Goldendale Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goldendale Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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	8% 7% 2 6% 4 4 4 3 5% 7% 50%	135286
	Night	10% 7% 3 6% 4 4 4 3 5% 7% 46%	130733
Transparency	Day	21% 39% 8% 15% 12% 5%	130016
	Night	23% 40% 8% 15% 10% 3	127007
Seeing	Day	14% 17% 29% 24% 13% 3	15526
	Night	14% 12% 25% 30% 17% 3	24480

By Month

Percentage Cloud Cover SW (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	21% 17% 5% 15% 7% 6% 5% 4 5% 5% 10%	3639
	11th to 20th	Day	14% 12% 3 7% 4 3 4 4 6% 6% 37%	3640
	21st to end	Day	19% 12% 4 9% 4 4 4 3 5% 4 31%	4096
February	1st to 10th	Day	14% 16% 4 10% 5% 5% 5% 5% 5% 6% 27%	1800
	11th to 20th	Day	14% 12% 3 8% 6% 4 5% 4 6% 6% 32%	1755
	21st to end	Day	11% 10% 3 9% 6% 6% 6% 6% 6% 7% 28%	1649
March	1st to 10th	Day	8% 9% 3 8% 5% 5% 7% 5% 9% 10% 32%	4518
	11th to 20th	Day	9% 12% 3 8% 4 4 4 3 5% 7% 39%	4952
	21st to end	Day	9% 10% 3 11% 7% 6% 7% 5% 7% 9% 24%	5786
April	1st to 10th	Day	8% 10% 3 8% 6% 6% 6% 5% 7% 9% 33%	2400
	11th to 20th	Day	8% 9% 3 6% 5% 5% 5% 4 6% 8% 41%	2369
	21st to end	Day	5% 6% 2 6% 5% 5% 5% 4 7% 9% 45%	2555
May	1st to 10th	Day	9% 5% 1 4 3 4 4 3 5% 6% 55%	6320
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 6% 8% 53%	6277
	21st to end	Day	5% 4 2 4 4 5% 5% 4 6% 8% 53%	6902
June	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 49%	2800
	11th to 20th	Day	4 4 2 5% 3 4 4 4 6% 9% 55%	2800
	21st to end	Day	3 3 1 4 2 2 3 3 4 6% 68%	2800
July	1st to 10th	Day	1 1 1 2 1 1 2 2 3 4 83%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 3 3 85%	6320
	21st to end	Day	2 2 1 2 1 2 2 2 3 5% 79%	6880
August	1st to 10th	Day	3 3 1 3 2 2 3 2 5% 5% 70%	6150
	11th to 20th	Day	2 2 1 3 2 2 3 3 5% 6% 72%	5796
	21st to end	Day	5% 4 2 5% 3 3 3 2 4 6% 63%	5981
September	1st to 10th	Day	3 2 1 2 2 2 3 2 5% 6% 73%	2317
	11th to 20th	Day	4 4 1 5% 4 4 4 4 5% 6% 60%	2280
	21st to end	Day	7% 5% 2 4 4 3 4 3 4 6% 58%	2042
October	1st to 10th	Day	5% 4 1 4 2 3 4 3 6% 7% 59%	3180
	11th to 20th	Day	7% 6% 3 7% 5% 5% 5% 4 7% 8% 43%	3161
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 5% 8% 8% 36%	3201
November	1st to 10th	Day	12% 11% 4 11% 5% 5% 5% 4 7% 8% 28%	1749
	11th to 20th	Day	16% 12% 5% 11% 6% 5% 6% 5% 5% 7% 22%	1600
	21st to end	Day	14% 11% 4 10% 7% 5% 6% 4 6% 6% 28%	1600
December	1st to 10th	Day	10% 8% 3 10% 6% 5% 5% 4 6% 11% 31%	2620
	11th to 20th	Day	20% 16% 6% 15% 8% 6% 5% 4 4 4 12%	3028
	21st to end	Day	18% 15% 7% 13% 6% 6% 5% 4 5% 5% 15%	4004
January	1st to 10th	Night	21% 15% 5% 12% 8% 6% 6% 4 5% 6% 13%	6306
	11th to 20th	Night	15% 10% 3 7% 4 3 4 3 4 7% 40%	6320
	21st to end	Night	18% 10% 3 8% 4 5% 5% 3 4 5% 35%	6847
February	1st to 10th	Night	14% 15% 4 9% 6% 5% 4 4 5% 7% 29%	2600
