Cadillac Mountain Summit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cadillac Mountain Summit clear sky chart from 2005-11-06 to 2026-03-18.

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	19% 9% 3 6% 4 4 4 3 5% 7% 37%	130536
	Night	19% 10% 3 6% 4 4 4 3 5% 6% 36%	131001
Transparency	Day	47% 4 12% 22% 13% 2	134070
	Night	49% 4 11% 22% 13% 2	135555
Seeing	Day	24% 16% 32% 20% 7% 1	17605
	Night	25% 16% 28% 22% 8% 1	26017

By Month

Percentage Cloud Cover NE (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	15% 10% 3 7% 5% 5% 5% 4 5% 6% 35%	4644
	11th to 20th	Day	17% 12% 3 6% 4 4 4 2 3 5% 40%	4650
	21st to end	Day	11% 10% 3 6% 3 4 4 3 5% 6% 44%	5397
February	1st to 10th	Day	16% 12% 3 7% 5% 5% 5% 4 6% 6% 32%	1890
	11th to 20th	Day	15% 8% 2 8% 4 4 5% 4 6% 6% 37%	1932
	21st to end	Day	13% 10% 3 6% 6% 4 5% 3 6% 7% 36%	1730
March	1st to 10th	Day	24% 11% 3 7% 4 4 4 3 4 5% 31%	4669
	11th to 20th	Day	21% 11% 2 6% 4 4 4 3 5% 6% 35%	5057
	21st to end	Day	29% 9% 2 6% 4 3 4 3 5% 6% 30%	5466
April	1st to 10th	Day	21% 10% 2 5% 5% 4 3 4 5% 6% 34%	2338
	11th to 20th	Day	20% 8% 3 5% 4 3 3 3 5% 7% 39%	2569
	21st to end	Day	20% 9% 2 6% 4 4 4 3 4 6% 37%	2600
May	1st to 10th	Day	29% 12% 3 7% 4 3 3 3 4 6% 26%	5886
	11th to 20th	Day	19% 9% 3 8% 5% 4 4 4 5% 6% 34%	5861
	21st to end	Day	20% 10% 3 6% 4 4 5% 4 5% 7% 32%	7049
June	1st to 10th	Day	22% 8% 3 7% 5% 3 4 4 5% 8% 32%	3000
	11th to 20th	Day	19% 8% 2 6% 4 3 3 3 6% 7% 40%	3000
	21st to end	Day	26% 9% 2 6% 4 3 3 3 5% 6% 32%	3000
July	1st to 10th	Day	19% 9% 3 7% 4 4 5% 4 6% 9% 31%	6638
	11th to 20th	Day	17% 11% 3 6% 3 3 3 3 5% 8% 38%	6360
	21st to end	Day	16% 6% 2 5% 3 3 4 3 6% 8% 43%	6704
August	1st to 10th	Day	19% 8% 2 6% 4 4 4 4 5% 7% 36%	4235
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 3 5% 7% 36%	4175
	21st to end	Day	9% 5% 2 5% 3 3 3 3 6% 8% 52%	4675
September	1st to 10th	Day	12% 5% 1 5% 4 4 3 3 6% 7% 49%	2299
	11th to 20th	Day	13% 6% 2 4 3 3 4 3 3 7% 53%	2200
	21st to end	Day	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2200
October	1st to 10th	Day	16% 8% 2 5% 4 4 4 3 5% 6% 43%	2121
	11th to 20th	Day	17% 7% 3 5% 5% 3 3 3 4 7% 42%	2000
	21st to end	Day	21% 10% 2 5% 3 3 3 3 5% 6% 39%	2005
November	1st to 10th	Day	18% 6% 2 7% 4 3 5% 3 5% 5% 42%	1851
	11th to 20th	Day	20% 6% 2 5% 3 3 3 3 4 7% 42%	1816
