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 2026-10-14.

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	18% 9% 3 6% 4 3 4 3 5% 6% 39%	158701
	Night	23% 11% 3 6% 4 3 3 3 4 5% 34%	150494
Transparency	Day	44% 8% 14% 19% 12% 4	153470
	Night	51% 7% 11% 16% 11% 4	146726
Seeing	Day	23% 9% 24% 28% 14% 3	17319
	Night	28% 6% 15% 28% 20% 3	26196

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	41% 16% 4 8% 4 4 4 3 3 3 10%	4722
	11th to 20th	Day	23% 6% 1 4 2 3 2 3 5% 7% 44%	5022
	21st to end	Day	30% 10% 3 8% 4 3 4 3 4 4 28%	5843
February	1st to 10th	Day	33% 12% 4 8% 6% 5% 4 3 5% 5% 17%	1890
	11th to 20th	Day	32% 11% 4 8% 5% 3 4 3 5% 5% 19%	1845
	21st to end	Day	32% 16% 4 8% 5% 3 4 2 4 3 20%	1595
March	1st to 10th	Day	23% 18% 3 8% 5% 5% 5% 4 6% 6% 18%	5057
	11th to 20th	Day	34% 13% 3 7% 4 3 3 2 3 3 23%	5110
	21st to end	Day	32% 14% 4 11% 6% 5% 5% 3 4 5% 10%	5607
April	1st to 10th	Day	31% 12% 3 9% 5% 4 4 4 5% 6% 17%	2502
	11th to 20th	Day	26% 11% 3 8% 5% 4 5% 3 5% 6% 25%	2530
	21st to end	Day	24% 10% 4 7% 5% 4 4 4 6% 7% 26%	2730
May	1st to 10th	Day	14% 12% 3 6% 4 3 4 3 5% 8% 39%	7683
	11th to 20th	Day	12% 8% 3 7% 4 4 5% 4 7% 8% 38%	8160
	21st to end	Day	14% 7% 2 6% 4 4 4 4 6% 10% 39%	8992
June	1st to 10th	Day	24% 8% 3 6% 3 4 4 3 5% 6% 34%	2940
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 3 6% 7% 37%	2940
	21st to end	Day	12% 7% 2 6% 3 3 4 3 5% 7% 48%	2940
July	1st to 10th	Day	2 3 1 3 2 2 2 2 4 6% 72%	8219
	11th to 20th	Day	5% 5% 2 4 2 2 2 2 3 6% 66%	8220
	21st to end	Day	6% 7% 2 5% 2 2 3 2 4 6% 61%	8493
August	1st to 10th	Day	4 6% 2 4 3 3 3 2 4 7% 62%	7547
	11th to 20th	Day	7% 5% 2 5% 4 3 4 3 6% 9% 51%	7563
	21st to end	Day	6% 7% 3 6% 3 4 4 3 5% 8% 50%	8072
September	1st to 10th	Day	8% 4 1 4 3 2 4 3 5% 6% 60%	2520
	11th to 20th	Day	12% 7% 2 6% 4 4 4 3 5% 8% 45%	2423
	21st to end	Day	15% 6% 3 5% 4 4 4 3 4 7% 46%	2268
October	1st to 10th	Day	15% 6% 2 5% 4 3 3 3 4 4 51%	3380
	11th to 20th	Day	23% 9% 2 6% 3 5% 5% 3 6% 8% 30%	3292
	21st to end	Day	28% 10% 2 6% 4 3 4 4 6% 7% 25%	3558
November	1st to 10th	Day	35% 10% 3 6% 5% 4 4 3 5% 5% 19%	1778
	11th to 20th	Day	36% 10% 3 7% 4 4 3 3 5% 7% 18%	1680
	21st to end	Day	31% 10% 3 6% 3 4 4 3 5% 6% 24%	1680
December	1st to 10th	Day	24% 7% 2 6% 4 3 3 3 4 6% 37%	2700
	11th to 20th	Day	40% 12% 3 8% 5% 4 4 3 4 4 13%	3108
	21st to end	Day	44% 15% 3 8% 4 3 3 2 3 4 11%	4092
January	1st to 10th	Night	43% 13% 3 7% 5% 4 3 2 3 4 12%	8172
	11th to 20th	Night	23% 8% 2 5% 3 2 2 2 3 5% 45%	7936
	21st to end	Night	31% 11% 3 6% 3 3 3 2 3 4 31%	8371
February	1st to 10th	Night	30% 12% 4 8% 5% 4 4 3 4 6% 19%	2730
	11th to 20th	Night	31% 12% 4 7% 4 4 4 3 4 5% 23%	2662
	21st to end	Night	33% 11% 3 7% 4 4 4 3 5% 5% 20%	2210
March	1st to 10th	Night	25% 18% 4 7% 5% 5% 4 3 5% 4 18%	5054
