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 2026-02-16.

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% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	131104
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	129754
Transparency	Day	39% 7% 12% 19% 17% 6%	134802
	Night	36% 7% 12% 20% 18% 6%	134126
Seeing	Day	22% 14% 24% 21% 13% 6%	16746
	Night	19% 13% 18% 27% 19% 4	26872

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	14% 5% 2 4 3 3 3 2 5% 6% 53%	5258
	11th to 20th	Day	8% 5% 2 4 3 2 3 3 4 4 63%	5280
	21st to end	Day	18% 7% 3 5% 4 3 4 3 4 6% 43%	5780
February	1st to 10th	Day	13% 7% 2 5% 5% 5% 4 4 5% 7% 44%	1961
	11th to 20th	Day	17% 8% 2 6% 4 3 4 3 5% 7% 41%	1998
	21st to end	Day	17% 7% 1 5% 5% 4 5% 3 6% 5% 41%	1650
March	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 5% 6% 43%	4862
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 4 7% 54%	4980
	21st to end	Day	16% 6% 2 5% 4 3 4 4 5% 6% 45%	5465
April	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 5% 7% 9% 44%	2200
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 8% 44%	2385
	21st to end	Day	13% 6% 2 6% 4 5% 4 4 6% 7% 45%	2600
May	1st to 10th	Day	11% 8% 3 8% 6% 6% 6% 5% 6% 9% 32%	5862
	11th to 20th	Day	18% 7% 2 8% 6% 6% 7% 5% 7% 7% 26%	5861
	21st to end	Day	13% 6% 2 7% 4 5% 5% 5% 6% 9% 38%	6433
June	1st to 10th	Day	10% 7% 2 8% 6% 6% 6% 5% 8% 9% 32%	2600
	11th to 20th	Day	7% 6% 2 7% 6% 6% 6% 6% 9% 10% 34%	2600
	21st to end	Day	8% 5% 3 8% 6% 6% 7% 6% 8% 10% 34%	2600
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 8% 6% 8% 10% 33%	5900
	11th to 20th	Day	7% 6% 3 9% 8% 8% 8% 6% 9% 11% 27%	5900
	21st to end	Day	9% 8% 4 11% 8% 8% 8% 6% 8% 9% 20%	6424
August	1st to 10th	Day	15% 8% 3 8% 6% 7% 7% 6% 8% 10% 23%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 7% 7% 6% 9% 11% 32%	4174
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	4336
September	1st to 10th	Day	11% 7% 2 8% 5% 6% 6% 5% 6% 8% 37%	2200
	11th to 20th	Day	17% 7% 2 6% 5% 5% 6% 6% 6% 8% 32%	2200
	21st to end	Day	16% 8% 2 6% 4 4 5% 4 6% 7% 36%	2200
October	1st to 10th	Day	15% 5% 2 6% 3 3 3 4 5% 6% 48%	2150
	11th to 20th	Day	11% 6% 1 4 3 3 3 3 4 6% 56%	2000
	21st to end	Day	15% 5% 2 4 3 2 2 2 4 6% 55%	2200
November	1st to 10th	Day	10% 7% 2 4 3 3 3 3 3 7% 55%	1983
	11th to 20th	Day	11% 4 2 5% 3 4 3 3 6% 7% 52%	1890
	21st to end	Day	14% 5% 1 5% 3 3 4 4 5% 8% 49%	1890
December	1st to 10th	Day	12% 6% 2 5% 4 3 5% 3 5% 6% 49%	3020
	11th to 20th	Day	14% 7% 2 4 3 4 4 4 6% 7% 45%	3463
	21st to end	Day	20% 6% 2 3 3 3 4 3 4 7% 45%	4565
January	1st to 10th	Night	14% 5% 1 4 3 3 3 3 6% 6% 53%	7635
	11th to 20th	Night	9% 5% 2 5% 3 3 3 3 4 6% 58%	7680
	21st to end	Night	15% 6% 2 5% 3 4 4 3 5% 6% 47%	8401
February	1st to 10th	Night	13% 6% 1 5% 4 4 5% 5% 6% 7% 45%	2656
	11th to 20th	Night	18% 6% 2 6% 3 3 4 3 5% 6% 44%	2399
