Starry Knoll
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Knoll clear sky chart from 2005-11-05 to 2024-10-14.

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	14% 12% 5% 10% 6% 5% 5% 4 5% 7% 28%	101224
	Night	14% 13% 5% 11% 6% 5% 4 4 5% 6% 27%	97321
Transparency	Day	54% 7% 11% 18% 9% 1	100990
	Night	56% 7% 11% 17% 8% 1	97179
Seeing	Day	24% 19% 29% 17% 8% 3	14530
	Night	23% 19% 28% 20% 9% 1	23886

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% 14% 6% 4 3 2 4 4 15%	2517
	11th to 20th	Day	9% 21% 9% 21% 7% 5% 4 3 3 4 15%	2724
	21st to end	Day	17% 18% 10% 16% 9% 6% 5% 3 3 4 9%	3124
February	1st to 10th	Day	14% 19% 6% 17% 9% 6% 4 3 3 4 15%	1710
	11th to 20th	Day	10% 16% 8% 19% 8% 5% 4 3 4 4 19%	1663
	21st to end	Day	15% 17% 5% 14% 7% 5% 4 3 4 4 22%	1511
March	1st to 10th	Day	17% 15% 8% 10% 5% 3 3 3 4 5% 28%	3401
	11th to 20th	Day	8% 22% 8% 10% 4 4 3 3 4 6% 28%	3480
	21st to end	Day	14% 13% 6% 13% 6% 4 4 4 5% 6% 26%	3836
April	1st to 10th	Day	15% 18% 4 8% 4 3 4 3 5% 6% 29%	2280
	11th to 20th	Day	17% 15% 4 7% 4 4 4 3 5% 5% 32%	2254
	21st to end	Day	20% 12% 4 8% 6% 4 3 3 4 5% 31%	2422
May	1st to 10th	Day	21% 10% 3 8% 5% 4 4 3 4 7% 31%	4130
	11th to 20th	Day	16% 11% 4 9% 6% 6% 5% 4 7% 7% 25%	4398
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 5% 7% 40%	4837
June	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 6% 8% 34%	2660
	11th to 20th	Day	13% 7% 3 8% 6% 5% 5% 5% 6% 8% 34%	2660
	21st to end	Day	15% 7% 3 6% 5% 5% 5% 4 6% 8% 36%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 6% 7% 5% 7% 10% 35%	4440
	11th to 20th	Day	9% 6% 3 7% 5% 5% 7% 5% 8% 10% 36%	4440
	21st to end	Day	9% 6% 3 8% 6% 6% 6% 5% 7% 9% 35%	4541
August	1st to 10th	Day	18% 6% 3 7% 5% 5% 5% 4 6% 8% 33%	4104
	11th to 20th	Day	14% 7% 3 9% 7% 7% 8% 6% 7% 10% 23%	4044
	21st to end	Day	13% 6% 3 8% 5% 5% 5% 4 6% 10% 36%	4217
September	1st to 10th	Day	15% 8% 3 7% 4 5% 4 3 6% 8% 37%	2280
	11th to 20th	Day	14% 6% 2 7% 4 5% 4 4 6% 7% 41%	2252
	21st to end	Day	19% 8% 3 8% 5% 5% 6% 4 6% 6% 31%	2000
October	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	1900
	11th to 20th	Day	20% 13% 3 8% 5% 4 4 4 4 6% 28%	1830
	21st to end	Day	22% 18% 4 9% 4 4 4 3 4 6% 22%	1980
November	1st to 10th	Day	12% 14% 4 9% 6% 5% 4 4 5% 5% 31%	1691
	11th to 20th	Day	14% 22% 5% 9% 6% 5% 3 3 5% 7% 22%	1520
	21st to end	Day	14% 23% 7% 11% 6% 4 4 3 4 4 20%	1520
December	1st to 10th	Day	14% 25% 9% 17% 6% 3 4 3 4 4 12%	1520
	11th to 20th	Day	14% 21% 7% 16% 7% 5% 4 3 5% 5% 15%	1906
	21st to end	Day	19% 27% 7% 16% 6% 4 3 2 3 4 10%	2772
January	1st to 10th	Night	12% 21% 10% 18% 6% 5% 5% 3 4 4 12%	4429
	11th to 20th	Night	9% 21% 10% 19% 9% 6% 5% 3 4 4 10%	4234
	21st to end	Night	15% 18% 10% 17% 10% 6% 5% 3 3 3 11%	4532
February	1st to 10th	Night	12% 18% 6% 16% 11% 6% 4 2 4 5% 15%	2470
	11th to 20th	Night	10% 14% 7% 18% 9% 6% 6% 4 5% 5% 17%	2403
	21st to end	Night	14% 14% 6% 18% 8% 4 4 4 4 4 20%	1942
March	1st to 10th	Night	17% 15% 5% 9% 6% 5% 4 3 4 5% 27%	3426
	11th to 20th	Night	13% 18% 9% 12% 5% 4 4 3 4 6% 23%	3479
	21st to end	Night	12% 11% 4 12% 6% 4 4 3 5% 6% 33%	3795
April	1st to 10th	Night	15% 15% 5% 9% 5% 4 5% 3 4 6% 29%	1900
	11th to 20th	Night	17% 14% 2 7% 4 4 5% 3 4 6% 34%	1875
