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 2024-12-06.

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% 8% 2 6% 4 4 4 3 5% 7% 37%	101506
	Night	20% 9% 3 6% 4 4 4 3 5% 6% 35%	98229
Transparency	Day	46% 4 13% 23% 13% 1	105057
	Night	48% 4 12% 22% 12% 1	102768
Seeing	Day	24% 15% 32% 21% 7% 1	16000
	Night	25% 15% 28% 23% 8% 1	24287

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	18% 10% 2 6% 4 4 4 3 4 6% 38%	2500
	11th to 20th	Day	18% 8% 2 4 4 4 5% 2 4 5% 44%	2520
	21st to end	Day	17% 11% 3 7% 4 3 4 3 6% 6% 36%	2906
February	1st to 10th	Day	17% 12% 3 7% 5% 4 5% 4 6% 6% 31%	1710
	11th to 20th	Day	15% 9% 3 8% 4 4 6% 4 5% 6% 36%	1743
	21st to end	Day	14% 11% 3 7% 6% 4 5% 3 6% 7% 35%	1570
March	1st to 10th	Day	26% 12% 3 6% 3 4 3 3 4 5% 30%	3179
	11th to 20th	Day	18% 9% 3 7% 4 4 4 4 5% 7% 35%	3480
	21st to end	Day	28% 10% 2 6% 4 4 4 4 5% 6% 29%	3816
April	1st to 10th	Day	21% 10% 2 5% 5% 4 4 4 5% 6% 34%	2221
	11th to 20th	Day	20% 8% 3 5% 4 3 3 3 5% 7% 39%	2439
	21st to end	Day	20% 9% 2 6% 4 4 4 3 4 7% 36%	2470
May	1st to 10th	Day	19% 10% 3 7% 4 4 3 4 6% 7% 34%	4106
	11th to 20th	Day	18% 8% 2 7% 4 4 4 4 5% 7% 37%	4081
	21st to end	Day	18% 9% 3 6% 4 4 5% 4 6% 8% 34%	4909
June	1st to 10th	Day	23% 8% 3 7% 5% 3 4 4 5% 8% 31%	2850
	11th to 20th	Day	19% 8% 2 6% 4 3 3 3 6% 7% 39%	2850
	21st to end	Day	26% 10% 2 6% 4 3 3 3 5% 6% 31%	2850
July	1st to 10th	Day	19% 8% 3 6% 4 4 5% 4 5% 8% 34%	4634
	11th to 20th	Day	17% 8% 2 5% 3 4 3 4 5% 9% 41%	4440
	21st to end	Day	20% 8% 2 5% 3 4 4 4 5% 7% 37%	4662
August	1st to 10th	Day	20% 8% 2 6% 4 4 4 4 5% 7% 35%	4105
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 3 5% 7% 36%	4045
	21st to end	Day	9% 5% 2 6% 3 3 3 3 6% 8% 52%	4532
September	1st to 10th	Day	13% 5% 1 5% 4 3 3 3 6% 7% 49%	2185
	11th to 20th	Day	13% 6% 2 4 3 3 4 3 3 7% 52%	2090
	21st to end	Day	18% 7% 2 5% 4 3 4 3 5% 6% 43%	2090
October	1st to 10th	Day	16% 8% 2 6% 4 4 4 3 5% 7% 41%	2015
	11th to 20th	Day	17% 7% 3 5% 5% 3 3 3 4 7% 43%	1900
	21st to end	Day	22% 9% 2 4 3 3 3 3 5% 6% 39%	1905
November	1st to 10th	Day	18% 6% 2 7% 4 3 4 3 5% 5% 42%	1761
	11th to 20th	Day	21% 6% 2 5% 2 4 3 4 5% 7% 42%	1730
	21st to end	Day	20% 10% 3 6% 3 3 3 3 4 6% 39%	1600
December	1st to 10th	Day	23% 9% 2 6% 4 5% 4 3 4 7% 33%	1513
	11th to 20th	Day	24% 10% 3 6% 4 4 4 3 5% 6% 32%	1668
	21st to end	Day	25% 9% 3 6% 3 3 3 3 4 6% 34%	2431
January	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 4 7% 39%	4430
	11th to 20th	Night	14% 11% 4 9% 5% 4 4 3 5% 6% 35%	4440
	21st to end	Night	18% 12% 4 9% 4 4 4 3 5% 7% 32%	4747
February	1st to 10th	Night	18% 10% 3 7% 5% 4 5% 3 6% 6% 31%	2470
	11th to 20th	Night	14% 11% 3 7% 4 4 4 3 6% 6% 38%	2322
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 38%	1884
