Weeping Water
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weeping Water clear sky chart from 2005-11-06 to 2025-10-04.

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% 7% 3 7% 4 4 4 3 5% 7% 45%	126085
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 48%	123575
Transparency	Day	38% 3 13% 27% 17% 2	129723
	Night	36% 3 12% 27% 20% 3	128000
Seeing	Day	14% 9% 30% 30% 15% 3	17076
	Night	13% 9% 33% 34% 11% 1	26855

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	9% 12% 5% 14% 8% 6% 4 3 5% 5% 29%	4077
	11th to 20th	Day	7% 9% 3 9% 5% 5% 6% 3 5% 6% 42%	4080
	21st to end	Day	6% 10% 5% 11% 5% 5% 5% 3 5% 7% 38%	4488
February	1st to 10th	Day	10% 12% 5% 9% 6% 4 4 3 6% 7% 34%	1800
	11th to 20th	Day	10% 10% 3 8% 6% 4 4 4 5% 6% 40%	1794
	21st to end	Day	10% 7% 2 6% 5% 4 4 3 5% 7% 45%	1650
March	1st to 10th	Day	15% 8% 3 5% 3 2 2 2 3 4 52%	4884
	11th to 20th	Day	11% 7% 2 5% 3 3 3 3 4 7% 51%	4980
	21st to end	Day	17% 11% 4 8% 4 4 4 4 6% 7% 32%	5462
April	1st to 10th	Day	16% 7% 3 6% 4 3 4 3 5% 6% 44%	2255
	11th to 20th	Day	15% 8% 3 6% 4 4 4 4 5% 6% 42%	2482
	21st to end	Day	20% 7% 3 7% 3 4 4 4 5% 6% 38%	2600
May	1st to 10th	Day	12% 7% 3 6% 4 4 4 3 5% 6% 45%	5862
	11th to 20th	Day	14% 6% 2 6% 3 3 3 3 4 5% 51%	5862
	21st to end	Day	18% 6% 3 7% 4 4 4 4 6% 7% 37%	6558
June	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 8% 50%	2800
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 9% 48%	2800
	21st to end	Day	7% 4 2 5% 5% 5% 4 5% 6% 7% 48%	2797
July	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 6% 8% 47%	5900
	11th to 20th	Day	8% 4 2 6% 5% 4 4 4 7% 8% 47%	5900
	21st to end	Day	7% 4 1 5% 3 4 4 4 7% 9% 52%	6422
August	1st to 10th	Day	6% 4 2 6% 4 5% 5% 5% 7% 10% 46%	4234
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 8% 44%	4171
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 8% 50%	4585
September	1st to 10th	Day	13% 4 2 4 3 3 3 3 4 7% 54%	2320
	11th to 20th	Day	11% 5% 1 5% 4 4 3 3 5% 8% 53%	2200
	21st to end	Day	11% 4 1 4 3 3 4 2 5% 5% 58%	2200
October	1st to 10th	Day	14% 5% 2 5% 3 2 4 3 4 6% 52%	1979
	11th to 20th	Day	10% 6% 2 4 4 2 3 2 4 5% 57%	1900
	21st to end	Day	12% 8% 3 6% 4 3 4 3 5% 5% 48%	2090
November	1st to 10th	Day	10% 5% 2 5% 3 4 3 3 4 6% 54%	1796
	11th to 20th	Day	9% 8% 3 7% 4 4 4 3 4 6% 49%	1755
	21st to end	Day	12% 7% 3 7% 4 4 4 3 5% 7% 45%	1600
December	1st to 10th	Day	5% 5% 2 6% 5% 4 4 3 5% 6% 54%	2610
	11th to 20th	Day	9% 9% 3 9% 6% 4 3 3 6% 6% 42%	3008
	21st to end	Day	17% 10% 5% 13% 5% 4 4 3 4 5% 31%	4184
January	1st to 10th	Night	10% 10% 4 18% 8% 5% 4 3 5% 6% 27%	5888
	11th to 20th	Night	7% 8% 3 8% 4 4 6% 4 6% 7% 44%	5900
	21st to end	Night	9% 11% 5% 9% 4 4 4 3 5% 5% 42%	6490
February	1st to 10th	Night	11% 11% 3 8% 5% 5% 4 3 5% 5% 39%	2600
	11th to 20th	Night	9% 8% 3 8% 5% 5% 4 4 5% 7% 42%	2511
