Starry Knight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Knight Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	9% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	105801
	Night	7% 10% 4 9% 6% 5% 5% 4 7% 8% 35%	102307
Transparency	Day	42% 8% 16% 24% 9% 1	105543
	Night	44% 8% 14% 23% 10% 2	102211
Seeing	Day	12% 7% 24% 31% 20% 6%	15491
	Night	12% 5% 27% 38% 16% 2	24570

By Month

Percentage Cloud Cover NW (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	4 12% 5% 13% 7% 5% 5% 4 6% 7% 31%	2219
	11th to 20th	Day	4 9% 4 11% 7% 5% 7% 6% 9% 8% 30%	2199
	21st to end	Day	5% 9% 4 10% 7% 5% 5% 4 6% 9% 37%	2737
February	1st to 10th	Day	7% 14% 4 11% 7% 7% 5% 4 7% 7% 27%	1524
	11th to 20th	Day	6% 14% 5% 12% 7% 6% 7% 5% 7% 8% 25%	1665
	21st to end	Day	5% 14% 5% 11% 10% 7% 5% 4 6% 8% 25%	1486
March	1st to 10th	Day	4 14% 6% 13% 9% 6% 6% 5% 5% 7% 26%	3138
	11th to 20th	Day	6% 9% 3 8% 5% 4 4 4 6% 9% 41%	3485
	21st to end	Day	9% 20% 7% 15% 6% 4 4 3 4 5% 23%	3840
April	1st to 10th	Day	9% 13% 4 8% 6% 6% 5% 5% 7% 8% 30%	2364
	11th to 20th	Day	12% 13% 4 8% 5% 5% 5% 5% 7% 8% 29%	2440
	21st to end	Day	12% 10% 3 8% 7% 5% 4 4 6% 7% 32%	2470
May	1st to 10th	Day	20% 12% 4 7% 4 5% 5% 4 5% 7% 28%	4394
	11th to 20th	Day	10% 8% 3 8% 5% 5% 6% 5% 7% 9% 32%	4694
	21st to end	Day	15% 8% 3 9% 7% 6% 6% 5% 7% 7% 27%	5161
June	1st to 10th	Day	14% 6% 3 7% 5% 6% 5% 5% 7% 9% 33%	2850
	11th to 20th	Day	18% 8% 4 8% 6% 5% 7% 5% 7% 7% 27%	2850
	21st to end	Day	8% 4 2 6% 6% 5% 6% 5% 8% 10% 41%	2850
July	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 50%	4740
	11th to 20th	Day	7% 3 2 4 4 4 5% 4 7% 10% 50%	4740
	21st to end	Day	4 3 2 5% 4 4 4 4 6% 9% 56%	5123
August	1st to 10th	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 9% 41%	4401
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 4 8% 11% 42%	4043
	21st to end	Day	11% 4 2 4 4 4 4 4 6% 8% 50%	4521
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 6% 8% 46%	2379
	11th to 20th	Day	15% 8% 2 5% 4 3 4 3 6% 7% 43%	2090
	21st to end	Day	8% 7% 3 6% 4 4 5% 3 6% 9% 45%	2090
October	1st to 10th	Day	7% 7% 2 8% 4 5% 5% 5% 6% 8% 42%	3303
	11th to 20th	Day	6% 7% 3 8% 5% 4 5% 4 6% 10% 41%	2949
	21st to end	Day	8% 9% 3 8% 5% 5% 5% 4 5% 6% 42%	3101
November	1st to 10th	Day	9% 16% 6% 11% 5% 4 5% 4 5% 8% 26%	1587
	11th to 20th	Day	8% 12% 5% 10% 6% 4 4 4 5% 7% 33%	1535
	21st to end	Day	6% 12% 3 11% 6% 6% 6% 4 6% 8% 31%	1379
December	1st to 10th	Day	7% 14% 5% 11% 8% 8% 6% 4 5% 7% 27%	1330
	11th to 20th	Day	4 11% 6% 13% 8% 6% 5% 4 7% 7% 28%	1682
	21st to end	Day	3 9% 4 9% 5% 5% 6% 3 5% 8% 43%	2442
January	1st to 10th	Night	4 14% 6% 11% 8% 6% 6% 5% 7% 9% 24%	4726
	11th to 20th	Night	3 9% 4 13% 7% 6% 7% 5% 6% 8% 31%	4699
	21st to end	Night	4 11% 4 11% 5% 5% 5% 5% 6% 8% 35%	4949
February	1st to 10th	Night	6% 12% 5% 13% 7% 5% 5% 4 6% 8% 28%	2655
	11th to 20th	Night	5% 14% 5% 12% 7% 6% 6% 4 7% 6% 27%	2402
