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 2024-06-30.

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	9% 10% 4 9% 6% 5% 5% 4 6% 8% 35%	89393
	Night	7% 10% 4 10% 6% 5% 5% 4 7% 8% 33%	89794
Transparency	Day	45% 8% 15% 22% 9% 1	89096
	Night	46% 8% 14% 21% 9% 2	89671
Seeing	Day	12% 7% 24% 31% 20% 6%	14922
	Night	12% 5% 27% 38% 16% 2	24052

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%	2836
July	1st to 10th	Day	8% 5% 2 5% 5% 5% 5% 5% 8% 10% 41%	2700
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 8% 9% 43%	2700
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 9% 53%	2936
August	1st to 10th	Day	9% 6% 2 5% 4 4 5% 4 7% 9% 45%	2507
	11th to 20th	Day	9% 5% 1 4 4 4 5% 3 7% 10% 48%	2314
	21st to end	Day	10% 4 2 5% 4 4 5% 4 6% 8% 48%	2574
September	1st to 10th	Day	11% 6% 2 7% 4 4 4 3 6% 8% 45%	2254
	11th to 20th	Day	15% 8% 2 5% 4 3 4 3 6% 7% 44%	1980
	21st to end	Day	9% 8% 3 6% 4 5% 4 3 6% 9% 45%	1980
October	1st to 10th	Day	13% 11% 3 7% 4 4 4 3 5% 7% 40%	1877
	11th to 20th	Day	8% 8% 3 9% 6% 4 5% 5% 6% 7% 39%	1688
	21st to end	Day	8% 11% 3 9% 5% 6% 5% 5% 5% 8% 35%	1782
November	1st to 10th	Day	10% 17% 6% 11% 5% 4 5% 4 4 8% 26%	1506
	11th to 20th	Day	8% 12% 4 10% 7% 4 4 4 6% 7% 33%	1459
	21st to end	Day	6% 12% 3 11% 6% 6% 5% 4 6% 8% 32%	1330
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%	1323
July	1st to 10th	Night	9% 5% 1 5% 6% 5% 6% 5% 7% 9% 42%	1260
	11th to 20th	Night	8% 4 2 7% 6% 6% 6% 6% 8% 8% 39%	1260
	21st to end	Night	4 4 2 5% 4 4 4 4 7% 10% 51%	1379
August	1st to 10th	Night	8% 4 2 6% 5% 5% 5% 5% 8% 10% 42%	1432
	11th to 20th	Night	8% 7% 2 5% 5% 4 3 4 7% 10% 45%	1586
	21st to end	Night	8% 5% 2 6% 3 3 4 4 6% 9% 49%	1782
September	1st to 10th	Night	10% 5% 3 5% 4 4 5% 3 6% 8% 48%	1702
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 5% 8% 44%	1980
	21st to end	Night	9% 8% 2 6% 4 4 4 3 7% 9% 46%	1980
October	1st to 10th	Night	12% 9% 2 7% 4 5% 4 5% 4 8% 40%	2083
	11th to 20th	Night	8% 9% 3 8% 5% 5% 5% 4 6% 8% 39%	2271
	21st to end	Night	7% 10% 4 11% 5% 4 5% 4 7% 8% 35%	2574
November	1st to 10th	Night	10% 15% 5% 8% 5% 5% 5% 3 6% 8% 31%	2553
	11th to 20th	Night	5% 11% 5% 9% 7% 6% 6% 4 7% 8% 33%	2721
	21st to end	Night	5% 11% 4 10% 7% 5% 5% 5% 7% 9% 33%	2850
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	2836
July	1st to 10th	Day	34% 10% 20% 27% 8% 1	2626
	11th to 20th	Day	35% 11% 19% 28% 7%	2619
	21st to end	Day	26% 9% 21% 31% 12% 1	2773
August	1st to 10th	Day	33% 10% 19% 28% 8% 1	2490
	11th to 20th	Day	31% 8% 22% 29% 9% 1	2314
	21st to end	Day	31% 9% 19% 28% 12% 1	2574
September	1st to 10th	Day	36% 7% 16% 27% 11% 4	2254
	11th to 20th	Day	39% 7% 13% 29% 10% 2	1980
	21st to end	Day	36% 7% 17% 25% 11% 3	1980
