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 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	16% 11% 4 9% 5% 5% 5% 4 5% 7% 29%	101704
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	97882
Transparency	Day	52% 6% 11% 20% 9% 1	105265
	Night	54% 6% 12% 19% 9% 1	102409
Seeing	Day	25% 16% 29% 18% 9% 3	14761
	Night	24% 16% 26% 24% 10% 1	24052

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% 18% 9% 13% 6% 4 4 3 4 5% 19%	2517
	11th to 20th	Day	12% 17% 10% 19% 7% 5% 4 3 3 5% 15%	2566
	21st to end	Day	17% 19% 9% 12% 10% 5% 4 3 4 4 13%	3124
February	1st to 10th	Day	16% 17% 5% 15% 7% 5% 4 4 3 3 20%	1710
	11th to 20th	Day	13% 15% 6% 15% 9% 5% 4 3 4 4 21%	1682
	21st to end	Day	19% 14% 3 13% 8% 4 3 3 4 4 24%	1570
March	1st to 10th	Day	20% 16% 6% 11% 4 3 3 2 3 5% 25%	3242
	11th to 20th	Day	10% 19% 7% 10% 4 4 3 3 4 6% 30%	3480
	21st to end	Day	17% 13% 4 12% 5% 4 5% 3 4 6% 28%	3956
April	1st to 10th	Day	16% 16% 4 9% 5% 4 4 3 5% 6% 29%	2280
	11th to 20th	Day	17% 12% 3 8% 5% 4 4 4 5% 6% 33%	2254
	21st to end	Day	18% 12% 3 8% 4 4 5% 3 5% 6% 32%	2313
May	1st to 10th	Day	23% 10% 3 7% 4 4 4 3 4 6% 33%	4290
	11th to 20th	Day	19% 10% 3 8% 5% 6% 5% 4 6% 7% 27%	4398
	21st to end	Day	12% 7% 2 6% 5% 4 5% 4 6% 7% 41%	4837
June	1st to 10th	Day	18% 9% 3 7% 4 5% 5% 4 6% 7% 33%	2660
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 5% 7% 9% 35%	2660
	21st to end	Day	12% 8% 3 7% 5% 5% 6% 4 7% 9% 34%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 8% 12% 35%	4440
	11th to 20th	Day	8% 6% 2 7% 5% 6% 7% 6% 10% 12% 32%	4440
	21st to end	Day	11% 6% 3 7% 6% 6% 6% 5% 7% 8% 35%	4735
August	1st to 10th	Day	20% 6% 3 7% 4 5% 5% 4 7% 8% 30%	4104
	11th to 20th	Day	18% 7% 2 8% 5% 5% 5% 4 7% 9% 28%	3951
	21st to end	Day	16% 8% 2 6% 4 5% 5% 4 6% 7% 37%	4180
September	1st to 10th	Day	17% 7% 3 6% 4 5% 4 4 5% 7% 39%	2280
	11th to 20th	Day	14% 7% 3 5% 5% 4 4 4 4 8% 42%	2280
	21st to end	Day	20% 8% 3 6% 6% 5% 5% 4 5% 6% 33%	2014
October	1st to 10th	Day	18% 8% 2 8% 5% 5% 4 4 6% 7% 33%	1900
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 4 6% 6% 31%	1900
	21st to end	Day	21% 15% 3 8% 5% 4 4 4 5% 5% 26%	2047
November	1st to 10th	Day	14% 14% 3 9% 5% 4 4 3 5% 5% 35%	1761
	11th to 20th	Day	15% 17% 4 10% 5% 4 5% 4 5% 5% 26%	1677
	21st to end	Day	19% 18% 4 11% 5% 5% 5% 3 4 6% 20%	1598
December	1st to 10th	Day	18% 21% 7% 11% 5% 5% 4 3 5% 5% 16%	1520
	11th to 20th	Day	19% 15% 7% 14% 5% 4 3 3 4 5% 21%	1906
	21st to end	Day	23% 21% 6% 12% 6% 4 3 3 4 4 14%	2772
January	1st to 10th	Night	16% 16% 6% 14% 7% 5% 5% 3 5% 5% 18%	4429
	11th to 20th	Night	13% 17% 7% 16% 8% 6% 4 3 4 5% 18%	4376
	21st to end	Night	22% 17% 7% 15% 9% 5% 4 2 3 3 14%	4532
February	1st to 10th	Night	15% 15% 5% 12% 7% 6% 5% 4 5% 4 22%	2470
	11th to 20th	Night	12% 16% 6% 14% 8% 5% 5% 4 4 5% 21%	2382
