Golden
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden clear sky chart from 2005-11-06 to 2026-06-01.

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	6% 10% 4 11% 7% 7% 7% 5% 7% 8% 28%	136644
	Night	4 10% 4 12% 8% 7% 7% 5% 7% 8% 28%	135209
Transparency	Day	47% 13% 18% 16% 5% 1	136359
	Night	49% 14% 18% 14% 4	135074
Seeing	Day	12% 16% 32% 26% 11% 2	17556
	Night	10% 12% 31% 33% 13% 1	26180

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	2 10% 7% 20% 11% 9% 9% 6% 8% 7% 10%	4125
	11th to 20th	Day	2 10% 3 9% 6% 5% 6% 5% 8% 10% 35%	4633
	21st to end	Day	3 12% 6% 13% 7% 7% 7% 5% 9% 7% 25%	5186
February	1st to 10th	Day	2 13% 6% 13% 11% 9% 9% 5% 7% 8% 16%	1680
	11th to 20th	Day	2 9% 6% 16% 9% 8% 8% 7% 9% 8% 18%	1789
	21st to end	Day	1 12% 5% 16% 11% 13% 8% 7% 7% 6% 15%	1730
March	1st to 10th	Day	1 10% 6% 15% 9% 7% 8% 7% 9% 8% 19%	4618
	11th to 20th	Day	2 10% 4 13% 9% 8% 8% 7% 8% 7% 23%	4812
	21st to end	Day	3 17% 6% 15% 9% 9% 8% 6% 7% 6% 14%	6011
April	1st to 10th	Day	4 18% 6% 15% 9% 7% 6% 6% 6% 6% 17%	2520
	11th to 20th	Day	4 16% 6% 14% 7% 7% 6% 6% 7% 7% 20%	2646
	21st to end	Day	7% 19% 6% 12% 7% 5% 6% 5% 8% 7% 20%	2784
May	1st to 10th	Day	7% 11% 4 8% 5% 4 5% 5% 7% 9% 35%	6460
	11th to 20th	Day	9% 12% 4 11% 8% 7% 7% 5% 7% 8% 21%	6647
	21st to end	Day	11% 12% 4 9% 6% 5% 6% 4 6% 7% 30%	7570
June	1st to 10th	Day	17% 13% 4 10% 6% 5% 5% 5% 7% 6% 23%	3001
	11th to 20th	Day	16% 13% 4 11% 7% 6% 6% 4 6% 8% 18%	3120
	21st to end	Day	10% 9% 3 10% 7% 6% 7% 6% 7% 8% 28%	3200
July	1st to 10th	Day	5% 4 2 5% 4 4 4 4 7% 8% 54%	7056
	11th to 20th	Day	6% 4 2 6% 4 4 6% 5% 8% 9% 46%	6738
	21st to end	Day	6% 6% 2 7% 5% 5% 5% 5% 8% 10% 42%	6874
August	1st to 10th	Day	4 5% 2 7% 6% 6% 6% 5% 7% 8% 44%	4541
	11th to 20th	Day	7% 5% 3 9% 6% 7% 6% 5% 8% 9% 36%	4406
	21st to end	Day	7% 7% 3 8% 5% 5% 6% 5% 6% 8% 40%	4574
September	1st to 10th	Day	8% 8% 4 9% 6% 5% 5% 4 6% 8% 38%	2400
	11th to 20th	Day	10% 8% 4 9% 7% 6% 6% 4 6% 7% 33%	2290
	21st to end	Day	9% 11% 5% 12% 7% 6% 5% 4 6% 8% 28%	2200
October	1st to 10th	Day	8% 8% 3 10% 8% 6% 7% 5% 7% 9% 29%	3441
	11th to 20th	Day	6% 10% 4 11% 6% 7% 7% 5% 7% 9% 28%	2965
	21st to end	Day	3 13% 5% 11% 8% 8% 7% 7% 8% 8% 22%	3200
November	1st to 10th	Day	5% 16% 6% 15% 10% 8% 8% 6% 7% 6% 14%	1828
	11th to 20th	Day	3 13% 6% 15% 11% 9% 9% 6% 8% 7% 13%	1482
	21st to end	Day	3 13% 5% 14% 12% 11% 9% 5% 8% 6% 13%	1470
December	1st to 10th	Day	3 9% 4 13% 9% 8% 8% 5% 9% 10% 24%	2360
	11th to 20th	Day	1 14% 6% 22% 12% 11% 8% 6% 7% 6% 7%	2712
	21st to end	Day	1 11% 6% 17% 12% 10% 9% 6% 8% 8% 11%	3575
January	1st to 10th	Night	1 12% 9% 20% 11% 10% 9% 6% 7% 6% 10%	8768
	11th to 20th	Night	2 8% 3 10% 7% 7% 8% 10% 10% 9% 26%	8322
	21st to end	Night	3 15% 7% 13% 6% 6% 6% 5% 6% 7% 24%	8994
February	1st to 10th	Night	3 13% 5% 16% 11% 9% 8% 6% 8% 7% 14%	2940
