Gardner
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gardner clear sky chart from 2005-11-06 to 2025-11-18.

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	2 4 2 4 3 4 4 4 6% 8% 58%	135363
	Night	2 4 2 4 3 3 3 3 5% 7% 63%	132477
Transparency	Day	20% 8% 11% 23% 25% 13%	130355
	Night	19% 6% 11% 24% 27% 11%	128489
Seeing	Day	8% 17% 32% 26% 13% 3	16822
	Night	5% 13% 35% 31% 14% 2	26843

By Month

Percentage Cloud Cover SW (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	1 5% 3 6% 2 2 3 2 4 8% 64%	3638
	11th to 20th	Day	2 2 5% 3 3 4 3 5% 6% 68%	3985
	21st to end	Day	1 8% 2 5% 3 3 3 3 4 5% 63%	4510
February	1st to 10th	Day	5% 3 6% 3 2 2 2 5% 8% 64%	1826
	11th to 20th	Day	1 3 2 4 3 3 3 3 6% 7% 65%	1949
	21st to end	Day	1 4 2 6% 2 3 3 3 6% 7% 61%	1650
March	1st to 10th	Day	1 4 2 4 3 3 3 3 5% 6% 65%	4500
	11th to 20th	Day	2 11% 4 8% 4 4 3 3 5% 7% 50%	4994
	21st to end	Day	1 4 2 4 2 3 3 3 6% 8% 62%	5793
April	1st to 10th	Day	2 5% 1 5% 3 4 4 3 7% 8% 58%	2400
	11th to 20th	Day	3 6% 2 5% 3 4 4 3 5% 9% 56%	2371
	21st to end	Day	4 8% 2 5% 4 4 5% 5% 6% 8% 50%	2400
May	1st to 10th	Day	6% 8% 2 5% 4 3 4 4 7% 8% 49%	5548
	11th to 20th	Day	4 5% 1 4 3 3 4 4 7% 8% 57%	6078
	21st to end	Day	3 3 1 3 3 3 4 4 7% 9% 59%	6925
June	1st to 10th	Day	3 4 1 4 4 5% 5% 5% 7% 10% 51%	2800
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 8% 62%	2800
	21st to end	Day	2 3 1 4 5% 4 5% 6% 8% 9% 51%	2800
July	1st to 10th	Day	2 2 1 2 3 4 5% 6% 8% 8% 58%	6339
	11th to 20th	Day	1 2 1 4 5% 7% 8% 7% 11% 10% 43%	6340
	21st to end	Day	3 3 1 6% 5% 6% 7% 6% 9% 10% 45%	6498
August	1st to 10th	Day	2 3 1 5% 5% 6% 8% 7% 10% 11% 42%	5653
	11th to 20th	Day	2 2 1 4 4 4 6% 6% 9% 11% 52%	5366
	21st to end	Day	4 3 2 5% 4 5% 6% 5% 8% 11% 47%	5984
September	1st to 10th	Day	4 4 2 5% 4 4 5% 4 7% 8% 53%	2400
	11th to 20th	Day	4 3 1 3 3 3 4 3 6% 8% 62%	2377
	21st to end	Day	4 3 2 4 3 3 3 3 5% 6% 65%	2200
October	1st to 10th	Day	3 3 1 2 2 2 3 2 4 5% 73%	3307
	11th to 20th	Day	2 3 1 4 3 3 3 3 5% 7% 66%	3250
	21st to end	Day	2 2 1 3 1 2 2 2 3 6% 76%	3521
November	1st to 10th	Day	1 3 1 3 2 2 2 3 5% 8% 71%	1853
	11th to 20th	Day	3 1 4 2 2 2 3 5% 7% 71%	1863
	21st to end	Day	1 5% 2 5% 2 2 2 3 5% 7% 66%	1795
December	1st to 10th	Day	3 1 3 2 3 2 2 3 5% 77%	2620
	11th to 20th	Day	3 1 2 2 3 3 2 5% 8% 70%	3026
	21st to end	Day	1 4 2 6% 3 3 3 3 4 7% 64%	4004
January	1st to 10th	Night	5% 3 7% 3 3 3 2 4 8% 62%	6327
	11th to 20th	Night	3 1 4 3 3 3 3 4 6% 68%	6036
	21st to end	Night	1 4 2 5% 3 3 3 3 4 7% 67%	6468
February	1st to 10th	Night	1 4 2 6% 4 2 2 2 4 5% 66%	2571
	11th to 20th	Night	1 4 2 6% 4 2 3 3 4 6% 65%	2338
	21st to end	Night	1 4 3 5% 4 2 3 3 4 6% 67%	1980
March	1st to 10th	Night	1 6% 2 4 3 2 3 2 4 6% 68%	5374
	11th to 20th	Night	2 10% 2 4 2 3 3 3 5% 6% 60%	5004