	21st to end	Night	16% 14% 5% 14% 7% 4 4 4 4 5% 23%	1884
March	1st to 10th	Night	19% 15% 5% 10% 5% 3 4 3 4 4 27%	3596
	11th to 20th	Night	13% 20% 5% 10% 5% 5% 3 3 4 5% 26%	3479
	21st to end	Night	16% 13% 4 12% 5% 4 4 3 4 5% 30%	3674
April	1st to 10th	Night	18% 13% 4 8% 4 4 4 3 5% 7% 29%	1900
	11th to 20th	Night	21% 11% 4 6% 4 4 4 3 5% 5% 34%	1875
	21st to end	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 36%	1881
May	1st to 10th	Night	24% 10% 3 7% 4 4 4 3 5% 5% 30%	2651
	11th to 20th	Night	18% 10% 3 7% 5% 5% 5% 4 5% 8% 32%	2495
	21st to end	Night	11% 7% 2 7% 5% 4 5% 5% 6% 8% 39%	2738
June	1st to 10th	Night	16% 8% 2 5% 4 5% 4 4 5% 8% 38%	1520
	11th to 20th	Night	12% 9% 3 6% 4 4 4 5% 6% 9% 38%	1520
	21st to end	Night	13% 5% 2 6% 4 4 6% 4 6% 8% 42%	1520
July	1st to 10th	Night	10% 8% 3 8% 5% 4 4 4 6% 8% 41%	2520
	11th to 20th	Night	10% 6% 2 6% 3 5% 5% 4 6% 10% 43%	2520
	21st to end	Night	14% 7% 2 6% 4 5% 4 3 6% 7% 41%	2815
August	1st to 10th	Night	19% 8% 2 7% 4 4 5% 4 6% 7% 35%	2825
	11th to 20th	Night	18% 6% 2 6% 4 4 4 3 4 8% 41%	2844
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 8% 41%	3476
September	1st to 10th	Night	14% 7% 3 6% 5% 4 3 3 5% 6% 44%	1900
	11th to 20th	Night	13% 7% 1 5% 4 4 3 3 5% 6% 49%	1900
	21st to end	Night	18% 7% 2 7% 4 5% 5% 3 5% 6% 38%	2163
October	1st to 10th	Night	18% 9% 3 8% 4 4 5% 3 5% 8% 34%	2280
	11th to 20th	Night	20% 9% 3 6% 4 4 3 3 5% 7% 35%	2280
	21st to end	Night	24% 14% 3 6% 4 4 4 3 4 5% 28%	2550
November	1st to 10th	Night	13% 13% 3 7% 4 5% 3 3 4 6% 39%	2537
	11th to 20th	Night	17% 15% 4 9% 5% 4 4 3 3 6% 30%	2720
	21st to end	Night	15% 16% 5% 8% 5% 4 5% 4 6% 6% 25%	2798
December	1st to 10th	Night	18% 17% 6% 11% 6% 5% 4 4 5% 5% 19%	2660
	11th to 20th	Night	19% 16% 5% 12% 7% 4 4 3 4 4 21%	3288
	21st to end	Night	24% 18% 6% 10% 6% 5% 4 3 5% 5% 15%	4884

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	68% 4 12% 14% 3	2518
	11th to 20th	Day	72% 5% 9% 10% 4	2566
	21st to end	Day	74% 4 10% 9% 2	3124
February	1st to 10th	Day	69% 4 9% 12% 5% 1	1710
	11th to 20th	Day	68% 4 8% 14% 5%	1691
	21st to end	Day	63% 4 10% 16% 6% 1	1570
March	1st to 10th	Day	64% 3 8% 19% 6% 1	3245
	11th to 20th	Day	56% 5% 11% 18% 8% 1	3480
	21st to end	Day	56% 4 7% 21% 10% 1	3956
April	1st to 10th	Day	56% 5% 8% 21% 9% 2	2280
	11th to 20th	Day	52% 6% 10% 18% 13% 1	2254
	21st to end	Day	52% 5% 7% 19% 14% 2	2313
May	1st to 10th	Day	53% 5% 9% 20% 12% 2	4302
	11th to 20th	Day	54% 9% 10% 19% 7% 1	4402
	21st to end	Day	40% 7% 11% 26% 15% 2	4837
June	1st to 10th	Day	48% 7% 10% 20% 14% 1	2660
	11th to 20th	Day	44% 7% 15% 22% 11% 1	2660
	21st to end	Day	44% 8% 13% 21% 12% 1	2660
July	1st to 10th	Day	39% 8% 17% 26% 10% 1	4370
	11th to 20th	Day	38% 9% 16% 25% 11% 1	4365
	21st to end	Day	44% 7% 15% 21% 12% 1	4584
August	1st to 10th	Day	49% 7% 13% 20% 10%	4091