	21st to end	Day	20% 10% 3 6% 3 3 3 3 5% 6% 38%	1680
December	1st to 10th	Day	20% 9% 2 4 3 3 3 3 5% 6% 42%	2598
	11th to 20th	Day	21% 8% 2 5% 4 3 4 3 4 5% 40%	2688
	21st to end	Day	20% 13% 4 5% 3 3 3 3 3 6% 37%	3553
January	1st to 10th	Night	13% 12% 4 8% 5% 4 4 3 4 6% 39%	8235
	11th to 20th	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 30%	8235
	21st to end	Night	12% 10% 3 7% 4 4 4 3 5% 7% 41%	8781
February	1st to 10th	Night	18% 10% 3 7% 5% 4 5% 3 6% 6% 33%	2730
	11th to 20th	Night	14% 11% 3 7% 4 4 4 3 5% 6% 39%	2572
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 4 6% 38%	2076
March	1st to 10th	Night	26% 11% 3 6% 5% 4 3 3 4 4 31%	5391
	11th to 20th	Night	17% 11% 3 6% 5% 4 5% 4 6% 7% 31%	5057
	21st to end	Night	27% 9% 2 6% 4 4 4 4 5% 6% 30%	5466
April	1st to 10th	Night	23% 11% 3 6% 4 4 4 3 4 6% 33%	2060
	11th to 20th	Night	21% 9% 2 6% 5% 3 4 3 6% 7% 34%	1779
	21st to end	Night	24% 10% 3 6% 4 3 3 3 4 6% 34%	1800
May	1st to 10th	Night	28% 11% 3 7% 4 4 3 3 4 5% 26%	4054
	11th to 20th	Night	24% 8% 3 6% 5% 4 4 4 6% 6% 30%	4033
	21st to end	Night	17% 12% 4 8% 5% 4 3 4 5% 7% 31%	3865
June	1st to 10th	Night	26% 10% 2 6% 4 4 4 4 6% 7% 28%	1400
	11th to 20th	Night	20% 10% 3 6% 4 3 4 4 6% 7% 36%	1400
	21st to end	Night	28% 10% 3 5% 4 4 3 3 5% 7% 30%	1400
July	1st to 10th	Night	18% 10% 4 8% 5% 5% 5% 4 8% 8% 25%	3329
	11th to 20th	Night	20% 13% 3 6% 3 4 5% 4 6% 7% 29%	3600
	21st to end	Night	14% 8% 2 6% 4 5% 5% 4 7% 8% 39%	4102
August	1st to 10th	Night	24% 10% 3 7% 4 4 4 4 5% 6% 29%	2915
	11th to 20th	Night	19% 9% 3 7% 4 4 4 5% 6% 8% 30%	2872
	21st to end	Night	10% 6% 3 6% 4 4 5% 3 5% 8% 45%	3223
September	1st to 10th	Night	14% 5% 2 4 4 3 4 3 5% 6% 48%	2096
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 7% 50%	2200
	21st to end	Night	17% 7% 2 4 4 3 4 3 5% 7% 45%	2200
October	1st to 10th	Night	19% 6% 2 5% 4 4 4 3 5% 6% 43%	2278
	11th to 20th	Night	19% 7% 2 5% 3 3 4 3 5% 6% 43%	2400
	21st to end	Night	23% 9% 2 6% 4 3 4 3 4 6% 37%	2831
November	1st to 10th	Night	18% 7% 2 5% 4 4 4 4 5% 6% 43%	2667
	11th to 20th	Night	17% 8% 2 6% 4 3 4 4 6% 5% 41%	2800
	21st to end	Night	18% 8% 3 6% 4 4 4 3 5% 7% 38%	2940
December	1st to 10th	Night	19% 9% 3 5% 4 4 4 4 6% 6% 36%	4806
	11th to 20th	Night	23% 8% 2 5% 3 2 3 3 4 6% 42%	5741
	21st to end	Night	23% 10% 3 6% 4 3 3 2 4 5% 36%	7667

