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 2024-11-02.

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	14% 5% 2 5% 4 4 5% 4 6% 8% 43%	101115
	Night	15% 5% 2 5% 4 4 4 4 6% 7% 44%	97805
Transparency	Day	20% 50% 7% 11% 10% 2	100928
	Night	21% 50% 6% 10% 10% 3	97662
Seeing	Day	16% 9% 22% 24% 18% 9%	15112
	Night	16% 7% 22% 31% 20% 3	25157

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	17% 4 1 4 3 2 2 3 3 8% 54%	2836
	11th to 20th	Day	14% 7% 2 4 3 3 3 3 3 4 54%	2840
	21st to end	Day	25% 5% 1 4 2 2 2 2 4 4 47%	3124
February	1st to 10th	Day	16% 6% 2 4 4 3 4 3 6% 7% 45%	1771
	11th to 20th	Day	19% 6% 3 5% 4 3 3 3 4 5% 46%	1848
	21st to end	Day	19% 6% 2 6% 4 4 5% 4 4 6% 41%	1570
March	1st to 10th	Day	25% 6% 2 5% 2 3 3 2 4 4 44%	3400
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 4 6% 53%	3480
	21st to end	Day	21% 6% 2 4 3 3 3 4 5% 7% 43%	3815
April	1st to 10th	Day	12% 5% 2 4 4 4 4 5% 5% 7% 49%	2090
	11th to 20th	Day	13% 5% 2 5% 4 5% 4 4 6% 7% 46%	2244
	21st to end	Day	13% 4 2 5% 4 3 5% 4 5% 7% 47%	2470
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4082
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 4 6% 7% 36%	4081
	21st to end	Day	8% 4 2 5% 4 5% 6% 4 8% 11% 43%	4476
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 3 3 2 4 4 58%	2090
November	1st to 10th	Day	12% 5% 2 4 2 3 3 2 3 6% 57%	1824
	11th to 20th	Day	14% 4 1 4 3 3 3 3 5% 6% 54%	1710
	21st to end	Day	15% 4 1 3 4 3 4 3 4 6% 52%	1710
December	1st to 10th	Day	19% 6% 2 7% 4 3 4 4 5% 6% 41%	1710
	11th to 20th	Day	16% 5% 1 3 3 3 3 3 5% 6% 52%	2153
	21st to end	Day	22% 4 2 4 3 3 3 4 5% 6% 45%	3124
January	1st to 10th	Night	17% 4 1 4 2 3 3 3 4 5% 54%	4109
	11th to 20th	Night	12% 6% 2 5% 3 4 4 4 5% 5% 52%	4120
	21st to end	Night	24% 5% 1 4 3 3 3 3 4 5% 44%	4532
February	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 5% 50%	2404
	11th to 20th	Night	20% 6% 2 4 4 3 3 3 5% 4 46%	2218
	21st to end	Night	16% 6% 2 6% 5% 4 5% 3 5% 6% 43%	1884
March	1st to 10th	Night	22% 7% 2 6% 4 4 4 3 5% 5% 39%	3451
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 5% 7% 54%	3480
	21st to end	Night	21% 4 2 5% 4 3 4 3 5% 5% 43%	3817
April	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 5% 7% 50%	2090
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 8% 49%	1898
	21st to end	Night	12% 5% 2 4 4 4 3 4 5% 5% 51%	1710
May	1st to 10th	Night	14% 6% 2 7% 4 5% 5% 4 7% 8% 40%	2813
	11th to 20th	Night	17% 5% 2 7% 4 4 4 4 6% 7% 38%	2812
	21st to end	Night	9% 5% 1 6% 5% 5% 4 5% 7% 11% 43%	3079
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% 3 1 4 3 3 3 3 3 4 59%	2508
November	1st to 10th	Night	15% 4 2 4 3 3 3 3 4 4 54%	2276
	11th to 20th	Night	15% 5% 1 4 3 3 4 3 4 6% 53%	2470
	21st to end	Night	15% 5% 1 4 3 3 4 3 6% 7% 49%	2470
December	1st to 10th	Night	19% 7% 2 6% 3 3 4 3 4 6% 43%	2470
	11th to 20th	Night	16% 5% 2 3 3 3 3 2 4 6% 54%	3042
	21st to end	Night	22% 5% 2 5% 3 4 4 3 4 6% 42%	4532