October	1st to 10th	Day	42% 7% 15% 24% 9% 1	1877
	11th to 20th	Day	42% 8% 16% 24% 9% 1	1688
	21st to end	Day	46% 8% 12% 21% 12% 1	1782
November	1st to 10th	Day	56% 6% 12% 17% 7% 2	1506
	11th to 20th	Day	49% 8% 12% 23% 8% 1	1459
	21st to end	Day	47% 8% 16% 20% 8% 1	1330
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% 16% 27% 9% 1	1323
July	1st to 10th	Night	36% 10% 20% 25% 8% 1	1225
	11th to 20th	Night	37% 11% 21% 22% 9% 1	1218
	21st to end	Night	26% 11% 20% 29% 13% 1	1302
August	1st to 10th	Night	33% 10% 22% 26% 8% 1	1424
	11th to 20th	Night	33% 8% 18% 30% 9% 1	1586
	21st to end	Night	30% 8% 18% 30% 12% 3	1782
September	1st to 10th	Night	33% 7% 16% 26% 13% 6%	1702
	11th to 20th	Night	37% 7% 14% 25% 12% 4	1980
	21st to end	Night	34% 5% 17% 27% 15% 3	1980
October	1st to 10th	Night	42% 6% 14% 25% 12% 1	2083
	11th to 20th	Night	41% 8% 16% 22% 10% 2	2271
	21st to end	Night	44% 9% 15% 23% 8% 1	2574
November	1st to 10th	Night	50% 7% 12% 21% 9% 1	2553
	11th to 20th	Night	46% 8% 15% 19% 11% 1	2721
	21st to end	Night	46% 9% 17% 19% 7% 2	2850
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% 22% 31% 25% 7%	676
July	1st to 10th	Day	10% 4 18% 34% 26% 8%	621
	11th to 20th	Day	12% 4 22% 33% 23% 6%	618
	21st to end	Day	7% 4 19% 33% 28% 10%	682
August	1st to 10th	Day	10% 5% 23% 32% 19% 10%	447
	11th to 20th	Day	9% 3 20% 31% 31% 7%	437
	21st to end	Day	10% 8% 20% 29% 23% 10%	495
September	1st to 10th	Day	15% 7% 28% 28% 18% 4	450
	11th to 20th	Day	17% 5% 24% 28% 21% 5%	450
	21st to end	Day	12% 13% 26% 28% 16% 5%	450
October	1st to 10th	Day	18% 7% 20% 29% 19% 6%	347
	11th to 20th	Day	11% 9% 31% 29% 16% 5%	270
	21st to end	Day	15% 12% 32% 27% 12% 1	297
November	1st to 10th	Day	20% 7% 25% 34% 10% 4	270
	11th to 20th	Day	14% 7% 29% 33% 15% 2	241
	21st to end	Day	7% 4 32% 28% 19% 9%	180
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 22% 39% 21% 2	378
July	1st to 10th	Night	11% 2 18% 43% 25% 1	350
	11th to 20th	Night	11% 3 20% 43% 21% 2	348
	21st to end	Night	4 3 21% 41% 29% 2	394
August	1st to 10th	Night	11% 2 17% 42% 27% 1	358
	11th to 20th	Night	9% 3 18% 44% 24% 1	518
	21st to end	Night	9% 3 22% 41% 24%	594
September	1st to 10th	Night	14% 2 23% 42% 18% 2	590
	11th to 20th	Night	15% 5% 21% 38% 21% 1	720
	21st to end	Night	11% 3 28% 38% 17% 2	720
October	1st to 10th	Night	16% 5% 24% 36% 18% 1	720
	11th to 20th	Night	12% 5% 28% 38% 14% 2	720
	21st to end	Night	10% 8% 31% 37% 14% 1	792
November	1st to 10th	Night	15% 8% 30% 36% 10% 1	888
	11th to 20th	Night	9% 7% 38% 34% 11% 2	950
	21st to end	Night	9% 4 32% 40% 14% 2	950
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 2024-06-26 20:18:46. Version ac07

Copyright © 2024 Attilla Danko.