Starlight Cascade Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Cascade Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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	16% 10% 3 8% 5% 4 4 4 5% 7% 33%	132488
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 32%	130645
Transparency	Day	50% 6% 12% 21% 11% 1	136005
	Night	51% 6% 11% 20% 11% 1	135215
Seeing	Day	23% 16% 31% 19% 8% 2	16432
	Night	22% 13% 31% 24% 9% 1	25688

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	14% 14% 4 11% 6% 5% 5% 4 6% 6% 27%	4661
	11th to 20th	Day	11% 21% 9% 15% 7% 5% 4 3 4 4 17%	4650
	21st to end	Day	11% 16% 7% 15% 7% 7% 5% 3 4 5% 20%	5637
February	1st to 10th	Day	15% 16% 3 12% 6% 4 5% 4 6% 5% 24%	1890
	11th to 20th	Day	12% 16% 4 11% 8% 6% 5% 3 4 5% 27%	1843
	21st to end	Day	19% 15% 5% 10% 7% 6% 4 3 4 5% 23%	1705
March	1st to 10th	Day	19% 13% 4 10% 5% 4 3 3 4 6% 30%	4735
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 4 5% 6% 32%	5090
	21st to end	Day	20% 11% 3 7% 5% 4 3 3 3 5% 37%	5791
April	1st to 10th	Day	20% 14% 3 8% 5% 4 3 3 3 6% 32%	2520
	11th to 20th	Day	22% 10% 2 5% 4 4 3 2 4 6% 36%	2494
	21st to end	Day	22% 10% 3 8% 5% 3 4 3 5% 6% 32%	2641
May	1st to 10th	Day	23% 10% 3 8% 5% 4 4 3 5% 6% 28%	6431
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 3 5% 7% 35%	6458
	21st to end	Day	20% 8% 2 6% 4 4 5% 4 6% 7% 34%	7103
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 8% 39%	2800
	21st to end	Day	17% 8% 3 6% 5% 4 4 4 6% 8% 35%	2800
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 10% 38%	6360
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	6360
	21st to end	Day	9% 5% 2 5% 5% 4 5% 4 7% 10% 44%	6926
August	1st to 10th	Day	16% 8% 3 6% 4 4 4 4 6% 8% 38%	4309
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 9% 37%	4156
	21st to end	Day	14% 5% 2 6% 4 4 4 3 7% 10% 41%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 5% 8% 44%	2400
	11th to 20th	Day	10% 6% 2 5% 4 3 4 2 5% 8% 50%	2400
	21st to end	Day	18% 6% 3 6% 4 4 4 3 6% 8% 38%	2112
October	1st to 10th	Day	19% 7% 3 7% 4 4 3 3 5% 7% 38%	2000
	11th to 20th	Day	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	2000
	21st to end	Day	26% 9% 3 8% 4 5% 5% 4 5% 6% 27%	2110
November	1st to 10th	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	1840
	11th to 20th	Day	16% 12% 4 9% 5% 4 4 4 5% 5% 31%	1680
	21st to end	Day	20% 15% 4 9% 5% 4 4 4 5% 5% 25%	1680
December	1st to 10th	Day	21% 15% 4 10% 5% 6% 4 3 5% 6% 20%	2680
	11th to 20th	Day	18% 21% 4 10% 4 4 3 3 4 4 24%	3066
	21st to end	Day	23% 15% 4 10% 5% 4 3 2 3 5% 25%	4048
January	1st to 10th	Night	15% 14% 6% 13% 6% 5% 5% 4 4 6% 23%	8234
	11th to 20th	Night	12% 18% 7% 16% 8% 6% 5% 3 4 5% 16%	8235
	21st to end	Night	13% 14% 6% 11% 7% 6% 6% 4 5% 5% 25%	8539
February	1st to 10th	Night	15% 14% 5% 10% 7% 5% 5% 4 5% 5% 26%	2730
