Dill Knob Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dill Knob Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 39%	101381
	Night	14% 6% 2 6% 4 4 4 4 6% 8% 42%	98176
Transparency	Day	40% 7% 12% 20% 17% 5%	105123
	Night	38% 7% 12% 20% 18% 6%	102573
Seeing	Day	22% 13% 23% 22% 14% 7%	15170
	Night	19% 12% 18% 28% 20% 4	25236

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	16% 4 2 4 2 3 3 2 5% 8% 51%	2836
	11th to 20th	Day	13% 7% 2 5% 3 3 4 4 4 5% 50%	2840
	21st to end	Day	24% 6% 2 3 3 3 3 3 5% 5% 42%	3124
February	1st to 10th	Day	14% 7% 2 5% 5% 5% 4 4 5% 7% 43%	1773
	11th to 20th	Day	16% 8% 2 6% 4 3 4 3 5% 6% 42%	1848
	21st to end	Day	17% 7% 1 6% 5% 5% 5% 3 6% 5% 40%	1570
March	1st to 10th	Day	24% 6% 2 5% 3 3 3 3 4 6% 41%	3390
	11th to 20th	Day	12% 5% 2 4 4 3 4 3 4 6% 52%	3480
	21st to end	Day	19% 6% 2 5% 4 3 4 4 6% 6% 40%	3815
April	1st to 10th	Day	11% 6% 2 4 4 5% 5% 5% 7% 9% 44%	2090
	11th to 20th	Day	15% 6% 3 6% 4 4 4 4 5% 8% 43%	2264
	21st to end	Day	13% 6% 2 6% 4 4 3 4 5% 7% 45%	2470
May	1st to 10th	Day	12% 8% 2 7% 6% 5% 5% 5% 6% 8% 35%	4082
	11th to 20th	Day	17% 7% 3 7% 5% 5% 6% 5% 7% 7% 31%	4081
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 40%	4476
June	1st to 10th	Day	11% 7% 2 8% 6% 6% 6% 5% 8% 9% 31%	2470
	11th to 20th	Day	7% 6% 2 7% 6% 6% 6% 6% 9% 10% 34%	2470
	21st to end	Day	8% 6% 3 8% 7% 6% 7% 6% 8% 10% 33%	2470
July	1st to 10th	Day	7% 6% 3 8% 7% 7% 8% 6% 8% 10% 30%	4120
	11th to 20th	Day	8% 6% 3 8% 7% 8% 7% 6% 9% 10% 29%	4120
	21st to end	Day	11% 9% 4 12% 8% 8% 8% 6% 9% 8% 16%	4466
August	1st to 10th	Day	14% 8% 2 8% 6% 7% 7% 6% 8% 11% 23%	4104
	11th to 20th	Day	8% 5% 2 7% 6% 6% 7% 6% 9% 11% 32%	4044
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	4204
September	1st to 10th	Day	11% 7% 2 8% 5% 6% 6% 5% 5% 8% 36%	2090
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 5% 5% 8% 32%	2090
	21st to end	Day	16% 8% 2 6% 4 4 5% 4 6% 7% 36%	2090
October	1st to 10th	Day	15% 5% 2 6% 3 3 3 3 5% 6% 48%	2043
	11th to 20th	Day	11% 6% 1 4 3 3 3 3 4 6% 56%	1900
	21st to end	Day	14% 4 2 4 3 2 2 2 4 6% 55%	2090
November	1st to 10th	Day	10% 7% 2 4 3 3 3 3 4 7% 55%	1887
	11th to 20th	Day	12% 5% 2 6% 3 4 3 3 6% 7% 51%	1800
	21st to end	Day	14% 5% 1 5% 3 3 4 4 5% 8% 49%	1797
December	1st to 10th	Day	17% 8% 2 7% 4 4 5% 4 5% 6% 38%	1710
	11th to 20th	Day	15% 5% 2 4 3 3 3 4 5% 7% 49%	2153
	21st to end	Day	20% 6% 2 4 3 4 5% 4 5% 6% 42%	3124
January	1st to 10th	Night	16% 5% 1 4 3 3 4 3 5% 6% 50%	4109
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 7% 49%	4120
	21st to end	Night	22% 7% 3 4 3 4 3 3 5% 5% 41%	4532
February	1st to 10th	Night	13% 6% 1 5% 4 3 5% 5% 6% 7% 46%	2404
	11th to 20th	Night	17% 6% 2 6% 4 3 4 3 5% 6% 44%	2218
	21st to end	Night	16% 7% 2 5% 5% 5% 4 4 6% 7% 39%	1884
March	1st to 10th	Night	22% 9% 3 5% 4 4 4 4 6% 8% 31%	3462
