Starry Knoll
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Knoll clear sky chart from 2005-11-06 to 2024-02-10.

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	15% 12% 5% 9% 7% 4 5% 5% 5% 6% 27%	78247
	Night	14% 13% 6% 10% 7% 4 5% 5% 5% 6% 26%	80713
Transparency	Day	56% 7% 11% 16% 8% 1	77961
	Night	58% 7% 11% 15% 8% 1	80533
Seeing	Day	24% 19% 29% 17% 8% 3	13556
	Night	23% 19% 28% 20% 9% 1	23093

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	11% 23% 14% 13% 7% 3 3 3 4 4 15%	2517
	11th to 20th	Day	9% 21% 10% 19% 9% 4 4 3 3 4 15%	2724
	21st to end	Day	17% 17% 11% 14% 11% 5% 5% 4 3 4 9%	3124
February	1st to 10th	Day	14% 17% 8% 15% 10% 5% 5% 4 3 4 15%	1701
	11th to 20th	Day	11% 14% 9% 17% 9% 4 5% 5% 4 4 18%	1573
	21st to end	Day	16% 16% 6% 12% 9% 4 4 3 4 4 21%	1424
March	1st to 10th	Day	13% 14% 10% 13% 7% 3 4 4 4 5% 24%	1958
	11th to 20th	Day	12% 17% 8% 8% 6% 3 5% 4 4 6% 28%	1980
	21st to end	Day	17% 13% 6% 10% 7% 3 4 4 4 5% 26%	2186
April	1st to 10th	Day	14% 16% 6% 8% 4 3 4 4 5% 6% 29%	2160
	11th to 20th	Day	17% 13% 4 5% 5% 3 4 4 5% 6% 33%	2134
	21st to end	Day	20% 11% 5% 7% 6% 3 4 4 4 5% 31%	2294
May	1st to 10th	Day	17% 11% 4 8% 7% 3 5% 4 4 7% 30%	2348
	11th to 20th	Day	17% 8% 4 7% 6% 4 5% 5% 5% 7% 31%	2478
	21st to end	Day	12% 7% 3 6% 6% 4 5% 6% 5% 8% 38%	2725
June	1st to 10th	Day	17% 7% 3 6% 5% 3 5% 5% 5% 8% 36%	2520
	11th to 20th	Day	14% 7% 4 6% 7% 4 5% 6% 6% 8% 35%	2520
	21st to end	Day	15% 6% 3 6% 5% 3 5% 5% 6% 8% 37%	2520
July	1st to 10th	Day	10% 6% 3 6% 6% 4 7% 7% 6% 8% 38%	2520
	11th to 20th	Day	12% 7% 3 5% 7% 3 6% 6% 7% 10% 34%	2520
	21st to end	Day	13% 5% 3 6% 7% 4 7% 6% 7% 9% 32%	2594
August	1st to 10th	Day	12% 5% 2 7% 6% 4 5% 6% 7% 9% 36%	2327
	11th to 20th	Day	12% 7% 3 8% 8% 5% 7% 6% 6% 10% 28%	2303
	21st to end	Day	15% 6% 3 7% 6% 4 6% 5% 6% 9% 34%	2399
September	1st to 10th	Day	17% 7% 3 6% 5% 3 5% 4 6% 7% 36%	2160
	11th to 20th	Day	15% 6% 3 6% 6% 3 4 5% 6% 7% 40%	2134
	21st to end	Day	17% 8% 3 7% 6% 3 6% 6% 6% 6% 32%	1895
October	1st to 10th	Day	19% 9% 3 7% 6% 4 5% 5% 5% 7% 31%	1800
	11th to 20th	Day	21% 12% 4 8% 6% 3 4 5% 4 6% 27%	1800
	21st to end	Day	22% 17% 5% 8% 5% 2 4 4 4 6% 22%	1980
November	1st to 10th	Day	12% 13% 5% 8% 7% 4 5% 5% 5% 5% 31%	1691
	11th to 20th	Day	15% 21% 6% 8% 7% 4 4 3 5% 7% 22%	1520
	21st to end	Day	14% 21% 8% 10% 7% 3 5% 4 4 4 20%	1520
December	1st to 10th	Day	14% 22% 11% 16% 7% 3 4 4 4 4 12%	1520
	11th to 20th	Day	14% 19% 8% 15% 8% 3 4 4 5% 5% 15%	1906
	21st to end	Day	19% 26% 8% 14% 7% 3 3 2 3 4 10%	2772
January	1st to 10th	Night	12% 20% 10% 16% 8% 4 5% 4 4 4 12%	4429
	11th to 20th	Night	9% 20% 10% 16% 12% 5% 6% 4 4 5% 10%	4234
	21st to end	Night	16% 17% 11% 16% 11% 4 5% 4 3 3 11%	4532
February	1st to 10th	Night	12% 15% 9% 14% 14% 4 5% 3 4 5% 15%	2464
	11th to 20th	Night	11% 13% 7% 16% 9% 5% 8% 5% 5% 5% 17%	2273