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% 3 12% 25% 10% 1	4645
	11th to 20th	Day	49% 4 10% 23% 13% 2	4680
	21st to end	Day	43% 2 10% 23% 18% 4	5397
February	1st to 10th	Day	52% 3 12% 19% 11% 2	1890
	11th to 20th	Day	47% 5% 13% 21% 13% 2	1940
	21st to end	Day	48% 3 11% 22% 12% 4	1730
March	1st to 10th	Day	56% 4 9% 11% 15% 5%	4673
	11th to 20th	Day	50% 4 14% 20% 10% 1	5057
	21st to end	Day	56% 3 5% 18% 15% 3	5466
April	1st to 10th	Day	51% 4 8% 19% 15% 3	2338
	11th to 20th	Day	45% 4 10% 24% 14% 3	2569
	21st to end	Day	47% 4 9% 20% 16% 3	2600
May	1st to 10th	Day	60% 4 11% 18% 6% 1	5897
	11th to 20th	Day	51% 5% 11% 23% 7% 2	5865
	21st to end	Day	51% 5% 11% 20% 11% 1	7049
June	1st to 10th	Day	51% 5% 12% 21% 10%	3000
	11th to 20th	Day	44% 5% 12% 21% 15% 2	3000
	21st to end	Day	53% 5% 11% 18% 11% 2	3000
July	1st to 10th	Day	51% 4 15% 20% 10%	6566
	11th to 20th	Day	46% 4 14% 22% 12% 1	6285
	21st to end	Day	39% 5% 14% 27% 14% 1	6511
August	1st to 10th	Day	48% 6% 14% 25% 8%	4222
	11th to 20th	Day	47% 4 18% 21% 9%	4214
	21st to end	Day	30% 5% 14% 30% 21% 1	4675
September	1st to 10th	Day	34% 5% 13% 29% 18% 1	2299
	11th to 20th	Day	34% 5% 11% 28% 21% 2	2200
	21st to end	Day	41% 4 9% 27% 17% 1	2200
October	1st to 10th	Day	46% 5% 12% 24% 12% 1	3459
	11th to 20th	Day	32% 4 9% 34% 20%	3240
	21st to end	Day	34% 3 18% 24% 18% 3	3217
November	1st to 10th	Day	43% 5% 14% 24% 13% 1	1851
	11th to 20th	Day	43% 4 10% 23% 16% 3	1816
	21st to end	Day	48% 4 15% 24% 8% 1	1680
December	1st to 10th	Day	44% 3 15% 24% 13% 1	2598
	11th to 20th	Day	48% 3 12% 19% 13% 6%	2688
	21st to end	Day	51% 4 11% 19% 12% 3	3553
January	1st to 10th	Night	48% 3 12% 25% 12% 1	8235
	11th to 20th	Night	55% 4 10% 19% 11% 1	8280
	21st to end	Night	43% 3 9% 24% 17% 4	8781
February	1st to 10th	Night	52% 4 11% 20% 12% 2	2730
	11th to 20th	Night	46% 4 11% 21% 15% 2	2575
	21st to end	Night	47% 3 9% 23% 14% 3	2076
March	1st to 10th	Night	57% 3 7% 13% 13% 7%	5400
	11th to 20th	Night	50% 4 20% 17% 8% 1	5058
	21st to end	Night	56% 3 5% 18% 16% 2	5466
April	1st to 10th	Night	53% 4 7% 16% 16% 4	2060
	11th to 20th	Night	50% 3 9% 21% 15% 2	1779
	21st to end	Night	52% 3 9% 18% 14% 3	1800
May	1st to 10th	Night	61% 4 11% 15% 8% 1	4060
	11th to 20th	Night	53% 4 13% 20% 8% 1	4034
	21st to end	Night	54% 4 12% 21% 9%	3866
June	1st to 10th	Night	55% 5% 10% 21% 8% 1	1400
	11th to 20th	Night	46% 6% 12% 22% 12% 2	1400
	21st to end	Night	55% 4 9% 20% 10% 2	1400
July	1st to 10th	Night	56% 5% 12% 20% 8%	3291
	11th to 20th	Night	54% 5% 12% 20% 9%	3552
	21st to end	Night	42% 5% 17% 24% 11% 1	3981
August	1st to 10th	Night	57% 5% 11% 20% 7%	2903
	11th to 20th	Night	50% 6% 13% 22% 8%	2899
	21st to end	Night	37% 5% 11% 25% 20% 1	3223
September	1st to 10th	Night	36% 4 12% 29% 18% 1	2096
	11th to 20th	Night	37% 3 11% 27% 20% 2	2200
	21st to end	Night	40% 4 9% 28% 17% 1	2200
October	1st to 10th	Night	41% 5% 13% 25% 15% 1	3720
	11th to 20th	Night	33% 3 10% 30% 23% 1	3899
	21st to end	Night	40% 3 10% 30% 15% 2	4569
November	1st to 10th	Night	43% 4 12% 25% 15% 1	2667
	11th to 20th	Night	44% 4 12% 23% 15% 2	2800
	21st to end	Night	46% 5% 14% 21% 13% 1	2940
December	1st to 10th	Night	48% 3 11% 27% 11%	4806
	11th to 20th	Night	46% 3 12% 21% 16% 2	5742
	21st to end	Night	51% 3 11% 19% 15% 1	7667