	11th to 20th	Night	9% 5% 1 4 3 5% 5% 4 6% 8% 49%	3480
	21st to end	Night	20% 5% 2 5% 4 4 3 4 5% 7% 42%	3817
April	1st to 10th	Night	12% 5% 2 6% 4 3 3 4 6% 8% 47%	2090
	11th to 20th	Night	12% 8% 2 5% 3 2 3 3 6% 8% 48%	1879
	21st to end	Night	12% 5% 2 4 4 3 4 3 5% 7% 50%	1710
May	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 9% 39%	2813
	11th to 20th	Night	19% 7% 2 6% 4 4 3 4 6% 8% 36%	2812
	21st to end	Night	10% 4 1 6% 4 4 5% 5% 7% 11% 43%	3079
June	1st to 10th	Night	10% 7% 3 7% 5% 4 6% 5% 9% 10% 34%	1710
	11th to 20th	Night	9% 6% 2 6% 6% 4 4 4 7% 11% 41%	1710
	21st to end	Night	8% 4 2 6% 6% 5% 6% 5% 8% 10% 41%	1710
July	1st to 10th	Night	7% 6% 3 8% 6% 6% 7% 5% 9% 10% 34%	2840
	11th to 20th	Night	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 37%	2840
	21st to end	Night	11% 9% 4 10% 8% 7% 7% 6% 9% 9% 21%	3087
August	1st to 10th	Night	12% 9% 3 8% 5% 6% 6% 5% 8% 9% 30%	2825
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 6% 9% 9% 31%	2785
	21st to end	Night	7% 6% 2 5% 4 4 5% 5% 7% 9% 47%	3415
September	1st to 10th	Night	10% 8% 3 7% 6% 4 4 4 5% 7% 41%	2090
	11th to 20th	Night	18% 8% 2 7% 4 5% 5% 4 5% 6% 35%	2090
	21st to end	Night	17% 8% 2 5% 3 3 4 3 4 6% 44%	2090
October	1st to 10th	Night	15% 6% 1 6% 4 4 3 3 4 5% 48%	2136
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	2280
	21st to end	Night	14% 5% 1 4 2 3 2 2 5% 6% 56%	2508
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 7% 50%	2408
	11th to 20th	Night	14% 5% 1 4 3 3 4 4 5% 7% 51%	2600
	21st to end	Night	13% 4 2 5% 4 4 4 3 6% 7% 48%	2599
December	1st to 10th	Night	17% 7% 2 7% 4 5% 3 4 5% 6% 40%	2470
	11th to 20th	Night	14% 6% 2 6% 4 3 3 3 6% 6% 47%	3042
	21st to end	Night	22% 5% 2 4 3 4 4 4 6% 7% 38%	4532

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	32% 3 6% 23% 29% 7%	2837
	11th to 20th	Day	34% 6% 6% 17% 30% 7%	2840
	21st to end	Day	42% 5% 4 17% 26% 6%	3124
February	1st to 10th	Day	40% 4 9% 21% 21% 5%	1773
	11th to 20th	Day	42% 5% 8% 20% 19% 6%	1858
	21st to end	Day	45% 4 9% 16% 19% 7%	1570
March	1st to 10th	Day	45% 3 7% 19% 17% 9%	3390
	11th to 20th	Day	33% 6% 8% 20% 23% 11%	3480
	21st to end	Day	43% 5% 9% 23% 15% 5%	3815
April	1st to 10th	Day	35% 6% 12% 23% 20% 5%	2090
	11th to 20th	Day	39% 4 9% 18% 22% 6%	2264
	21st to end	Day	37% 6% 12% 26% 16% 3	2470
May	1st to 10th	Day	45% 7% 15% 20% 12% 1	4120
	11th to 20th	Day	49% 9% 12% 20% 10% 1	4085
	21st to end	Day	36% 8% 16% 21% 18% 1	4489
June	1st to 10th	Day	44% 9% 18% 19% 8% 1	2470
	11th to 20th	Day	39% 11% 17% 20% 11% 2	2470
	21st to end	Day	43% 9% 15% 18% 12% 2	2470
July	1st to 10th	Day	42% 15% 18% 19% 6% 1	4055
	11th to 20th	Day	43% 12% 22% 17% 5% 1	4051
	21st to end	Day	59% 12% 14% 10% 4 1	4324
August	1st to 10th	Day	49% 11% 18% 18% 3	4091
	11th to 20th	Day	37% 12% 24% 14% 10% 3	4083