	11th to 20th	Night	29% 15% 4 8% 4 4 3 2 3 3 25%	5110
	21st to end	Night	34% 16% 4 9% 5% 4 4 3 4 4 13%	5610
April	1st to 10th	Night	31% 12% 4 7% 4 4 4 3 4 6% 21%	2116
	11th to 20th	Night	24% 13% 4 7% 4 3 4 3 4 5% 29%	2033
	21st to end	Night	24% 12% 3 6% 4 4 4 3 4 6% 29%	1890
May	1st to 10th	Night	15% 14% 4 7% 3 3 3 3 4 5% 40%	5262
	11th to 20th	Night	15% 11% 3 7% 5% 4 4 3 5% 7% 36%	4700
	21st to end	Night	16% 11% 2 5% 2 3 3 3 5% 8% 41%	5181
June	1st to 10th	Night	19% 8% 3 7% 5% 4 4 4 5% 5% 36%	1680
	11th to 20th	Night	15% 7% 2 6% 3 4 3 3 5% 9% 44%	1680
	21st to end	Night	14% 8% 2 5% 3 3 3 3 4 6% 50%	1680
July	1st to 10th	Night	2 7% 1 3 2 2 2 3 4 5% 68%	4740
	11th to 20th	Night	4 10% 3 5% 3 2 2 2 3 4 63%	4740
	21st to end	Night	7% 14% 3 5% 3 3 3 2 4 6% 50%	5603
August	1st to 10th	Night	6% 11% 2 5% 3 3 3 3 4 6% 54%	5275
	11th to 20th	Night	9% 13% 4 8% 4 4 5% 3 5% 7% 39%	5292
	21st to end	Night	8% 14% 4 7% 3 3 3 2 3 6% 48%	6158
September	1st to 10th	Night	11% 7% 3 4 2 3 2 2 5% 6% 56%	2100
	11th to 20th	Night	12% 8% 2 6% 4 3 3 3 4 7% 48%	2194
	21st to end	Night	16% 7% 2 4 3 3 3 2 4 6% 49%	2352
October	1st to 10th	Night	11% 7% 3 5% 3 3 3 3 4 6% 52%	4040
	11th to 20th	Night	20% 13% 3 6% 4 4 4 3 5% 7% 30%	3933
	21st to end	Night	32% 10% 3 7% 4 3 3 3 5% 5% 25%	4253
November	1st to 10th	Night	33% 9% 3 6% 3 4 4 3 6% 6% 23%	2735
	11th to 20th	Night	36% 9% 3 7% 4 4 3 3 4 5% 22%	2940
	21st to end	Night	26% 9% 2 8% 4 4 4 3 4 5% 29%	2940
December	1st to 10th	Night	24% 9% 2 4 3 3 3 3 5% 6% 39%	4700
	11th to 20th	Night	43% 11% 3 8% 4 3 3 2 4 5% 14%	5316
	21st to end	Night	41% 13% 3 8% 4 3 3 3 3 4 15%	7106

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	76% 7% 7% 6% 4 1	4723
	11th to 20th	Day	40% 5% 8% 17% 18% 12%	5022
	21st to end	Day	58% 6% 5% 10% 12% 8%	5843
February	1st to 10th	Day	67% 8% 10% 10% 3 2	1890
	11th to 20th	Day	64% 9% 11% 10% 4 2	1854
	21st to end	Day	67% 6% 9% 11% 6% 2	1595
March	1st to 10th	Day	59% 10% 15% 12% 3	5057
	11th to 20th	Day	61% 9% 7% 13% 8% 1	5110
	21st to end	Day	71% 10% 10% 6% 3	5607
April	1st to 10th	Day	64% 10% 12% 10% 3	2502
	11th to 20th	Day	58% 9% 12% 13% 6% 2	2533
	21st to end	Day	54% 11% 14% 15% 6% 1	2730
May	1st to 10th	Day	41% 9% 12% 27% 10%	7683
	11th to 20th	Day	38% 10% 25% 20% 6% 1	8163
	21st to end	Day	37% 11% 27% 22% 3	8994
June	1st to 10th	Day	49% 8% 15% 21% 7%	2940
	11th to 20th	Day	42% 11% 20% 21% 6% 1	2940
	21st to end	Day	34% 9% 20% 26% 9% 2	2940
July	1st to 10th	Day	14% 6% 15% 30% 19% 16%	8151
	11th to 20th	Day	20% 5% 8% 16% 39% 13%	8145
	21st to end	Day	25% 6% 17% 33% 18% 3	8304
August	1st to 10th	Day	22% 7% 10% 20% 28% 13%	5976
	11th to 20th	Day	27% 9% 21% 32% 9% 2	5962
	21st to end	Day	28% 8% 19% 26% 15% 4	6327
September	1st to 10th	Day	24% 7% 16% 29% 16% 8%	2520
