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 2024-08-30.

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 7% 5% 4 4 4 5% 7% 34%	95922
	Night	18% 10% 3 8% 5% 4 4 3 5% 6% 33%	93127
Transparency	Day	49% 7% 12% 21% 10% 1	95641
	Night	50% 7% 12% 20% 10% 1	92962
Seeing	Day	22% 16% 31% 20% 9% 3	14257
	Night	22% 13% 31% 24% 9% 1	23409

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	15% 16% 4 8% 5% 4 4 3 5% 4 30%	2517
	11th to 20th	Day	13% 17% 7% 12% 6% 6% 5% 4 4 5% 21%	2520
	21st to end	Day	18% 20% 7% 13% 6% 4 4 3 4 4 18%	3037
February	1st to 10th	Day	15% 17% 3 12% 6% 5% 4 4 6% 5% 23%	1710
	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	12% 7% 3 7% 4 5% 4 5% 7% 8% 39%	2504
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 5% 6% 9% 39%	2428
	21st to end	Day	13% 6% 2 6% 4 4 4 3 7% 8% 41%	2486
September	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 4 5% 8% 43%	2160
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 5% 8% 49%	2160
	21st to end	Day	18% 6% 2 6% 4 4 4 3 6% 8% 38%	1902
October	1st to 10th	Day	21% 7% 3 7% 5% 4 3 3 4 7% 36%	1800
	11th to 20th	Day	22% 8% 3 8% 5% 5% 4 3 5% 7% 30%	1800
	21st to end	Day	27% 10% 3 7% 4 5% 5% 4 4 6% 26%	1900
November	1st to 10th	Day	16% 9% 3 6% 5% 5% 5% 4 6% 7% 34%	1662
	11th to 20th	Day	17% 12% 4 9% 5% 4 5% 4 5% 5% 31%	1520
	21st to end	Day	21% 14% 4 9% 5% 4 4 4 5% 5% 25%	1520
December	1st to 10th	Day	22% 16% 5% 9% 5% 5% 4 4 6% 5% 21%	1520
	11th to 20th	Day	20% 16% 4 10% 5% 4 4 4 5% 5% 26%	1906
	21st to end	Day	28% 16% 4 11% 5% 4 4 2 3 4 21%	2772
January	1st to 10th	Night	19% 13% 5% 11% 6% 5% 4 4 4 6% 23%	4429
	11th to 20th	Night	15% 14% 6% 14% 8% 5% 5% 4 5% 5% 20%	4440
	21st to end	Night	20% 16% 6% 11% 6% 5% 5% 3 4 3 21%	4614
February	1st to 10th	Night	16% 14% 4 10% 7% 5% 5% 4 4 5% 24%	2470
	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	10% 5% 2 6% 4 4 4 3 6% 9% 47%	1652
	11th to 20th	Night	10% 6% 2 6% 4 3 4 4 7% 8% 45%	1688
	21st to end	Night	10% 5% 3 5% 4 4 4 5% 7% 8% 46%	2065
September	1st to 10th	Night	13% 6% 2 5% 4 4 3 3 5% 8% 46%	1800
	11th to 20th	Night	13% 5% 1 5% 3 3 4 3 5% 6% 52%	1800
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 7% 43%	2055
October	1st to 10th	Night	17% 8% 3 6% 5% 4 5% 4 5% 5% 37%	2160
	11th to 20th	Night	21% 8% 3 8% 6% 5% 5% 4 4 6% 32%	2160
	21st to end	Night	23% 11% 2 9% 4 4 4 4 5% 6% 29%	2456
November	1st to 10th	Night	19% 10% 3 6% 3 4 4 3 5% 6% 38%	2415
	11th to 20th	Night	19% 10% 3 6% 4 4 5% 4 5% 7% 33%	2660
	21st to end	Night	21% 11% 3 8% 4 5% 5% 4 5% 5% 28%	2660
December	1st to 10th	Night	20% 16% 5% 9% 5% 4 4 3 5% 6% 22%	2660
	11th to 20th	Night	20% 16% 5% 8% 5% 4 4 3 4 5% 28%	3288
	21st to end	Night	30% 15% 4 9% 4 4 4 3 4 4 18%	4884

