Spruce Knob Mountain Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spruce Knob Mountain Center 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	12% 9% 3 9% 6% 6% 5% 4 6% 7% 33%	101207
	Night	11% 9% 4 9% 6% 5% 5% 4 6% 7% 34%	98448
Transparency	Day	46% 9% 10% 20% 12% 3	104857
	Night	44% 11% 10% 19% 12% 3	102937
Seeing	Day	23% 20% 27% 17% 9% 3	15016
	Night	20% 21% 24% 23% 10% 1	24902

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% 10% 6% 12% 6% 6% 5% 4 5% 7% 30%	2836
	11th to 20th	Day	7% 14% 7% 16% 7% 7% 5% 3 4 5% 25%	2840
	21st to end	Day	11% 12% 6% 12% 5% 5% 4 3 5% 6% 30%	3124
February	1st to 10th	Day	9% 12% 3 10% 7% 6% 5% 4 6% 8% 31%	1710
	11th to 20th	Day	11% 10% 3 12% 5% 5% 5% 4 7% 9% 30%	1663
	21st to end	Day	11% 12% 3 9% 6% 6% 4 4 5% 6% 33%	1629
March	1st to 10th	Day	15% 9% 5% 9% 5% 5% 5% 4 6% 8% 30%	3435
	11th to 20th	Day	8% 9% 3 9% 5% 5% 4 4 5% 6% 42%	3480
	21st to end	Day	13% 12% 3 9% 7% 5% 5% 3 5% 5% 34%	3815
April	1st to 10th	Day	10% 10% 4 10% 7% 5% 4 4 6% 7% 34%	2196
	11th to 20th	Day	12% 9% 4 7% 4 4 4 3 6% 7% 39%	2254
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	2413
May	1st to 10th	Day	17% 11% 3 9% 7% 5% 5% 4 6% 6% 26%	4082
	11th to 20th	Day	21% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	4081
	21st to end	Day	9% 7% 3 8% 6% 7% 7% 6% 8% 9% 31%	4557
June	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 5% 6% 7% 35%	2660
	11th to 20th	Day	10% 7% 3 8% 7% 6% 6% 5% 7% 8% 32%	2660
	21st to end	Day	9% 6% 3 7% 6% 6% 7% 5% 8% 8% 34%	2634
July	1st to 10th	Day	7% 6% 3 8% 7% 7% 7% 6% 8% 9% 34%	4120
	11th to 20th	Day	9% 6% 2 7% 6% 6% 7% 5% 7% 10% 35%	4120
	21st to end	Day	13% 11% 4 11% 7% 6% 6% 5% 6% 7% 24%	4466
August	1st to 10th	Day	12% 7% 3 9% 7% 7% 7% 5% 8% 9% 25%	4104
	11th to 20th	Day	8% 6% 3 10% 7% 8% 7% 6% 8% 9% 26%	4044
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 9% 41%	4219
September	1st to 10th	Day	13% 7% 3 7% 6% 6% 5% 3 5% 7% 38%	2280
	11th to 20th	Day	11% 8% 2 7% 6% 5% 4 4 6% 8% 39%	2115
	21st to end	Day	20% 9% 3 6% 4 4 4 4 5% 6% 34%	2073
October	1st to 10th	Day	14% 7% 2 7% 5% 5% 4 3 5% 6% 42%	1900
	11th to 20th	Day	13% 11% 3 8% 4 4 4 3 4 5% 42%	1900
	21st to end	Day	12% 9% 3 6% 4 4 4 3 6% 7% 42%	2090
November	1st to 10th	Day	9% 8% 2 6% 5% 4 4 4 4 7% 47%	1957
	11th to 20th	Day	12% 7% 3 7% 5% 5% 4 4 6% 7% 38%	1751
	21st to end	Day	11% 10% 4 8% 5% 5% 4 4 4 7% 39%	1600
December	1st to 10th	Day	11% 11% 6% 10% 6% 5% 6% 4 6% 7% 28%	1560
	11th to 20th	Day	12% 8% 4 10% 5% 5% 5% 4 6% 6% 35%	1910
	21st to end	Day	13% 10% 5% 9% 6% 6% 5% 4 7% 7% 26%	2929
January	1st to 10th	Night	8% 11% 7% 16% 8% 6% 6% 4 6% 6% 23%	4109
	11th to 20th	Night	9% 12% 4 10% 9% 6% 4 4 5% 7% 31%	4120
	21st to end	Night	12% 13% 4 8% 5% 5% 5% 4 5% 7% 31%	4532
February	1st to 10th	Night	8% 8% 4 9% 6% 5% 6% 5% 7% 9% 32%	2470
	11th to 20th	Night	11% 9% 3 9% 8% 7% 7% 4 6% 7% 28%	2403
