Feather River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Feather River Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	10% 3 1 3 3 2 3 3 4 6% 64%	74746
	Night	13% 4 1 3 3 2 3 3 4 6% 59%	75032
Transparency	Day	24% 3 8% 18% 24% 22%	74460
	Night	27% 4 8% 18% 22% 21%	74840
Seeing	Day	11% 6% 19% 29% 27% 8%	13995
	Night	13% 3 13% 34% 32% 6%	23370

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	28% 5% 2 3 4 3 4 3 5% 6% 37%	1519
	11th to 20th	Day	20% 4 2 3 4 2 3 3 3 6% 49%	1597
	21st to end	Day	20% 6% 2 4 3 2 4 3 5% 7% 44%	1782
February	1st to 10th	Day	21% 4 2 3 3 2 3 3 4 6% 47%	1620
	11th to 20th	Day	18% 5% 2 4 4 2 3 3 4 6% 49%	1656
	21st to end	Day	21% 5% 1 3 3 3 4 3 5% 7% 47%	1480
March	1st to 10th	Day	21% 6% 2 5% 4 3 5% 4 4 8% 38%	1874
	11th to 20th	Day	23% 6% 2 4 4 2 4 3 5% 7% 41%	1980
	21st to end	Day	20% 5% 2 4 4 2 3 4 5% 8% 45%	2247
April	1st to 10th	Day	16% 5% 3 4 4 2 3 3 5% 8% 46%	2160
	11th to 20th	Day	13% 4 1 4 3 2 3 3 5% 6% 56%	2129
	21st to end	Day	7% 4 2 3 3 2 3 4 4 8% 61%	2160
May	1st to 10th	Day	7% 4 1 3 2 2 4 3 4 6% 63%	2258
	11th to 20th	Day	5% 3 1 3 3 2 3 4 4 6% 65%	2477
	21st to end	Day	6% 3 1 3 3 2 3 4 5% 7% 63%	2723
June	1st to 10th	Day	6% 3 1 3 2 1 4 3 5% 7% 64%	2520
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 5% 79%	2520
	21st to end	Day	2 1 1 1 1 1 1 2 3 85%	2520
July	1st to 10th	Day	1 1 1 1 2 2 2 3 88%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 89%	2520
	21st to end	Day	1 1 1 1 1 1 2 2 2 3 85%	2563
August	1st to 10th	Day	2 1 1 1 1 1 1 2 2 4 84%	2328
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 88%	2194
	21st to end	Day	1 1 1 1 1 1 2 91%	2376
September	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	2160
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	2160
	21st to end	Day	4 2 2 2 1 1 2 3 5% 78%	1929
October	1st to 10th	Day	5% 2 1 2 2 2 3 3 3 4 72%	1800
	11th to 20th	Day	7% 2 1 2 2 1 3 3 4 6% 68%	1800
	21st to end	Day	10% 2 1 2 3 2 3 4 4 6% 63%	1980
November	1st to 10th	Day	14% 4 1 3 3 2 4 4 4 8% 53%	1717
	11th to 20th	Day	15% 3 1 3 4 3 4 4 5% 7% 51%	1710
	21st to end	Day	14% 4 2 3 4 2 3 3 4 6% 54%	1525
December	1st to 10th	Day	19% 4 2 3 4 2 3 4 4 6% 49%	1520
	11th to 20th	Day	33% 6% 3 6% 3 2 4 3 3 6% 31%	1928
	21st to end	Day	20% 7% 2 6% 4 3 5% 4 5% 8% 36%	2794
January	1st to 10th	Night	23% 6% 2 4 4 2 3 4 4 7% 41%	2646
	11th to 20th	Night	19% 6% 2 3 3 3 3 4 4 6% 47%	2438
	21st to end	Night	19% 5% 2 4 3 2 3 4 4 6% 47%	2574
February	1st to 10th	Night	19% 4 1 3 3 2 2 3 4 6% 51%	2340
	11th to 20th	Night	16% 5% 2 4 4 2 4 4 5% 6% 50%	2190
	21st to end	Night	20% 5% 2 3 3 2 3 4 4 5% 49%	1776
March	1st to 10th	Night	23% 7% 3 5% 5% 2 3 4 4 5% 39%	2084
	11th to 20th	Night	21% 5% 2 4 3 2 3 4 5% 9% 43%	1980
	21st to end	Night	19% 5% 2 4 3 2 4 4 5% 6% 47%	2107
