Redmond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Redmond clear sky chart from 2005-11-06 to 2025-05-26.

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	7% 7% 2 6% 4 4 4 3 5% 6% 50%	118137
	Night	7% 8% 3 7% 4 4 4 4 5% 6% 46%	119939
Transparency	Day	35% 3 10% 23% 19% 10%	117880
	Night	38% 3 12% 25% 16% 6%	119785
Seeing	Day	12% 11% 23% 26% 19% 8%	15281
	Night	12% 6% 21% 38% 20% 2	24436

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	12% 14% 5% 11% 7% 7% 6% 4 6% 7% 20%	3639
	11th to 20th	Day	13% 12% 3 7% 5% 4 5% 3 4 5% 39%	3640
	21st to end	Day	9% 11% 3 7% 4 4 5% 3 5% 7% 42%	4297
February	1st to 10th	Day	8% 12% 4 8% 6% 6% 5% 5% 6% 7% 33%	1800
	11th to 20th	Day	8% 12% 4 8% 5% 5% 5% 4 7% 8% 33%	1765
	21st to end	Day	7% 12% 3 10% 6% 4 6% 5% 7% 8% 31%	1650
March	1st to 10th	Day	6% 10% 4 9% 6% 5% 5% 4 6% 10% 34%	4552
	11th to 20th	Day	7% 14% 4 9% 6% 5% 4 4 5% 6% 38%	5000
	21st to end	Day	8% 12% 4 11% 7% 6% 6% 5% 6% 8% 27%	5741
April	1st to 10th	Day	9% 12% 4 9% 6% 6% 6% 4 5% 7% 32%	2400
	11th to 20th	Day	9% 10% 3 8% 6% 4 4 4 5% 7% 40%	2369
	21st to end	Day	7% 7% 3 6% 4 5% 4 4 7% 7% 45%	2460
May	1st to 10th	Day	11% 8% 2 7% 4 4 4 4 5% 6% 46%	4560
	11th to 20th	Day	6% 4 2 4 3 3 3 3 5% 6% 61%	4517
	21st to end	Day	7% 6% 2 5% 4 4 5% 4 6% 8% 49%	4886
June	1st to 10th	Day	10% 8% 3 6% 5% 5% 4 4 6% 7% 43%	2660
	11th to 20th	Day	6% 5% 2 5% 3 4 4 4 5% 7% 55%	2660
	21st to end	Day	4 3 1 3 3 2 3 3 5% 6% 66%	2660
July	1st to 10th	Day	1 1 1 1 2 1 2 2 3 85%	4420
	11th to 20th	Day	2 1 1 2 1 2 2 2 2 4 81%	4420
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 82%	4790
August	1st to 10th	Day	3 2 1 3 2 2 3 3 5% 5% 71%	4219
	11th to 20th	Day	2 1 1 3 2 3 3 2 4 7% 72%	3996
	21st to end	Day	4 3 1 3 2 2 2 2 3 5% 74%	4180
September	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 77%	2280
	11th to 20th	Day	4 3 1 5% 3 3 3 4 6% 6% 61%	2280
	21st to end	Day	7% 6% 1 5% 2 3 3 3 4 6% 60%	2037
October	1st to 10th	Day	5% 4 1 4 3 3 3 3 3 4 66%	3180
	11th to 20th	Day	6% 5% 2 5% 4 5% 5% 4 6% 10% 48%	3161
	21st to end	Day	10% 8% 3 7% 5% 6% 6% 4 6% 6% 40%	3277
November	1st to 10th	Day	11% 10% 3 7% 5% 5% 5% 3 6% 8% 36%	1764
	11th to 20th	Day	10% 11% 4 8% 6% 6% 6% 5% 7% 7% 29%	1625
	21st to end	Day	9% 10% 3 8% 5% 4 5% 6% 6% 8% 36%	1600
December	1st to 10th	Day	8% 7% 3 5% 4 3 3 3 5% 8% 51%	2620
	11th to 20th	Day	11% 13% 4 10% 7% 7% 6% 5% 6% 7% 24%	3028
	21st to end	Day	8% 14% 5% 11% 7% 6% 6% 5% 7% 7% 24%	4004
January	1st to 10th	Night	13% 14% 5% 12% 7% 7% 6% 5% 6% 7% 18%	6306
	11th to 20th	Night	11% 11% 4 7% 5% 5% 5% 3 4 5% 40%	6320
	21st to end	Night	10% 12% 4 8% 5% 4 5% 3 4 5% 40%	6671
February	1st to 10th	Night	8% 14% 4 10% 6% 5% 5% 5% 6% 7% 30%	2600
	11th to 20th	Night	9% 12% 4 8% 5% 5% 5% 4 5% 7% 37%	2522
	21st to end	Night	7% 13% 4 9% 5% 5% 6% 5% 6% 8% 31%	1980
