Windy Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windy Hills Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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 6% 4 4 4 3 5% 7% 46%	100913
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 50%	98249
Transparency	Day	36% 6% 12% 26% 18% 3	104576
	Night	34% 5% 11% 26% 20% 4	102713
Seeing	Day	13% 10% 30% 29% 15% 3	15689
	Night	13% 9% 33% 34% 11% 1	25528

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	13% 9% 3 11% 5% 4 4 3 5% 6% 35%	2847
	11th to 20th	Day	9% 11% 4 10% 5% 6% 5% 3 4 5% 38%	2850
	21st to end	Day	12% 15% 7% 8% 4 3 4 3 4 5% 37%	3135
February	1st to 10th	Day	14% 10% 4 7% 4 4 4 3 4 6% 41%	1710
	11th to 20th	Day	10% 10% 4 6% 4 4 4 3 6% 8% 42%	1707
	21st to end	Day	8% 10% 3 6% 4 4 4 3 6% 7% 45%	1584
March	1st to 10th	Day	12% 8% 2 6% 3 3 3 3 4 6% 50%	3436
	11th to 20th	Day	12% 6% 1 4 3 3 4 3 5% 6% 53%	3480
	21st to end	Day	15% 11% 6% 7% 5% 4 3 3 4 6% 37%	3814
April	1st to 10th	Day	13% 7% 3 5% 3 4 3 3 5% 7% 48%	2147
	11th to 20th	Day	13% 8% 3 6% 4 4 4 4 5% 7% 42%	2281
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 39%	2470
May	1st to 10th	Day	17% 8% 3 7% 4 3 3 3 5% 6% 40%	4082
	11th to 20th	Day	16% 7% 3 6% 3 4 4 3 6% 8% 40%	4082
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 7% 44%	4477
June	1st to 10th	Day	6% 4 2 5% 4 5% 5% 5% 7% 10% 49%	2532
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 6% 8% 49%	2647
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 9% 51%	2470
July	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 7% 8% 43%	4120
	11th to 20th	Day	5% 3 2 4 4 4 5% 4 7% 10% 52%	4120
	21st to end	Day	5% 3 2 5% 4 4 5% 4 8% 9% 51%	4465
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 8% 53%	4104
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 48%	4041
	21st to end	Day	6% 3 2 5% 3 4 4 4 5% 9% 55%	4356
September	1st to 10th	Day	11% 4 2 4 4 4 3 3 5% 7% 54%	2215
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 6% 6% 50%	2090
	21st to end	Day	9% 5% 2 4 3 4 4 4 5% 6% 56%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 7% 54%	1933
	11th to 20th	Day	10% 5% 2 5% 3 2 3 3 4 4 59%	1900
	21st to end	Day	15% 6% 2 5% 3 2 4 3 4 6% 51%	2090
November	1st to 10th	Day	9% 4 2 5% 4 4 4 3 4 6% 56%	1851
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 4 5% 57%	1710
	21st to end	Day	15% 7% 2 5% 3 3 3 2 4 5% 51%	1554
December	1st to 10th	Day	9% 6% 3 7% 4 4 4 3 6% 7% 48%	1520
	11th to 20th	Day	11% 9% 4 8% 6% 4 4 3 4 5% 43%	1918
	21st to end	Day	15% 14% 7% 13% 5% 4 4 3 4 5% 26%	3085
January	1st to 10th	Night	8% 9% 3 15% 5% 3 3 3 5% 6% 39%	4108
	11th to 20th	Night	9% 9% 4 7% 4 7% 5% 3 4 5% 41%	4120
	21st to end	Night	15% 12% 4 8% 4 4 4 3 4 5% 39%	4532
February	1st to 10th	Night	10% 12% 3 6% 5% 4 4 3 5% 7% 40%	2470
	11th to 20th	Night	10% 8% 3 8% 4 3 4 4 4 6% 46%	2375