	11th to 20th	Day	48% 8% 14% 24% 5%	3990
	21st to end	Day	44% 6% 10% 31% 8% 1	4180
September	1st to 10th	Day	44% 6% 10% 26% 13% 1	2280
	11th to 20th	Day	41% 5% 10% 25% 17% 1	2280
	21st to end	Day	51% 6% 9% 21% 11% 2	2014
October	1st to 10th	Day	44% 6% 12% 24% 13% 1	3160
	11th to 20th	Day	48% 6% 10% 20% 16% 1	3140
	21st to end	Day	44% 6% 15% 26% 8% 1	3349
November	1st to 10th	Day	51% 5% 12% 20% 11% 2	1761
	11th to 20th	Day	57% 6% 12% 16% 7% 2	1677
	21st to end	Day	64% 6% 14% 13% 3	1598
December	1st to 10th	Day	69% 5% 12% 10% 4	1520
	11th to 20th	Day	68% 5% 13% 10% 4	1906
	21st to end	Day	74% 5% 9% 10% 2	2772
January	1st to 10th	Night	67% 5% 14% 10% 3	4429
	11th to 20th	Night	68% 6% 10% 12% 4	4376
	21st to end	Night	76% 3 7% 10% 3	4532
February	1st to 10th	Night	64% 5% 11% 12% 7%	2470
	11th to 20th	Night	66% 4 11% 13% 5% 1	2384
	21st to end	Night	63% 4 11% 13% 8% 1	1884
March	1st to 10th	Night	60% 5% 10% 17% 7% 1	3606
	11th to 20th	Night	60% 5% 11% 18% 6%	3480
	21st to end	Night	55% 5% 7% 21% 10% 2	3674
April	1st to 10th	Night	54% 5% 12% 18% 10% 1	1900
	11th to 20th	Night	52% 5% 9% 19% 14% 1	1875
	21st to end	Night	48% 6% 10% 19% 14% 3	1881
May	1st to 10th	Night	55% 6% 8% 19% 9% 2	2658
	11th to 20th	Night	48% 9% 14% 18% 9% 1	2496
	21st to end	Night	40% 9% 12% 20% 17% 2	2739
June	1st to 10th	Night	44% 6% 11% 24% 14% 1	1520
	11th to 20th	Night	41% 7% 15% 23% 12% 2	1520
	21st to end	Night	38% 9% 13% 26% 13% 1	1520
July	1st to 10th	Night	41% 6% 15% 22% 15% 1	2480
	11th to 20th	Night	34% 8% 14% 28% 14%	2472
	21st to end	Night	42% 7% 12% 21% 16% 2	2725
August	1st to 10th	Night	46% 8% 15% 22% 8%	2814
	11th to 20th	Night	42% 7% 14% 27% 9%	2871
	21st to end	Night	40% 5% 12% 31% 10% 1	3476
September	1st to 10th	Night	40% 7% 13% 24% 14% 2	1900
	11th to 20th	Night	36% 5% 12% 29% 17% 1	1900
	21st to end	Night	47% 6% 12% 22% 13% 1	2163
October	1st to 10th	Night	50% 7% 10% 22% 11%	3800
	11th to 20th	Night	44% 5% 13% 20% 15% 4	3779
	21st to end	Night	43% 6% 15% 27% 9% 1	4198
November	1st to 10th	Night	47% 5% 12% 21% 13% 2	2537
	11th to 20th	Night	56% 5% 11% 18% 8% 2	2720
	21st to end	Night	57% 8% 15% 16% 4	2798
December	1st to 10th	Night	67% 6% 13% 11% 3	2660
	11th to 20th	Night	67% 5% 10% 14% 4	3288
	21st to end	Night	71% 7% 10% 11% 2	4884

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	33% 19% 34% 10% 4	180
	11th to 20th	Day	37% 31% 24% 5% 3 1	195
	21st to end	Day	28% 27% 35% 7% 2	297
February	1st to 10th	Day	35% 30% 28% 6% 2	270
	11th to 20th	Day	37% 28% 31% 4	289
	21st to end	Day	37% 23% 29% 9% 2	382
March	1st to 10th	Day	36% 22% 25% 13% 3	460
	11th to 20th	Day	35% 23% 26% 11% 5%	460
	21st to end	Day	34% 24% 26% 11% 4 1	506
April	1st to 10th	Day	33% 20% 28% 14% 4 1	460
	11th to 20th	Day	32% 24% 24% 11% 7% 3	452
	21st to end	Day	34% 15% 29% 13% 7% 1	460
