Adams Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adams Observing Site clear sky chart from 2005-11-06 to 2026-09-14.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	148648
	Night	14% 9% 3 8% 5% 4 4 3 5% 7% 37%	142443
Transparency	Day	46% 5% 10% 23% 14% 2	152335
	Night	46% 5% 9% 22% 15% 2	146827
Seeing	Day	23% 11% 25% 22% 14% 6%	17266
	Night	21% 9% 23% 28% 16% 2	27265

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	18% 17% 6% 12% 5% 4 3 3 4 5% 24%	5258
	11th to 20th	Day	13% 15% 6% 14% 5% 3 3 2 3 4 32%	5280
	21st to end	Day	20% 14% 4 9% 6% 4 4 3 5% 5% 25%	5780
February	1st to 10th	Day	19% 12% 4 11% 5% 4 4 2 4 5% 30%	1979
	11th to 20th	Day	20% 11% 4 10% 4 4 4 2 5% 5% 29%	2048
	21st to end	Day	19% 12% 4 7% 5% 3 4 4 5% 5% 32%	1730
March	1st to 10th	Day	18% 13% 3 7% 4 4 4 3 4 5% 34%	4721
	11th to 20th	Day	13% 8% 3 6% 4 4 5% 3 6% 8% 41%	5090
	21st to end	Day	16% 8% 2 8% 5% 4 5% 3 6% 7% 36%	5586
April	1st to 10th	Day	15% 9% 3 7% 5% 4 4 3 5% 7% 38%	2393
	11th to 20th	Day	16% 8% 3 6% 5% 4 4 4 5% 7% 39%	2577
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 5% 7% 37%	2730
May	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 5% 6% 8% 29%	7616
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 4 6% 7% 35%	7626
	21st to end	Day	18% 8% 4 8% 5% 6% 6% 5% 7% 9% 26%	8391
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 7% 41%	2730
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	2730
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	2730
July	1st to 10th	Day	10% 6% 3 8% 5% 5% 5% 4 7% 10% 38%	7680
	11th to 20th	Day	11% 6% 3 7% 6% 6% 6% 5% 7% 10% 34%	7680
	21st to end	Day	12% 8% 3 8% 6% 6% 7% 5% 7% 9% 30%	8340
August	1st to 10th	Day	10% 7% 2 7% 5% 6% 6% 4 8% 10% 35%	6014
	11th to 20th	Day	10% 6% 3 7% 5% 6% 6% 5% 8% 11% 33%	5951
	21st to end	Day	5% 3 1 4 3 4 4 4 6% 9% 55%	6203
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 8% 46%	2336
	11th to 20th	Day	11% 6% 2 5% 3 4 5% 4 5% 9% 47%	2233
	21st to end	Day	17% 5% 3 7% 4 4 3 3 4 6% 44%	2200
October	1st to 10th	Day	11% 4 2 5% 3 4 3 2 5% 8% 52%	2200
	11th to 20th	Day	14% 6% 2 6% 3 3 3 3 4 6% 51%	2001
	21st to end	Day	21% 7% 2 6% 3 3 3 3 4 6% 41%	2135
November	1st to 10th	Day	12% 7% 2 5% 3 4 3 3 4 5% 52%	1852
	11th to 20th	Day	15% 10% 3 7% 3 4 3 3 5% 5% 41%	1890
	21st to end	Day	18% 11% 3 7% 4 3 3 3 4 6% 37%	1890
December	1st to 10th	Day	19% 13% 4 8% 4 3 3 2 4 3 36%	3020
	11th to 20th	Day	21% 14% 5% 8% 4 5% 4 3 4 4 27%	3463
	21st to end	Day	19% 16% 5% 10% 6% 5% 4 3 4 6% 21%	4565
January	1st to 10th	Night	16% 13% 6% 12% 6% 4 4 3 5% 6% 25%	7635
	11th to 20th	Night	16% 15% 5% 11% 4 3 3 3 4 4 30%	7680
	21st to end	Night	17% 12% 5% 9% 5% 4 4 2 4 4 33%	8401
February	1st to 10th	Night	20% 13% 4 8% 5% 5% 4 3 4 5% 29%	2637
	11th to 20th	Night	22% 11% 4 9% 5% 4 4 3 4 5% 30%	2458
	21st to end	Night	22% 12% 4 9% 4 4 4 3 4 5% 30%	2076