April	1st to 10th	Night	12% 6% 2 4 4 2 4 4 5% 8% 48%	1800
	11th to 20th	Night	11% 3 2 3 3 2 2 4 4 8% 56%	1779
	21st to end	Night	8% 3 1 2 3 2 3 3 4 7% 64%	1800
May	1st to 10th	Night	7% 3 1 2 3 2 3 3 4 6% 65%	1699
	11th to 20th	Night	5% 2 1 2 4 2 4 5% 5% 8% 61%	1416
	21st to end	Night	6% 3 1 3 3 2 3 4 5% 6% 65%	1552
June	1st to 10th	Night	5% 3 1 2 3 1 3 4 5% 7% 64%	1440
	11th to 20th	Night	2 1 1 2 2 3 3 4 7% 76%	1440
	21st to end	Night	2 1 1 2 2 1 2 2 3 3 81%	1440
July	1st to 10th	Night	1 1 2 1 1 2 2 2 89%	1440
	11th to 20th	Night	1 1 1 1 1 2 2 2 89%	1440
	21st to end	Night	1 1 1 1 1 1 2 3 3 85%	1751
August	1st to 10th	Night	2 2 1 2 2 1 2 2 2 4 81%	1611
	11th to 20th	Night	1 1 1 1 2 2 3 3 84%	1705
	21st to end	Night	1 1 1 1 1 1 2 2 3 88%	1980
September	1st to 10th	Night	2 1 1 1 1 2 1 2 3 88%	1800
	11th to 20th	Night	3 2 2 2 1 2 2 3 4 78%	1800
	21st to end	Night	3 1 1 1 1 1 2 3 3 5% 80%	2027
October	1st to 10th	Night	6% 3 1 2 3 1 2 2 2 4 74%	2160
	11th to 20th	Night	6% 2 1 2 2 2 2 3 4 5% 71%	2160
	21st to end	Night	8% 3 1 2 2 1 2 2 5% 6% 68%	2376
November	1st to 10th	Night	16% 4 1 3 2 2 3 3 5% 7% 54%	2360
	11th to 20th	Night	13% 3 1 3 3 2 3 4 6% 7% 55%	2470
	21st to end	Night	14% 4 1 3 3 3 3 3 4 6% 56%	2653
December	1st to 10th	Night	22% 4 1 3 3 1 2 3 4 7% 49%	2660
	11th to 20th	Night	34% 5% 2 3 4 2 3 4 4 6% 33%	3276
	21st to end	Night	24% 6% 2 5% 5% 3 4 4 4 6% 36%	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	49% 6% 10% 21% 10% 5%	1519
	11th to 20th	Day	39% 4 8% 17% 17% 15%	1597
	21st to end	Day	41% 4 9% 16% 21% 9%	1782
February	1st to 10th	Day	38% 3 10% 20% 19% 9%	1620
	11th to 20th	Day	36% 5% 9% 20% 23% 8%	1665
	21st to end	Day	38% 3 9% 24% 18% 8%	1480
March	1st to 10th	Day	44% 6% 10% 19% 16% 6%	1874
	11th to 20th	Day	44% 4 9% 20% 17% 6%	1980
	21st to end	Day	38% 6% 12% 20% 18% 5%	2247
April	1st to 10th	Day	37% 5% 10% 23% 20% 6%	2160
	11th to 20th	Day	29% 4 11% 23% 24% 9%	2132
	21st to end	Day	22% 5% 12% 30% 26% 7%	2160
May	1st to 10th	Day	21% 4 10% 24% 28% 13%	2258
	11th to 20th	Day	19% 4 9% 27% 29% 12%	2480
	21st to end	Day	20% 5% 14% 28% 24% 9%	2724
June	1st to 10th	Day	19% 5% 10% 25% 25% 15%	2520
	11th to 20th	Day	10% 3 8% 20% 31% 29%	2520
	21st to end	Day	7% 2 4 14% 35% 39%	2520
July	1st to 10th	Day	5% 1 3 9% 28% 54%	2451
	11th to 20th	Day	5% 1 3 12% 25% 55%	2445
	21st to end	Day	7% 1 3 7% 25% 56%	2421
August	1st to 10th	Day	7% 2 3 12% 31% 45%	2312
	11th to 20th	Day	6% 1 2 8% 36% 47%	2194
	21st to end	Day	4 1 2 10% 36% 47%	2376
September	1st to 10th	Day	5% 1 2 8% 27% 57%	2160
	11th to 20th	Day	12% 2 5% 20% 38% 23%	2160
	21st to end	Day	11% 2 5% 20% 32% 31%	1929
October	1st to 10th	Day	16% 3 7% 16% 30% 29%	1800
	11th to 20th	Day	17% 5% 6% 18% 23% 31%	1800
	21st to end	Day	22% 3 7% 20% 24% 23%	1980
November	1st to 10th	Day	29% 5% 8% 25% 19% 15%	1717
