Knoll
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Knoll clear sky chart from 2005-11-06 to 2024-02-25.

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	5% 6% 3 6% 5% 3 5% 5% 5% 7% 51%	79054
	Night	6% 7% 3 6% 6% 4 5% 5% 5% 7% 46%	80272
Transparency	Day	31% 5% 11% 19% 20% 13%	78770
	Night	35% 5% 12% 20% 18% 10%	80077
Seeing	Day	7% 5% 16% 28% 29% 16%	13774
	Night	8% 3 17% 41% 26% 4	23569

By Month

Percentage Cloud Cover SW (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	5% 14% 5% 12% 10% 5% 6% 4 5% 6% 28%	2539
	11th to 20th	Day	6% 13% 7% 13% 9% 4 4 5% 5% 6% 28%	2855
	21st to end	Day	7% 12% 6% 13% 12% 8% 8% 5% 5% 5% 17%	3146
February	1st to 10th	Day	6% 11% 4 9% 9% 5% 7% 6% 6% 7% 32%	1710
	11th to 20th	Day	6% 8% 4 7% 6% 4 6% 5% 7% 7% 39%	1816
	21st to end	Day	4 10% 4 8% 6% 4 4 5% 6% 8% 41%	1521
March	1st to 10th	Day	6% 8% 3 7% 5% 4 5% 4 7% 9% 41%	1858
	11th to 20th	Day	4 7% 3 7% 7% 4 6% 7% 6% 9% 40%	1980
	21st to end	Day	9% 9% 3 7% 6% 4 5% 5% 5% 8% 40%	2178
April	1st to 10th	Day	7% 6% 3 5% 6% 3 4 7% 6% 8% 46%	2042
	11th to 20th	Day	6% 7% 3 5% 4 3 4 4 5% 7% 52%	2257
	21st to end	Day	8% 5% 2 4 4 2 4 3 5% 8% 54%	2340
May	1st to 10th	Day	5% 4 2 5% 6% 3 5% 5% 7% 7% 52%	2340
	11th to 20th	Day	6% 3 1 4 6% 3 5% 7% 7% 8% 49%	2301
	21st to end	Day	7% 5% 2 4 6% 4 6% 5% 6% 9% 48%	2530
June	1st to 10th	Day	3 3 1 4 3 2 4 5% 6% 9% 59%	2340
	11th to 20th	Day	5% 3 1 2 3 2 3 4 5% 7% 65%	2515
	21st to end	Day	2 2 1 2 3 2 3 3 3 5% 74%	2520
July	1st to 10th	Day	2 2 1 3 4 2 3 5% 6% 8% 64%	2520
	11th to 20th	Day	3 2 1 2 4 2 4 3 5% 7% 67%	2417
	21st to end	Day	3 2 1 3 3 2 4 6% 6% 8% 62%	2545
August	1st to 10th	Day	2 3 1 3 3 2 5% 4 6% 7% 64%	2328
	11th to 20th	Day	3 2 1 2 4 2 4 4 5% 6% 69%	2299
	21st to end	Day	3 3 1 3 3 2 4 4 4 6% 68%	2520
September	1st to 10th	Day	2 2 1 2 3 2 2 3 5% 5% 74%	2028
	11th to 20th	Day	3 2 1 2 3 2 3 3 5% 6% 71%	1980
	21st to end	Day	5% 2 1 3 2 2 2 3 3 5% 73%	1980
October	1st to 10th	Day	7% 3 1 3 4 3 4 4 4 6% 60%	1958
	11th to 20th	Day	5% 5% 1 3 3 2 3 4 5% 7% 63%	1800
	21st to end	Day	4 4 2 4 3 2 4 5% 5% 7% 60%	1882
November	1st to 10th	Day	5% 5% 3 5% 7% 4 5% 5% 6% 8% 48%	1674
	11th to 20th	Day	7% 6% 1 5% 5% 2 4 6% 7% 7% 49%	1710
	21st to end	Day	7% 8% 4 7% 7% 3 4 4 4 7% 45%	1710
December	1st to 10th	Day	7% 11% 4 8% 7% 4 5% 5% 6% 6% 37%	1710
	11th to 20th	Day	8% 11% 5% 10% 9% 6% 6% 6% 6% 7% 25%	2169
	21st to end	Day	5% 10% 5% 11% 9% 6% 6% 6% 6% 7% 29%	3036
January	1st to 10th	Night	6% 11% 4 8% 7% 4 7% 6% 6% 9% 32%	4401
	11th to 20th	Night	10% 10% 6% 9% 7% 5% 6% 5% 6% 8% 29%	4110
	21st to end	Night	7% 11% 5% 13% 14% 6% 7% 4 4 5% 21%	4521
February	1st to 10th	Night	7% 9% 4 7% 7% 4 5% 6% 6% 10% 35%	2470
	11th to 20th	Night	6% 9% 3 7% 7% 4 5% 4 5% 7% 42%	2249
	21st to end	Night	4 9% 4 7% 6% 3 6% 6% 6% 8% 43%	1829
