Seven Mile Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seven Mile Ridge 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	12% 7% 3 7% 6% 6% 6% 5% 7% 8% 35%	101188
	Night	11% 7% 2 6% 5% 5% 5% 4 7% 8% 39%	97858
Transparency	Day	41% 6% 12% 20% 16% 5%	104930
	Night	38% 6% 12% 21% 17% 6%	102255
Seeing	Day	20% 15% 25% 21% 12% 6%	15107
	Night	18% 14% 21% 26% 17% 3	25156

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	11% 7% 2 6% 4 4 3 3 6% 10% 43%	2836
	11th to 20th	Day	10% 7% 3 7% 4 4 5% 4 5% 7% 42%	2840
	21st to end	Day	18% 7% 2 7% 5% 4 3 4 6% 6% 38%	3124
February	1st to 10th	Day	10% 9% 3 5% 5% 5% 6% 5% 7% 8% 37%	1754
	11th to 20th	Day	11% 11% 3 7% 5% 5% 5% 4 5% 7% 37%	1848
	21st to end	Day	11% 9% 2 8% 6% 5% 5% 4 6% 7% 38%	1570
March	1st to 10th	Day	19% 7% 2 6% 4 4 3 4 6% 7% 38%	3395
	11th to 20th	Day	9% 6% 2 6% 5% 4 4 4 6% 6% 49%	3480
	21st to end	Day	17% 8% 2 7% 5% 4 4 4 6% 7% 37%	3815
April	1st to 10th	Day	9% 6% 2 6% 6% 6% 6% 5% 6% 8% 41%	2090
	11th to 20th	Day	13% 7% 3 6% 5% 4 5% 3 6% 8% 40%	2268
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 4 6% 6% 42%	2470
May	1st to 10th	Day	11% 8% 3 8% 6% 6% 6% 5% 8% 7% 32%	4082
	11th to 20th	Day	16% 7% 3 9% 7% 6% 6% 6% 8% 7% 26%	4081
	21st to end	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 10% 37%	4476
June	1st to 10th	Day	10% 7% 3 8% 7% 6% 6% 6% 7% 9% 31%	2470
	11th to 20th	Day	8% 7% 3 8% 7% 7% 7% 6% 8% 9% 30%	2470
	21st to end	Day	8% 6% 2 8% 8% 6% 8% 5% 7% 10% 31%	2470
July	1st to 10th	Day	7% 6% 3 8% 7% 8% 7% 6% 9% 10% 30%	4120
	11th to 20th	Day	8% 7% 3 10% 8% 7% 7% 6% 9% 9% 26%	4120
	21st to end	Day	12% 9% 4 12% 10% 9% 8% 6% 8% 8% 15%	4466
August	1st to 10th	Day	15% 8% 3 9% 6% 8% 7% 6% 9% 10% 21%	4104
	11th to 20th	Day	8% 6% 2 8% 7% 8% 8% 6% 9% 11% 26%	4044
	21st to end	Day	7% 5% 2 8% 5% 6% 7% 5% 7% 8% 39%	4235
September	1st to 10th	Day	12% 7% 3 8% 7% 6% 6% 4 7% 7% 34%	2090
	11th to 20th	Day	18% 7% 3 8% 5% 5% 6% 5% 7% 8% 29%	2090
	21st to end	Day	18% 6% 2 7% 6% 4 5% 4 6% 7% 34%	2090
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 7% 44%	2033
	11th to 20th	Day	10% 6% 3 5% 3 4 4 3 5% 5% 51%	1900
	21st to end	Day	12% 6% 2 5% 4 3 4 3 4 7% 51%	2090
November	1st to 10th	Day	10% 7% 2 4 4 3 4 3 5% 6% 52%	1860
	11th to 20th	Day	10% 5% 2 4 5% 4 4 4 6% 8% 49%	1710
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 6% 48%	1710
December	1st to 10th	Day	11% 9% 4 9% 6% 5% 5% 4 6% 7% 34%	1710
	11th to 20th	Day	11% 5% 2 4 4 5% 5% 4 8% 9% 44%	2153
	21st to end	Day	15% 6% 3 6% 4 5% 5% 4 6% 7% 38%	3124
January	1st to 10th	Night	11% 6% 2 5% 5% 5% 4 5% 7% 10% 38%	4109
	11th to 20th	Night	9% 8% 3 8% 6% 5% 4 3 5% 8% 42%	4120
	21st to end	Night	15% 9% 2 8% 6% 5% 4 3 5% 5% 37%	4532
February	1st to 10th	Night	8% 7% 2 7% 5% 5% 6% 4 7% 8% 41%	2423
	11th to 20th	Night	12% 8% 3 6% 5% 4 5% 4 6% 7% 39%	2218
	21st to end	Night	10% 8% 3 8% 5% 5% 5% 6% 8% 7% 36%	1884