	21st to end	Night	14% 13% 3 8% 4 5% 4 4 5% 8% 32%	1773
May	1st to 10th	Night	22% 9% 4 7% 5% 5% 4 3 5% 6% 30%	2808
	11th to 20th	Night	16% 10% 4 7% 5% 5% 5% 4 5% 7% 33%	2495
	21st to end	Night	12% 6% 2 7% 4 4 4 4 6% 8% 44%	2738
June	1st to 10th	Night	13% 6% 2 6% 5% 6% 5% 5% 7% 9% 35%	1520
	11th to 20th	Night	10% 6% 2 7% 4 4 4 5% 6% 10% 40%	1520
	21st to end	Night	10% 8% 3 6% 5% 5% 5% 5% 5% 7% 42%	1520
July	1st to 10th	Night	8% 8% 3 9% 5% 4 4 4 6% 9% 39%	2520
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 5% 6% 8% 45%	2520
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 43%	3009
August	1st to 10th	Night	13% 9% 3 7% 5% 5% 4 5% 6% 8% 37%	2825
	11th to 20th	Night	14% 8% 3 8% 5% 4 5% 4 6% 8% 35%	2785
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 5% 9% 44%	3406
September	1st to 10th	Night	16% 6% 2 5% 4 4 3 3 6% 7% 44%	1900
	11th to 20th	Night	14% 7% 2 5% 4 3 3 4 5% 7% 47%	1926
	21st to end	Night	18% 9% 3 6% 5% 4 4 4 5% 7% 34%	2180
October	1st to 10th	Night	16% 9% 2 7% 5% 4 4 4 6% 7% 37%	2280
	11th to 20th	Night	18% 12% 4 7% 5% 4 4 3 6% 7% 29%	2203
	21st to end	Night	25% 13% 4 7% 5% 4 4 4 5% 5% 24%	2376
November	1st to 10th	Night	12% 15% 3 8% 4 4 4 4 5% 5% 35%	2380
	11th to 20th	Night	13% 17% 5% 10% 6% 5% 5% 5% 6% 6% 23%	2660
	21st to end	Night	13% 19% 7% 12% 7% 4 4 3 4 5% 21%	2660
December	1st to 10th	Night	14% 23% 8% 15% 7% 5% 5% 4 4 4 12%	2660
	11th to 20th	Night	15% 20% 9% 16% 6% 5% 4 3 4 4 14%	3288
	21st to end	Night	20% 20% 8% 14% 7% 5% 4 3 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	1710
	11th to 20th	Day	69% 5% 6% 13% 6%	1672
	21st to end	Day	65% 6% 10% 14% 5% 1	1511
March	1st to 10th	Day	58% 6% 9% 21% 5%	3404
	11th to 20th	Day	56% 7% 14% 15% 7% 1	3480
	21st to end	Day	56% 8% 8% 20% 7% 1	3836
April	1st to 10th	Day	57% 5% 10% 16% 11% 1	2280
	11th to 20th	Day	51% 7% 10% 18% 12% 1	2254
	21st to end	Day	54% 7% 8% 16% 13% 1	2422
May	1st to 10th	Day	52% 6% 9% 20% 10% 2	4142
	11th to 20th	Day	53% 11% 11% 17% 7% 1	4402
	21st to end	Day	40% 9% 12% 23% 13% 2	4837
June	1st to 10th	Day	46% 8% 12% 20% 13% 1	2660
	11th to 20th	Day	45% 8% 14% 20% 11% 1	2660
	21st to end	Day	43% 9% 12% 23% 12%	2660
July	1st to 10th	Day	40% 9% 14% 25% 11% 1	4370
	11th to 20th	Day	40% 8% 13% 22% 16%	4365
	21st to end	Day	42% 10% 13% 20% 14%	4396
August	1st to 10th	Day	48% 8% 13% 20% 11%	4091
	11th to 20th	Day	52% 10% 13% 20% 5%	4083
	21st to end	Day	44% 7% 11% 29% 8% 1	4217
September	1st to 10th	Day	44% 8% 11% 24% 11% 2	2280
	11th to 20th	Day	41% 7% 12% 25% 14% 1	2252
	21st to end	Day	51% 8% 10% 20% 11% 1	2000
October	1st to 10th	Day	49% 9% 12% 17% 12% 1	1900
	11th to 20th	Day	57% 7% 13% 15% 8% 1	1831
	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	2470
	11th to 20th	Night	69% 7% 9% 10% 5%	2405
	21st to end	Night	67% 6% 8% 12% 7% 1	1942
March	1st to 10th	Night	59% 6% 11% 18% 5%	3436
	11th to 20th	Night	62% 8% 10% 15% 5%	3480
	21st to end	Night	50% 8% 9% 20% 12% 2	3795
April	1st to 10th	Night	56% 6% 10% 18% 10%	1900
	11th to 20th	Night	51% 6% 12% 17% 12% 1	1875
	21st to end	Night	49% 7% 12% 18% 12% 2	1773
May	1st to 10th	Night	53% 9% 9% 19% 9% 2	2815
	11th to 20th	Night	48% 11% 15% 19% 7% 1	2496
	21st to end	Night	35% 11% 13% 21% 17% 3	2739
