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 2025-02-06.

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% 11% 5% 12% 8% 7% 6% 5% 7% 7% 26%	112536
	Night	4 11% 5% 12% 8% 7% 6% 5% 7% 8% 26%	114347
Transparency	Day	51% 13% 15% 15% 6% 1	112292
	Night	52% 14% 16% 13% 4	114238
Seeing	Day	13% 16% 31% 26% 11% 2	15782
	Night	10% 12% 31% 32% 13% 1	24531

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 12% 9% 23% 13% 9% 8% 4 7% 5% 9%	3179
	11th to 20th	Day	2 11% 4 12% 8% 6% 7% 6% 9% 11% 26%	3547
	21st to end	Day	4 15% 8% 15% 7% 6% 5% 5% 6% 6% 24%	4004
February	1st to 10th	Day	2 14% 6% 14% 11% 10% 9% 5% 7% 7% 15%	1560
	11th to 20th	Day	3 9% 6% 16% 9% 8% 9% 7% 8% 7% 17%	1614
	21st to end	Day	1 12% 5% 17% 11% 13% 8% 6% 6% 6% 14%	1570
March	1st to 10th	Day	1 12% 6% 17% 11% 8% 9% 6% 7% 6% 17%	3138
	11th to 20th	Day	2 13% 5% 14% 9% 7% 7% 6% 6% 6% 26%	3290
	21st to end	Day	2 20% 7% 17% 9% 8% 6% 5% 6% 5% 14%	4103
April	1st to 10th	Day	5% 19% 6% 16% 9% 8% 6% 6% 5% 6% 15%	2280
	11th to 20th	Day	5% 16% 6% 14% 7% 6% 6% 6% 7% 7% 19%	2391
	21st to end	Day	7% 20% 6% 12% 7% 5% 6% 5% 7% 6% 19%	2518
May	1st to 10th	Day	9% 16% 5% 10% 6% 5% 5% 5% 6% 8% 23%	4420
	11th to 20th	Day	10% 13% 4 9% 7% 6% 6% 5% 7% 8% 25%	4532
	21st to end	Day	15% 17% 5% 11% 7% 6% 7% 5% 7% 6% 15%	5161
June	1st to 10th	Day	17% 14% 4 10% 6% 5% 5% 5% 7% 6% 21%	2850
	11th to 20th	Day	17% 13% 4 11% 7% 6% 6% 4 6% 7% 18%	2964
	21st to end	Day	10% 9% 3 9% 7% 6% 7% 6% 7% 8% 28%	3040
July	1st to 10th	Day	6% 4 2 6% 5% 4 5% 4 8% 8% 48%	4932
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 7% 8% 53%	4712
	21st to end	Day	4 5% 2 7% 5% 5% 5% 5% 7% 9% 46%	4790
August	1st to 10th	Day	4 4 2 6% 6% 6% 6% 5% 7% 8% 46%	4401
	11th to 20th	Day	7% 5% 3 9% 6% 6% 6% 5% 8% 9% 36%	4268
	21st to end	Day	7% 7% 3 8% 5% 5% 6% 5% 6% 8% 39%	4434
September	1st to 10th	Day	8% 8% 4 9% 6% 5% 5% 4 6% 8% 37%	2280
	11th to 20th	Day	10% 9% 5% 9% 7% 6% 6% 4 6% 7% 31%	2176
	21st to end	Day	9% 11% 5% 12% 7% 6% 5% 4 6% 8% 27%	2090
October	1st to 10th	Day	8% 9% 3 10% 7% 6% 6% 5% 7% 10% 29%	3336
	11th to 20th	Day	6% 10% 4 11% 6% 7% 7% 4 7% 9% 28%	2874
	21st to end	Day	4 13% 5% 12% 8% 8% 7% 6% 8% 8% 22%	3101
November	1st to 10th	Day	5% 16% 7% 16% 10% 7% 8% 6% 7% 6% 13%	1739
	11th to 20th	Day	3 13% 6% 15% 11% 9% 9% 6% 7% 7% 14%	1412
	21st to end	Day	3 14% 6% 14% 13% 10% 9% 5% 8% 6% 13%	1400
December	1st to 10th	Day	2 9% 4 13% 9% 8% 7% 5% 9% 10% 25%	2290
	11th to 20th	Day	1 13% 6% 23% 12% 11% 8% 6% 7% 6% 7%	2642
	21st to end	Day	1 11% 6% 18% 12% 10% 9% 6% 8% 7% 11%	3498
January	1st to 10th	Night	2 14% 10% 23% 11% 10% 7% 5% 5% 4 8%	6766
	11th to 20th	Night	2 9% 4 12% 8% 8% 9% 9% 10% 9% 20%	6394
	21st to end	Night	4 18% 9% 13% 6% 6% 5% 4 5% 6% 23%	6952
February	1st to 10th	Night	3 14% 6% 17% 11% 9% 8% 6% 7% 6% 12%	2730
	11th to 20th	Night	2 14% 6% 15% 8% 8% 8% 5% 8% 7% 21%	2451