	11th to 20th	Night	12% 12% 3 7% 6% 4 4 3 5% 6% 36%	2532
	21st to end	Night	11% 13% 5% 8% 4 5% 4 4 6% 7% 33%	1980
March	1st to 10th	Night	7% 8% 3 8% 5% 6% 6% 5% 8% 9% 36%	5376
	11th to 20th	Night	9% 8% 3 8% 4 5% 4 4 5% 7% 43%	5044
	21st to end	Night	9% 9% 3 9% 6% 6% 7% 6% 8% 8% 29%	5187
April	1st to 10th	Night	9% 8% 3 6% 4 5% 5% 4 6% 10% 38%	2000
	11th to 20th	Night	8% 7% 2 5% 4 5% 3 3 7% 6% 51%	1979
	21st to end	Night	6% 5% 2 7% 4 4 4 6% 7% 10% 46%	1842
May	1st to 10th	Night	8% 6% 2 4 3 3 2 2 4 5% 60%	3640
	11th to 20th	Night	4 4 2 4 3 2 3 3 5% 8% 61%	3616
	21st to end	Night	7% 5% 2 3 2 3 3 3 5% 8% 59%	3972
June	1st to 10th	Night	10% 5% 1 4 4 4 4 4 6% 7% 51%	1600
	11th to 20th	Night	5% 5% 2 3 3 3 3 3 4 8% 60%	1600
	21st to end	Night	2 3 1 5% 3 3 3 3 4 4 68%	1600
July	1st to 10th	Night	1 1 2 1 2 2 2 3 4 82%	3640
	11th to 20th	Night	1 1 1 1 1 2 2 3 3 85%	3640
	21st to end	Night	2 2 1 1 1 1 1 4 6% 81%	3970
August	1st to 10th	Night	3 2 1 3 3 3 3 3 4 6% 69%	3641
	11th to 20th	Night	3 2 1 3 2 2 3 3 4 5% 72%	4052
	21st to end	Night	3 4 1 5% 3 3 3 3 5% 6% 66%	5015
September	1st to 10th	Night	2 1 2 2 2 3 2 5% 5% 74%	1930
	11th to 20th	Night	4 3 1 4 4 4 4 3 4 5% 63%	1900
	21st to end	Night	6% 4 1 4 3 3 4 3 6% 6% 62%	2136
October	1st to 10th	Night	4 4 1 4 3 3 3 3 5% 7% 64%	3800
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	3777
	21st to end	Night	10% 6% 2 6% 4 5% 6% 5% 7% 8% 41%	4358
November	1st to 10th	Night	16% 9% 3 8% 4 4 5% 4 6% 7% 35%	2545
	11th to 20th	Night	18% 10% 3 8% 5% 5% 5% 5% 6% 7% 29%	2800
	21st to end	Night	12% 9% 3 10% 5% 5% 5% 5% 6% 7% 33%	2800
December	1st to 10th	Night	9% 7% 3 9% 5% 6% 4 3 5% 8% 41%	4560
	11th to 20th	Night	23% 16% 4 11% 7% 6% 5% 4 5% 5% 14%	5176
	21st to end	Night	21% 12% 5% 10% 5% 5% 5% 4 5% 5% 24%	6952

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% 35% 9% 7%	3639
	11th to 20th	Day	32% 30% 14% 18% 6%	3640
	21st to end	Day	41% 32% 3 14% 9%	4096
February	1st to 10th	Day	25% 64% 6% 4 1	1800
	11th to 20th	Day	24% 64% 6% 4 2	1764
	21st to end	Day	20% 66% 5% 4 5%	1649
March	1st to 10th	Day	28% 33% 11% 17% 10% 1	4518
	11th to 20th	Day	30% 30% 9% 24% 7%	4952
	21st to end	Day	38% 34% 13% 12% 3	5786
April	1st to 10th	Day	16% 64% 8% 9% 3	2400
	11th to 20th	Day	13% 64% 7% 9% 6% 1	2372
	21st to end	Day	11% 63% 8% 12% 5% 1	2555
May	1st to 10th	Day	20% 29% 6% 17% 25% 4	6320
	11th to 20th	Day	18% 29% 12% 25% 13% 2	6280
	21st to end	Day	16% 32% 17% 26% 9% 1	6904
June	1st to 10th	Day	8% 62% 6% 14% 9% 2	2800
	11th to 20th	Day	8% 61% 5% 14% 9% 2	2800
	21st to end	Day	6% 60% 6% 14% 11% 3	2800
July	1st to 10th	Day	6% 24% 2 15% 25% 27%	6251
	11th to 20th	Day	4 25% 2 10% 25% 34%	6245
	21st to end	Day	10% 25% 5% 26% 25% 10%	6681
August	1st to 10th	Day	11% 35% 2 8% 22% 21%	4476
	11th to 20th	Day	10% 36% 7% 30% 14% 3	4195
	21st to end	Day	17% 36% 6% 16% 22% 4	4311
