Transit Dreams Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Transit Dreams Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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% 5% 2 5% 4 4 4 4 6% 7% 44%	114529
	Night	15% 5% 2 5% 4 4 4 3 5% 7% 46%	114748
Transparency	Day	36% 7% 12% 19% 19% 6%	118271
	Night	37% 7% 10% 18% 21% 7%	119145
Seeing	Day	17% 9% 22% 24% 19% 9%	15826
	Night	17% 7% 23% 30% 20% 3	25947

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	14% 5% 2 4 2 2 2 2 4 6% 57%	4056
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 3 3 62%	4060
	21st to end	Day	19% 5% 2 6% 4 3 3 2 3 5% 47%	4466
February	1st to 10th	Day	16% 6% 2 5% 4 3 4 4 5% 7% 44%	1870
	11th to 20th	Day	21% 6% 2 4 4 3 3 2 4 6% 44%	1948
	21st to end	Day	19% 6% 2 5% 4 4 5% 3 4 5% 43%	1650
March	1st to 10th	Day	21% 6% 2 5% 3 4 4 3 4 5% 43%	4889
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 4 6% 55%	4980
	21st to end	Day	20% 5% 2 4 3 3 4 3 4 5% 46%	5465
April	1st to 10th	Day	14% 4 2 4 4 4 4 5% 6% 7% 47%	2200
	11th to 20th	Day	14% 5% 2 3 5% 4 4 3 5% 7% 48%	2357
	21st to end	Day	12% 5% 2 5% 4 4 4 3 6% 7% 48%	2600
May	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 5% 7% 8% 39%	4212
	11th to 20th	Day	18% 7% 3 7% 4 4 5% 4 6% 7% 35%	4211
	21st to end	Day	9% 4 2 6% 4 4 5% 5% 8% 11% 43%	4541
June	1st to 10th	Day	10% 6% 3 6% 6% 6% 6% 6% 9% 10% 33%	2470
	11th to 20th	Day	6% 5% 2 5% 6% 5% 7% 6% 9% 10% 39%	2470
	21st to end	Day	8% 4 2 5% 6% 5% 7% 6% 9% 10% 38%	2470
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 6% 5% 9% 10% 36%	4120
	11th to 20th	Day	8% 5% 2 7% 5% 5% 7% 5% 8% 11% 36%	4120
	21st to end	Day	10% 8% 3 10% 7% 7% 8% 6% 9% 10% 22%	4466
August	1st to 10th	Day	16% 7% 2 7% 5% 6% 6% 5% 8% 10% 29%	4104
	11th to 20th	Day	9% 4 2 6% 5% 6% 7% 5% 8% 12% 36%	4044
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 8% 53%	4176
September	1st to 10th	Day	8% 4 2 6% 5% 6% 6% 5% 6% 8% 44%	2090
	11th to 20th	Day	15% 7% 2 7% 4 5% 4 4 6% 8% 40%	2090
	21st to end	Day	16% 6% 2 6% 4 5% 4 4 5% 6% 43%	2090
October	1st to 10th	Day	16% 4 1 3 2 3 3 2 4 5% 55%	2039
	11th to 20th	Day	13% 4 1 4 2 2 3 2 4 6% 61%	1900
	21st to end	Day	13% 3 2 5% 3 3 3 3 3 5% 58%	2090
November	1st to 10th	Day	14% 4 1 5% 3 2 2 2 4 7% 55%	1916
	11th to 20th	Day	15% 4 1 4 3 2 4 3 4 7% 53%	1800
	21st to end	Day	16% 5% 1 4 3 3 3 3 4 5% 53%	1800
December	1st to 10th	Day	16% 5% 2 5% 3 2 3 3 4 5% 53%	2930
	11th to 20th	Day	19% 6% 2 5% 4 4 3 3 5% 7% 41%	3373
	21st to end	Day	24% 4 1 4 2 3 3 2 4 6% 47%	4466
January	1st to 10th	Night	15% 3 1 3 2 3 3 2 3 4 61%	5889
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 4 5% 57%	5900
	21st to end	Night	19% 6% 2 4 3 3 3 2 4 6% 49%	6490
February	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 49%	2525
	11th to 20th	Night	22% 6% 2 5% 4 3 3 3 4 4 45%	2338