	21st to end	Night	3 11% 4 10% 7% 6% 6% 5% 7% 11% 30%	1965
March	1st to 10th	Night	3 10% 5% 15% 10% 8% 6% 4 7% 7% 26%	3736
	11th to 20th	Night	6% 8% 3 9% 5% 5% 6% 6% 8% 8% 36%	3494
	21st to end	Night	7% 20% 7% 16% 6% 6% 5% 4 6% 7% 16%	3812
April	1st to 10th	Night	9% 11% 4 8% 7% 6% 5% 5% 7% 7% 31%	1815
	11th to 20th	Night	9% 10% 5% 11% 6% 6% 5% 5% 7% 8% 28%	1691
	21st to end	Night	11% 11% 3 8% 6% 5% 5% 5% 7% 7% 32%	1710
May	1st to 10th	Night	20% 12% 3 8% 5% 4 4 3 5% 7% 28%	2557
	11th to 20th	Night	9% 7% 3 8% 6% 6% 6% 5% 8% 10% 33%	2199
	21st to end	Night	16% 11% 5% 11% 6% 5% 6% 5% 5% 6% 23%	2414
June	1st to 10th	Night	14% 10% 3 7% 6% 4 6% 5% 7% 8% 30%	1330
	11th to 20th	Night	16% 8% 3 10% 7% 6% 6% 5% 7% 7% 24%	1330
	21st to end	Night	10% 6% 2 6% 7% 5% 5% 5% 6% 9% 40%	1330
July	1st to 10th	Night	7% 5% 2 7% 6% 5% 6% 4 7% 8% 44%	2220
	11th to 20th	Night	5% 3 2 6% 4 5% 5% 5% 9% 11% 45%	2220
	21st to end	Night	4 4 2 5% 5% 3 4 4 7% 10% 51%	2414
August	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 7% 9% 44%	2529
	11th to 20th	Night	6% 5% 2 7% 5% 5% 5% 4 8% 12% 41%	2795
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 9% 48%	3146
September	1st to 10th	Night	10% 5% 3 5% 3 4 5% 3 6% 8% 49%	1797
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 5% 7% 44%	2090
	21st to end	Night	8% 7% 2 6% 4 4 4 3 7% 9% 46%	2090
October	1st to 10th	Night	9% 6% 2 5% 4 4 5% 4 6% 8% 46%	3671
	11th to 20th	Night	6% 9% 2 7% 5% 5% 5% 4 7% 9% 42%	3978
	21st to end	Night	6% 8% 3 9% 5% 5% 5% 5% 7% 7% 40%	4457
November	1st to 10th	Night	9% 14% 5% 8% 5% 5% 5% 3 6% 7% 32%	2691
	11th to 20th	Night	5% 11% 5% 10% 7% 6% 6% 4 7% 8% 32%	2865
	21st to end	Night	5% 11% 4 11% 7% 6% 5% 5% 7% 9% 32%	2956
December	1st to 10th	Night	6% 13% 4 12% 7% 6% 4 4 6% 8% 31%	2850
	11th to 20th	Night	3 10% 5% 12% 7% 7% 7% 4 7% 8% 30%	3510
	21st to end	Night	4 8% 3 8% 5% 5% 5% 4 6% 8% 43%	5214

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	49% 7% 15% 20% 9% 1	2219
	11th to 20th	Day	47% 8% 14% 13% 16% 3	2220
	21st to end	Day	42% 7% 16% 27% 7%	2737
February	1st to 10th	Day	55% 6% 14% 15% 9% 1	1524
	11th to 20th	Day	55% 7% 14% 16% 8% 1	1674
	21st to end	Day	57% 7% 10% 17% 10%	1486
March	1st to 10th	Day	56% 6% 15% 14% 9%	3138
	11th to 20th	Day	38% 9% 19% 23% 12%	3486
	21st to end	Day	62% 7% 11% 15% 5%	3840
April	1st to 10th	Day	49% 8% 17% 17% 8% 1	2364
	11th to 20th	Day	49% 7% 14% 21% 8% 1	2440
	21st to end	Day	49% 8% 14% 21% 8% 1	2470
May	1st to 10th	Day	54% 7% 12% 22% 5%	4394
	11th to 20th	Day	43% 10% 14% 25% 9%	4698
	21st to end	Day	50% 9% 16% 18% 6% 1	5162
June	1st to 10th	Day	45% 9% 15% 21% 8% 1	2850
	11th to 20th	Day	52% 9% 13% 19% 6% 1	2850
	21st to end	Day	34% 10% 19% 28% 8% 1	2850
July	1st to 10th	Day	28% 8% 18% 28% 16% 2	4666
	11th to 20th	Day	27% 9% 17% 36% 11% 1	4659
	21st to end	Day	23% 7% 16% 30% 20% 5%	4961
