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 2025-02-06.

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%	108623
	Night	17% 11% 4 8% 5% 4 4 4 5% 6% 32%	109620
Transparency	Day	49% 6% 12% 22% 10% 1	112188
	Night	50% 6% 11% 20% 11% 1	114219
Seeing	Day	22% 16% 31% 20% 9% 3	14720
	Night	22% 13% 31% 24% 9% 1	24046

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	13% 13% 4 10% 5% 4 5% 4 6% 6% 30%	3597
	11th to 20th	Day	11% 18% 8% 13% 7% 6% 4 4 4 5% 20%	3570
	21st to end	Day	14% 18% 7% 15% 6% 5% 4 3 4 4 20%	4351
February	1st to 10th	Day	15% 17% 3 12% 6% 4 4 4 5% 5% 23%	1755
	11th to 20th	Day	12% 16% 5% 11% 7% 6% 5% 3 4 5% 28%	1663
	21st to end	Day	20% 14% 4 8% 7% 5% 4 3 4 5% 24%	1547
March	1st to 10th	Day	21% 13% 4 9% 5% 5% 3 3 3 6% 30%	3230
	11th to 20th	Day	11% 16% 5% 9% 5% 5% 4 4 4 5% 31%	3480
	21st to end	Day	14% 10% 3 6% 5% 4 3 3 4 7% 42%	3960
April	1st to 10th	Day	20% 14% 3 7% 5% 4 3 3 3 5% 33%	2280
	11th to 20th	Day	22% 10% 2 5% 4 4 3 2 4 6% 38%	2254
	21st to end	Day	22% 10% 3 8% 5% 4 4 3 5% 5% 32%	2389
May	1st to 10th	Day	20% 9% 3 7% 5% 4 4 4 5% 7% 32%	4386
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 5% 8% 33%	4398
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	4837
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	2660
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 5% 6% 8% 39%	2660
	21st to end	Day	17% 8% 3 6% 5% 4 4 4 6% 8% 35%	2660
July	1st to 10th	Day	11% 5% 2 7% 4 5% 5% 5% 6% 11% 38%	4440
	11th to 20th	Day	13% 6% 2 5% 3 4 5% 5% 7% 10% 42%	4440
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 8% 9% 39%	4814
August	1st to 10th	Day	16% 8% 3 6% 4 4 4 4 6% 8% 36%	4177
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 9% 37%	4026
	21st to end	Day	14% 5% 2 6% 4 4 4 3 7% 10% 41%	4180
September	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 4 5% 8% 43%	2280
	11th to 20th	Day	11% 6% 2 5% 4 3 4 2 5% 9% 49%	2280
	21st to end	Day	18% 6% 3 6% 4 4 4 3 6% 8% 38%	2007
October	1st to 10th	Day	20% 7% 3 7% 5% 4 3 3 5% 7% 36%	1900
	11th to 20th	Day	21% 8% 3 7% 5% 5% 3 3 5% 7% 31%	1900
	21st to end	Day	26% 10% 3 8% 4 5% 5% 4 5% 6% 26%	2005
November	1st to 10th	Day	16% 9% 3 6% 5% 5% 5% 4 6% 7% 34%	1751
	11th to 20th	Day	16% 12% 4 9% 5% 4 5% 4 5% 5% 32%	1600
	21st to end	Day	21% 14% 4 9% 5% 4 4 4 5% 5% 25%	1600
December	1st to 10th	Day	21% 14% 4 10% 5% 6% 4 4 6% 6% 20%	2600
	11th to 20th	Day	18% 21% 5% 10% 4 4 3 3 4 4 24%	2986
	21st to end	Day	23% 15% 4 10% 5% 4 4 2 3 5% 25%	3960
January	1st to 10th	Night	15% 14% 5% 12% 6% 5% 5% 4 4 6% 24%	6349
	11th to 20th	Night	12% 15% 7% 15% 9% 6% 6% 3 5% 5% 18%	6315
	21st to end	Night	16% 15% 7% 13% 7% 5% 5% 3 4 4 21%	6600
February	1st to 10th	Night	16% 14% 5% 10% 7% 5% 5% 4 4 5% 25%	2536
	11th to 20th	Night	14% 13% 5% 11% 6% 5% 4 3 5% 5% 30%	2403
