Pisony Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pisony Ranch clear sky chart from 2005-11-06 to 2026-07-16.

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	6% 8% 3 7% 5% 4 5% 4 7% 9% 43%	142150
	Night	4 7% 3 7% 5% 4 5% 4 7% 9% 44%	139249
Transparency	Day	35% 6% 16% 26% 13% 3	141862
	Night	35% 6% 19% 26% 12% 2	139120
Seeing	Day	21% 20% 28% 20% 9% 2	17497
	Night	16% 17% 28% 26% 11% 1	26579

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	1 7% 3 11% 7% 5% 4 4 7% 11% 40%	4125
	11th to 20th	Day	1 6% 4 10% 6% 6% 6% 4 7% 8% 43%	4472
	21st to end	Day	1 7% 3 8% 5% 4 5% 5% 7% 9% 46%	5186
February	1st to 10th	Day	2 8% 4 10% 7% 7% 7% 4 7% 10% 33%	1696
	11th to 20th	Day	2 11% 4 11% 7% 5% 6% 5% 7% 10% 33%	1845
	21st to end	Day	1 9% 4 12% 7% 5% 7% 5% 8% 9% 34%	1729
March	1st to 10th	Day	2 8% 4 8% 5% 4 4 4 6% 10% 46%	4618
	11th to 20th	Day	2 8% 3 7% 5% 5% 6% 4 8% 10% 41%	5051
	21st to end	Day	4 16% 7% 13% 5% 4 5% 4 7% 9% 25%	5695
April	1st to 10th	Day	5% 14% 3 9% 6% 6% 5% 4 8% 8% 31%	2547
	11th to 20th	Day	7% 15% 5% 9% 5% 4 4 4 7% 8% 31%	2700
	21st to end	Day	9% 14% 5% 8% 5% 4 5% 4 6% 7% 32%	2730
May	1st to 10th	Day	10% 13% 3 7% 5% 4 4 4 5% 6% 37%	7787
	11th to 20th	Day	9% 9% 3 8% 6% 6% 6% 5% 8% 9% 31%	8655
	21st to end	Day	12% 6% 2 5% 4 5% 6% 5% 7% 11% 37%	9649
June	1st to 10th	Day	13% 9% 3 8% 6% 6% 6% 5% 7% 7% 32%	3150
	11th to 20th	Day	16% 8% 3 8% 6% 5% 6% 5% 7% 7% 31%	3150
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	3150
July	1st to 10th	Day	6% 4 1 4 4 4 5% 4 6% 8% 54%	6930
	11th to 20th	Day	8% 3 2 4 3 4 4 4 7% 8% 54%	6856
	21st to end	Day	7% 3 1 3 2 3 4 3 6% 8% 59%	6975
August	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 7% 8% 45%	4541
	11th to 20th	Day	7% 3 2 3 3 4 4 4 7% 9% 55%	4159
	21st to end	Day	6% 4 1 4 3 3 4 3 6% 7% 58%	4664
September	1st to 10th	Day	11% 5% 2 4 3 3 4 3 6% 7% 50%	2442
	11th to 20th	Day	11% 7% 2 4 4 3 5% 3 7% 8% 47%	2200
	21st to end	Day	9% 7% 2 4 3 3 4 3 6% 8% 50%	2200
October	1st to 10th	Day	6% 8% 3 5% 4 3 4 4 5% 8% 50%	3485
	11th to 20th	Day	3 6% 2 6% 4 4 5% 5% 6% 10% 49%	3011
	21st to end	Day	5% 8% 2 7% 4 4 5% 3 7% 10% 47%	3200
November	1st to 10th	Day	5% 11% 4 7% 5% 5% 4 5% 8% 8% 38%	1787
	11th to 20th	Day	2 7% 3 6% 4 4 5% 5% 9% 9% 45%	1648
	21st to end	Day	3 10% 3 10% 6% 4 4 4 7% 9% 40%	1470
December	1st to 10th	Day	1 6% 2 7% 4 4 4 5% 6% 11% 50%	2360
	11th to 20th	Day	2 7% 3 10% 5% 4 5% 5% 7% 10% 41%	2712
	21st to end	Day	1 7% 4 8% 6% 5% 5% 4 8% 11% 42%	3575
January	1st to 10th	Night	2 7% 4 10% 6% 4 5% 5% 8% 9% 40%	8768
	11th to 20th	Night	1 5% 3 8% 5% 5% 6% 6% 7% 10% 44%	8482
	21st to end	Night	1 7% 3 8% 5% 5% 5% 5% 7% 10% 44%	8994
February	1st to 10th	Night	2 11% 4 10% 8% 5% 5% 5% 6% 9% 34%	2923
	11th to 20th	Night	1 11% 4 10% 6% 6% 5% 4 7% 9% 36%	2662
	21st to end	Night	1 7% 4 12% 6% 6% 6% 5% 6% 8% 38%	2076