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% 30% 28% 11% 3	220
	11th to 20th	Day	33% 26% 27% 12% 2	220
	21st to end	Day	21% 28% 34% 13% 4	334
February	1st to 10th	Day	27% 26% 29% 15% 3	430
	11th to 20th	Day	26% 29% 33% 9% 2	473
	21st to end	Day	25% 24% 34% 15% 2	446
March	1st to 10th	Day	29% 22% 33% 14% 1	540
	11th to 20th	Day	26% 25% 31% 16% 3	528
	21st to end	Day	30% 23% 28% 14% 5% 1	550
April	1st to 10th	Day	31% 22% 30% 13% 3 1	500
	11th to 20th	Day	29% 18% 35% 13% 5% 1	492
	21st to end	Day	25% 15% 38% 15% 5% 1	500
May	1st to 10th	Day	28% 19% 32% 17% 3 1	503
	11th to 20th	Day	19% 17% 35% 23% 5% 2	527
	21st to end	Day	26% 11% 34% 20% 8% 1	697
June	1st to 10th	Day	25% 10% 31% 24% 8% 1	730
	11th to 20th	Day	25% 9% 31% 22% 11% 2	730
	21st to end	Day	29% 8% 28% 25% 8% 1	730
July	1st to 10th	Day	23% 9% 30% 26% 11% 1	645
	11th to 20th	Day	20% 7% 33% 29% 10% 2	524
	21st to end	Day	17% 6% 36% 29% 11% 1	576
August	1st to 10th	Day	15% 6% 33% 33% 12% 1	526
	11th to 20th	Day	20% 5% 29% 30% 13% 3	519
	21st to end	Day	15% 9% 31% 30% 12% 3	583
September	1st to 10th	Day	17% 8% 33% 30% 10% 2	530
	11th to 20th	Day	18% 9% 33% 24% 11% 6%	530
	21st to end	Day	19% 10% 35% 24% 9% 3	530
October	1st to 10th	Day	16% 16% 27% 28% 10% 2	486
	11th to 20th	Day	20% 18% 31% 21% 8% 1	420
	21st to end	Day	29% 16% 32% 18% 5%	462
November	1st to 10th	Day	24% 23% 27% 20% 5% 1	425
	11th to 20th	Day	27% 24% 30% 15% 3 1	430
	21st to end	Day	30% 25% 26% 15% 3	430
December	1st to 10th	Day	29% 19% 33% 15% 3	377
	11th to 20th	Day	33% 30% 30% 6% 2	220
	21st to end	Day	31% 26% 26% 14% 2	242
January	1st to 10th	Night	25% 28% 29% 16% 3	840
	11th to 20th	Night	29% 24% 30% 13% 4	840
	21st to end	Night	22% 29% 31% 16% 3	924
February	1st to 10th	Night	26% 24% 34% 13% 3	840
	11th to 20th	Night	23% 31% 28% 15% 3	823
	21st to end	Night	23% 21% 34% 18% 4	692
March	1st to 10th	Night	26% 20% 34% 17% 2	840
	11th to 20th	Night	24% 20% 30% 20% 6%	829
	21st to end	Night	25% 16% 34% 18% 6%	880
April	1st to 10th	Night	32% 15% 31% 17% 4	800
	11th to 20th	Night	27% 10% 34% 24% 4	595
	21st to end	Night	30% 10% 29% 23% 8% 1	600
May	1st to 10th	Night	27% 8% 30% 26% 8% 2	600
	11th to 20th	Night	25% 8% 31% 27% 8% 1	592
	21st to end	Night	25% 6% 27% 29% 11% 1	539
June	1st to 10th	Night	31% 7% 22% 32% 8% 1	400
	11th to 20th	Night	24% 4 26% 32% 13% 1	400
	21st to end	Night	33% 4 19% 32% 12% 1	400
July	1st to 10th	Night	23% 5% 22% 38% 12%	390
	11th to 20th	Night	25% 3 23% 33% 16% 1	388
	21st to end	Night	24% 2 22% 39% 12% 1	512
August	1st to 10th	Night	22% 3 23% 36% 15% 1	598
	11th to 20th	Night	22% 4 19% 38% 17% 1	592
	21st to end	Night	17% 5% 22% 35% 19% 2	660
September	1st to 10th	Night	17% 5% 25% 36% 15% 2	770
	11th to 20th	Night	20% 7% 25% 30% 16% 4	800
	21st to end	Night	20% 7% 28% 29% 13% 3	800
October	1st to 10th	Night	22% 11% 24% 27% 15% 1	800
	11th to 20th	Night	23% 15% 26% 24% 11% 1	800
	21st to end	Night	29% 18% 29% 19% 5%	880
November	1st to 10th	Night	25% 16% 29% 22% 7% 1	820
	11th to 20th	Night	24% 25% 26% 19% 6% 1	878
	21st to end	Night	26% 24% 30% 14% 6%	950
December	1st to 10th	Night	31% 19% 32% 14% 3	950
	11th to 20th	Night	30% 27% 27% 14% 2	950
	21st to end	Night	29% 23% 31% 14% 3	1045

Page generated at 2026-03-15 02:23:50. Version ac07

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