August	1st to 10th	Day	35% 11% 16% 30% 8% 1	4384
	11th to 20th	Day	32% 9% 23% 29% 6% 1	4082
	21st to end	Day	30% 7% 22% 30% 10% 1	4520
September	1st to 10th	Day	34% 7% 16% 26% 11% 5%	2379
	11th to 20th	Day	40% 7% 14% 28% 10% 2	2090
	21st to end	Day	36% 7% 16% 26% 11% 4	2090
October	1st to 10th	Day	38% 7% 20% 27% 7% 1	3303
	11th to 20th	Day	37% 6% 19% 26% 10% 2	2949
	21st to end	Day	41% 7% 9% 33% 10% 1	3101
November	1st to 10th	Day	56% 6% 12% 18% 6% 2	1587
	11th to 20th	Day	49% 8% 12% 22% 8% 1	1535
	21st to end	Day	49% 8% 15% 20% 7% 1	1379
December	1st to 10th	Day	56% 6% 12% 15% 9% 2	1330
	11th to 20th	Day	52% 8% 15% 20% 4 1	1684
	21st to end	Day	38% 6% 12% 23% 17% 4	2442
January	1st to 10th	Night	53% 8% 13% 19% 6% 2	4726
	11th to 20th	Night	50% 6% 11% 16% 14% 3	4740
	21st to end	Night	45% 8% 14% 24% 8% 1	4949
February	1st to 10th	Night	53% 6% 11% 19% 10% 1	2655
	11th to 20th	Night	53% 7% 11% 16% 10% 2	2403
	21st to end	Night	46% 8% 13% 21% 11% 1	1965
March	1st to 10th	Night	54% 7% 13% 19% 6% 1	3736
	11th to 20th	Night	40% 8% 23% 20% 9% 1	3494
	21st to end	Night	65% 8% 11% 11% 4	3812
April	1st to 10th	Night	49% 9% 14% 17% 12% 1	1815
	11th to 20th	Night	50% 7% 14% 21% 7% 1	1691
	21st to end	Night	48% 8% 13% 22% 8% 2	1710
May	1st to 10th	Night	55% 7% 9% 21% 6% 1	2557
	11th to 20th	Night	41% 9% 13% 26% 10%	2199
	21st to end	Night	58% 9% 12% 16% 4 1	2414
June	1st to 10th	Night	49% 9% 13% 20% 9%	1330
	11th to 20th	Night	55% 9% 12% 16% 7% 2	1330
	21st to end	Night	38% 9% 17% 27% 9% 1	1330
July	1st to 10th	Night	35% 9% 16% 23% 16% 1	2185
	11th to 20th	Night	28% 9% 17% 36% 7% 3	2178
	21st to end	Night	26% 8% 15% 29% 19% 4	2337
August	1st to 10th	Night	34% 8% 16% 32% 9% 1	2521
	11th to 20th	Night	32% 10% 21% 30% 6% 1	2822
	21st to end	Night	31% 7% 21% 31% 9% 2	3146
September	1st to 10th	Night	33% 7% 15% 25% 13% 6%	1797
	11th to 20th	Night	38% 7% 14% 26% 11% 4	2090
	21st to end	Night	34% 5% 16% 27% 15% 3	2090
October	1st to 10th	Night	34% 6% 19% 27% 13% 1	3671
	11th to 20th	Night	37% 7% 17% 28% 11% 1	3978
	21st to end	Night	40% 8% 13% 30% 9% 1	4457
November	1st to 10th	Night	50% 6% 12% 22% 9% 1	2691
	11th to 20th	Night	47% 8% 15% 19% 11% 1	2865
	21st to end	Night	47% 9% 16% 19% 7% 2	2956
December	1st to 10th	Night	52% 7% 11% 20% 9% 2	2850
	11th to 20th	Night	49% 10% 16% 18% 6% 1	3507
	21st to end	Night	37% 6% 13% 25% 15% 4	5214

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	7% 5% 25% 32% 22% 9%	180
	11th to 20th	Day	8% 5% 31% 33% 22% 2	180
	21st to end	Day	8% 9% 24% 31% 21% 7%	198
February	1st to 10th	Day	13% 8% 24% 34% 15% 6%	182
	11th to 20th	Day	11% 7% 24% 36% 19% 4	270
	21st to end	Day	8% 5% 22% 39% 20% 5%	298
March	1st to 10th	Day	10% 6% 29% 32% 18% 6%	460
	11th to 20th	Day	8% 4 26% 37% 18% 7%	460
	21st to end	Day	12% 6% 29% 30% 16% 7%	506
April	1st to 10th	Day	11% 12% 28% 31% 14% 4	460
	11th to 20th	Day	14% 8% 30% 28% 15% 5%	452
