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 2024-01-15.

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 6% 6% 4 5% 5% 6% 7% 39%	74626
	Night	12% 7% 3 5% 5% 3 5% 5% 6% 8% 41%	75155
Transparency	Day	45% 5% 12% 22% 14% 2	74347
	Night	42% 5% 13% 23% 14% 2	74953
Seeing	Day	24% 14% 26% 21% 11% 4	13784
	Night	21% 13% 25% 28% 12% 1	23656

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	8% 9% 5% 8% 7% 4 6% 4 6% 5% 38%	1706
	11th to 20th	Day	10% 10% 5% 7% 6% 4 6% 6% 5% 7% 34%	1662
	21st to end	Day	10% 10% 5% 8% 5% 3 5% 5% 5% 6% 37%	1782
February	1st to 10th	Day	10% 9% 5% 7% 6% 5% 5% 6% 5% 7% 35%	1620
	11th to 20th	Day	11% 8% 5% 9% 6% 3 5% 5% 5% 8% 36%	1573
	21st to end	Day	12% 9% 4 7% 5% 4 4 4 4 6% 40%	1525
March	1st to 10th	Day	10% 7% 3 6% 6% 3 5% 4 5% 7% 46%	1980
	11th to 20th	Day	14% 9% 3 6% 6% 4 5% 4 4 6% 38%	1980
	21st to end	Day	14% 8% 4 8% 7% 3 5% 4 6% 6% 35%	2178
April	1st to 10th	Day	10% 7% 4 7% 6% 3 5% 5% 6% 6% 41%	2096
	11th to 20th	Day	13% 6% 3 6% 4 3 4 4 6% 7% 44%	2134
	21st to end	Day	16% 7% 3 6% 6% 3 5% 5% 6% 7% 37%	2268
May	1st to 10th	Day	17% 6% 3 5% 6% 4 6% 5% 6% 7% 34%	2340
	11th to 20th	Day	19% 7% 3 7% 5% 3 5% 4 5% 9% 34%	2301
	21st to end	Day	12% 5% 3 6% 7% 4 6% 6% 6% 8% 37%	2629
June	1st to 10th	Day	13% 5% 2 4 5% 4 5% 6% 7% 8% 41%	2520
	11th to 20th	Day	11% 5% 3 6% 5% 5% 7% 6% 5% 10% 37%	2520
	21st to end	Day	9% 4 2 5% 6% 4 6% 6% 7% 9% 41%	2520
July	1st to 10th	Day	9% 5% 3 6% 7% 5% 7% 6% 7% 8% 36%	2384
	11th to 20th	Day	6% 5% 2 5% 6% 6% 7% 8% 6% 10% 38%	2340
	21st to end	Day	11% 6% 3 6% 8% 4 6% 7% 7% 8% 35%	2547
August	1st to 10th	Day	10% 6% 3 6% 7% 5% 7% 8% 7% 9% 32%	2327
	11th to 20th	Day	11% 4 3 7% 8% 5% 6% 7% 7% 8% 34%	2303
	21st to end	Day	10% 5% 3 5% 7% 5% 6% 7% 7% 10% 36%	2389
September	1st to 10th	Day	15% 5% 2 5% 6% 3 4 6% 5% 6% 43%	2160
	11th to 20th	Day	11% 6% 3 6% 5% 3 5% 5% 5% 6% 45%	2030
	21st to end	Day	18% 6% 2 6% 6% 4 4 5% 4 6% 39%	1949
October	1st to 10th	Day	15% 6% 3 5% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Day	16% 8% 3 5% 4 3 4 4 4 5% 43%	1800
	21st to end	Day	13% 7% 2 5% 5% 3 4 4 4 7% 46%	1980
November	1st to 10th	Day	9% 6% 2 4 5% 3 4 4 4 6% 53%	1857
	11th to 20th	Day	12% 7% 4 4 5% 2 4 5% 6% 8% 42%	1635
	21st to end	Day	12% 7% 4 5% 5% 3 5% 4 6% 6% 44%	1520
December	1st to 10th	Day	12% 10% 4 7% 7% 4 5% 4 6% 6% 35%	1520
	11th to 20th	Day	13% 10% 4 6% 4 3 4 4 4 6% 40%	1910
	21st to end	Day	15% 9% 4 7% 7% 4 5% 5% 6% 8% 31%	2841
January	1st to 10th	Night	8% 10% 3 7% 6% 3 5% 6% 6% 8% 38%	2459
	11th to 20th	Night	10% 9% 3 7% 6% 3 5% 5% 6% 8% 36%	2404
