Squirrel Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Squirrel Valley Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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% 5% 2 5% 4 4 4 4 6% 7% 45%	114541
	Night	14% 5% 2 5% 4 4 4 4 5% 7% 46%	114749
Transparency	Day	21% 43% 7% 12% 12% 5%	118283
	Night	22% 42% 6% 12% 14% 5%	119146
Seeing	Day	17% 10% 22% 24% 18% 9%	15818
	Night	16% 7% 23% 31% 20% 3	25940

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	14% 4 2 5% 3 2 2 2 3 6% 58%	4056
	11th to 20th	Day	11% 5% 2 3 3 3 2 2 3 3 63%	4060
	21st to end	Day	18% 5% 1 5% 4 4 3 3 4 5% 48%	4466
February	1st to 10th	Day	15% 6% 2 4 4 3 4 3 6% 7% 45%	1865
	11th to 20th	Day	19% 6% 2 5% 4 3 3 3 4 5% 45%	1948
	21st to end	Day	18% 6% 2 6% 4 4 5% 4 4 6% 42%	1650
March	1st to 10th	Day	21% 6% 2 5% 3 4 4 3 4 5% 44%	4886
	11th to 20th	Day	10% 5% 2 5% 4 3 3 2 4 6% 55%	4980
	21st to end	Day	19% 6% 2 4 3 3 3 3 4 6% 47%	5465
April	1st to 10th	Day	13% 5% 2 4 4 4 4 5% 5% 7% 48%	2200
	11th to 20th	Day	13% 5% 2 5% 4 5% 4 3 6% 7% 47%	2364
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 5% 7% 47%	2600
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4212
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 6% 7% 35%	4211
	21st to end	Day	8% 4 2 5% 4 5% 6% 4 8% 11% 43%	4541
June	1st to 10th	Day	9% 6% 3 6% 6% 6% 7% 5% 8% 12% 33%	2470
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 6% 9% 11% 39%	2470
	21st to end	Day	8% 4 2 6% 5% 6% 6% 6% 8% 10% 38%	2470
July	1st to 10th	Day	8% 4 2 7% 6% 6% 6% 5% 9% 11% 36%	4120
	11th to 20th	Day	7% 5% 2 7% 6% 5% 7% 5% 9% 10% 35%	4120
	21st to end	Day	10% 8% 3 9% 8% 8% 8% 6% 9% 10% 22%	4466
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 6% 5% 8% 10% 29%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 7% 5% 8% 12% 36%	4044
	21st to end	Day	7% 3 2 5% 5% 4 4 3 6% 9% 52%	4195
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 8% 42%	2090
	11th to 20th	Day	17% 5% 2 7% 4 3 4 4 6% 7% 41%	2090
	21st to end	Day	18% 5% 2 6% 4 3 4 4 5% 7% 42%	2090
October	1st to 10th	Day	16% 4 1 4 3 3 3 2 4 6% 55%	2038
	11th to 20th	Day	13% 4 2 3 2 2 2 2 3 5% 60%	1900
	21st to end	Day	14% 4 2 3 3 2 3 2 4 4 58%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 2 3 6% 56%	1911
	11th to 20th	Day	14% 4 1 4 3 3 3 2 5% 7% 54%	1800
	21st to end	Day	15% 4 1 4 3 4 3 3 4 6% 52%	1800
December	1st to 10th	Day	15% 4 1 5% 3 3 3 3 4 5% 54%	2930
	11th to 20th	Day	18% 5% 1 4 3 4 4 3 6% 7% 44%	3373
	21st to end	Day	23% 4 1 4 2 2 3 3 4 6% 48%	4466
January	1st to 10th	Night	14% 4 1 3 2 2 2 2 3 4 62%	5889
	11th to 20th	Night	12% 5% 1 4 2 3 3 3 4 4 59%	5900
	21st to end	Night	18% 6% 1 4 3 3 3 3 4 6% 49%	6490
February	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	2530
	11th to 20th	Night	20% 6% 2 4 4 3 3 3 5% 4 45%	2338
	21st to end	Night	15% 5% 2 5% 5% 4 5% 3 5% 6% 45%	1980