	21st to end	Night	15% 13% 7% 15% 11% 3 4 5% 4 4 20%	1831
March	1st to 10th	Night	11% 13% 8% 12% 9% 5% 5% 4 4 5% 24%	1988
	11th to 20th	Night	14% 14% 6% 9% 7% 4 5% 4 4 6% 28%	1979
	21st to end	Night	13% 13% 5% 9% 8% 3 5% 5% 5% 6% 27%	2169
April	1st to 10th	Night	15% 12% 7% 8% 6% 3 5% 4 4 6% 30%	1800
	11th to 20th	Night	17% 13% 2 6% 5% 3 5% 4 4 6% 35%	1775
	21st to end	Night	15% 13% 4 7% 6% 3 4 5% 5% 7% 32%	1680
May	1st to 10th	Night	16% 9% 4 7% 6% 4 6% 5% 6% 7% 31%	1609
	11th to 20th	Night	11% 7% 4 6% 6% 5% 6% 5% 7% 7% 36%	1415
	21st to end	Night	10% 5% 2 5% 6% 3 5% 4 6% 8% 46%	1550
June	1st to 10th	Night	13% 6% 2 5% 6% 4 5% 7% 6% 9% 36%	1440
	11th to 20th	Night	11% 6% 3 6% 4 3 5% 5% 6% 10% 41%	1440
	21st to end	Night	10% 6% 3 5% 6% 3 5% 6% 4 7% 44%	1440
July	1st to 10th	Night	6% 5% 2 8% 5% 3 5% 3 8% 9% 45%	1440
	11th to 20th	Night	9% 5% 2 5% 5% 3 5% 5% 5% 8% 48%	1440
	21st to end	Night	10% 5% 3 5% 5% 3 5% 6% 6% 9% 43%	1721
August	1st to 10th	Night	8% 5% 3 6% 6% 4 5% 5% 6% 9% 45%	1611
	11th to 20th	Night	11% 6% 3 6% 6% 4 4 5% 6% 9% 40%	1598
	21st to end	Night	11% 5% 3 5% 5% 4 5% 5% 5% 9% 42%	1938
September	1st to 10th	Night	16% 6% 2 4 5% 2 4 4 7% 7% 44%	1800
	11th to 20th	Night	15% 7% 2 4 4 2 3 5% 5% 7% 46%	1824
	21st to end	Night	16% 7% 3 5% 6% 3 4 6% 6% 7% 36%	2065
October	1st to 10th	Night	17% 9% 2 6% 6% 3 4 5% 5% 7% 37%	2160
	11th to 20th	Night	18% 12% 4 6% 6% 4 4 4 6% 8% 29%	2160
	21st to end	Night	25% 12% 3 6% 6% 3 4 5% 5% 6% 24%	2376
November	1st to 10th	Night	12% 14% 4 7% 5% 3 4 4 5% 5% 35%	2380
	11th to 20th	Night	13% 16% 6% 9% 6% 3 5% 5% 5% 7% 23%	2660
	21st to end	Night	13% 18% 8% 12% 7% 3 4 4 4 6% 21%	2660
December	1st to 10th	Night	15% 20% 10% 14% 7% 4 5% 5% 4 4 12%	2660
	11th to 20th	Night	15% 19% 10% 15% 7% 3 5% 4 3 4 14%	3288
	21st to end	Night	20% 19% 9% 12% 8% 4 5% 4 5% 4 9%	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	73% 5% 8% 9% 4	2518
	11th to 20th	Day	74% 5% 7% 11% 4	2724
	21st to end	Day	78% 6% 8% 6% 2	3124
February	1st to 10th	Day	73% 6% 8% 8% 4	1701
	11th to 20th	Day	70% 5% 6% 13% 6%	1582
	21st to end	Day	67% 5% 9% 13% 4 1	1424
March	1st to 10th	Day	63% 5% 11% 15% 5% 1	1961
	11th to 20th	Day	58% 6% 10% 15% 9% 2	1980
	21st to end	Day	60% 5% 7% 16% 10% 2	2186
April	1st to 10th	Day	56% 6% 10% 17% 11% 1	2160
	11th to 20th	Day	51% 7% 11% 18% 12% 2	2134
	21st to end	Day	55% 6% 9% 17% 12% 1	2294
May	1st to 10th	Day	54% 7% 10% 18% 9% 2	2348
	11th to 20th	Day	52% 7% 10% 18% 11% 1	2482
	21st to end	Day	44% 8% 16% 20% 11% 2	2725
June	1st to 10th	Day	46% 8% 12% 20% 13% 1	2520
	11th to 20th	Day	46% 8% 14% 21% 11% 1	2520
	21st to end	Day	43% 9% 12% 23% 12%	2520
July	1st to 10th	Day	41% 10% 13% 25% 11% 1	2450
	11th to 20th	Day	44% 9% 15% 21% 12%	2445
	21st to end	Day	44% 11% 13% 20% 10% 1	2449