March	1st to 10th	Night	6% 10% 3 7% 7% 4 6% 6% 5% 8% 38%	2102
	11th to 20th	Night	4 6% 3 6% 6% 4 7% 5% 7% 9% 42%	1980
	21st to end	Night	8% 8% 3 6% 6% 4 5% 5% 6% 8% 41%	2178
April	1st to 10th	Night	8% 6% 3 5% 6% 3 6% 4 5% 7% 46%	1913
	11th to 20th	Night	7% 6% 3 5% 5% 4 5% 4 5% 7% 49%	1651
	21st to end	Night	8% 5% 3 5% 4 3 3 4 5% 7% 53%	1620
May	1st to 10th	Night	8% 5% 2 5% 5% 3 4 5% 6% 7% 51%	1620
	11th to 20th	Night	7% 4 2 4 5% 4 4 5% 7% 9% 48%	1594
	21st to end	Night	8% 6% 3 6% 5% 3 6% 6% 6% 8% 43%	1746
June	1st to 10th	Night	5% 4 2 4 5% 3 4 5% 5% 7% 56%	1619
	11th to 20th	Night	5% 3 1 4 4 2 3 3 4 7% 63%	1440
	21st to end	Night	2 2 1 3 3 2 4 3 5% 6% 68%	1440
July	1st to 10th	Night	3 3 1 4 5% 3 4 6% 5% 8% 58%	1440
	11th to 20th	Night	3 5% 3 5% 4 3 4 4 6% 7% 55%	1538
	21st to end	Night	4 2 1 5% 5% 3 5% 6% 7% 8% 54%	1773
August	1st to 10th	Night	4 4 1 4 5% 3 4 5% 5% 8% 57%	1611
	11th to 20th	Night	2 3 1 4 4 3 5% 4 6% 6% 61%	1602
	21st to end	Night	3 3 2 3 4 3 4 4 5% 7% 62%	1833
September	1st to 10th	Night	2 2 1 3 4 2 4 4 4 5% 69%	1930
	11th to 20th	Night	4 2 1 3 4 2 3 3 5% 6% 67%	1980
	21st to end	Night	5% 3 1 2 3 2 3 3 3 4 71%	1980
October	1st to 10th	Night	5% 3 2 4 4 3 4 4 4 6% 61%	2002
	11th to 20th	Night	5% 4 1 3 3 2 4 4 4 6% 64%	2160
	21st to end	Night	5% 3 1 3 3 2 4 3 5% 7% 65%	2470
November	1st to 10th	Night	6% 5% 3 5% 5% 3 4 4 5% 9% 51%	2405
	11th to 20th	Night	5% 5% 3 5% 5% 3 4 5% 5% 8% 53%	2470
	21st to end	Night	5% 7% 3 5% 5% 4 5% 4 5% 7% 50%	2470
December	1st to 10th	Night	7% 8% 3 7% 6% 3 5% 5% 6% 7% 42%	2470
	11th to 20th	Night	7% 10% 3 9% 9% 5% 7% 5% 7% 9% 28%	3041
	21st to end	Night	7% 10% 5% 9% 8% 5% 8% 7% 6% 8% 26%	4614

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	56% 6% 18% 16% 3	2539
	11th to 20th	Day	56% 8% 16% 17% 4	2855
	21st to end	Day	57% 12% 15% 12% 3	3146
February	1st to 10th	Day	48% 10% 14% 18% 8% 2	1710
	11th to 20th	Day	39% 8% 20% 21% 11% 1	1826
	21st to end	Day	39% 6% 16% 27% 11% 1	1521
March	1st to 10th	Day	37% 6% 17% 24% 14% 2	1858
	11th to 20th	Day	38% 6% 13% 25% 15% 2	1980
	21st to end	Day	42% 6% 13% 25% 12% 3	2178
April	1st to 10th	Day	35% 7% 11% 23% 17% 7%	2042
	11th to 20th	Day	32% 4 11% 23% 25% 5%	2260
	21st to end	Day	29% 4 10% 27% 24% 6%	2340
May	1st to 10th	Day	29% 5% 8% 21% 29% 8%	2340
	11th to 20th	Day	28% 6% 11% 22% 25% 9%	2304
	21st to end	Day	32% 7% 10% 22% 22% 8%	2530
June	1st to 10th	Day	20% 5% 9% 18% 34% 14%	2340
	11th to 20th	Day	18% 4 8% 16% 28% 26%	2515
	21st to end	Day	14% 2 5% 10% 28% 42%	2520
July	1st to 10th	Day	17% 3 6% 11% 23% 40%	2451
	11th to 20th	Day	16% 3 6% 11% 21% 43%	2343
	21st to end	Day	17% 4 9% 11% 25% 33%	2404
August	1st to 10th	Day	19% 4 7% 13% 23% 34%	2313
	11th to 20th	Day	16% 3 7% 9% 31% 34%	2299
	21st to end	Day	18% 3 6% 13% 30% 31%	2520