March	1st to 10th	Night	19% 5% 2 5% 3 3 4 3 5% 6% 45%	4965
	11th to 20th	Night	10% 4 2 3 3 3 3 3 5% 7% 56%	4980
	21st to end	Night	17% 4 2 5% 4 3 4 4 5% 5% 46%	5467
April	1st to 10th	Night	13% 5% 2 5% 4 3 4 4 5% 6% 50%	2200
	11th to 20th	Night	12% 5% 2 5% 3 2 3 3 5% 8% 50%	1999
	21st to end	Night	12% 5% 2 4 4 4 3 4 6% 6% 50%	1800
May	1st to 10th	Night	13% 6% 2 7% 4 5% 5% 4 7% 9% 40%	2903
	11th to 20th	Night	18% 5% 2 7% 4 4 4 4 6% 7% 38%	2902
	21st to end	Night	9% 4 2 6% 5% 5% 4 5% 7% 11% 43%	3130
June	1st to 10th	Night	10% 5% 3 7% 5% 5% 6% 6% 10% 11% 32%	1710
	11th to 20th	Night	10% 7% 2 5% 5% 5% 5% 5% 7% 11% 38%	1710
	21st to end	Night	9% 5% 2 6% 5% 6% 6% 5% 7% 10% 39%	1710
July	1st to 10th	Night	9% 6% 3 8% 7% 7% 7% 6% 9% 9% 29%	2840
	11th to 20th	Night	9% 6% 2 7% 5% 6% 6% 6% 9% 12% 33%	2840
	21st to end	Night	12% 9% 4 9% 6% 7% 7% 6% 9% 11% 20%	3087
August	1st to 10th	Night	15% 8% 3 8% 5% 6% 5% 6% 7% 10% 27%	2825
	11th to 20th	Night	12% 6% 2 8% 6% 6% 6% 5% 8% 9% 30%	2785
	21st to end	Night	7% 5% 2 6% 5% 5% 6% 4 7% 8% 44%	3422
September	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 4 7% 8% 40%	2090
	11th to 20th	Night	17% 7% 3 7% 5% 4 5% 4 6% 8% 34%	2090
	21st to end	Night	18% 6% 2 5% 4 4 4 3 5% 7% 43%	2090
October	1st to 10th	Night	17% 4 2 4 4 3 4 3 4 5% 51%	2141
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 4 6% 54%	2280
	21st to end	Night	14% 4 1 4 3 3 3 3 3 4 59%	2508
November	1st to 10th	Night	16% 4 2 4 3 3 3 3 4 5% 53%	2386
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 4 6% 53%	2600
	21st to end	Night	14% 5% 1 4 3 3 4 3 5% 7% 51%	2600
December	1st to 10th	Night	14% 6% 1 4 3 3 3 2 4 5% 55%	4250
	11th to 20th	Night	20% 5% 2 5% 3 3 4 2 4 6% 45%	4822
	21st to end	Night	22% 4 1 4 3 3 3 3 4 5% 48%	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	22% 26% 3 13% 29% 7%	4057
	11th to 20th	Day	19% 26% 3 10% 32% 10%	4060
	21st to end	Day	29% 28% 3 13% 20% 7%	4466
February	1st to 10th	Day	14% 62% 4 10% 7% 2	1865
	11th to 20th	Day	18% 61% 3 7% 8% 2	1958
	21st to end	Day	17% 63% 2 4 11% 2	1650
March	1st to 10th	Day	34% 29% 5% 10% 11% 10%	4886
	11th to 20th	Day	19% 30% 4 9% 21% 18%	4980
	21st to end	Day	28% 29% 3 18% 17% 5%	5465
April	1st to 10th	Day	15% 63% 5% 7% 9% 2	2200
	11th to 20th	Day	15% 64% 3 9% 6% 3	2364
	21st to end	Day	15% 62% 6% 10% 6% 1	2600
May	1st to 10th	Day	25% 43% 11% 13% 7% 1	4250
	11th to 20th	Day	30% 41% 6% 14% 9%	4215
	21st to end	Day	18% 42% 11% 14% 13% 2	4554
June	1st to 10th	Day	16% 67% 6% 7% 3 1	2470
	11th to 20th	Day	10% 68% 8% 9% 5%	2470
	21st to end	Day	14% 67% 8% 7% 4	2470
July	1st to 10th	Day	23% 44% 14% 14% 5%	4055
	11th to 20th	Day	24% 42% 19% 14% 1	4051
	21st to end	Day	40% 42% 8% 7% 2 1	4324
August	1st to 10th	Day	32% 41% 12% 13% 2	4091
	11th to 20th	Day	18% 44% 19% 11% 8% 2	4083