	21st to end	Night	2 5% 2 4 2 2 3 2 4 6% 69%	5168
April	1st to 10th	Night	1 4 2 4 3 2 3 2 5% 7% 66%	2000
	11th to 20th	Night	3 7% 2 4 3 3 3 4 4 7% 60%	1977
	21st to end	Night	4 7% 2 5% 2 3 3 3 5% 8% 59%	2000
May	1st to 10th	Night	6% 6% 2 5% 3 3 4 3 5% 7% 56%	4430
	11th to 20th	Night	6% 5% 1 3 2 2 3 3 4 6% 64%	3821
	21st to end	Night	6% 5% 2 4 3 3 4 2 5% 6% 61%	3972
June	1st to 10th	Night	4 4 1 3 3 4 4 4 6% 9% 58%	1600
	11th to 20th	Night	2 3 1 3 3 3 4 4 5% 9% 65%	1600
	21st to end	Night	3 3 1 4 3 4 6% 5% 8% 10% 54%	1600
July	1st to 10th	Night	4 3 1 4 3 4 5% 4 6% 9% 56%	3640
	11th to 20th	Night	3 3 1 4 4 5% 7% 6% 10% 13% 47%	3640
	21st to end	Night	4 3 2 5% 4 5% 6% 6% 10% 11% 45%	4371
August	1st to 10th	Night	3 3 2 5% 5% 5% 6% 6% 8% 10% 48%	4156
	11th to 20th	Night	3 2 1 3 4 5% 5% 5% 9% 14% 48%	4483
	21st to end	Night	5% 5% 2 6% 4 5% 6% 5% 9% 13% 41%	4993
September	1st to 10th	Night	4 4 2 4 4 4 5% 4 7% 8% 55%	2000
	11th to 20th	Night	5% 3 1 3 2 2 3 4 4 7% 65%	2022
	21st to end	Night	5% 4 1 3 3 2 3 3 5% 6% 65%	2200
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 5% 75%	3877
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 6% 67%	3898
	21st to end	Night	2 3 1 3 1 2 2 2 3 5% 75%	4252
November	1st to 10th	Night	1 3 2 3 2 2 2 2 4 6% 73%	2659
	11th to 20th	Night	1 3 1 3 2 2 2 2 3 5% 75%	2692
	21st to end	Night	2 5% 1 4 2 2 2 2 4 8% 68%	2603
December	1st to 10th	Night	1 2 1 4 2 2 2 2 4 5% 76%	4570
	11th to 20th	Night	1 4 1 3 2 2 2 2 4 7% 72%	5181
	21st to end	Night	1 5% 2 5% 3 3 3 3 5% 7% 63%	6974

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	17% 7% 10% 28% 26% 12%	3639
	11th to 20th	Day	17% 5% 9% 22% 27% 19%	3985
	21st to end	Day	22% 7% 7% 22% 29% 13%	4510
February	1st to 10th	Day	20% 4 11% 30% 24% 11%	1826
	11th to 20th	Day	15% 5% 11% 29% 31% 9%	1959
	21st to end	Day	19% 5% 9% 21% 29% 17%	1650
March	1st to 10th	Day	16% 5% 7% 15% 36% 20%	4500
	11th to 20th	Day	30% 7% 9% 20% 26% 9%	4994
	21st to end	Day	16% 5% 8% 45% 22% 4	5793
April	1st to 10th	Day	20% 8% 11% 24% 24% 14%	2400
	11th to 20th	Day	24% 8% 8% 26% 22% 13%	2374
	21st to end	Day	27% 9% 11% 22% 24% 7%	2400
May	1st to 10th	Day	28% 9% 10% 22% 20% 11%	5548
	11th to 20th	Day	21% 9% 10% 19% 25% 16%	6082
	21st to end	Day	18% 8% 11% 20% 25% 18%	6926
June	1st to 10th	Day	23% 9% 14% 22% 21% 12%	2800
	11th to 20th	Day	16% 8% 11% 17% 24% 24%	2800
	21st to end	Day	23% 9% 12% 22% 21% 13%	2800
July	1st to 10th	Day	17% 9% 12% 17% 24% 21%	6271
	11th to 20th	Day	26% 14% 17% 28% 12% 3	6265
	21st to end	Day	28% 12% 17% 20% 15% 7%	6311
August	1st to 10th	Day	33% 15% 21% 17% 10% 5%	4115
	11th to 20th	Day	20% 11% 17% 21% 18% 14%	3882
	21st to end	Day	24% 11% 20% 22% 21% 3	4311
September	1st to 10th	Day	25% 9% 12% 23% 22% 10%	2400