March	1st to 10th	Night	18% 12% 3 6% 4 4 4 3 5% 6% 37%	5337
	11th to 20th	Night	13% 7% 2 6% 3 3 4 3 5% 7% 46%	5090
	21st to end	Night	14% 9% 3 8% 6% 5% 5% 4 6% 7% 33%	5588
April	1st to 10th	Night	15% 7% 2 5% 4 4 4 5% 6% 7% 40%	2244
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 7% 7% 43%	1990
	21st to end	Night	16% 7% 2 7% 5% 4 4 3 5% 7% 39%	1890
May	1st to 10th	Night	17% 9% 3 8% 5% 5% 6% 4 6% 7% 30%	5237
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 5% 7% 9% 36%	5234
	21st to end	Night	16% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	5761
June	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 7% 9% 46%	1890
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 5% 7% 9% 46%	1890
	21st to end	Night	9% 5% 2 4 4 4 5% 5% 8% 11% 43%	1890
July	1st to 10th	Night	7% 6% 2 7% 5% 5% 5% 4 6% 10% 43%	5278
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 5% 7% 9% 38%	5277
	21st to end	Night	10% 7% 4 8% 6% 6% 6% 4 7% 10% 34%	5736
August	1st to 10th	Night	9% 7% 3 9% 6% 6% 6% 4 7% 9% 35%	4135
	11th to 20th	Night	9% 7% 3 8% 5% 5% 5% 4 7% 9% 37%	4095
	21st to end	Night	4 4 2 4 3 4 4 4 5% 9% 58%	4906
September	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 49%	2263
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 6% 7% 50%	2234
	21st to end	Night	13% 6% 2 7% 5% 4 4 3 3 6% 46%	2200
October	1st to 10th	Night	11% 4 2 4 3 4 3 3 5% 6% 55%	2200
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 7% 49%	2398
	21st to end	Night	19% 8% 2 5% 4 3 3 3 4 5% 43%	2702
November	1st to 10th	Night	13% 7% 2 5% 4 4 3 3 4 5% 50%	2666
	11th to 20th	Night	17% 8% 3 6% 3 3 3 4 5% 6% 43%	2730
	21st to end	Night	19% 11% 3 5% 4 4 3 3 4 6% 38%	2730
December	1st to 10th	Night	18% 13% 4 8% 4 3 3 2 4 4 36%	4380
	11th to 20th	Night	20% 12% 6% 8% 4 4 3 3 4 5% 32%	4952
	21st to end	Night	19% 18% 4 10% 5% 5% 5% 3 5% 6% 20%	6633

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	63% 4 8% 17% 7%	5259
	11th to 20th	Day	59% 2 5% 19% 13% 2	5280
	21st to end	Day	62% 3 7% 21% 6% 1	5780
February	1st to 10th	Day	58% 3 8% 19% 11% 1	1979
	11th to 20th	Day	58% 3 7% 18% 11% 2	2058
	21st to end	Day	55% 3 8% 22% 11% 2	1730
March	1st to 10th	Day	53% 4 5% 17% 15% 5%	4721
	11th to 20th	Day	41% 4 9% 25% 19% 2	5090
	21st to end	Day	47% 5% 10% 25% 13% 1	5586
April	1st to 10th	Day	47% 4 10% 25% 12% 3	2393
	11th to 20th	Day	45% 4 8% 22% 16% 4	2577
	21st to end	Day	46% 6% 10% 23% 12% 2	2730
May	1st to 10th	Day	50% 6% 11% 22% 10% 1	7651
	11th to 20th	Day	47% 6% 10% 23% 13% 1	7630
	21st to end	Day	51% 7% 11% 17% 11% 3	8405
June	1st to 10th	Day	39% 7% 11% 25% 17% 1	2730
	11th to 20th	Day	39% 7% 14% 21% 17% 2	2730
	21st to end	Day	39% 7% 13% 22% 16% 3	2730
July	1st to 10th	Day	41% 7% 13% 24% 14% 1	7615
	11th to 20th	Day	43% 7% 12% 27% 10% 1	7611
	21st to end	Day	48% 7% 11% 21% 13% 1	8156