March	1st to 10th	Night	28% 13% 3 6% 4 3 3 2 4 4 31%	3661
	11th to 20th	Night	14% 11% 3 7% 5% 5% 6% 5% 7% 8% 28%	3479
	21st to end	Night	29% 8% 3 6% 4 4 5% 4 4 5% 29%	3816
April	1st to 10th	Night	23% 11% 3 5% 4 4 4 3 4 6% 34%	1957
	11th to 20th	Night	21% 9% 2 7% 5% 3 4 3 6% 7% 34%	1689
	21st to end	Night	23% 10% 3 6% 4 3 3 3 4 6% 34%	1710
May	1st to 10th	Night	23% 8% 3 6% 4 4 4 3 5% 7% 33%	2834
	11th to 20th	Night	19% 7% 3 7% 6% 5% 5% 5% 7% 8% 29%	2813
	21st to end	Night	15% 11% 4 7% 5% 4 4 4 5% 7% 34%	2698
June	1st to 10th	Night	26% 10% 2 6% 4 4 4 4 6% 7% 28%	1330
	11th to 20th	Night	20% 10% 3 5% 4 3 4 4 6% 7% 35%	1330
	21st to end	Night	28% 10% 3 5% 4 4 3 3 6% 6% 28%	1330
July	1st to 10th	Night	19% 10% 4 7% 4 6% 5% 4 7% 8% 26%	2327
	11th to 20th	Night	20% 8% 2 6% 3 4 5% 4 6% 8% 34%	2520
	21st to end	Night	18% 9% 2 7% 4 5% 5% 4 6% 7% 34%	2859
August	1st to 10th	Night	24% 11% 3 7% 4 4 4 4 5% 5% 28%	2825
	11th to 20th	Night	19% 10% 3 7% 5% 4 5% 5% 6% 8% 29%	2782
	21st to end	Night	10% 6% 3 6% 4 4 5% 3 5% 8% 46%	3124
September	1st to 10th	Night	14% 6% 2 4 4 3 4 3 5% 6% 48%	1990
	11th to 20th	Night	17% 7% 2 4 3 3 3 2 4 6% 49%	2090
	21st to end	Night	18% 7% 2 4 4 3 4 3 5% 7% 45%	2090
October	1st to 10th	Night	20% 6% 2 5% 4 4 4 3 5% 6% 41%	2164
	11th to 20th	Night	19% 6% 2 5% 4 3 4 3 5% 6% 43%	2280
	21st to end	Night	23% 9% 2 6% 4 3 3 3 4 6% 38%	2689
November	1st to 10th	Night	17% 7% 2 5% 4 4 4 4 5% 6% 42%	2537
	11th to 20th	Night	17% 8% 2 6% 4 3 4 4 5% 5% 41%	2666
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 7% 38%	2800
December	1st to 10th	Night	25% 9% 3 6% 4 4 4 3 5% 6% 30%	2779
	11th to 20th	Night	25% 8% 2 5% 3 2 4 3 5% 7% 36%	3531
	21st to end	Night	25% 9% 3 5% 4 3 3 3 4 5% 35%	5236

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 15% 25% 8% 1	2501
	11th to 20th	Day	45% 4 12% 26% 11% 2	2520
	21st to end	Day	50% 2 15% 21% 11%	2906
February	1st to 10th	Day	53% 3 13% 18% 11% 2	1710
	11th to 20th	Day	48% 5% 12% 20% 13% 1	1751
	21st to end	Day	49% 4 11% 22% 10% 5%	1570
March	1st to 10th	Day	58% 3 9% 15% 13% 3	3183
	11th to 20th	Day	47% 4 13% 21% 12% 2	3480
	21st to end	Day	57% 3 6% 16% 15% 4	3816
April	1st to 10th	Day	50% 4 8% 19% 15% 3	2221
	11th to 20th	Day	44% 4 10% 24% 14% 3	2439
	21st to end	Day	48% 4 9% 19% 17% 3	2470
May	1st to 10th	Day	50% 5% 14% 23% 8% 1	4120
	11th to 20th	Day	46% 5% 15% 25% 9% 1	4085
	21st to end	Day	48% 6% 12% 20% 13% 1	4909
June	1st to 10th	Day	52% 5% 13% 21% 9%	2850
	11th to 20th	Day	45% 5% 12% 20% 15% 2	2850
	21st to end	Day	54% 5% 12% 17% 10% 2	2850
July	1st to 10th	Day	49% 5% 13% 22% 12%	4562
	11th to 20th	Day	42% 4 17% 25% 11%	4365
	21st to end	Day	46% 5% 13% 22% 13% 1	4513
August	1st to 10th	Day	49% 6% 14% 25% 7%	4092
	11th to 20th	Day	48% 5% 18% 21% 9%	4084
	21st to end	Day	30% 5% 14% 29% 21% 1	4532