	11th to 20th	Night	1 13% 5% 15% 8% 8% 8% 5% 8% 8% 21%	2716
	21st to end	Night	1 12% 5% 14% 10% 9% 8% 5% 8% 7% 21%	2076
March	1st to 10th	Night	1 8% 4 13% 8% 7% 8% 5% 8% 10% 26%	5496
	11th to 20th	Night	1 11% 3 10% 7% 8% 8% 7% 8% 8% 28%	5407
	21st to end	Night	3 14% 5% 14% 7% 7% 7% 6% 7% 9% 21%	5192
April	1st to 10th	Night	3 13% 5% 9% 7% 6% 8% 6% 9% 9% 26%	2100
	11th to 20th	Night	3 12% 5% 10% 7% 6% 6% 5% 8% 8% 29%	1925
	21st to end	Night	4 11% 4 8% 6% 5% 6% 5% 8% 8% 34%	1832
May	1st to 10th	Night	6% 9% 3 8% 5% 4 4 4 7% 7% 42%	3720
	11th to 20th	Night	8% 9% 3 9% 5% 5% 6% 5% 8% 11% 30%	3465
	21st to end	Night	9% 7% 2 6% 5% 4 4 4 6% 8% 43%	3547
June	1st to 10th	Night	13% 11% 2 7% 5% 5% 5% 5% 5% 7% 34%	1400
	11th to 20th	Night	10% 11% 4 11% 8% 7% 6% 5% 6% 8% 25%	1273
	21st to end	Night	6% 6% 2 5% 6% 5% 5% 5% 9% 11% 39%	1200
July	1st to 10th	Night	3 4 1 4 3 4 4 4 5% 7% 61%	2899
	11th to 20th	Night	5% 4 1 6% 4 4 5% 4 6% 8% 54%	3219
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 7% 8% 51%	3969
August	1st to 10th	Night	5% 4 2 5% 4 4 4 4 7% 8% 51%	2609
	11th to 20th	Night	6% 6% 2 4 3 5% 5% 5% 8% 10% 48%	2642
	21st to end	Night	7% 6% 2 5% 3 4 4 4 7% 9% 46%	3334
September	1st to 10th	Night	7% 7% 3 6% 4 6% 5% 3 6% 6% 47%	2000
	11th to 20th	Night	10% 7% 2 6% 5% 6% 5% 4 5% 6% 43%	2110
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 6% 7% 8% 39%	2200
October	1st to 10th	Night	5% 6% 3 7% 7% 7% 6% 5% 8% 11% 36%	3755
	11th to 20th	Night	7% 9% 3 9% 6% 5% 5% 4 6% 8% 37%	4183
	21st to end	Night	4 9% 4 10% 8% 7% 5% 4 8% 9% 32%	4600
November	1st to 10th	Night	7% 16% 7% 14% 10% 8% 6% 5% 7% 6% 15%	2688
	11th to 20th	Night	3 14% 6% 15% 11% 10% 8% 6% 6% 7% 13%	3115
	21st to end	Night	3 16% 7% 17% 11% 9% 8% 5% 6% 6% 11%	3150
December	1st to 10th	Night	3 10% 5% 13% 11% 11% 8% 7% 8% 9% 16%	5040
	11th to 20th	Night	1 13% 6% 20% 13% 11% 8% 5% 7% 6% 8%	5700
	21st to end	Night	2 13% 7% 19% 12% 12% 8% 5% 6% 5% 10%	7623

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	64% 13% 14% 8% 1	4125
	11th to 20th	Day	39% 13% 20% 19% 7% 2	4657
	21st to end	Day	52% 14% 18% 14% 2	5187
February	1st to 10th	Day	63% 12% 11% 8% 6%	1680
	11th to 20th	Day	58% 16% 13% 9% 4	1797
	21st to end	Day	63% 13% 12% 6% 4 1	1730
March	1st to 10th	Day	52% 15% 14% 12% 7%	4618
	11th to 20th	Day	46% 14% 20% 17% 3	4812
	21st to end	Day	59% 16% 14% 8% 4	6011
April	1st to 10th	Day	64% 13% 15% 7% 2	2520
	11th to 20th	Day	59% 12% 15% 11% 3	2646
	21st to end	Day	60% 13% 14% 11% 2	2784
May	1st to 10th	Day	41% 10% 23% 20% 6%	6460
	11th to 20th	Day	52% 13% 19% 14% 2	6651
	21st to end	Day	48% 14% 20% 15% 2	7571
June	1st to 10th	Day	58% 11% 12% 13% 4 1	3001
	11th to 20th	Day	63% 12% 11% 12% 3	3120
	21st to end	Day	50% 12% 16% 16% 6% 1	3200
July	1st to 10th	Day	25% 9% 17% 30% 18% 2	6981
	11th to 20th	Day	29% 10% 22% 25% 13% 1	6657
	21st to end	Day	31% 10% 23% 22% 12% 2	6681
