Hayes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hayes Observatory clear sky chart from 2005-11-06 to 2025-02-25.

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% 7% 2 6% 4 4 4 4 6% 7% 41%	109402
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 44%	109220
Transparency	Day	40% 6% 10% 22% 18% 4	113149
	Night	39% 5% 9% 21% 20% 5%	113612
Seeing	Day	17% 11% 23% 23% 18% 8%	15371
	Night	17% 9% 24% 28% 18% 3	25055

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	16% 11% 4 8% 3 3 3 3 4 5% 40%	3661
	11th to 20th	Day	17% 6% 3 10% 3 3 3 3 3 5% 45%	4068
	21st to end	Day	21% 9% 3 5% 4 3 4 2 4 6% 38%	4972
February	1st to 10th	Day	20% 11% 3 6% 3 3 4 3 4 7% 38%	2000
	11th to 20th	Day	22% 9% 4 7% 5% 3 3 3 4 5% 35%	1948
	21st to end	Day	22% 8% 3 6% 5% 3 3 3 4 5% 38%	1610
March	1st to 10th	Day	24% 11% 3 7% 4 4 4 3 5% 5% 30%	3120
	11th to 20th	Day	15% 7% 2 6% 3 3 3 3 5% 7% 46%	3306
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 7% 40%	4068
April	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 6% 44%	2280
	11th to 20th	Day	15% 7% 2 6% 4 4 3 2 5% 7% 44%	2254
	21st to end	Day	12% 6% 2 6% 6% 4 4 4 6% 8% 42%	2280
May	1st to 10th	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 39%	4069
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 4 5% 7% 38%	4081
	21st to end	Day	13% 7% 2 6% 4 4 4 5% 6% 9% 40%	4476
June	1st to 10th	Day	9% 6% 2 7% 6% 5% 5% 4 7% 8% 41%	2470
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 5% 7% 10% 45%	2600
	21st to end	Day	6% 5% 2 5% 6% 7% 6% 5% 8% 10% 40%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 11% 34%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 6% 7% 5% 8% 11% 34%	4258
	21st to end	Day	17% 9% 3 8% 6% 6% 6% 5% 7% 8% 24%	4448
August	1st to 10th	Day	4 3 2 5% 3 5% 6% 5% 7% 10% 51%	3785
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	3729
	21st to end	Day	7% 4 1 5% 5% 4 5% 3 6% 7% 53%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 6% 5% 5% 7% 8% 41%	2261
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 3 6% 8% 43%	2090
	21st to end	Day	11% 5% 2 5% 4 3 5% 3 6% 7% 50%	2090
October	1st to 10th	Day	11% 4 2 5% 3 3 3 3 4 6% 56%	2090
	11th to 20th	Day	10% 5% 2 4 3 3 3 3 5% 6% 54%	2044
	21st to end	Day	16% 5% 1 5% 3 3 3 3 4 5% 50%	1933
November	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 4 5% 54%	1762
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 5% 5% 49%	1800
	21st to end	Day	16% 7% 2 4 4 4 4 4 6% 7% 43%	1800
December	1st to 10th	Day	17% 8% 2 5% 5% 4 3 3 4 4 46%	2930
	11th to 20th	Day	24% 10% 3 6% 4 4 3 2 4 5% 36%	3373
	21st to end	Day	20% 10% 3 7% 3 4 4 4 6% 7% 34%	4466
January	1st to 10th	Night	17% 11% 4 7% 3 3 3 3 4 5% 39%	6256
	11th to 20th	Night	18% 9% 3 8% 3 2 3 3 3 3 44%	5834
	21st to end	Night	20% 10% 3 6% 3 3 3 3 4 5% 40%	5984
February	1st to 10th	Night	20% 10% 3 6% 4 3 3 3 5% 6% 37%	2400