	21st to end	Night	10% 7% 2 6% 4 4 4 4 5% 5% 50%	1870
March	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	3419
	11th to 20th	Night	9% 5% 2 4 3 3 4 2 5% 7% 55%	3480
	21st to end	Night	17% 9% 3 6% 4 4 3 3 5% 6% 40%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 5% 6% 53%	2033
	11th to 20th	Night	13% 7% 2 6% 3 4 4 3 4 7% 46%	1846
	21st to end	Night	16% 6% 3 6% 3 4 4 3 6% 6% 44%	1710
May	1st to 10th	Night	16% 8% 2 5% 4 4 3 3 4 8% 43%	2823
	11th to 20th	Night	14% 7% 2 6% 4 4 3 3 5% 8% 44%	2823
	21st to end	Night	11% 5% 2 5% 3 2 3 4 5% 7% 53%	3090
June	1st to 10th	Night	5% 4 1 4 4 3 3 3 6% 9% 57%	1636
	11th to 20th	Night	6% 4 2 4 3 4 5% 4 7% 9% 53%	1520
	21st to end	Night	4 3 1 4 3 3 4 3 6% 10% 59%	1708
July	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 5% 6% 51%	2850
	11th to 20th	Night	2 2 1 3 3 4 5% 4 6% 10% 61%	2850
	21st to end	Night	6% 4 2 5% 3 4 4 4 6% 12% 52%	3098
August	1st to 10th	Night	2 2 1 4 3 4 5% 4 7% 11% 58%	2836
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 5% 7% 50%	2798
	21st to end	Night	5% 4 2 5% 3 3 3 3 6% 7% 60%	3303
September	1st to 10th	Night	10% 4 2 4 3 4 3 2 5% 6% 57%	1962
	11th to 20th	Night	9% 4 1 4 3 4 4 3 5% 8% 55%	2090
	21st to end	Night	7% 4 2 4 3 3 3 3 4 6% 61%	2090
October	1st to 10th	Night	11% 5% 2 5% 3 2 4 3 4 5% 56%	2227
	11th to 20th	Night	12% 4 1 4 3 3 3 2 4 6% 59%	2280
	21st to end	Night	14% 7% 2 5% 2 3 3 2 4 5% 54%	2508
November	1st to 10th	Night	9% 4 2 4 3 3 2 3 4 5% 61%	2383
	11th to 20th	Night	10% 6% 1 3 3 3 3 4 4 6% 57%	2470
	21st to end	Night	13% 7% 1 4 3 3 3 2 5% 6% 54%	2622
December	1st to 10th	Night	9% 8% 2 5% 4 4 4 5% 5% 6% 49%	2660
	11th to 20th	Night	11% 8% 2 7% 4 3 3 3 5% 5% 47%	3279
	21st to end	Night	18% 14% 6% 9% 4 3 3 2 3 4 33%	4563

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	48% 5% 12% 23% 11% 1	2848
	11th to 20th	Day	50% 4 15% 19% 12% 1	2850
	21st to end	Day	50% 4 13% 19% 13% 1	3135
February	1st to 10th	Day	46% 5% 13% 22% 11% 3	1710
	11th to 20th	Day	41% 6% 11% 25% 14% 3	1716
	21st to end	Day	38% 4 11% 23% 18% 4	1584
March	1st to 10th	Day	37% 3 10% 22% 23% 5%	3436
	11th to 20th	Day	32% 5% 12% 27% 22% 3	3480
	21st to end	Day	48% 6% 15% 25% 6% 1	3814
April	1st to 10th	Day	38% 4 11% 23% 21% 3	2147
	11th to 20th	Day	42% 5% 11% 22% 17% 1	2281
	21st to end	Day	46% 5% 10% 27% 11% 1	2470
May	1st to 10th	Day	44% 6% 10% 23% 15% 2	4120
	11th to 20th	Day	41% 7% 13% 22% 17%	4086
	21st to end	Day	37% 7% 11% 29% 14% 2	4489
June	1st to 10th	Day	27% 9% 16% 29% 18% 2	2532
	11th to 20th	Day	31% 7% 13% 29% 18% 2	2647
	21st to end	Day	29% 7% 14% 29% 17% 4	2470
July	1st to 10th	Day	37% 7% 12% 23% 18% 3	4056
	11th to 20th	Day	25% 7% 12% 33% 19% 3	4051
	21st to end	Day	25% 8% 15% 31% 17% 3	4325
August	1st to 10th	Day	28% 7% 11% 27% 22% 4	4090
