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 2024-03-18.

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	24% 9% 3 6% 5% 3 4 4 4 6% 33%	78681
	Night	27% 10% 3 6% 4 2 3 3 4 6% 31%	81122
Transparency	Day	51% 9% 14% 16% 9% 2	78392
	Night	55% 8% 11% 14% 9% 3	80932
Seeing	Day	23% 8% 22% 29% 15% 3	13935
	Night	29% 6% 14% 27% 21% 3	23056

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% 18% 4 7% 4 2 4 4 3 4 12%	2539
	11th to 20th	Day	43% 11% 2 5% 4 3 3 3 3 4 19%	2682
	21st to end	Day	41% 12% 3 6% 4 3 3 4 4 4 15%	3146
February	1st to 10th	Day	34% 11% 4 7% 7% 4 4 4 5% 5% 16%	1710
	11th to 20th	Day	32% 11% 4 7% 5% 2 4 4 5% 5% 20%	1665
	21st to end	Day	33% 14% 4 7% 6% 3 4 3 4 3 19%	1447
March	1st to 10th	Day	34% 12% 4 7% 6% 3 5% 4 5% 5% 15%	2085
	11th to 20th	Day	35% 10% 3 5% 6% 3 3 4 5% 5% 20%	2059
	21st to end	Day	34% 12% 4 9% 6% 3 4 4 4 4 15%	2178
April	1st to 10th	Day	34% 11% 4 8% 6% 3 4 4 4 5% 16%	2144
	11th to 20th	Day	28% 11% 3 7% 6% 3 5% 4 5% 6% 22%	2163
	21st to end	Day	25% 10% 4 6% 5% 3 4 4 5% 7% 26%	2340
May	1st to 10th	Day	19% 10% 3 7% 5% 3 4 5% 6% 7% 32%	2358
	11th to 20th	Day	24% 10% 3 6% 6% 3 5% 4 4 7% 28%	2477
	21st to end	Day	25% 8% 3 6% 5% 3 4 5% 5% 10% 26%	2723
June	1st to 10th	Day	26% 7% 3 6% 4 3 5% 4 5% 6% 32%	2520
	11th to 20th	Day	20% 7% 4 6% 5% 3 4 4 5% 8% 34%	2520
	21st to end	Day	12% 7% 3 5% 4 2 3 3 5% 8% 50%	2520
July	1st to 10th	Day	6% 5% 2 4 4 3 3 3 5% 7% 57%	2520
	11th to 20th	Day	11% 5% 1 3 3 1 3 2 4 7% 60%	2520
	21st to end	Day	5% 3 2 3 3 2 3 3 3 7% 66%	2608
August	1st to 10th	Day	4 7% 3 4 4 3 3 4 4 8% 56%	2328
	11th to 20th	Day	7% 5% 1 3 4 2 3 4 5% 7% 59%	2298
	21st to end	Day	7% 5% 2 4 4 2 4 4 5% 8% 55%	2481
September	1st to 10th	Day	7% 3 1 3 3 2 3 4 4 6% 65%	2160
	11th to 20th	Day	13% 7% 2 5% 4 3 5% 4 5% 8% 45%	2078
	21st to end	Day	15% 6% 3 5% 4 3 4 3 5% 7% 45%	1944
October	1st to 10th	Day	19% 6% 3 6% 6% 3 4 5% 5% 6% 39%	1800
	11th to 20th	Day	23% 6% 2 5% 4 3 4 4 5% 6% 36%	1800
	21st to end	Day	26% 10% 2 5% 5% 3 3 4 5% 6% 32%	1980
November	1st to 10th	Day	35% 10% 3 5% 6% 3 4 5% 5% 5% 20%	1606
	11th to 20th	Day	35% 8% 3 6% 5% 3 4 3 5% 7% 20%	1520
	21st to end	Day	32% 8% 4 5% 4 3 5% 4 4 6% 25%	1520
December	1st to 10th	Day	29% 9% 2 6% 6% 3 4 3 5% 5% 26%	1520
	11th to 20th	Day	34% 11% 3 7% 6% 4 4 5% 5% 4 18%	1928
	21st to end	Day	41% 13% 3 6% 4 3 3 4 4 5% 14%	2794
January	1st to 10th	Night	41% 15% 3 7% 6% 3 3 3 3 4 11%	4406
	11th to 20th	Night	42% 13% 3 6% 4 2 3 2 2 3 19%	4266
	21st to end	Night	47% 12% 3 5% 3 2 2 2 3 4 16%	4521
February	1st to 10th	Night	32% 11% 4 7% 6% 3 5% 4 4 6% 19%	2470
	11th to 20th	Night	31% 11% 4 6% 5% 3 4 4 4 5% 24%	2402
	21st to end	Night	33% 11% 3 6% 5% 3 4 5% 5% 5% 20%	2006
March	1st to 10th	Night	33% 13% 4 6% 4 2 3 4 5% 5% 21%	2092
	11th to 20th	Night	31% 10% 3 6% 6% 3 5% 3 3 5% 25%	2067
	21st to end	Night	35% 12% 4 7% 5% 2 4 3 4 5% 17%	2178
April	1st to 10th	Night	33% 11% 4 7% 5% 3 4 4 4 5% 21%	1814
	11th to 20th	Night	26% 11% 5% 6% 5% 2 4 4 4 5% 28%	1740
	21st to end	Night	25% 11% 4 6% 4 3 5% 4 5% 6% 28%	1620