	11th to 20th	Night	15% 13% 5% 11% 6% 4 4 3 5% 5% 29%	2663
	21st to end	Night	16% 13% 5% 8% 6% 5% 4 3 6% 6% 29%	2100
March	1st to 10th	Night	19% 12% 4 8% 5% 5% 4 3 4 5% 30%	5309
	11th to 20th	Night	14% 12% 4 8% 5% 4 4 4 5% 8% 32%	5089
	21st to end	Night	20% 10% 3 7% 4 3 3 2 4 7% 37%	5383
April	1st to 10th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 33%	2100
	11th to 20th	Night	19% 9% 3 6% 5% 3 5% 3 4 6% 37%	2075
	21st to end	Night	20% 9% 3 6% 4 4 5% 3 6% 6% 34%	1995
May	1st to 10th	Night	27% 10% 3 7% 4 4 4 3 5% 6% 26%	3726
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 5% 7% 41%	3655
	21st to end	Night	18% 7% 2 6% 5% 4 5% 4 6% 7% 36%	4014
June	1st to 10th	Night	16% 6% 2 8% 5% 5% 6% 5% 6% 8% 35%	1600
	11th to 20th	Night	12% 6% 3 6% 5% 4 4 4 5% 9% 43%	1600
	21st to end	Night	16% 5% 2 6% 5% 4 5% 4 7% 7% 38%	1600
July	1st to 10th	Night	11% 6% 3 7% 4 5% 5% 5% 6% 10% 38%	3600
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 6% 8% 46%	3600
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	3926
August	1st to 10th	Night	11% 7% 2 6% 4 3 4 4 5% 8% 45%	2838
	11th to 20th	Night	13% 6% 2 5% 3 3 4 4 6% 7% 46%	2875
	21st to end	Night	9% 4 3 5% 5% 5% 5% 5% 8% 9% 41%	3570
September	1st to 10th	Night	12% 6% 2 6% 4 4 3 3 5% 8% 48%	2000
	11th to 20th	Night	12% 5% 1 5% 3 4 4 3 5% 6% 53%	2000
	21st to end	Night	17% 6% 2 6% 4 4 5% 3 5% 6% 42%	2284
October	1st to 10th	Night	16% 8% 2 6% 4 4 5% 4 5% 5% 40%	2400
	11th to 20th	Night	20% 7% 3 8% 6% 5% 5% 4 4 7% 33%	2400
	21st to end	Night	21% 10% 2 9% 4 4 4 4 5% 6% 31%	2730
November	1st to 10th	Night	18% 10% 3 6% 4 4 4 4 5% 6% 38%	2677
	11th to 20th	Night	18% 11% 3 7% 4 4 5% 3 5% 7% 33%	2940
	21st to end	Night	21% 12% 3 9% 4 5% 5% 4 5% 5% 27%	2940
December	1st to 10th	Night	20% 15% 4 9% 6% 5% 5% 3 6% 6% 20%	4720
	11th to 20th	Night	21% 17% 4 8% 4 4 3 3 4 5% 26%	5348
	21st to end	Night	27% 15% 4 9% 4 4 4 3 4 4 22%	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	57% 7% 11% 18% 6% 1	4662
	11th to 20th	Day	71% 5% 8% 9% 7% 1	4680
	21st to end	Day	67% 5% 7% 10% 10% 1	5637
February	1st to 10th	Day	62% 6% 9% 16% 6% 1	1890
	11th to 20th	Day	59% 6% 9% 16% 9% 1	1852
	21st to end	Day	64% 5% 9% 12% 9% 1	1705
March	1st to 10th	Day	56% 4 10% 14% 15% 2	4738
	11th to 20th	Day	52% 5% 18% 12% 10% 2	5090
	21st to end	Day	50% 4 5% 21% 16% 3	5791
April	1st to 10th	Day	56% 4 8% 17% 13% 3	2520
	11th to 20th	Day	50% 4 7% 21% 15% 2	2494
	21st to end	Day	54% 5% 8% 17% 13% 3	2641
May	1st to 10th	Day	57% 5% 9% 18% 9% 2	6442
	11th to 20th	Day	49% 7% 11% 18% 14% 1	6462
	21st to end	Day	47% 7% 13% 22% 10% 2	7103
June	1st to 10th	Day	48% 8% 12% 18% 13% 1	2800
	11th to 20th	Day	41% 7% 12% 25% 13% 2	2800
	21st to end	Day	44% 8% 14% 21% 12% 1	2800
July	1st to 10th	Day	40% 6% 15% 27% 12%	6290
	11th to 20th	Day	35% 7% 15% 29% 14%	6285
	21st to end	Day	34% 7% 14% 35% 10%	6728