June	1st to 10th	Night	42% 9% 11% 24% 13% 1	1520
	11th to 20th	Night	38% 9% 15% 23% 13% 1	1520
	21st to end	Night	40% 10% 12% 25% 12% 1	1520
July	1st to 10th	Night	42% 7% 13% 21% 14% 2	2480
	11th to 20th	Night	35% 9% 15% 27% 13% 1	2472
	21st to end	Night	38% 8% 14% 24% 15% 2	2913
August	1st to 10th	Night	45% 7% 15% 25% 7% 1	2814
	11th to 20th	Night	46% 9% 14% 24% 7%	2812
	21st to end	Night	36% 9% 14% 32% 8% 1	3406
September	1st to 10th	Night	38% 7% 14% 26% 12% 2	1900
	11th to 20th	Night	37% 6% 14% 26% 16% 2	1926
	21st to end	Night	48% 8% 14% 18% 12% 1	2180
October	1st to 10th	Night	45% 8% 13% 19% 14% 1	2280
	11th to 20th	Night	53% 7% 13% 17% 9% 1	2207
	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	38% 31% 24% 7%	270
	11th to 20th	Day	36% 32% 30% 2 1	270
	21st to end	Day	41% 27% 26% 5%	323
March	1st to 10th	Day	32% 26% 27% 12% 2	460
	11th to 20th	Day	30% 27% 29% 9% 4	460
	21st to end	Day	35% 24% 26% 11% 3 1	506
April	1st to 10th	Day	33% 24% 27% 11% 5% 1	460
	11th to 20th	Day	32% 25% 25% 10% 6% 3	452
	21st to end	Day	30% 23% 29% 13% 5% 1	460
May	1st to 10th	Day	30% 19% 27% 15% 6% 3	463
	11th to 20th	Day	22% 17% 32% 19% 9% 2	487
	21st to end	Day	17% 16% 31% 23% 11% 3	529
June	1st to 10th	Day	20% 19% 31% 21% 7% 2	490
	11th to 20th	Day	17% 14% 32% 21% 14% 2	490
	21st to end	Day	19% 15% 37% 21% 6% 2	490
July	1st to 10th	Day	12% 11% 32% 28% 13% 5%	485
	11th to 20th	Day	12% 11% 30% 30% 12% 5%	484
	21st to end	Day	12% 10% 38% 26% 9% 4	532
August	1st to 10th	Day	14% 11% 28% 25% 16% 6%	486
	11th to 20th	Day	15% 9% 30% 24% 15% 6%	479
	21st to end	Day	13% 11% 31% 24% 14% 7%	539
September	1st to 10th	Day	17% 15% 26% 21% 15% 7%	490
	11th to 20th	Day	13% 9% 26% 22% 21% 9%	490
	21st to end	Day	23% 17% 26% 18% 13% 4	490
October	1st to 10th	Day	22% 15% 29% 18% 13% 3	490
	11th to 20th	Day	30% 22% 27% 16% 4 1	462
	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	760
	11th to 20th	Night	29% 29% 30% 10% 1	743
	21st to end	Night	31% 28% 28% 12% 1	628
March	1st to 10th	Night	27% 25% 31% 14% 3	760
	11th to 20th	Night	31% 24% 25% 16% 4	760
	21st to end	Night	24% 24% 31% 15% 5% 1	836
April	1st to 10th	Night	26% 23% 30% 19% 2	760
	11th to 20th	Night	28% 18% 29% 18% 6% 1	751
	21st to end	Night	23% 14% 30% 27% 7%	633
May	1st to 10th	Night	22% 14% 25% 28% 11% 1	558
	11th to 20th	Night	15% 13% 33% 31% 7% 1	374
	21st to end	Night	14% 9% 29% 31% 16% 1	411
June	1st to 10th	Night	14% 11% 30% 33% 11% 1	380
	11th to 20th	Night	14% 11% 26% 36% 12%	380
	21st to end	Night	11% 7% 36% 34% 12%	380
July	1st to 10th	Night	9% 6% 25% 41% 16% 2	370
	11th to 20th	Night	9% 5% 29% 36% 20% 1	368
	21st to end	Night	12% 5% 26% 35% 20% 2	572
August	1st to 10th	Night	12% 5% 25% 35% 21% 2	567
	11th to 20th	Night	13% 6% 23% 31% 25% 2	564
	21st to end	Night	12% 7% 26% 31% 22% 2	792
September	1st to 10th	Night	19% 8% 25% 28% 18% 3	760
	11th to 20th	Night	17% 7% 21% 24% 27% 4	760
	21st to end	Night	20% 14% 23% 24% 16% 3	760
October	1st to 10th	Night	21% 13% 27% 21% 16% 1	760
	11th to 20th	Night	26% 18% 30% 20% 5% 1	735
	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 2024-10-11 10:49:57. Version ac07

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