August	1st to 10th	Day	30% 11% 15% 33% 11%	4524
	11th to 20th	Day	36% 13% 23% 21% 7%	4448
	21st to end	Day	38% 12% 25% 19% 5%	4573
September	1st to 10th	Day	43% 10% 19% 21% 6% 1	2400
	11th to 20th	Day	47% 11% 16% 20% 6%	2290
	21st to end	Day	53% 11% 17% 15% 4	2200
October	1st to 10th	Day	43% 14% 27% 14% 2	3441
	11th to 20th	Day	48% 13% 22% 15% 2	2965
	21st to end	Day	49% 17% 21% 11% 2	3200
November	1st to 10th	Day	68% 14% 9% 8% 1	1828
	11th to 20th	Day	66% 15% 10% 5% 4	1482
	21st to end	Day	65% 17% 9% 4 4 1	1470
December	1st to 10th	Day	52% 20% 19% 7% 1	2360
	11th to 20th	Day	70% 14% 10% 5% 1	2714
	21st to end	Day	54% 19% 20% 5% 2	3575
January	1st to 10th	Night	66% 15% 13% 5% 1	8769
	11th to 20th	Night	43% 17% 19% 12% 7% 1	8360
	21st to end	Night	56% 14% 16% 13% 1	8994
February	1st to 10th	Night	65% 11% 11% 7% 5% 1	2940
	11th to 20th	Night	60% 14% 12% 9% 5%	2718
	21st to end	Night	60% 12% 13% 9% 4 1	2076
March	1st to 10th	Night	47% 14% 21% 14% 5%	5496
	11th to 20th	Night	43% 16% 20% 16% 5%	5408
	21st to end	Night	53% 19% 14% 12% 3	5192
April	1st to 10th	Night	50% 18% 19% 10% 2	2100
	11th to 20th	Night	48% 15% 19% 14% 5%	1925
	21st to end	Night	44% 16% 19% 17% 4	1832
May	1st to 10th	Night	37% 10% 26% 22% 4 1	3717
	11th to 20th	Night	42% 15% 23% 18% 3	3465
	21st to end	Night	35% 15% 25% 22% 3	3547
June	1st to 10th	Night	45% 14% 13% 22% 5% 1	1400
	11th to 20th	Night	55% 14% 15% 12% 5%	1273
	21st to end	Night	35% 15% 20% 24% 6% 1	1200
July	1st to 10th	Night	21% 7% 20% 33% 17% 1	2866
	11th to 20th	Night	27% 9% 21% 30% 13% 1	3177
	21st to end	Night	26% 10% 26% 25% 12% 1	3857
August	1st to 10th	Night	27% 10% 18% 36% 8%	2601
	11th to 20th	Night	28% 13% 31% 21% 7%	2666
	21st to end	Night	32% 13% 30% 19% 6%	3334
September	1st to 10th	Night	36% 9% 20% 27% 7%	2000
	11th to 20th	Night	39% 13% 18% 20% 9% 1	2110
	21st to end	Night	40% 14% 22% 18% 6%	2200
October	1st to 10th	Night	36% 18% 27% 15% 4	3755
	11th to 20th	Night	44% 11% 27% 16% 2	4183
	21st to end	Night	45% 16% 24% 14% 1	4600
November	1st to 10th	Night	69% 12% 10% 6% 3	2688
	11th to 20th	Night	70% 13% 9% 5% 3	3115
	21st to end	Night	72% 12% 8% 5% 3	3150
December	1st to 10th	Night	57% 22% 15% 6% 1	5040
	11th to 20th	Night	70% 14% 8% 6% 1	5697
	21st to end	Night	65% 16% 12% 6% 1	7623

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% 12% 37% 30% 10% 4	220
	11th to 20th	Day	5% 18% 35% 30% 11% 1	220
	21st to end	Day	5% 18% 39% 28% 7% 3	242
February	1st to 10th	Day	9% 22% 40% 19% 8% 3	220
	11th to 20th	Day	5% 16% 36% 32% 9% 2	341
	21st to end	Day	6% 17% 41% 27% 8% 2	446
March	1st to 10th	Day	8% 23% 38% 20% 9% 2	540
	11th to 20th	Day	11% 20% 36% 22% 9% 2	540
	21st to end	Day	15% 21% 32% 22% 9% 2	594
April	1st to 10th	Day	12% 23% 34% 21% 9% 1	540
	11th to 20th	Day	9% 22% 33% 23% 10% 2	532
	21st to end	Day	12% 20% 30% 23% 11% 4	540
