The Knob
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Knob 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	16% 11% 4 10% 5% 5% 5% 4 5% 6% 29%	131192
	Night	16% 12% 5% 11% 6% 5% 4 3 5% 6% 28%	129615
Transparency	Day	54% 6% 11% 19% 9% 1	134735
	Night	55% 6% 11% 18% 9% 1	134158
Seeing	Day	26% 17% 28% 17% 9% 3	16226
	Night	24% 16% 26% 24% 9% 1	25624

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	14% 17% 8% 21% 9% 3 3 2 4 4 14%	4661
	11th to 20th	Day	10% 15% 9% 20% 9% 6% 5% 3 4 5% 13%	4752
	21st to end	Day	13% 13% 6% 11% 10% 8% 7% 4 5% 4 18%	5780
February	1st to 10th	Day	15% 17% 6% 15% 8% 6% 4 4 3 3 20%	1890
	11th to 20th	Day	13% 16% 7% 16% 8% 5% 4 3 4 4 20%	1819
	21st to end	Day	20% 13% 4 13% 8% 4 3 3 4 4 24%	1650
March	1st to 10th	Day	17% 15% 7% 12% 6% 3 3 2 3 4 28%	4658
	11th to 20th	Day	11% 17% 6% 8% 4 4 3 3 4 6% 34%	4980
	21st to end	Day	15% 14% 5% 13% 5% 5% 5% 3 4 5% 27%	5662
April	1st to 10th	Day	17% 16% 4 9% 5% 4 4 3 5% 6% 28%	2400
	11th to 20th	Day	17% 13% 3 7% 5% 4 4 3 5% 6% 32%	2374
	21st to end	Day	18% 12% 3 8% 4 4 4 3 5% 6% 33%	2435
May	1st to 10th	Day	28% 12% 3 6% 4 4 4 3 4 5% 27%	6154
	11th to 20th	Day	20% 11% 3 7% 5% 5% 4 4 5% 7% 29%	6318
	21st to end	Day	21% 10% 3 7% 5% 4 5% 3 6% 6% 31%	6949
June	1st to 10th	Day	18% 8% 3 7% 4 5% 5% 4 6% 7% 33%	2800
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 5% 6% 9% 34%	2800
	21st to end	Day	12% 8% 3 7% 5% 5% 6% 4 7% 9% 35%	2800
July	1st to 10th	Day	10% 6% 2 7% 4 5% 6% 5% 7% 10% 37%	6360
	11th to 20th	Day	8% 7% 2 8% 5% 6% 7% 6% 9% 11% 31%	6360
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	6805
August	1st to 10th	Day	19% 6% 3 7% 4 5% 5% 4 6% 8% 32%	4234
	11th to 20th	Day	18% 7% 2 8% 5% 5% 5% 4 7% 9% 29%	4078
	21st to end	Day	16% 8% 2 6% 4 4 5% 4 6% 7% 37%	4312
September	1st to 10th	Day	16% 6% 3 6% 4 5% 4 3 5% 7% 40%	2400
	11th to 20th	Day	14% 7% 3 5% 5% 4 4 4 4 8% 43%	2400
	21st to end	Day	20% 7% 3 7% 6% 5% 5% 5% 5% 6% 32%	2120
October	1st to 10th	Day	17% 8% 2 7% 5% 5% 4 4 6% 7% 36%	2000
	11th to 20th	Day	19% 11% 3 8% 5% 4 4 4 6% 6% 30%	2000
	21st to end	Day	21% 15% 3 7% 5% 4 4 4 5% 6% 27%	2155
November	1st to 10th	Day	14% 15% 3 9% 5% 5% 4 3 5% 5% 34%	1851
	11th to 20th	Day	14% 17% 4 11% 4 4 5% 4 5% 5% 26%	1761
	21st to end	Day	18% 19% 5% 11% 5% 5% 5% 3 4 6% 20%	1680
December	1st to 10th	Day	16% 20% 9% 18% 5% 4 4 3 4 5% 13%	2680
	11th to 20th	Day	19% 16% 8% 12% 5% 4 3 3 3 4 23%	3066
	21st to end	Day	19% 17% 6% 15% 7% 5% 3 3 5% 6% 13%	4048
January	1st to 10th	Night	13% 16% 7% 21% 9% 5% 4 2 4 4 14%	8234
	11th to 20th	Night	9% 16% 8% 19% 9% 6% 4 3 4 5% 16%	8115
	21st to end	Night	13% 12% 6% 13% 9% 8% 7% 4 5% 5% 19%	8401
February	1st to 10th	Night	14% 15% 5% 13% 7% 6% 6% 4 5% 5% 21%	2730
	11th to 20th	Night	12% 16% 6% 15% 8% 5% 5% 4 4 5% 21%	2576
