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 2024-11-02.

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% 37%	101449
	Night	25% 11% 3 6% 4 3 3 3 4 5% 33%	97701
Transparency	Day	46% 9% 14% 16% 11% 4	101200
	Night	52% 8% 12% 15% 9% 4	97539
Seeing	Day	23% 8% 23% 29% 15% 3	14851
	Night	28% 6% 15% 27% 21% 3	23767

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	39% 19% 4 7% 4 3 4 3 3 4 12%	2539
	11th to 20th	Day	42% 11% 2 6% 4 3 2 2 3 4 19%	2682
	21st to end	Day	41% 13% 3 7% 3 4 3 3 4 4 15%	3146
February	1st to 10th	Day	34% 12% 4 7% 6% 5% 4 3 5% 5% 16%	1710
	11th to 20th	Day	31% 11% 4 8% 5% 3 4 3 5% 5% 20%	1665
	21st to end	Day	32% 16% 4 8% 5% 4 4 2 4 3 19%	1447
March	1st to 10th	Day	24% 20% 3 8% 4 4 5% 3 5% 5% 19%	3437
	11th to 20th	Day	26% 10% 3 7% 4 3 3 3 4 4 33%	3490
	21st to end	Day	32% 16% 4 10% 5% 5% 4 3 4 4 13%	3825
April	1st to 10th	Day	33% 13% 4 9% 5% 4 4 3 4 5% 17%	2264
	11th to 20th	Day	27% 12% 3 8% 5% 4 5% 3 5% 6% 23%	2286
	21st to end	Day	25% 10% 4 7% 5% 4 4 4 6% 7% 25%	2470
May	1st to 10th	Day	20% 11% 3 7% 4 4 3 3 5% 6% 34%	4141
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 5% 7% 50%	4377
	21st to end	Day	18% 7% 2 7% 4 5% 5% 5% 6% 10% 30%	4813
June	1st to 10th	Day	26% 8% 2 6% 3 4 4 3 5% 6% 32%	2660
	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	18% 7% 3 6% 5% 3 4 4 5% 5% 41%	1900
	11th to 20th	Day	23% 7% 2 6% 3 5% 4 3 5% 6% 35%	1900
	21st to end	Day	26% 10% 2 7% 4 3 4 3 5% 5% 31%	2090
November	1st to 10th	Day	35% 10% 3 6% 5% 4 3 3 5% 5% 19%	1617
	11th to 20th	Day	35% 8% 3 7% 4 5% 3 3 5% 7% 19%	1520
	21st to end	Day	31% 10% 3 6% 3 5% 4 3 5% 5% 24%	1520
December	1st to 10th	Day	29% 10% 3 7% 5% 3 3 3 5% 5% 26%	1520
	11th to 20th	Day	34% 11% 3 8% 5% 4 4 4 5% 4 17%	1928
	21st to end	Day	41% 13% 3 7% 4 3 4 3 4 5% 14%	2794
January	1st to 10th	Night	41% 16% 3 8% 5% 4 3 2 3 4 11%	4406
	11th to 20th	Night	41% 14% 3 6% 4 3 3 2 3 3 19%	4266
	21st to end	Night	47% 12% 3 6% 3 2 2 2 3 4 16%	4521
February	1st to 10th	Night	31% 12% 3 8% 5% 4 4 3 4 6% 19%	2470
	11th to 20th	Night	31% 12% 3 7% 4 4 4 3 4 5% 24%	2402
	21st to end	Night	33% 11% 2 7% 5% 4 4 3 5% 5% 20%	2006
March	1st to 10th	Night	26% 21% 3 5% 4 4 3 3 5% 5% 21%	3434
	11th to 20th	Night	22% 14% 4 6% 4 3 3 2 3 3 36%	3490
	21st to end	Night	32% 17% 3 9% 4 4 3 3 4 4 16%	3828
April	1st to 10th	Night	32% 12% 4 7% 4 4 3 3 4 6% 21%	1914
	11th to 20th	Night	25% 12% 4 7% 4 3 4 3 4 5% 28%	1837
	21st to end	Night	25% 12% 3 6% 4 4 4 3 4 6% 27%	1710
May	1st to 10th	Night	24% 10% 2 6% 3 3 3 2 3 4 39%	2828
	11th to 20th	Night	12% 9% 2 5% 3 2 3 3 4 7% 50%	2516
	21st to end	Night	19% 11% 3 6% 3 3 3 3 5% 7% 36%	2762
June	1st to 10th	Night	20% 8% 3 6% 5% 4 4 4 5% 5% 34%	1520
	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	17% 7% 3 6% 4 3 3 3 4 5% 45%	2280
	11th to 20th	Night	21% 7% 3 6% 4 3 4 3 5% 7% 38%	2280
	21st to end	Night	28% 9% 3 6% 4 2 3 2 4 4 33%	2508
November	1st to 10th	Night	34% 9% 3 6% 3 4 4 3 6% 5% 23%	2490
	11th to 20th	Night	35% 9% 3 7% 4 4 3 3 4 6% 22%	2660
	21st to end	Night	26% 9% 2 8% 4 4 4 3 5% 5% 30%	2660
December	1st to 10th	Night	29% 11% 3 5% 5% 3 3 3 5% 6% 27%	2660
	11th to 20th	Night	34% 10% 3 8% 5% 4 3 3 5% 6% 20%	3276
	21st to end	Night	36% 13% 3 8% 4 4 3 3 3 4 19%	4862

