Adolphson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adolphson Observatory clear sky chart from 2005-11-06 to 2025-04-11.

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	12% 8% 3 7% 5% 4 4 4 6% 7% 39%	113585
	Night	12% 9% 3 8% 4 4 4 3 5% 6% 40%	114911
Transparency	Day	42% 6% 12% 23% 15% 2	117166
	Night	42% 6% 12% 23% 16% 2	119472
Seeing	Day	15% 10% 28% 26% 15% 5%	16275
	Night	16% 10% 32% 30% 12% 1	26289

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	10% 12% 6% 14% 7% 7% 5% 3 4 6% 27%	3617
	11th to 20th	Day	9% 9% 5% 11% 7% 6% 7% 4 6% 5% 30%	3694
	21st to end	Day	13% 15% 7% 11% 6% 5% 4 3 4 5% 27%	4488
February	1st to 10th	Day	15% 11% 5% 10% 6% 7% 5% 3 4 6% 27%	1800
	11th to 20th	Day	14% 11% 3 8% 5% 5% 5% 4 4 7% 34%	1861
	21st to end	Day	13% 12% 3 11% 5% 3 3 3 4 6% 36%	1650
March	1st to 10th	Day	17% 11% 4 5% 3 3 3 2 4 5% 44%	4541
	11th to 20th	Day	8% 7% 2 6% 4 5% 5% 4 6% 8% 46%	4980
	21st to end	Day	19% 11% 4 9% 5% 4 4 4 5% 6% 28%	5755
April	1st to 10th	Day	15% 12% 3 7% 5% 5% 3 3 5% 7% 35%	2400
	11th to 20th	Day	15% 10% 3 7% 5% 4 4 3 5% 5% 38%	2254
	21st to end	Day	21% 7% 3 8% 5% 4 4 3 5% 6% 34%	2280
May	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 9% 35%	4123
	11th to 20th	Day	17% 7% 2 6% 4 4 3 4 5% 8% 39%	4399
	21st to end	Day	11% 6% 2 5% 4 4 4 4 5% 7% 45%	4824
June	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 46%	2660
	11th to 20th	Day	7% 6% 2 6% 5% 4 5% 3 6% 7% 49%	2660
	21st to end	Day	10% 6% 2 6% 6% 5% 4 4 7% 10% 41%	2660
July	1st to 10th	Day	9% 7% 2 7% 5% 6% 6% 5% 8% 10% 36%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 10% 50%	4440
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 8% 12% 40%	4754
August	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 4 8% 12% 43%	4104
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 10% 41%	3829
	21st to end	Day	6% 5% 2 5% 4 5% 4 4 6% 9% 50%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 6% 7% 50%	2280
	11th to 20th	Day	10% 4 1 4 4 3 4 3 5% 8% 52%	2268
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 48%	2057
October	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 4 5% 51%	1900
	11th to 20th	Day	15% 9% 2 7% 4 3 3 2 4 6% 45%	1900
	21st to end	Day	19% 9% 2 5% 4 3 3 3 4 6% 40%	2024
November	1st to 10th	Day	11% 8% 2 5% 5% 3 3 4 6% 7% 46%	1762
	11th to 20th	Day	15% 11% 3 8% 4 4 3 3 4 7% 38%	1800
	21st to end	Day	15% 13% 3 7% 5% 4 3 2 4 5% 38%	1601
December	1st to 10th	Day	8% 9% 3 7% 5% 4 4 3 4 6% 46%	2610
	11th to 20th	Day	14% 12% 5% 14% 7% 4 4 3 6% 5% 26%	3008
	21st to end	Day	21% 21% 9% 13% 5% 3 3 2 3 4 15%	3982
January	1st to 10th	Night	12% 12% 6% 14% 4 4 4 3 4 5% 31%	6348
	11th to 20th	Night	10% 13% 6% 13% 7% 5% 5% 4 7% 4 26%	6271
	21st to end	Night	15% 13% 5% 11% 5% 4 4 3 4 4 32%	6490
February	1st to 10th	Night	15% 10% 5% 9% 5% 4 4 3 5% 6% 33%	2600
