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 2026-08-15.

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	11% 8% 3 8% 5% 4 5% 4 6% 8% 39%	144281
	Night	12% 9% 3 8% 4 4 4 3 5% 7% 41%	137944
Transparency	Day	42% 6% 13% 24% 14% 2	147818
	Night	42% 5% 12% 23% 16% 2	142486
Seeing	Day	15% 11% 29% 26% 15% 5%	18261
	Night	16% 10% 32% 30% 12% 1	28017

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% 5% 13% 6% 7% 5% 4 5% 7% 27%	4691
	11th to 20th	Day	7% 9% 5% 11% 8% 6% 7% 5% 6% 6% 30%	4812
	21st to end	Day	11% 14% 6% 11% 7% 5% 5% 3 5% 5% 29%	5812
February	1st to 10th	Day	14% 11% 5% 10% 6% 6% 5% 3 5% 6% 28%	1890
	11th to 20th	Day	14% 11% 3 8% 5% 5% 5% 4 4 7% 34%	1957
	21st to end	Day	13% 12% 4 11% 6% 3 3 3 4 6% 36%	1730
March	1st to 10th	Day	17% 11% 4 6% 3 3 3 2 3 5% 44%	4642
	11th to 20th	Day	8% 7% 2 6% 4 5% 5% 4 6% 8% 45%	5090
	21st to end	Day	19% 11% 4 9% 5% 4 4 4 5% 6% 29%	5882
April	1st to 10th	Day	15% 12% 3 7% 5% 5% 4 3 5% 7% 35%	2520
	11th to 20th	Day	14% 10% 3 7% 5% 4 5% 3 5% 6% 37%	2494
	21st to end	Day	19% 7% 3 8% 5% 5% 4 3 5% 6% 35%	2520
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 4 4 6% 8% 37%	7684
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 7% 43%	8222
	21st to end	Day	12% 7% 3 8% 5% 5% 5% 4 6% 7% 37%	9047
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	2940
	11th to 20th	Day	7% 6% 2 6% 5% 3 5% 3 6% 8% 48%	2940
	21st to end	Day	10% 6% 2 6% 6% 5% 4 4 7% 9% 41%	2940
July	1st to 10th	Day	7% 6% 2 7% 5% 5% 6% 4 7% 10% 42%	8280
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 4 6% 9% 47%	8280
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 10% 38%	8875
August	1st to 10th	Day	7% 4 2 6% 4 5% 5% 4 8% 11% 43%	4364
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 10% 41%	4004
	21st to end	Day	6% 5% 2 5% 4 5% 5% 4 6% 9% 49%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 6% 7% 50%	2400
	11th to 20th	Day	10% 4 1 4 4 3 4 4 6% 8% 52%	2387
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 5% 8% 49%	2165
October	1st to 10th	Day	12% 7% 2 6% 4 3 3 3 4 5% 51%	2000
	11th to 20th	Day	14% 8% 2 7% 4 4 4 2 4 6% 45%	2000
	21st to end	Day	19% 9% 2 6% 4 3 3 3 4 6% 40%	2130
November	1st to 10th	Day	10% 8% 2 6% 5% 3 3 4 6% 7% 46%	1852
	11th to 20th	Day	15% 11% 3 8% 4 4 3 3 4 7% 38%	1890
	21st to end	Day	15% 13% 3 7% 5% 4 3 3 4 5% 38%	1681
December	1st to 10th	Day	8% 9% 3 8% 5% 4 4 3 4 6% 45%	2690
	11th to 20th	Day	15% 12% 5% 14% 6% 4 4 3 6% 5% 26%	3088
	21st to end	Day	20% 21% 9% 13% 5% 3 3 2 3 4 15%	4070
January	1st to 10th	Night	11% 13% 6% 13% 5% 4 4 3 4 5% 33%	8232
	11th to 20th	Night	8% 11% 5% 12% 8% 6% 6% 4 7% 4 28%	8163
	21st to end	Night	12% 13% 5% 11% 5% 4 4 3 4 5% 35%	8402
February	1st to 10th	Night	14% 10% 5% 9% 5% 4 4 3 5% 6% 34%	2730
	11th to 20th	Night	13% 11% 4 7% 5% 4 4 4 5% 7% 37%	2549