August	1st to 10th	Day	44% 5% 15% 24% 11% 1	4295
	11th to 20th	Day	42% 7% 14% 28% 9% 1	4195
	21st to end	Day	38% 6% 15% 31% 10%	4312
September	1st to 10th	Day	37% 8% 15% 28% 11% 1	2400
	11th to 20th	Day	33% 5% 13% 32% 16% 1	2400
	21st to end	Day	44% 7% 12% 27% 10%	2112
October	1st to 10th	Day	40% 5% 13% 31% 10%	3260
	11th to 20th	Day	44% 6% 16% 26% 9% 1	3240
	21st to end	Day	50% 5% 13% 23% 8%	3387
November	1st to 10th	Day	48% 8% 13% 21% 9% 1	1840
	11th to 20th	Day	53% 6% 11% 18% 11% 1	1680
	21st to end	Day	60% 6% 13% 13% 8%	1680
December	1st to 10th	Day	64% 6% 16% 10% 4	2680
	11th to 20th	Day	64% 5% 10% 13% 7%	3066
	21st to end	Day	63% 4 8% 18% 6%	4048
January	1st to 10th	Night	61% 6% 12% 14% 7%	8234
	11th to 20th	Night	69% 7% 8% 10% 6%	8280
	21st to end	Night	60% 6% 8% 13% 12% 1	8539
February	1st to 10th	Night	59% 7% 9% 17% 6% 1	2730
	11th to 20th	Night	57% 4 10% 20% 9% 1	2665
	21st to end	Night	55% 6% 10% 19% 9% 1	2100
March	1st to 10th	Night	56% 5% 7% 18% 11% 4	5319
	11th to 20th	Night	49% 5% 16% 18% 9% 2	5090
	21st to end	Night	48% 4 7% 23% 16% 2	5383
April	1st to 10th	Night	51% 5% 8% 20% 14% 2	2100
	11th to 20th	Night	49% 5% 9% 19% 17% 1	2075
	21st to end	Night	50% 5% 8% 18% 15% 3	1995
May	1st to 10th	Night	58% 6% 8% 15% 10% 3	3732
	11th to 20th	Night	42% 8% 13% 21% 14% 1	3656
	21st to end	Night	46% 6% 12% 19% 15% 1	4015
June	1st to 10th	Night	46% 8% 11% 22% 13% 1	1600
	11th to 20th	Night	37% 7% 13% 21% 19% 2	1600
	21st to end	Night	43% 8% 13% 23% 13% 1	1600
July	1st to 10th	Night	40% 7% 15% 20% 17% 1	3560
	11th to 20th	Night	36% 6% 12% 33% 13%	3552
	21st to end	Night	32% 6% 14% 33% 13% 2	3809
August	1st to 10th	Night	37% 7% 14% 27% 14% 1	2828
	11th to 20th	Night	36% 7% 14% 32% 11% 1	2902
	21st to end	Night	34% 9% 14% 31% 11% 1	3570
September	1st to 10th	Night	34% 6% 15% 30% 13% 1	2000
	11th to 20th	Night	30% 5% 15% 34% 15% 1	2000
	21st to end	Night	42% 6% 11% 28% 13% 1	2284
October	1st to 10th	Night	37% 6% 10% 27% 19% 1	3920
	11th to 20th	Night	42% 5% 14% 28% 10%	3899
	21st to end	Night	47% 6% 13% 24% 9%	4403
November	1st to 10th	Night	46% 5% 13% 23% 11% 1	2677
	11th to 20th	Night	50% 6% 12% 20% 10% 2	2940
	21st to end	Night	57% 7% 12% 17% 6%	2940
December	1st to 10th	Night	62% 7% 13% 15% 4	4720
	11th to 20th	Night	60% 6% 10% 14% 10% 1	5348
	21st to end	Night	66% 4 9% 11% 10%	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	27% 18% 37% 13% 5%	220
	11th to 20th	Day	32% 20% 30% 15% 2	220
	21st to end	Day	25% 24% 30% 16% 4	336
February	1st to 10th	Day	32% 25% 30% 12% 2	330
	11th to 20th	Day	28% 27% 36% 8%	330
	21st to end	Day	33% 23% 34% 9% 2	421
March	1st to 10th	Day	27% 20% 32% 15% 5%	540
	11th to 20th	Day	32% 22% 29% 14% 4	540
	21st to end	Day	35% 20% 28% 13% 5% 1	594
April	1st to 10th	Day	32% 21% 30% 11% 5%	540
	11th to 20th	Day	33% 21% 23% 12% 7% 2	532