	21st to end	Night	16% 6% 2 5% 4 3 4 3 5% 6% 45%	1980
March	1st to 10th	Night	20% 5% 2 5% 3 3 4 2 5% 6% 45%	4962
	11th to 20th	Night	10% 4 1 4 3 3 3 3 5% 8% 55%	4980
	21st to end	Night	17% 4 2 5% 3 4 4 3 5% 6% 46%	5467
April	1st to 10th	Night	14% 5% 2 5% 3 3 4 3 5% 6% 49%	2200
	11th to 20th	Night	12% 5% 2 6% 3 3 3 3 5% 6% 52%	2007
	21st to end	Night	13% 5% 2 5% 4 3 4 4 5% 5% 51%	1800
May	1st to 10th	Night	14% 6% 2 6% 5% 4 5% 4 6% 8% 40%	2903
	11th to 20th	Night	19% 5% 2 6% 5% 4 4 4 5% 7% 38%	2902
	21st to end	Night	9% 4 2 6% 5% 5% 5% 4 7% 10% 43%	3130
June	1st to 10th	Night	10% 6% 2 6% 6% 6% 6% 6% 9% 12% 31%	1710
	11th to 20th	Night	11% 6% 1 6% 4 5% 6% 5% 8% 9% 39%	1710
	21st to end	Night	9% 6% 1 7% 6% 6% 6% 5% 7% 10% 38%	1710
July	1st to 10th	Night	10% 7% 3 8% 7% 7% 7% 6% 9% 8% 29%	2840
	11th to 20th	Night	8% 7% 2 6% 5% 6% 6% 6% 9% 13% 32%	2840
	21st to end	Night	12% 10% 3 10% 6% 7% 7% 5% 9% 11% 20%	3087
August	1st to 10th	Night	15% 9% 3 8% 6% 5% 6% 5% 7% 10% 26%	2825
	11th to 20th	Night	12% 7% 3 10% 6% 6% 6% 4 8% 9% 30%	2785
	21st to end	Night	7% 5% 2 7% 4 5% 5% 4 6% 9% 45%	3430
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 3 6% 10% 41%	2090
	11th to 20th	Night	17% 8% 3 6% 5% 4 5% 4 5% 7% 35%	2090
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	16% 4 2 4 4 3 3 3 4 5% 51%	2139
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 5% 54%	2280
	21st to end	Night	14% 4 2 4 3 3 3 2 3 5% 59%	2508
November	1st to 10th	Night	15% 5% 1 4 3 3 3 3 4 5% 54%	2379
	11th to 20th	Night	15% 5% 1 4 3 3 3 3 4 6% 52%	2600
	21st to end	Night	15% 5% 2 3 3 3 4 3 6% 5% 50%	2600
December	1st to 10th	Night	17% 6% 1 4 3 2 2 2 4 5% 54%	4250
	11th to 20th	Night	21% 6% 2 5% 3 3 4 3 4 5% 44%	4822
	21st to end	Night	22% 5% 2 4 3 3 3 3 4 5% 46%	6490

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	31% 4 5% 20% 32% 8%	4057
	11th to 20th	Day	30% 4 4 14% 37% 11%	4060
	21st to end	Day	40% 2 6% 18% 25% 10%	4466
February	1st to 10th	Day	39% 4 11% 20% 20% 6%	1870
	11th to 20th	Day	43% 4 8% 18% 21% 6%	1958
	21st to end	Day	44% 6% 7% 15% 21% 7%	1650
March	1st to 10th	Day	43% 5% 6% 16% 17% 13%	4889
	11th to 20th	Day	30% 5% 7% 13% 25% 20%	4980
	21st to end	Day	39% 5% 7% 22% 21% 5%	5465
April	1st to 10th	Day	34% 6% 11% 20% 23% 6%	2200
	11th to 20th	Day	35% 6% 9% 19% 21% 9%	2357
	21st to end	Day	34% 6% 14% 24% 18% 4	2600
May	1st to 10th	Day	39% 11% 16% 18% 14% 2	4250
	11th to 20th	Day	44% 9% 13% 19% 14% 1	4215
	21st to end	Day	30% 11% 17% 23% 18% 2	4554
June	1st to 10th	Day	39% 12% 17% 21% 8% 2	2470
	11th to 20th	Day	33% 12% 20% 22% 12% 1	2470
	21st to end	Day	35% 13% 17% 18% 13% 3	2470
July	1st to 10th	Day	38% 13% 19% 19% 9% 2	4055
	11th to 20th	Day	37% 13% 26% 18% 5% 1	4051
	21st to end	Day	52% 14% 16% 12% 5% 1	4324
August	1st to 10th	Day	48% 10% 16% 21% 5%	4091
	11th to 20th	Day	36% 13% 21% 17% 11% 2	4083
