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 2026-09-29.

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 6% 4 4 5% 4 6% 8% 43%	148933
	Night	14% 6% 2 5% 4 4 4 4 6% 7% 44%	142484
Transparency	Day	25% 36% 9% 14% 12% 4	152631
	Night	26% 36% 8% 13% 13% 5%	146858
Seeing	Day	17% 10% 22% 24% 18% 9%	17668
	Night	16% 7% 23% 31% 20% 3	27677

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	15% 5% 2 5% 3 2 2 2 3 6% 54%	5258
	11th to 20th	Day	10% 5% 1 3 3 2 2 2 3 3 65%	5280
	21st to end	Day	19% 7% 2 6% 4 4 3 3 4 5% 44%	5780
February	1st to 10th	Day	15% 6% 2 4 4 3 4 3 6% 7% 46%	1959
	11th to 20th	Day	19% 6% 2 5% 4 3 3 4 4 6% 45%	2048
	21st to end	Day	18% 5% 2 6% 4 4 5% 4 4 6% 42%	1730
March	1st to 10th	Day	20% 5% 2 5% 3 4 4 3 5% 5% 44%	4995
	11th to 20th	Day	11% 5% 2 5% 4 3 3 2 4 6% 55%	5090
	21st to end	Day	19% 6% 2 4 3 3 3 3 4 6% 48%	5586
April	1st to 10th	Day	13% 5% 2 4 4 4 4 5% 5% 7% 48%	2310
	11th to 20th	Day	12% 4 2 5% 4 5% 4 3 6% 7% 48%	2483
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 5% 7% 47%	2730
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	7616
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 7% 8% 38%	7626
	21st to end	Day	16% 7% 2 7% 4 5% 6% 4 7% 9% 32%	8391
June	1st to 10th	Day	9% 5% 3 6% 5% 5% 7% 6% 8% 12% 34%	2730
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 6% 8% 11% 39%	2730
	21st to end	Day	8% 4 2 5% 5% 6% 6% 6% 8% 11% 39%	2730
July	1st to 10th	Day	5% 3 2 6% 5% 6% 6% 6% 9% 12% 40%	7680
	11th to 20th	Day	8% 5% 2 8% 6% 6% 7% 6% 9% 11% 32%	7680
	21st to end	Day	9% 6% 3 8% 6% 7% 7% 6% 9% 11% 28%	8340
August	1st to 10th	Day	16% 7% 3 8% 5% 6% 7% 6% 9% 11% 23%	6014
	11th to 20th	Day	6% 4 2 5% 4 5% 7% 5% 8% 13% 41%	5951
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 9% 50%	6107
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 8% 44%	2310
	11th to 20th	Day	16% 5% 2 7% 4 3 4 4 6% 7% 42%	2310
	21st to end	Day	18% 5% 2 6% 4 3 4 4 5% 7% 42%	2288
October	1st to 10th	Day	15% 4 1 4 3 3 3 2 4 6% 55%	2145
	11th to 20th	Day	13% 4 2 3 2 2 3 2 3 5% 61%	2000
	21st to end	Day	14% 4 2 3 3 3 3 2 4 4 58%	2200
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 2 3 5% 57%	2008
	11th to 20th	Day	14% 4 1 3 3 2 3 2 5% 7% 55%	1890
	21st to end	Day	15% 4 2 4 3 4 3 3 4 6% 52%	1890
December	1st to 10th	Day	15% 5% 1 5% 3 3 4 3 4 5% 53%	3020
	11th to 20th	Day	18% 5% 1 4 3 4 4 3 6% 7% 45%	3463
	21st to end	Day	23% 4 1 3 2 2 3 3 4 6% 48%	4565
January	1st to 10th	Night	15% 4 1 3 2 2 2 2 3 4 59%	7635
	11th to 20th	Night	11% 5% 2 4 2 3 3 2 4 4 60%	7680
	21st to end	Night	18% 6% 2 5% 3 3 3 3 4 5% 47%	8401
February	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 5% 50%	2656
	11th to 20th	Night	20% 6% 2 4 4 3 3 3 5% 4 45%	2458
	21st to end	Night	15% 5% 2 6% 5% 4 5% 3 5% 6% 44%	2076