	21st to end	Night	16% 14% 5% 15% 7% 4 4 4 5% 5% 22%	1980
March	1st to 10th	Night	16% 13% 6% 12% 8% 4 4 3 4 5% 26%	5180
	11th to 20th	Night	14% 16% 4 9% 4 4 3 3 4 6% 34%	4979
	21st to end	Night	16% 13% 5% 14% 6% 5% 4 3 4 4 26%	5268
April	1st to 10th	Night	19% 14% 4 8% 4 5% 4 3 5% 6% 28%	2000
	11th to 20th	Night	20% 12% 4 6% 4 4 4 3 5% 5% 34%	1975
	21st to end	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 36%	1980
May	1st to 10th	Night	30% 11% 3 7% 4 4 4 3 5% 4 24%	3787
	11th to 20th	Night	19% 10% 3 7% 4 4 5% 3 5% 7% 33%	3575
	21st to end	Night	21% 10% 2 7% 4 4 5% 4 5% 6% 31%	3926
June	1st to 10th	Night	17% 8% 2 5% 4 5% 4 4 5% 7% 38%	1600
	11th to 20th	Night	14% 9% 3 6% 4 4 4 5% 6% 9% 38%	1600
	21st to end	Night	13% 5% 2 6% 4 4 6% 4 6% 9% 42%	1600
July	1st to 10th	Night	10% 8% 3 8% 5% 4 4 4 6% 10% 40%	3600
	11th to 20th	Night	11% 7% 2 7% 4 5% 5% 4 7% 10% 39%	3600
	21st to end	Night	12% 7% 2 5% 4 5% 4 3 5% 7% 46%	4030
August	1st to 10th	Night	19% 8% 2 7% 4 4 5% 4 6% 7% 36%	2915
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 4 7% 41%	2936
	21st to end	Night	14% 7% 2 6% 4 4 4 3 6% 8% 41%	3586
September	1st to 10th	Night	13% 7% 3 6% 4 4 3 3 5% 6% 45%	2000
	11th to 20th	Night	13% 6% 1 5% 4 4 3 3 5% 7% 49%	2000
	21st to end	Night	18% 7% 2 7% 4 5% 5% 3 5% 6% 38%	2277
October	1st to 10th	Night	17% 8% 3 7% 4 4 5% 3 5% 7% 36%	2400
	11th to 20th	Night	20% 9% 3 6% 4 4 3 3 5% 7% 35%	2400
	21st to end	Night	23% 14% 3 7% 4 4 4 3 4 5% 29%	2684
November	1st to 10th	Night	13% 13% 3 7% 4 5% 3 3 4 6% 38%	2667
	11th to 20th	Night	17% 15% 4 9% 5% 4 4 4 3 6% 29%	2856
	21st to end	Night	15% 17% 5% 9% 6% 4 5% 4 6% 6% 24%	2940
December	1st to 10th	Night	13% 16% 8% 16% 7% 5% 4 4 5% 5% 16%	4720
	11th to 20th	Night	20% 16% 6% 10% 5% 3 4 3 3 4 25%	5348
	21st to end	Night	21% 18% 6% 11% 7% 4 4 3 4 4 17%	7150

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	73% 3 10% 11% 2	4662
	11th to 20th	Day	73% 6% 7% 8% 5% 1	4782
	21st to end	Day	65% 6% 9% 14% 5%	5780
February	1st to 10th	Day	69% 5% 9% 12% 5% 1	1890
	11th to 20th	Day	69% 4 8% 14% 5%	1828
	21st to end	Day	63% 4 10% 16% 6% 1	1650
March	1st to 10th	Day	62% 3 9% 16% 9%	4661
	11th to 20th	Day	51% 4 17% 17% 8% 2	4980
	21st to end	Day	57% 5% 7% 17% 11% 2	5662
April	1st to 10th	Day	57% 5% 7% 20% 9% 2	2400
	11th to 20th	Day	52% 6% 10% 18% 13% 1	2374
	21st to end	Day	52% 5% 8% 20% 13% 2	2435
May	1st to 10th	Day	59% 5% 9% 15% 10% 1	6163
	11th to 20th	Day	54% 8% 9% 19% 10% 1	6322
	21st to end	Day	51% 7% 10% 20% 11% 1	6949
June	1st to 10th	Day	48% 7% 10% 20% 14% 1	2800
	11th to 20th	Day	45% 7% 15% 22% 11% 1	2800
	21st to end	Day	44% 8% 14% 21% 13% 1	2800
July	1st to 10th	Day	39% 7% 15% 27% 11% 1	6290
	11th to 20th	Day	39% 10% 16% 24% 11% 1	6285
	21st to end	Day	41% 6% 12% 25% 15%	6609
August	1st to 10th	Day	48% 7% 14% 19% 11% 1	4221