	21st to end	Day	12% 39% 9% 23% 16% 1	4195
September	1st to 10th	Day	14% 63% 5% 9% 8% 1	2090
	11th to 20th	Day	18% 62% 5% 7% 6% 2	2090
	21st to end	Day	18% 61% 6% 9% 6%	2090
October	1st to 10th	Day	15% 39% 5% 12% 22% 7%	3389
	11th to 20th	Day	8% 37% 3 10% 21% 21%	3140
	21st to end	Day	17% 37% 3 16% 13% 14%	3428
November	1st to 10th	Day	19% 56% 3 9% 10% 3	1911
	11th to 20th	Day	15% 57% 3 9% 12% 4	1800
	21st to end	Day	13% 57% 5% 10% 12% 3	1800
December	1st to 10th	Day	20% 36% 4 13% 20% 7%	2930
	11th to 20th	Day	28% 34% 6% 10% 17% 5%	3370
	21st to end	Day	29% 27% 6% 22% 14% 2	4466
January	1st to 10th	Night	20% 26% 3 13% 31% 8%	5889
	11th to 20th	Night	20% 28% 4 11% 30% 8%	5900
	21st to end	Night	26% 29% 3 13% 19% 8%	6490
February	1st to 10th	Night	14% 62% 4 10% 8% 1	2530
	11th to 20th	Night	20% 61% 4 6% 8% 2	2339
	21st to end	Night	15% 62% 3 7% 9% 3	1980
March	1st to 10th	Night	31% 31% 5% 9% 19% 5%	4965
	11th to 20th	Night	16% 29% 4 11% 24% 17%	4980
	21st to end	Night	27% 30% 4 17% 15% 7%	5467
April	1st to 10th	Night	15% 63% 4 8% 9% 2	2200
	11th to 20th	Night	15% 63% 3 9% 7% 3	1999
	21st to end	Night	14% 63% 6% 10% 7% 1	1800
May	1st to 10th	Night	26% 43% 8% 15% 7% 1	2930
	11th to 20th	Night	26% 41% 9% 14% 10%	2903
	21st to end	Night	17% 43% 10% 20% 10% 1	3138
June	1st to 10th	Night	15% 68% 6% 6% 4 1	1710
	11th to 20th	Night	12% 69% 8% 7% 4	1710
	21st to end	Night	13% 66% 9% 6% 6%	1710
July	1st to 10th	Night	29% 43% 13% 11% 4	2795
	11th to 20th	Night	24% 43% 17% 13% 2	2786
	21st to end	Night	40% 42% 9% 7% 1 1	2988
August	1st to 10th	Night	34% 42% 13% 9% 2	2814
	11th to 20th	Night	27% 46% 13% 9% 6%	2812
	21st to end	Night	17% 41% 7% 23% 11% 1	3422
September	1st to 10th	Night	14% 63% 7% 8% 7% 1	2090
	11th to 20th	Night	19% 63% 6% 6% 5% 1	2090
	21st to end	Night	19% 61% 7% 8% 5%	2090
October	1st to 10th	Night	18% 42% 7% 10% 18% 6%	3570
	11th to 20th	Night	9% 37% 3 12% 21% 18%	3779
	21st to end	Night	18% 38% 3 12% 17% 13%	4120
November	1st to 10th	Night	20% 56% 3 9% 8% 4	2386
	11th to 20th	Night	15% 57% 4 7% 12% 6%	2600
	21st to end	Night	14% 57% 3 11% 13% 2	2600
December	1st to 10th	Night	20% 36% 4 15% 20% 6%	4250
	11th to 20th	Night	31% 33% 5% 11% 14% 6%	4824
	21st to end	Night	30% 27% 8% 18% 16% 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	21% 20% 38% 18% 4	300
	11th to 20th	Day	24% 23% 29% 19% 5%	300
	21st to end	Day	21% 19% 39% 17% 5%	330
February	1st to 10th	Day	18% 19% 38% 18% 7%	300
	11th to 20th	Day	36% 21% 30% 12% 1	300
	21st to end	Day	27% 25% 31% 14% 4	249
March	1st to 10th	Day	23% 16% 29% 23% 8% 1	475
	11th to 20th	Day	21% 17% 34% 22% 5% 1	500
	21st to end	Day	22% 19% 31% 21% 6% 1	550
April	1st to 10th	Day	20% 17% 31% 21% 10% 1	500
	11th to 20th	Day	15% 16% 29% 22% 15% 2	492
	21st to end	Day	18% 10% 28% 24% 14% 6%	500