	21st to end	Night	9% 7% 3 6% 3 4 3 3 4 5% 52%	1980
March	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 6% 51%	4972
	11th to 20th	Night	9% 6% 2 4 3 3 3 3 4 6% 58%	4980
	21st to end	Night	14% 10% 2 7% 5% 4 4 4 6% 7% 37%	5467
April	1st to 10th	Night	12% 7% 2 6% 5% 3 3 3 6% 6% 47%	2144
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 4 7% 47%	1866
	21st to end	Night	18% 6% 3 5% 4 4 4 3 4 6% 45%	1800
May	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 4 6% 51%	4053
	11th to 20th	Night	14% 4 2 4 2 2 3 2 4 7% 56%	4053
	21st to end	Night	18% 6% 2 5% 4 3 4 3 5% 7% 44%	4315
June	1st to 10th	Night	5% 4 2 4 5% 5% 4 3 6% 9% 54%	1600
	11th to 20th	Night	6% 4 2 3 4 4 5% 4 7% 9% 52%	1600
	21st to end	Night	4 3 1 4 4 4 4 4 7% 9% 57%	1600
July	1st to 10th	Night	8% 4 2 5% 4 4 4 4 5% 8% 53%	4074
	11th to 20th	Night	6% 4 2 5% 4 3 4 4 6% 9% 54%	4077
	21st to end	Night	6% 4 1 4 3 4 5% 4 6% 9% 54%	4449
August	1st to 10th	Night	4 3 2 4 3 4 4 3 5% 10% 59%	2926
	11th to 20th	Night	11% 5% 1 5% 3 4 3 3 5% 7% 52%	2888
	21st to end	Night	7% 4 2 5% 3 3 3 3 6% 8% 57%	3320
September	1st to 10th	Night	9% 3 2 4 3 3 3 3 5% 6% 59%	2076
	11th to 20th	Night	9% 3 1 4 3 3 4 4 5% 8% 57%	2200
	21st to end	Night	9% 5% 1 4 3 3 3 3 4 5% 60%	2200
October	1st to 10th	Night	11% 5% 2 4 3 3 4 4 5% 6% 52%	2247
	11th to 20th	Night	11% 6% 1 4 2 3 3 2 4 6% 57%	2280
	21st to end	Night	13% 6% 2 4 3 3 4 3 5% 5% 52%	2508
November	1st to 10th	Night	9% 4 1 4 3 3 4 3 5% 7% 56%	2501
	11th to 20th	Night	9% 7% 2 6% 3 3 3 3 4 6% 54%	2641
	21st to end	Night	11% 8% 2 5% 4 3 2 3 4 6% 52%	2800
December	1st to 10th	Night	5% 5% 2 5% 4 4 4 3 5% 7% 56%	4580
	11th to 20th	Night	9% 7% 3 8% 4 3 4 3 5% 7% 46%	5199
	21st to end	Night	16% 13% 5% 11% 4 3 3 3 4 5% 34%	6790

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	58% 3 10% 21% 8% 1	4078
	11th to 20th	Day	43% 2 13% 22% 18% 2	4080
	21st to end	Day	47% 2 13% 23% 14% 1	4488
February	1st to 10th	Day	49% 4 15% 20% 10% 2	1800
	11th to 20th	Day	45% 3 11% 24% 15% 3	1803
	21st to end	Day	38% 3 14% 25% 17% 2	1650
March	1st to 10th	Day	38% 2 8% 28% 18% 7%	4884
	11th to 20th	Day	35% 2 8% 27% 24% 4	4980
	21st to end	Day	52% 3 21% 18% 5% 2	5464
April	1st to 10th	Day	41% 3 12% 28% 14% 2	2255
	11th to 20th	Day	43% 3 13% 23% 15% 2	2482
	21st to end	Day	47% 3 11% 25% 13% 1	2600
May	1st to 10th	Day	39% 3 10% 29% 18% 2	5900
	11th to 20th	Day	37% 2 8% 25% 24% 4	5866
	21st to end	Day	45% 4 10% 25% 15% 1	6572
June	1st to 10th	Day	31% 5% 17% 30% 15% 2	2800
	11th to 20th	Day	33% 4 13% 32% 16% 2	2800
	21st to end	Day	33% 5% 14% 30% 14% 4	2797
July	1st to 10th	Day	34% 4 13% 32% 16% 1	5836
	11th to 20th	Day	34% 5% 13% 29% 17% 2	5831
	21st to end	Day	28% 6% 18% 31% 17% 2	6240
August	1st to 10th	Day	31% 5% 16% 28% 17% 2	4220
	11th to 20th	Day	38% 5% 15% 26% 16%	4210