	11th to 20th	Night	21% 10% 3 7% 4 4 4 2 3 4 38%	2338
	21st to end	Night	24% 8% 3 6% 4 4 4 4 5% 4 35%	1939
March	1st to 10th	Night	25% 9% 2 6% 4 4 3 3 4 6% 34%	3733
	11th to 20th	Night	13% 8% 2 5% 3 4 4 3 5% 6% 47%	3653
	21st to end	Night	16% 7% 2 6% 6% 4 4 3 5% 5% 40%	3577
April	1st to 10th	Night	12% 7% 2 6% 4 3 4 3 5% 8% 47%	1900
	11th to 20th	Night	15% 6% 2 4 3 3 4 3 5% 7% 48%	1875
	21st to end	Night	12% 7% 2 4 5% 3 4 3 5% 9% 46%	1900
May	1st to 10th	Night	16% 7% 2 6% 5% 4 3 3 5% 7% 42%	2823
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 3 6% 7% 42%	2812
	21st to end	Night	9% 6% 2 6% 4 5% 5% 4 6% 10% 44%	3079
June	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 6% 10% 42%	1710
	11th to 20th	Night	3 3 1 4 3 4 5% 5% 8% 9% 55%	1572
	21st to end	Night	5% 5% 1 5% 3 4 5% 4 7% 10% 50%	1520
July	1st to 10th	Night	8% 5% 3 7% 6% 5% 7% 6% 8% 11% 36%	2530
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 5% 9% 12% 38%	2701
	21st to end	Night	12% 9% 3 11% 6% 6% 6% 5% 6% 9% 27%	3101
August	1st to 10th	Night	3 2 1 3 3 4 4 4 6% 10% 59%	3144
	11th to 20th	Night	5% 4 1 5% 3 4 5% 4 6% 11% 51%	3100
	21st to end	Night	5% 4 1 4 3 3 4 3 5% 9% 59%	3476
September	1st to 10th	Night	10% 6% 2 6% 4 3 4 4 6% 8% 48%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 8% 46%	2089
	21st to end	Night	10% 4 2 4 4 4 4 3 5% 7% 54%	2090
October	1st to 10th	Night	10% 4 1 3 3 3 2 3 4 6% 61%	2090
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2133
	21st to end	Night	14% 6% 2 4 3 3 3 3 4 6% 52%	2663
November	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 4 6% 52%	2536
	11th to 20th	Night	13% 6% 2 4 3 4 3 3 5% 6% 51%	2600
	21st to end	Night	17% 8% 2 5% 4 3 4 3 5% 5% 47%	2600
December	1st to 10th	Night	19% 10% 2 5% 3 3 3 2 4 5% 44%	4250
	11th to 20th	Night	27% 8% 2 4 3 2 2 2 4 4 42%	4822
	21st to end	Night	22% 9% 4 7% 4 4 4 3 4 6% 33%	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	48% 3 8% 21% 18% 2	3662
	11th to 20th	Day	43% 3 5% 21% 26% 1	4068
	21st to end	Day	48% 3 7% 19% 19% 4	4972
February	1st to 10th	Day	49% 3 8% 20% 18% 3	2000
	11th to 20th	Day	53% 4 5% 19% 15% 4	1958
	21st to end	Day	50% 3 8% 15% 17% 7%	1610
March	1st to 10th	Day	56% 5% 6% 11% 13% 9%	3120
	11th to 20th	Day	39% 5% 7% 26% 17% 6%	3306
	21st to end	Day	43% 6% 11% 23% 15% 2	4068
April	1st to 10th	Day	40% 5% 9% 23% 18% 5%	2280
	11th to 20th	Day	41% 4 7% 20% 22% 6%	2254
	21st to end	Day	38% 6% 10% 26% 16% 2	2280
May	1st to 10th	Day	43% 8% 11% 22% 15% 2	4107
	11th to 20th	Day	44% 7% 12% 24% 12%	4085
	21st to end	Day	39% 8% 10% 24% 18% 1	4489
June	1st to 10th	Day	40% 8% 12% 23% 16% 2	2470
	11th to 20th	Day	31% 9% 14% 25% 18% 2	2600
	21st to end	Day	35% 10% 16% 20% 15% 4	2660
July	1st to 10th	Day	39% 9% 21% 23% 6% 2	4371
	11th to 20th	Day	39% 10% 20% 24% 7% 1	4184
	21st to end	Day	55% 9% 12% 18% 5%	4306
August	1st to 10th	Day	25% 8% 15% 34% 17% 2	3773
