Redwood Loop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Redwood Loop Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	21% 9% 3 6% 4 4 4 3 5% 6% 36%	123834
	Night	25% 11% 3 6% 4 3 3 3 4 5% 33%	123237
Transparency	Day	47% 8% 14% 16% 11% 4	123586
	Night	53% 8% 11% 15% 10% 4	123072
Seeing	Day	23% 8% 23% 28% 14% 3	15543
	Night	28% 6% 15% 27% 20% 3	24561

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	42% 16% 4 8% 4 3 4 3 3 3 12%	3639
	11th to 20th	Day	30% 8% 2 5% 3 3 2 2 4 6% 35%	3852
	21st to end	Day	31% 10% 3 6% 3 3 3 3 4 4 31%	4510
February	1st to 10th	Day	33% 12% 4 8% 6% 5% 4 3 5% 5% 16%	1800
	11th to 20th	Day	32% 11% 4 8% 5% 3 4 3 5% 6% 20%	1755
	21st to end	Day	31% 16% 4 8% 5% 3 4 2 4 3 20%	1521
March	1st to 10th	Day	23% 18% 3 8% 5% 5% 5% 4 6% 6% 18%	4947
	11th to 20th	Day	34% 13% 3 7% 4 3 3 2 3 3 24%	5000
	21st to end	Day	33% 15% 4 11% 6% 5% 5% 3 4 5% 10%	5486
April	1st to 10th	Day	33% 12% 3 9% 5% 4 4 3 4 5% 16%	2383
	11th to 20th	Day	26% 11% 3 8% 5% 4 5% 3 5% 6% 25%	2408
	21st to end	Day	25% 10% 4 7% 5% 4 4 4 6% 7% 26%	2600
May	1st to 10th	Day	17% 10% 3 6% 4 3 3 3 4 6% 40%	5924
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 6% 7% 37%	6277
	21st to end	Day	16% 7% 2 7% 4 5% 4 4 6% 10% 35%	6902
June	1st to 10th	Day	24% 8% 2 6% 3 4 4 3 5% 6% 35%	2789
	11th to 20th	Day	19% 8% 4 6% 5% 4 4 3 6% 8% 35%	2660
	21st to end	Day	12% 7% 3 5% 3 3 3 2 5% 7% 49%	2660
July	1st to 10th	Day	4 4 1 3 2 2 2 2 3 5% 73%	4420
	11th to 20th	Day	7% 6% 1 5% 2 2 2 2 3 6% 64%	4420
	21st to end	Day	5% 4 2 3 2 2 2 2 3 6% 68%	4556
August	1st to 10th	Day	3 9% 3 6% 4 3 4 3 5% 8% 55%	4091
	11th to 20th	Day	8% 6% 2 5% 4 4 4 4 6% 9% 50%	4026
	21st to end	Day	7% 5% 2 5% 3 4 4 3 5% 8% 55%	4350
September	1st to 10th	Day	7% 4 1 4 2 2 4 3 4 6% 63%	2280
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 3 6% 8% 44%	2193
	21st to end	Day	15% 6% 3 5% 3 4 4 3 4 7% 46%	2052
October	1st to 10th	Day	15% 6% 2 5% 4 3 3 3 4 4 51%	3180
	11th to 20th	Day	24% 9% 2 6% 4 5% 5% 3 6% 8% 29%	3161
	21st to end	Day	28% 10% 2 6% 4 3 4 3 6% 7% 25%	3448
November	1st to 10th	Day	34% 10% 3 7% 5% 4 3 3 5% 5% 20%	1692
	11th to 20th	Day	36% 9% 3 7% 4 4 3 3 5% 7% 19%	1600
	21st to end	Day	31% 10% 3 6% 3 4 4 3 5% 6% 25%	1600
December	1st to 10th	Day	23% 7% 2 6% 4 4 3 3 4 6% 38%	2620
	11th to 20th	Day	40% 12% 3 8% 5% 4 4 3 4 3 13%	3028
	21st to end	Day	44% 15% 3 8% 4 3 3 2 3 4 10%	4004
January	1st to 10th	Night	44% 13% 3 7% 5% 4 3 2 3 4 12%	6306
	11th to 20th	Night	29% 10% 2 5% 3 2 3 2 3 5% 35%	6101
	21st to end	Night	36% 10% 3 5% 2 2 2 1 2 4 33%	6468
February	1st to 10th	Night	31% 12% 4 8% 5% 4 4 3 4 6% 19%	2600
	11th to 20th	Night	32% 12% 3 7% 3 4 4 3 4 5% 24%	2532
	21st to end	Night	33% 11% 3 7% 5% 4 4 3 5% 5% 21%	2108
March	1st to 10th	Night	25% 18% 4 7% 5% 5% 4 3 5% 5% 18%	4944