	21st to end	Night	13% 11% 4 8% 5% 3 3 3 4 5% 42%	2076
March	1st to 10th	Night	18% 10% 3 6% 3 4 4 3 3 5% 41%	5475
	11th to 20th	Night	11% 7% 2 6% 3 3 3 2 5% 6% 50%	5090
	21st to end	Night	16% 11% 5% 10% 5% 5% 5% 4 5% 6% 29%	5289
April	1st to 10th	Night	15% 9% 3 7% 5% 4 3 3 5% 7% 40%	2100
	11th to 20th	Night	14% 10% 2 7% 3 4 3 3 6% 5% 42%	2075
	21st to end	Night	16% 7% 3 7% 5% 4 4 3 5% 7% 38%	2100
May	1st to 10th	Night	15% 8% 3 7% 4 5% 4 3 5% 7% 39%	5165
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 10% 42%	4670
	21st to end	Night	12% 8% 2 7% 4 4 5% 4 5% 8% 40%	5139
June	1st to 10th	Night	8% 4 2 5% 4 4 3 5% 6% 8% 50%	1680
	11th to 20th	Night	7% 6% 2 5% 4 3 4 3 7% 10% 48%	1680
	21st to end	Night	9% 6% 2 5% 4 4 4 4 6% 8% 47%	1680
July	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 7% 11% 44%	4708
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 6% 9% 52%	4707
	21st to end	Night	9% 6% 2 7% 4 4 5% 4 7% 8% 45%	5228
August	1st to 10th	Night	4 4 2 4 4 3 4 5% 6% 9% 56%	3016
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 7% 53%	3134
	21st to end	Night	5% 3 2 5% 4 4 4 4 6% 8% 55%	3586
September	1st to 10th	Night	10% 5% 1 4 3 3 3 2 5% 7% 58%	2000
	11th to 20th	Night	9% 4 2 5% 4 3 4 4 6% 8% 52%	2000
	21st to end	Night	8% 5% 2 5% 5% 4 3 4 6% 8% 50%	2222
October	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 5% 5% 55%	2400
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 5% 6% 49%	2400
	21st to end	Night	16% 8% 2 6% 4 4 4 4 5% 6% 40%	2708
November	1st to 10th	Night	11% 7% 2 5% 3 2 3 2 5% 6% 52%	2666
	11th to 20th	Night	13% 10% 3 7% 4 4 4 3 5% 7% 41%	2730
	21st to end	Night	16% 10% 4 8% 4 4 3 3 4 6% 38%	2935
December	1st to 10th	Night	8% 10% 3 7% 5% 4 4 3 4 6% 46%	4720
	11th to 20th	Night	15% 11% 4 11% 5% 4 4 4 4 5% 32%	5339
	21st to end	Night	22% 18% 6% 11% 5% 5% 4 3 4 4 17%	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	56% 5% 13% 18% 7% 1	4692
	11th to 20th	Day	52% 5% 9% 18% 13% 3	4812
	21st to end	Day	57% 4 11% 20% 7% 1	5812
February	1st to 10th	Day	56% 5% 14% 17% 6% 1	1890
	11th to 20th	Day	50% 6% 12% 20% 10% 2	1966
	21st to end	Day	50% 5% 11% 23% 10% 2	1730
March	1st to 10th	Day	45% 5% 8% 23% 17% 2	4642
	11th to 20th	Day	34% 6% 11% 31% 18%	5090
	21st to end	Day	54% 7% 14% 20% 5% 1	5884
April	1st to 10th	Day	49% 6% 12% 22% 12%	2520
	11th to 20th	Day	46% 6% 10% 23% 12% 2	2494
	21st to end	Day	49% 6% 11% 20% 13% 1	2520
May	1st to 10th	Day	43% 7% 11% 21% 17% 1	7720
	11th to 20th	Day	40% 5% 11% 26% 14% 3	8226
	21st to end	Day	44% 7% 10% 20% 17% 1	9061
June	1st to 10th	Day	34% 8% 15% 25% 16% 2	2940
	11th to 20th	Day	34% 6% 11% 24% 22% 3	2940
	21st to end	Day	37% 8% 15% 22% 15% 2	2940
July	1st to 10th	Day	35% 6% 15% 27% 15% 1	8211
	11th to 20th	Day	32% 6% 15% 28% 17% 1	8205
	21st to end	Day	39% 7% 19% 25% 10%	8680
August	1st to 10th	Day	31% 8% 18% 31% 11% 1	4350