	11th to 20th	Day	37% 9% 17% 21% 12% 4	2423
	21st to end	Day	37% 8% 14% 21% 16% 4	2268
October	1st to 10th	Day	36% 5% 9% 19% 23% 7%	3380
	11th to 20th	Day	51% 8% 15% 15% 10% 1	3292
	21st to end	Day	55% 7% 10% 16% 10% 2	3558
November	1st to 10th	Day	64% 9% 9% 13% 5%	1778
	11th to 20th	Day	65% 8% 11% 7% 6% 3	1680
	21st to end	Day	59% 8% 9% 9% 10% 5%	1680
December	1st to 10th	Day	47% 6% 10% 14% 20% 3	2700
	11th to 20th	Day	73% 7% 10% 7% 3	3108
	21st to end	Day	75% 7% 8% 7% 2 1	4092
January	1st to 10th	Night	75% 6% 8% 7% 3 1	8172
	11th to 20th	Night	43% 5% 8% 16% 18% 11%	7936
	21st to end	Night	59% 4 5% 8% 15% 9%	8371
February	1st to 10th	Night	65% 9% 9% 11% 5% 1	2730
	11th to 20th	Night	63% 7% 12% 11% 6% 2	2664
	21st to end	Night	65% 8% 9% 10% 6% 2	2210
March	1st to 10th	Night	64% 10% 11% 11% 3	5054
	11th to 20th	Night	62% 8% 10% 11% 7% 3	5110
	21st to end	Night	71% 10% 11% 7% 1	5610
April	1st to 10th	Night	63% 8% 13% 12% 4	2116
	11th to 20th	Night	56% 10% 11% 15% 5% 3	2033
	21st to end	Night	56% 9% 13% 15% 6% 1	1890
May	1st to 10th	Night	44% 8% 12% 26% 9% 1	5260
	11th to 20th	Night	45% 11% 18% 19% 5% 2	4700
	21st to end	Night	39% 10% 28% 20% 2	5182
June	1st to 10th	Night	47% 10% 17% 22% 4	1680
	11th to 20th	Night	37% 10% 20% 25% 7% 1	1680
	21st to end	Night	35% 10% 17% 27% 9% 3	1680
July	1st to 10th	Night	18% 7% 14% 26% 18% 17%	4700
	11th to 20th	Night	27% 6% 7% 13% 32% 15%	4692
	21st to end	Night	36% 8% 14% 21% 18% 3	5480
August	1st to 10th	Night	28% 8% 8% 18% 24% 14%	4169
	11th to 20th	Night	39% 10% 14% 25% 10% 2	4169
	21st to end	Night	34% 7% 11% 31% 15% 2	4829
September	1st to 10th	Night	29% 6% 12% 24% 19% 10%	2100
	11th to 20th	Night	37% 7% 16% 22% 13% 6%	2194
	21st to end	Night	36% 6% 15% 20% 17% 6%	2352
October	1st to 10th	Night	33% 6% 10% 23% 23% 5%	4040
	11th to 20th	Night	53% 6% 14% 15% 10% 2	3933
	21st to end	Night	60% 6% 9% 15% 7% 3	4253
November	1st to 10th	Night	60% 9% 12% 12% 8% 1	2735
	11th to 20th	Night	64% 7% 10% 10% 6% 3	2940
	21st to end	Night	56% 8% 9% 11% 10% 6%	2940
December	1st to 10th	Night	46% 5% 8% 17% 22% 2	4700
	11th to 20th	Night	74% 6% 8% 7% 5%	5316
	21st to end	Night	70% 8% 11% 8% 2 1	7106

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	50% 10% 22% 12% 6%	220
	11th to 20th	Day	37% 8% 19% 19% 13% 3	320
	21st to end	Day	36% 8% 17% 21% 15% 3	473
February	1st to 10th	Day	37% 9% 19% 23% 12% 1	430
	11th to 20th	Day	36% 13% 20% 21% 8% 1	425
	21st to end	Day	38% 13% 21% 21% 7% 1	376
March	1st to 10th	Day	37% 14% 23% 19% 7% 1	540
	11th to 20th	Day	35% 9% 21% 23% 10% 2	540
	21st to end	Day	34% 13% 25% 19% 7% 1	594
April	1st to 10th	Day	33% 12% 23% 20% 12% 1	540
	11th to 20th	Day	30% 13% 25% 22% 7% 3	532
	21st to end	Day	25% 12% 26% 27% 9% 2	540
May	1st to 10th	Day	20% 12% 29% 25% 13% 2	543