	11th to 20th	Day	18% 7% 11% 19% 30% 15%	2377
	21st to end	Day	19% 6% 8% 21% 34% 12%	2200
October	1st to 10th	Day	14% 5% 7% 16% 36% 22%	3307
	11th to 20th	Day	17% 5% 8% 26% 33% 11%	3250
	21st to end	Day	12% 3 6% 19% 43% 17%	3521
November	1st to 10th	Day	12% 5% 9% 23% 36% 15%	1853
	11th to 20th	Day	13% 4 8% 32% 31% 12%	1863
	21st to end	Day	18% 4 9% 21% 33% 16%	1795
December	1st to 10th	Day	12% 4 8% 30% 36% 10%	2620
	11th to 20th	Day	12% 4 10% 27% 35% 12%	3024
	21st to end	Day	17% 5% 9% 30% 27% 13%	4004
January	1st to 10th	Night	20% 5% 9% 30% 28% 8%	6327
	11th to 20th	Night	15% 6% 8% 27% 30% 14%	6036
	21st to end	Night	17% 6% 10% 26% 27% 14%	6468
February	1st to 10th	Night	20% 4 10% 29% 25% 12%	2571
	11th to 20th	Night	20% 5% 11% 30% 27% 8%	2338
	21st to end	Night	18% 3 8% 22% 35% 14%	1980
March	1st to 10th	Night	18% 4 6% 13% 43% 16%	5374
	11th to 20th	Night	24% 5% 9% 20% 31% 10%	5004
	21st to end	Night	17% 4 10% 43% 22% 4	5168
April	1st to 10th	Night	17% 5% 11% 29% 27% 12%	2000
	11th to 20th	Night	23% 6% 11% 24% 27% 11%	1977
	21st to end	Night	24% 8% 13% 27% 22% 7%	2000
May	1st to 10th	Night	26% 7% 9% 26% 20% 11%	4427
	11th to 20th	Night	20% 6% 9% 26% 26% 13%	3822
	21st to end	Night	23% 6% 12% 15% 27% 16%	3972
June	1st to 10th	Night	21% 9% 16% 22% 18% 15%	1600
	11th to 20th	Night	15% 8% 11% 19% 25% 23%	1600
	21st to end	Night	23% 10% 13% 19% 21% 14%	1600
July	1st to 10th	Night	21% 11% 12% 18% 23% 15%	3600
	11th to 20th	Night	24% 11% 25% 26% 10% 3	3592
	21st to end	Night	28% 12% 18% 19% 17% 6%	4246
August	1st to 10th	Night	36% 14% 20% 16% 10% 4	3018
	11th to 20th	Night	25% 11% 24% 17% 15% 8%	3243
	21st to end	Night	28% 12% 20% 23% 15% 3	3597
September	1st to 10th	Night	23% 8% 15% 26% 20% 8%	2000
	11th to 20th	Night	18% 7% 11% 20% 26% 18%	2022
	21st to end	Night	18% 6% 10% 22% 34% 10%	2200
October	1st to 10th	Night	13% 4 8% 22% 35% 18%	3877
	11th to 20th	Night	18% 6% 10% 24% 31% 11%	3898
	21st to end	Night	13% 4 4 24% 40% 15%	4252
November	1st to 10th	Night	12% 3 9% 26% 35% 15%	2659
	11th to 20th	Night	12% 3 7% 32% 33% 13%	2692
	21st to end	Night	16% 4 9% 22% 35% 13%	2603
December	1st to 10th	Night	13% 3 8% 33% 33% 10%	4570
	11th to 20th	Night	12% 5% 8% 26% 39% 10%	5182
	21st to end	Night	19% 7% 12% 22% 29% 12%	6974

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	12% 25% 30% 23% 8% 2	300
	11th to 20th	Day	11% 25% 42% 17% 5% 1	300
	21st to end	Day	6% 22% 42% 21% 9% 1	330
February	1st to 10th	Day	8% 35% 42% 12% 2 2	300
	11th to 20th	Day	8% 33% 41% 13% 3 1	300
	21st to end	Day	15% 29% 38% 16% 2	249
March	1st to 10th	Day	10% 34% 29% 21% 5%	300
	11th to 20th	Day	12% 28% 37% 18% 4 1	494
	21st to end	Day	15% 36% 34% 12% 3	550
April	1st to 10th	Day	11% 31% 39% 15% 4 1	500
	11th to 20th	Day	16% 31% 38% 12% 2 1	492