	11th to 20th	Day	33% 7% 15% 26% 15% 4	3765
	21st to end	Day	29% 7% 10% 26% 25% 3	4179
September	1st to 10th	Day	38% 8% 13% 19% 18% 5%	2261
	11th to 20th	Day	38% 7% 11% 20% 21% 4	2090
	21st to end	Day	33% 6% 11% 23% 20% 7%	2090
October	1st to 10th	Day	21% 4 5% 16% 39% 14%	3480
	11th to 20th	Day	21% 3 5% 21% 32% 18%	3375
	21st to end	Day	28% 3 6% 22% 31% 9%	3158
November	1st to 10th	Day	34% 4 6% 20% 29% 7%	1762
	11th to 20th	Day	37% 3 6% 21% 25% 8%	1800
	21st to end	Day	40% 4 8% 21% 22% 5%	1800
December	1st to 10th	Day	43% 3 4 25% 21% 3	2930
	11th to 20th	Day	53% 4 6% 19% 15% 4	3370
	21st to end	Day	49% 5% 10% 24% 11% 2	4466
January	1st to 10th	Night	49% 2 8% 19% 19% 3	6256
	11th to 20th	Night	46% 4 5% 17% 24% 5%	5834
	21st to end	Night	47% 3 5% 19% 20% 7%	5984
February	1st to 10th	Night	48% 4 8% 18% 17% 3	2400
	11th to 20th	Night	53% 3 6% 17% 15% 5%	2339
	21st to end	Night	51% 4 5% 16% 18% 6%	1939
March	1st to 10th	Night	52% 5% 8% 12% 15% 8%	3733
	11th to 20th	Night	38% 5% 8% 22% 18% 10%	3653
	21st to end	Night	46% 5% 8% 19% 20% 1	3577
April	1st to 10th	Night	37% 5% 12% 21% 21% 4	1900
	11th to 20th	Night	36% 5% 8% 18% 23% 9%	1875
	21st to end	Night	36% 5% 11% 26% 19% 3	1900
May	1st to 10th	Night	41% 7% 11% 23% 16% 2	2850
	11th to 20th	Night	40% 8% 13% 22% 15% 1	2813
	21st to end	Night	35% 8% 13% 26% 17% 2	3087
June	1st to 10th	Night	36% 9% 13% 22% 18% 3	1710
	11th to 20th	Night	22% 7% 19% 29% 20% 3	1572
	21st to end	Night	27% 9% 16% 26% 19% 4	1520
July	1st to 10th	Night	37% 11% 20% 23% 7% 2	2490
	11th to 20th	Night	34% 11% 22% 24% 7% 2	2652
	21st to end	Night	52% 9% 14% 17% 7%	3002
August	1st to 10th	Night	19% 8% 12% 36% 23% 1	3132
	11th to 20th	Night	26% 8% 23% 26% 15% 2	3130
	21st to end	Night	22% 6% 13% 30% 25% 3	3476
September	1st to 10th	Night	32% 8% 14% 24% 17% 6%	1900
	11th to 20th	Night	35% 7% 12% 18% 24% 3	2089
	21st to end	Night	30% 6% 8% 24% 23% 8%	2090
October	1st to 10th	Night	21% 3 7% 17% 37% 16%	3480
	11th to 20th	Night	21% 3 4 18% 33% 21%	3541
	21st to end	Night	24% 4 5% 27% 27% 14%	4388
November	1st to 10th	Night	34% 5% 7% 22% 24% 9%	2536
	11th to 20th	Night	34% 3 7% 20% 27% 10%	2600
	21st to end	Night	40% 3 7% 20% 24% 6%	2600
December	1st to 10th	Night	45% 3 5% 19% 26% 2	4250
	11th to 20th	Night	48% 3 4 20% 23% 3	4824
	21st to end	Night	53% 4 8% 23% 10% 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	28% 23% 32% 13% 3 1	300
	11th to 20th	Day	31% 23% 31% 11% 2 2	300
	21st to end	Day	25% 28% 33% 11% 3	330
February	1st to 10th	Day	29% 23% 31% 14% 3	300
	11th to 20th	Day	39% 23% 27% 9% 1 1	300
	21st to end	Day	37% 29% 23% 9% 3	237
March	1st to 10th	Day	27% 21% 34% 14% 3	270
	11th to 20th	Day	25% 19% 35% 17% 5% 1	351
	21st to end	Day	26% 18% 34% 15% 7%	506
April	1st to 10th	Day	24% 15% 32% 18% 10% 2	460
	11th to 20th	Day	22% 14% 32% 21% 10% 1	452