May	1st to 10th	Day	13% 13% 31% 27% 12% 5%	503
	11th to 20th	Day	18% 8% 21% 27% 19% 8%	527
	21st to end	Day	14% 5% 19% 25% 23% 13%	549
June	1st to 10th	Day	11% 3 18% 31% 23% 12%	490
	11th to 20th	Day	11% 4 16% 27% 24% 18%	490
	21st to end	Day	10% 4 15% 29% 26% 15%	490
July	1st to 10th	Day	8% 2 10% 25% 29% 26%	485
	11th to 20th	Day	8% 2 7% 25% 33% 25%	484
	21st to end	Day	6% 3 10% 28% 30% 23%	532
August	1st to 10th	Day	18% 2 14% 22% 26% 19%	486
	11th to 20th	Day	11% 2 11% 29% 29% 18%	479
	21st to end	Day	12% 2 12% 19% 31% 23%	539
September	1st to 10th	Day	9% 3 14% 25% 31% 18%	490
	11th to 20th	Day	19% 4 11% 19% 30% 16%	490
	21st to end	Day	20% 5% 17% 27% 23% 8%	490
October	1st to 10th	Day	19% 5% 14% 28% 23% 11%	490
	11th to 20th	Day	14% 9% 22% 29% 21% 5%	490
	21st to end	Day	19% 7% 19% 32% 18% 5%	539
November	1st to 10th	Day	22% 9% 23% 26% 15% 4	449
	11th to 20th	Day	17% 16% 33% 25% 7% 2	300
	21st to end	Day	12% 16% 33% 24% 12% 2	300
December	1st to 10th	Day	26% 15% 32% 21% 7%	300
	11th to 20th	Day	22% 15% 30% 26% 7%	300
	21st to end	Day	26% 12% 32% 19% 8% 1	330
January	1st to 10th	Night	20% 14% 34% 27% 6%	800
	11th to 20th	Night	20% 11% 34% 31% 5%	800
	21st to end	Night	18% 11% 37% 30% 3	880
February	1st to 10th	Night	17% 12% 32% 36% 3	800
	11th to 20th	Night	23% 13% 39% 25% 2	783
	21st to end	Night	17% 13% 40% 28% 3	660
March	1st to 10th	Night	18% 12% 31% 34% 6%	800
	11th to 20th	Night	19% 13% 33% 28% 7% 1	800
	21st to end	Night	19% 10% 33% 31% 7%	880
April	1st to 10th	Night	16% 13% 31% 29% 10%	800
	11th to 20th	Night	16% 11% 27% 32% 14% 1	739
	21st to end	Night	14% 6% 25% 37% 18% 1	600
May	1st to 10th	Night	14% 7% 25% 35% 20% 1	600
	11th to 20th	Night	17% 5% 20% 31% 25% 3	591
	21st to end	Night	15% 2 10% 32% 35% 5%	634
June	1st to 10th	Night	11% 2 13% 34% 36% 5%	570
	11th to 20th	Night	12% 3 11% 30% 31% 13%	570
	21st to end	Night	8% 2 11% 29% 42% 8%	570
July	1st to 10th	Night	11% 2 6% 25% 48% 9%	555
	11th to 20th	Night	9% 1 5% 23% 49% 12%	552
	21st to end	Night	8% 2 8% 29% 43% 12%	624
August	1st to 10th	Night	15% 2 7% 26% 40% 10%	567
	11th to 20th	Night	14% 2 7% 28% 38% 10%	564
	21st to end	Night	12% 3 6% 25% 45% 9%	705
September	1st to 10th	Night	12% 2 9% 29% 39% 9%	760
	11th to 20th	Night	19% 3 12% 25% 35% 7%	760
	21st to end	Night	20% 4 14% 31% 28% 3	760
October	1st to 10th	Night	18% 4 16% 28% 28% 6%	760
	11th to 20th	Night	17% 6% 22% 32% 22% 2	760
	21st to end	Night	15% 6% 21% 37% 19% 2	836
November	1st to 10th	Night	17% 6% 21% 37% 17% 2	780
	11th to 20th	Night	15% 9% 28% 36% 12% 1	800
	21st to end	Night	16% 9% 27% 32% 14% 1	800
December	1st to 10th	Night	23% 9% 27% 34% 8%	800
	11th to 20th	Night	19% 7% 30% 35% 9% 1	800
	21st to end	Night	26% 8% 27% 33% 7%	880

Page generated at 2025-05-23 09:21:01. Version ac07

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