Cave Mountain Observatory Retreat
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cave Mountain Observatory Retreat clear sky chart from 2005-11-06 to 2024-11-05.

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% 5% 5% 5% 4 6% 7% 39%	100993
	Night	12% 7% 3 7% 5% 4 5% 4 6% 7% 40%	97985
Transparency	Day	44% 5% 11% 24% 14% 3	104643
	Night	42% 5% 13% 24% 14% 2	102474
Seeing	Day	24% 14% 26% 21% 11% 4	14922
	Night	21% 13% 25% 28% 12% 1	24679

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	12% 13% 4 7% 5% 5% 4 3 5% 5% 37%	2836
	11th to 20th	Day	8% 12% 6% 12% 8% 5% 5% 4 5% 6% 30%	2840
	21st to end	Day	11% 11% 5% 9% 6% 5% 5% 3 5% 6% 35%	3124
February	1st to 10th	Day	10% 9% 4 8% 5% 6% 5% 4 6% 7% 36%	1710
	11th to 20th	Day	11% 9% 3 10% 5% 4 5% 3 5% 7% 36%	1663
	21st to end	Day	11% 10% 3 8% 5% 5% 4 4 5% 5% 40%	1617
March	1st to 10th	Day	15% 9% 3 7% 5% 4 4 3 5% 7% 37%	3435
	11th to 20th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 49%	3480
	21st to end	Day	13% 10% 3 8% 6% 5% 5% 3 5% 5% 37%	3815
April	1st to 10th	Day	10% 9% 3 7% 6% 5% 4 4 6% 6% 39%	2213
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 5% 7% 44%	2254
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 6% 7% 37%	2394
May	1st to 10th	Day	20% 7% 3 7% 6% 6% 5% 4 6% 7% 28%	4082
	11th to 20th	Day	20% 9% 3 7% 4 4 4 3 5% 8% 33%	4081
	21st to end	Day	10% 5% 2 7% 6% 6% 6% 5% 7% 10% 37%	4657
June	1st to 10th	Day	12% 5% 2 4 5% 5% 6% 5% 7% 8% 41%	2660
	11th to 20th	Day	10% 5% 3 6% 5% 7% 6% 5% 6% 10% 38%	2660
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	2660
July	1st to 10th	Day	6% 4 2 6% 6% 6% 6% 5% 8% 10% 42%	4192
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 9% 41%	4120
	21st to end	Day	12% 7% 3 8% 7% 5% 6% 5% 6% 8% 33%	4466
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 6% 5% 7% 9% 32%	4104
	11th to 20th	Day	8% 4 2 7% 7% 6% 6% 6% 7% 8% 38%	4044
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 10% 47%	4193
September	1st to 10th	Day	14% 5% 2 6% 5% 4 5% 4 5% 6% 44%	2280
	11th to 20th	Day	12% 6% 3 7% 4 4 4 4 5% 7% 45%	2142
	21st to end	Day	20% 6% 2 7% 5% 5% 4 4 5% 6% 38%	2057
October	1st to 10th	Day	14% 6% 3 6% 4 4 3 2 5% 6% 46%	1900
	11th to 20th	Day	15% 8% 2 6% 4 4 4 3 4 5% 45%	1900
	21st to end	Day	13% 7% 2 6% 4 4 4 3 4 7% 47%	2090
November	1st to 10th	Day	9% 7% 2 5% 4 4 4 3 4 6% 53%	1898
	11th to 20th	Day	12% 8% 3 5% 4 3 4 4 6% 8% 42%	1635
	21st to end	Day	12% 8% 3 6% 5% 4 5% 3 6% 6% 44%	1520
December	1st to 10th	Day	12% 11% 4 8% 6% 5% 5% 3 6% 6% 35%	1520
	11th to 20th	Day	13% 10% 4 6% 4 4 4 3 4 6% 40%	1910
	21st to end	Day	15% 9% 4 8% 6% 5% 5% 4 7% 7% 31%	2841
January	1st to 10th	Night	8% 13% 5% 9% 5% 5% 5% 4 6% 6% 33%	4109
	11th to 20th	Night	11% 10% 3 10% 5% 4 4 3 5% 6% 39%	4120
	21st to end	Night	15% 11% 3 8% 5% 4 4 4 4 6% 36%	4532
February	1st to 10th	Night	9% 9% 3 7% 5% 5% 5% 4 6% 8% 39%	2470