	21st to end	Day	33% 9% 15% 31% 10% 1	4204
September	1st to 10th	Day	43% 8% 12% 19% 15% 3	2090
	11th to 20th	Day	47% 8% 10% 18% 16% 2	2090
	21st to end	Day	45% 6% 10% 19% 15% 5%	2090
October	1st to 10th	Day	27% 5% 9% 19% 32% 9%	3394
	11th to 20th	Day	21% 3 5% 19% 27% 25%	3140
	21st to end	Day	27% 4 6% 24% 22% 17%	3428
November	1st to 10th	Day	31% 4 9% 21% 27% 9%	1887
	11th to 20th	Day	33% 3 6% 23% 27% 8%	1800
	21st to end	Day	33% 6% 6% 23% 27% 6%	1797
December	1st to 10th	Day	47% 5% 6% 20% 17% 5%	1710
	11th to 20th	Day	34% 4 8% 19% 26% 9%	2150
	21st to end	Day	40% 6% 6% 22% 21% 4	3124
January	1st to 10th	Night	35% 4 6% 17% 29% 8%	4109
	11th to 20th	Night	34% 6% 6% 16% 28% 10%	4120
	21st to end	Night	45% 4 6% 15% 23% 8%	4532
February	1st to 10th	Night	36% 5% 11% 21% 22% 5%	2404
	11th to 20th	Night	41% 4 7% 20% 21% 6%	2219
	21st to end	Night	43% 5% 9% 17% 20% 5%	1884
March	1st to 10th	Night	49% 7% 8% 15% 16% 5%	3462
	11th to 20th	Night	30% 6% 9% 22% 20% 13%	3480
	21st to end	Night	43% 5% 8% 24% 14% 7%	3817
April	1st to 10th	Night	35% 4 11% 24% 22% 4	2090
	11th to 20th	Night	34% 5% 11% 23% 22% 6%	1879
	21st to end	Night	33% 7% 15% 26% 18% 3	1710
May	1st to 10th	Night	41% 7% 16% 24% 10% 1	2840
	11th to 20th	Night	44% 7% 17% 21% 11%	2813
	21st to end	Night	31% 8% 19% 29% 11% 1	3087
June	1st to 10th	Night	41% 10% 19% 21% 7% 1	1710
	11th to 20th	Night	35% 8% 24% 23% 9% 1	1710
	21st to end	Night	34% 11% 19% 20% 13% 3	1710
July	1st to 10th	Night	41% 13% 20% 19% 6% 1	2795
	11th to 20th	Night	36% 14% 27% 17% 4 1	2786
	21st to end	Night	52% 15% 17% 12% 3 1	2988
August	1st to 10th	Night	46% 11% 24% 15% 4	2814
	11th to 20th	Night	40% 14% 23% 14% 9% 1	2812
	21st to end	Night	30% 10% 16% 33% 10% 1	3415
September	1st to 10th	Night	41% 9% 13% 21% 14% 3	2090
	11th to 20th	Night	48% 7% 11% 18% 15% 1	2090
	21st to end	Night	41% 5% 11% 21% 18% 3	2090
October	1st to 10th	Night	28% 6% 10% 20% 27% 8%	3565
	11th to 20th	Night	21% 4 6% 22% 26% 21%	3779
	21st to end	Night	30% 3 5% 22% 25% 15%	4120
November	1st to 10th	Night	35% 4 9% 20% 23% 10%	2408
	11th to 20th	Night	33% 4 6% 20% 27% 10%	2600
	21st to end	Night	34% 5% 6% 22% 26% 7%	2599
December	1st to 10th	Night	44% 5% 9% 18% 18% 5%	2470
	11th to 20th	Night	35% 7% 8% 16% 28% 6%	3044
	21st to end	Night	44% 4 8% 19% 21% 4	4532

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	31% 27% 31% 9% 1	270
	11th to 20th	Day	37% 24% 26% 13% 1	270
	21st to end	Day	29% 31% 33% 6% 2	297
February	1st to 10th	Day	30% 23% 35% 11% 1	270
	11th to 20th	Day	46% 23% 26% 4	270
	21st to end	Day	42% 29% 21% 8%	225
March	1st to 10th	Day	27% 22% 28% 17% 5%	426
	11th to 20th	Day	33% 22% 27% 14% 4 1	460
	21st to end	Day	30% 21% 26% 16% 5% 1	506
April	1st to 10th	Day	26% 22% 25% 18% 7% 1	460
	11th to 20th	Day	21% 22% 27% 18% 10% 2	452
	21st to end	Day	21% 17% 27% 18% 12% 5%	460