	21st to end	Night	17% 13% 4 7% 5% 5% 4 3 6% 6% 30%	1906
March	1st to 10th	Night	18% 11% 4 7% 5% 4 4 3 4 6% 32%	3608
	11th to 20th	Night	18% 15% 5% 9% 5% 4 4 4 4 6% 27%	3479
	21st to end	Night	16% 9% 2 6% 4 3 3 2 5% 7% 42%	3672
April	1st to 10th	Night	22% 10% 3 7% 4 4 3 3 5% 5% 34%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 3 5% 3 4 5% 38%	1875
	21st to end	Night	20% 9% 3 6% 4 4 5% 3 6% 6% 34%	1805
May	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 5% 6% 31%	2551
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 6% 7% 37%	2495
	21st to end	Night	13% 6% 2 5% 5% 5% 5% 4 6% 7% 43%	2738
June	1st to 10th	Night	16% 6% 2 8% 4 5% 6% 5% 6% 8% 35%	1520
	11th to 20th	Night	12% 5% 3 5% 5% 4 5% 4 6% 9% 43%	1520
	21st to end	Night	17% 5% 2 6% 5% 4 6% 4 7% 7% 38%	1520
July	1st to 10th	Night	11% 5% 2 8% 5% 5% 6% 5% 6% 8% 40%	2520
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 5% 8% 45%	2520
	21st to end	Night	10% 6% 2 5% 3 4 4 4 6% 8% 47%	2739
August	1st to 10th	Night	12% 7% 2 6% 4 3 4 4 5% 8% 45%	2750
	11th to 20th	Night	14% 7% 2 5% 3 3 4 4 6% 8% 45%	2785
	21st to end	Night	9% 4 3 5% 5% 5% 5% 5% 8% 10% 41%	3461
September	1st to 10th	Night	12% 6% 2 5% 4 4 3 3 5% 8% 47%	1900
	11th to 20th	Night	12% 5% 1 5% 3 4 4 3 5% 6% 53%	1900
	21st to end	Night	18% 5% 2 6% 4 4 5% 3 5% 7% 42%	2170
October	1st to 10th	Night	16% 8% 3 6% 4 4 5% 4 5% 6% 38%	2280
	11th to 20th	Night	21% 7% 3 8% 5% 5% 5% 4 4 6% 33%	2280
	21st to end	Night	22% 10% 2 9% 4 4 4 4 5% 6% 30%	2593
November	1st to 10th	Night	18% 10% 3 6% 4 4 4 3 5% 6% 38%	2546
	11th to 20th	Night	19% 11% 3 6% 4 4 5% 4 5% 7% 33%	2800
	21st to end	Night	21% 12% 3 9% 4 5% 5% 4 5% 5% 28%	2800
December	1st to 10th	Night	20% 15% 4 9% 6% 5% 5% 4 6% 6% 20%	4580
	11th to 20th	Night	22% 17% 4 8% 4 4 3 3 4 5% 26%	5208
	21st to end	Night	27% 15% 4 9% 4 4 4 3 4 4 22%	6996

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	53% 8% 10% 20% 7% 1	3598
	11th to 20th	Day	67% 6% 10% 11% 6% 1	3600
	21st to end	Day	68% 6% 7% 9% 10% 1	4351
February	1st to 10th	Day	62% 6% 9% 16% 5% 1	1755
	11th to 20th	Day	59% 6% 9% 16% 9% 1	1672
	21st to end	Day	63% 5% 10% 13% 9% 1	1547
March	1st to 10th	Day	57% 4 11% 18% 9% 1	3233
	11th to 20th	Day	54% 6% 15% 13% 10% 2	3480
	21st to end	Day	42% 5% 7% 26% 15% 4	3960
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2280
	11th to 20th	Day	49% 4 8% 22% 15% 2	2254
	21st to end	Day	54% 5% 8% 17% 13% 4	2389
May	1st to 10th	Day	51% 6% 10% 22% 10% 2	4400
	11th to 20th	Day	47% 9% 13% 21% 9% 1	4402
	21st to end	Day	38% 8% 13% 25% 14% 2	4837
June	1st to 10th	Day	48% 8% 12% 18% 13% 1	2660
	11th to 20th	Day	41% 7% 12% 25% 13% 2	2660
	21st to end	Day	45% 8% 14% 21% 11% 1	2660
July	1st to 10th	Day	39% 7% 15% 27% 13% 1	4370
	11th to 20th	Day	34% 7% 16% 33% 9%	4365
	21st to end	Day	37% 8% 15% 29% 10%	4661
August	1st to 10th	Day	45% 6% 15% 23% 11% 1	4163