	11th to 20th	Night	12% 8% 3 9% 6% 6% 6% 5% 5% 6% 34%	2403
	21st to end	Night	12% 9% 4 8% 4 4 5% 5% 6% 7% 37%	1832
March	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 5% 6% 35%	3418
	11th to 20th	Night	8% 10% 6% 6% 5% 3 3 3 5% 6% 45%	3480
	21st to end	Night	12% 7% 2 6% 4 4 5% 4 6% 6% 45%	3817
April	1st to 10th	Night	10% 9% 2 7% 5% 5% 5% 4 5% 8% 40%	1967
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 6% 8% 44%	1875
	21st to end	Night	15% 6% 2 5% 4 5% 4 4 6% 7% 42%	1800
May	1st to 10th	Night	20% 9% 3 8% 5% 4 4 4 6% 8% 30%	2813
	11th to 20th	Night	22% 8% 3 6% 5% 4 4 3 4 6% 35%	2812
	21st to end	Night	10% 5% 2 5% 5% 5% 6% 4 7% 9% 42%	2894
June	1st to 10th	Night	11% 3 1 5% 5% 5% 5% 4 6% 9% 47%	1520
	11th to 20th	Night	8% 5% 2 6% 4 5% 5% 4 6% 10% 44%	1520
	21st to end	Night	8% 4 1 5% 4 5% 6% 5% 7% 10% 45%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 8% 11% 44%	2762
	11th to 20th	Night	7% 5% 3 7% 4 6% 5% 4 7% 10% 41%	2840
	21st to end	Night	9% 6% 3 7% 6% 5% 6% 4 7% 10% 36%	3087
August	1st to 10th	Night	14% 4 2 6% 4 4 6% 5% 6% 10% 38%	2825
	11th to 20th	Night	10% 6% 2 7% 5% 5% 6% 4 7% 9% 40%	2785
	21st to end	Night	7% 4 2 6% 4 4 5% 4 7% 9% 49%	3430
September	1st to 10th	Night	13% 5% 1 6% 3 4 4 4 6% 6% 48%	1900
	11th to 20th	Night	12% 4 1 5% 5% 4 5% 3 6% 8% 48%	2033
	21st to end	Night	19% 6% 2 6% 4 4 4 3 5% 5% 42%	2121
October	1st to 10th	Night	17% 5% 2 5% 3 3 4 3 5% 6% 47%	2280
	11th to 20th	Night	13% 7% 3 4 3 3 4 3 5% 7% 49%	2280
	21st to end	Night	13% 7% 2 5% 4 4 4 3 6% 6% 47%	2508
November	1st to 10th	Night	8% 8% 3 6% 4 3 4 4 6% 7% 48%	2280
	11th to 20th	Night	11% 7% 3 6% 4 4 4 4 7% 7% 43%	2537
	21st to end	Night	12% 7% 3 7% 5% 4 5% 4 6% 6% 41%	2660
December	1st to 10th	Night	12% 10% 4 8% 6% 5% 6% 4 6% 7% 34%	2660
	11th to 20th	Night	13% 7% 3 7% 5% 5% 4 5% 6% 7% 39%	3285
	21st to end	Night	14% 9% 3 8% 6% 5% 6% 5% 6% 8% 32%	4810

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	50% 4 7% 24% 13% 3	2837
	11th to 20th	Day	56% 3 7% 17% 14% 2	2840
	21st to end	Day	52% 3 8% 20% 15% 2	3124
February	1st to 10th	Day	49% 5% 10% 21% 14% 2	1710
	11th to 20th	Day	49% 3 10% 21% 15% 2	1672
	21st to end	Day	48% 3 12% 19% 15% 3	1617
March	1st to 10th	Day	49% 4 9% 25% 12% 2	3435
	11th to 20th	Day	37% 3 7% 31% 20% 2	3480
	21st to end	Day	51% 4 9% 19% 14% 2	3815
April	1st to 10th	Day	45% 5% 12% 19% 15% 4	2213
	11th to 20th	Day	40% 4 10% 22% 19% 5%	2254
	21st to end	Day	47% 4 10% 24% 12% 3	2394
May	1st to 10th	Day	55% 5% 9% 21% 8% 1	4120
	11th to 20th	Day	52% 6% 11% 23% 7% 1	4085
	21st to end	Day	41% 8% 14% 22% 13% 3	4671
June	1st to 10th	Day	40% 7% 15% 23% 14% 1	2660
	11th to 20th	Day	42% 7% 15% 23% 12% 1	2660
	21st to end	Day	39% 6% 15% 25% 13% 2	2660
July	1st to 10th	Day	39% 6% 18% 23% 10% 5%	4127
	11th to 20th	Day	40% 5% 14% 30% 9% 1	4051
	21st to end	Day	50% 5% 9% 22% 12% 1	4324