September	1st to 10th	Day	14% 3 7% 14% 28% 35%	2028
	11th to 20th	Day	15% 4 7% 18% 28% 27%	1980
	21st to end	Day	17% 2 6% 18% 36% 20%	1980
October	1st to 10th	Day	26% 4 9% 18% 33% 10%	1958
	11th to 20th	Day	21% 4 9% 34% 27% 6%	1800
	21st to end	Day	24% 4 13% 34% 21% 3	1882
November	1st to 10th	Day	31% 7% 17% 24% 19% 2	1674
	11th to 20th	Day	31% 6% 15% 34% 13%	1710
	21st to end	Day	38% 6% 16% 26% 13% 1	1710
December	1st to 10th	Day	44% 8% 17% 21% 8% 1	1710
	11th to 20th	Day	54% 9% 18% 15% 4	2168
	21st to end	Day	50% 8% 16% 15% 11% 1	3036
January	1st to 10th	Night	45% 8% 19% 23% 6%	4401
	11th to 20th	Night	51% 8% 20% 15% 5%	4110
	21st to end	Night	61% 8% 13% 12% 5%	4521
February	1st to 10th	Night	43% 7% 17% 23% 7% 1	2470
	11th to 20th	Night	40% 5% 13% 24% 16% 1	2250
	21st to end	Night	37% 6% 13% 28% 14% 2	1829
March	1st to 10th	Night	43% 5% 14% 24% 12% 2	2102
	11th to 20th	Night	36% 7% 12% 25% 17% 3	1980
	21st to end	Night	39% 6% 14% 24% 14% 3	2178
April	1st to 10th	Night	37% 6% 10% 23% 16% 9%	1913
	11th to 20th	Night	35% 4 9% 24% 23% 5%	1651
	21st to end	Night	31% 4 11% 22% 27% 5%	1620
May	1st to 10th	Night	31% 4 9% 19% 30% 6%	1620
	11th to 20th	Night	28% 6% 9% 22% 24% 10%	1595
	21st to end	Night	36% 8% 11% 20% 19% 6%	1746
June	1st to 10th	Night	26% 5% 8% 17% 30% 14%	1619
	11th to 20th	Night	22% 3 7% 17% 30% 21%	1440
	21st to end	Night	16% 3 6% 11% 26% 38%	1440
July	1st to 10th	Night	23% 4 7% 13% 18% 36%	1400
	11th to 20th	Night	26% 5% 6% 9% 19% 36%	1489
	21st to end	Night	24% 4 10% 11% 21% 30%	1674
August	1st to 10th	Night	24% 4 7% 12% 23% 30%	1602
	11th to 20th	Night	23% 3 7% 8% 27% 32%	1602
	21st to end	Night	21% 3 7% 11% 24% 34%	1833
September	1st to 10th	Night	18% 3 5% 13% 25% 37%	1930
	11th to 20th	Night	18% 3 7% 13% 27% 32%	1980
	21st to end	Night	18% 3 5% 13% 32% 29%	1980
October	1st to 10th	Night	24% 4 9% 18% 33% 12%	2002
	11th to 20th	Night	22% 4 6% 24% 34% 9%	2160
	21st to end	Night	20% 4 8% 34% 29% 6%	2470
November	1st to 10th	Night	30% 5% 12% 29% 20% 5%	2405
	11th to 20th	Night	28% 5% 12% 35% 17% 2	2470
	21st to end	Night	34% 4 12% 34% 16% 1	2470
December	1st to 10th	Night	39% 7% 17% 23% 12% 2	2470
	11th to 20th	Night	48% 8% 19% 19% 6%	3041
	21st to end	Night	50% 7% 19% 15% 9%	4614

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	13% 4 18% 31% 22% 12%	180
	11th to 20th	Day	9% 5% 17% 33% 25% 10%	268
	21st to end	Day	11% 2 12% 34% 27% 14%	297
February	1st to 10th	Day	12% 4 20% 37% 19% 8%	270
	11th to 20th	Day	9% 5% 21% 35% 24% 6%	421
	21st to end	Day	6% 7% 25% 36% 21% 5%	363
March	1st to 10th	Day	10% 8% 15% 34% 28% 4	420
	11th to 20th	Day	8% 5% 21% 33% 25% 9%	420
	21st to end	Day	15% 6% 27% 29% 18% 4	462
April	1st to 10th	Day	10% 11% 22% 25% 23% 9%	420
	11th to 20th	Day	9% 11% 29% 26% 19% 6%	412