March	1st to 10th	Night	18% 10% 3 8% 8% 7% 4 4 5% 6% 28%	3458
	11th to 20th	Night	7% 6% 2 6% 5% 4 6% 4 7% 9% 45%	3480
	21st to end	Night	16% 6% 2 5% 4 4 5% 4 6% 8% 40%	3817
April	1st to 10th	Night	8% 6% 2 7% 5% 6% 5% 4 6% 9% 43%	2090
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 8% 45%	1874
	21st to end	Night	10% 7% 2 5% 5% 5% 4 4 5% 7% 46%	1710
May	1st to 10th	Night	12% 7% 2 7% 5% 5% 5% 4 7% 10% 34%	2813
	11th to 20th	Night	16% 8% 3 7% 5% 5% 5% 5% 7% 8% 30%	2812
	21st to end	Night	8% 5% 2 6% 4 5% 5% 5% 8% 11% 41%	3079
June	1st to 10th	Night	9% 7% 2 6% 5% 5% 6% 6% 9% 11% 35%	1710
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 6% 8% 10% 40%	1710
	21st to end	Night	7% 4 2 6% 7% 6% 5% 5% 8% 12% 39%	1710
July	1st to 10th	Night	5% 6% 2 7% 7% 8% 8% 6% 8% 10% 34%	2840
	11th to 20th	Night	7% 5% 2 6% 4 5% 6% 5% 8% 12% 40%	2840
	21st to end	Night	7% 10% 4 11% 7% 8% 7% 6% 10% 10% 21%	3087
August	1st to 10th	Night	12% 8% 3 7% 5% 5% 6% 5% 8% 10% 32%	2825
	11th to 20th	Night	8% 7% 2 8% 7% 8% 6% 5% 7% 9% 32%	2785
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 46%	3369
September	1st to 10th	Night	11% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	2090
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 3 5% 8% 33%	2090
	21st to end	Night	18% 8% 2 6% 4 4 3 3 3 6% 43%	2090
October	1st to 10th	Night	16% 6% 2 5% 4 4 4 3 5% 6% 46%	2147
	11th to 20th	Night	12% 7% 2 5% 4 4 3 4 4 5% 49%	2280
	21st to end	Night	12% 6% 1 5% 3 3 4 3 5% 6% 52%	2508
November	1st to 10th	Night	12% 8% 2 5% 4 3 4 4 6% 6% 47%	2374
	11th to 20th	Night	10% 6% 2 5% 4 4 5% 4 6% 7% 48%	2470
	21st to end	Night	11% 5% 2 5% 4 4 5% 5% 7% 6% 46%	2470
December	1st to 10th	Night	11% 8% 3 7% 6% 7% 5% 5% 7% 7% 34%	2470
	11th to 20th	Night	11% 7% 3 7% 5% 6% 5% 4 6% 6% 40%	3042
	21st to end	Night	17% 7% 4 6% 5% 4 5% 4 7% 8% 31%	4532

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% 6% 5% 22% 29% 6%	2837
	11th to 20th	Day	38% 5% 6% 16% 29% 6%	2840
	21st to end	Day	43% 3 4 19% 24% 6%	3124
February	1st to 10th	Day	39% 5% 10% 21% 19% 6%	1754
	11th to 20th	Day	43% 4 9% 19% 19% 5%	1858
	21st to end	Day	43% 5% 10% 18% 18% 7%	1570
March	1st to 10th	Day	44% 3 7% 20% 17% 9%	3395
	11th to 20th	Day	33% 4 9% 21% 22% 11%	3480
	21st to end	Day	44% 4 8% 25% 15% 4	3815
April	1st to 10th	Day	34% 6% 12% 24% 19% 5%	2090
	11th to 20th	Day	40% 4 9% 20% 20% 6%	2268
	21st to end	Day	39% 5% 12% 26% 15% 2	2470
May	1st to 10th	Day	46% 6% 14% 22% 11% 1	4120
	11th to 20th	Day	51% 6% 11% 22% 9% 1	4085
	21st to end	Day	38% 6% 16% 21% 17% 1	4489
June	1st to 10th	Day	46% 8% 17% 19% 9% 1	2470
	11th to 20th	Day	43% 9% 16% 18% 12% 1	2470
	21st to end	Day	43% 9% 15% 20% 11% 2	2470
July	1st to 10th	Day	42% 14% 18% 18% 7% 1	4055
	11th to 20th	Day	46% 11% 21% 16% 5% 1	4051
	21st to end	Day	59% 12% 13% 11% 4 1	4324
August	1st to 10th	Day	50% 9% 19% 17% 3	4091