	11th to 20th	Day	48% 8% 14% 24% 6%	4117
	21st to end	Day	44% 6% 10% 31% 8% 1	4312
September	1st to 10th	Day	43% 6% 9% 28% 13% 1	2400
	11th to 20th	Day	40% 5% 10% 27% 17% 1	2400
	21st to end	Day	51% 6% 10% 20% 11% 2	2120
October	1st to 10th	Day	43% 6% 12% 25% 14% 1	3260
	11th to 20th	Day	48% 6% 10% 20% 16% 1	3240
	21st to end	Day	44% 6% 14% 26% 9% 1	3457
November	1st to 10th	Day	52% 5% 12% 20% 10% 2	1851
	11th to 20th	Day	58% 6% 11% 16% 7% 2	1761
	21st to end	Day	64% 6% 14% 13% 3	1680
December	1st to 10th	Day	72% 6% 9% 10% 3	2680
	11th to 20th	Day	66% 5% 11% 11% 7%	3066
	21st to end	Day	69% 6% 11% 10% 4	4048
January	1st to 10th	Night	72% 5% 10% 9% 4	8234
	11th to 20th	Night	67% 6% 9% 11% 6% 1	8160
	21st to end	Night	63% 7% 8% 12% 9% 1	8401
February	1st to 10th	Night	64% 5% 11% 13% 7%	2730
	11th to 20th	Night	66% 4 11% 13% 5% 1	2578
	21st to end	Night	63% 4 11% 14% 8% 1	1980
March	1st to 10th	Night	60% 5% 12% 14% 9% 1	5190
	11th to 20th	Night	53% 4 17% 17% 6% 4	4980
	21st to end	Night	59% 6% 7% 18% 10% 1	5268
April	1st to 10th	Night	55% 5% 11% 18% 9% 2	2000
	11th to 20th	Night	53% 5% 10% 18% 14% 1	1975
	21st to end	Night	48% 6% 10% 19% 14% 3	1980
May	1st to 10th	Night	62% 6% 7% 15% 8% 2	3794
	11th to 20th	Night	49% 8% 13% 19% 10% 1	3576
	21st to end	Night	52% 8% 10% 17% 12% 1	3927
June	1st to 10th	Night	44% 6% 11% 24% 15% 1	1600
	11th to 20th	Night	43% 6% 15% 23% 12% 2	1600
	21st to end	Night	38% 8% 13% 26% 14% 1	1600
July	1st to 10th	Night	40% 6% 15% 25% 13% 1	3560
	11th to 20th	Night	38% 9% 14% 25% 14% 1	3552
	21st to end	Night	36% 6% 12% 26% 18% 2	3911
August	1st to 10th	Night	45% 8% 15% 22% 9% 1	2904
	11th to 20th	Night	42% 7% 14% 27% 10%	2963
	21st to end	Night	40% 5% 12% 32% 10% 1	3586
September	1st to 10th	Night	39% 7% 13% 25% 14% 2	2000
	11th to 20th	Night	35% 4 12% 31% 16% 1	2000
	21st to end	Night	47% 6% 12% 21% 13% 1	2277
October	1st to 10th	Night	49% 6% 10% 22% 12% 1	3920
	11th to 20th	Night	45% 5% 12% 20% 15% 4	3899
	21st to end	Night	43% 6% 14% 27% 10% 1	4332
November	1st to 10th	Night	48% 5% 12% 20% 13% 2	2667
	11th to 20th	Night	57% 5% 11% 18% 8% 2	2856
	21st to end	Night	58% 8% 14% 16% 4	2940
December	1st to 10th	Night	66% 7% 13% 12% 2	4720
	11th to 20th	Night	63% 4 10% 13% 10%	5348
	21st to end	Night	70% 6% 8% 10% 6%	7150

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	34% 25% 30% 9% 3	220
	11th to 20th	Day	41% 29% 23% 5% 2	239
	21st to end	Day	33% 27% 31% 6% 2	363
February	1st to 10th	Day	37% 28% 27% 7% 2	330
	11th to 20th	Day	38% 27% 31% 4	336
	21st to end	Day	36% 24% 29% 8% 2	414
March	1st to 10th	Day	36% 23% 26% 12% 3	500
	11th to 20th	Day	35% 23% 26% 11% 4	500
	21st to end	Day	33% 24% 27% 11% 4 1	550
April	1st to 10th	Day	35% 21% 26% 13% 4 1	500
	11th to 20th	Day	34% 24% 24% 10% 6% 3	492
	21st to end	Day	33% 16% 30% 13% 7% 1	500