March	1st to 10th	Night	6% 10% 3 8% 5% 5% 6% 5% 7% 9% 35%	5337
	11th to 20th	Night	6% 10% 2 8% 5% 5% 5% 4 6% 7% 42%	5000
	21st to end	Night	8% 10% 4 11% 7% 6% 6% 5% 7% 8% 26%	5232
April	1st to 10th	Night	10% 13% 4 7% 4 4 4 5% 7% 7% 36%	2000
	11th to 20th	Night	8% 13% 3 8% 5% 4 4 3 6% 6% 40%	1979
	21st to end	Night	9% 8% 3 6% 4 5% 5% 4 6% 8% 41%	1935
May	1st to 10th	Night	11% 9% 3 7% 4 4 4 3 6% 7% 44%	2620
	11th to 20th	Night	4 4 2 4 4 3 4 3 5% 5% 62%	2596
	21st to end	Night	8% 6% 2 5% 4 4 4 3 6% 7% 53%	2805
June	1st to 10th	Night	11% 7% 2 6% 4 4 3 3 6% 6% 47%	1520
	11th to 20th	Night	6% 6% 2 4 3 3 2 3 5% 9% 58%	1520
	21st to end	Night	4 4 1 3 2 3 3 3 4 6% 69%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 3 86%	2540
	11th to 20th	Night	2 2 1 2 2 2 2 2 2 4 82%	2540
	21st to end	Night	1 1 1 2 1 2 2 2 2 3 84%	2761
August	1st to 10th	Night	1 2 1 4 2 3 2 3 5% 5% 72%	2713
	11th to 20th	Night	1 1 1 3 2 3 3 3 4 6% 73%	2841
	21st to end	Night	2 3 1 3 2 2 2 2 4 4 76%	3498
September	1st to 10th	Night	2 2 1 2 1 1 2 2 4 5% 78%	1900
	11th to 20th	Night	4 4 1 5% 3 3 4 3 5% 6% 62%	1900
	21st to end	Night	7% 4 1 4 2 3 3 3 4 6% 62%	2139
October	1st to 10th	Night	5% 4 1 3 2 2 3 2 3 5% 69%	3800
	11th to 20th	Night	6% 5% 2 6% 4 3 4 3 6% 9% 51%	3777
	21st to end	Night	8% 7% 3 7% 5% 6% 5% 5% 6% 7% 42%	4273
November	1st to 10th	Night	12% 10% 4 8% 6% 4 5% 4 5% 7% 36%	2535
	11th to 20th	Night	12% 10% 3 9% 6% 5% 5% 5% 6% 7% 31%	2771
	21st to end	Night	9% 9% 3 6% 5% 4 5% 5% 6% 8% 40%	2800
December	1st to 10th	Night	6% 7% 2 5% 3 3 3 3 4 7% 56%	4560
	11th to 20th	Night	10% 13% 5% 12% 7% 6% 6% 5% 6% 7% 22%	5176
	21st to end	Night	11% 14% 4 10% 6% 6% 5% 4 6% 6% 28%	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	62% 3 13% 18% 4	3639
	11th to 20th	Day	47% 2 11% 25% 13% 2	3640
	21st to end	Day	41% 3 11% 21% 17% 7%	4297
February	1st to 10th	Day	49% 4 15% 23% 9% 1	1800
	11th to 20th	Day	47% 4 14% 22% 11% 1	1774
	21st to end	Day	49% 5% 15% 18% 11% 1	1650
March	1st to 10th	Day	46% 2 7% 26% 16% 3	4552
	11th to 20th	Day	46% 3 11% 25% 14%	5000
	21st to end	Day	53% 4 12% 24% 7% 1	5741
April	1st to 10th	Day	50% 3 12% 20% 13% 2	2400
	11th to 20th	Day	45% 3 12% 21% 16% 3	2372
	21st to end	Day	38% 3 13% 29% 15% 3	2460
May	1st to 10th	Day	41% 1 7% 26% 23% 1	4560
	11th to 20th	Day	26% 2 7% 28% 33% 5%	4520
	21st to end	Day	34% 2 16% 32% 15% 1	4887
June	1st to 10th	Day	41% 2 10% 30% 15% 2	2660
	11th to 20th	Day	30% 3 10% 33% 21% 4	2660
	21st to end	Day	20% 2 8% 30% 30% 10%	2660
July	1st to 10th	Day	8% 1 4 13% 22% 52%	4351
	11th to 20th	Day	10% 1 3 9% 23% 54%	4345
	21st to end	Day	9% 2 3 17% 38% 32%	4639
August	1st to 10th	Day	16% 2 3 16% 37% 25%	4203
	11th to 20th	Day	14% 2 6% 30% 32% 16%	4035
	21st to end	Day	16% 2 5% 26% 30% 20%	4179