March	1st to 10th	Night	1 8% 3 11% 6% 5% 6% 5% 6% 9% 40%	5496
	11th to 20th	Night	2 6% 3 7% 5% 5% 5% 5% 8% 10% 45%	5167
	21st to end	Night	5% 17% 7% 13% 4 3 4 4 7% 9% 28%	5521
April	1st to 10th	Night	7% 12% 3 8% 5% 4 4 4 6% 8% 39%	2072
	11th to 20th	Night	7% 11% 3 9% 4 3 4 4 7% 9% 38%	1871
	21st to end	Night	6% 13% 5% 7% 5% 5% 5% 4 6% 7% 36%	1890
May	1st to 10th	Night	9% 11% 3 6% 4 3 4 3 5% 7% 45%	5149
	11th to 20th	Night	9% 8% 3 7% 5% 4 5% 4 8% 10% 37%	4191
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 5% 6% 8% 42%	4522
June	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 4 7% 9% 38%	1470
	11th to 20th	Night	15% 7% 2 6% 3 5% 6% 5% 5% 8% 36%	1470
	21st to end	Night	6% 5% 2 4 4 4 5% 5% 7% 9% 49%	1470
July	1st to 10th	Night	6% 4 2 3 3 3 4 3 6% 8% 59%	3250
	11th to 20th	Night	6% 3 1 4 3 3 5% 3 5% 8% 60%	3215
	21st to end	Night	13% 5% 2 4 2 2 3 3 3 4 59%	3865
August	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 5% 6% 52%	2609
	11th to 20th	Night	5% 4 1 4 4 4 5% 6% 7% 9% 50%	2898
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 8% 58%	3245
September	1st to 10th	Night	9% 4 2 4 3 3 3 2 5% 7% 58%	1955
	11th to 20th	Night	11% 7% 1 4 2 2 3 3 7% 8% 51%	2200
	21st to end	Night	9% 6% 2 4 3 3 4 3 5% 9% 52%	2200
October	1st to 10th	Night	6% 6% 2 4 3 2 3 3 5% 7% 58%	3710
	11th to 20th	Night	3 5% 1 3 2 4 4 3 8% 12% 55%	4120
	21st to end	Night	3 6% 3 6% 3 4 4 4 6% 9% 52%	4600
November	1st to 10th	Night	4 11% 4 8% 5% 4 5% 5% 6% 8% 40%	2709
	11th to 20th	Night	1 7% 3 7% 5% 4 5% 5% 8% 11% 44%	2966
	21st to end	Night	2 9% 4 9% 5% 5% 4 4 7% 11% 41%	3150
December	1st to 10th	Night	2 6% 3 8% 4 4 4 5% 7% 11% 45%	5040
	11th to 20th	Night	2 8% 4 10% 6% 5% 6% 6% 8% 10% 35%	5700
	21st to end	Night	1 10% 5% 10% 6% 5% 5% 4 7% 8% 39%	7623

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	39% 6% 19% 21% 14% 2	4125
	11th to 20th	Day	37% 6% 20% 21% 12% 4	4496
	21st to end	Day	34% 6% 19% 29% 12%	5187
February	1st to 10th	Day	43% 9% 18% 19% 10% 3	1696
	11th to 20th	Day	43% 9% 18% 20% 9% 2	1854
	21st to end	Day	42% 8% 16% 23% 9% 2	1729
March	1st to 10th	Day	32% 7% 16% 24% 19% 2	4618
	11th to 20th	Day	32% 7% 19% 27% 14% 1	5052
	21st to end	Day	53% 7% 17% 16% 7%	5695
April	1st to 10th	Day	43% 10% 19% 21% 7%	2547
	11th to 20th	Day	46% 8% 16% 20% 8% 1	2700
	21st to end	Day	48% 7% 15% 21% 9% 1	2730
May	1st to 10th	Day	44% 4 11% 25% 15% 1	7787
	11th to 20th	Day	42% 7% 13% 25% 12% 1	8659
	21st to end	Day	36% 7% 19% 27% 11%	9650
June	1st to 10th	Day	46% 9% 14% 20% 10% 1	3150
	11th to 20th	Day	48% 7% 11% 19% 12% 1	3150
	21st to end	Day	34% 8% 15% 28% 13% 2	3150
July	1st to 10th	Day	26% 4 12% 26% 24% 8%	6856
	11th to 20th	Day	27% 3 14% 31% 18% 6%	6775
	21st to end	Day	24% 3 13% 29% 19% 11%	6779
August	1st to 10th	Day	34% 5% 15% 26% 17% 4	4524
	11th to 20th	Day	25% 4 21% 36% 13% 2	4198
	21st to end	Day	23% 5% 11% 41% 18% 2	4663