May	1st to 10th	Day	30% 17% 30% 12% 7% 3	503
	11th to 20th	Day	24% 17% 31% 16% 9% 3	527
	21st to end	Day	21% 13% 31% 21% 10% 4	573
June	1st to 10th	Day	18% 18% 31% 21% 10% 2	530
	11th to 20th	Day	18% 15% 27% 26% 12% 2	530
	21st to end	Day	16% 16% 34% 22% 9% 2	530
July	1st to 10th	Day	11% 10% 33% 26% 15% 5%	525
	11th to 20th	Day	11% 8% 30% 30% 17% 4	524
	21st to end	Day	13% 8% 38% 26% 12% 3	576
August	1st to 10th	Day	15% 8% 28% 25% 18% 6%	526
	11th to 20th	Day	17% 7% 31% 24% 13% 8%	519
	21st to end	Day	16% 11% 27% 23% 14% 9%	583
September	1st to 10th	Day	19% 12% 20% 28% 13% 8%	530
	11th to 20th	Day	14% 8% 24% 22% 21% 11%	530
	21st to end	Day	24% 14% 28% 18% 12% 4	530
October	1st to 10th	Day	23% 13% 24% 21% 14% 5%	530
	11th to 20th	Day	29% 17% 28% 17% 7% 1	530
	21st to end	Day	33% 17% 29% 17% 4	558
November	1st to 10th	Day	29% 20% 22% 17% 9% 1	425
	11th to 20th	Day	33% 23% 27% 14% 4	301
	21st to end	Day	42% 20% 29% 7% 2	220
December	1st to 10th	Day	35% 25% 29% 8% 2 1	220
	11th to 20th	Day	37% 26% 29% 6% 1	220
	21st to end	Day	37% 22% 35% 6%	242
January	1st to 10th	Night	26% 26% 30% 16% 2	840
	11th to 20th	Night	28% 22% 28% 19% 3	840
	21st to end	Night	25% 24% 31% 18% 2	924
February	1st to 10th	Night	28% 21% 30% 20% 1	840
	11th to 20th	Night	30% 21% 34% 14% 1	804
	21st to end	Night	31% 23% 27% 17% 3	660
March	1st to 10th	Night	27% 25% 27% 19% 2	800
	11th to 20th	Night	29% 20% 30% 17% 4	800
	21st to end	Night	27% 22% 27% 16% 7% 1	880
April	1st to 10th	Night	29% 20% 28% 20% 3	800
	11th to 20th	Night	29% 20% 25% 19% 7% 1	791
	21st to end	Night	24% 14% 29% 24% 8%	780
May	1st to 10th	Night	26% 13% 21% 31% 9% 1	490
	11th to 20th	Night	16% 12% 27% 32% 12% 1	394
	21st to end	Night	13% 10% 26% 39% 12% 1	433
June	1st to 10th	Night	20% 7% 27% 32% 14% 1	400
	11th to 20th	Night	17% 10% 20% 40% 13% 1	400
	21st to end	Night	15% 6% 23% 40% 16%	400
July	1st to 10th	Night	9% 4 25% 41% 19% 3	390
	11th to 20th	Night	12% 4 20% 44% 20% 1	388
	21st to end	Night	15% 3 19% 40% 21% 2	480
August	1st to 10th	Night	12% 4 18% 38% 26% 2	597
	11th to 20th	Night	12% 7% 15% 36% 28% 3	629
	21st to end	Night	15% 6% 20% 34% 23% 2	880
September	1st to 10th	Night	17% 10% 21% 31% 19% 2	800
	11th to 20th	Night	17% 6% 17% 28% 28% 4	800
	21st to end	Night	21% 9% 25% 26% 17% 2	800
October	1st to 10th	Night	22% 10% 26% 23% 17% 2	800
	11th to 20th	Night	26% 15% 26% 26% 7% 1	800
	21st to end	Night	32% 14% 28% 22% 4	880
November	1st to 10th	Night	24% 16% 27% 25% 8%	820
	11th to 20th	Night	29% 18% 28% 18% 6% 1	840
	21st to end	Night	27% 21% 28% 20% 4	840
December	1st to 10th	Night	28% 24% 28% 16% 4	840
	11th to 20th	Night	29% 23% 28% 18% 3	840
	21st to end	Night	30% 22% 29% 17% 1	924

Page generated at 2026-02-13 01:42:16. Version ac07

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