	11th to 20th	Night	13% 11% 4 7% 5% 4 4 4 5% 7% 36%	2425
	21st to end	Night	14% 11% 4 8% 4 3 3 3 4 5% 42%	1980
March	1st to 10th	Night	18% 10% 3 6% 3 4 4 3 3 5% 41%	5355
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	4980
	21st to end	Night	16% 11% 5% 10% 5% 5% 5% 4 5% 6% 29%	5174
April	1st to 10th	Night	14% 9% 3 7% 5% 4 3 4 5% 7% 41%	2000
	11th to 20th	Night	14% 10% 2 6% 3 4 3 3 6% 5% 43%	1881
	21st to end	Night	17% 6% 3 7% 5% 4 4 3 5% 7% 38%	1900
May	1st to 10th	Night	18% 8% 3 7% 5% 4 4 3 6% 8% 33%	2772
	11th to 20th	Night	12% 7% 2 6% 4 5% 4 3 6% 8% 42%	2506
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 6% 8% 49%	2743
June	1st to 10th	Night	8% 4 2 5% 5% 4 3 5% 6% 9% 50%	1520
	11th to 20th	Night	7% 6% 2 5% 4 3 4 3 7% 10% 48%	1520
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 47%	1520
July	1st to 10th	Night	13% 6% 2 6% 5% 4 6% 4 7% 9% 39%	2530
	11th to 20th	Night	4 3 1 4 4 4 4 4 6% 9% 58%	2530
	21st to end	Night	6% 4 2 6% 4 4 5% 4 7% 9% 48%	2805
August	1st to 10th	Night	4 4 2 4 4 3 4 4 5% 9% 57%	2836
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 5% 7% 54%	3001
	21st to end	Night	5% 4 2 5% 4 4 4 4 6% 8% 55%	3476
September	1st to 10th	Night	11% 5% 1 4 2 3 3 2 5% 7% 57%	1900
	11th to 20th	Night	10% 4 2 5% 4 3 4 4 6% 7% 52%	1900
	21st to end	Night	8% 5% 2 5% 5% 4 4 4 6% 9% 50%	2110
October	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 4 5% 54%	2280
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 5% 6% 50%	2280
	21st to end	Night	16% 8% 2 6% 4 4 4 4 5% 6% 40%	2572
November	1st to 10th	Night	11% 7% 2 5% 3 2 3 2 5% 7% 52%	2536
	11th to 20th	Night	13% 10% 3 7% 4 3 4 3 5% 7% 41%	2600
	21st to end	Night	16% 10% 4 7% 4 4 3 3 4 6% 38%	2795
December	1st to 10th	Night	8% 10% 3 7% 4 4 4 3 4 6% 47%	4580
	11th to 20th	Night	15% 11% 4 11% 5% 4 4 4 4 5% 32%	5199
	21st to end	Night	22% 18% 6% 12% 5% 5% 4 3 4 4 16%	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	58% 5% 10% 19% 7% 1	3618
	11th to 20th	Day	54% 5% 10% 14% 14% 4	3694
	21st to end	Day	59% 5% 10% 18% 7% 1	4488
February	1st to 10th	Day	57% 5% 14% 16% 6% 2	1800
	11th to 20th	Day	50% 6% 12% 20% 11% 1	1870
	21st to end	Day	50% 5% 11% 22% 11% 2	1650
March	1st to 10th	Day	44% 5% 9% 23% 17% 3	4541
	11th to 20th	Day	34% 6% 11% 31% 18%	4980
	21st to end	Day	54% 7% 14% 19% 5% 1	5757
April	1st to 10th	Day	48% 6% 12% 22% 12%	2400
	11th to 20th	Day	46% 6% 10% 23% 13% 2	2254
	21st to end	Day	50% 6% 10% 19% 13% 1	2280
May	1st to 10th	Day	42% 10% 13% 21% 14% 1	4159
	11th to 20th	Day	43% 7% 11% 29% 10%	4403
	21st to end	Day	36% 8% 11% 22% 21% 2	4837
June	1st to 10th	Day	33% 8% 15% 25% 16% 2	2660
	11th to 20th	Day	34% 7% 11% 24% 22% 3	2660
	21st to end	Day	37% 8% 15% 22% 15% 2	2660
July	1st to 10th	Day	41% 7% 14% 25% 11% 2	4371
	11th to 20th	Day	28% 7% 17% 28% 18% 2	4365
	21st to end	Day	33% 8% 22% 21% 15% 1	4604