	21st to end	Night	10% 11% 4 10% 6% 5% 5% 4 6% 7% 31%	1822
March	1st to 10th	Night	17% 12% 3 7% 6% 6% 5% 5% 6% 6% 28%	3418
	11th to 20th	Night	8% 8% 4 12% 5% 5% 4 3 5% 7% 39%	3480
	21st to end	Night	11% 9% 3 7% 5% 5% 5% 3 5% 6% 40%	3817
April	1st to 10th	Night	10% 8% 5% 7% 6% 6% 5% 4 6% 7% 35%	1983
	11th to 20th	Night	10% 9% 3 6% 6% 4 5% 4 6% 8% 38%	1875
	21st to end	Night	12% 8% 3 7% 5% 5% 5% 4 6% 6% 38%	1781
May	1st to 10th	Night	18% 11% 4 10% 6% 5% 5% 4 6% 6% 25%	2813
	11th to 20th	Night	21% 12% 3 7% 5% 4 4 4 5% 6% 31%	2812
	21st to end	Night	9% 7% 3 9% 6% 6% 6% 5% 7% 10% 34%	2994
June	1st to 10th	Night	10% 6% 2 7% 4 4 6% 4 8% 10% 40%	1520
	11th to 20th	Night	8% 6% 3 8% 6% 4 6% 5% 7% 10% 39%	1520
	21st to end	Night	7% 5% 2 5% 4 5% 6% 5% 7% 10% 42%	1540
July	1st to 10th	Night	5% 5% 3 7% 6% 6% 6% 5% 8% 11% 40%	2840
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 5% 8% 11% 38%	2840
	21st to end	Night	9% 8% 4 12% 7% 6% 5% 4 8% 8% 29%	3087
August	1st to 10th	Night	13% 6% 3 8% 6% 7% 5% 4 7% 10% 32%	2825
	11th to 20th	Night	9% 9% 4 9% 6% 6% 5% 4 7% 7% 35%	2785
	21st to end	Night	6% 5% 2 6% 5% 4 5% 4 7% 10% 46%	3403
September	1st to 10th	Night	12% 6% 2 7% 4 4 6% 4 5% 6% 44%	1900
	11th to 20th	Night	10% 7% 3 7% 5% 5% 4 3 5% 7% 44%	2061
	21st to end	Night	17% 10% 2 6% 5% 5% 5% 4 5% 6% 35%	2105
October	1st to 10th	Night	13% 8% 3 6% 4 4 5% 3 5% 7% 41%	2280
	11th to 20th	Night	10% 8% 3 8% 4 4 4 3 6% 8% 42%	2280
	21st to end	Night	12% 9% 3 7% 5% 4 5% 4 5% 6% 42%	2508
November	1st to 10th	Night	7% 9% 3 7% 4 5% 5% 4 6% 6% 43%	2341
	11th to 20th	Night	11% 9% 4 9% 4 4 6% 4 6% 7% 36%	2640
	21st to end	Night	10% 9% 4 8% 6% 6% 6% 3 6% 7% 35%	2800
December	1st to 10th	Night	10% 10% 5% 12% 6% 7% 5% 4 8% 7% 25%	2737
	11th to 20th	Night	12% 9% 4 11% 6% 5% 5% 4 6% 7% 33%	3285
	21st to end	Night	12% 8% 6% 9% 7% 6% 6% 5% 7% 8% 25%	4722

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	52% 11% 4 18% 12% 3	2837
	11th to 20th	Day	59% 11% 5% 13% 10% 3	2840
	21st to end	Day	54% 9% 5% 15% 14% 2	3124
February	1st to 10th	Day	51% 9% 7% 17% 13% 2	1710
	11th to 20th	Day	50% 12% 7% 16% 14% 2	1672
	21st to end	Day	51% 10% 7% 15% 13% 4	1629
March	1st to 10th	Day	49% 9% 9% 21% 10% 2	3435
	11th to 20th	Day	39% 10% 7% 26% 15% 2	3480
	21st to end	Day	52% 8% 7% 16% 14% 3	3815
April	1st to 10th	Day	48% 8% 10% 16% 14% 3	2196
	11th to 20th	Day	44% 8% 8% 20% 16% 4	2254
	21st to end	Day	49% 8% 9% 20% 11% 2	2413
May	1st to 10th	Day	57% 9% 8% 19% 7% 1	4120
	11th to 20th	Day	53% 9% 10% 21% 5% 1	4085
	21st to end	Day	43% 13% 13% 17% 10% 3	4571
June	1st to 10th	Day	45% 10% 12% 21% 12%	2660
	11th to 20th	Day	45% 12% 14% 18% 11% 1	2660
	21st to end	Day	43% 11% 13% 22% 10% 1	2634
July	1st to 10th	Day	42% 11% 15% 20% 8% 4	4055
	11th to 20th	Day	40% 10% 14% 28% 8%	4051
	21st to end	Day	55% 8% 10% 18% 9% 1	4324
August	1st to 10th	Day	49% 11% 15% 18% 6%	4091