	21st to end	Day	13% 29% 38% 15% 3 1	500
May	1st to 10th	Day	12% 23% 40% 18% 5% 2	546
	11th to 20th	Day	12% 15% 34% 27% 10% 2	725
	21st to end	Day	8% 17% 30% 30% 13% 2	789
June	1st to 10th	Day	5% 12% 28% 32% 19% 4	730
	11th to 20th	Day	5% 11% 35% 29% 16% 5%	730
	21st to end	Day	3 11% 33% 30% 18% 5%	730
July	1st to 10th	Day	5% 4 26% 37% 21% 7%	721
	11th to 20th	Day	4 3 16% 35% 33% 8%	718
	21st to end	Day	6% 2 16% 36% 30% 10%	620
August	1st to 10th	Day	4 4 26% 35% 23% 8%	527
	11th to 20th	Day	6% 4 27% 34% 24% 4	517
	21st to end	Day	7% 4 24% 39% 20% 5%	583
September	1st to 10th	Day	6% 8% 25% 34% 21% 7%	530
	11th to 20th	Day	3 11% 38% 30% 15% 3	507
	21st to end	Day	5% 11% 26% 34% 18% 6%	330
October	1st to 10th	Day	6% 15% 29% 27% 18% 6%	330
	11th to 20th	Day	6% 22% 38% 21% 9% 4	330
	21st to end	Day	10% 15% 42% 22% 10% 1	363
November	1st to 10th	Day	6% 25% 35% 25% 7% 1	330
	11th to 20th	Day	5% 23% 43% 16% 11% 2	321
	21st to end	Day	5% 22% 40% 25% 7% 1	300
December	1st to 10th	Day	9% 23% 38% 19% 10% 1	300
	11th to 20th	Day	7% 32% 39% 16% 5% 1	300
	21st to end	Day	13% 25% 38% 19% 4	330
January	1st to 10th	Night	3 21% 40% 26% 9% 1	1000
	11th to 20th	Night	4 22% 42% 24% 7% 2	865
	21st to end	Night	4 13% 45% 29% 8% 1	880
February	1st to 10th	Night	2 19% 52% 22% 4	800
	11th to 20th	Night	3 22% 49% 19% 6%	784
	21st to end	Night	3 17% 55% 22% 3	660
March	1st to 10th	Night	4 23% 46% 21% 5% 1	800
	11th to 20th	Night	6% 15% 39% 32% 8% 1	800
	21st to end	Night	4 21% 44% 27% 4	740
April	1st to 10th	Night	6% 18% 48% 25% 3	600
	11th to 20th	Night	10% 13% 43% 27% 7%	593
	21st to end	Night	10% 15% 36% 32% 7% 1	600
May	1st to 10th	Night	10% 9% 40% 31% 9%	600
	11th to 20th	Night	11% 9% 31% 34% 13% 2	591
	21st to end	Night	10% 10% 32% 32% 14% 2	650
June	1st to 10th	Night	4 8% 24% 44% 19% 2	600
	11th to 20th	Night	3 7% 33% 40% 17% 1	600
	21st to end	Night	5% 2 27% 38% 26% 2	600
July	1st to 10th	Night	8% 2 15% 42% 30% 3	585
	11th to 20th	Night	5% 1 10% 38% 39% 6%	582
	21st to end	Night	7% 2 7% 37% 41% 6%	657
August	1st to 10th	Night	6% 2 11% 37% 40% 5%	597
	11th to 20th	Night	5% 2 11% 45% 34% 3	594
	21st to end	Night	6% 2 13% 42% 31% 5%	660
September	1st to 10th	Night	6% 3 15% 45% 26% 5%	600
	11th to 20th	Night	7% 5% 23% 40% 21% 4	600
	21st to end	Night	7% 7% 25% 42% 16% 4	600
October	1st to 10th	Night	7% 6% 33% 38% 14% 3	770
	11th to 20th	Night	4 9% 40% 31% 14% 2	800
	21st to end	Night	6% 11% 37% 30% 13% 3	880
November	1st to 10th	Night	3 13% 41% 32% 10% 1	1019
	11th to 20th	Night	3 17% 42% 28% 9% 1	1036
	21st to end	Night	5% 14% 41% 30% 9% 1	1000
December	1st to 10th	Night	5% 15% 42% 29% 9% 1	1000
	11th to 20th	Night	4 20% 45% 21% 10%	1000
	21st to end	Night	4 22% 45% 25% 4 1	1100

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