August	1st to 10th	Day	42% 8% 13% 26% 11% 1	6001
	11th to 20th	Day	43% 7% 14% 25% 11% 1	5990
	21st to end	Day	24% 5% 16% 32% 21% 2	6202
September	1st to 10th	Day	37% 5% 12% 22% 19% 6%	2336
	11th to 20th	Day	35% 3 10% 25% 23% 3	2233
	21st to end	Day	41% 4 9% 24% 21% 2	2200
October	1st to 10th	Day	23% 3 7% 27% 38% 2	3590
	11th to 20th	Day	27% 3 8% 29% 30% 2	3241
	21st to end	Day	32% 3 8% 29% 22% 5%	3424
November	1st to 10th	Day	36% 3 8% 27% 22% 4	1852
	11th to 20th	Day	46% 2 7% 23% 19% 3	1890
	21st to end	Day	51% 3 8% 21% 16% 1	1890
December	1st to 10th	Day	54% 3 6% 21% 16%	3020
	11th to 20th	Day	61% 3 8% 18% 10% 1	3460
	21st to end	Day	64% 5% 9% 16% 5% 1	4565
January	1st to 10th	Night	61% 4 10% 18% 7%	7636
	11th to 20th	Night	58% 3 4 18% 14% 3	7680
	21st to end	Night	56% 2 8% 21% 11% 2	8401
February	1st to 10th	Night	58% 3 9% 19% 10% 1	2637
	11th to 20th	Night	57% 3 6% 20% 11% 1	2459
	21st to end	Night	58% 3 9% 15% 11% 3	2076
March	1st to 10th	Night	50% 3 5% 24% 14% 4	5337
	11th to 20th	Night	37% 5% 8% 28% 21% 1	5090
	21st to end	Night	49% 5% 8% 22% 14% 1	5588
April	1st to 10th	Night	41% 6% 10% 24% 18% 2	2244
	11th to 20th	Night	39% 5% 10% 23% 18% 6%	1990
	21st to end	Night	45% 5% 11% 23% 14% 2	1890
May	1st to 10th	Night	52% 6% 9% 21% 10% 2	5264
	11th to 20th	Night	43% 8% 14% 21% 13% 1	5235
	21st to end	Night	50% 7% 12% 17% 13% 2	5771
June	1st to 10th	Night	32% 7% 14% 25% 18% 3	1890
	11th to 20th	Night	33% 7% 14% 24% 19% 3	1890
	21st to end	Night	34% 8% 15% 23% 15% 4	1890
July	1st to 10th	Night	37% 8% 11% 26% 16% 2	5235
	11th to 20th	Night	41% 8% 14% 24% 12% 1	5226
	21st to end	Night	45% 6% 11% 23% 13% 2	5606
August	1st to 10th	Night	45% 7% 12% 24% 12% 1	4124
	11th to 20th	Night	42% 7% 14% 24% 12% 1	4122
	21st to end	Night	22% 6% 15% 35% 20% 3	4906
September	1st to 10th	Night	33% 6% 11% 23% 20% 7%	2263
	11th to 20th	Night	33% 4 10% 24% 25% 3	2234
	21st to end	Night	39% 5% 7% 21% 24% 3	2200
October	1st to 10th	Night	25% 4 7% 25% 36% 3	3590
	11th to 20th	Night	26% 3 7% 25% 34% 4	3897
	21st to end	Night	32% 3 6% 23% 29% 7%	4363
November	1st to 10th	Night	38% 4 8% 24% 23% 4	2666
	11th to 20th	Night	43% 3 7% 21% 21% 5%	2730
	21st to end	Night	49% 4 8% 24% 14% 1	2730
December	1st to 10th	Night	53% 3 10% 21% 13% 1	4380
	11th to 20th	Night	56% 3 9% 21% 10% 1	4954
	21st to end	Night	65% 5% 8% 15% 7%	6633

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	34% 19% 31% 12% 3 1	330
	11th to 20th	Day	41% 19% 30% 10%	330
	21st to end	Day	36% 24% 29% 10% 2	363
February	1st to 10th	Day	32% 21% 34% 11% 2	330
	11th to 20th	Day	43% 21% 28% 6% 2	330
	21st to end	Day	36% 16% 38% 9% 1	273
March	1st to 10th	Day	36% 18% 29% 12% 5%	393
	11th to 20th	Day	30% 20% 29% 16% 4	540
	21st to end	Day	34% 16% 31% 15% 5%	594
April	1st to 10th	Day	29% 16% 29% 17% 7% 2	540
	11th to 20th	Day	25% 16% 30% 19% 6% 3	532
	21st to end	Day	25% 15% 33% 19% 6% 3	540