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	21% 36% 2 16% 18% 7%	2837
	11th to 20th	Day	22% 37% 3 9% 25% 5%	2840
	21st to end	Day	27% 39% 2 10% 18% 4	3124
February	1st to 10th	Day	14% 65% 3 9% 7% 2	1771
	11th to 20th	Day	17% 64% 3 7% 7% 2	1858
	21st to end	Day	17% 66% 2 4 8% 2	1570
March	1st to 10th	Day	33% 40% 5% 9% 6% 6%	3400
	11th to 20th	Day	16% 41% 4 9% 20% 10%	3480
	21st to end	Day	25% 40% 3 14% 15% 3	3815
April	1st to 10th	Day	13% 66% 4 6% 9% 2	2090
	11th to 20th	Day	15% 67% 3 7% 5% 2	2244
	21st to end	Day	13% 65% 5% 10% 6% 1	2470
May	1st to 10th	Day	25% 44% 10% 13% 7% 1	4120
	11th to 20th	Day	29% 42% 5% 14% 9%	4085
	21st to end	Day	18% 43% 12% 14% 13% 1	4489
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	13% 61% 5% 8% 11% 2	2038
	11th to 20th	Day	10% 59% 4 10% 11% 5%	1900
	21st to end	Day	13% 58% 2 11% 11% 6%	2090
November	1st to 10th	Day	17% 58% 3 8% 10% 3	1824
	11th to 20th	Day	15% 59% 3 8% 11% 3	1710
	21st to end	Day	13% 60% 4 9% 10% 3	1710
December	1st to 10th	Day	20% 60% 3 10% 5% 3	1710
	11th to 20th	Day	16% 47% 2 10% 18% 7%	2150
	21st to end	Day	26% 38% 4 15% 14% 3	3124
January	1st to 10th	Night	22% 36% 3 12% 21% 6%	4109
	11th to 20th	Night	20% 39% 5% 9% 22% 6%	4120
	21st to end	Night	28% 41% 3 9% 15% 5%	4532
February	1st to 10th	Night	13% 65% 4 8% 9% 1	2404
	11th to 20th	Night	18% 64% 3 6% 8% 2	2219
	21st to end	Night	16% 65% 4 6% 7% 3	1884
March	1st to 10th	Night	34% 43% 6% 8% 6% 3	3451
	11th to 20th	Night	14% 40% 3 12% 18% 13%	3480
	21st to end	Night	26% 41% 4 11% 13% 6%	3817
April	1st to 10th	Night	14% 66% 3 7% 8% 2	2090
	11th to 20th	Night	15% 67% 3 7% 5% 3	1898
	21st to end	Night	12% 66% 5% 10% 7% 1	1710
May	1st to 10th	Night	25% 44% 8% 15% 7% 1	2840
	11th to 20th	Night	25% 42% 9% 14% 10%	2813
	21st to end	Night	17% 43% 9% 21% 9% 1	3087
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	16% 61% 5% 7% 9% 2	2141
	11th to 20th	Night	12% 60% 4 11% 9% 5%	2280
	21st to end	Night	11% 59% 2 9% 13% 6%	2508
November	1st to 10th	Night	18% 58% 2 8% 9% 4	2276
	11th to 20th	Night	14% 60% 3 6% 11% 6%	2470
	21st to end	Night	14% 60% 3 10% 11% 2	2470
December	1st to 10th	Night	22% 60% 3 7% 6% 2	2470
	11th to 20th	Night	15% 48% 3 9% 19% 5%	3044
	21st to end	Night	29% 38% 4 14% 13% 2	4532

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% 19% 37% 19% 4	270
	11th to 20th	Day	24% 21% 30% 19% 5%	270
	21st to end	Day	22% 18% 39% 16% 5%	297
February	1st to 10th	Day	19% 20% 35% 18% 7%	270
	11th to 20th	Day	34% 22% 31% 12% 1	270
	21st to end	Day	28% 27% 30% 12% 4	225
March	1st to 10th	Day	20% 16% 30% 23% 9% 1	436
	11th to 20th	Day	20% 17% 35% 22% 5% 1	460
	21st to end	Day	22% 18% 31% 22% 7% 1	506
April	1st to 10th	Day	18% 17% 31% 22% 11% 1	460
	11th to 20th	Day	16% 16% 27% 22% 16% 2	452
	21st to end	Day	18% 10% 28% 24% 13% 6%	460
May	1st to 10th	Day	12% 13% 30% 27% 12% 6%	463
	11th to 20th	Day	17% 7% 21% 27% 20% 8%	487
	21st to end	Day	15% 4 18% 25% 24% 13%	529
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	21% 9% 22% 27% 16% 5%	416
	11th to 20th	Day	17% 17% 32% 26% 7% 2	270
	21st to end	Day	11% 15% 33% 26% 13% 2	270
December	1st to 10th	Day	26% 14% 32% 21% 7%	270
	11th to 20th	Day	21% 15% 30% 26% 7%	270
	21st to end	Day	26% 13% 35% 18% 8% 1	297
January	1st to 10th	Night	20% 13% 34% 27% 6%	760
	11th to 20th	Night	20% 10% 33% 32% 5%	760
	21st to end	Night	19% 11% 36% 31% 3	836
February	1st to 10th	Night	17% 11% 32% 36% 3	760
	11th to 20th	Night	22% 13% 39% 25% 2	743
	21st to end	Night	17% 13% 39% 27% 3	628
March	1st to 10th	Night	18% 11% 30% 35% 6%	760
	11th to 20th	Night	19% 12% 33% 28% 7% 1	760
	21st to end	Night	19% 9% 33% 31% 8%	836
April	1st to 10th	Night	16% 13% 31% 29% 11%	760
	11th to 20th	Night	16% 11% 26% 32% 14% 1	702
	21st to end	Night	14% 6% 25% 37% 18% 1	570
May	1st to 10th	Night	13% 7% 24% 34% 20% 1	570
	11th to 20th	Night	17% 4 19% 32% 25% 3	561
	21st to end	Night	15% 2 9% 32% 36% 6%	617
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	16% 6% 21% 37% 17% 3	745
	11th to 20th	Night	15% 9% 27% 36% 12% 1	760
	21st to end	Night	17% 8% 27% 32% 15% 1	760
December	1st to 10th	Night	23% 8% 27% 34% 8%	760
	11th to 20th	Night	18% 7% 30% 36% 9% 1	760
	21st to end	Night	26% 8% 27% 32% 7%	836

Page generated at 2024-10-30 01:22:56. Version ac07

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