August	1st to 10th	Day	30% 8% 18% 31% 11% 1	4090
	11th to 20th	Day	38% 7% 15% 27% 14% 1	3867
	21st to end	Day	30% 7% 14% 31% 15% 3	4179
September	1st to 10th	Day	32% 7% 12% 24% 21% 4	2280
	11th to 20th	Day	29% 5% 12% 27% 23% 4	2268
	21st to end	Day	32% 7% 12% 28% 20% 2	2057
October	1st to 10th	Day	23% 4 6% 23% 42% 2	3160
	11th to 20th	Day	28% 3 9% 23% 32% 5%	3140
	21st to end	Day	41% 4 9% 25% 19% 3	3314
November	1st to 10th	Day	36% 5% 16% 24% 15% 3	1762
	11th to 20th	Day	46% 5% 11% 24% 13% 2	1800
	21st to end	Day	49% 5% 14% 23% 9% 1	1601
December	1st to 10th	Day	39% 4 14% 33% 9%	2610
	11th to 20th	Day	58% 5% 11% 17% 7% 2	3005
	21st to end	Day	74% 4 8% 10% 3	3982
January	1st to 10th	Night	54% 6% 11% 21% 7% 1	6348
	11th to 20th	Night	59% 4 11% 12% 12% 2	6271
	21st to end	Night	56% 4 8% 19% 12% 1	6490
February	1st to 10th	Night	53% 4 13% 19% 11% 1	2600
	11th to 20th	Night	47% 5% 12% 23% 12% 1	2426
	21st to end	Night	45% 3 9% 25% 15% 2	1980
March	1st to 10th	Night	46% 5% 7% 25% 15% 2	5355
	11th to 20th	Night	33% 5% 9% 29% 18% 5%	4980
	21st to end	Night	53% 8% 13% 17% 7% 1	5174
April	1st to 10th	Night	42% 6% 11% 25% 14% 2	2000
	11th to 20th	Night	42% 5% 10% 22% 17% 4	1881
	21st to end	Night	45% 6% 12% 20% 14% 3	1900
May	1st to 10th	Night	46% 9% 14% 18% 13% 1	2801
	11th to 20th	Night	37% 11% 15% 26% 11%	2507
	21st to end	Night	30% 8% 13% 24% 23% 2	2751
June	1st to 10th	Night	29% 9% 16% 24% 18% 4	1520
	11th to 20th	Night	29% 7% 12% 25% 23% 5%	1520
	21st to end	Night	34% 7% 16% 19% 20% 3	1520
July	1st to 10th	Night	40% 6% 15% 23% 13% 2	2490
	11th to 20th	Night	23% 6% 14% 32% 24% 2	2482
	21st to end	Night	30% 7% 19% 22% 19% 3	2716
August	1st to 10th	Night	22% 7% 18% 33% 18% 2	2826
	11th to 20th	Night	29% 6% 16% 32% 17% 1	3029
	21st to end	Night	26% 7% 16% 31% 16% 4	3476
September	1st to 10th	Night	27% 5% 12% 26% 25% 5%	1900
	11th to 20th	Night	29% 7% 11% 26% 21% 6%	1900
	21st to end	Night	31% 6% 12% 25% 24% 3	2110
October	1st to 10th	Night	22% 4 7% 25% 38% 4	3800
	11th to 20th	Night	25% 3 9% 22% 35% 5%	3779
	21st to end	Night	41% 5% 9% 20% 22% 4	4232
November	1st to 10th	Night	33% 5% 13% 26% 19% 4	2536
	11th to 20th	Night	42% 5% 12% 24% 16% 2	2600
	21st to end	Night	48% 5% 11% 24% 13% 1	2795
December	1st to 10th	Night	39% 4 13% 33% 12% 1	4580
	11th to 20th	Night	53% 5% 12% 21% 9%	5201
	21st to end	Night	71% 5% 9% 11% 4	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	20% 18% 33% 22% 6% 1	300
	11th to 20th	Day	23% 21% 39% 13% 4	300
	21st to end	Day	20% 20% 36% 18% 6%	330
February	1st to 10th	Day	22% 17% 40% 18% 3	300
	11th to 20th	Day	21% 19% 36% 19% 4 1	300
	21st to end	Day	23% 17% 42% 16% 2	249
March	1st to 10th	Day	19% 16% 43% 18% 3	300
	11th to 20th	Day	27% 17% 32% 15% 8%	300
	21st to end	Day	28% 19% 33% 15% 5% 1	455
April	1st to 10th	Day	25% 14% 33% 23% 5%	500
	11th to 20th	Day	19% 17% 32% 20% 11% 1	452
