StarEffects Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the StarEffects Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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% 7% 2 6% 4 4 5% 4 6% 7% 38%	101433
	Night	17% 7% 2 6% 4 4 4 4 5% 7% 41%	97767
Transparency	Day	43% 6% 12% 23% 15% 2	105009
	Night	42% 5% 12% 23% 16% 2	102279
Seeing	Day	20% 13% 28% 23% 12% 4	14929
	Night	20% 10% 28% 30% 12% 1	24243

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% 7% 3 5% 4 4 4 5% 6% 6% 42%	2517
	11th to 20th	Day	14% 11% 5% 9% 6% 5% 5% 3 5% 6% 30%	2657
	21st to end	Day	20% 12% 3 8% 5% 4 4 3 4 5% 31%	3124
February	1st to 10th	Day	16% 7% 2 7% 5% 5% 5% 5% 6% 7% 35%	1710
	11th to 20th	Day	14% 8% 4 6% 4 5% 4 3 5% 8% 38%	1748
	21st to end	Day	19% 8% 3 8% 5% 4 5% 3 5% 5% 35%	1570
March	1st to 10th	Day	25% 6% 2 5% 4 4 4 3 5% 6% 36%	3227
	11th to 20th	Day	10% 6% 2 7% 6% 5% 4 4 6% 7% 43%	3480
	21st to end	Day	22% 8% 2 5% 4 3 3 2 4 5% 43%	3971
April	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 6% 8% 36%	2280
	11th to 20th	Day	16% 8% 2 6% 4 4 5% 3 5% 6% 41%	2254
	21st to end	Day	17% 5% 2 7% 4 5% 4 4 6% 8% 39%	2280
May	1st to 10th	Day	29% 6% 2 6% 4 4 4 3 5% 7% 30%	4121
	11th to 20th	Day	25% 9% 3 7% 5% 4 4 4 5% 6% 28%	4398
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 44%	4837
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 38%	2660
	11th to 20th	Day	14% 5% 2 6% 4 5% 6% 5% 6% 9% 38%	2660
	21st to end	Day	11% 5% 2 5% 5% 5% 6% 4 7% 11% 41%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 7% 7% 6% 8% 10% 36%	4440
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 40%	4440
	21st to end	Day	11% 8% 3 8% 6% 5% 6% 4 6% 7% 35%	4638
August	1st to 10th	Day	20% 6% 2 7% 5% 5% 5% 5% 6% 8% 31%	4104
	11th to 20th	Day	15% 5% 2 5% 3 4 5% 5% 7% 8% 41%	3829
	21st to end	Day	14% 5% 2 4 3 3 3 3 6% 9% 47%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 4 5% 46%	2280
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 5% 6% 51%	2280
	21st to end	Day	20% 8% 2 6% 5% 3 4 3 4 5% 38%	2033
October	1st to 10th	Day	19% 6% 2 4 3 3 4 3 5% 7% 43%	1900
	11th to 20th	Day	17% 5% 2 5% 3 4 5% 3 5% 6% 46%	1900
	21st to end	Day	19% 6% 1 5% 3 3 3 4 5% 8% 42%	2066
November	1st to 10th	Day	14% 7% 1 4 3 3 3 3 4 8% 51%	1761
	11th to 20th	Day	18% 6% 2 5% 3 4 3 4 6% 7% 44%	1710
	21st to end	Day	17% 5% 2 5% 4 4 4 4 6% 7% 42%	1520
December	1st to 10th	Day	18% 9% 2 7% 6% 4 4 4 6% 7% 34%	1520
	11th to 20th	Day	21% 6% 2 6% 3 4 4 4 6% 7% 38%	1906
	21st to end	Day	19% 9% 2 8% 5% 5% 5% 4 6% 7% 30%	2772
January	1st to 10th	Night	16% 6% 3 7% 4 4 4 3 5% 7% 40%	4429
	11th to 20th	Night	17% 8% 2 6% 4 5% 4 4 5% 7% 37%	4299
	21st to end	Night	23% 9% 3 8% 4 3 3 3 4 5% 35%	4532
February	1st to 10th	Night	17% 9% 2 6% 4 4 5% 4 5% 6% 39%	2470
	11th to 20th	Night	17% 6% 3 8% 5% 3 5% 3 5% 6% 39%	2318