	21st to end	Day	27% 21% 33% 13% 5% 1	540
May	1st to 10th	Day	25% 18% 28% 21% 6% 2	543
	11th to 20th	Day	19% 15% 37% 18% 9% 2	567
	21st to end	Day	19% 17% 31% 21% 11% 2	617
June	1st to 10th	Day	22% 14% 34% 21% 8% 2	530
	11th to 20th	Day	14% 14% 36% 23% 10% 2	530
	21st to end	Day	19% 14% 33% 22% 9% 2	530
July	1st to 10th	Day	13% 10% 30% 30% 14% 4	525
	11th to 20th	Day	14% 8% 31% 27% 15% 5%	524
	21st to end	Day	13% 7% 36% 30% 10% 4	576
August	1st to 10th	Day	13% 8% 30% 27% 17% 5%	526
	11th to 20th	Day	14% 7% 27% 31% 16% 6%	519
	21st to end	Day	14% 12% 32% 25% 10% 8%	583
September	1st to 10th	Day	14% 10% 31% 26% 12% 7%	530
	11th to 20th	Day	11% 8% 25% 25% 20% 11%	530
	21st to end	Day	19% 11% 28% 26% 13% 3	530
October	1st to 10th	Day	24% 14% 29% 17% 13% 4	530
	11th to 20th	Day	25% 20% 30% 17% 6% 2	530
	21st to end	Day	31% 17% 28% 20% 4	533
November	1st to 10th	Day	29% 19% 25% 19% 7%	414
	11th to 20th	Day	24% 22% 35% 12% 6% 1	220
	21st to end	Day	26% 23% 36% 11% 3	220
December	1st to 10th	Day	30% 22% 33% 10% 4	220
	11th to 20th	Day	32% 25% 31% 9% 4	220
	21st to end	Day	34% 20% 32% 12% 3	242
January	1st to 10th	Night	29% 17% 33% 18% 3	840
	11th to 20th	Night	30% 18% 29% 18% 5%	840
	21st to end	Night	23% 16% 35% 22% 4	924
February	1st to 10th	Night	24% 18% 35% 21% 1	840
	11th to 20th	Night	23% 16% 39% 18% 3	823
	21st to end	Night	26% 19% 34% 18% 2	692
March	1st to 10th	Night	25% 16% 34% 21% 3	840
	11th to 20th	Night	27% 18% 30% 21% 4	840
	21st to end	Night	24% 15% 35% 18% 6%	924
April	1st to 10th	Night	27% 15% 34% 21% 3	840
	11th to 20th	Night	23% 18% 32% 19% 7% 1	831
	21st to end	Night	25% 12% 31% 24% 9%	735
May	1st to 10th	Night	26% 8% 28% 26% 11% 1	446
	11th to 20th	Night	15% 10% 35% 32% 8%	414
	21st to end	Night	13% 9% 36% 31% 11% 1	455
June	1st to 10th	Night	16% 8% 35% 31% 11%	400
	11th to 20th	Night	14% 8% 32% 34% 12% 1	400
	21st to end	Night	18% 7% 25% 37% 13%	400
July	1st to 10th	Night	8% 6% 28% 37% 20%	390
	11th to 20th	Night	12% 5% 27% 37% 19% 1	388
	21st to end	Night	11% 3 29% 42% 15% 1	438
August	1st to 10th	Night	11% 4 23% 37% 23% 1	546
	11th to 20th	Night	12% 5% 22% 34% 23% 3	594
	21st to end	Night	11% 6% 31% 33% 18% 2	864
September	1st to 10th	Night	14% 7% 28% 32% 17% 2	800
	11th to 20th	Night	13% 5% 22% 27% 27% 6%	800
	21st to end	Night	19% 10% 23% 29% 17% 3	800
October	1st to 10th	Night	21% 12% 28% 21% 17% 2	800
	11th to 20th	Night	24% 16% 30% 22% 9% 1	800
	21st to end	Night	26% 14% 32% 22% 5%	880
November	1st to 10th	Night	27% 14% 28% 22% 8%	820
	11th to 20th	Night	25% 16% 34% 17% 7%	840
	21st to end	Night	30% 18% 29% 17% 6%	840
December	1st to 10th	Night	31% 19% 28% 19% 3	840
	11th to 20th	Night	28% 21% 33% 15% 3 1	840
	21st to end	Night	35% 16% 30% 16% 3	924

Page generated at 2026-05-29 01:53:30. Version ac07

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