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	73% 10% 9% 4 3 1	2539
	11th to 20th	Day	68% 7% 8% 9% 5% 4	2682
	21st to end	Day	69% 10% 6% 7% 6% 2	3146
February	1st to 10th	Day	68% 8% 10% 9% 3 2	1710
	11th to 20th	Day	64% 9% 11% 10% 4 2	1674
	21st to end	Day	68% 6% 10% 11% 4 2	1447
March	1st to 10th	Day	58% 12% 15% 12% 3	3437
	11th to 20th	Day	49% 11% 9% 17% 11% 2	3490
	21st to end	Day	69% 12% 9% 7% 4	3825
April	1st to 10th	Day	66% 10% 11% 9% 4	2264
	11th to 20th	Day	60% 9% 12% 12% 6% 2	2289
	21st to end	Day	55% 11% 15% 13% 6% 1	2470
May	1st to 10th	Day	45% 12% 17% 14% 12%	4141
	11th to 20th	Day	31% 10% 23% 23% 12% 1	4380
	21st to end	Day	44% 15% 28% 12% 1	4814
June	1st to 10th	Day	52% 8% 15% 20% 5%	2660
	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	43% 8% 14% 16% 16% 4	1900
	11th to 20th	Day	48% 9% 13% 16% 13% 2	1900
	21st to end	Day	53% 8% 10% 13% 11% 4	2090
November	1st to 10th	Day	64% 9% 9% 13% 5%	1617
	11th to 20th	Day	63% 8% 11% 8% 7% 3	1520
	21st to end	Day	60% 8% 8% 7% 11% 6%	1520
December	1st to 10th	Day	57% 8% 12% 11% 11% 1	1520
	11th to 20th	Day	66% 8% 13% 9% 4	1928
	21st to end	Day	71% 9% 10% 7% 3 1	2794
January	1st to 10th	Night	75% 9% 7% 4 3 2	4406
	11th to 20th	Night	70% 6% 8% 9% 5% 3	4266
	21st to end	Night	74% 5% 6% 8% 6% 2	4521
February	1st to 10th	Night	66% 9% 9% 10% 4 1	2470
	11th to 20th	Night	62% 7% 12% 11% 6% 1	2404
	21st to end	Night	65% 8% 9% 10% 5% 2	2006
March	1st to 10th	Night	60% 11% 13% 13% 3	3434
	11th to 20th	Night	50% 9% 12% 16% 10% 4	3490
	21st to end	Night	66% 11% 12% 9% 1	3828
April	1st to 10th	Night	63% 8% 13% 11% 5%	1914
	11th to 20th	Night	58% 10% 10% 14% 4 3	1837
	21st to end	Night	57% 10% 12% 14% 5% 2	1710
May	1st to 10th	Night	45% 11% 15% 19% 9% 1	2828
	11th to 20th	Night	33% 12% 19% 23% 10% 3	2516
	21st to end	Night	43% 16% 27% 12% 2	2762
June	1st to 10th	Night	48% 10% 18% 21% 3	1520
	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	41% 7% 11% 21% 15% 5%	2280
	11th to 20th	Night	46% 7% 13% 17% 14% 3	2280
	21st to end	Night	54% 6% 10% 13% 12% 5%	2508
November	1st to 10th	Night	60% 8% 11% 12% 8% 1	2490
	11th to 20th	Night	64% 7% 10% 10% 6% 4	2660
	21st to end	Night	55% 8% 9% 10% 11% 7%	2660
December	1st to 10th	Night	58% 7% 10% 12% 12% 1	2660
	11th to 20th	Night	65% 8% 10% 9% 7% 1	3276
	21st to end	Night	66% 10% 10% 10% 3 1	4862