	21st to end	Night	19% 7% 3 5% 5% 4 4 4 5% 6% 38%	1884
March	1st to 10th	Night	23% 10% 2 6% 4 4 3 3 4 5% 37%	3610
	11th to 20th	Night	11% 7% 2 6% 4 5% 3 4 4 6% 47%	3479
	21st to end	Night	17% 8% 2 5% 4 3 3 2 4 5% 46%	3659
April	1st to 10th	Night	18% 6% 3 6% 5% 3 4 3 7% 8% 37%	1900
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 3 5% 7% 42%	1875
	21st to end	Night	19% 5% 2 5% 4 3 3 4 5% 5% 44%	1900
May	1st to 10th	Night	27% 7% 3 5% 4 4 4 3 5% 7% 31%	2848
	11th to 20th	Night	25% 8% 3 7% 5% 4 4 4 5% 6% 29%	2495
	21st to end	Night	14% 6% 2 6% 4 4 4 4 5% 9% 42%	2738
June	1st to 10th	Night	16% 7% 2 6% 4 3 3 4 6% 8% 42%	1520
	11th to 20th	Night	13% 5% 2 5% 4 5% 5% 4 7% 9% 42%	1520
	21st to end	Night	11% 4 2 6% 3 4 5% 5% 6% 10% 44%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 6% 6% 8% 40%	2520
	11th to 20th	Night	8% 5% 2 7% 5% 5% 5% 6% 8% 11% 38%	2520
	21st to end	Night	14% 7% 2 6% 4 5% 4 4 6% 7% 39%	2912
August	1st to 10th	Night	20% 7% 2 6% 5% 4 4 3 7% 7% 35%	2825
	11th to 20th	Night	14% 7% 2 8% 4 4 4 3 5% 7% 41%	2966
	21st to end	Night	13% 5% 2 4 3 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 3 3 3 5% 6% 48%	1900
	11th to 20th	Night	13% 5% 1 5% 4 3 3 3 5% 6% 51%	1900
	21st to end	Night	20% 7% 2 5% 4 4 5% 3 4 6% 41%	2145
October	1st to 10th	Night	21% 6% 2 4 3 3 3 3 4 6% 44%	2280
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 6% 48%	2280
	21st to end	Night	19% 5% 2 4 3 3 3 3 5% 7% 46%	2530
November	1st to 10th	Night	11% 5% 2 4 3 4 4 3 5% 6% 53%	2537
	11th to 20th	Night	16% 7% 3 5% 4 3 4 3 4 5% 45%	2488
	21st to end	Night	15% 5% 2 6% 4 4 4 3 5% 8% 43%	2660
December	1st to 10th	Night	19% 8% 2 6% 5% 4 5% 4 5% 7% 35%	2660
	11th to 20th	Night	18% 7% 2 6% 4 4 5% 4 5% 6% 39%	3288
	21st to end	Night	19% 8% 3 6% 4 4 5% 4 6% 6% 34%	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	42% 5% 14% 26% 10% 2	2518
	11th to 20th	Day	54% 5% 12% 16% 11% 2	2657
	21st to end	Day	55% 5% 12% 20% 8% 1	3124
February	1st to 10th	Day	47% 7% 13% 21% 11% 1	1710
	11th to 20th	Day	46% 5% 10% 24% 13% 2	1757
	21st to end	Day	52% 4 11% 20% 10% 3	1570
March	1st to 10th	Day	48% 5% 10% 27% 8% 2	3230
	11th to 20th	Day	37% 7% 12% 27% 14% 3	3480
	21st to end	Day	45% 4 9% 20% 19% 2	3971
April	1st to 10th	Day	45% 5% 10% 21% 14% 5%	2280
	11th to 20th	Day	43% 5% 11% 22% 15% 4	2254
	21st to end	Day	43% 5% 11% 21% 16% 4	2280
May	1st to 10th	Day	53% 7% 9% 19% 10% 2	4133
	11th to 20th	Day	55% 7% 11% 17% 8% 1	4402
	21st to end	Day	35% 8% 12% 28% 16% 2	4837
June	1st to 10th	Day	40% 8% 13% 23% 15% 2	2660
	11th to 20th	Day	41% 8% 14% 24% 11% 3	2660
	21st to end	Day	36% 7% 14% 26% 15% 1	2660
July	1st to 10th	Day	41% 8% 14% 22% 14% 2	4370
	11th to 20th	Day	37% 7% 16% 25% 14% 1	4365
	21st to end	Day	47% 5% 10% 19% 16% 2	4490
August	1st to 10th	Day	49% 6% 11% 23% 10%	4091
	11th to 20th	Day	39% 6% 11% 31% 13% 1	3868