September	1st to 10th	Day	5% 59% 6% 16% 10% 3	2317
	11th to 20th	Day	11% 60% 8% 11% 7% 2	2280
	21st to end	Day	12% 61% 7% 12% 7% 1	2042
October	1st to 10th	Day	12% 37% 8% 23% 18% 1	3180
	11th to 20th	Day	25% 39% 11% 15% 9%	3161
	21st to end	Day	28% 39% 9% 19% 4	3201
November	1st to 10th	Day	22% 59% 7% 10% 2	1749
	11th to 20th	Day	26% 60% 7% 5% 2 1	1600
	21st to end	Day	23% 60% 6% 6% 4 1	1600
December	1st to 10th	Day	26% 41% 13% 16% 3	2620
	11th to 20th	Day	51% 38% 6% 3 1	3028
	21st to end	Day	50% 35% 8% 6% 1	4004
January	1st to 10th	Night	48% 38% 8% 6% 1	6306
	11th to 20th	Night	30% 29% 15% 21% 5%	6320
	21st to end	Night	38% 34% 4 14% 10%	6847
February	1st to 10th	Night	25% 63% 7% 4 1	2600
	11th to 20th	Night	22% 63% 6% 7% 2 1	2534
	21st to end	Night	19% 64% 4 9% 3 1	1980
March	1st to 10th	Night	26% 33% 11% 19% 9% 1	5376
	11th to 20th	Night	28% 30% 11% 22% 8%	5044
	21st to end	Night	34% 36% 13% 16% 1	5187
April	1st to 10th	Night	15% 64% 8% 11% 2	2000
	11th to 20th	Night	12% 63% 7% 11% 7%	1979
	21st to end	Night	10% 63% 6% 13% 6% 1	1842
May	1st to 10th	Night	20% 29% 4 16% 29% 2	3637
	11th to 20th	Night	13% 29% 13% 28% 15% 1	3616
	21st to end	Night	13% 31% 23% 26% 8%	3972
June	1st to 10th	Night	8% 62% 5% 16% 7% 2	1600
	11th to 20th	Night	6% 62% 6% 14% 11% 1	1600
	21st to end	Night	8% 60% 6% 14% 12% 2	1600
July	1st to 10th	Night	6% 24% 3 16% 25% 25%	3600
	11th to 20th	Night	5% 24% 3 7% 31% 30%	3592
	21st to end	Night	6% 24% 5% 25% 27% 13%	3857
August	1st to 10th	Night	10% 35% 2 8% 24% 21%	2647
	11th to 20th	Night	9% 36% 7% 33% 12% 3	2929
	21st to end	Night	12% 36% 8% 18% 19% 8%	3608
September	1st to 10th	Night	5% 59% 7% 13% 12% 4	1930
	11th to 20th	Night	12% 60% 5% 14% 5% 4	1900
	21st to end	Night	10% 60% 6% 14% 8% 2	2136
October	1st to 10th	Night	10% 37% 8% 23% 23%	3800
	11th to 20th	Night	22% 38% 12% 17% 10%	3777
	21st to end	Night	27% 39% 8% 21% 6%	4358
November	1st to 10th	Night	22% 58% 6% 11% 4	2545
	11th to 20th	Night	24% 60% 7% 6% 2	2800
	21st to end	Night	20% 60% 7% 8% 5%	2800
December	1st to 10th	Night	22% 42% 9% 23% 4	4560
	11th to 20th	Night	51% 37% 7% 3 1	5176
	21st to end	Night	42% 36% 11% 8% 2	6952

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	25% 21% 25% 19% 9% 3	200
	11th to 20th	Day	25% 16% 26% 24% 9% 2	200
	21st to end	Day	22% 15% 26% 24% 12% 2	260
February	1st to 10th	Day	25% 19% 29% 20% 7% 1	400
	11th to 20th	Day	26% 22% 25% 22% 5%	395
	21st to end	Day	21% 24% 25% 21% 8% 1	414
March	1st to 10th	Day	19% 24% 32% 17% 7% 1	500
	11th to 20th	Day	20% 21% 28% 22% 8% 1	500
	21st to end	Day	22% 23% 31% 17% 7%	550
April	1st to 10th	Day	21% 22% 29% 17% 9% 2	500
	11th to 20th	Day	17% 27% 30% 16% 8% 2	492
	21st to end	Day	14% 26% 32% 19% 8% 2	500
May	1st to 10th	Day	15% 20% 30% 23% 10% 3	503