	11th to 20th	Day	42% 7% 15% 27% 9%	4065
	21st to end	Day	38% 6% 15% 30% 10% 1	4180
September	1st to 10th	Day	37% 8% 15% 27% 12% 1	2280
	11th to 20th	Day	34% 5% 13% 31% 16% 1	2280
	21st to end	Day	44% 7% 12% 27% 9%	2007
October	1st to 10th	Day	41% 5% 13% 31% 9%	3160
	11th to 20th	Day	44% 6% 16% 27% 8%	3140
	21st to end	Day	50% 6% 13% 23% 8%	3282
November	1st to 10th	Day	47% 8% 14% 21% 9% 1	1751
	11th to 20th	Day	53% 6% 11% 18% 12% 1	1600
	21st to end	Day	59% 7% 13% 13% 8%	1600
December	1st to 10th	Day	64% 6% 16% 10% 4	2600
	11th to 20th	Day	64% 5% 10% 13% 7%	2986
	21st to end	Day	63% 4 9% 18% 6%	3960
January	1st to 10th	Night	59% 7% 12% 15% 7%	6349
	11th to 20th	Night	66% 8% 10% 11% 5%	6360
	21st to end	Night	65% 6% 8% 10% 10% 1	6600
February	1st to 10th	Night	61% 7% 10% 17% 6% 1	2536
	11th to 20th	Night	56% 5% 10% 20% 9%	2405
	21st to end	Night	55% 6% 11% 18% 9% 1	1906
March	1st to 10th	Night	52% 5% 9% 23% 10% 1	3618
	11th to 20th	Night	56% 6% 12% 16% 9% 1	3480
	21st to end	Night	41% 5% 7% 26% 18% 3	3672
April	1st to 10th	Night	51% 5% 7% 20% 14% 2	1900
	11th to 20th	Night	48% 5% 9% 19% 17% 2	1875
	21st to end	Night	50% 5% 9% 16% 16% 3	1805
May	1st to 10th	Night	52% 7% 9% 17% 12% 2	2557
	11th to 20th	Night	44% 10% 11% 23% 9% 2	2496
	21st to end	Night	37% 7% 13% 20% 21% 2	2739
June	1st to 10th	Night	45% 8% 12% 22% 12% 1	1520
	11th to 20th	Night	37% 7% 14% 21% 19% 2	1520
	21st to end	Night	43% 8% 13% 22% 13% 1	1520
July	1st to 10th	Night	40% 7% 11% 23% 18% 1	2480
	11th to 20th	Night	37% 6% 12% 34% 12%	2472
	21st to end	Night	34% 7% 17% 27% 12% 2	2651
August	1st to 10th	Night	38% 7% 13% 27% 14% 1	2740
	11th to 20th	Night	36% 7% 14% 32% 10% 1	2812
	21st to end	Night	34% 9% 14% 30% 11% 1	3461
September	1st to 10th	Night	35% 7% 15% 29% 13% 1	1900
	11th to 20th	Night	30% 5% 15% 34% 15% 1	1900
	21st to end	Night	41% 6% 11% 29% 12% 1	2170
October	1st to 10th	Night	38% 7% 10% 27% 18% 1	3800
	11th to 20th	Night	42% 5% 14% 28% 10%	3779
	21st to end	Night	48% 6% 14% 24% 8%	4266
November	1st to 10th	Night	46% 5% 13% 24% 10% 1	2546
	11th to 20th	Night	50% 6% 12% 20% 11% 2	2800
	21st to end	Night	57% 7% 13% 17% 6%	2800
December	1st to 10th	Night	63% 7% 13% 15% 3	4580
	11th to 20th	Night	60% 6% 10% 14% 10% 1	5208
	21st to end	Night	66% 4 9% 11% 10%	6996

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	28% 19% 36% 13% 6%	200
	11th to 20th	Day	29% 21% 32% 17% 3	200
	21st to end	Day	26% 24% 31% 16% 4	305
February	1st to 10th	Day	32% 27% 29% 10% 1	285
	11th to 20th	Day	27% 27% 37% 9%	270
	21st to end	Day	34% 23% 32% 9% 2	359
March	1st to 10th	Day	25% 19% 34% 16% 6%	460
	11th to 20th	Day	28% 22% 31% 15% 5%	460
	21st to end	Day	32% 19% 29% 13% 5% 1	506
April	1st to 10th	Day	30% 20% 32% 12% 5%	460
	11th to 20th	Day	32% 21% 23% 13% 8% 3	452
	21st to end	Day	27% 22% 32% 12% 6% 2	460