	11th to 20th	Day	46% 10% 12% 22% 10%	4083
	21st to end	Day	36% 10% 14% 24% 15% 1	4219
September	1st to 10th	Day	45% 7% 10% 16% 18% 4	2280
	11th to 20th	Day	43% 7% 8% 22% 17% 4	2115
	21st to end	Day	50% 5% 8% 19% 15% 2	2073
October	1st to 10th	Day	30% 5% 8% 23% 26% 8%	3160
	11th to 20th	Day	36% 5% 8% 23% 14% 13%	3140
	21st to end	Day	30% 6% 8% 26% 20% 10%	3428
November	1st to 10th	Day	37% 8% 7% 22% 19% 6%	1957
	11th to 20th	Day	42% 9% 8% 16% 20% 5%	1751
	21st to end	Day	46% 9% 9% 19% 16% 2	1600
December	1st to 10th	Day	55% 10% 7% 14% 10% 2	1560
	11th to 20th	Day	45% 14% 6% 18% 14% 3	1906
	21st to end	Day	53% 11% 9% 15% 11% 1	2929
January	1st to 10th	Night	54% 17% 4 10% 12% 3	4109
	11th to 20th	Night	50% 13% 7% 15% 12% 3	4120
	21st to end	Night	53% 12% 6% 14% 13% 2	4532
February	1st to 10th	Night	48% 11% 10% 17% 12% 2	2470
	11th to 20th	Night	54% 11% 7% 15% 10% 3	2405
	21st to end	Night	53% 9% 8% 15% 10% 4	1822
March	1st to 10th	Night	53% 9% 8% 19% 10% 2	3418
	11th to 20th	Night	41% 11% 9% 25% 12% 1	3480
	21st to end	Night	43% 9% 9% 19% 17% 3	3817
April	1st to 10th	Night	46% 9% 10% 18% 14% 2	1983
	11th to 20th	Night	41% 11% 12% 20% 13% 3	1875
	21st to end	Night	45% 9% 11% 23% 11% 2	1781
May	1st to 10th	Night	56% 10% 10% 17% 6% 1	2840
	11th to 20th	Night	52% 11% 11% 20% 5% 1	2813
	21st to end	Night	39% 16% 17% 19% 5% 3	3001
June	1st to 10th	Night	35% 14% 13% 27% 11%	1520
	11th to 20th	Night	38% 13% 16% 23% 10% 1	1520
	21st to end	Night	33% 12% 17% 26% 12% 1	1540
July	1st to 10th	Night	35% 13% 20% 19% 11% 2	2795
	11th to 20th	Night	36% 12% 18% 26% 7% 1	2786
	21st to end	Night	46% 12% 15% 19% 9%	2988
August	1st to 10th	Night	43% 12% 19% 20% 6%	2814
	11th to 20th	Night	43% 9% 14% 23% 11% 1	2812
	21st to end	Night	31% 9% 18% 31% 11% 1	3403
September	1st to 10th	Night	38% 9% 14% 18% 18% 3	1900
	11th to 20th	Night	38% 7% 10% 26% 16% 3	2061
	21st to end	Night	48% 9% 10% 18% 14% 1	2105
October	1st to 10th	Night	35% 8% 9% 25% 19% 4	3800
	11th to 20th	Night	35% 7% 9% 18% 16% 15%	3779
	21st to end	Night	28% 8% 8% 25% 19% 12%	4120
November	1st to 10th	Night	40% 8% 10% 17% 18% 7%	2341
	11th to 20th	Night	44% 12% 5% 15% 19% 4	2640
	21st to end	Night	46% 11% 9% 17% 14% 3	2800
December	1st to 10th	Night	55% 11% 7% 15% 9% 2	2737
	11th to 20th	Night	50% 11% 7% 12% 17% 2	3288
	21st to end	Night	51% 15% 8% 15% 10% 1	4722

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	35% 34% 19% 9% 3	270
	11th to 20th	Day	39% 33% 23% 6% 1	270
	21st to end	Day	38% 28% 27% 6% 1	297
February	1st to 10th	Day	37% 35% 20% 7% 1	270
	11th to 20th	Day	49% 29% 19% 3 1	270
	21st to end	Day	39% 31% 22% 8%	306
March	1st to 10th	Day	33% 26% 27% 11% 3	460
	11th to 20th	Day	32% 30% 21% 12% 4	460
	21st to end	Day	29% 28% 28% 11% 5%	506
April	1st to 10th	Day	27% 30% 28% 11% 4 1	460
	11th to 20th	Day	27% 22% 28% 12% 8% 2	452