May	1st to 10th	Day	19% 19% 28% 20% 10% 5%	463
	11th to 20th	Day	22% 10% 22% 24% 14% 8%	487
	21st to end	Day	19% 6% 22% 24% 15% 14%	529
June	1st to 10th	Day	16% 6% 23% 29% 17% 9%	490
	11th to 20th	Day	13% 5% 22% 25% 23% 12%	490
	21st to end	Day	11% 6% 28% 28% 16% 11%	490
July	1st to 10th	Day	12% 2 14% 28% 29% 15%	485
	11th to 20th	Day	10% 3 13% 30% 25% 19%	484
	21st to end	Day	8% 4 13% 30% 27% 18%	532
August	1st to 10th	Day	21% 4 19% 22% 17% 16%	486
	11th to 20th	Day	14% 4 15% 30% 19% 17%	479
	21st to end	Day	17% 2 13% 27% 26% 15%	539
September	1st to 10th	Day	13% 3 16% 30% 23% 14%	490
	11th to 20th	Day	23% 4 13% 24% 26% 9%	490
	21st to end	Day	23% 6% 19% 27% 22% 4	490
October	1st to 10th	Day	23% 7% 20% 26% 18% 7%	490
	11th to 20th	Day	18% 14% 25% 25% 14% 4	490
	21st to end	Day	21% 12% 26% 28% 10% 2	539
November	1st to 10th	Day	22% 13% 29% 23% 11% 2	425
	11th to 20th	Day	22% 24% 33% 16% 5%	300
	21st to end	Day	22% 22% 32% 18% 5% 1	299
December	1st to 10th	Day	31% 22% 34% 12% 1	270
	11th to 20th	Day	25% 21% 34% 16% 3 1	270
	21st to end	Day	31% 19% 32% 14% 3 1	297
January	1st to 10th	Night	22% 25% 23% 24% 7%	760
	11th to 20th	Night	24% 21% 24% 26% 5%	760
	21st to end	Night	20% 24% 28% 25% 4	836
February	1st to 10th	Night	19% 19% 25% 32% 4	760
	11th to 20th	Night	26% 25% 24% 23% 3	743
	21st to end	Night	25% 22% 25% 24% 3	628
March	1st to 10th	Night	19% 23% 23% 30% 5%	760
	11th to 20th	Night	24% 18% 27% 21% 8% 1	760
	21st to end	Night	23% 17% 27% 24% 9%	836
April	1st to 10th	Night	20% 19% 26% 26% 9% 1	760
	11th to 20th	Night	21% 17% 22% 26% 13% 2	679
	21st to end	Night	15% 12% 21% 33% 17% 2	570
May	1st to 10th	Night	17% 11% 22% 28% 19% 2	570
	11th to 20th	Night	19% 7% 17% 29% 26% 2	561
	21st to end	Night	16% 4 11% 26% 35% 8%	617
June	1st to 10th	Night	14% 3 10% 35% 31% 7%	570
	11th to 20th	Night	12% 3 11% 29% 34% 11%	570
	21st to end	Night	8% 2 12% 32% 37% 9%	570
July	1st to 10th	Night	12% 2 6% 26% 45% 9%	555
	11th to 20th	Night	10% 4 4 23% 46% 13%	552
	21st to end	Night	8% 3 4 28% 44% 12%	624
August	1st to 10th	Night	17% 2 9% 21% 41% 10%	567
	11th to 20th	Night	15% 2 8% 27% 38% 10%	564
	21st to end	Night	14% 1 5% 26% 45% 10%	692
September	1st to 10th	Night	14% 3 10% 25% 38% 9%	760
	11th to 20th	Night	22% 4 8% 23% 36% 7%	760
	21st to end	Night	24% 5% 11% 29% 26% 4	760
October	1st to 10th	Night	18% 7% 20% 21% 26% 8%	760
	11th to 20th	Night	20% 11% 18% 30% 18% 3	760
	21st to end	Night	19% 13% 15% 35% 14% 4	836
November	1st to 10th	Night	19% 9% 20% 32% 16% 4	780
	11th to 20th	Night	19% 15% 21% 31% 12% 1	800
	21st to end	Night	20% 16% 20% 30% 13% 1	800
December	1st to 10th	Night	23% 20% 18% 30% 9%	760
	11th to 20th	Night	18% 17% 23% 33% 8% 1	760
	21st to end	Night	28% 15% 20% 31% 6%	836

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