	21st to end	Day	32% 5% 14% 26% 17% 5%	4584
September	1st to 10th	Day	32% 3 10% 30% 19% 5%	2320
	11th to 20th	Day	32% 3 12% 32% 19% 2	2200
	21st to end	Day	30% 3 9% 32% 26% 2	2200
October	1st to 10th	Day	21% 2 7% 19% 48% 3	3265
	11th to 20th	Day	21% 2 11% 31% 28% 7%	3140
	21st to end	Day	34% 3 10% 29% 22% 3	3428
November	1st to 10th	Day	32% 3 13% 30% 20% 3	1796
	11th to 20th	Day	37% 3 12% 27% 20% 1	1755
	21st to end	Day	40% 3 11% 30% 14% 1	1600
December	1st to 10th	Day	31% 3 17% 31% 18% 1	2610
	11th to 20th	Day	42% 2 17% 28% 10%	3005
	21st to end	Day	58% 2 11% 22% 7% 1	4184
January	1st to 10th	Night	58% 3 10% 17% 12%	5888
	11th to 20th	Night	40% 2 13% 25% 18% 2	5900
	21st to end	Night	45% 2 12% 20% 18% 3	6490
February	1st to 10th	Night	47% 3 12% 22% 14% 3	2600
	11th to 20th	Night	41% 4 13% 24% 15% 3	2512
	21st to end	Night	36% 3 10% 25% 22% 5%	1980
March	1st to 10th	Night	36% 2 6% 29% 24% 3	4972
	11th to 20th	Night	30% 2 7% 26% 27% 8%	4980
	21st to end	Night	46% 4 19% 24% 7% 1	5467
April	1st to 10th	Night	38% 3 9% 28% 19% 3	2144
	11th to 20th	Night	38% 3 10% 28% 17% 4	1866
	21st to end	Night	42% 3 12% 24% 18% 1	1800
May	1st to 10th	Night	37% 3 10% 27% 22% 2	4080
	11th to 20th	Night	32% 2 11% 22% 28% 5%	4054
	21st to end	Night	42% 3 13% 23% 17% 2	4323
June	1st to 10th	Night	26% 5% 14% 33% 18% 3	1600
	11th to 20th	Night	26% 5% 15% 29% 20% 5%	1600
	21st to end	Night	23% 4 15% 32% 23% 3	1600
July	1st to 10th	Night	30% 5% 12% 30% 19% 3	4031
	11th to 20th	Night	28% 5% 14% 29% 21% 2	4026
	21st to end	Night	25% 7% 17% 28% 22% 1	4320
August	1st to 10th	Night	22% 4 17% 34% 21% 3	2916
	11th to 20th	Night	33% 4 14% 29% 18% 1	2915
	21st to end	Night	26% 4 16% 28% 18% 8%	3320
September	1st to 10th	Night	27% 3 11% 29% 23% 7%	2076
	11th to 20th	Night	27% 3 12% 33% 21% 3	2200
	21st to end	Night	27% 3 8% 28% 30% 4	2200
October	1st to 10th	Night	20% 3 7% 18% 47% 6%	3728
	11th to 20th	Night	21% 2 7% 30% 30% 9%	3779
	21st to end	Night	34% 2 8% 30% 24% 2	4120
November	1st to 10th	Night	27% 3 14% 27% 24% 5%	2501
	11th to 20th	Night	33% 2 10% 31% 20% 3	2641
	21st to end	Night	35% 2 12% 28% 20% 2	2800
December	1st to 10th	Night	29% 3 15% 36% 17% 1	4580
	11th to 20th	Night	38% 3 15% 30% 14%	5201
	21st to end	Night	55% 2 11% 24% 8% 1	6790

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	18% 14% 35% 22% 8% 2	300
	11th to 20th	Day	18% 16% 37% 22% 6% 1	300
	21st to end	Day	12% 12% 45% 23% 6% 1	330
February	1st to 10th	Day	16% 21% 40% 20% 3	300
	11th to 20th	Day	18% 15% 36% 25% 5% 1	300
	21st to end	Day	14% 16% 41% 24% 4 1	249
March	1st to 10th	Day	17% 14% 40% 24% 5%	300
	11th to 20th	Day	29% 7% 35% 20% 8% 1	300
	21st to end	Day	31% 14% 36% 16% 2	330
April	1st to 10th	Day	20% 19% 36% 20% 4	355
	11th to 20th	Day	21% 16% 34% 24% 6%	600
	21st to end	Day	24% 14% 33% 20% 8% 2	700