May	1st to 10th	Day	28% 17% 27% 17% 8% 3	543
	11th to 20th	Day	22% 11% 29% 21% 12% 5%	567
	21st to end	Day	19% 8% 24% 25% 16% 7%	617
June	1st to 10th	Day	15% 6% 25% 29% 18% 8%	570
	11th to 20th	Day	14% 6% 24% 31% 17% 8%	570
	21st to end	Day	14% 6% 24% 27% 18% 11%	570
July	1st to 10th	Day	17% 2 15% 25% 21% 20%	565
	11th to 20th	Day	13% 4 18% 30% 20% 14%	564
	21st to end	Day	15% 3 17% 28% 23% 14%	620
August	1st to 10th	Day	14% 3 18% 27% 27% 12%	566
	11th to 20th	Day	13% 4 17% 31% 23% 12%	559
	21st to end	Day	9% 3 14% 31% 28% 15%	627
September	1st to 10th	Day	15% 3 14% 27% 28% 12%	570
	11th to 20th	Day	14% 2 13% 27% 32% 13%	542
	21st to end	Day	22% 6% 21% 22% 22% 6%	530
October	1st to 10th	Day	14% 4 21% 30% 23% 8%	530
	11th to 20th	Day	18% 11% 27% 26% 13% 5%	530
	21st to end	Day	30% 8% 29% 23% 10% 1	518
November	1st to 10th	Day	20% 11% 38% 22% 6% 3	330
	11th to 20th	Day	32% 12% 32% 16% 7% 1	330
	21st to end	Day	31% 17% 32% 14% 5% 1	330
December	1st to 10th	Day	33% 19% 30% 13% 5% 1	330
	11th to 20th	Day	34% 14% 33% 15% 5%	330
	21st to end	Day	37% 16% 30% 12% 4	363
January	1st to 10th	Night	29% 19% 29% 20% 4	840
	11th to 20th	Night	34% 18% 27% 19% 2	840
	21st to end	Night	26% 19% 32% 21% 2	924
February	1st to 10th	Night	31% 14% 31% 22% 3	840
	11th to 20th	Night	33% 17% 31% 17% 2	823
	21st to end	Night	32% 15% 34% 17% 2	692
March	1st to 10th	Night	27% 15% 30% 23% 5%	840
	11th to 20th	Night	28% 16% 28% 20% 7% 1	840
	21st to end	Night	23% 15% 31% 25% 7%	924
April	1st to 10th	Night	23% 12% 30% 26% 9%	774
	11th to 20th	Night	20% 12% 29% 28% 10% 1	623
	21st to end	Night	20% 8% 33% 28% 9% 1	630
May	1st to 10th	Night	22% 7% 27% 29% 12% 2	630
	11th to 20th	Night	18% 5% 22% 35% 19% 1	621
	21st to end	Night	14% 3 19% 34% 25% 5%	683
June	1st to 10th	Night	11% 3 17% 43% 24% 3	630
	11th to 20th	Night	9% 3 15% 40% 29% 4	630
	21st to end	Night	13% 2 16% 37% 28% 5%	630
July	1st to 10th	Night	14% 2 11% 28% 36% 11%	615
	11th to 20th	Night	8% 1 11% 36% 38% 5%	612
	21st to end	Night	12% 2 9% 33% 37% 7%	690
August	1st to 10th	Night	10% 2 8% 34% 39% 7%	627
	11th to 20th	Night	10% 2 8% 36% 37% 7%	624
	21st to end	Night	10% 1 9% 33% 40% 8%	693
September	1st to 10th	Night	13% 2 9% 34% 36% 6%	793
	11th to 20th	Night	15% 2 11% 31% 35% 6%	813
	21st to end	Night	15% 5% 18% 32% 28% 2	800
October	1st to 10th	Night	13% 4 17% 31% 30% 5%	800
	11th to 20th	Night	19% 7% 23% 32% 17% 2	800
	21st to end	Night	23% 10% 26% 27% 13% 1	880
November	1st to 10th	Night	18% 8% 26% 31% 15% 2	820
	11th to 20th	Night	24% 12% 28% 26% 10%	840
	21st to end	Night	28% 11% 23% 28% 9% 1	840
December	1st to 10th	Night	31% 14% 26% 25% 5%	840
	11th to 20th	Night	25% 15% 28% 26% 5%	840
	21st to end	Night	32% 14% 27% 24% 3	924

Page generated at 2026-09-11 04:11:57. Version ac07

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