	21st to end	Day	35% 5% 11% 28% 20% 2	4180
September	1st to 10th	Day	40% 6% 10% 20% 20% 4	2280
	11th to 20th	Day	33% 5% 10% 25% 24% 3	2280
	21st to end	Day	47% 5% 8% 17% 20% 2	2033
October	1st to 10th	Day	38% 4 8% 21% 25% 5%	3160
	11th to 20th	Day	29% 3 11% 28% 23% 5%	3140
	21st to end	Day	27% 3 14% 25% 27% 4	3380
November	1st to 10th	Day	34% 4 14% 25% 20% 3	1761
	11th to 20th	Day	40% 5% 11% 23% 19% 2	1710
	21st to end	Day	40% 6% 13% 30% 9% 2	1520
December	1st to 10th	Day	50% 6% 15% 19% 10% 1	1520
	11th to 20th	Day	46% 4 16% 26% 8% 1	1906
	21st to end	Day	51% 6% 15% 19% 8%	2772
January	1st to 10th	Night	42% 5% 14% 26% 10% 3	4429
	11th to 20th	Night	46% 5% 14% 23% 10% 2	4299
	21st to end	Night	52% 4 9% 25% 9% 1	4532
February	1st to 10th	Night	45% 4 13% 25% 10% 2	2470
	11th to 20th	Night	46% 4 9% 20% 17% 3	2320
	21st to end	Night	46% 4 11% 21% 15% 3	1884
March	1st to 10th	Night	49% 5% 9% 23% 12% 1	3620
	11th to 20th	Night	36% 5% 14% 29% 15% 2	3480
	21st to end	Night	42% 3 8% 19% 23% 5%	3659
April	1st to 10th	Night	44% 5% 11% 21% 15% 4	1900
	11th to 20th	Night	40% 7% 11% 20% 20% 2	1875
	21st to end	Night	40% 6% 10% 22% 17% 5%	1900
May	1st to 10th	Night	53% 7% 8% 19% 11% 2	2855
	11th to 20th	Night	54% 8% 12% 13% 11% 1	2496
	21st to end	Night	39% 8% 12% 24% 14% 4	2739
June	1st to 10th	Night	40% 7% 11% 22% 19% 2	1520
	11th to 20th	Night	37% 9% 12% 26% 14% 2	1520
	21st to end	Night	34% 8% 14% 28% 14% 2	1520
July	1st to 10th	Night	40% 8% 15% 17% 15% 5%	2480
	11th to 20th	Night	39% 6% 15% 25% 14% 1	2472
	21st to end	Night	43% 6% 13% 17% 19% 1	2819
August	1st to 10th	Night	48% 5% 17% 20% 9% 1	2814
	11th to 20th	Night	43% 5% 10% 24% 16% 1	2993
	21st to end	Night	34% 5% 11% 30% 18% 1	3476
September	1st to 10th	Night	38% 5% 11% 23% 20% 4	1900
	11th to 20th	Night	33% 5% 8% 25% 25% 3	1900
	21st to end	Night	44% 6% 8% 18% 21% 2	2145
October	1st to 10th	Night	44% 4 9% 21% 22% 2	3800
	11th to 20th	Night	29% 3 8% 30% 25% 4	3779
	21st to end	Night	27% 3 12% 32% 24% 2	4166
November	1st to 10th	Night	32% 5% 12% 26% 20% 4	2537
	11th to 20th	Night	41% 4 9% 25% 17% 4	2488
	21st to end	Night	39% 5% 13% 28% 14% 1	2660
December	1st to 10th	Night	48% 5% 13% 20% 13% 1	2660
	11th to 20th	Night	45% 6% 13% 21% 13% 2	3288
	21st to end	Night	47% 7% 15% 22% 9%	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	24% 24% 30% 14% 6% 1	180
	11th to 20th	Day	31% 22% 31% 13% 2	220
	21st to end	Day	23% 24% 33% 14% 4 2	297
February	1st to 10th	Day	26% 21% 33% 16% 4 1	270
	11th to 20th	Day	26% 23% 35% 14% 1	355
	21st to end	Day	30% 17% 30% 20% 3	382
March	1st to 10th	Day	24% 20% 32% 21% 4	460
	11th to 20th	Day	23% 25% 32% 14% 4 1	460
	21st to end	Day	28% 18% 31% 16% 5% 1	506
April	1st to 10th	Day	25% 20% 31% 16% 7% 2	460
	11th to 20th	Day	22% 20% 28% 18% 8% 3	452
	21st to end	Day	26% 15% 32% 19% 6% 3	460