	21st to end	Night	15% 6% 2 5% 5% 5% 4 4 6% 7% 40%	1980
March	1st to 10th	Night	18% 7% 2 5% 4 4 5% 4 6% 7% 40%	4990
	11th to 20th	Night	9% 4 1 3 3 4 4 4 7% 9% 51%	4980
	21st to end	Night	17% 5% 2 6% 4 4 3 4 5% 6% 43%	5467
April	1st to 10th	Night	12% 5% 2 6% 4 3 3 4 6% 8% 46%	2200
	11th to 20th	Night	12% 7% 2 5% 3 2 3 3 6% 8% 48%	1979
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	1800
May	1st to 10th	Night	13% 7% 2 7% 5% 4 5% 5% 8% 10% 35%	4033
	11th to 20th	Night	20% 7% 2 7% 4 4 5% 5% 6% 9% 30%	4032
	21st to end	Night	15% 5% 2 6% 4 5% 5% 4 6% 10% 38%	4421
June	1st to 10th	Night	10% 7% 3 7% 5% 5% 6% 5% 9% 10% 34%	1800
	11th to 20th	Night	9% 6% 2 6% 6% 4 5% 4 8% 12% 40%	1800
	21st to end	Night	7% 4 2 6% 6% 5% 6% 5% 8% 10% 41%	1800
July	1st to 10th	Night	7% 6% 3 7% 6% 6% 6% 5% 8% 10% 36%	4058
	11th to 20th	Night	8% 6% 2 7% 5% 6% 7% 6% 8% 12% 33%	4057
	21st to end	Night	10% 8% 4 9% 7% 6% 6% 6% 8% 10% 25%	4427
August	1st to 10th	Night	13% 9% 3 8% 5% 6% 5% 5% 8% 9% 29%	2915
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 6% 9% 9% 30%	2875
	21st to end	Night	7% 6% 2 5% 4 5% 5% 4 7% 9% 47%	3523
September	1st to 10th	Night	9% 8% 3 8% 6% 5% 4 4 5% 8% 40%	2200
	11th to 20th	Night	18% 8% 2 7% 5% 5% 6% 4 5% 6% 35%	2200
	21st to end	Night	17% 8% 3 5% 4 3 4 3 4 7% 42%	2200
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 6% 47%	2249
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 51%	2400
	21st to end	Night	14% 6% 1 4 2 3 2 2 5% 6% 55%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 7% 51%	2532
	11th to 20th	Night	13% 5% 1 4 3 3 4 4 5% 7% 52%	2730
	21st to end	Night	13% 4 2 5% 4 4 3 4 6% 7% 48%	2730
December	1st to 10th	Night	12% 5% 2 5% 3 4 3 3 5% 6% 51%	4380
	11th to 20th	Night	16% 7% 3 7% 5% 4 4 4 6% 6% 40%	4952
	21st to end	Night	21% 4 2 4 3 3 3 4 6% 7% 45%	6633

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	33% 3 8% 20% 30% 5%	5259
	11th to 20th	Day	25% 4 4 13% 38% 16%	5280
	21st to end	Day	42% 5% 5% 16% 22% 10%	5780
February	1st to 10th	Day	39% 5% 9% 22% 21% 5%	1961
	11th to 20th	Day	43% 5% 8% 20% 19% 6%	2008
	21st to end	Day	44% 4 8% 16% 21% 7%	1650
March	1st to 10th	Day	42% 4 5% 16% 21% 12%	4862
	11th to 20th	Day	32% 4 6% 17% 22% 19%	4980
	21st to end	Day	40% 4 8% 26% 16% 6%	5465
April	1st to 10th	Day	35% 6% 12% 23% 20% 5%	2200
	11th to 20th	Day	38% 5% 9% 20% 22% 6%	2385
	21st to end	Day	37% 6% 12% 26% 15% 3	2600
May	1st to 10th	Day	47% 7% 15% 19% 11% 1	5897
	11th to 20th	Day	51% 10% 13% 17% 8% 1	5865
	21st to end	Day	40% 8% 13% 19% 17% 2	6447
June	1st to 10th	Day	44% 9% 18% 20% 8% 1	2600
	11th to 20th	Day	39% 11% 18% 19% 10% 2	2600
	21st to end	Day	42% 9% 16% 19% 12% 2	2600
July	1st to 10th	Day	40% 14% 17% 21% 7% 1	5835
	11th to 20th	Day	44% 14% 24% 14% 4	5831
	21st to end	Day	53% 13% 16% 13% 5%	6240
August	1st to 10th	Day	50% 11% 18% 18% 3	4221
	11th to 20th	Day	38% 12% 24% 14% 10% 3	4213