September	1st to 10th	Day	13% 1 4 26% 34% 23%	2280
	11th to 20th	Day	24% 3 8% 27% 26% 12%	2280
	21st to end	Day	27% 2 8% 27% 25% 11%	2037
October	1st to 10th	Day	24% 2 9% 23% 26% 16%	3180
	11th to 20th	Day	31% 4 17% 27% 19% 3	3161
	21st to end	Day	42% 4 10% 25% 17% 2	3277
November	1st to 10th	Day	46% 3 13% 25% 12% 1	1764
	11th to 20th	Day	50% 4 18% 19% 9%	1625
	21st to end	Day	43% 5% 15% 21% 15% 1	1600
December	1st to 10th	Day	32% 3 12% 30% 22% 1	2620
	11th to 20th	Day	58% 4 17% 17% 4	3028
	21st to end	Day	56% 4 14% 20% 4 1	4004
January	1st to 10th	Night	64% 4 14% 14% 4	6306
	11th to 20th	Night	47% 3 9% 28% 12% 2	6320
	21st to end	Night	47% 2 10% 18% 17% 6%	6671
February	1st to 10th	Night	52% 4 17% 18% 9%	2600
	11th to 20th	Night	46% 5% 16% 22% 10% 1	2524
	21st to end	Night	50% 5% 13% 23% 9% 1	1980
March	1st to 10th	Night	43% 3 10% 27% 15% 2	5337
	11th to 20th	Night	38% 5% 14% 32% 11%	5000
	21st to end	Night	53% 6% 15% 21% 5%	5232
April	1st to 10th	Night	47% 4 18% 21% 10% 1	2000
	11th to 20th	Night	45% 3 14% 23% 14% 2	1979
	21st to end	Night	40% 5% 15% 26% 12% 2	1935
May	1st to 10th	Night	42% 2 9% 30% 17%	2620
	11th to 20th	Night	25% 3 10% 38% 22% 2	2596
	21st to end	Night	33% 2 28% 30% 7%	2805
June	1st to 10th	Night	39% 4 12% 31% 13% 1	1520
	11th to 20th	Night	26% 3 14% 39% 15% 3	1520
	21st to end	Night	19% 2 11% 35% 26% 7%	1520
July	1st to 10th	Night	7% 1 5% 16% 27% 44%	2500
	11th to 20th	Night	11% 2 4 15% 21% 48%	2492
	21st to end	Night	9% 2 3 19% 39% 28%	2674
August	1st to 10th	Night	16% 2 4 19% 40% 19%	2705
	11th to 20th	Night	12% 3 8% 38% 29% 10%	2868
	21st to end	Night	14% 3 9% 29% 31% 14%	3498
September	1st to 10th	Night	11% 2 5% 29% 36% 17%	1900
	11th to 20th	Night	24% 3 9% 26% 26% 12%	1900
	21st to end	Night	24% 2 8% 29% 25% 11%	2139
October	1st to 10th	Night	21% 2 7% 26% 34% 9%	3800
	11th to 20th	Night	30% 4 21% 24% 18% 3	3777
	21st to end	Night	39% 5% 11% 29% 14% 1	4273
November	1st to 10th	Night	48% 3 12% 22% 13% 2	2535
	11th to 20th	Night	50% 5% 15% 23% 7%	2771
	21st to end	Night	41% 4 16% 23% 16% 1	2800
December	1st to 10th	Night	29% 4 11% 33% 22% 1	4560
	11th to 20th	Night	59% 4 15% 17% 5%	5176
	21st to end	Night	54% 5% 15% 20% 5%	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	23% 13% 31% 22% 11% 1	200
	11th to 20th	Day	19% 10% 28% 27% 13% 5%	200
	21st to end	Day	16% 12% 26% 26% 17% 3	344
February	1st to 10th	Day	19% 15% 23% 28% 13% 1	400
	11th to 20th	Day	17% 18% 28% 22% 12% 2	400
	21st to end	Day	21% 14% 28% 25% 10% 1	414
March	1st to 10th	Day	19% 18% 23% 31% 8% 1	500
	11th to 20th	Day	15% 16% 24% 27% 14% 3	500
	21st to end	Day	19% 19% 23% 25% 14% 1	550
April	1st to 10th	Day	19% 15% 24% 23% 12% 6%	500
	11th to 20th	Day	14% 18% 25% 23% 13% 6%	492
	21st to end	Day	11% 18% 24% 24% 17% 6%	500
May	1st to 10th	Day	12% 13% 27% 23% 18% 8%	503
