Weis Farm observing site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weis Farm observing site clear sky chart from 2005-11-06 to 2026-01-17.

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	6% 4 1 4 3 3 3 3 5% 7% 60%	136074
	Night	6% 4 2 4 3 3 4 3 5% 7% 58%	132939
Transparency	Day	23% 4 10% 24% 28% 11%	131051
	Night	25% 4 9% 23% 26% 13%	128969
Seeing	Day	8% 6% 27% 34% 20% 4	17047
	Night	7% 7% 36% 38% 10%	27077

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	7% 9% 3 5% 3 3 3 3 4 5% 55%	3718
	11th to 20th	Day	3 5% 2 7% 3 4 4 3 5% 5% 59%	3801
	21st to end	Day	5% 5% 2 5% 3 3 3 3 4 6% 60%	4782
February	1st to 10th	Day	6% 7% 2 6% 3 3 4 2 4 5% 56%	2000
	11th to 20th	Day	4 8% 3 7% 3 2 4 2 4 6% 56%	1949
	21st to end	Day	4 5% 2 4 3 2 3 3 4 6% 64%	1650
March	1st to 10th	Day	5% 6% 2 5% 3 3 3 2 3 5% 64%	4500
	11th to 20th	Day	5% 4 2 5% 3 4 4 3 5% 7% 58%	4804
	21st to end	Day	5% 4 1 4 3 3 3 4 6% 7% 59%	5665
April	1st to 10th	Day	7% 4 1 3 2 3 3 3 5% 5% 64%	2400
	11th to 20th	Day	9% 4 2 4 3 3 3 3 5% 6% 59%	2371
	21st to end	Day	10% 5% 2 4 3 3 3 3 4 8% 55%	2490
May	1st to 10th	Day	12% 4 1 4 3 3 3 3 5% 6% 55%	5900
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 6% 65%	5862
	21st to end	Day	11% 5% 1 4 3 3 3 3 5% 6% 56%	6446
June	1st to 10th	Day	4 3 1 5% 4 3 4 4 6% 9% 56%	2638
	11th to 20th	Day	5% 3 1 3 3 3 3 4 5% 8% 63%	2800
	21st to end	Day	3 3 1 4 3 4 4 5% 6% 9% 58%	2800
July	1st to 10th	Day	5% 3 1 5% 3 4 4 4 7% 9% 55%	6339
	11th to 20th	Day	5% 2 1 2 2 2 3 3 5% 9% 66%	6255
	21st to end	Day	4 2 1 4 3 3 4 3 6% 8% 61%	6424
August	1st to 10th	Day	8% 4 2 5% 3 3 4 4 5% 9% 53%	5693
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 9% 61%	5366
	21st to end	Day	8% 4 1 5% 3 4 4 4 7% 9% 50%	5984
September	1st to 10th	Day	8% 5% 1 5% 3 3 3 3 4 6% 60%	2375
	11th to 20th	Day	6% 4 1 4 3 3 4 3 5% 6% 62%	2200
	21st to end	Day	5% 3 1 4 2 3 3 3 4 6% 67%	2200
October	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	3590
	11th to 20th	Day	4 3 2 4 3 3 3 3 4 6% 66%	3466
	21st to end	Day	5% 3 1 2 1 2 2 2 4 4 75%	3190
November	1st to 10th	Day	5% 4 1 3 2 2 3 2 3 5% 69%	1853
	11th to 20th	Day	3 4 1 3 3 2 3 2 3 6% 70%	1890
	21st to end	Day	7% 5% 1 3 3 2 3 3 4 4 64%	1890
December	1st to 10th	Day	1 4 1 3 2 2 2 2 3 5% 74%	3030
	11th to 20th	Day	4 4 1 3 2 2 3 3 4 6% 68%	3481
	21st to end	Day	6% 9% 3 8% 4 4 3 3 4 6% 51%	4272
January	1st to 10th	Night	5% 7% 3 6% 5% 4 4 3 4 5% 54%	6467
	11th to 20th	Night	2 4 2 5% 3 3 3 3 4 6% 64%	6280
	21st to end	Night	5% 6% 2 6% 4 3 3 2 4 6% 59%	6241
February	1st to 10th	Night	4 6% 3 6% 3 4 3 3 4 5% 59%	2400
	11th to 20th	Night	5% 6% 3 7% 4 4 4 3 5% 6% 52%	2338
	21st to end	Night	5% 5% 2 4 3 3 3 3 4 7% 63%	1980
March	1st to 10th	Night	4 5% 2 4 2 2 2 2 3 6% 67%	5374