August	1st to 10th	Day	41% 10% 15% 23% 10%	2314
	11th to 20th	Day	48% 11% 14% 20% 7% 1	2303
	21st to end	Day	47% 8% 13% 21% 9% 2	2399
September	1st to 10th	Day	45% 8% 11% 23% 10% 2	2160
	11th to 20th	Day	42% 7% 12% 24% 14% 1	2134
	21st to end	Day	49% 8% 10% 21% 11% 1	1895
October	1st to 10th	Day	50% 9% 12% 16% 12% 1	1800
	11th to 20th	Day	57% 7% 13% 15% 8% 1	1800
	21st to end	Day	64% 6% 10% 13% 6% 2	1980
November	1st to 10th	Day	52% 8% 12% 14% 11% 2	1691
	11th to 20th	Day	62% 7% 10% 14% 5% 2	1520
	21st to end	Day	68% 5% 10% 11% 4 1	1520
December	1st to 10th	Day	77% 6% 6% 8% 3	1520
	11th to 20th	Day	71% 6% 12% 8% 2 1	1906
	21st to end	Day	79% 6% 7% 8% 1	2772
January	1st to 10th	Night	74% 7% 8% 7% 3	4429
	11th to 20th	Night	74% 7% 9% 8% 2	4234
	21st to end	Night	80% 5% 5% 8% 2	4532
February	1st to 10th	Night	71% 6% 9% 9% 4	2464
	11th to 20th	Night	69% 7% 9% 10% 5%	2275
	21st to end	Night	67% 5% 8% 12% 7% 1	1831
March	1st to 10th	Night	63% 6% 10% 16% 5% 1	1998
	11th to 20th	Night	58% 6% 11% 16% 8% 1	1980
	21st to end	Night	58% 6% 8% 14% 11% 2	2169
April	1st to 10th	Night	56% 6% 11% 18% 10%	1800
	11th to 20th	Night	51% 6% 12% 17% 13% 1	1775
	21st to end	Night	51% 7% 11% 18% 12% 2	1680
May	1st to 10th	Night	51% 9% 9% 19% 10% 2	1609
	11th to 20th	Night	44% 11% 11% 22% 12% 1	1416
	21st to end	Night	35% 11% 15% 23% 14% 2	1551
June	1st to 10th	Night	41% 9% 12% 24% 13% 1	1440
	11th to 20th	Night	38% 9% 15% 23% 14% 2	1440
	21st to end	Night	38% 10% 13% 26% 12% 2	1440
July	1st to 10th	Night	34% 10% 14% 24% 16% 2	1400
	11th to 20th	Night	35% 8% 14% 27% 15% 1	1392
	21st to end	Night	36% 9% 16% 24% 14% 1	1625
August	1st to 10th	Night	35% 8% 17% 29% 9% 1	1600
	11th to 20th	Night	40% 10% 15% 27% 9%	1598
	21st to end	Night	37% 10% 14% 25% 11% 2	1938
September	1st to 10th	Night	39% 8% 14% 26% 11% 2	1800
	11th to 20th	Night	37% 6% 13% 27% 15% 2	1824
	21st to end	Night	45% 8% 15% 19% 12% 1	2065
October	1st to 10th	Night	45% 9% 14% 18% 13% 1	2160
	11th to 20th	Night	53% 7% 13% 17% 9% 1	2160
	21st to end	Night	61% 6% 10% 14% 6% 2	2376
November	1st to 10th	Night	50% 7% 12% 19% 10% 3	2380
	11th to 20th	Night	59% 8% 11% 13% 6% 2	2660
	21st to end	Night	64% 8% 11% 13% 4	2660
December	1st to 10th	Night	75% 7% 8% 8% 2	2660
	11th to 20th	Night	73% 6% 10% 9% 2	3288
	21st to end	Night	77% 8% 8% 7% 1	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	31% 32% 28% 6% 3	180
	11th to 20th	Day	29% 36% 28% 5% 2 1	240
	21st to end	Day	27% 34% 29% 7% 3	297
February	1st to 10th	Day	37% 31% 24% 7%	267
	11th to 20th	Day	37% 33% 28% 2	240
	21st to end	Day	42% 28% 25% 5%	290
March	1st to 10th	Day	33% 28% 26% 11% 2	420
	11th to 20th	Day	29% 27% 30% 9% 4	420
	21st to end	Day	35% 24% 24% 12% 4 1	462
April	1st to 10th	Day	32% 24% 27% 11% 6% 1	420
	11th to 20th	Day	31% 24% 25% 11% 6% 3	412
	21st to end	Day	30% 23% 28% 13% 5% 1	420