	21st to end	Night	1 12% 5% 15% 11% 9% 7% 5% 8% 7% 20%	1884
March	1st to 10th	Night	1 9% 4 16% 10% 8% 8% 5% 8% 8% 22%	3736
	11th to 20th	Night	2 14% 3 10% 7% 6% 6% 6% 7% 8% 31%	3689
	21st to end	Night	2 17% 6% 14% 7% 6% 6% 6% 7% 8% 21%	3536
April	1st to 10th	Night	3 14% 5% 10% 7% 7% 8% 6% 8% 8% 25%	1900
	11th to 20th	Night	4 12% 5% 11% 7% 7% 5% 5% 9% 8% 28%	1740
	21st to end	Night	5% 12% 4 8% 6% 5% 6% 5% 8% 8% 33%	1658
May	1st to 10th	Night	6% 13% 4 10% 6% 5% 6% 4 6% 7% 32%	2540
	11th to 20th	Night	8% 8% 2 8% 5% 5% 6% 5% 7% 11% 35%	2360
	21st to end	Night	13% 9% 3 8% 6% 5% 5% 5% 7% 9% 29%	2414
June	1st to 10th	Night	14% 11% 2 8% 5% 5% 5% 5% 5% 7% 32%	1330
	11th to 20th	Night	11% 11% 4 11% 8% 6% 6% 5% 6% 7% 25%	1210
	21st to end	Night	6% 6% 2 5% 6% 5% 5% 5% 8% 11% 39%	1140
July	1st to 10th	Night	3 4 1 5% 3 4 4 4 5% 6% 62%	2023
	11th to 20th	Night	3 3 1 4 3 3 4 4 5% 8% 61%	2245
	21st to end	Night	3 3 1 4 4 5% 5% 4 7% 9% 56%	2762
August	1st to 10th	Night	5% 4 2 4 4 4 4 4 7% 8% 53%	2529
	11th to 20th	Night	6% 6% 2 4 3 4 5% 5% 8% 10% 48%	2560
	21st to end	Night	7% 7% 2 6% 4 5% 4 4 7% 9% 45%	3232
September	1st to 10th	Night	7% 8% 3 6% 4 6% 5% 3 6% 6% 46%	1900
	11th to 20th	Night	10% 7% 2 6% 4 7% 5% 5% 5% 6% 42%	2004
	21st to end	Night	10% 7% 2 7% 4 5% 5% 6% 7% 8% 38%	2090
October	1st to 10th	Night	5% 6% 3 7% 7% 7% 6% 5% 8% 11% 36%	3640
	11th to 20th	Night	8% 9% 3 9% 6% 5% 5% 4 6% 8% 36%	4054
	21st to end	Night	5% 9% 4 10% 8% 7% 5% 4 8% 9% 31%	4457
November	1st to 10th	Night	8% 17% 7% 14% 10% 8% 6% 5% 7% 6% 14%	2557
	11th to 20th	Night	3 14% 5% 15% 11% 10% 9% 6% 6% 6% 14%	2966
	21st to end	Night	3 17% 7% 17% 11% 9% 8% 5% 6% 6% 11%	3000
December	1st to 10th	Night	3 10% 5% 13% 11% 11% 8% 7% 8% 9% 16%	4890
	11th to 20th	Night	1 12% 6% 21% 14% 11% 8% 5% 7% 6% 9%	5550
	21st to end	Night	2 14% 7% 19% 12% 12% 8% 5% 6% 5% 10%	7458

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	71% 11% 9% 7% 1	3179
	11th to 20th	Day	48% 11% 15% 15% 8% 3	3571
	21st to end	Day	58% 11% 16% 13% 2	4004
February	1st to 10th	Day	67% 12% 10% 6% 5%	1560
	11th to 20th	Day	61% 16% 11% 8% 4	1622
	21st to end	Day	66% 13% 9% 6% 5% 1	1570
March	1st to 10th	Day	59% 16% 10% 9% 6%	3138
	11th to 20th	Day	49% 15% 20% 15% 2	3290
	21st to end	Day	62% 15% 12% 7% 3	4103
April	1st to 10th	Day	68% 12% 12% 7% 1	2280
	11th to 20th	Day	61% 11% 14% 11% 3	2391
	21st to end	Day	63% 13% 13% 10% 2	2518
May	1st to 10th	Day	55% 11% 17% 14% 3	4420
	11th to 20th	Day	51% 13% 17% 17% 2	4536
	21st to end	Day	62% 16% 12% 8% 2	5162
June	1st to 10th	Day	60% 11% 11% 12% 4 1	2850
	11th to 20th	Day	65% 12% 10% 10% 3	2964
	21st to end	Day	51% 12% 15% 16% 6% 1	3040
July	1st to 10th	Day	29% 9% 13% 25% 21% 3	4857
	11th to 20th	Day	27% 8% 15% 31% 18% 2	4631
	21st to end	Day	30% 9% 16% 25% 16% 3	4639