September	1st to 10th	Day	34% 5% 13% 28% 18% 2	2185
	11th to 20th	Day	34% 5% 11% 28% 20% 3	2090
	21st to end	Day	42% 4 9% 28% 16% 1	2090
October	1st to 10th	Day	47% 5% 12% 23% 12% 1	3353
	11th to 20th	Day	32% 4 9% 35% 21%	3140
	21st to end	Day	34% 3 18% 24% 18% 3	3117
November	1st to 10th	Day	43% 4 14% 25% 13% 1	1761
	11th to 20th	Day	43% 5% 10% 23% 17% 3	1730
	21st to end	Day	48% 4 16% 24% 8% 1	1600
December	1st to 10th	Day	53% 4 13% 21% 8% 1	1513
	11th to 20th	Day	55% 3 9% 22% 9% 1	1668
	21st to end	Day	54% 4 13% 19% 8% 2	2431
January	1st to 10th	Night	47% 4 15% 26% 8% 1	4430
	11th to 20th	Night	50% 5% 12% 22% 10% 1	4440
	21st to end	Night	53% 3 12% 22% 9%	4747
February	1st to 10th	Night	53% 4 12% 18% 11% 2	2470
	11th to 20th	Night	47% 4 11% 21% 15% 2	2325
	21st to end	Night	48% 3 10% 21% 14% 4	1884
March	1st to 10th	Night	59% 2 8% 15% 12% 3	3670
	11th to 20th	Night	49% 6% 17% 17% 10% 1	3480
	21st to end	Night	59% 3 5% 17% 14% 2	3816
April	1st to 10th	Night	53% 4 7% 16% 16% 4	1957
	11th to 20th	Night	50% 3 8% 22% 15% 2	1689
	21st to end	Night	52% 4 9% 18% 14% 3	1710
May	1st to 10th	Night	51% 5% 16% 20% 8% 1	2840
	11th to 20th	Night	51% 6% 16% 19% 6% 1	2814
	21st to end	Night	50% 5% 13% 20% 10% 1	2699
June	1st to 10th	Night	55% 5% 11% 20% 7% 1	1330
	11th to 20th	Night	47% 6% 12% 21% 11% 2	1330
	21st to end	Night	57% 4 9% 19% 9% 2	1330
July	1st to 10th	Night	55% 5% 11% 18% 10% 1	2289
	11th to 20th	Night	48% 6% 13% 24% 9%	2472
	21st to end	Night	48% 5% 13% 20% 13% 1	2768
August	1st to 10th	Night	58% 5% 11% 20% 7%	2813
	11th to 20th	Night	51% 6% 13% 22% 8%	2809
	21st to end	Night	37% 5% 11% 25% 21% 1	3124
September	1st to 10th	Night	36% 4 12% 29% 17% 1	1990
	11th to 20th	Night	37% 4 11% 27% 19% 2	2090
	21st to end	Night	40% 4 9% 29% 17% 1	2090
October	1st to 10th	Night	42% 5% 13% 25% 15% 1	3606
	11th to 20th	Night	33% 3 10% 29% 24% 1	3779
	21st to end	Night	39% 3 10% 30% 15% 2	4427
November	1st to 10th	Night	43% 4 12% 26% 14% 1	2537
	11th to 20th	Night	44% 4 11% 23% 16% 2	2666
	21st to end	Night	46% 5% 14% 21% 12% 1	2800
December	1st to 10th	Night	55% 3 12% 20% 10%	2779
	11th to 20th	Night	49% 4 11% 22% 13% 1	3532
	21st to end	Night	53% 4 13% 18% 11% 1	5236

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	25% 29% 29% 13% 3	180
	11th to 20th	Day	30% 26% 30% 12% 2 1	180
	21st to end	Day	19% 24% 36% 16% 5%	280
February	1st to 10th	Day	27% 26% 28% 15% 4	370
	11th to 20th	Day	25% 30% 34% 9% 1	404
	21st to end	Day	25% 21% 35% 17% 2	382
March	1st to 10th	Day	27% 21% 35% 15% 2	460
	11th to 20th	Day	23% 24% 33% 17% 3	460
	21st to end	Day	29% 22% 29% 15% 5% 1	506
April	1st to 10th	Day	29% 21% 31% 13% 3 1	460
	11th to 20th	Day	27% 17% 35% 15% 5% 1	452
	21st to end	Day	25% 15% 38% 16% 6% 1	460