	11th to 20th	Night	4 4 1 4 3 3 4 4 5% 7% 60%	5149
	21st to end	Night	4 4 2 4 3 3 4 4 6% 8% 58%	5259
April	1st to 10th	Night	7% 5% 2 4 3 3 3 3 5% 7% 59%	2000
	11th to 20th	Night	8% 5% 2 4 3 2 3 3 5% 8% 57%	1977
	21st to end	Night	11% 5% 2 4 3 3 4 3 5% 7% 53%	1909
May	1st to 10th	Night	13% 5% 2 5% 4 4 3 3 4 6% 51%	4080
	11th to 20th	Night	6% 3 2 4 3 3 4 3 4 6% 62%	4053
	21st to end	Night	12% 6% 2 5% 3 4 4 3 4 6% 51%	4451
June	1st to 10th	Night	4 3 2 4 3 4 5% 4 8% 10% 54%	1755
	11th to 20th	Night	3 4 1 3 3 4 5% 5% 7% 8% 57%	1600
	21st to end	Night	4 4 2 5% 4 4 4 4 8% 10% 53%	1600
July	1st to 10th	Night	5% 4 2 4 4 4 4 4 6% 10% 53%	3640
	11th to 20th	Night	3 3 2 6% 4 5% 4 4 8% 14% 48%	3722
	21st to end	Night	4 3 2 5% 4 5% 5% 5% 8% 11% 48%	4449
August	1st to 10th	Night	9% 5% 2 5% 4 4 5% 5% 8% 9% 44%	4101
	11th to 20th	Night	4 3 1 5% 4 4 5% 5% 10% 13% 45%	4483
	21st to end	Night	13% 6% 2 5% 4 4 5% 5% 7% 10% 40%	4993
September	1st to 10th	Night	7% 3 1 4 3 3 3 2 4 7% 62%	2024
	11th to 20th	Night	6% 4 1 4 3 3 3 3 6% 7% 60%	2200
	21st to end	Night	5% 3 1 3 2 3 3 3 4 6% 66%	2200
October	1st to 10th	Night	6% 2 1 2 1 1 2 2 3 5% 74%	3590
	11th to 20th	Night	6% 3 1 4 3 3 3 3 4 5% 64%	3637
	21st to end	Night	6% 4 1 3 2 2 2 2 4 5% 69%	4610
November	1st to 10th	Night	4 3 1 3 3 2 2 2 4 7% 69%	2665
	11th to 20th	Night	2 2 1 2 3 3 3 3 3 6% 73%	2730
	21st to end	Night	6% 4 1 3 3 2 3 3 4 6% 65%	2730
December	1st to 10th	Night	2 4 2 4 3 2 2 2 3 6% 72%	4380
	11th to 20th	Night	4 3 1 4 3 2 2 2 4 6% 70%	4946
	21st to end	Night	6% 6% 2 5% 3 4 4 3 5% 7% 55%	6926

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	32% 3 7% 29% 23% 6%	3719
	11th to 20th	Day	26% 4 9% 18% 28% 15%	3801
	21st to end	Day	27% 3 7% 21% 35% 8%	4782
February	1st to 10th	Day	30% 3 10% 22% 23% 11%	2000
	11th to 20th	Day	30% 3 8% 26% 22% 11%	1959
	21st to end	Day	22% 2 6% 21% 31% 18%	1650
March	1st to 10th	Day	25% 2 5% 15% 28% 25%	4500
	11th to 20th	Day	25% 4 7% 16% 32% 16%	4804
	21st to end	Day	23% 4 10% 34% 24% 5%	5665
April	1st to 10th	Day	22% 3 8% 24% 27% 16%	2400
	11th to 20th	Day	26% 4 9% 23% 23% 14%	2374
	21st to end	Day	28% 4 10% 24% 25% 9%	2490
May	1st to 10th	Day	29% 4 13% 21% 20% 12%	5900
	11th to 20th	Day	19% 5% 10% 18% 25% 23%	5866
	21st to end	Day	29% 6% 11% 18% 23% 13%	6447
June	1st to 10th	Day	23% 7% 15% 27% 20% 8%	2638
	11th to 20th	Day	19% 6% 10% 21% 28% 16%	2800
	21st to end	Day	20% 5% 13% 26% 24% 11%	2800
July	1st to 10th	Day	25% 5% 14% 22% 30% 5%	6271
	11th to 20th	Day	17% 3 13% 31% 30% 6%	6180
	21st to end	Day	21% 4 13% 34% 22% 6%	6240
August	1st to 10th	Day	28% 6% 15% 25% 23% 4	4137
	11th to 20th	Day	19% 4 14% 24% 31% 9%	3882
	21st to end	Day	22% 4 11% 30% 26% 7%	4311
September	1st to 10th	Day	26% 4 9% 22% 25% 13%	2375