	11th to 20th	Night	29% 15% 4 7% 4 4 3 2 3 3 25%	5000
	21st to end	Night	35% 16% 4 9% 5% 4 4 3 4 4 13%	5489
April	1st to 10th	Night	32% 12% 4 7% 4 4 3 3 4 6% 21%	2015
	11th to 20th	Night	24% 12% 4 7% 4 3 4 3 4 5% 30%	1935
	21st to end	Night	25% 12% 3 6% 4 4 4 3 4 6% 28%	1800
May	1st to 10th	Night	18% 8% 3 6% 3 3 3 3 3 5% 44%	4054
	11th to 20th	Night	17% 11% 3 7% 4 3 4 3 4 7% 37%	3616
	21st to end	Night	18% 11% 2 5% 3 3 3 3 5% 7% 40%	3972
June	1st to 10th	Night	19% 8% 3 6% 5% 4 4 4 5% 5% 36%	1595
	11th to 20th	Night	16% 7% 2 6% 3 4 3 3 5% 8% 42%	1520
	21st to end	Night	13% 8% 2 5% 2 3 3 3 4 6% 51%	1520
July	1st to 10th	Night	4 4 1 3 1 2 1 1 3 5% 74%	2540
	11th to 20th	Night	6% 10% 2 4 3 2 3 2 3 5% 60%	2540
	21st to end	Night	7% 7% 2 4 3 3 2 2 4 7% 60%	3001
August	1st to 10th	Night	3 14% 3 7% 4 3 3 3 5% 8% 46%	2848
	11th to 20th	Night	8% 14% 3 6% 3 3 4 3 5% 6% 44%	2812
	21st to end	Night	8% 7% 2 5% 3 3 2 2 3 7% 58%	3321
September	1st to 10th	Night	9% 7% 3 3 2 3 2 1 4 6% 59%	1900
	11th to 20th	Night	13% 8% 2 6% 4 4 3 2 4 7% 48%	1985
	21st to end	Night	17% 7% 2 4 3 3 3 2 4 7% 49%	2128
October	1st to 10th	Night	12% 7% 3 5% 3 3 3 3 4 5% 52%	3800
	11th to 20th	Night	20% 14% 3 6% 4 4 4 3 6% 7% 29%	3777
	21st to end	Night	32% 10% 3 7% 4 3 3 3 5% 5% 25%	4121
November	1st to 10th	Night	33% 9% 3 6% 3 4 4 3 6% 6% 23%	2601
	11th to 20th	Night	37% 9% 3 7% 4 4 3 3 4 6% 21%	2800
	21st to end	Night	27% 9% 2 8% 4 4 4 3 4 5% 30%	2800
December	1st to 10th	Night	23% 9% 2 4 3 3 3 3 4 6% 40%	4560
	11th to 20th	Night	43% 11% 3 8% 5% 3 3 2 4 5% 14%	5176
	21st to end	Night	41% 13% 3 8% 4 3 3 3 3 4 15%	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	74% 8% 7% 6% 4 1	3639
	11th to 20th	Day	50% 6% 8% 19% 13% 3	3852
	21st to end	Day	55% 7% 5% 10% 14% 8%	4510
February	1st to 10th	Day	68% 8% 10% 10% 3 1	1800
	11th to 20th	Day	64% 9% 11% 9% 4 2	1764
	21st to end	Day	67% 6% 10% 11% 5% 2	1521
March	1st to 10th	Day	59% 10% 15% 13% 3	4947
	11th to 20th	Day	61% 9% 7% 13% 8% 1	5000
	21st to end	Day	71% 10% 10% 6% 3	5486
April	1st to 10th	Day	66% 10% 12% 9% 4	2383
	11th to 20th	Day	58% 9% 11% 14% 7% 2	2411
	21st to end	Day	54% 11% 15% 14% 6% 1	2600
May	1st to 10th	Day	41% 9% 13% 25% 12%	5924
	11th to 20th	Day	41% 11% 22% 17% 8% 1	6280
	21st to end	Day	40% 12% 30% 16% 2	6904
June	1st to 10th	Day	50% 8% 15% 20% 7%	2789
	11th to 20th	Day	44% 11% 21% 19% 5%	2660
	21st to end	Day	33% 9% 21% 26% 9% 3	2660
July	1st to 10th	Day	16% 5% 11% 14% 25% 29%	4351
	11th to 20th	Day	23% 6% 10% 18% 29% 16%	4345
	21st to end	Day	19% 5% 16% 29% 27% 5%	4412
August	1st to 10th	Day	29% 9% 13% 24% 17% 8%	4076
	11th to 20th	Day	29% 10% 21% 28% 9% 2	4065
	21st to end	Day	24% 9% 20% 23% 19% 5%	4349
September	1st to 10th	Day	22% 7% 16% 30% 17% 9%	2280