	21st to end	Day	33% 9% 15% 31% 11% 1	4336
September	1st to 10th	Day	42% 8% 13% 19% 15% 3	2200
	11th to 20th	Day	46% 9% 11% 18% 15% 2	2200
	21st to end	Day	45% 7% 11% 18% 15% 5%	2200
October	1st to 10th	Day	27% 5% 9% 19% 32% 8%	3501
	11th to 20th	Day	21% 3 5% 19% 27% 25%	3240
	21st to end	Day	27% 4 6% 24% 22% 17%	3538
November	1st to 10th	Day	30% 4 9% 21% 27% 9%	1983
	11th to 20th	Day	32% 3 7% 24% 27% 8%	1890
	21st to end	Day	33% 5% 6% 23% 27% 6%	1890
December	1st to 10th	Day	35% 5% 6% 18% 28% 8%	3020
	11th to 20th	Day	37% 5% 11% 18% 23% 7%	3460
	21st to end	Day	39% 5% 9% 26% 17% 4	4565
January	1st to 10th	Night	31% 4 9% 24% 25% 7%	7636
	11th to 20th	Night	27% 5% 5% 17% 33% 14%	7680
	21st to end	Night	38% 4 7% 17% 22% 11%	8401
February	1st to 10th	Night	36% 5% 11% 22% 20% 5%	2656
	11th to 20th	Night	42% 4 8% 20% 20% 6%	2400
	21st to end	Night	42% 5% 9% 17% 21% 6%	1980
March	1st to 10th	Night	40% 6% 6% 15% 23% 9%	4990
	11th to 20th	Night	27% 5% 7% 20% 22% 18%	4980
	21st to end	Night	40% 5% 9% 26% 14% 6%	5467
April	1st to 10th	Night	36% 4 11% 23% 21% 4	2200
	11th to 20th	Night	33% 5% 11% 23% 22% 6%	1979
	21st to end	Night	34% 7% 15% 25% 17% 2	1800
May	1st to 10th	Night	41% 9% 16% 24% 9% 1	4060
	11th to 20th	Night	48% 8% 17% 18% 8%	4033
	21st to end	Night	38% 8% 18% 23% 12% 1	4429
June	1st to 10th	Night	41% 10% 19% 21% 8% 1	1800
	11th to 20th	Night	35% 9% 24% 22% 9% 1	1800
	21st to end	Night	34% 11% 19% 21% 13% 2	1800
July	1st to 10th	Night	39% 13% 20% 22% 6%	4015
	11th to 20th	Night	39% 16% 29% 13% 3 1	4006
	21st to end	Night	48% 14% 19% 14% 5%	4297
August	1st to 10th	Night	47% 11% 23% 15% 4	2904
	11th to 20th	Night	41% 14% 22% 14% 9% 1	2902
	21st to end	Night	31% 10% 16% 33% 10% 1	3523
September	1st to 10th	Night	41% 9% 14% 20% 14% 3	2200
	11th to 20th	Night	47% 7% 11% 18% 15% 1	2200
	21st to end	Night	42% 6% 12% 21% 17% 3	2200
October	1st to 10th	Night	28% 6% 10% 21% 27% 8%	3678
	11th to 20th	Night	21% 4 6% 22% 26% 21%	3899
	21st to end	Night	30% 4 5% 21% 25% 15%	4252
November	1st to 10th	Night	34% 4 9% 20% 24% 9%	2532
	11th to 20th	Night	32% 4 7% 21% 27% 9%	2730
	21st to end	Night	34% 5% 6% 23% 25% 7%	2730
December	1st to 10th	Night	33% 5% 8% 21% 25% 8%	4380
	11th to 20th	Night	40% 8% 9% 17% 21% 5%	4954
	21st to end	Night	38% 4 12% 21% 21% 4	6633

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% 27% 28% 8% 1	330
	11th to 20th	Day	41% 22% 25% 11% 1	330
	21st to end	Day	32% 31% 30% 5% 2	363
February	1st to 10th	Day	29% 27% 32% 10% 2	330
	11th to 20th	Day	49% 23% 24% 4	315
	21st to end	Day	39% 30% 22% 8%	249
March	1st to 10th	Day	29% 22% 27% 17% 5%	464
	11th to 20th	Day	33% 22% 28% 13% 4 1	500
	21st to end	Day	31% 22% 26% 15% 5% 1	550
April	1st to 10th	Day	27% 22% 25% 17% 7% 1	500
	11th to 20th	Day	21% 22% 29% 17% 10% 2	492
	21st to end	Day	21% 17% 27% 19% 11% 4	500