August	1st to 10th	Day	48% 5% 17% 23% 8%	4091
	11th to 20th	Day	43% 4 12% 28% 13%	4083
	21st to end	Day	35% 5% 16% 29% 14% 1	4193
September	1st to 10th	Day	41% 5% 12% 18% 19% 4	2280
	11th to 20th	Day	41% 5% 8% 25% 18% 3	2142
	21st to end	Day	48% 4 9% 21% 15% 2	2057
October	1st to 10th	Day	31% 2 9% 24% 28% 5%	3160
	11th to 20th	Day	36% 2 7% 26% 18% 11%	3140
	21st to end	Day	28% 2 9% 31% 23% 7%	3428
November	1st to 10th	Day	35% 3 9% 26% 21% 5%	1898
	11th to 20th	Day	41% 3 11% 20% 21% 4	1635
	21st to end	Day	42% 3 11% 26% 16% 2	1520
December	1st to 10th	Day	51% 4 12% 21% 11% 2	1520
	11th to 20th	Day	44% 6% 9% 22% 15% 3	1906
	21st to end	Day	51% 6% 12% 20% 10% 1	2841
January	1st to 10th	Night	51% 5% 8% 21% 13% 2	4109
	11th to 20th	Night	47% 3 11% 24% 12% 3	4120
	21st to end	Night	51% 4 8% 25% 11% 1	4532
February	1st to 10th	Night	45% 5% 14% 24% 12% 1	2470
	11th to 20th	Night	52% 4 9% 21% 12% 2	2405
	21st to end	Night	48% 4 12% 21% 10% 4	1832
March	1st to 10th	Night	51% 4 8% 25% 9% 2	3418
	11th to 20th	Night	41% 4 9% 29% 16% 1	3480
	21st to end	Night	41% 4 11% 24% 17% 3	3817
April	1st to 10th	Night	45% 5% 12% 21% 15% 2	1967
	11th to 20th	Night	39% 5% 13% 23% 16% 4	1875
	21st to end	Night	41% 5% 13% 26% 12% 3	1800
May	1st to 10th	Night	54% 7% 13% 18% 8% 2	2840
	11th to 20th	Night	52% 6% 11% 24% 7%	2813
	21st to end	Night	38% 7% 20% 25% 7% 3	2901
June	1st to 10th	Night	35% 9% 15% 28% 13% 1	1520
	11th to 20th	Night	37% 8% 17% 25% 11% 1	1520
	21st to end	Night	33% 7% 18% 25% 15% 1	1520
July	1st to 10th	Night	33% 8% 24% 20% 11% 2	2717
	11th to 20th	Night	39% 6% 18% 27% 9% 1	2786
	21st to end	Night	44% 6% 16% 23% 11%	2988
August	1st to 10th	Night	42% 6% 19% 25% 7%	2814
	11th to 20th	Night	41% 4 17% 23% 15% 1	2812
	21st to end	Night	32% 5% 17% 33% 11% 1	3430
September	1st to 10th	Night	36% 6% 16% 20% 18% 4	1900
	11th to 20th	Night	36% 5% 10% 30% 17% 2	2033
	21st to end	Night	45% 5% 11% 24% 15% 1	2121
October	1st to 10th	Night	36% 2 11% 27% 21% 3	3800
	11th to 20th	Night	32% 3 11% 22% 25% 8%	3779
	21st to end	Night	27% 2 11% 30% 24% 5%	4120
November	1st to 10th	Night	38% 3 12% 21% 20% 5%	2280
	11th to 20th	Night	40% 4 10% 25% 18% 4	2537
	21st to end	Night	44% 4 12% 23% 15% 3	2660
December	1st to 10th	Night	50% 4 12% 22% 9% 2	2660
	11th to 20th	Night	46% 5% 10% 22% 16% 1	3288
	21st to end	Night	49% 7% 13% 22% 10%	4810

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	39% 24% 24% 9% 4	270
	11th to 20th	Day	38% 20% 33% 7% 2	270
	21st to end	Day	40% 22% 31% 6% 1	297
February	1st to 10th	Day	37% 25% 27% 10%	270
	11th to 20th	Day	47% 23% 25% 4	270
	21st to end	Day	42% 18% 28% 12% 1	320
March	1st to 10th	Day	33% 19% 28% 16% 3	460
	11th to 20th	Day	35% 23% 24% 13% 4 1	460
	21st to end	Day	32% 21% 29% 14% 4 1	506
April	1st to 10th	Day	29% 23% 27% 16% 5%	460
	11th to 20th	Day	28% 18% 27% 17% 7% 3	452