	21st to end	Day	10% 10% 25% 25% 20% 10%	420
May	1st to 10th	Day	6% 9% 25% 30% 22% 9%	423
	11th to 20th	Day	7% 6% 21% 27% 26% 14%	448
	21st to end	Day	9% 4 17% 28% 27% 15%	485
June	1st to 10th	Day	3 7% 15% 27% 29% 19%	450
	11th to 20th	Day	5% 6% 18% 30% 25% 15%	450
	21st to end	Day	2 2 15% 30% 36% 15%	450
July	1st to 10th	Day	2 1 9% 30% 39% 18%	446
	11th to 20th	Day	3 1 9% 27% 42% 18%	444
	21st to end	Day	2 1 6% 22% 42% 27%	487
August	1st to 10th	Day	4 2 8% 29% 33% 24%	447
	11th to 20th	Day	3 2 7% 26% 34% 29%	437
	21st to end	Day	3 2 10% 20% 39% 25%	495
September	1st to 10th	Day	2 3 9% 22% 31% 33%	450
	11th to 20th	Day	3 3 14% 22% 33% 25%	450
	21st to end	Day	7% 3 11% 22% 31% 26%	450
October	1st to 10th	Day	5% 5% 14% 27% 24% 25%	428
	11th to 20th	Day	4 3 13% 26% 26% 29%	270
	21st to end	Day	6% 4 15% 29% 35% 11%	297
November	1st to 10th	Day	6% 6% 17% 29% 25% 17%	270
	11th to 20th	Day	7% 3 15% 26% 35% 14%	270
	21st to end	Day	11% 5% 10% 28% 30% 16%	270
December	1st to 10th	Day	11% 1 12% 38% 25% 13%	270
	11th to 20th	Day	13% 3 13% 30% 33% 8%	270
	21st to end	Day	11% 8% 17% 32% 24% 8%	264
January	1st to 10th	Night	13% 3 15% 39% 24% 7%	760
	11th to 20th	Night	11% 3 15% 38% 26% 7%	760
	21st to end	Night	11% 3 15% 41% 24% 6%	836
February	1st to 10th	Night	10% 4 19% 44% 19% 4	760
	11th to 20th	Night	10% 3 17% 48% 20% 3	744
	21st to end	Night	8% 4 23% 45% 18% 2	610
March	1st to 10th	Night	11% 4 17% 45% 20% 2	720
	11th to 20th	Night	6% 3 21% 46% 21% 3	720
	21st to end	Night	11% 4 24% 43% 16% 1	792
April	1st to 10th	Night	11% 6% 22% 42% 16% 3	720
	11th to 20th	Night	9% 7% 30% 38% 16% 1	583
	21st to end	Night	9% 6% 27% 38% 20% 1	540
May	1st to 10th	Night	9% 6% 26% 41% 16% 2	540
	11th to 20th	Night	9% 6% 18% 36% 27% 4	531
	21st to end	Night	10% 7% 19% 35% 27% 3	584
June	1st to 10th	Night	6% 6% 19% 41% 25% 3	539
	11th to 20th	Night	8% 4 21% 45% 23%	360
	21st to end	Night	2 1 20% 44% 32% 1	360
July	1st to 10th	Night	4 1 15% 42% 34% 4	350
	11th to 20th	Night	5% 2 16% 50% 26% 2	445
	21st to end	Night	4 1 9% 45% 38% 3	591
August	1st to 10th	Night	5% 2 12% 43% 36% 1	537
	11th to 20th	Night	3 2 13% 47% 33% 2	534
	21st to end	Night	5% 2 12% 43% 33% 5%	645
September	1st to 10th	Night	3 2 11% 38% 39% 8%	720
	11th to 20th	Night	5% 2 13% 36% 37% 8%	720
	21st to end	Night	6% 3 13% 33% 35% 10%	720
October	1st to 10th	Night	7% 3 17% 39% 29% 6%	720
	11th to 20th	Night	7% 2 15% 37% 34% 6%	720
	21st to end	Night	6% 3 18% 37% 31% 6%	792
November	1st to 10th	Night	8% 3 15% 40% 29% 5%	740
	11th to 20th	Night	8% 2 16% 45% 24% 5%	760
	21st to end	Night	8% 2 17% 40% 27% 7%	760
December	1st to 10th	Night	11% 2 15% 48% 21% 4	760
	11th to 20th	Night	12% 3 17% 39% 24% 4	760
	21st to end	Night	16% 4 18% 42% 18% 3	836

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