May	1st to 10th	Day	19% 9% 33% 24% 12% 1	703
	11th to 20th	Day	17% 9% 32% 28% 12% 3	725
	21st to end	Day	20% 8% 29% 28% 14% 2	789
June	1st to 10th	Day	8% 6% 22% 34% 25% 5%	730
	11th to 20th	Day	9% 4 30% 34% 18% 4	730
	21st to end	Day	7% 7% 35% 35% 14% 3	730
July	1st to 10th	Day	9% 3 17% 34% 27% 9%	721
	11th to 20th	Day	7% 2 21% 40% 22% 7%	718
	21st to end	Day	7% 3 16% 41% 28% 5%	794
August	1st to 10th	Day	7% 3 21% 40% 25% 4	726
	11th to 20th	Day	10% 3 18% 44% 23% 3	715
	21st to end	Day	10% 3 20% 38% 24% 5%	752
September	1st to 10th	Day	14% 3 24% 38% 16% 6%	450
	11th to 20th	Day	8% 4 28% 34% 19% 7%	330
	21st to end	Day	16% 5% 29% 27% 18% 5%	330
October	1st to 10th	Day	20% 6% 24% 29% 14% 7%	309
	11th to 20th	Day	10% 16% 40% 22% 12% 1	300
	21st to end	Day	17% 15% 38% 20% 8% 2	330
November	1st to 10th	Day	18% 11% 35% 26% 8% 2	300
	11th to 20th	Day	16% 14% 40% 23% 7%	300
	21st to end	Day	20% 14% 33% 23% 10%	300
December	1st to 10th	Day	8% 15% 41% 29% 5% 2	300
	11th to 20th	Day	15% 14% 37% 26% 8%	300
	21st to end	Day	20% 17% 38% 20% 4 1	330
January	1st to 10th	Night	12% 13% 36% 33% 5% 1	1000
	11th to 20th	Night	15% 14% 37% 27% 7%	1000
	21st to end	Night	15% 9% 40% 30% 6%	1100
February	1st to 10th	Night	17% 12% 40% 27% 4	1000
	11th to 20th	Night	13% 12% 42% 28% 5%	957
	21st to end	Night	14% 13% 43% 25% 5%	660
March	1st to 10th	Night	12% 15% 40% 25% 7%	629
	11th to 20th	Night	20% 9% 36% 29% 7%	600
	21st to end	Night	23% 9% 39% 23% 6%	660
April	1st to 10th	Night	18% 15% 38% 25% 5%	600
	11th to 20th	Night	14% 14% 39% 28% 3 1	593
	21st to end	Night	20% 10% 34% 28% 8% 1	600
May	1st to 10th	Night	20% 7% 32% 32% 9% 1	600
	11th to 20th	Night	16% 8% 30% 36% 9% 1	591
	21st to end	Night	18% 6% 29% 33% 14%	650
June	1st to 10th	Night	6% 5% 25% 45% 19%	600
	11th to 20th	Night	7% 4 31% 43% 14% 1	600
	21st to end	Night	6% 3 33% 44% 14%	600
July	1st to 10th	Night	8% 2 14% 43% 32% 1	585
	11th to 20th	Night	3 2 19% 49% 26% 1	582
	21st to end	Night	4 1 15% 53% 26% 1	657
August	1st to 10th	Night	6% 1 19% 50% 23% 2	597
	11th to 20th	Night	7% 3 16% 47% 25% 2	594
	21st to end	Night	9% 2 19% 43% 23% 3	660
September	1st to 10th	Night	11% 2 25% 39% 23% 2	600
	11th to 20th	Night	10% 2 27% 42% 18% 2	600
	21st to end	Night	10% 5% 30% 38% 17% 1	600
October	1st to 10th	Night	14% 6% 31% 32% 14% 2	703
	11th to 20th	Night	14% 9% 36% 31% 9%	760
	21st to end	Night	18% 10% 31% 32% 8%	836
November	1st to 10th	Night	10% 11% 31% 37% 10% 1	941
	11th to 20th	Night	13% 13% 39% 28% 7%	1000
	21st to end	Night	16% 11% 36% 29% 8% 1	1000
December	1st to 10th	Night	13% 12% 38% 32% 5% 1	1000
	11th to 20th	Night	16% 11% 35% 32% 6% 1	1000
	21st to end	Night	20% 12% 34% 31% 4	1100

Page generated at 2025-10-01 00:39:07. Version ac07

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