	11th to 20th	Day	37% 6% 14% 25% 17% 1	4080
	21st to end	Day	26% 7% 16% 29% 17% 6%	4355
September	1st to 10th	Day	30% 5% 11% 26% 20% 7%	2215
	11th to 20th	Day	34% 6% 9% 26% 22% 3	2090
	21st to end	Day	29% 5% 9% 29% 25% 3	2090
October	1st to 10th	Day	19% 3 7% 22% 42% 7%	3206
	11th to 20th	Day	19% 3 5% 29% 34% 11%	3140
	21st to end	Day	30% 4 9% 28% 25% 4	3428
November	1st to 10th	Day	31% 4 12% 28% 20% 5%	1851
	11th to 20th	Day	33% 4 9% 28% 23% 4	1710
	21st to end	Day	37% 4 9% 26% 22% 2	1554
December	1st to 10th	Day	35% 5% 14% 31% 14% 1	1520
	11th to 20th	Day	44% 5% 12% 25% 13% 1	1915
	21st to end	Day	61% 5% 9% 17% 8% 1	3085
January	1st to 10th	Night	47% 5% 13% 21% 13% 1	4108
	11th to 20th	Night	45% 5% 12% 22% 15% 1	4120
	21st to end	Night	49% 4 14% 19% 13% 2	4532
February	1st to 10th	Night	44% 5% 11% 22% 15% 3	2470
	11th to 20th	Night	40% 4 11% 25% 16% 4	2376
	21st to end	Night	36% 4 9% 23% 21% 7%	1870
March	1st to 10th	Night	34% 4 8% 27% 23% 4	3419
	11th to 20th	Night	29% 4 10% 26% 27% 5%	3480
	21st to end	Night	44% 7% 16% 24% 8% 1	3817
April	1st to 10th	Night	33% 4 11% 24% 23% 5%	2033
	11th to 20th	Night	37% 6% 9% 26% 19% 3	1846
	21st to end	Night	41% 5% 11% 25% 16% 2	1710
May	1st to 10th	Night	40% 7% 12% 22% 15% 3	2850
	11th to 20th	Night	38% 7% 12% 26% 17% 1	2824
	21st to end	Night	31% 5% 14% 30% 18% 1	3099
June	1st to 10th	Night	24% 7% 16% 33% 16% 3	1636
	11th to 20th	Night	26% 7% 12% 32% 19% 3	1520
	21st to end	Night	20% 6% 14% 34% 22% 4	1708
July	1st to 10th	Night	34% 6% 12% 24% 20% 6%	2805
	11th to 20th	Night	18% 6% 14% 35% 25% 3	2796
	21st to end	Night	24% 7% 18% 31% 18% 1	2999
August	1st to 10th	Night	20% 7% 17% 26% 23% 6%	2826
	11th to 20th	Night	33% 7% 13% 26% 20% 2	2825
	21st to end	Night	24% 5% 13% 35% 18% 5%	3303
September	1st to 10th	Night	30% 4 9% 27% 22% 9%	1962
	11th to 20th	Night	28% 4 11% 27% 25% 5%	2090
	21st to end	Night	27% 4 8% 26% 31% 4	2090
October	1st to 10th	Night	21% 3 5% 19% 46% 7%	3721
	11th to 20th	Night	20% 2 5% 30% 30% 13%	3779
	21st to end	Night	30% 3 7% 29% 27% 3	4120
November	1st to 10th	Night	27% 4 11% 28% 24% 6%	2383
	11th to 20th	Night	29% 4 11% 28% 24% 4	2470
	21st to end	Night	33% 3 10% 29% 21% 3	2622
December	1st to 10th	Night	36% 5% 12% 28% 17% 1	2660
	11th to 20th	Night	39% 5% 9% 30% 16% 1	3281
	21st to end	Night	56% 4 8% 21% 9% 2	4563

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% 16% 34% 23% 8%	270
	11th to 20th	Day	21% 17% 39% 19% 3	270
	21st to end	Day	12% 12% 49% 23% 3	297
February	1st to 10th	Day	20% 20% 39% 17% 3	270
	11th to 20th	Day	16% 18% 46% 13% 7%	270
	21st to end	Day	13% 24% 44% 15% 3	225
March	1st to 10th	Day	16% 20% 41% 20% 3	270
	11th to 20th	Day	24% 14% 36% 21% 5%	270
	21st to end	Day	26% 21% 39% 10% 3 1	297
April	1st to 10th	Day	22% 17% 34% 23% 5%	327
	11th to 20th	Day	18% 15% 38% 23% 5% 1	479