May	1st to 10th	Day	31% 18% 28% 14% 6% 3	423
	11th to 20th	Day	23% 17% 31% 19% 8% 2	447
	21st to end	Day	17% 16% 30% 23% 11% 4	485
June	1st to 10th	Day	20% 19% 32% 21% 7% 2	450
	11th to 20th	Day	19% 14% 32% 20% 14% 2	450
	21st to end	Day	18% 14% 38% 21% 6% 2	450
July	1st to 10th	Day	12% 10% 31% 28% 14% 5%	445
	11th to 20th	Day	11% 11% 31% 30% 13% 5%	444
	21st to end	Day	13% 10% 40% 25% 8% 4	488
August	1st to 10th	Day	11% 10% 30% 26% 16% 7%	446
	11th to 20th	Day	15% 8% 32% 24% 16% 6%	439
	21st to end	Day	13% 12% 32% 23% 13% 7%	495
September	1st to 10th	Day	18% 14% 26% 21% 14% 6%	450
	11th to 20th	Day	14% 10% 27% 22% 20% 8%	450
	21st to end	Day	20% 17% 26% 18% 14% 4	450
October	1st to 10th	Day	22% 15% 29% 18% 13% 4	450
	11th to 20th	Day	30% 22% 27% 15% 4 1	450
	21st to end	Day	36% 22% 25% 15% 2	495
November	1st to 10th	Day	25% 22% 28% 15% 8% 2	363
	11th to 20th	Day	37% 23% 26% 12% 1 1	180
	21st to end	Day	28% 32% 32% 7% 1	180
December	1st to 10th	Day	38% 27% 26% 4 4 1	180
	11th to 20th	Day	38% 28% 25% 7% 2	180
	21st to end	Day	40% 22% 32% 5% 1	198
January	1st to 10th	Night	29% 26% 31% 11% 3	760
	11th to 20th	Night	27% 29% 28% 14% 2	760
	21st to end	Night	23% 31% 30% 14% 2	836
February	1st to 10th	Night	27% 29% 30% 13% 1	759
	11th to 20th	Night	29% 29% 30% 10% 1	703
	21st to end	Night	31% 28% 28% 12% 1	592
March	1st to 10th	Night	27% 26% 31% 14% 3	720
	11th to 20th	Night	30% 23% 26% 17% 4	720
	21st to end	Night	23% 23% 32% 16% 5% 1	792
April	1st to 10th	Night	25% 23% 31% 19% 2	720
	11th to 20th	Night	28% 18% 29% 18% 6% 1	711
	21st to end	Night	23% 13% 31% 27% 7%	600
May	1st to 10th	Night	22% 14% 25% 27% 11% 1	529
	11th to 20th	Night	15% 13% 33% 31% 8% 1	354
	21st to end	Night	13% 10% 29% 30% 16% 1	389
June	1st to 10th	Night	15% 10% 30% 33% 11% 1	360
	11th to 20th	Night	15% 11% 26% 36% 13%	360
	21st to end	Night	10% 8% 36% 34% 12%	360
July	1st to 10th	Night	8% 5% 26% 41% 17% 2	350
	11th to 20th	Night	9% 5% 30% 35% 20% 1	348
	21st to end	Night	12% 5% 27% 35% 19% 2	541
August	1st to 10th	Night	12% 4 26% 35% 21% 3	537
	11th to 20th	Night	13% 6% 22% 32% 25% 2	534
	21st to end	Night	12% 7% 26% 30% 22% 2	750
September	1st to 10th	Night	19% 7% 25% 28% 18% 3	720
	11th to 20th	Night	18% 8% 22% 24% 25% 4	720
	21st to end	Night	18% 14% 23% 25% 17% 3	720
October	1st to 10th	Night	22% 13% 26% 21% 16% 1	720
	11th to 20th	Night	26% 18% 30% 20% 5% 1	720
	21st to end	Night	35% 17% 28% 16% 3	792
November	1st to 10th	Night	24% 18% 30% 21% 7%	740
	11th to 20th	Night	28% 24% 28% 12% 6% 2	760
	21st to end	Night	27% 26% 28% 14% 4	760
December	1st to 10th	Night	33% 26% 28% 9% 3	760
	11th to 20th	Night	30% 27% 30% 12% 2	760
	21st to end	Night	29% 28% 31% 11% 1	836

Page generated at 2024-02-07 06:11:56. Version ac07

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