	11th to 20th	Day	38% 9% 17% 20% 12% 5%	2193
	21st to end	Day	37% 9% 14% 21% 15% 4	2052
October	1st to 10th	Day	36% 5% 9% 19% 23% 8%	3180
	11th to 20th	Day	52% 8% 15% 15% 10% 1	3161
	21st to end	Day	55% 7% 10% 16% 10% 2	3448
November	1st to 10th	Day	64% 9% 9% 13% 5%	1692
	11th to 20th	Day	64% 8% 11% 8% 7% 3	1600
	21st to end	Day	59% 8% 9% 9% 10% 5%	1600
December	1st to 10th	Day	46% 6% 10% 14% 21% 3	2620
	11th to 20th	Day	73% 7% 11% 7% 3	3028
	21st to end	Day	76% 7% 8% 6% 2 1	4004
January	1st to 10th	Night	75% 7% 6% 7% 4 1	6306
	11th to 20th	Night	52% 5% 8% 18% 13% 3	6101
	21st to end	Night	58% 4 4 10% 14% 10%	6468
February	1st to 10th	Night	66% 9% 9% 11% 5% 1	2600
	11th to 20th	Night	63% 7% 12% 10% 6% 2	2534
	21st to end	Night	64% 8% 9% 11% 6% 2	2108
March	1st to 10th	Night	64% 10% 11% 12% 3	4944
	11th to 20th	Night	62% 8% 10% 12% 7% 3	5000
	21st to end	Night	71% 10% 11% 7% 1	5489
April	1st to 10th	Night	64% 8% 13% 11% 4	2015
	11th to 20th	Night	56% 10% 10% 16% 6% 3	1935
	21st to end	Night	57% 9% 13% 15% 5% 2	1800
May	1st to 10th	Night	39% 9% 12% 27% 11% 1	4051
	11th to 20th	Night	45% 11% 18% 17% 7% 2	3616
	21st to end	Night	41% 12% 29% 16% 2	3972
June	1st to 10th	Night	46% 10% 17% 22% 4	1595
	11th to 20th	Night	38% 11% 22% 23% 5%	1520
	21st to end	Night	33% 10% 17% 28% 8% 3	1520
July	1st to 10th	Night	17% 5% 10% 16% 21% 31%	2500
	11th to 20th	Night	28% 6% 8% 13% 24% 22%	2492
	21st to end	Night	27% 7% 11% 23% 26% 6%	2907
August	1st to 10th	Night	35% 10% 10% 21% 16% 8%	2839
	11th to 20th	Night	39% 9% 15% 24% 10% 3	2839
	21st to end	Night	27% 7% 12% 30% 21% 3	3321
September	1st to 10th	Night	27% 6% 12% 25% 20% 11%	1900
	11th to 20th	Night	38% 7% 16% 21% 13% 6%	1985
	21st to end	Night	35% 7% 15% 20% 17% 6%	2128
October	1st to 10th	Night	33% 6% 9% 23% 23% 5%	3800
	11th to 20th	Night	53% 7% 14% 15% 9% 2	3777
	21st to end	Night	61% 6% 9% 14% 7% 3	4121
November	1st to 10th	Night	59% 9% 12% 12% 8% 1	2601
	11th to 20th	Night	64% 7% 10% 10% 6% 3	2800
	21st to end	Night	56% 8% 9% 11% 10% 6%	2800
December	1st to 10th	Night	45% 5% 8% 17% 22% 3	4560
	11th to 20th	Night	74% 6% 8% 6% 5%	5176
	21st to end	Night	70% 9% 11% 8% 2 1	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	51% 10% 21% 11% 7% 1	200
	11th to 20th	Day	40% 9% 19% 17% 12% 4	295
	21st to end	Day	36% 9% 15% 21% 16% 3	440
February	1st to 10th	Day	37% 10% 19% 22% 12% 1	400
	11th to 20th	Day	37% 11% 20% 22% 9% 1	395
	21st to end	Day	37% 13% 20% 22% 7% 1	350
March	1st to 10th	Day	36% 14% 22% 21% 7% 1	500
	11th to 20th	Day	35% 8% 20% 24% 11% 2	500
	21st to end	Day	35% 12% 25% 20% 7% 1	550
April	1st to 10th	Day	34% 12% 22% 19% 11% 1	500
	11th to 20th	Day	30% 12% 26% 22% 8% 3	492
	21st to end	Day	26% 11% 25% 26% 9% 2	500
May	1st to 10th	Day	20% 12% 29% 25% 13% 2	503