	11th to 20th	Day	38% 6% 15% 27% 14% 1	4042
	21st to end	Day	30% 7% 14% 31% 15% 3	4311
September	1st to 10th	Day	31% 7% 12% 26% 21% 4	2400
	11th to 20th	Day	29% 5% 13% 28% 22% 4	2387
	21st to end	Day	32% 7% 12% 27% 21% 2	2165
October	1st to 10th	Day	23% 4 6% 23% 42% 2	3260
	11th to 20th	Day	28% 3 9% 23% 31% 5%	3240
	21st to end	Day	41% 4 9% 25% 19% 3	3420
November	1st to 10th	Day	36% 5% 16% 25% 15% 3	1852
	11th to 20th	Day	46% 5% 11% 24% 12% 2	1890
	21st to end	Day	50% 4 14% 23% 9% 1	1681
December	1st to 10th	Day	40% 4 14% 33% 9% 1	2690
	11th to 20th	Day	58% 5% 11% 17% 7% 2	3085
	21st to end	Day	74% 4 8% 10% 4	4070
January	1st to 10th	Night	52% 6% 14% 21% 7%	8233
	11th to 20th	Night	55% 4 10% 16% 13% 1	8163
	21st to end	Night	53% 3 12% 20% 11% 1	8402
February	1st to 10th	Night	51% 4 13% 20% 11% 1	2730
	11th to 20th	Night	46% 5% 11% 24% 12% 1	2550
	21st to end	Night	45% 3 9% 25% 15% 2	2076
March	1st to 10th	Night	46% 5% 7% 25% 15% 2	5475
	11th to 20th	Night	34% 5% 9% 29% 18% 5%	5090
	21st to end	Night	53% 8% 13% 17% 7% 1	5289
April	1st to 10th	Night	43% 5% 11% 25% 14% 2	2100
	11th to 20th	Night	42% 5% 10% 22% 16% 4	2075
	21st to end	Night	44% 6% 12% 21% 14% 3	2100
May	1st to 10th	Night	43% 7% 10% 22% 17% 2	5194
	11th to 20th	Night	35% 8% 15% 23% 15% 4	4671
	21st to end	Night	41% 6% 10% 21% 20% 2	5149
June	1st to 10th	Night	29% 8% 15% 25% 18% 4	1680
	11th to 20th	Night	29% 7% 12% 25% 23% 4	1680
	21st to end	Night	34% 8% 15% 20% 20% 3	1680
July	1st to 10th	Night	32% 6% 17% 26% 17% 2	4670
	11th to 20th	Night	28% 6% 13% 28% 23% 2	4662
	21st to end	Night	35% 6% 18% 27% 13% 2	5112
August	1st to 10th	Night	23% 7% 18% 32% 18% 2	3006
	11th to 20th	Night	29% 6% 17% 31% 16% 1	3162
	21st to end	Night	26% 6% 16% 32% 16% 4	3586
September	1st to 10th	Night	27% 5% 12% 27% 25% 5%	2000
	11th to 20th	Night	29% 7% 11% 27% 21% 5%	2000
	21st to end	Night	30% 6% 12% 24% 25% 3	2222
October	1st to 10th	Night	22% 4 7% 25% 38% 4	3920
	11th to 20th	Night	26% 4 9% 22% 35% 5%	3899
	21st to end	Night	41% 5% 8% 20% 22% 4	4368
November	1st to 10th	Night	33% 5% 12% 27% 19% 4	2666
	11th to 20th	Night	42% 5% 12% 24% 15% 2	2730
	21st to end	Night	48% 4 10% 23% 12% 1	2935
December	1st to 10th	Night	40% 4 12% 32% 12% 1	4720
	11th to 20th	Night	53% 5% 12% 21% 9%	5341
	21st to end	Night	71% 5% 9% 11% 4	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	19% 18% 34% 23% 6% 1	330
	11th to 20th	Day	22% 21% 40% 13% 4	330
	21st to end	Day	19% 22% 36% 17% 5%	363
February	1st to 10th	Day	21% 18% 41% 17% 3	330
	11th to 20th	Day	22% 19% 37% 18% 4 1	330
	21st to end	Day	22% 18% 44% 15% 1	273
March	1st to 10th	Day	20% 15% 44% 18% 3	330
	11th to 20th	Day	27% 17% 32% 15% 8%	330
	21st to end	Day	26% 19% 35% 14% 5% 1	494
April	1st to 10th	Day	26% 15% 33% 21% 5%	540
	11th to 20th	Day	20% 18% 33% 19% 9% 1	532