	21st to end	Night	10% 10% 4 7% 5% 3 5% 5% 5% 6% 39%	2574
February	1st to 10th	Night	10% 8% 3 6% 6% 4 5% 6% 6% 8% 38%	2340
	11th to 20th	Night	11% 8% 4 8% 7% 5% 7% 6% 5% 6% 33%	2273
	21st to end	Night	13% 8% 4 8% 5% 3 5% 5% 6% 7% 37%	1726
March	1st to 10th	Night	10% 7% 3 4 5% 3 5% 4 5% 7% 47%	1980
	11th to 20th	Night	12% 8% 3 6% 7% 3 5% 5% 6% 6% 40%	1980
	21st to end	Night	13% 7% 3 5% 6% 3 6% 5% 6% 7% 39%	2178
April	1st to 10th	Night	10% 8% 3 7% 5% 4 5% 5% 5% 8% 41%	1864
	11th to 20th	Night	10% 6% 2 6% 5% 3 4 5% 6% 9% 45%	1775
	21st to end	Night	16% 6% 2 4 5% 4 4 5% 6% 8% 42%	1706
May	1st to 10th	Night	14% 7% 3 5% 6% 3 5% 5% 6% 8% 39%	1620
	11th to 20th	Night	16% 6% 3 5% 6% 3 5% 5% 5% 7% 40%	1592
	21st to end	Night	12% 5% 2 3 5% 3 5% 5% 7% 9% 45%	1642
June	1st to 10th	Night	11% 3 1 4 5% 3 4 5% 5% 10% 48%	1440
	11th to 20th	Night	9% 5% 2 5% 5% 4 5% 6% 6% 10% 44%	1440
	21st to end	Night	8% 3 1 5% 4 3 6% 6% 7% 11% 46%	1440
July	1st to 10th	Night	9% 5% 2 4 5% 3 5% 6% 7% 10% 43%	1570
	11th to 20th	Night	6% 3 2 4 4 4 5% 6% 7% 10% 50%	1620
	21st to end	Night	8% 4 2 4 5% 3 6% 5% 7% 12% 43%	1771
August	1st to 10th	Night	7% 5% 2 5% 5% 3 6% 6% 6% 10% 44%	1611
	11th to 20th	Night	11% 5% 2 5% 5% 3 6% 5% 6% 10% 42%	1598
	21st to end	Night	9% 6% 2 6% 5% 3 5% 6% 7% 9% 42%	1948
September	1st to 10th	Night	13% 5% 2 4 4 3 4 5% 6% 7% 48%	1800
	11th to 20th	Night	11% 4 2 4 5% 3 4 4 5% 8% 49%	1926
	21st to end	Night	17% 6% 3 5% 5% 3 4 5% 5% 5% 43%	2009
October	1st to 10th	Night	17% 5% 2 4 4 3 4 4 5% 6% 46%	2160
	11th to 20th	Night	13% 7% 3 3 4 3 4 4 5% 7% 48%	2160
	21st to end	Night	14% 7% 2 4 5% 3 5% 4 6% 6% 45%	2376
November	1st to 10th	Night	9% 8% 3 5% 4 2 4 4 6% 6% 49%	2221
	11th to 20th	Night	11% 6% 3 5% 5% 3 4 5% 6% 7% 43%	2537
	21st to end	Night	12% 7% 3 6% 6% 3 5% 5% 5% 6% 42%	2660
December	1st to 10th	Night	12% 9% 5% 7% 7% 4 6% 5% 6% 7% 34%	2660
	11th to 20th	Night	13% 7% 3 6% 6% 3 4 5% 6% 7% 40%	3285
	21st to end	Night	14% 9% 3 7% 7% 4 6% 6% 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	49% 3 9% 21% 15% 3	1707
	11th to 20th	Day	52% 3 12% 19% 13% 1	1662
	21st to end	Day	49% 3 11% 19% 14% 4	1782
February	1st to 10th	Day	50% 5% 10% 21% 12% 2	1620
	11th to 20th	Day	50% 3 10% 21% 14% 2	1582
	21st to end	Day	47% 3 12% 20% 15% 3	1525
March	1st to 10th	Day	42% 3 11% 25% 17% 2	1980
	11th to 20th	Day	48% 4 9% 21% 15% 3	1980
	21st to end	Day	52% 4 10% 19% 12% 3	2178
April	1st to 10th	Day	44% 4 12% 19% 15% 4	2096
	11th to 20th	Day	40% 4 10% 22% 19% 5%	2134
	21st to end	Day	48% 4 11% 23% 12% 3	2268
May	1st to 10th	Day	50% 5% 12% 19% 12% 1	2340