	21st to end	Day	25% 13% 33% 20% 8% 2	460
May	1st to 10th	Day	20% 10% 34% 26% 8% 2	547
	11th to 20th	Day	19% 13% 28% 24% 13% 2	675
	21st to end	Day	15% 8% 30% 26% 15% 7%	734
June	1st to 10th	Day	8% 5% 26% 31% 23% 6%	680
	11th to 20th	Day	7% 4 28% 36% 20% 4	680
	21st to end	Day	10% 9% 31% 31% 15% 5%	680
July	1st to 10th	Day	10% 4 17% 32% 25% 13%	671
	11th to 20th	Day	9% 3 23% 36% 21% 9%	668
	21st to end	Day	8% 3 19% 35% 28% 7%	739
August	1st to 10th	Day	6% 3 21% 35% 27% 8%	676
	11th to 20th	Day	9% 6% 18% 29% 28% 11%	543
	21st to end	Day	6% 4 15% 33% 31% 11%	539
September	1st to 10th	Day	12% 6% 17% 31% 26% 8%	490
	11th to 20th	Day	8% 2 17% 35% 26% 11%	490
	21st to end	Day	12% 8% 27% 25% 23% 7%	457
October	1st to 10th	Day	12% 8% 30% 28% 17% 5%	300
	11th to 20th	Day	19% 18% 30% 20% 12% 1	300
	21st to end	Day	30% 15% 32% 18% 5% 1	330
November	1st to 10th	Day	13% 12% 36% 25% 10% 3	300
	11th to 20th	Day	21% 16% 35% 20% 7% 1	300
	21st to end	Day	27% 13% 31% 25% 4	300
December	1st to 10th	Day	14% 19% 39% 20% 5% 3	300
	11th to 20th	Day	21% 16% 37% 19% 7%	300
	21st to end	Day	24% 21% 35% 16% 3	330
January	1st to 10th	Night	16% 16% 41% 21% 6%	1000
	11th to 20th	Night	19% 16% 39% 21% 5% 1	1000
	21st to end	Night	19% 13% 38% 27% 3	1100
February	1st to 10th	Night	22% 13% 39% 22% 4	1000
	11th to 20th	Night	19% 16% 36% 25% 3	870
	21st to end	Night	20% 15% 41% 21% 3	660
March	1st to 10th	Night	21% 14% 39% 22% 4	795
	11th to 20th	Night	19% 13% 35% 27% 7%	600
	21st to end	Night	24% 12% 35% 24% 4	660
April	1st to 10th	Night	19% 14% 38% 26% 3	600
	11th to 20th	Night	20% 13% 33% 27% 7%	565
	21st to end	Night	20% 10% 34% 30% 6%	570
May	1st to 10th	Night	15% 10% 37% 31% 6% 1	570
	11th to 20th	Night	17% 7% 27% 35% 13% 1	561
	21st to end	Night	11% 6% 31% 32% 19% 1	617
June	1st to 10th	Night	10% 4 24% 44% 17% 1	570
	11th to 20th	Night	9% 4 26% 40% 20%	570
	21st to end	Night	11% 4 30% 37% 18% 1	570
July	1st to 10th	Night	9% 2 12% 41% 32% 4	555
	11th to 20th	Night	5% 1 20% 45% 26% 3	552
	21st to end	Night	6% 2 13% 47% 30% 1	624
August	1st to 10th	Night	6% 1 15% 46% 29% 3	567
	11th to 20th	Night	7% 2 16% 41% 29% 5%	564
	21st to end	Night	7% 1 14% 45% 32% 2	627
September	1st to 10th	Night	12% 4 18% 38% 25% 3	570
	11th to 20th	Night	12% 3 18% 36% 27% 4	570
	21st to end	Night	10% 6% 24% 35% 21% 3	751
October	1st to 10th	Night	11% 7% 29% 32% 19% 2	760
	11th to 20th	Night	16% 12% 32% 29% 12%	760
	21st to end	Night	21% 13% 33% 26% 7%	836
November	1st to 10th	Night	17% 9% 39% 27% 8% 1	780
	11th to 20th	Night	18% 15% 38% 24% 6%	800
	21st to end	Night	21% 13% 36% 24% 6%	995
December	1st to 10th	Night	18% 13% 40% 24% 4 1	1000
	11th to 20th	Night	22% 11% 35% 26% 6%	1000
	21st to end	Night	27% 15% 33% 22% 2	1100

Page generated at 2025-04-08 08:17:25. Version ac07

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