May	1st to 10th	Night	18% 12% 3 6% 4 2 4 4 3 6% 38%	1602
	11th to 20th	Night	22% 13% 4 6% 5% 2 4 4 4 7% 30%	1416
	21st to end	Night	21% 10% 4 6% 4 3 4 5% 5% 8% 31%	1552
June	1st to 10th	Night	20% 8% 4 6% 6% 3 5% 5% 5% 6% 34%	1440
	11th to 20th	Night	17% 7% 3 6% 4 2 3 4 5% 9% 41%	1440
	21st to end	Night	13% 8% 2 4 3 2 3 3 4 6% 52%	1440
July	1st to 10th	Night	7% 7% 2 4 3 3 3 3 4 7% 58%	1440
	11th to 20th	Night	9% 5% 2 5% 3 2 3 3 4 7% 59%	1440
	21st to end	Night	4 5% 3 4 3 2 3 3 3 7% 65%	1707
August	1st to 10th	Night	4 8% 2 4 4 3 3 4 6% 9% 52%	1611
	11th to 20th	Night	6% 6% 2 4 3 2 3 3 4 7% 59%	1602
	21st to end	Night	8% 8% 3 4 3 2 2 4 3 8% 56%	1873
September	1st to 10th	Night	10% 6% 2 3 3 2 2 2 4 6% 61%	1800
	11th to 20th	Night	13% 7% 3 5% 4 3 4 3 4 7% 48%	1880
	21st to end	Night	17% 6% 2 3 4 2 3 3 4 7% 48%	2016
October	1st to 10th	Night	18% 7% 3 5% 5% 2 3 4 3 5% 44%	2160
	11th to 20th	Night	22% 6% 3 4 4 2 4 3 5% 7% 40%	2160
	21st to end	Night	27% 10% 3 6% 5% 2 3 3 4 5% 34%	2376
November	1st to 10th	Night	33% 9% 3 5% 4 3 4 4 6% 6% 23%	2467
	11th to 20th	Night	35% 8% 3 6% 5% 3 4 4 4 5% 23%	2660
	21st to end	Night	27% 8% 2 7% 5% 3 4 4 5% 5% 30%	2660
December	1st to 10th	Night	30% 10% 3 5% 5% 3 4 4 5% 6% 27%	2660
	11th to 20th	Night	34% 10% 3 7% 5% 3 3 4 5% 7% 20%	3276
	21st to end	Night	36% 13% 3 7% 5% 3 4 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	68% 8% 11% 10% 3	2085
	11th to 20th	Day	63% 8% 11% 12% 6% 1	2059
	21st to end	Day	71% 9% 9% 9% 2	2178
April	1st to 10th	Day	67% 9% 11% 9% 4	2144
	11th to 20th	Day	61% 9% 12% 11% 5% 2	2166
	21st to end	Day	56% 10% 14% 13% 6% 1	2340
May	1st to 10th	Day	49% 9% 18% 16% 7% 1	2358
	11th to 20th	Day	54% 10% 16% 13% 6% 1	2480
	21st to end	Day	52% 12% 18% 15% 2	2724
June	1st to 10th	Day	52% 8% 15% 20% 5%	2520
	11th to 20th	Day	45% 11% 22% 18% 4	2520
	21st to end	Day	33% 9% 21% 26% 9% 3	2520
July	1st to 10th	Day	27% 8% 20% 23% 19% 3	2451
	11th to 20th	Day	26% 7% 14% 25% 20% 7%	2445
	21st to end	Day	20% 6% 17% 32% 23% 4	2463
August	1st to 10th	Day	29% 11% 17% 29% 11% 4	2312
	11th to 20th	Day	24% 10% 17% 30% 15% 4	2298
	21st to end	Day	25% 10% 18% 25% 19% 3	2481
September	1st to 10th	Day	21% 7% 17% 29% 17% 9%	2160
	11th to 20th	Day	38% 9% 16% 20% 12% 5%	2078
	21st to end	Day	38% 9% 13% 20% 15% 4	1944
October	1st to 10th	Day	43% 8% 14% 15% 15% 4	1800
	11th to 20th	Day	46% 9% 13% 17% 13% 2	1800
	21st to end	Day	52% 9% 11% 13% 12% 4	1980
November	1st to 10th	Day	64% 9% 9% 13% 5%	1606
	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	64% 8% 10% 12% 5%	2092
	11th to 20th	Night	62% 7% 11% 13% 7% 1	2067
	21st to end	Night	68% 8% 12% 11% 2	2178
April	1st to 10th	Night	65% 8% 12% 11% 5%	1814
	11th to 20th	Night	58% 10% 10% 14% 4 3	1740
	21st to end	Night	58% 9% 12% 14% 6% 2	1620
May	1st to 10th	Night	47% 10% 15% 20% 7% 2	1602
	11th to 20th	Night	55% 8% 14% 15% 5% 3	1416
	21st to end	Night	51% 12% 17% 16% 3	1552
June	1st to 10th	Night	48% 10% 18% 22% 2	1440
	11th to 20th	Night	40% 11% 22% 22% 4	1440