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	56% 9% 13% 15% 5% 2	2518
	11th to 20th	Day	66% 8% 11% 9% 6%	2520
	21st to end	Day	70% 7% 8% 9% 5% 1	3037
February	1st to 10th	Day	62% 6% 9% 16% 5% 1	1710
	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	39% 8% 16% 25% 11% 1	2490
	11th to 20th	Day	39% 8% 16% 26% 11% 1	2428
	21st to end	Day	38% 7% 14% 28% 12% 1	2486
September	1st to 10th	Day	37% 8% 16% 26% 12% 1	2160
	11th to 20th	Day	34% 6% 13% 31% 16% 1	2160
	21st to end	Day	43% 8% 12% 28% 9%	1902
October	1st to 10th	Day	48% 6% 12% 22% 12%	1800
	11th to 20th	Day	51% 7% 16% 19% 6% 1	1800
	21st to end	Day	59% 5% 10% 18% 7%	1900
November	1st to 10th	Day	47% 8% 14% 21% 9% 1	1662
	11th to 20th	Day	54% 6% 11% 18% 11% 1	1520
	21st to end	Day	59% 7% 13% 13% 8%	1520
December	1st to 10th	Day	64% 6% 12% 12% 5% 1	1520
	11th to 20th	Day	61% 7% 14% 12% 5%	1906
	21st to end	Day	69% 4 8% 15% 5%	2772
January	1st to 10th	Night	60% 9% 14% 13% 4	4429
	11th to 20th	Night	63% 9% 11% 11% 4 1	4440
	21st to end	Night	65% 7% 9% 12% 6% 1	4614
February	1st to 10th	Night	61% 7% 10% 16% 6%	2470
	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	34% 8% 16% 28% 13% 1	1642
	11th to 20th	Night	34% 9% 15% 28% 13% 1	1688
	21st to end	Night	33% 9% 14% 29% 13% 1	2065
September	1st to 10th	Night	35% 7% 15% 28% 13% 1	1800
	11th to 20th	Night	31% 6% 15% 33% 14% 1	1800
	21st to end	Night	40% 7% 11% 30% 11% 1	2055
October	1st to 10th	Night	47% 8% 10% 20% 14% 1	2160
	11th to 20th	Night	51% 6% 14% 20% 8% 1	2160
	21st to end	Night	56% 7% 13% 14% 10% 1	2456
November	1st to 10th	Night	46% 5% 14% 23% 11% 1	2415
	11th to 20th	Night	50% 6% 12% 20% 10% 2	2660
	21st to end	Night	56% 7% 13% 17% 6%	2660
December	1st to 10th	Night	62% 6% 12% 15% 4	2660
	11th to 20th	Night	59% 6% 12% 16% 7% 1	3288
	21st to end	Night	69% 5% 11% 12% 3	4884

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	29% 18% 33% 14% 6%	180
	11th to 20th	Day	31% 19% 32% 16% 2	180
	21st to end	Day	25% 21% 32% 18% 4	274
February	1st to 10th	Day	32% 27% 30% 10% 1	270
	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% 11% 32% 26% 10% 8%	532
September	1st to 10th	Day	13% 9% 33% 25% 12% 7%	450
	11th to 20th	Day	12% 9% 28% 23% 18% 10%	450
	21st to end	Day	18% 12% 28% 25% 14% 4	450
October	1st to 10th	Day	26% 15% 27% 16% 13% 4	450
	11th to 20th	Day	26% 20% 29% 18% 6% 1	450
	21st to end	Day	32% 17% 27% 20% 4	455
November	1st to 10th	Day	26% 19% 25% 21% 9% 1	356
	11th to 20th	Day	26% 20% 33% 14% 4 2	180
	21st to end	Day	22% 24% 38% 13% 3 1	180
December	1st to 10th	Day	28% 24% 32% 11% 4 1	180
	11th to 20th	Day	28% 27% 33% 8% 4	180
	21st to end	Day	33% 21% 33% 11% 2	198
January	1st to 10th	Night	30% 16% 31% 19% 4	760
	11th to 20th	Night	29% 18% 29% 19% 5%	760
	21st to end	Night	22% 16% 35% 23% 4	836
February	1st to 10th	Night	25% 18% 35% 20% 1	760
	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	10% 6% 30% 33% 18% 2	817
September	1st to 10th	Night	14% 6% 28% 32% 16% 3	720
	11th to 20th	Night	14% 6% 23% 28% 25% 5%	720
	21st to end	Night	19% 10% 23% 28% 18% 3	720
October	1st to 10th	Night	22% 13% 27% 20% 16% 2	720
	11th to 20th	Night	24% 16% 29% 22% 8% 1	720
	21st to end	Night	27% 14% 31% 23% 5%	792
November	1st to 10th	Night	27% 13% 28% 23% 9%	740
	11th to 20th	Night	25% 17% 33% 17% 8%	760
	21st to end	Night	30% 17% 29% 18% 7%	760
December	1st to 10th	Night	32% 19% 28% 18% 3	760
	11th to 20th	Night	27% 20% 33% 17% 3 1	760
	21st to end	Night	35% 16% 31% 16% 2	836

Page generated at 2024-08-27 09:49:42. Version ac07

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