May	1st to 10th	Day	17% 17% 29% 23% 13% 3	543
	11th to 20th	Day	15% 11% 27% 28% 16% 3	668
	21st to end	Day	17% 13% 22% 28% 16% 3	844
June	1st to 10th	Day	19% 18% 29% 24% 9% 1	731
	11th to 20th	Day	20% 16% 29% 23% 11% 2	850
	21st to end	Day	13% 14% 28% 30% 13% 2	930
July	1st to 10th	Day	13% 13% 28% 31% 14% 2	840
	11th to 20th	Day	12% 13% 30% 28% 15% 2	702
	21st to end	Day	6% 14% 32% 29% 15% 4	575
August	1st to 10th	Day	8% 11% 29% 32% 15% 4	527
	11th to 20th	Day	10% 14% 34% 28% 11% 3	517
	21st to end	Day	11% 16% 24% 29% 14% 5%	583
September	1st to 10th	Day	13% 16% 30% 22% 13% 6%	530
	11th to 20th	Day	14% 12% 30% 30% 12% 2	530
	21st to end	Day	15% 20% 38% 19% 7% 1	530
October	1st to 10th	Day	15% 14% 34% 25% 11% 2	530
	11th to 20th	Day	13% 18% 33% 23% 12% 1	350
	21st to end	Day	13% 18% 37% 24% 6% 2	363
November	1st to 10th	Day	12% 17% 40% 22% 8% 2	316
	11th to 20th	Day	13% 20% 37% 22% 7%	220
	21st to end	Day	6% 20% 37% 24% 7% 6%	220
December	1st to 10th	Day	9% 12% 38% 29% 9% 3	220
	11th to 20th	Day	10% 15% 43% 24% 8%	220
	21st to end	Day	5% 14% 35% 33% 10% 3	242
January	1st to 10th	Night	11% 16% 38% 27% 7% 1	1050
	11th to 20th	Night	9% 14% 39% 30% 7% 1	889
	21st to end	Night	8% 13% 39% 30% 9% 1	924
February	1st to 10th	Night	9% 15% 38% 26% 11% 1	840
	11th to 20th	Night	8% 12% 32% 37% 10% 1	824
	21st to end	Night	7% 11% 35% 31% 15% 1	692
March	1st to 10th	Night	7% 13% 37% 31% 13%	840
	11th to 20th	Night	8% 14% 34% 34% 10%	840
	21st to end	Night	9% 13% 34% 28% 14% 2	924
April	1st to 10th	Night	7% 12% 28% 37% 16% 1	840
	11th to 20th	Night	9% 10% 34% 35% 12%	677
	21st to end	Night	8% 15% 25% 37% 15% 1	572
May	1st to 10th	Night	9% 9% 22% 40% 20%	420
	11th to 20th	Night	10% 7% 27% 37% 19% 1	414
	21st to end	Night	13% 9% 21% 36% 20% 1	455
June	1st to 10th	Night	17% 7% 27% 35% 12% 1	400
	11th to 20th	Night	14% 12% 29% 29% 17% 1	400
	21st to end	Night	9% 7% 22% 42% 20% 1	400
July	1st to 10th	Night	10% 4 17% 45% 24% 1	390
	11th to 20th	Night	9% 6% 23% 40% 20% 1	388
	21st to end	Night	6% 4 15% 46% 28% 1	438
August	1st to 10th	Night	7% 4 12% 42% 33% 2	398
	11th to 20th	Night	7% 5% 16% 42% 29% 2	435
	21st to end	Night	8% 7% 19% 40% 25% 1	710
September	1st to 10th	Night	11% 7% 21% 35% 22% 4	800
	11th to 20th	Night	12% 8% 17% 37% 22% 4	800
	21st to end	Night	15% 9% 28% 35% 13% 1	800
October	1st to 10th	Night	11% 9% 28% 38% 14% 1	800
	11th to 20th	Night	13% 11% 32% 33% 10% 1	800
	21st to end	Night	12% 15% 36% 26% 10% 1	880
November	1st to 10th	Night	17% 16% 38% 23% 6% 1	820
	11th to 20th	Night	11% 18% 38% 26% 7%	1015
	21st to end	Night	11% 14% 34% 31% 9% 1	1050
December	1st to 10th	Night	11% 12% 39% 27% 10% 1	1050
	11th to 20th	Night	12% 14% 36% 29% 9%	1050
	21st to end	Night	9% 13% 40% 28% 9% 1	1155

Page generated at 2026-05-28 23:53:31. Version ac07

Copyright © 2026 Attilla Danko.