	21st to end	Day	18% 15% 31% 22% 11% 2	460
May	1st to 10th	Day	20% 11% 31% 20% 14% 4	463
	11th to 20th	Day	13% 7% 28% 27% 17% 9%	487
	21st to end	Day	12% 6% 22% 29% 18% 12%	529
June	1st to 10th	Day	11% 6% 19% 27% 24% 12%	490
	11th to 20th	Day	6% 3 18% 29% 28% 16%	620
	21st to end	Day	8% 3 20% 32% 25% 12%	680
July	1st to 10th	Day	9% 2 15% 29% 28% 16%	671
	11th to 20th	Day	10% 4 10% 25% 30% 20%	565
	21st to end	Day	10% 3 10% 28% 30% 19%	532
August	1st to 10th	Day	9% 3 11% 27% 34% 16%	486
	11th to 20th	Day	10% 3 12% 31% 34% 10%	479
	21st to end	Day	13% 3 9% 24% 32% 19%	539
September	1st to 10th	Day	12% 3 12% 29% 31% 13%	490
	11th to 20th	Day	13% 3 13% 27% 25% 18%	490
	21st to end	Day	15% 6% 15% 29% 28% 7%	490
October	1st to 10th	Day	13% 3 22% 29% 23% 9%	490
	11th to 20th	Day	12% 13% 30% 29% 14% 3	444
	21st to end	Day	22% 12% 28% 28% 8% 1	330
November	1st to 10th	Day	20% 12% 29% 24% 12% 3	300
	11th to 20th	Day	16% 17% 41% 20% 6%	300
	21st to end	Day	21% 20% 29% 18% 10% 2	300
December	1st to 10th	Day	28% 19% 32% 15% 6%	300
	11th to 20th	Day	25% 22% 34% 11% 8%	300
	21st to end	Day	28% 21% 34% 13% 5%	330
January	1st to 10th	Night	25% 17% 31% 22% 4	960
	11th to 20th	Night	27% 20% 28% 20% 5%	811
	21st to end	Night	23% 14% 39% 21% 3	880
February	1st to 10th	Night	23% 15% 35% 23% 4	800
	11th to 20th	Night	27% 17% 32% 21% 2	783
	21st to end	Night	29% 18% 31% 20% 2	647
March	1st to 10th	Night	21% 18% 31% 26% 5%	760
	11th to 20th	Night	22% 14% 34% 23% 6% 1	760
	21st to end	Night	20% 14% 32% 25% 9%	699
April	1st to 10th	Night	16% 13% 35% 25% 11% 1	570
	11th to 20th	Night	18% 10% 32% 28% 11% 1	563
	21st to end	Night	15% 9% 35% 26% 14% 1	570
May	1st to 10th	Night	13% 6% 30% 31% 18% 2	570
	11th to 20th	Night	14% 6% 22% 35% 19% 4	561
	21st to end	Night	11% 2 17% 36% 28% 5%	617
June	1st to 10th	Night	10% 3 15% 35% 31% 6%	570
	11th to 20th	Night	4 2 11% 37% 40% 6%	570
	21st to end	Night	6% 2 13% 36% 35% 8%	570
July	1st to 10th	Night	9% 3 11% 26% 40% 12%	555
	11th to 20th	Night	8% 2 8% 29% 37% 16%	552
	21st to end	Night	9% 2 9% 30% 39% 11%	624
August	1st to 10th	Night	5% 1 7% 26% 52% 10%	567
	11th to 20th	Night	10% 2 10% 37% 37% 5%	564
	21st to end	Night	11% 1 8% 31% 40% 11%	627
September	1st to 10th	Night	11% 2 11% 31% 36% 8%	570
	11th to 20th	Night	13% 2 16% 30% 33% 7%	759
	21st to end	Night	11% 3 17% 32% 33% 4	760
October	1st to 10th	Night	11% 4 21% 30% 27% 7%	760
	11th to 20th	Night	16% 8% 23% 34% 18% 2	760
	21st to end	Night	16% 8% 25% 30% 19% 1	836
November	1st to 10th	Night	15% 9% 24% 31% 18% 2	780
	11th to 20th	Night	15% 11% 35% 25% 13% 1	800
	21st to end	Night	20% 11% 29% 29% 10% 1	800
December	1st to 10th	Night	25% 14% 27% 27% 7%	800
	11th to 20th	Night	25% 12% 31% 24% 8% 1	800
	21st to end	Night	26% 16% 28% 26% 4	880

Page generated at 2025-02-22 05:51:37. Version ac07

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