	11th to 20th	Day	40% 10% 23% 16% 8% 3	4083
	21st to end	Day	35% 8% 14% 33% 7% 2	4235
September	1st to 10th	Day	45% 7% 12% 19% 14% 3	2090
	11th to 20th	Day	48% 7% 9% 20% 14% 2	2090
	21st to end	Day	46% 6% 11% 18% 15% 4	2090
October	1st to 10th	Day	29% 3 8% 19% 29% 12%	3384
	11th to 20th	Day	22% 2 6% 22% 25% 24%	3140
	21st to end	Day	26% 3 7% 27% 21% 16%	3428
November	1st to 10th	Day	32% 3 8% 22% 27% 8%	1860
	11th to 20th	Day	32% 3 7% 22% 25% 9%	1710
	21st to end	Day	35% 4 6% 23% 25% 7%	1710
December	1st to 10th	Day	46% 5% 7% 20% 17% 5%	1710
	11th to 20th	Day	32% 4 10% 19% 26% 10%	2150
	21st to end	Day	41% 4 6% 23% 22% 4	3124
January	1st to 10th	Night	35% 6% 7% 16% 27% 9%	4109
	11th to 20th	Night	36% 5% 6% 15% 29% 9%	4120
	21st to end	Night	45% 3 7% 16% 22% 7%	4532
February	1st to 10th	Night	36% 5% 11% 22% 22% 4	2423
	11th to 20th	Night	41% 4 8% 20% 20% 6%	2219
	21st to end	Night	41% 6% 11% 19% 18% 6%	1884
March	1st to 10th	Night	53% 5% 7% 15% 15% 5%	3458
	11th to 20th	Night	32% 6% 8% 24% 17% 13%	3480
	21st to end	Night	41% 4 11% 25% 13% 6%	3817
April	1st to 10th	Night	34% 6% 13% 23% 20% 5%	2090
	11th to 20th	Night	35% 4 10% 23% 21% 6%	1874
	21st to end	Night	35% 5% 15% 28% 16% 2	1710
May	1st to 10th	Night	41% 7% 17% 25% 9% 1	2840
	11th to 20th	Night	46% 6% 17% 22% 9%	2813
	21st to end	Night	32% 6% 20% 30% 11% 1	3087
June	1st to 10th	Night	39% 9% 21% 22% 8% 1	1710
	11th to 20th	Night	36% 7% 24% 23% 9% 1	1710
	21st to end	Night	34% 10% 19% 21% 13% 2	1710
July	1st to 10th	Night	39% 12% 21% 21% 6% 1	2795
	11th to 20th	Night	34% 12% 29% 21% 4 1	2786
	21st to end	Night	51% 15% 16% 13% 4	2988
August	1st to 10th	Night	43% 9% 26% 16% 5%	2814
	11th to 20th	Night	38% 10% 24% 17% 10% 1	2812
	21st to end	Night	32% 6% 18% 33% 9% 1	3369
September	1st to 10th	Night	43% 7% 13% 19% 15% 3	2090
	11th to 20th	Night	48% 6% 10% 20% 15% 1	2090
	21st to end	Night	43% 4 10% 22% 18% 3	2090
October	1st to 10th	Night	29% 4 9% 21% 24% 13%	3576
	11th to 20th	Night	23% 3 6% 22% 27% 19%	3779
	21st to end	Night	29% 3 6% 23% 25% 14%	4120
November	1st to 10th	Night	34% 4 8% 22% 22% 9%	2374
	11th to 20th	Night	32% 4 7% 20% 26% 10%	2470
	21st to end	Night	33% 5% 6% 24% 25% 6%	2470
December	1st to 10th	Night	44% 6% 8% 20% 18% 5%	2470
	11th to 20th	Night	35% 5% 8% 17% 27% 7%	3044
	21st to end	Night	44% 5% 8% 19% 21% 3	4532

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	31% 29% 31% 8% 1	270
	11th to 20th	Day	33% 22% 33% 12% 1	270
	21st to end	Day	26% 35% 31% 7% 1	297
February	1st to 10th	Day	25% 25% 37% 11% 2	270
	11th to 20th	Day	37% 28% 30% 4	270
	21st to end	Day	38% 30% 25% 6% 1	225
March	1st to 10th	Day	26% 26% 29% 16% 4	431
	11th to 20th	Day	26% 27% 31% 13% 3 1	460
	21st to end	Day	26% 26% 29% 13% 5%	506
April	1st to 10th	Day	26% 24% 23% 19% 7% 2	460
	11th to 20th	Day	21% 22% 25% 21% 9% 2	452
	21st to end	Day	23% 18% 27% 18% 10% 4	460