March	1st to 10th	Night	19% 5% 2 5% 3 3 4 3 5% 6% 45%	5076
	11th to 20th	Night	10% 4 2 3 3 3 3 3 5% 7% 56%	5090
	21st to end	Night	17% 4 2 5% 4 3 4 4 5% 6% 46%	5588
April	1st to 10th	Night	13% 5% 2 5% 4 3 4 4 5% 6% 49%	2310
	11th to 20th	Night	12% 5% 2 5% 3 2 3 3 6% 8% 51%	2100
	21st to end	Night	12% 6% 2 4 4 4 3 4 6% 6% 50%	1890
May	1st to 10th	Night	13% 6% 2 7% 5% 5% 5% 4 8% 10% 37%	5237
	11th to 20th	Night	17% 5% 2 7% 4 5% 4 3 6% 8% 38%	5234
	21st to end	Night	18% 7% 2 7% 5% 5% 4 4 6% 8% 33%	5761
June	1st to 10th	Night	9% 5% 3 7% 5% 5% 7% 6% 10% 11% 32%	1890
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 5% 7% 11% 38%	1890
	21st to end	Night	8% 5% 2 6% 5% 6% 6% 5% 7% 11% 40%	1890
July	1st to 10th	Night	7% 5% 3 7% 6% 7% 8% 6% 9% 10% 33%	5278
	11th to 20th	Night	11% 6% 2 8% 6% 6% 6% 6% 9% 12% 28%	5277
	21st to end	Night	13% 9% 3 9% 6% 6% 6% 5% 8% 12% 24%	5736
August	1st to 10th	Night	18% 8% 3 9% 6% 6% 6% 6% 7% 11% 22%	4135
	11th to 20th	Night	9% 6% 2 7% 6% 5% 6% 5% 8% 11% 35%	4095
	21st to end	Night	8% 6% 2 7% 5% 5% 6% 4 7% 8% 42%	4965
September	1st to 10th	Night	11% 5% 3 6% 5% 5% 4 4 7% 8% 42%	2310
	11th to 20th	Night	16% 7% 3 7% 6% 4 5% 4 6% 7% 35%	2310
	21st to end	Night	19% 5% 2 5% 4 4 4 3 5% 7% 42%	2289
October	1st to 10th	Night	17% 4 2 4 4 3 4 3 4 5% 50%	2254
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 4 6% 55%	2400
	21st to end	Night	15% 4 1 4 2 3 3 3 3 4 59%	2640
November	1st to 10th	Night	15% 4 2 4 4 3 3 3 4 5% 54%	2508
	11th to 20th	Night	14% 5% 1 4 3 3 4 3 4 6% 55%	2730
	21st to end	Night	14% 5% 1 4 3 4 4 3 5% 7% 51%	2730
December	1st to 10th	Night	14% 6% 2 4 3 3 3 2 4 5% 54%	4380
	11th to 20th	Night	20% 5% 2 5% 3 3 4 2 4 6% 45%	4952
	21st to end	Night	22% 4 1 4 3 3 3 3 4 5% 48%	6633

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	28% 21% 7% 15% 24% 6%	5259
	11th to 20th	Day	19% 21% 3 8% 33% 16%	5280
	21st to end	Day	35% 22% 3 13% 17% 9%	5780
February	1st to 10th	Day	16% 59% 4 11% 8% 2	1959
	11th to 20th	Day	19% 59% 4 8% 8% 2	2058
	21st to end	Day	18% 60% 3 4 11% 3	1730
March	1st to 10th	Day	34% 29% 5% 10% 11% 10%	4995
	11th to 20th	Day	20% 29% 4 9% 21% 18%	5090
	21st to end	Day	27% 28% 4 19% 17% 5%	5586
April	1st to 10th	Day	16% 60% 5% 8% 9% 2	2310
	11th to 20th	Day	15% 61% 3 10% 8% 3	2483
	21st to end	Day	15% 60% 6% 12% 7% 1	2730
May	1st to 10th	Day	32% 28% 12% 19% 9% 1	7651
	11th to 20th	Day	33% 26% 10% 18% 10% 2	7630
	21st to end	Day	39% 28% 10% 12% 10% 2	8405
June	1st to 10th	Day	17% 61% 7% 9% 4 1	2730
	11th to 20th	Day	12% 63% 10% 10% 5%	2730
	21st to end	Day	14% 62% 9% 10% 5%	2730
July	1st to 10th	Day	24% 30% 19% 21% 6%	7615
	11th to 20th	Day	32% 30% 22% 14% 2	7611
	21st to end	Day	38% 28% 13% 14% 7% 1	8156
August	1st to 10th	Day	40% 35% 14% 10% 2	6001
	11th to 20th	Day	17% 33% 24% 18% 7% 1	5990
	21st to end	Day	18% 31% 11% 25% 15% 1	6107