	11th to 20th	Day	51% 5% 16% 19% 8% 2	2305
	21st to end	Day	46% 7% 16% 22% 9% 1	2629
June	1st to 10th	Day	40% 7% 15% 23% 14% 1	2520
	11th to 20th	Day	43% 7% 15% 21% 12% 1	2520
	21st to end	Day	40% 6% 15% 25% 12% 2	2520
July	1st to 10th	Day	45% 6% 13% 20% 13% 2	2319
	11th to 20th	Day	41% 8% 14% 24% 12% 2	2271
	21st to end	Day	46% 7% 11% 20% 14% 2	2405
August	1st to 10th	Day	47% 7% 15% 21% 9%	2314
	11th to 20th	Day	47% 6% 15% 20% 11% 1	2303
	21st to end	Day	43% 6% 15% 23% 11% 2	2389
September	1st to 10th	Day	42% 6% 13% 18% 17% 3	2160
	11th to 20th	Day	40% 5% 8% 26% 18% 4	2030
	21st to end	Day	47% 4 9% 22% 16% 2	1949
October	1st to 10th	Day	42% 4 11% 23% 15% 4	1800
	11th to 20th	Day	45% 3 10% 22% 19% 2	1800
	21st to end	Day	41% 3 9% 26% 18% 4	1980
November	1st to 10th	Day	35% 3 9% 26% 21% 5%	1857
	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	45% 5% 10% 21% 14% 3	2459
	11th to 20th	Night	47% 5% 13% 21% 12% 2	2404
	21st to end	Night	48% 3 10% 24% 12% 2	2574
February	1st to 10th	Night	45% 5% 14% 23% 11% 1	2340
	11th to 20th	Night	52% 5% 9% 20% 12% 2	2275
	21st to end	Night	49% 4 11% 21% 10% 4	1726
March	1st to 10th	Night	39% 5% 10% 29% 14% 3	1980
	11th to 20th	Night	46% 4 12% 23% 12% 1	1980
	21st to end	Night	45% 6% 13% 20% 13% 3	2178
April	1st to 10th	Night	44% 5% 12% 22% 15% 2	1864
	11th to 20th	Night	38% 5% 13% 23% 16% 4	1775
	21st to end	Night	42% 5% 13% 25% 12% 3	1706
May	1st to 10th	Night	45% 6% 16% 20% 10% 3	1620
	11th to 20th	Night	46% 6% 15% 21% 12% 1	1593
	21st to end	Night	37% 8% 22% 24% 9% 1	1643
June	1st to 10th	Night	35% 8% 16% 28% 13% 1	1440
	11th to 20th	Night	38% 9% 17% 24% 11% 1	1440
	21st to end	Night	32% 8% 18% 26% 15% 1	1440
July	1st to 10th	Night	37% 8% 21% 20% 12% 2	1525
	11th to 20th	Night	29% 9% 20% 27% 13% 2	1566
	21st to end	Night	33% 7% 20% 26% 14%	1672
August	1st to 10th	Night	35% 8% 21% 24% 12%	1600
	11th to 20th	Night	37% 6% 20% 25% 11% 1	1598
	21st to end	Night	38% 7% 16% 26% 11% 2	1948
September	1st to 10th	Night	36% 7% 17% 20% 17% 3	1800
	11th to 20th	Night	34% 5% 10% 31% 17% 2	1926
	21st to end	Night	43% 5% 11% 24% 16% 1	2009
October	1st to 10th	Night	41% 3 13% 26% 15% 3	2160
	11th to 20th	Night	38% 4 12% 27% 18% 2	2160
	21st to end	Night	40% 4 10% 24% 19% 3	2376
November	1st to 10th	Night	38% 3 12% 21% 20% 5%	2221
	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	36% 20% 34% 8% 2	254
	21st to end	Day	42% 22% 28% 7% 2	264
February	1st to 10th	Day	40% 26% 25% 8%	240
	11th to 20th	Day	46% 24% 26% 4	240
	21st to end	Day	42% 17% 29% 11%	288
March	1st to 10th	Day	33% 20% 29% 16% 3	420