	11th to 20th	Day	17% 18% 30% 20% 12% 3	528
	21st to end	Day	12% 16% 28% 28% 12% 3	573
June	1st to 10th	Day	12% 22% 25% 25% 13% 4	530
	11th to 20th	Day	12% 25% 34% 20% 6% 2	530
	21st to end	Day	7% 16% 29% 31% 14% 3	530
July	1st to 10th	Day	3 9% 39% 30% 15% 3	526
	11th to 20th	Day	4 10% 36% 30% 16% 3	524
	21st to end	Day	3 9% 29% 33% 21% 5%	575
August	1st to 10th	Day	6% 7% 28% 30% 20% 8%	527
	11th to 20th	Day	3 8% 25% 32% 25% 7%	517
	21st to end	Day	7% 12% 28% 27% 20% 6%	583
September	1st to 10th	Day	5% 11% 27% 30% 18% 8%	503
	11th to 20th	Day	9% 10% 30% 30% 18% 3	490
	21st to end	Day	8% 17% 27% 28% 18% 2	490
October	1st to 10th	Day	12% 16% 28% 22% 17% 4	490
	11th to 20th	Day	16% 18% 21% 26% 15% 4	490
	21st to end	Day	18% 19% 27% 19% 12% 4	393
November	1st to 10th	Day	18% 20% 26% 24% 11% 1	293
	11th to 20th	Day	24% 23% 19% 23% 11% 2	200
	21st to end	Day	21% 15% 27% 22% 14% 2	200
December	1st to 10th	Day	21% 16% 23% 21% 14% 7%	200
	11th to 20th	Day	26% 18% 28% 23% 6% 1	200
	21st to end	Day	23% 21% 23% 21% 11%	220
January	1st to 10th	Night	26% 15% 22% 28% 8% 1	800
	11th to 20th	Night	24% 10% 22% 27% 15% 2	800
	21st to end	Night	21% 10% 19% 31% 17% 2	880
February	1st to 10th	Night	22% 14% 24% 25% 14% 1	800
	11th to 20th	Night	18% 16% 24% 28% 13% 1	784
	21st to end	Night	20% 17% 26% 26% 10% 1	660
March	1st to 10th	Night	16% 13% 29% 27% 14% 1	800
	11th to 20th	Night	15% 15% 26% 31% 11% 2	800
	21st to end	Night	16% 19% 30% 24% 10% 2	880
April	1st to 10th	Night	16% 16% 28% 25% 13% 2	800
	11th to 20th	Night	14% 19% 30% 21% 14% 3	791
	21st to end	Night	9% 19% 30% 27% 14% 1	642
May	1st to 10th	Night	8% 17% 28% 31% 15% 2	400
	11th to 20th	Night	11% 9% 26% 32% 20% 2	394
	21st to end	Night	9% 6% 29% 36% 17% 3	433
June	1st to 10th	Night	12% 14% 26% 30% 17% 2	400
	11th to 20th	Night	9% 17% 33% 28% 12% 1	400
	21st to end	Night	5% 12% 23% 39% 20% 1	400
July	1st to 10th	Night	4 5% 27% 41% 22% 1	390
	11th to 20th	Night	1 6% 32% 42% 16% 2	388
	21st to end	Night	2 7% 20% 43% 26% 3	438
August	1st to 10th	Night	3 6% 18% 44% 25% 5%	418
	11th to 20th	Night	4 3 19% 32% 29% 12%	594
	21st to end	Night	3 9% 24% 36% 23% 5%	880
September	1st to 10th	Night	3 6% 23% 35% 29% 4	772
	11th to 20th	Night	6% 6% 24% 28% 28% 8%	760
	21st to end	Night	8% 9% 22% 29% 28% 5%	760
October	1st to 10th	Night	11% 9% 23% 34% 21% 3	760
	11th to 20th	Night	15% 11% 20% 28% 22% 4	760
	21st to end	Night	18% 12% 24% 28% 14% 4	836
November	1st to 10th	Night	20% 12% 24% 32% 12%	780
	11th to 20th	Night	24% 13% 25% 24% 13% 1	800
	21st to end	Night	15% 12% 24% 29% 17% 3	800
December	1st to 10th	Night	18% 12% 24% 29% 16% 2	800
	11th to 20th	Night	26% 10% 24% 29% 11% 1	800
	21st to end	Night	25% 17% 25% 25% 8%	880

Page generated at 2025-08-31 22:51:02. Version ac07

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