	21st to end	Day	28% 9% 14% 27% 19% 2	4176
September	1st to 10th	Day	35% 11% 13% 19% 18% 4	2090
	11th to 20th	Day	41% 7% 14% 16% 19% 3	2090
	21st to end	Day	41% 7% 10% 19% 18% 5%	2090
October	1st to 10th	Day	25% 6% 7% 19% 32% 10%	3390
	11th to 20th	Day	19% 3 6% 18% 29% 25%	3140
	21st to end	Day	28% 4 5% 23% 24% 17%	3428
November	1st to 10th	Day	32% 5% 8% 18% 28% 9%	1916
	11th to 20th	Day	33% 5% 7% 21% 25% 9%	1800
	21st to end	Day	35% 4 8% 22% 24% 7%	1800
December	1st to 10th	Day	35% 3 5% 19% 29% 9%	2930
	11th to 20th	Day	43% 5% 10% 16% 20% 8%	3370
	21st to end	Day	38% 4 9% 27% 19% 3	4466
January	1st to 10th	Night	29% 3 6% 19% 35% 9%	5889
	11th to 20th	Night	30% 5% 6% 14% 36% 9%	5900
	21st to end	Night	37% 3 6% 17% 27% 9%	6490
February	1st to 10th	Night	38% 5% 9% 21% 21% 6%	2525
	11th to 20th	Night	43% 5% 7% 16% 23% 6%	2339
	21st to end	Night	39% 6% 9% 17% 22% 7%	1980
March	1st to 10th	Night	39% 6% 8% 12% 27% 8%	4962
	11th to 20th	Night	26% 5% 8% 14% 29% 18%	4980
	21st to end	Night	39% 5% 7% 22% 20% 8%	5467
April	1st to 10th	Night	36% 5% 10% 18% 24% 6%	2200
	11th to 20th	Night	33% 5% 8% 23% 23% 9%	2007
	21st to end	Night	34% 7% 11% 23% 20% 4	1800
May	1st to 10th	Night	39% 9% 14% 21% 14% 2	2930
	11th to 20th	Night	42% 9% 15% 19% 14% 1	2903
	21st to end	Night	30% 12% 16% 26% 14% 2	3138
June	1st to 10th	Night	39% 13% 18% 19% 10% 2	1710
	11th to 20th	Night	37% 12% 18% 21% 10% 1	1710
	21st to end	Night	37% 14% 17% 15% 13% 4	1710
July	1st to 10th	Night	47% 14% 16% 16% 7% 1	2795
	11th to 20th	Night	38% 14% 25% 18% 3 1	2786
	21st to end	Night	54% 15% 15% 12% 4 1	2988
August	1st to 10th	Night	50% 11% 20% 14% 4	2814
	11th to 20th	Night	47% 13% 18% 13% 8% 1	2812
	21st to end	Night	34% 10% 13% 26% 16% 2	3430
September	1st to 10th	Night	38% 10% 15% 19% 15% 4	2090
	11th to 20th	Night	45% 10% 13% 14% 16% 2	2090
	21st to end	Night	41% 7% 10% 19% 18% 5%	2090
October	1st to 10th	Night	30% 7% 11% 17% 28% 8%	3568
	11th to 20th	Night	22% 3 6% 19% 27% 23%	3779
	21st to end	Night	29% 3 5% 20% 26% 17%	4120
November	1st to 10th	Night	35% 5% 7% 18% 25% 10%	2379
	11th to 20th	Night	33% 5% 7% 17% 27% 11%	2600
	21st to end	Night	35% 5% 6% 21% 27% 7%	2600
December	1st to 10th	Night	34% 3 6% 19% 29% 8%	4250
	11th to 20th	Night	43% 5% 9% 16% 19% 8%	4824
	21st to end	Night	39% 5% 10% 23% 20% 2	6490

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% 20% 38% 18% 4	300
	11th to 20th	Day	25% 19% 32% 17% 6%	300
	21st to end	Day	22% 16% 41% 17% 4	330
February	1st to 10th	Day	19% 21% 34% 19% 7%	300
	11th to 20th	Day	37% 17% 31% 13% 2	300
	21st to end	Day	28% 22% 31% 15% 4	249
March	1st to 10th	Day	22% 16% 30% 23% 8% 1	478
	11th to 20th	Day	19% 17% 35% 22% 6% 1	500
	21st to end	Day	22% 15% 35% 21% 7%	550
April	1st to 10th	Day	19% 14% 31% 23% 11% 1	500
	11th to 20th	Day	14% 14% 30% 26% 13% 2	492