	21st to end	Day	29% 18% 29% 15% 6% 2	460
May	1st to 10th	Day	30% 15% 25% 17% 9% 3	463
	11th to 20th	Day	28% 13% 29% 20% 8% 3	487
	21st to end	Day	19% 9% 27% 23% 17% 5%	529
June	1st to 10th	Day	16% 12% 27% 25% 14% 6%	490
	11th to 20th	Day	15% 11% 30% 22% 17% 5%	490
	21st to end	Day	11% 13% 28% 31% 14% 3	490
July	1st to 10th	Day	12% 6% 27% 27% 20% 9%	485
	11th to 20th	Day	7% 4 30% 32% 19% 8%	484
	21st to end	Day	13% 9% 23% 27% 21% 7%	532
August	1st to 10th	Day	13% 7% 20% 31% 19% 8%	486
	11th to 20th	Day	13% 3 25% 31% 18% 9%	479
	21st to end	Day	11% 6% 19% 32% 20% 11%	539
September	1st to 10th	Day	16% 8% 20% 28% 20% 8%	490
	11th to 20th	Day	15% 4 19% 32% 21% 9%	490
	21st to end	Day	29% 8% 25% 23% 12% 3	490
October	1st to 10th	Day	19% 8% 23% 29% 17% 4	490
	11th to 20th	Day	25% 14% 25% 23% 11% 3	490
	21st to end	Day	24% 17% 30% 19% 8% 2	539
November	1st to 10th	Day	18% 15% 30% 25% 10% 2	472
	11th to 20th	Day	32% 15% 27% 19% 6% 1	253
	21st to end	Day	29% 14% 37% 16% 3	180
December	1st to 10th	Day	36% 19% 30% 11% 4	180
	11th to 20th	Day	37% 17% 27% 15% 4	180
	21st to end	Day	36% 18% 29% 14% 3	219
January	1st to 10th	Night	31% 22% 29% 15% 2	760
	11th to 20th	Night	28% 20% 29% 21% 2	760
	21st to end	Night	27% 23% 34% 15% 2	836
February	1st to 10th	Night	26% 22% 31% 20% 2	760
	11th to 20th	Night	32% 26% 29% 13% 1	743
	21st to end	Night	29% 21% 33% 17% 1	628
March	1st to 10th	Night	25% 21% 31% 20% 2	760
	11th to 20th	Night	30% 20% 25% 19% 5% 1	760
	21st to end	Night	23% 19% 31% 21% 5%	836
April	1st to 10th	Night	23% 22% 30% 20% 5%	760
	11th to 20th	Night	21% 17% 28% 25% 8% 1	751
	21st to end	Night	25% 12% 29% 28% 6%	660
May	1st to 10th	Night	22% 11% 25% 28% 13% 1	570
	11th to 20th	Night	18% 8% 26% 33% 13%	561
	21st to end	Night	14% 3 26% 36% 18% 3	509
June	1st to 10th	Night	11% 5% 25% 38% 20% 1	380
	11th to 20th	Night	12% 5% 20% 44% 18% 2	380
	21st to end	Night	8% 4 26% 46% 16% 1	380
July	1st to 10th	Night	11% 2 15% 41% 27% 4	503
	11th to 20th	Night	6% 3 16% 41% 30% 3	552
	21st to end	Night	9% 2 17% 42% 27% 2	624
August	1st to 10th	Night	10% 2 14% 44% 28% 2	567
	11th to 20th	Night	12% 2 12% 46% 25% 4	564
	21st to end	Night	11% 2 16% 40% 29% 2	803
September	1st to 10th	Night	15% 4 15% 37% 24% 5%	760
	11th to 20th	Night	14% 4 15% 35% 28% 4	760
	21st to end	Night	21% 6% 20% 31% 20% 1	760
October	1st to 10th	Night	21% 8% 18% 31% 19% 3	760
	11th to 20th	Night	20% 14% 27% 27% 11% 1	760
	21st to end	Night	22% 12% 29% 28% 8% 1	836
November	1st to 10th	Night	18% 13% 26% 32% 11% 1	760
	11th to 20th	Night	24% 13% 30% 23% 8% 1	760
	21st to end	Night	24% 18% 30% 23% 6% 1	760
December	1st to 10th	Night	29% 18% 30% 20% 4	760
	11th to 20th	Night	23% 18% 32% 24% 3	760
	21st to end	Night	27% 15% 32% 24% 2	836

Page generated at 2024-11-03 02:11:27. Version ac07

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