	21st to end	Day	29% 25% 27% 12% 5% 2	460
May	1st to 10th	Day	28% 23% 25% 13% 8% 3	463
	11th to 20th	Day	24% 20% 28% 19% 5% 3	487
	21st to end	Day	18% 15% 28% 21% 14% 5%	529
June	1st to 10th	Day	17% 19% 29% 19% 12% 4	490
	11th to 20th	Day	16% 14% 32% 21% 13% 5%	490
	21st to end	Day	11% 19% 34% 22% 10% 3	490
July	1st to 10th	Day	11% 13% 29% 23% 16% 8%	485
	11th to 20th	Day	7% 11% 34% 29% 11% 8%	484
	21st to end	Day	15% 10% 29% 24% 17% 6%	532
August	1st to 10th	Day	15% 10% 25% 26% 14% 10%	486
	11th to 20th	Day	12% 11% 28% 24% 15% 10%	479
	21st to end	Day	10% 9% 27% 27% 19% 8%	539
September	1st to 10th	Day	16% 11% 24% 24% 17% 8%	490
	11th to 20th	Day	15% 7% 24% 28% 19% 8%	490
	21st to end	Day	26% 15% 25% 18% 12% 3	490
October	1st to 10th	Day	19% 14% 26% 23% 15% 3	490
	11th to 20th	Day	22% 20% 27% 19% 10% 2	490
	21st to end	Day	21% 24% 30% 16% 8% 1	539
November	1st to 10th	Day	18% 26% 26% 19% 9% 2	495
	11th to 20th	Day	31% 24% 26% 13% 4 1	285
	21st to end	Day	32% 22% 35% 9% 3	200
December	1st to 10th	Day	32% 32% 25% 8% 2 1	190
	11th to 20th	Day	37% 25% 23% 12% 2 1	180
	21st to end	Day	31% 29% 24% 12% 3	242
January	1st to 10th	Night	28% 36% 22% 11% 3	760
	11th to 20th	Night	28% 31% 27% 13% 1	760
	21st to end	Night	25% 36% 25% 12% 1	836
February	1st to 10th	Night	24% 34% 25% 15% 1	760
	11th to 20th	Night	32% 37% 23% 8% 1	743
	21st to end	Night	31% 34% 26% 9% 1	628
March	1st to 10th	Night	26% 30% 25% 17% 2	760
	11th to 20th	Night	30% 28% 23% 14% 4 1	760
	21st to end	Night	25% 28% 26% 16% 5%	836
April	1st to 10th	Night	21% 30% 29% 15% 3	760
	11th to 20th	Night	20% 23% 26% 21% 9%	751
	21st to end	Night	20% 20% 29% 25% 5%	641
May	1st to 10th	Night	20% 19% 23% 26% 11% 1	570
	11th to 20th	Night	19% 16% 26% 28% 10% 2	561
	21st to end	Night	14% 9% 27% 29% 18% 3	570
June	1st to 10th	Night	11% 10% 29% 29% 19% 1	380
	11th to 20th	Night	12% 7% 23% 40% 16% 1	380
	21st to end	Night	9% 8% 30% 38% 16% 1	400
July	1st to 10th	Night	11% 6% 22% 33% 23% 5%	555
	11th to 20th	Night	7% 5% 23% 34% 26% 5%	552
	21st to end	Night	11% 5% 21% 32% 29% 2	624
August	1st to 10th	Night	10% 4 16% 41% 26% 2	567
	11th to 20th	Night	10% 9% 16% 36% 25% 4	564
	21st to end	Night	11% 6% 21% 37% 23% 4	789
September	1st to 10th	Night	15% 6% 20% 32% 21% 5%	760
	11th to 20th	Night	13% 8% 18% 31% 25% 4	760
	21st to end	Night	23% 13% 23% 23% 17% 1	760
October	1st to 10th	Night	18% 13% 19% 28% 18% 3	760
	11th to 20th	Night	19% 20% 23% 24% 11% 1	760
	21st to end	Night	21% 21% 27% 21% 8% 1	836
November	1st to 10th	Night	16% 22% 26% 25% 9% 2	780
	11th to 20th	Night	25% 23% 25% 19% 7% 1	800
	21st to end	Night	25% 24% 28% 17% 5% 1	800
December	1st to 10th	Night	26% 33% 22% 15% 4	783
	11th to 20th	Night	22% 32% 25% 17% 4	760
	21st to end	Night	24% 28% 28% 18% 2	836

Page generated at 2024-12-03 06:45:10. Version ac07

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