	11th to 20th	Day	27% 12% 23% 24% 12% 3	528
	21st to end	Day	17% 10% 27% 30% 14% 2	573
June	1st to 10th	Day	23% 6% 27% 28% 14% 2	527
	11th to 20th	Day	18% 9% 35% 28% 10% 1	490
	21st to end	Day	9% 5% 24% 43% 17% 2	490
July	1st to 10th	Day	8% 3 28% 40% 18% 2	486
	11th to 20th	Day	8% 3 28% 38% 22% 2	484
	21st to end	Day	3 3 27% 43% 21% 4	531
August	1st to 10th	Day	6% 3 22% 44% 21% 5%	487
	11th to 20th	Day	5% 4 16% 43% 28% 4	477
	21st to end	Day	8% 5% 24% 39% 20% 5%	539
September	1st to 10th	Day	8% 4 23% 37% 23% 6%	490
	11th to 20th	Day	14% 7% 22% 32% 22% 2	490
	21st to end	Day	15% 8% 24% 31% 19% 4	490
October	1st to 10th	Day	20% 7% 24% 28% 18% 4	490
	11th to 20th	Day	25% 7% 16% 27% 18% 7%	490
	21st to end	Day	29% 10% 22% 23% 12% 4	539
November	1st to 10th	Day	31% 12% 22% 22% 13% 1	297
	11th to 20th	Day	39% 10% 15% 24% 12% 2	200
	21st to end	Day	36% 9% 16% 24% 16%	200
December	1st to 10th	Day	32% 10% 22% 21% 14% 3	200
	11th to 20th	Day	47% 9% 20% 20% 5% 1	200
	21st to end	Day	43% 13% 16% 22% 4 1	220
January	1st to 10th	Night	46% 9% 17% 16% 11% 2	800
	11th to 20th	Night	39% 7% 14% 23% 15% 2	800
	21st to end	Night	36% 5% 14% 28% 14% 3	880
February	1st to 10th	Night	37% 6% 15% 25% 15% 2	800
	11th to 20th	Night	37% 8% 14% 26% 14% 1	784
	21st to end	Night	38% 10% 15% 23% 14% 1	660
March	1st to 10th	Night	35% 10% 16% 26% 12% 1	800
	11th to 20th	Night	35% 9% 12% 27% 15% 2	800
	21st to end	Night	38% 9% 17% 24% 12% 1	880
April	1st to 10th	Night	36% 8% 16% 21% 17% 2	800
	11th to 20th	Night	30% 8% 18% 26% 16% 3	747
	21st to end	Night	30% 6% 15% 28% 20% 1	600
May	1st to 10th	Night	24% 5% 21% 28% 20% 3	580
	11th to 20th	Night	26% 4 15% 27% 25% 3	394
	21st to end	Night	23% 6% 19% 25% 24% 2	433
June	1st to 10th	Night	22% 3 15% 35% 23% 2	399
	11th to 20th	Night	18% 3 19% 38% 19% 3	380
	21st to end	Night	16% 4 12% 34% 31% 2	380
July	1st to 10th	Night	9% 4 12% 38% 35% 2	370
	11th to 20th	Night	10% 4 14% 45% 26% 2	368
	21st to end	Night	7% 3 10% 39% 35% 5%	555
August	1st to 10th	Night	11% 5% 9% 30% 38% 7%	567
	11th to 20th	Night	10% 3 7% 29% 41% 11%	564
	21st to end	Night	12% 3 14% 34% 33% 5%	724
September	1st to 10th	Night	11% 3 12% 30% 39% 5%	760
	11th to 20th	Night	15% 3 13% 29% 31% 10%	760
	21st to end	Night	19% 4 14% 31% 29% 5%	760
October	1st to 10th	Night	21% 2 17% 29% 25% 6%	760
	11th to 20th	Night	24% 4 10% 29% 25% 7%	760
	21st to end	Night	30% 7% 17% 24% 18% 4	836
November	1st to 10th	Night	35% 7% 14% 26% 17% 1	780
	11th to 20th	Night	39% 7% 15% 24% 14% 2	800
	21st to end	Night	28% 8% 16% 29% 17% 2	800
December	1st to 10th	Night	32% 8% 15% 27% 17% 1	800
	11th to 20th	Night	41% 7% 16% 23% 13% 1	800
	21st to end	Night	44% 10% 16% 22% 7%	880

Page generated at 2025-06-07 07:28:19. Version ac07

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