	11th to 20th	Day	18% 13% 22% 22% 17% 9%	528
	21st to end	Day	12% 9% 20% 25% 21% 13%	550
June	1st to 10th	Day	11% 12% 20% 23% 20% 13%	490
	11th to 20th	Day	10% 15% 24% 26% 19% 6%	490
	21st to end	Day	5% 7% 20% 29% 27% 13%	490
July	1st to 10th	Day	2 5% 25% 31% 26% 11%	486
	11th to 20th	Day	2 6% 27% 24% 29% 12%	484
	21st to end	Day	2 4 26% 27% 26% 15%	531
August	1st to 10th	Day	2 4 21% 31% 26% 16%	487
	11th to 20th	Day	2 4 17% 30% 27% 20%	477
	21st to end	Day	5% 7% 19% 27% 28% 15%	539
September	1st to 10th	Day	3 3 23% 26% 29% 16%	490
	11th to 20th	Day	6% 7% 19% 30% 29% 10%	490
	21st to end	Day	10% 7% 20% 27% 28% 8%	490
October	1st to 10th	Day	11% 10% 19% 27% 23% 10%	490
	11th to 20th	Day	14% 9% 20% 26% 24% 7%	490
	21st to end	Day	17% 11% 23% 24% 20% 5%	443
November	1st to 10th	Day	16% 10% 24% 32% 15% 2	300
	11th to 20th	Day	21% 15% 20% 25% 15% 4	213
	21st to end	Day	17% 11% 25% 30% 17% 2	200
December	1st to 10th	Day	11% 16% 22% 28% 13% 12%	200
	11th to 20th	Day	17% 14% 36% 30% 5%	200
	21st to end	Day	17% 15% 29% 28% 9% 2	220
January	1st to 10th	Night	18% 9% 30% 29% 13% 2	800
	11th to 20th	Night	17% 9% 24% 30% 18% 3	800
	21st to end	Night	14% 7% 22% 38% 16% 2	880
February	1st to 10th	Night	15% 10% 27% 34% 12% 1	800
	11th to 20th	Night	14% 7% 26% 39% 13% 1	784
	21st to end	Night	15% 10% 28% 36% 10%	660
March	1st to 10th	Night	16% 12% 25% 36% 11% 1	800
	11th to 20th	Night	13% 9% 23% 39% 15% 2	800
	21st to end	Night	14% 10% 26% 34% 14% 1	880
April	1st to 10th	Night	17% 9% 22% 33% 19% 1	800
	11th to 20th	Night	15% 8% 26% 32% 17% 2	791
	21st to end	Night	11% 8% 24% 36% 19% 1	735
May	1st to 10th	Night	12% 6% 17% 43% 21% 2	400
	11th to 20th	Night	10% 5% 17% 42% 25% 1	394
	21st to end	Night	11% 5% 14% 41% 26% 3	422
June	1st to 10th	Night	14% 5% 17% 42% 21% 1	380
	11th to 20th	Night	8% 4 22% 46% 20% 1	380
	21st to end	Night	6% 2 14% 52% 26% 1	380
July	1st to 10th	Night	2 2 9% 56% 31% 1	370
	11th to 20th	Night	2 1 14% 59% 23% 1	368
	21st to end	Night	1 11% 54% 32% 2	416
August	1st to 10th	Night	2 1 6% 48% 40% 3	484
	11th to 20th	Night	2 1 6% 42% 42% 8%	580
	21st to end	Night	3 2 16% 44% 32% 3	836
September	1st to 10th	Night	3 1 15% 44% 33% 4	760
	11th to 20th	Night	6% 2 13% 40% 34% 6%	760
	21st to end	Night	8% 4 14% 41% 27% 5%	760
October	1st to 10th	Night	10% 4 14% 42% 27% 3	760
	11th to 20th	Night	11% 4 18% 39% 24% 4	760
	21st to end	Night	15% 6% 22% 36% 17% 4	836
November	1st to 10th	Night	16% 6% 21% 41% 15% 1	780
	11th to 20th	Night	18% 9% 26% 32% 14% 2	800
	21st to end	Night	13% 8% 24% 36% 17% 2	800
December	1st to 10th	Night	15% 7% 21% 35% 20% 2	800
	11th to 20th	Night	18% 9% 27% 32% 14% 1	800
	21st to end	Night	21% 10% 31% 28% 9% 1	880

Page generated at 2025-05-23 06:20:57. Version ac07

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