May	1st to 10th	Day	19% 22% 29% 18% 8% 5%	463
	11th to 20th	Day	22% 14% 24% 19% 14% 7%	487
	21st to end	Day	17% 9% 23% 23% 16% 11%	529
June	1st to 10th	Day	16% 10% 22% 30% 14% 9%	490
	11th to 20th	Day	13% 7% 23% 26% 22% 10%	490
	21st to end	Day	10% 10% 30% 24% 16% 9%	490
July	1st to 10th	Day	11% 4 17% 28% 25% 15%	485
	11th to 20th	Day	10% 4 14% 30% 27% 15%	484
	21st to end	Day	10% 5% 14% 33% 25% 14%	532
August	1st to 10th	Day	20% 5% 21% 23% 18% 14%	486
	11th to 20th	Day	12% 6% 17% 30% 21% 14%	479
	21st to end	Day	15% 3 16% 28% 23% 15%	539
September	1st to 10th	Day	14% 4 19% 30% 21% 12%	490
	11th to 20th	Day	22% 8% 14% 23% 24% 8%	490
	21st to end	Day	26% 7% 20% 27% 16% 4	490
October	1st to 10th	Day	26% 8% 21% 24% 14% 7%	490
	11th to 20th	Day	16% 15% 29% 26% 11% 3	490
	21st to end	Day	21% 12% 28% 26% 9% 3	539
November	1st to 10th	Day	24% 14% 30% 23% 8% 2	416
	11th to 20th	Day	19% 22% 39% 15% 4 1	270
	21st to end	Day	21% 23% 32% 17% 6% 1	270
December	1st to 10th	Day	26% 26% 36% 11% 1	270
	11th to 20th	Day	19% 20% 43% 15% 3 1	270
	21st to end	Day	25% 20% 38% 13% 4	297
January	1st to 10th	Night	20% 25% 29% 20% 5%	760
	11th to 20th	Night	20% 21% 31% 22% 4	760
	21st to end	Night	19% 25% 31% 21% 4	836
February	1st to 10th	Night	15% 22% 32% 27% 4	760
	11th to 20th	Night	25% 26% 28% 20% 2	743
	21st to end	Night	20% 27% 32% 18% 3	628
March	1st to 10th	Night	18% 24% 30% 25% 4	760
	11th to 20th	Night	22% 19% 31% 20% 7% 1	760
	21st to end	Night	20% 20% 30% 22% 7%	836
April	1st to 10th	Night	19% 21% 27% 25% 7% 1	760
	11th to 20th	Night	21% 19% 22% 24% 12% 2	686
	21st to end	Night	15% 14% 24% 33% 14% 1	570
May	1st to 10th	Night	16% 14% 28% 26% 14% 2	570
	11th to 20th	Night	20% 7% 19% 29% 22% 2	561
	21st to end	Night	17% 6% 14% 27% 29% 7%	617
June	1st to 10th	Night	14% 4 16% 32% 28% 6%	570
	11th to 20th	Night	12% 4 16% 28% 31% 9%	570
	21st to end	Night	9% 2 17% 32% 34% 7%	570
July	1st to 10th	Night	11% 4 7% 30% 41% 7%	555
	11th to 20th	Night	11% 3 7% 28% 42% 9%	552
	21st to end	Night	8% 3 8% 31% 40% 10%	624
August	1st to 10th	Night	16% 2 9% 29% 37% 7%	567
	11th to 20th	Night	15% 3 10% 28% 37% 7%	564
	21st to end	Night	15% 3 6% 28% 39% 9%	694
September	1st to 10th	Night	16% 5% 9% 26% 36% 8%	760
	11th to 20th	Night	25% 5% 7% 24% 33% 6%	760
	21st to end	Night	25% 5% 14% 29% 24% 3	760
October	1st to 10th	Night	21% 10% 16% 21% 23% 8%	760
	11th to 20th	Night	21% 12% 22% 27% 14% 3	760
	21st to end	Night	18% 14% 20% 33% 11% 4	836
November	1st to 10th	Night	20% 12% 21% 29% 16% 2	771
	11th to 20th	Night	20% 16% 19% 33% 11% 1	760
	21st to end	Night	18% 17% 23% 28% 12% 2	760
December	1st to 10th	Night	19% 20% 28% 26% 7%	760
	11th to 20th	Night	17% 18% 28% 28% 7% 1	760
	21st to end	Night	25% 16% 25% 29% 5%	836

Page generated at 2024-11-05 08:15:48. Version ac07

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