	21st to end	Night	33% 10% 17% 27% 9% 3	1440
July	1st to 10th	Night	29% 8% 18% 24% 17% 6%	1400
	11th to 20th	Night	26% 7% 14% 21% 25% 7%	1392
	21st to end	Night	21% 5% 16% 27% 25% 5%	1612
August	1st to 10th	Night	29% 10% 16% 29% 12% 4	1602
	11th to 20th	Night	26% 6% 15% 30% 17% 5%	1602
	21st to end	Night	26% 8% 13% 30% 18% 5%	1873
September	1st to 10th	Night	26% 6% 12% 25% 20% 11%	1800
	11th to 20th	Night	38% 7% 15% 21% 13% 6%	1880
	21st to end	Night	36% 7% 14% 18% 18% 6%	2016
October	1st to 10th	Night	42% 7% 12% 20% 14% 6%	2160
	11th to 20th	Night	44% 7% 13% 18% 15% 3	2160
	21st to end	Night	53% 7% 10% 12% 13% 5%	2376
November	1st to 10th	Night	60% 9% 11% 12% 8% 1	2467
	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% 25% 12% 1	449
	21st to end	Day	35% 12% 24% 20% 8% 1	462
April	1st to 10th	Day	36% 12% 20% 19% 11% 1	420
	11th to 20th	Day	33% 12% 23% 21% 7% 3	412
	21st to end	Day	27% 11% 25% 27% 9% 2	420
May	1st to 10th	Day	19% 10% 29% 26% 13% 2	423
	11th to 20th	Day	30% 11% 21% 23% 13% 2	448
	21st to end	Day	18% 10% 26% 30% 14% 2	485
June	1st to 10th	Day	24% 5% 26% 29% 14% 2	450
	11th to 20th	Day	18% 8% 35% 28% 10%	450
	21st to end	Day	9% 4 22% 45% 18% 1	450
July	1st to 10th	Day	9% 2 26% 41% 19% 2	446
	11th to 20th	Day	8% 2 26% 40% 22% 2	444
	21st to end	Day	3 2 25% 44% 22% 4	487
August	1st to 10th	Day	6% 2 19% 45% 22% 5%	447
	11th to 20th	Day	5% 3 14% 44% 29% 4	437
	21st to end	Day	8% 3 23% 41% 20% 4	495
September	1st to 10th	Day	8% 3 23% 36% 24% 6%	450
	11th to 20th	Day	14% 6% 21% 33% 24% 2	450
	21st to end	Day	15% 8% 23% 32% 18% 4	450
October	1st to 10th	Day	20% 7% 24% 27% 17% 4	450
	11th to 20th	Day	25% 6% 15% 27% 19% 8%	450
	21st to end	Day	28% 9% 21% 24% 13% 5%	495
November	1st to 10th	Day	31% 11% 22% 21% 14% 1	271
	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% 1	752
	21st to end	Night	38% 8% 16% 24% 13% 1	792
April	1st to 10th	Night	38% 8% 16% 19% 17% 2	720
	11th to 20th	Night	32% 8% 16% 26% 16% 3	672
	21st to end	Night	31% 6% 15% 27% 20% 1	540
May	1st to 10th	Night	25% 6% 21% 26% 20% 3	522
	11th to 20th	Night	27% 4 14% 26% 26% 3	354
	21st to end	Night	24% 6% 20% 25% 23% 2	389
June	1st to 10th	Night	23% 3 13% 36% 24% 2	360
	11th to 20th	Night	19% 3 18% 38% 20% 3	360
	21st to end	Night	16% 4 12% 34% 31% 3	360
July	1st to 10th	Night	9% 4 12% 37% 36% 2	350
	11th to 20th	Night	11% 3 14% 43% 26% 2	348
	21st to end	Night	6% 3 10% 40% 37% 5%	525
August	1st to 10th	Night	11% 3 9% 30% 40% 7%	537
	11th to 20th	Night	9% 2 8% 28% 41% 11%	534
	21st to end	Night	12% 4 13% 34% 33% 4	685
September	1st to 10th	Night	11% 2 12% 30% 40% 5%	720
	11th to 20th	Night	15% 2 12% 28% 32% 11%	720
	21st to end	Night	19% 3 13% 31% 29% 5%	720
October	1st to 10th	Night	21% 2 17% 29% 25% 6%	720
	11th to 20th	Night	23% 4 10% 29% 26% 8%	720
	21st to end	Night	29% 6% 17% 24% 18% 5%	792
November	1st to 10th	Night	35% 6% 14% 25% 17% 1	740
	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 2024-03-15 11:01:44. Version ac07

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