 3	765
	21st to end	Night	15% 6% 20% 39% 20% 1	924
September	1st to 10th	Night	14% 6% 25% 36% 18% 2	840
	11th to 20th	Night	15% 7% 24% 28% 22% 5%	813
	21st to end	Night	17% 6% 29% 30% 16% 2	800
October	1st to 10th	Night	22% 11% 24% 26% 15% 2	800
	11th to 20th	Night	19% 13% 28% 31% 9% 1	800
	21st to end	Night	25% 14% 30% 26% 6%	880
November	1st to 10th	Night	18% 15% 33% 26% 8%	820
	11th to 20th	Night	22% 19% 29% 23% 6% 1	840
	21st to end	Night	20% 17% 34% 23% 6%	840
December	1st to 10th	Night	24% 16% 36% 20% 4	840
	11th to 20th	Night	26% 18% 31% 22% 4	840
	21st to end	Night	26% 18% 33% 21% 3	924

Page generated at 2026-09-11 04:11:52. Version ac07

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