May	1st to 10th	Day	26% 19% 33% 18% 3 2	463
	11th to 20th	Day	17% 16% 36% 24% 5% 2	487
	21st to end	Day	26% 10% 35% 19% 9% 1	647
June	1st to 10th	Day	25% 10% 31% 24% 9% 1	680
	11th to 20th	Day	24% 8% 31% 24% 11% 2	680
	21st to end	Day	30% 8% 28% 25% 9% 1	680
July	1st to 10th	Day	23% 9% 29% 27% 11% 1	599
	11th to 20th	Day	19% 7% 33% 30% 10% 2	484
	21st to end	Day	18% 5% 34% 29% 12% 2	532
August	1st to 10th	Day	16% 6% 32% 33% 12% 1	486
	11th to 20th	Day	21% 5% 30% 30% 12% 3	479
	21st to end	Day	16% 8% 29% 31% 13% 3	539
September	1st to 10th	Day	17% 7% 33% 30% 11% 2	490
	11th to 20th	Day	19% 8% 32% 24% 11% 6%	490
	21st to end	Day	20% 9% 34% 25% 10% 3	490
October	1st to 10th	Day	16% 16% 27% 28% 10% 2	450
	11th to 20th	Day	20% 18% 31% 22% 8% 2	390
	21st to end	Day	29% 15% 31% 18% 6%	429
November	1st to 10th	Day	23% 22% 28% 22% 5% 1	395
	11th to 20th	Day	27% 24% 30% 15% 4 1	400
	21st to end	Day	30% 25% 26% 16% 3	400
December	1st to 10th	Day	28% 18% 35% 16% 3	338
	11th to 20th	Day	33% 29% 29% 7% 2	180
	21st to end	Day	30% 27% 26% 15% 3	198
January	1st to 10th	Night	24% 27% 30% 16% 3	760
	11th to 20th	Night	28% 25% 31% 13% 3	760
	21st to end	Night	20% 29% 31% 17% 3	836
February	1st to 10th	Night	25% 24% 34% 13% 3	760
	11th to 20th	Night	23% 31% 29% 14% 2 1	743
	21st to end	Night	23% 20% 35% 18% 4	628
March	1st to 10th	Night	26% 20% 35% 18% 2	760
	11th to 20th	Night	23% 21% 30% 20% 6%	760
	21st to end	Night	25% 16% 35% 18% 6%	836
April	1st to 10th	Night	31% 14% 33% 18% 4	760
	11th to 20th	Night	27% 10% 34% 24% 5%	565
	21st to end	Night	29% 10% 29% 23% 8% 1	570
May	1st to 10th	Night	26% 7% 30% 26% 8% 2	570
	11th to 20th	Night	24% 8% 32% 27% 8% 1	562
	21st to end	Night	25% 6% 26% 30% 11% 1	512
June	1st to 10th	Night	31% 7% 21% 31% 8% 1	380
	11th to 20th	Night	24% 4 26% 32% 14% 1	380
	21st to end	Night	33% 4 18% 32% 12% 1	380
July	1st to 10th	Night	23% 5% 21% 38% 12%	370
	11th to 20th	Night	24% 2 23% 33% 17% 1	368
	21st to end	Night	24% 1 20% 40% 13% 1	486
August	1st to 10th	Night	23% 3 22% 36% 15% 1	568
	11th to 20th	Night	22% 4 19% 38% 17% 1	562
	21st to end	Night	17% 4 22% 35% 20% 2	627
September	1st to 10th	Night	17% 5% 26% 36% 14% 2	731
	11th to 20th	Night	20% 7% 25% 29% 15% 4	760
	21st to end	Night	20% 7% 27% 29% 14% 3	760
October	1st to 10th	Night	23% 10% 24% 27% 15% 1	760
	11th to 20th	Night	22% 15% 26% 24% 11% 1	760
	21st to end	Night	29% 18% 29% 19% 6%	836
November	1st to 10th	Night	23% 16% 29% 23% 8% 1	780
	11th to 20th	Night	23% 26% 26% 19% 6% 1	834
	21st to end	Night	26% 23% 30% 14% 6%	900
December	1st to 10th	Night	30% 19% 33% 15% 3	878
	11th to 20th	Night	28% 27% 28% 15% 2	850
	21st to end	Night	29% 23% 31% 14% 3	935

Page generated at 2024-12-03 06:45:09. Version ac07

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