May	1st to 10th	Day	29% 17% 31% 13% 8% 3	463
	11th to 20th	Day	22% 16% 32% 17% 10% 3	487
	21st to end	Day	18% 13% 31% 23% 11% 4	529
June	1st to 10th	Day	18% 16% 32% 21% 11% 2	490
	11th to 20th	Day	17% 14% 26% 28% 12% 2	490
	21st to end	Day	17% 15% 34% 21% 10% 2	490
July	1st to 10th	Day	12% 9% 31% 27% 16% 5%	485
	11th to 20th	Day	12% 7% 30% 30% 17% 4	484
	21st to end	Day	13% 8% 38% 25% 12% 4	532
August	1st to 10th	Day	16% 8% 28% 24% 18% 6%	486
	11th to 20th	Day	17% 8% 31% 23% 12% 8%	479
	21st to end	Day	16% 10% 27% 24% 14% 9%	539
September	1st to 10th	Day	19% 12% 21% 27% 13% 7%	490
	11th to 20th	Day	15% 8% 24% 22% 20% 10%	490
	21st to end	Day	24% 14% 27% 19% 12% 4	490
October	1st to 10th	Day	24% 13% 24% 20% 14% 5%	490
	11th to 20th	Day	27% 18% 28% 18% 8% 1	490
	21st to end	Day	34% 16% 29% 17% 4	516
November	1st to 10th	Day	28% 19% 24% 18% 10% 1	395
	11th to 20th	Day	33% 21% 27% 15% 4	277
	21st to end	Day	42% 18% 31% 8% 3	200
December	1st to 10th	Day	35% 22% 31% 8% 3 1	180
	11th to 20th	Day	34% 27% 30% 8% 1 1	180
	21st to end	Day	37% 22% 34% 6% 1	198
January	1st to 10th	Night	27% 25% 30% 16% 2	760
	11th to 20th	Night	28% 21% 28% 21% 3	760
	21st to end	Night	24% 23% 32% 19% 2	836
February	1st to 10th	Night	27% 21% 30% 20% 1	760
	11th to 20th	Night	29% 22% 34% 14% 1	743
	21st to end	Night	31% 22% 26% 18% 3	628
March	1st to 10th	Night	26% 24% 28% 20% 2	760
	11th to 20th	Night	28% 20% 30% 18% 4	760
	21st to end	Night	27% 22% 27% 17% 7% 1	836
April	1st to 10th	Night	28% 20% 28% 20% 3	760
	11th to 20th	Night	28% 19% 26% 20% 7% 1	751
	21st to end	Night	24% 14% 29% 24% 8%	741
May	1st to 10th	Night	24% 13% 22% 31% 9% 1	466
	11th to 20th	Night	15% 11% 28% 33% 12% 1	374
	21st to end	Night	12% 9% 27% 39% 13% 1	411
June	1st to 10th	Night	18% 7% 27% 33% 14% 1	380
	11th to 20th	Night	15% 10% 20% 41% 14% 1	380
	21st to end	Night	15% 6% 24% 40% 15%	380
July	1st to 10th	Night	9% 4 25% 40% 20% 3	370
	11th to 20th	Night	12% 4 19% 45% 20% 1	368
	21st to end	Night	15% 3 19% 39% 22% 2	456
August	1st to 10th	Night	12% 5% 18% 37% 26% 2	567
	11th to 20th	Night	12% 7% 15% 35% 27% 3	597
	21st to end	Night	15% 6% 20% 34% 24% 2	836
September	1st to 10th	Night	17% 10% 21% 31% 19% 2	760
	11th to 20th	Night	17% 6% 18% 28% 26% 5%	760
	21st to end	Night	21% 9% 25% 25% 17% 2	760
October	1st to 10th	Night	22% 10% 26% 23% 17% 2	760
	11th to 20th	Night	26% 14% 25% 26% 8% 1	760
	21st to end	Night	33% 14% 28% 21% 4	836
November	1st to 10th	Night	22% 17% 27% 25% 8%	780
	11th to 20th	Night	29% 18% 29% 18% 6% 1	800
	21st to end	Night	27% 21% 28% 20% 4	800
December	1st to 10th	Night	30% 23% 28% 15% 4	760
	11th to 20th	Night	28% 22% 29% 18% 3	760
	21st to end	Night	30% 22% 30% 17% 1	836

Page generated at 2024-11-27 17:30:48. Version ac07

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