September	1st to 10th	Day	31% 6% 13% 27% 18% 6%	2442
	11th to 20th	Day	32% 6% 13% 30% 17% 3	2200
	21st to end	Day	30% 7% 17% 31% 13% 2	2200
October	1st to 10th	Day	31% 5% 18% 35% 10% 1	3485
	11th to 20th	Day	29% 5% 22% 26% 16% 1	3011
	21st to end	Day	32% 5% 19% 28% 13% 3	3200
November	1st to 10th	Day	39% 11% 17% 21% 10% 1	1787
	11th to 20th	Day	31% 13% 22% 24% 10% 1	1648
	21st to end	Day	40% 7% 24% 19% 8% 2	1470
December	1st to 10th	Day	28% 7% 29% 26% 8% 1	2360
	11th to 20th	Day	36% 8% 28% 21% 6%	2714
	21st to end	Day	35% 7% 17% 25% 14% 2	3575
January	1st to 10th	Night	37% 8% 18% 26% 10% 1	8769
	11th to 20th	Night	36% 5% 20% 22% 11% 5%	8520
	21st to end	Night	34% 7% 22% 25% 11%	8994
February	1st to 10th	Night	45% 8% 15% 19% 11% 2	2923
	11th to 20th	Night	41% 9% 19% 21% 10% 1	2663
	21st to end	Night	41% 8% 15% 24% 10% 2	2076
March	1st to 10th	Night	37% 8% 18% 21% 14% 2	5496
	11th to 20th	Night	29% 7% 20% 28% 15% 1	5167
	21st to end	Night	52% 6% 20% 15% 6%	5521
April	1st to 10th	Night	41% 8% 17% 23% 9% 1	2072
	11th to 20th	Night	41% 7% 16% 29% 7%	1871
	21st to end	Night	44% 8% 13% 26% 8% 1	1890
May	1st to 10th	Night	39% 5% 13% 31% 12% 1	5146
	11th to 20th	Night	39% 6% 13% 32% 10%	4191
	21st to end	Night	37% 6% 18% 29% 10%	4526
June	1st to 10th	Night	40% 7% 17% 25% 10% 1	1470
	11th to 20th	Night	42% 8% 16% 20% 12% 1	1470
	21st to end	Night	27% 8% 19% 30% 14% 2	1470
July	1st to 10th	Night	23% 3 18% 26% 23% 6%	3215
	11th to 20th	Night	23% 3 18% 31% 17% 7%	3173
	21st to end	Night	29% 3 14% 25% 18% 11%	3756
August	1st to 10th	Night	33% 4 15% 25% 19% 4	2601
	11th to 20th	Night	28% 4 22% 30% 15% 2	2925
	21st to end	Night	23% 3 13% 39% 20% 2	3245
September	1st to 10th	Night	25% 5% 15% 33% 15% 6%	1955
	11th to 20th	Night	29% 6% 16% 30% 16% 3	2200
	21st to end	Night	29% 6% 19% 29% 14% 3	2200
October	1st to 10th	Night	26% 4 15% 34% 21% 1	3710
	11th to 20th	Night	22% 5% 23% 29% 19% 2	4120
	21st to end	Night	30% 6% 17% 38% 10%	4600
November	1st to 10th	Night	40% 9% 19% 21% 10% 1	2709
	11th to 20th	Night	31% 11% 22% 24% 11% 1	2966
	21st to end	Night	36% 10% 23% 19% 9% 2	3150
December	1st to 10th	Night	33% 6% 27% 22% 10% 2	5040
	11th to 20th	Night	40% 10% 24% 19% 7%	5697
	21st to end	Night	39% 7% 18% 21% 12% 3	7623

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% 24% 27% 15% 5% 6%	220
	11th to 20th	Day	22% 17% 32% 21% 6% 1	220
	21st to end	Day	20% 28% 36% 9% 5% 2	242
February	1st to 10th	Day	22% 22% 37% 13% 4 1	228
	11th to 20th	Day	15% 20% 37% 22% 5% 1	330
	21st to end	Day	26% 24% 32% 13% 5% 1	445
March	1st to 10th	Day	24% 27% 29% 14% 5% 2	540
	11th to 20th	Day	25% 24% 25% 16% 9% 1	540
	21st to end	Day	28% 26% 25% 13% 6% 2	594
April	1st to 10th	Day	23% 25% 31% 15% 5%	540
	11th to 20th	Day	24% 23% 31% 14% 6% 1	532
	21st to end	Day	26% 20% 25% 18% 8% 2	540
May	1st to 10th	Day	22% 18% 28% 19% 10% 2	543