	21st to end	Day	19% 8% 25% 28% 14% 6%	500
May	1st to 10th	Day	13% 13% 32% 22% 15% 5%	503
	11th to 20th	Day	18% 7% 17% 27% 22% 9%	527
	21st to end	Day	15% 6% 16% 26% 24% 14%	549
June	1st to 10th	Day	12% 3 15% 35% 23% 12%	490
	11th to 20th	Day	10% 4 13% 29% 24% 21%	490
	21st to end	Day	10% 2 15% 29% 26% 17%	490
July	1st to 10th	Day	9% 2 8% 23% 32% 27%	485
	11th to 20th	Day	8% 2 6% 27% 32% 25%	484
	21st to end	Day	7% 3 8% 29% 32% 21%	532
August	1st to 10th	Day	19% 3 10% 24% 26% 19%	486
	11th to 20th	Day	13% 3 9% 27% 31% 18%	479
	21st to end	Day	14% 2 9% 19% 31% 25%	539
September	1st to 10th	Day	10% 2 13% 23% 32% 19%	490
	11th to 20th	Day	20% 3 12% 17% 30% 18%	490
	21st to end	Day	21% 3 19% 25% 26% 7%	490
October	1st to 10th	Day	20% 3 15% 28% 24% 10%	490
	11th to 20th	Day	13% 6% 24% 28% 23% 5%	490
	21st to end	Day	17% 7% 19% 33% 19% 5%	539
November	1st to 10th	Day	22% 7% 23% 28% 16% 5%	454
	11th to 20th	Day	19% 13% 33% 26% 8% 2	300
	21st to end	Day	12% 15% 31% 28% 12% 2	300
December	1st to 10th	Day	26% 15% 34% 19% 7%	300
	11th to 20th	Day	25% 13% 29% 23% 9% 1	300
	21st to end	Day	28% 11% 32% 19% 8% 2	330
January	1st to 10th	Night	20% 15% 34% 26% 6%	800
	11th to 20th	Night	21% 13% 32% 29% 5%	800
	21st to end	Night	20% 12% 36% 30% 3	880
February	1st to 10th	Night	19% 12% 31% 34% 3	800
	11th to 20th	Night	24% 12% 39% 24% 2	783
	21st to end	Night	18% 13% 40% 27% 3	660
March	1st to 10th	Night	19% 12% 30% 35% 5%	800
	11th to 20th	Night	19% 13% 34% 26% 7% 1	800
	21st to end	Night	19% 11% 33% 29% 8%	880
April	1st to 10th	Night	16% 13% 32% 29% 10%	800
	11th to 20th	Night	15% 11% 29% 31% 14% 1	743
	21st to end	Night	16% 5% 27% 33% 19% 1	600
May	1st to 10th	Night	12% 7% 27% 34% 19%	600
	11th to 20th	Night	18% 5% 19% 33% 23% 3	591
	21st to end	Night	15% 3 12% 30% 35% 5%	634
June	1st to 10th	Night	12% 3 14% 32% 34% 5%	570
	11th to 20th	Night	13% 2 12% 30% 32% 11%	570
	21st to end	Night	10% 2 9% 31% 41% 8%	570
July	1st to 10th	Night	11% 1 7% 25% 46% 10%	555
	11th to 20th	Night	11% 1 7% 24% 47% 11%	552
	21st to end	Night	9% 2 8% 31% 42% 9%	624
August	1st to 10th	Night	16% 2 8% 26% 38% 10%	567
	11th to 20th	Night	14% 1 9% 29% 38% 9%	564
	21st to end	Night	12% 2 8% 26% 44% 9%	708
September	1st to 10th	Night	12% 3 11% 28% 40% 8%	760
	11th to 20th	Night	19% 2 13% 24% 35% 7%	760
	21st to end	Night	19% 3 16% 31% 28% 3	760
October	1st to 10th	Night	17% 3 17% 29% 28% 6%	760
	11th to 20th	Night	16% 6% 22% 32% 22% 2	760
	21st to end	Night	16% 5% 21% 37% 20% 2	836
November	1st to 10th	Night	17% 5% 21% 36% 17% 3	780
	11th to 20th	Night	17% 9% 28% 33% 12% 1	800
	21st to end	Night	17% 7% 30% 32% 13% 1	800
December	1st to 10th	Night	23% 10% 26% 33% 9%	800
	11th to 20th	Night	20% 8% 30% 33% 10% 1	800
	21st to end	Night	27% 8% 25% 33% 8%	880

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