May	1st to 10th	Day	29% 14% 25% 19% 10% 3	463
	11th to 20th	Day	22% 14% 31% 21% 9% 3	487
	21st to end	Day	18% 6% 26% 27% 16% 6%	529
June	1st to 10th	Day	15% 11% 31% 23% 15% 4	490
	11th to 20th	Day	18% 8% 30% 24% 17% 3	490
	21st to end	Day	15% 9% 29% 27% 15% 5%	490
July	1st to 10th	Day	13% 4 22% 29% 22% 9%	485
	11th to 20th	Day	8% 4 24% 33% 24% 7%	484
	21st to end	Day	12% 4 28% 32% 18% 5%	532
August	1st to 10th	Day	14% 3 21% 29% 22% 11%	486
	11th to 20th	Day	15% 4 19% 31% 21% 9%	479
	21st to end	Day	13% 5% 23% 29% 19% 12%	539
September	1st to 10th	Day	19% 7% 21% 23% 21% 9%	490
	11th to 20th	Day	14% 5% 20% 28% 21% 13%	490
	21st to end	Day	27% 11% 21% 20% 17% 4	490
October	1st to 10th	Day	24% 5% 24% 24% 16% 7%	490
	11th to 20th	Day	18% 13% 28% 24% 14% 3	490
	21st to end	Day	21% 12% 31% 23% 11% 2	526
November	1st to 10th	Day	16% 12% 27% 27% 14% 3	395
	11th to 20th	Day	19% 17% 32% 23% 8%	364
	21st to end	Day	21% 20% 33% 18% 7% 1	180
December	1st to 10th	Day	26% 20% 32% 14% 7% 1	180
	11th to 20th	Day	26% 23% 31% 15% 4 1	180
	21st to end	Day	27% 20% 26% 19% 6% 2	198
January	1st to 10th	Night	21% 15% 40% 21% 4	760
	11th to 20th	Night	25% 16% 30% 25% 4	760
	21st to end	Night	17% 16% 37% 27% 2	836
February	1st to 10th	Night	22% 15% 31% 29% 2	760
	11th to 20th	Night	23% 20% 37% 18% 2	743
	21st to end	Night	25% 16% 34% 21% 3	628
March	1st to 10th	Night	22% 16% 34% 24% 4	760
	11th to 20th	Night	24% 17% 32% 20% 5% 1	760
	21st to end	Night	22% 16% 34% 23% 5%	836
April	1st to 10th	Night	24% 17% 33% 22% 4	760
	11th to 20th	Night	18% 15% 35% 25% 7%	751
	21st to end	Night	23% 13% 29% 28% 8%	760
May	1st to 10th	Night	25% 9% 26% 30% 9%	585
	11th to 20th	Night	20% 7% 28% 34% 10% 1	374
	21st to end	Night	16% 5% 25% 36% 18% 1	411
June	1st to 10th	Night	17% 5% 23% 35% 20%	380
	11th to 20th	Night	15% 4 24% 42% 14% 1	380
	21st to end	Night	11% 3 22% 48% 15% 1	380
July	1st to 10th	Night	11% 3 21% 43% 20% 2	370
	11th to 20th	Night	10% 2 19% 40% 27% 2	368
	21st to end	Night	12% 3 16% 43% 25% 1	514
August	1st to 10th	Night	13% 3 11% 42% 28% 2	567
	11th to 20th	Night	15% 2 16% 34% 31% 2	667
	21st to end	Night	15% 3 17% 34% 28% 2	836
September	1st to 10th	Night	15% 3 22% 34% 23% 3	760
	11th to 20th	Night	14% 4 16% 35% 26% 5%	760
	21st to end	Night	24% 3 19% 32% 20% 2	760
October	1st to 10th	Night	24% 6% 22% 28% 17% 4	760
	11th to 20th	Night	20% 9% 24% 33% 13% 1	760
	21st to end	Night	22% 10% 26% 31% 11%	836
November	1st to 10th	Night	15% 8% 30% 33% 13% 1	780
	11th to 20th	Night	20% 14% 28% 29% 8% 1	765
	21st to end	Night	18% 13% 31% 31% 7%	760
December	1st to 10th	Night	26% 13% 32% 22% 6% 1	760
	11th to 20th	Night	21% 13% 33% 28% 6%	760
	21st to end	Night	23% 11% 33% 29% 3	836

Page generated at 2024-11-08 22:45:38. Version ac07

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