	11th to 20th	Day	23% 4 8% 23% 29% 13%	2200
	21st to end	Day	19% 4 8% 24% 29% 15%	2200
October	1st to 10th	Day	18% 3 5% 16% 41% 16%	3590
	11th to 20th	Day	22% 2 7% 23% 33% 13%	3466
	21st to end	Day	15% 2 5% 20% 40% 18%	3190
November	1st to 10th	Day	19% 3 7% 22% 35% 14%	1853
	11th to 20th	Day	18% 2 5% 27% 34% 12%	1890
	21st to end	Day	23% 3 8% 22% 30% 15%	1890
December	1st to 10th	Day	15% 2 6% 34% 33% 9%	3030
	11th to 20th	Day	18% 2 6% 25% 40% 9%	3479
	21st to end	Day	35% 4 7% 20% 26% 9%	4272
January	1st to 10th	Night	32% 3 8% 32% 20% 4	6467
	11th to 20th	Night	23% 3 11% 19% 29% 16%	6280
	21st to end	Night	28% 3 8% 17% 35% 9%	6241
February	1st to 10th	Night	27% 4 9% 21% 27% 11%	2400
	11th to 20th	Night	33% 4 9% 21% 23% 9%	2338
	21st to end	Night	22% 2 6% 19% 31% 20%	1980
March	1st to 10th	Night	21% 2 4 17% 27% 29%	5374
	11th to 20th	Night	22% 4 8% 15% 26% 25%	5149
	21st to end	Night	22% 6% 10% 32% 23% 7%	5259
April	1st to 10th	Night	25% 3 9% 21% 25% 17%	2000
	11th to 20th	Night	26% 5% 10% 22% 24% 13%	1977
	21st to end	Night	30% 4 14% 23% 21% 8%	1909
May	1st to 10th	Night	33% 6% 13% 19% 16% 13%	4080
	11th to 20th	Night	23% 5% 10% 17% 23% 22%	4054
	21st to end	Night	34% 6% 12% 18% 14% 17%	4452
June	1st to 10th	Night	23% 9% 19% 27% 15% 7%	1755
	11th to 20th	Night	21% 9% 13% 23% 23% 11%	1600
	21st to end	Night	24% 6% 14% 25% 20% 11%	1600
July	1st to 10th	Night	28% 6% 17% 28% 19% 3	3600
	11th to 20th	Night	27% 5% 14% 25% 24% 5%	3674
	21st to end	Night	28% 5% 12% 33% 16% 6%	4320
August	1st to 10th	Night	36% 6% 13% 19% 22% 4	2981
	11th to 20th	Night	26% 5% 13% 28% 22% 6%	3243
	21st to end	Night	29% 4 14% 25% 24% 5%	3597
September	1st to 10th	Night	23% 4 13% 21% 25% 13%	2024
	11th to 20th	Night	23% 5% 10% 22% 27% 13%	2200
	21st to end	Night	19% 5% 7% 24% 28% 16%	2200
October	1st to 10th	Night	15% 3 5% 16% 40% 20%	3590
	11th to 20th	Night	24% 2 7% 24% 27% 16%	3637
	21st to end	Night	20% 2 4 19% 40% 15%	4610
November	1st to 10th	Night	17% 3 9% 21% 31% 20%	2665
	11th to 20th	Night	14% 3 7% 25% 36% 16%	2730
	21st to end	Night	21% 3 8% 23% 28% 17%	2730
December	1st to 10th	Night	17% 2 6% 33% 36% 6%	4380
	11th to 20th	Night	18% 2 5% 24% 40% 12%	4947
	21st to end	Night	29% 4 9% 24% 27% 8%	6926

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	8% 7% 37% 36% 12% 2	330
	11th to 20th	Day	9% 13% 30% 32% 14% 2	318
	21st to end	Day	4 8% 38% 33% 15% 2	330
February	1st to 10th	Day	8% 11% 42% 33% 6%	300
	11th to 20th	Day	10% 8% 44% 25% 9% 3	300
	21st to end	Day	5% 7% 53% 31% 4	249
March	1st to 10th	Day	9% 8% 41% 29% 13%	300
	11th to 20th	Day	13% 10% 35% 28% 13% 1	300
	21st to end	Day	13% 12% 36% 28% 11% 1	415
April	1st to 10th	Day	10% 13% 39% 26% 11% 2	500
	11th to 20th	Day	11% 14% 40% 29% 6% 1	492
	21st to end	Day	15% 14% 37% 24% 9% 1	590