September	1st to 10th	Day	14% 58% 7% 11% 10% 1	2310
	11th to 20th	Day	19% 57% 6% 10% 7% 1	2310
	21st to end	Day	20% 56% 7% 9% 6% 1	2288
October	1st to 10th	Day	15% 38% 5% 13% 22% 7%	3496
	11th to 20th	Day	8% 36% 3 11% 21% 21%	3240
	21st to end	Day	18% 35% 3 16% 14% 14%	3538
November	1st to 10th	Day	19% 53% 3 9% 11% 4	2008
	11th to 20th	Day	15% 54% 4 11% 13% 4	1890
	21st to end	Day	14% 55% 5% 11% 12% 3	1890
December	1st to 10th	Day	21% 35% 4 13% 20% 7%	3020
	11th to 20th	Day	28% 33% 7% 10% 18% 6%	3460
	21st to end	Day	29% 27% 6% 23% 14% 2	4565
January	1st to 10th	Night	24% 21% 7% 18% 24% 6%	7636
	11th to 20th	Night	21% 22% 4 11% 32% 10%	7680
	21st to end	Night	31% 24% 5% 15% 18% 9%	8401
February	1st to 10th	Night	15% 60% 5% 10% 9% 2	2656
	11th to 20th	Night	21% 58% 4 7% 9% 1	2459
	21st to end	Night	17% 59% 4 7% 10% 4	2076
March	1st to 10th	Night	31% 30% 6% 10% 18% 5%	5076
	11th to 20th	Night	16% 29% 4 11% 24% 16%	5090
	21st to end	Night	27% 29% 5% 17% 15% 7%	5588
April	1st to 10th	Night	16% 60% 5% 8% 9% 2	2310
	11th to 20th	Night	14% 61% 4 11% 8% 3	2100
	21st to end	Night	15% 60% 6% 11% 8% 1	1890
May	1st to 10th	Night	33% 27% 11% 20% 8% 2	5264
	11th to 20th	Night	34% 26% 11% 19% 9% 1	5235
	21st to end	Night	39% 27% 9% 15% 8% 2	5771
June	1st to 10th	Night	17% 63% 7% 7% 5% 2	1890
	11th to 20th	Night	14% 63% 10% 8% 5%	1890
	21st to end	Night	15% 60% 11% 8% 7%	1890
July	1st to 10th	Night	31% 30% 20% 15% 3	5235
	11th to 20th	Night	36% 32% 20% 10% 2	5226
	21st to end	Night	43% 27% 13% 11% 4 2	5606
August	1st to 10th	Night	44% 34% 12% 9% 1	4124
	11th to 20th	Night	26% 35% 20% 16% 4	4122
	21st to end	Night	24% 32% 10% 24% 9% 1	4965
September	1st to 10th	Night	15% 58% 8% 10% 8% 1	2310
	11th to 20th	Night	21% 58% 7% 7% 6% 1	2310
	21st to end	Night	21% 57% 8% 8% 6%	2289
October	1st to 10th	Night	18% 41% 7% 11% 18% 5%	3683
	11th to 20th	Night	10% 36% 3 12% 22% 18%	3899
	21st to end	Night	18% 37% 3 12% 18% 12%	4252
November	1st to 10th	Night	20% 54% 3 9% 10% 4	2508
	11th to 20th	Night	15% 54% 4 8% 13% 6%	2730
	21st to end	Night	15% 55% 3 11% 13% 2	2730
December	1st to 10th	Night	21% 35% 4 15% 19% 6%	4380
	11th to 20th	Night	31% 32% 5% 11% 15% 6%	4954
	21st to end	Night	30% 27% 8% 19% 16% 2	6633

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	330
	11th to 20th	Day	24% 24% 29% 18% 5%	330
	21st to end	Day	22% 20% 37% 16% 4	363
February	1st to 10th	Day	17% 20% 38% 18% 6%	330
	11th to 20th	Day	36% 21% 30% 12% 1	330
	21st to end	Day	29% 24% 30% 13% 4	273
March	1st to 10th	Day	22% 16% 29% 23% 9% 1	514
	11th to 20th	Day	21% 17% 33% 23% 5% 1	540
	21st to end	Day	20% 19% 32% 22% 6% 1	594
April	1st to 10th	Day	19% 16% 30% 23% 11% 1	540
	11th to 20th	Day	15% 16% 29% 23% 15% 2	532
	21st to end	Day	18% 10% 28% 24% 13% 6%	540
May	1st to 10th	Day	14% 13% 31% 26% 11% 5%	543