	11th to 20th	Day	25% 17% 22% 21% 12% 4	738
	21st to end	Day	25% 13% 21% 25% 13% 3	844
June	1st to 10th	Day	23% 21% 24% 21% 10% 2	780
	11th to 20th	Day	26% 20% 24% 20% 9% 2	780
	21st to end	Day	14% 14% 29% 25% 14% 3	780
July	1st to 10th	Day	11% 14% 28% 27% 17% 3	771
	11th to 20th	Day	14% 16% 27% 26% 15% 2	744
	21st to end	Day	9% 15% 34% 26% 13% 3	624
August	1st to 10th	Day	13% 16% 27% 29% 10% 4	527
	11th to 20th	Day	10% 13% 36% 25% 12% 5%	517
	21st to end	Day	13% 17% 33% 23% 11% 3	583
September	1st to 10th	Day	18% 20% 24% 22% 12% 4	530
	11th to 20th	Day	19% 15% 29% 22% 12% 2	530
	21st to end	Day	28% 22% 28% 15% 6% 2	530
October	1st to 10th	Day	22% 21% 30% 17% 9% 2	467
	11th to 20th	Day	25% 20% 26% 17% 10% 2	330
	21st to end	Day	30% 23% 25% 14% 6% 1	363
November	1st to 10th	Day	29% 27% 21% 18% 3 1	330
	11th to 20th	Day	33% 23% 29% 12% 3	313
	21st to end	Day	28% 23% 24% 15% 6% 5%	220
December	1st to 10th	Day	25% 26% 23% 16% 8% 1	220
	11th to 20th	Day	30% 21% 31% 14% 4 1	220
	21st to end	Day	20% 22% 33% 14% 9% 2	242
January	1st to 10th	Night	20% 22% 31% 20% 5% 1	1050
	11th to 20th	Night	14% 23% 37% 21% 5% 1	945
	21st to end	Night	12% 26% 33% 21% 7% 1	924
February	1st to 10th	Night	16% 17% 34% 22% 9% 2	840
	11th to 20th	Night	14% 17% 33% 29% 6% 1	824
	21st to end	Night	15% 17% 33% 23% 12% 1	692
March	1st to 10th	Night	14% 19% 36% 21% 9% 1	840
	11th to 20th	Night	18% 20% 28% 24% 9% 1	840
	21st to end	Night	18% 18% 25% 29% 9% 2	924
April	1st to 10th	Night	16% 19% 28% 25% 10% 2	812
	11th to 20th	Night	16% 21% 28% 24% 11% 1	623
	21st to end	Night	17% 16% 28% 26% 12% 1	630
May	1st to 10th	Night	20% 12% 23% 28% 16% 1	572
	11th to 20th	Night	20% 8% 19% 29% 22% 2	414
	21st to end	Night	24% 8% 18% 30% 19% 2	455
June	1st to 10th	Night	21% 14% 21% 30% 13% 2	420
	11th to 20th	Night	23% 13% 24% 26% 14% 1	420
	21st to end	Night	10% 11% 20% 39% 20% 1	420
July	1st to 10th	Night	10% 7% 17% 40% 26%	410
	11th to 20th	Night	8% 7% 21% 44% 18% 1	398
	21st to end	Night	10% 7% 18% 40% 24% 2	438
August	1st to 10th	Night	9% 6% 13% 40% 29% 2	398
	11th to 20th	Night	9% 6% 21% 37% 24% 3	591
	21st to end	Night	12% 9% 23% 36% 18% 2	660
September	1st to 10th	Night	13% 9% 18% 34% 23% 4	740
	11th to 20th	Night	17% 10% 19% 30% 19% 5%	800
	21st to end	Night	17% 16% 27% 24% 13% 3	800
October	1st to 10th	Night	20% 12% 21% 32% 14% 2	800
	11th to 20th	Night	17% 18% 24% 27% 13% 1	800
	21st to end	Night	18% 23% 29% 22% 7% 1	880
November	1st to 10th	Night	21% 24% 28% 22% 5% 1	864
	11th to 20th	Night	22% 27% 29% 18% 4 1	1050
	21st to end	Night	15% 22% 36% 18% 7% 1	1050
December	1st to 10th	Night	15% 22% 31% 23% 8% 1	1050
	11th to 20th	Night	16% 23% 35% 21% 4	1050
	21st to end	Night	16% 23% 32% 21% 7% 1	1155

Page generated at 2026-07-13 01:14:47. Version ac07

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