	11th to 20th	Day	26% 13% 23% 23% 12% 3	568
	21st to end	Day	17% 11% 28% 29% 14% 2	617
June	1st to 10th	Day	22% 8% 27% 28% 13% 2	570
	11th to 20th	Day	16% 10% 35% 28% 10% 1	570
	21st to end	Day	10% 6% 26% 40% 16% 2	570
July	1st to 10th	Day	7% 4 30% 39% 17% 3	566
	11th to 20th	Day	7% 6% 30% 35% 21% 2	564
	21st to end	Day	4 4 27% 41% 20% 4	619
August	1st to 10th	Day	6% 5% 23% 41% 20% 5%	567
	11th to 20th	Day	6% 4 18% 41% 27% 4	557
	21st to end	Day	9% 4 24% 39% 19% 5%	627
September	1st to 10th	Day	10% 5% 24% 33% 22% 6%	570
	11th to 20th	Day	14% 8% 24% 31% 21% 3	570
	21st to end	Day	15% 8% 25% 30% 18% 4	570
October	1st to 10th	Day	19% 7% 24% 28% 18% 4	570
	11th to 20th	Day	24% 9% 17% 27% 17% 6%	543
	21st to end	Day	29% 9% 23% 23% 11% 4	583
November	1st to 10th	Day	32% 13% 21% 21% 12% 1	323
	11th to 20th	Day	38% 10% 17% 22% 12% 1	220
	21st to end	Day	35% 10% 15% 25% 15%	220
December	1st to 10th	Day	33% 10% 22% 20% 13% 3	220
	11th to 20th	Day	45% 10% 20% 18% 5% 1	220
	21st to end	Day	42% 13% 18% 21% 5% 1	242
January	1st to 10th	Night	46% 9% 17% 17% 10% 2	840
	11th to 20th	Night	37% 7% 15% 25% 15% 2	840
	21st to end	Night	35% 6% 15% 28% 14% 3	924
February	1st to 10th	Night	36% 6% 15% 25% 15% 2	840
	11th to 20th	Night	37% 8% 14% 26% 14% 1	824
	21st to end	Night	38% 10% 15% 23% 13% 1	692
March	1st to 10th	Night	35% 10% 16% 26% 12% 1	840
	11th to 20th	Night	35% 9% 13% 27% 14% 2	840
	21st to end	Night	37% 9% 17% 24% 12% 1	924
April	1st to 10th	Night	35% 8% 16% 21% 18% 2	840
	11th to 20th	Night	29% 9% 17% 26% 16% 3	785
	21st to end	Night	30% 6% 15% 28% 20% 1	630
May	1st to 10th	Night	25% 5% 20% 27% 21% 2	609
	11th to 20th	Night	26% 4 16% 27% 24% 3	414
	21st to end	Night	23% 6% 19% 26% 24% 2	455
June	1st to 10th	Night	22% 3 16% 35% 22% 2	420
	11th to 20th	Night	17% 4 19% 39% 19% 3	420
	21st to end	Night	16% 5% 12% 33% 31% 2	420
July	1st to 10th	Night	9% 4 13% 39% 34% 2	410
	11th to 20th	Night	10% 4 15% 44% 25% 2	408
	21st to end	Night	7% 4 10% 39% 35% 5%	614
August	1st to 10th	Night	11% 5% 10% 31% 37% 7%	627
	11th to 20th	Night	11% 4 7% 29% 39% 10%	624
	21st to end	Night	12% 4 13% 34% 32% 5%	800
September	1st to 10th	Night	13% 3 12% 30% 37% 5%	840
	11th to 20th	Night	15% 3 13% 30% 30% 10%	840
	21st to end	Night	18% 4 14% 31% 28% 5%	840
October	1st to 10th	Night	20% 2 16% 29% 26% 6%	840
	11th to 20th	Night	24% 4 12% 29% 24% 7%	812
	21st to end	Night	30% 7% 17% 25% 17% 4	880
November	1st to 10th	Night	35% 7% 14% 26% 16% 1	820
	11th to 20th	Night	39% 7% 15% 24% 13% 1	840
	21st to end	Night	28% 8% 16% 30% 16% 2	840
December	1st to 10th	Night	33% 8% 14% 28% 17% 1	840
	11th to 20th	Night	42% 7% 15% 22% 13% 1	840
	21st to end	Night	43% 10% 17% 22% 7%	924

Page generated at 2026-10-11 02:06:31. Version ac07

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