	21st to end	Day	22% 15% 36% 18% 9% 1	650
May	1st to 10th	Day	17% 15% 38% 23% 8% 1	653
	11th to 20th	Day	18% 9% 29% 29% 13% 2	675
	21st to end	Day	18% 9% 31% 26% 14% 3	734
June	1st to 10th	Day	5% 6% 23% 34% 27% 6%	680
	11th to 20th	Day	6% 5% 29% 37% 18% 5%	680
	21st to end	Day	7% 7% 33% 40% 11% 2	680
July	1st to 10th	Day	10% 3 17% 32% 30% 8%	671
	11th to 20th	Day	4 3 17% 41% 28% 7%	668
	21st to end	Day	6% 3 18% 39% 27% 7%	739
August	1st to 10th	Day	8% 2 17% 40% 28% 4	676
	11th to 20th	Day	9% 2 20% 42% 23% 4	665
	21st to end	Day	10% 2 15% 34% 32% 8%	650
September	1st to 10th	Day	12% 2 18% 36% 27% 5%	425
	11th to 20th	Day	5% 4 23% 38% 26% 5%	300
	21st to end	Day	15% 7% 25% 35% 15% 4	300
October	1st to 10th	Day	15% 6% 29% 28% 16% 6%	300
	11th to 20th	Day	8% 16% 43% 21% 11% 1	300
	21st to end	Day	19% 15% 36% 23% 6% 2	330
November	1st to 10th	Day	15% 11% 36% 28% 9% 1	291
	11th to 20th	Day	15% 16% 36% 25% 7% 1	270
	21st to end	Day	22% 9% 38% 22% 8% 1	270
December	1st to 10th	Day	8% 15% 40% 27% 7% 2	270
	11th to 20th	Day	19% 14% 37% 23% 7%	270
	21st to end	Day	19% 22% 37% 21% 1	297
January	1st to 10th	Night	12% 12% 38% 31% 7%	950
	11th to 20th	Night	15% 14% 35% 30% 5% 1	950
	21st to end	Night	14% 12% 40% 29% 4	1045
February	1st to 10th	Night	17% 13% 40% 27% 3	950
	11th to 20th	Night	14% 13% 39% 30% 3	901
	21st to end	Night	14% 14% 43% 24% 5%	614
March	1st to 10th	Night	13% 13% 42% 27% 5%	570
	11th to 20th	Night	18% 11% 35% 29% 6% 1	570
	21st to end	Night	22% 13% 38% 23% 4	627
April	1st to 10th	Night	12% 13% 44% 25% 5%	570
	11th to 20th	Night	15% 14% 39% 26% 5%	563
	21st to end	Night	19% 10% 39% 25% 6% 1	570
May	1st to 10th	Night	17% 9% 35% 32% 6% 1	570
	11th to 20th	Night	15% 8% 30% 36% 11%	561
	21st to end	Night	11% 7% 32% 35% 14% 1	617
June	1st to 10th	Night	6% 3 25% 43% 23% 1	570
	11th to 20th	Night	7% 3 30% 44% 16% 1	570
	21st to end	Night	5% 4 33% 45% 12% 1	570
July	1st to 10th	Night	8% 2 16% 45% 28% 1	555
	11th to 20th	Night	2 1 18% 52% 25% 1	552
	21st to end	Night	7% 1 16% 48% 27% 1	624
August	1st to 10th	Night	3 1 17% 50% 26% 2	567
	11th to 20th	Night	7% 1 16% 47% 26% 2	564
	21st to end	Night	6% 2 15% 43% 31% 2	627
September	1st to 10th	Night	12% 2 21% 42% 21% 2	570
	11th to 20th	Night	9% 2 23% 43% 21% 2	570
	21st to end	Night	8% 4 25% 44% 18% 1	570
October	1st to 10th	Night	13% 6% 28% 33% 18% 1	707
	11th to 20th	Night	13% 9% 40% 30% 8%	760
	21st to end	Night	18% 10% 35% 28% 9%	836
November	1st to 10th	Night	11% 9% 34% 34% 12%	843
	11th to 20th	Night	12% 12% 39% 30% 7%	950
	21st to end	Night	16% 11% 34% 31% 7%	950
December	1st to 10th	Night	13% 11% 38% 31% 6% 1	950
	11th to 20th	Night	18% 9% 38% 30% 5%	950
	21st to end	Night	18% 14% 38% 27% 4	1045

Page generated at 2024-11-05 07:15:54. Version ac07

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