May	1st to 10th	Day	10% 9% 35% 31% 12% 2	703
	11th to 20th	Day	10% 8% 30% 33% 15% 3	725
	21st to end	Day	9% 8% 34% 32% 17% 1	789
June	1st to 10th	Day	5% 5% 23% 37% 23% 7%	730
	11th to 20th	Day	5% 5% 29% 37% 21% 4	730
	21st to end	Day	3 4 24% 44% 22% 3	730
July	1st to 10th	Day	5% 2 14% 39% 32% 8%	721
	11th to 20th	Day	3 2 11% 39% 36% 10%	718
	21st to end	Day	5% 1 11% 38% 36% 9%	794
August	1st to 10th	Day	4 1 13% 39% 35% 8%	682
	11th to 20th	Day	3 1 17% 38% 33% 7%	517
	21st to end	Day	5% 2 13% 41% 30% 10%	583
September	1st to 10th	Day	8% 2 17% 38% 28% 7%	505
	11th to 20th	Day	3 2 17% 38% 29% 10%	330
	21st to end	Day	8% 3 22% 33% 26% 8%	330
October	1st to 10th	Day	11% 6% 22% 32% 19% 9%	330
	11th to 20th	Day	6% 5% 35% 32% 16% 6%	330
	21st to end	Day	15% 8% 26% 28% 18% 5%	363
November	1st to 10th	Day	8% 7% 31% 33% 17% 4	330
	11th to 20th	Day	7% 9% 32% 33% 18% 1	330
	21st to end	Day	12% 11% 28% 28% 16% 5%	330
December	1st to 10th	Day	4 4 36% 39% 15% 2	330
	11th to 20th	Day	8% 6% 35% 31% 19% 1	330
	21st to end	Day	12% 13% 33% 33% 9% 1	363
January	1st to 10th	Night	6% 9% 36% 40% 8%	1050
	11th to 20th	Night	8% 8% 34% 38% 11% 1	1031
	21st to end	Night	6% 7% 38% 40% 8% 1	994
February	1st to 10th	Night	7% 10% 40% 36% 7%	800
	11th to 20th	Night	8% 11% 48% 28% 5%	784
	21st to end	Night	9% 8% 50% 28% 4	660
March	1st to 10th	Night	8% 11% 41% 35% 5%	800
	11th to 20th	Night	9% 10% 41% 31% 8%	678
	21st to end	Night	10% 14% 49% 24% 2	660
April	1st to 10th	Night	10% 11% 45% 30% 4	600
	11th to 20th	Night	10% 14% 50% 22% 3	593
	21st to end	Night	12% 11% 45% 25% 6% 1	600
May	1st to 10th	Night	11% 11% 44% 29% 6%	600
	11th to 20th	Night	8% 8% 40% 35% 9% 1	591
	21st to end	Night	9% 10% 45% 30% 6%	650
June	1st to 10th	Night	4 6% 40% 39% 11%	600
	11th to 20th	Night	4 7% 47% 35% 6%	600
	21st to end	Night	4 5% 37% 44% 10%	600
July	1st to 10th	Night	5% 2 23% 51% 18% 1	585
	11th to 20th	Night	3 2 21% 52% 22%	582
	21st to end	Night	6% 2 19% 52% 21% 1	657
August	1st to 10th	Night	6% 2 20% 50% 23%	597
	11th to 20th	Night	9% 1 22% 50% 18%	594
	21st to end	Night	6% 2 22% 48% 22% 1	660
September	1st to 10th	Night	7% 1 26% 51% 15%	600
	11th to 20th	Night	7% 3 39% 40% 10% 2	600
	21st to end	Night	5% 5% 31% 43% 16%	600
October	1st to 10th	Night	11% 6% 31% 40% 11%	600
	11th to 20th	Night	7% 7% 37% 37% 11% 1	631
	21st to end	Night	10% 8% 32% 34% 15% 1	1100
November	1st to 10th	Night	6% 5% 35% 44% 10%	1025
	11th to 20th	Night	4 7% 39% 40% 10%	1050
	21st to end	Night	8% 9% 30% 39% 13% 1	1050
December	1st to 10th	Night	5% 7% 37% 41% 9%	1050
	11th to 20th	Night	8% 8% 39% 36% 8%	1050
	21st to end	Night	9% 11% 37% 36% 7%	1155

Page generated at 2026-01-14 00:14:30. Version ac07

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