	21st to end	Day	17% 10% 27% 30% 13% 3	460
May	1st to 10th	Day	19% 11% 20% 26% 19% 6%	558
	11th to 20th	Day	12% 8% 21% 35% 21% 4	675
	21st to end	Day	16% 6% 22% 26% 22% 7%	734
June	1st to 10th	Day	14% 9% 25% 33% 15% 4	680
	11th to 20th	Day	19% 9% 23% 30% 16% 4	680
	21st to end	Day	9% 5% 23% 31% 25% 7%	680
July	1st to 10th	Day	10% 3 18% 34% 27% 8%	671
	11th to 20th	Day	11% 4 21% 32% 25% 8%	668
	21st to end	Day	7% 4 20% 32% 27% 10%	736
August	1st to 10th	Day	10% 5% 23% 32% 20% 11%	487
	11th to 20th	Day	9% 3 19% 31% 30% 8%	477
	21st to end	Day	11% 9% 21% 28% 22% 9%	539
September	1st to 10th	Day	14% 6% 27% 28% 19% 6%	490
	11th to 20th	Day	18% 6% 23% 28% 21% 5%	490
	21st to end	Day	11% 14% 27% 28% 16% 4	490
October	1st to 10th	Day	17% 7% 21% 29% 19% 7%	381
	11th to 20th	Day	10% 8% 33% 29% 15% 5%	300
	21st to end	Day	15% 13% 30% 29% 12% 2	330
November	1st to 10th	Day	19% 7% 24% 34% 12% 4	300
	11th to 20th	Day	13% 7% 30% 33% 15% 2	267
	21st to end	Day	8% 5% 31% 27% 19% 9%	194
December	1st to 10th	Day	8% 5% 27% 33% 21% 7%	180
	11th to 20th	Day	7% 4 37% 34% 16% 3	180
	21st to end	Day	11% 2 19% 38% 24% 7%	198
January	1st to 10th	Night	11% 6% 30% 36% 15% 2	950
	11th to 20th	Night	11% 4 31% 38% 14% 2	950
	21st to end	Night	12% 7% 27% 40% 13% 2	884
February	1st to 10th	Night	10% 7% 25% 38% 18% 2	760
	11th to 20th	Night	11% 5% 31% 38% 15% 1	744
	21st to end	Night	8% 4 22% 39% 23% 4	628
March	1st to 10th	Night	10% 3 27% 40% 17% 3	760
	11th to 20th	Night	9% 4 27% 41% 16% 3	760
	21st to end	Night	14% 4 27% 36% 16% 2	836
April	1st to 10th	Night	13% 6% 28% 34% 16% 2	675
	11th to 20th	Night	15% 8% 29% 36% 11% 1	563
	21st to end	Night	15% 8% 27% 37% 12% 1	570
May	1st to 10th	Night	18% 7% 24% 37% 13% 1	492
	11th to 20th	Night	12% 4 30% 36% 17% 1	374
	21st to end	Night	18% 6% 25% 31% 19% 1	411
June	1st to 10th	Night	16% 9% 26% 34% 13% 1	380
	11th to 20th	Night	17% 3 33% 28% 18% 1	380
	21st to end	Night	13% 3 21% 39% 22% 2	380
July	1st to 10th	Night	11% 2 18% 44% 25% 1	370
	11th to 20th	Night	11% 3 19% 44% 22% 2	368
	21st to end	Night	4 2 22% 41% 29% 2	416
August	1st to 10th	Night	11% 2 17% 43% 26% 1	378
	11th to 20th	Night	8% 3 19% 44% 25% 1	548
	21st to end	Night	10% 3 22% 41% 24%	627
September	1st to 10th	Night	13% 3 22% 42% 18% 2	623
	11th to 20th	Night	16% 5% 21% 38% 21% 1	760
	21st to end	Night	11% 4 29% 38% 16% 1	760
October	1st to 10th	Night	15% 5% 25% 36% 18% 1	760
	11th to 20th	Night	12% 6% 28% 39% 14% 2	760
	21st to end	Night	10% 8% 30% 38% 14% 1	836
November	1st to 10th	Night	15% 8% 30% 36% 10% 1	936
	11th to 20th	Night	8% 7% 37% 34% 11% 2	1000
	21st to end	Night	9% 4 32% 40% 13% 2	986
December	1st to 10th	Night	11% 7% 28% 35% 17% 2	950
	11th to 20th	Night	10% 6% 31% 37% 14% 2	950
	21st to end	Night	11% 4 27% 40% 15% 2	1045

Page generated at 2024-11-24 22:22:21. Version ac07

Copyright © 2024 Attilla Danko.