August	1st to 10th	Day	29% 10% 14% 34% 11%	4384
	11th to 20th	Day	37% 13% 23% 21% 7%	4310
	21st to end	Day	39% 12% 25% 19% 4	4433
September	1st to 10th	Day	44% 10% 18% 21% 6% 1	2280
	11th to 20th	Day	49% 11% 16% 19% 6%	2176
	21st to end	Day	54% 11% 16% 15% 4	2090
October	1st to 10th	Day	44% 13% 26% 14% 2	3336
	11th to 20th	Day	49% 13% 22% 15% 1	2874
	21st to end	Day	50% 17% 21% 11% 2	3101
November	1st to 10th	Day	69% 13% 9% 8% 1	1739
	11th to 20th	Day	67% 15% 9% 6% 4	1412
	21st to end	Day	66% 17% 9% 4 4 1	1400
December	1st to 10th	Day	52% 20% 19% 7% 1	2290
	11th to 20th	Day	70% 15% 10% 4 1	2644
	21st to end	Day	55% 18% 20% 4 2	3498
January	1st to 10th	Night	75% 13% 7% 4 1	6766
	11th to 20th	Night	49% 16% 13% 12% 7% 2	6432
	21st to end	Night	61% 10% 16% 11% 2	6952
February	1st to 10th	Night	69% 11% 10% 6% 4 1	2730
	11th to 20th	Night	62% 14% 10% 9% 5%	2453
	21st to end	Night	62% 13% 11% 9% 4 1	1884
March	1st to 10th	Night	53% 15% 15% 11% 6%	3736
	11th to 20th	Night	44% 18% 21% 13% 3	3690
	21st to end	Night	56% 18% 13% 10% 3	3536
April	1st to 10th	Night	53% 19% 16% 10% 2	1900
	11th to 20th	Night	49% 15% 17% 14% 5%	1740
	21st to end	Night	47% 16% 18% 16% 4	1658
May	1st to 10th	Night	48% 13% 19% 17% 3	2540
	11th to 20th	Night	37% 17% 21% 21% 4	2360
	21st to end	Night	46% 17% 16% 17% 3	2414
June	1st to 10th	Night	47% 14% 13% 21% 5% 1	1330
	11th to 20th	Night	56% 14% 14% 11% 5%	1210
	21st to end	Night	35% 15% 20% 24% 6% 1	1140
July	1st to 10th	Night	22% 7% 13% 33% 23% 2	1990
	11th to 20th	Night	22% 7% 16% 35% 17% 2	2203
	21st to end	Night	22% 8% 20% 31% 18% 1	2674
August	1st to 10th	Night	26% 11% 18% 38% 8%	2521
	11th to 20th	Night	28% 13% 31% 21% 7%	2584
	21st to end	Night	33% 13% 31% 18% 5%	3232
September	1st to 10th	Night	37% 9% 19% 27% 7%	1900
	11th to 20th	Night	40% 13% 18% 19% 10% 1	2004
	21st to end	Night	41% 14% 21% 18% 7%	2090
October	1st to 10th	Night	37% 18% 26% 15% 4	3640
	11th to 20th	Night	45% 11% 27% 15% 2	4054
	21st to end	Night	46% 16% 23% 14% 1	4457
November	1st to 10th	Night	70% 11% 9% 6% 3	2557
	11th to 20th	Night	71% 12% 9% 5% 3	2966
	21st to end	Night	73% 11% 7% 5% 3	3000
December	1st to 10th	Night	57% 22% 15% 6% 1	4890
	11th to 20th	Night	71% 14% 7% 6% 1	5547
	21st to end	Night	65% 16% 12% 5% 1	7458

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	8% 11% 36% 31% 11% 5%	200
	11th to 20th	Day	6% 17% 34% 31% 12% 1	200
	21st to end	Day	5% 19% 39% 27% 7% 3	220
February	1st to 10th	Day	10% 22% 41% 18% 7% 2	190
	11th to 20th	Day	6% 17% 37% 30% 9% 2	286
	21st to end	Day	5% 16% 40% 28% 9% 2	382
March	1st to 10th	Day	7% 24% 38% 19% 9% 2	460
	11th to 20th	Day	9% 21% 36% 23% 10% 2	460
	21st to end	Day	14% 19% 31% 24% 9% 2	506
April	1st to 10th	Day	13% 23% 35% 21% 8%	460
	11th to 20th	Day	10% 22% 32% 23% 10% 2	452
	21st to end	Day	13% 22% 31% 22% 10% 3	460