May	1st to 10th	Day	19% 19% 30% 19% 9% 5%	503
	11th to 20th	Day	24% 11% 22% 23% 13% 7%	527
	21st to end	Day	21% 8% 23% 23% 14% 13%	573
June	1st to 10th	Day	16% 8% 24% 28% 16% 9%	530
	11th to 20th	Day	12% 5% 23% 26% 23% 11%	530
	21st to end	Day	11% 6% 27% 29% 18% 11%	530
July	1st to 10th	Day	11% 2 16% 29% 28% 14%	525
	11th to 20th	Day	10% 4 13% 29% 26% 18%	524
	21st to end	Day	8% 5% 12% 31% 26% 18%	576
August	1st to 10th	Day	24% 6% 18% 22% 16% 15%	526
	11th to 20th	Day	14% 4 15% 30% 19% 17%	519
	21st to end	Day	17% 3 14% 27% 25% 14%	583
September	1st to 10th	Day	12% 4 18% 30% 22% 13%	530
	11th to 20th	Day	21% 5% 15% 25% 25% 10%	530
	21st to end	Day	22% 7% 20% 27% 21% 4	530
October	1st to 10th	Day	21% 7% 21% 27% 17% 6%	530
	11th to 20th	Day	18% 14% 26% 25% 13% 4	530
	21st to end	Day	23% 14% 25% 26% 10% 2	583
November	1st to 10th	Day	23% 14% 30% 21% 10% 2	461
	11th to 20th	Day	20% 27% 33% 15% 4	330
	21st to end	Day	25% 22% 33% 16% 4 1	330
December	1st to 10th	Day	31% 25% 34% 10% 1	330
	11th to 20th	Day	28% 20% 35% 13% 4 1	330
	21st to end	Day	32% 21% 31% 13% 3 1	363
January	1st to 10th	Night	24% 24% 24% 22% 6%	840
	11th to 20th	Night	26% 22% 24% 23% 5%	840
	21st to end	Night	21% 24% 28% 22% 4	924
February	1st to 10th	Night	20% 20% 27% 30% 4	840
	11th to 20th	Night	28% 25% 24% 21% 2	804
	21st to end	Night	25% 22% 27% 23% 3	660
March	1st to 10th	Night	20% 23% 23% 29% 4	800
	11th to 20th	Night	24% 19% 28% 21% 8% 1	800
	21st to end	Night	24% 17% 27% 23% 8%	880
April	1st to 10th	Night	21% 19% 25% 26% 9% 1	800
	11th to 20th	Night	20% 18% 23% 25% 12% 2	715
	21st to end	Night	15% 12% 21% 33% 17% 2	600
May	1st to 10th	Night	17% 12% 25% 27% 18% 2	600
	11th to 20th	Night	20% 7% 17% 29% 25% 2	591
	21st to end	Night	18% 4 11% 25% 33% 8%	650
June	1st to 10th	Night	14% 4 12% 34% 30% 7%	600
	11th to 20th	Night	12% 3 13% 29% 33% 11%	600
	21st to end	Night	8% 2 12% 33% 37% 9%	600
July	1st to 10th	Night	12% 2 6% 27% 45% 8%	585
	11th to 20th	Night	9% 4 5% 24% 45% 13%	582
	21st to end	Night	8% 3 5% 29% 43% 12%	657
August	1st to 10th	Night	19% 3 8% 21% 39% 10%	597
	11th to 20th	Night	16% 2 8% 26% 38% 10%	594
	21st to end	Night	13% 2 6% 26% 43% 9%	729
September	1st to 10th	Night	14% 4 11% 26% 37% 9%	800
	11th to 20th	Night	22% 4 8% 23% 37% 7%	800
	21st to end	Night	24% 5% 12% 30% 26% 4	800
October	1st to 10th	Night	18% 7% 19% 23% 26% 8%	800
	11th to 20th	Night	20% 11% 19% 31% 18% 3	800
	21st to end	Night	20% 13% 15% 34% 14% 4	880
November	1st to 10th	Night	19% 10% 21% 31% 16% 4	820
	11th to 20th	Night	18% 16% 22% 31% 12% 1	840
	21st to end	Night	20% 16% 21% 29% 13% 1	840
December	1st to 10th	Night	22% 22% 21% 28% 8%	840
	11th to 20th	Night	20% 16% 24% 32% 7% 1	840
	21st to end	Night	27% 15% 21% 30% 6%	924

Page generated at 2026-02-13 01:42:12. Version ac07

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