	21st to end	Day	23% 14% 34% 20% 8% 1	540
May	1st to 10th	Day	18% 11% 34% 26% 8% 2	636
	11th to 20th	Day	19% 14% 28% 24% 13% 2	775
	21st to end	Day	15% 8% 31% 26% 14% 7%	844
June	1st to 10th	Day	9% 6% 27% 31% 22% 6%	780
	11th to 20th	Day	8% 6% 29% 34% 19% 4	780
	21st to end	Day	11% 8% 31% 32% 14% 4	780
July	1st to 10th	Day	9% 4 16% 33% 25% 12%	771
	11th to 20th	Day	9% 3 22% 35% 21% 10%	768
	21st to end	Day	9% 3 19% 35% 27% 7%	849
August	1st to 10th	Day	7% 3 21% 35% 26% 8%	776
	11th to 20th	Day	9% 5% 18% 29% 28% 11%	606
	21st to end	Day	6% 5% 16% 33% 30% 11%	583
September	1st to 10th	Day	12% 6% 17% 31% 26% 8%	530
	11th to 20th	Day	8% 2 16% 34% 28% 12%	530
	21st to end	Day	11% 7% 26% 25% 23% 8%	495
October	1st to 10th	Day	12% 8% 29% 28% 18% 5%	330
	11th to 20th	Day	17% 18% 29% 22% 12% 1	330
	21st to end	Day	29% 15% 32% 19% 4 1	363
November	1st to 10th	Day	13% 14% 38% 23% 10% 3	330
	11th to 20th	Day	20% 16% 36% 20% 7% 1	330
	21st to end	Day	27% 14% 29% 25% 5% 1	330
December	1st to 10th	Day	13% 18% 40% 22% 5% 3	330
	11th to 20th	Day	22% 16% 37% 19% 6%	330
	21st to end	Day	24% 21% 36% 16% 3	363
January	1st to 10th	Night	16% 16% 41% 21% 6%	1050
	11th to 20th	Night	19% 16% 40% 20% 5%	1050
	21st to end	Night	18% 14% 38% 27% 3	1155
February	1st to 10th	Night	21% 13% 39% 23% 5%	1050
	11th to 20th	Night	19% 16% 36% 25% 3	914
	21st to end	Night	19% 15% 42% 21% 3	692
March	1st to 10th	Night	21% 14% 39% 22% 4	835
	11th to 20th	Night	20% 13% 35% 26% 6%	630
	21st to end	Night	24% 13% 36% 23% 3	693
April	1st to 10th	Night	19% 14% 38% 25% 3	630
	11th to 20th	Night	20% 13% 33% 26% 6%	623
	21st to end	Night	20% 11% 34% 30% 6%	630
May	1st to 10th	Night	14% 9% 38% 31% 6% 1	630
	11th to 20th	Night	17% 8% 28% 34% 12% 1	621
	21st to end	Night	12% 7% 30% 32% 18% 1	683
June	1st to 10th	Night	10% 4 25% 43% 17% 1	630
	11th to 20th	Night	9% 5% 27% 40% 19%	630
	21st to end	Night	10% 4 30% 37% 18% 1	630
July	1st to 10th	Night	8% 2 13% 41% 32% 4	615
	11th to 20th	Night	6% 1 19% 44% 26% 3	612
	21st to end	Night	7% 3 13% 46% 30% 1	690
August	1st to 10th	Night	6% 2 16% 45% 29% 2	627
	11th to 20th	Night	7% 2 16% 42% 30% 4	606
	21st to end	Night	7% 1 13% 46% 31% 2	660
September	1st to 10th	Night	12% 4 18% 38% 26% 3	600
	11th to 20th	Night	11% 3 18% 37% 27% 4	600
	21st to end	Night	10% 6% 23% 35% 22% 3	791
October	1st to 10th	Night	11% 7% 29% 33% 19% 2	800
	11th to 20th	Night	16% 12% 32% 29% 12%	800
	21st to end	Night	21% 13% 34% 26% 6%	880
November	1st to 10th	Night	16% 10% 39% 27% 8%	820
	11th to 20th	Night	18% 15% 38% 24% 6%	840
	21st to end	Night	22% 13% 36% 24% 6%	1045
December	1st to 10th	Night	18% 13% 40% 25% 4	1050
	11th to 20th	Night	22% 12% 34% 26% 6%	1050
	21st to end	Night	27% 15% 34% 22% 2	1155

Page generated at 2026-08-12 02:37:20. Version ac07

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