May	1st to 10th	Day	19% 17% 27% 23% 11% 3	463
	11th to 20th	Day	15% 11% 27% 29% 16% 3	578
	21st to end	Day	18% 13% 22% 28% 16% 3	734
June	1st to 10th	Day	20% 18% 28% 24% 9% 1	680
	11th to 20th	Day	21% 16% 28% 22% 10% 2	794
	21st to end	Day	13% 15% 27% 30% 13% 2	870
July	1st to 10th	Day	13% 12% 28% 31% 14% 2	784
	11th to 20th	Day	12% 13% 29% 28% 15% 2	653
	21st to end	Day	5% 15% 33% 29% 15% 3	531
August	1st to 10th	Day	9% 11% 29% 32% 15% 4	487
	11th to 20th	Day	10% 13% 31% 30% 12% 3	477
	21st to end	Day	12% 17% 25% 30% 12% 3	539
September	1st to 10th	Day	14% 18% 32% 21% 11% 4	490
	11th to 20th	Day	15% 13% 30% 30% 10% 2	490
	21st to end	Day	16% 20% 36% 19% 8% 1	490
October	1st to 10th	Day	16% 14% 32% 26% 10% 1	490
	11th to 20th	Day	14% 19% 32% 22% 11% 1	319
	21st to end	Day	15% 18% 35% 24% 7% 2	330
November	1st to 10th	Day	11% 17% 39% 23% 8% 1	287
	11th to 20th	Day	12% 21% 38% 24% 6% 1	200
	21st to end	Day	7% 20% 38% 22% 8% 7%	200
December	1st to 10th	Day	8% 12% 36% 31% 10% 4	200
	11th to 20th	Day	7% 16% 44% 25% 9%	200
	21st to end	Day	5% 14% 34% 33% 10% 3	220
January	1st to 10th	Night	11% 17% 38% 27% 7% 1	1000
	11th to 20th	Night	9% 13% 39% 29% 8% 1	847
	21st to end	Night	8% 13% 40% 28% 10% 1	880
February	1st to 10th	Night	9% 16% 38% 25% 11% 1	780
	11th to 20th	Night	9% 13% 33% 34% 10% 1	744
	21st to end	Night	7% 11% 33% 32% 16% 1	628
March	1st to 10th	Night	7% 14% 37% 30% 12%	760
	11th to 20th	Night	7% 14% 34% 34% 10%	760
	21st to end	Night	8% 14% 33% 29% 15% 2	836
April	1st to 10th	Night	7% 13% 28% 36% 15% 1	760
	11th to 20th	Night	9% 10% 33% 35% 12%	612
	21st to end	Night	8% 15% 25% 36% 14% 1	518
May	1st to 10th	Night	9% 9% 23% 38% 21%	380
	11th to 20th	Night	10% 7% 25% 37% 21% 1	374
	21st to end	Night	15% 9% 20% 35% 19% 1	411
June	1st to 10th	Night	18% 7% 27% 34% 12% 1	380
	11th to 20th	Night	14% 11% 28% 29% 16% 1	380
	21st to end	Night	9% 6% 23% 42% 20% 1	380
July	1st to 10th	Night	10% 5% 17% 44% 24%	370
	11th to 20th	Night	9% 6% 23% 40% 20% 1	368
	21st to end	Night	7% 4 15% 47% 27% 1	416
August	1st to 10th	Night	7% 3 12% 43% 33% 2	378
	11th to 20th	Night	7% 5% 15% 41% 30% 2	413
	21st to end	Night	9% 8% 19% 41% 23% 1	674
September	1st to 10th	Night	12% 7% 22% 35% 21% 3	760
	11th to 20th	Night	12% 8% 18% 38% 20% 4	760
	21st to end	Night	15% 10% 26% 34% 14% 1	760
October	1st to 10th	Night	11% 9% 28% 37% 13% 1	760
	11th to 20th	Night	13% 11% 32% 33% 10% 1	760
	21st to end	Night	13% 15% 36% 25% 10% 1	836
November	1st to 10th	Night	17% 15% 38% 23% 6% 1	780
	11th to 20th	Night	11% 19% 38% 25% 6%	966
	21st to end	Night	11% 14% 35% 30% 10% 1	1000
December	1st to 10th	Night	11% 12% 39% 28% 10% 1	1000
	11th to 20th	Night	11% 14% 36% 29% 9%	1000
	21st to end	Night	9% 13% 40% 27% 9% 1	1100

Page generated at 2025-02-03 01:05:54. Version ac07

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