	11th to 20th	Day	17% 9% 21% 27% 18% 8%	567
	21st to end	Day	17% 7% 18% 24% 22% 11%	617
June	1st to 10th	Day	11% 5% 19% 30% 22% 12%	570
	11th to 20th	Day	9% 5% 19% 26% 24% 17%	570
	21st to end	Day	9% 4 14% 29% 27% 16%	570
July	1st to 10th	Day	7% 2 10% 27% 28% 26%	565
	11th to 20th	Day	8% 2 7% 25% 33% 25%	564
	21st to end	Day	7% 5% 10% 27% 30% 22%	620
August	1st to 10th	Day	19% 4 13% 22% 24% 18%	566
	11th to 20th	Day	11% 3 10% 27% 31% 19%	559
	21st to end	Day	11% 3 14% 21% 31% 21%	627
September	1st to 10th	Day	8% 3 14% 25% 31% 18%	570
	11th to 20th	Day	18% 4 11% 19% 31% 18%	570
	21st to end	Day	20% 5% 17% 27% 23% 8%	562
October	1st to 10th	Day	18% 5% 15% 29% 22% 11%	530
	11th to 20th	Day	14% 8% 22% 30% 22% 4	530
	21st to end	Day	19% 8% 21% 31% 17% 4	583
November	1st to 10th	Day	21% 10% 24% 27% 14% 4	486
	11th to 20th	Day	16% 17% 33% 25% 7% 2	330
	21st to end	Day	13% 16% 32% 25% 12% 2	330
December	1st to 10th	Day	27% 15% 32% 20% 6%	330
	11th to 20th	Day	22% 15% 31% 25% 7%	330
	21st to end	Day	26% 13% 32% 19% 8% 1	363
January	1st to 10th	Night	20% 14% 34% 27% 6%	840
	11th to 20th	Night	19% 11% 35% 30% 4	840
	21st to end	Night	18% 11% 38% 30% 3	924
February	1st to 10th	Night	17% 12% 32% 36% 3	840
	11th to 20th	Night	22% 13% 39% 24% 2	823
	21st to end	Night	18% 13% 39% 27% 3	692
March	1st to 10th	Night	18% 12% 31% 34% 5%	840
	11th to 20th	Night	18% 13% 32% 29% 7% 1	840
	21st to end	Night	18% 10% 34% 31% 7%	924
April	1st to 10th	Night	16% 13% 31% 30% 11%	840
	11th to 20th	Night	15% 11% 27% 32% 13% 1	776
	21st to end	Night	13% 6% 25% 37% 18% 1	630
May	1st to 10th	Night	13% 7% 25% 35% 19% 1	630
	11th to 20th	Night	17% 5% 19% 32% 25% 3	621
	21st to end	Night	17% 3 10% 31% 33% 5%	683
June	1st to 10th	Night	10% 2 13% 35% 35% 4	630
	11th to 20th	Night	12% 3 12% 30% 31% 12%	630
	21st to end	Night	8% 2 10% 29% 43% 8%	630
July	1st to 10th	Night	10% 2 6% 24% 48% 10%	615
	11th to 20th	Night	9% 2 5% 23% 48% 13%	612
	21st to end	Night	8% 2 8% 29% 42% 11%	690
August	1st to 10th	Night	17% 3 7% 25% 39% 9%	627
	11th to 20th	Night	15% 3 7% 27% 38% 11%	624
	21st to end	Night	12% 3 7% 26% 44% 9%	779
September	1st to 10th	Night	12% 2 8% 30% 39% 9%	840
	11th to 20th	Night	17% 3 12% 25% 36% 7%	840
	21st to end	Night	20% 4 14% 32% 28% 3	833
October	1st to 10th	Night	17% 4 16% 29% 28% 6%	800
	11th to 20th	Night	16% 6% 22% 33% 21% 2	800
	21st to end	Night	16% 7% 22% 36% 18% 2	880
November	1st to 10th	Night	16% 6% 21% 38% 16% 2	820
	11th to 20th	Night	15% 9% 28% 36% 11% 1	840
	21st to end	Night	16% 9% 28% 32% 14% 1	840
December	1st to 10th	Night	23% 9% 28% 34% 7%	840
	11th to 20th	Night	19% 7% 30% 35% 8%	840
	21st to end	Night	25% 8% 27% 33% 7%	924

Page generated at 2026-09-26 04:18:43. Version ac07

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