	11th to 20th	Day	34% 23% 24% 14% 4 1	420
	21st to end	Day	31% 21% 28% 14% 5% 1	462
April	1st to 10th	Day	28% 23% 26% 17% 6%	420
	11th to 20th	Day	27% 18% 26% 18% 7% 3	412
	21st to end	Day	29% 19% 29% 14% 6% 2	420
May	1st to 10th	Day	30% 16% 26% 16% 8% 4	423
	11th to 20th	Day	27% 14% 29% 20% 7% 3	447
	21st to end	Day	19% 8% 27% 23% 18% 5%	485
June	1st to 10th	Day	16% 11% 28% 26% 14% 6%	450
	11th to 20th	Day	16% 12% 30% 21% 17% 5%	450
	21st to end	Day	12% 13% 28% 31% 13% 3	450
July	1st to 10th	Day	13% 6% 25% 26% 20% 9%	445
	11th to 20th	Day	6% 4 29% 32% 19% 9%	444
	21st to end	Day	13% 9% 23% 26% 21% 8%	488
August	1st to 10th	Day	13% 7% 19% 32% 20% 9%	446
	11th to 20th	Day	13% 3 23% 31% 20% 10%	439
	21st to end	Day	12% 6% 20% 31% 20% 12%	495
September	1st to 10th	Day	17% 8% 19% 27% 21% 8%	450
	11th to 20th	Day	14% 4 19% 32% 22% 9%	450
	21st to end	Day	26% 9% 25% 24% 13% 4	450
October	1st to 10th	Day	20% 9% 23% 28% 18% 4	450
	11th to 20th	Day	26% 14% 25% 23% 10% 2	450
	21st to end	Day	26% 18% 30% 17% 7% 1	495
November	1st to 10th	Day	19% 15% 29% 25% 10% 2	455
	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	740
	21st to end	Night	26% 23% 33% 15% 2	792
February	1st to 10th	Night	27% 22% 31% 18% 2	720
	11th to 20th	Night	32% 26% 29% 13%	703
	21st to end	Night	29% 22% 32% 17% 1	592
March	1st to 10th	Night	24% 22% 32% 19% 2	720
	11th to 20th	Night	30% 19% 25% 19% 5% 1	720
	21st to end	Night	23% 18% 32% 21% 6% 1	792
April	1st to 10th	Night	24% 22% 29% 20% 5%	720
	11th to 20th	Night	21% 17% 27% 26% 9% 1	711
	21st to end	Night	25% 12% 29% 27% 6%	626
May	1st to 10th	Night	21% 12% 25% 28% 13% 1	540
	11th to 20th	Night	18% 8% 27% 34% 13%	531
	21st to end	Night	14% 4 25% 35% 18% 3	482
June	1st to 10th	Night	11% 5% 24% 39% 20% 1	360
	11th to 20th	Night	13% 5% 20% 43% 18% 2	360
	21st to end	Night	7% 4 26% 47% 16% 1	360
July	1st to 10th	Night	12% 2 15% 40% 28% 4	475
	11th to 20th	Night	7% 3 16% 39% 32% 4	522
	21st to end	Night	9% 3 17% 41% 28% 3	591
August	1st to 10th	Night	9% 2 14% 43% 29% 2	537
	11th to 20th	Night	12% 2 10% 46% 26% 4	534
	21st to end	Night	11% 2 16% 38% 30% 2	760
September	1st to 10th	Night	15% 4 15% 36% 25% 5%	720
	11th to 20th	Night	13% 4 15% 35% 28% 4	720
	21st to end	Night	20% 7% 20% 31% 21% 2	720
October	1st to 10th	Night	22% 8% 18% 31% 19% 3	720
	11th to 20th	Night	20% 15% 26% 27% 11% 1	720
	21st to end	Night	23% 12% 29% 27% 8% 1	792
November	1st to 10th	Night	18% 13% 26% 32% 11% 1	740
	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

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