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% 20% 12% 8% 1	180
	11th to 20th	Day	43% 9% 17% 15% 11% 4	270
	21st to end	Day	38% 8% 15% 20% 16% 3	407
February	1st to 10th	Day	36% 9% 19% 22% 13% 1	370
	11th to 20th	Day	37% 11% 19% 23% 9% 1	365
	21st to end	Day	36% 13% 21% 22% 8%	324
March	1st to 10th	Day	37% 13% 21% 22% 7% 1	460
	11th to 20th	Day	32% 8% 21% 26% 12% 2	460
	21st to end	Day	35% 13% 24% 20% 8% 1	506
April	1st to 10th	Day	34% 13% 21% 19% 12% 1	460
	11th to 20th	Day	31% 12% 25% 22% 7% 3	452
	21st to end	Day	27% 11% 25% 26% 9% 2	460
May	1st to 10th	Day	20% 11% 28% 26% 13% 2	463
	11th to 20th	Day	27% 10% 22% 25% 13% 3	488
	21st to end	Day	17% 10% 25% 31% 15% 2	529
June	1st to 10th	Day	24% 5% 26% 29% 14% 2	490
	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	33% 11% 21% 21% 13% 1	276
	11th to 20th	Day	35% 9% 16% 26% 13% 2	180
	21st to end	Day	36% 9% 17% 24% 15%	180
December	1st to 10th	Day	34% 10% 21% 21% 12% 3	180
	11th to 20th	Day	45% 8% 20% 21% 5% 1	180
	21st to end	Day	40% 13% 16% 25% 5% 2	198
January	1st to 10th	Night	46% 9% 16% 16% 11% 2	760
	11th to 20th	Night	41% 7% 13% 22% 15% 2	760
	21st to end	Night	37% 5% 14% 28% 14% 3	836
February	1st to 10th	Night	37% 6% 15% 25% 16% 2	760
	11th to 20th	Night	36% 8% 14% 26% 15% 1	744
	21st to end	Night	38% 10% 16% 22% 14% 1	628
March	1st to 10th	Night	35% 9% 16% 26% 13% 1	760
	11th to 20th	Night	34% 9% 12% 28% 16% 2	760
	21st to end	Night	37% 9% 16% 24% 12% 1	836
April	1st to 10th	Night	36% 8% 17% 19% 18% 2	760
	11th to 20th	Night	31% 8% 17% 26% 16% 3	709
	21st to end	Night	31% 6% 15% 27% 20% 1	570
May	1st to 10th	Night	25% 6% 21% 27% 19% 3	551
	11th to 20th	Night	26% 3 15% 27% 25% 3	374
	21st to end	Night	23% 6% 20% 25% 24% 2	411
June	1st to 10th	Night	23% 2 14% 36% 24% 2	380
	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	36% 6% 14% 25% 17% 1	748
	11th to 20th	Night	38% 7% 15% 25% 14% 2	760
	21st to end	Night	28% 8% 17% 30% 16% 2	760
December	1st to 10th	Night	33% 8% 14% 26% 16% 1	760
	11th to 20th	Night	40% 7% 16% 23% 13% 1	760
	21st to end	Night	44% 10% 16% 22% 8%	836

Page generated at 2024-10-30 10:19:25. Version ac07

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