May	1st to 10th	Day	23% 16% 29% 23% 7% 2	463
	11th to 20th	Day	19% 12% 37% 20% 9% 2	487
	21st to end	Day	16% 16% 31% 23% 12% 2	529
June	1st to 10th	Day	22% 13% 33% 21% 8% 2	490
	11th to 20th	Day	14% 14% 35% 24% 10% 3	490
	21st to end	Day	19% 14% 33% 22% 10% 3	490
July	1st to 10th	Day	13% 10% 29% 30% 14% 4	485
	11th to 20th	Day	14% 8% 31% 27% 15% 5%	484
	21st to end	Day	13% 7% 35% 31% 11% 4	532
August	1st to 10th	Day	14% 8% 30% 26% 16% 5%	486
	11th to 20th	Day	13% 7% 27% 31% 16% 6%	479
	21st to end	Day	13% 12% 31% 26% 10% 8%	539
September	1st to 10th	Day	14% 9% 33% 25% 12% 7%	490
	11th to 20th	Day	11% 9% 26% 24% 19% 12%	490
	21st to end	Day	18% 12% 27% 26% 13% 4	490
October	1st to 10th	Day	25% 15% 28% 16% 12% 4	490
	11th to 20th	Day	26% 20% 29% 17% 7% 2	490
	21st to end	Day	31% 18% 27% 20% 4	494
November	1st to 10th	Day	27% 19% 25% 20% 8% 1	385
	11th to 20th	Day	24% 21% 35% 13% 6% 2	200
	21st to end	Day	25% 23% 37% 12% 3 1	200
December	1st to 10th	Day	29% 23% 33% 11% 5% 1	200
	11th to 20th	Day	31% 26% 32% 8% 4	200
	21st to end	Day	33% 20% 32% 13% 3	220
January	1st to 10th	Night	29% 17% 32% 18% 4	800
	11th to 20th	Night	29% 18% 30% 19% 5%	800
	21st to end	Night	22% 16% 36% 22% 4	880
February	1st to 10th	Night	25% 18% 35% 20% 1	781
	11th to 20th	Night	22% 16% 40% 18% 3	743
	21st to end	Night	26% 19% 33% 19% 3	628
March	1st to 10th	Night	23% 16% 35% 22% 4	760
	11th to 20th	Night	26% 18% 29% 22% 4 1	760
	21st to end	Night	23% 15% 36% 19% 7%	836
April	1st to 10th	Night	26% 14% 36% 21% 3	760
	11th to 20th	Night	22% 18% 33% 19% 8% 1	751
	21st to end	Night	24% 12% 31% 23% 10%	665
May	1st to 10th	Night	25% 8% 28% 26% 12% 1	404
	11th to 20th	Night	14% 10% 34% 33% 9%	374
	21st to end	Night	11% 9% 36% 32% 11% 1	411
June	1st to 10th	Night	16% 8% 33% 32% 11%	380
	11th to 20th	Night	14% 7% 31% 35% 12% 1	380
	21st to end	Night	18% 6% 24% 38% 13%	380
July	1st to 10th	Night	8% 6% 28% 37% 21%	370
	11th to 20th	Night	12% 5% 27% 36% 20% 1	368
	21st to end	Night	12% 2 29% 41% 15% 1	416
August	1st to 10th	Night	12% 4 23% 36% 23% 2	518
	11th to 20th	Night	12% 6% 22% 34% 23% 3	564
	21st to end	Night	11% 6% 30% 33% 18% 2	821
September	1st to 10th	Night	14% 7% 28% 32% 16% 2	760
	11th to 20th	Night	13% 6% 22% 26% 27% 6%	760
	21st to end	Night	19% 10% 23% 29% 17% 3	760
October	1st to 10th	Night	22% 13% 27% 21% 16% 2	760
	11th to 20th	Night	24% 15% 29% 22% 9% 1	760
	21st to end	Night	27% 14% 31% 22% 6%	836
November	1st to 10th	Night	26% 14% 28% 23% 9%	780
	11th to 20th	Night	25% 16% 33% 17% 7%	800
	21st to end	Night	30% 17% 29% 17% 6%	800
December	1st to 10th	Night	31% 19% 29% 18% 3	800
	11th to 20th	Night	28% 20% 33% 16% 3 1	800
	21st to end	Night	35% 16% 31% 16% 3	880

Page generated at 2025-02-03 03:05:55. Version ac07

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