	11th to 20th	Day	34% 4 10% 22% 20% 9%	1710
	21st to end	Day	31% 5% 9% 21% 22% 13%	1525
December	1st to 10th	Day	36% 5% 9% 20% 21% 10%	1520
	11th to 20th	Day	57% 3 7% 13% 14% 5%	1928
	21st to end	Day	46% 6% 16% 18% 11% 4	2794
January	1st to 10th	Night	43% 4 13% 22% 12% 6%	2646
	11th to 20th	Night	39% 6% 9% 14% 17% 15%	2438
	21st to end	Night	39% 4 10% 15% 21% 10%	2574
February	1st to 10th	Night	36% 3 8% 20% 20% 13%	2340
	11th to 20th	Night	34% 4 9% 20% 23% 10%	2192
	21st to end	Night	37% 4 8% 22% 21% 9%	1776
March	1st to 10th	Night	47% 4 10% 15% 17% 6%	2084
	11th to 20th	Night	38% 4 9% 21% 18% 9%	1980
	21st to end	Night	38% 6% 10% 21% 18% 7%	2107
April	1st to 10th	Night	34% 6% 12% 20% 19% 9%	1800
	11th to 20th	Night	27% 5% 11% 24% 20% 13%	1779
	21st to end	Night	21% 5% 13% 28% 26% 9%	1800
May	1st to 10th	Night	20% 4 11% 20% 31% 14%	1699
	11th to 20th	Night	20% 6% 11% 29% 21% 15%	1416
	21st to end	Night	20% 5% 13% 28% 25% 9%	1552
June	1st to 10th	Night	18% 6% 12% 26% 26% 13%	1440
	11th to 20th	Night	9% 4 9% 19% 29% 30%	1440
	21st to end	Night	11% 2 3 13% 29% 42%	1440
July	1st to 10th	Night	5% 1 2 11% 26% 54%	1400
	11th to 20th	Night	5% 1 2 11% 20% 60%	1392
	21st to end	Night	7% 1 3 8% 22% 60%	1654
August	1st to 10th	Night	11% 1 3 13% 28% 45%	1602
	11th to 20th	Night	7% 1 3 9% 32% 47%	1705
	21st to end	Night	6% 1 3 10% 29% 52%	1980
September	1st to 10th	Night	6% 1 2 7% 28% 56%	1800
	11th to 20th	Night	11% 2 5% 16% 39% 26%	1800
	21st to end	Night	9% 2 4 17% 30% 37%	2027
October	1st to 10th	Night	17% 3 6% 16% 27% 32%	2160
	11th to 20th	Night	17% 3 6% 16% 27% 32%	2160
	21st to end	Night	18% 3 7% 20% 25% 27%	2376
November	1st to 10th	Night	30% 4 9% 22% 18% 16%	2360
	11th to 20th	Night	28% 5% 12% 25% 20% 11%	2470
	21st to end	Night	32% 4 6% 21% 23% 14%	2653
December	1st to 10th	Night	37% 4 10% 20% 16% 14%	2660
	11th to 20th	Night	52% 4 8% 14% 17% 6%	3276
	21st to end	Night	49% 7% 11% 17% 11% 4	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	45% 4 16% 21% 13% 2	180
	11th to 20th	Day	25% 7% 15% 30% 15% 6%	299
	21st to end	Day	20% 7% 20% 25% 22% 6%	374
February	1st to 10th	Day	21% 8% 17% 27% 23% 4	340
	11th to 20th	Day	19% 10% 26% 25% 17% 3	371
	21st to end	Day	19% 10% 24% 31% 11% 4	346
March	1st to 10th	Day	28% 10% 29% 19% 11% 2	420
	11th to 20th	Day	27% 9% 23% 21% 15% 5%	420
	21st to end	Day	18% 13% 26% 27% 15%	462
April	1st to 10th	Day	18% 10% 28% 24% 17% 4	420
	11th to 20th	Day	16% 12% 27% 24% 16% 6%	412
	21st to end	Day	7% 11% 23% 30% 22% 6%	420
May	1st to 10th	Day	8% 12% 27% 28% 20% 5%	423
	11th to 20th	Day	8% 10% 23% 29% 24% 7%	448
	21st to end	Day	5% 8% 21% 26% 30% 11%	485
June	1st to 10th	Day	5% 8% 19% 26% 31% 10%	450
	11th to 20th	Day	4 6% 21% 36% 25% 8%	450
	21st to end	Day	1 4 16% 37% 33% 9%	450
July	1st to 10th	Day	2 2 13% 38% 39% 6%	446
	11th to 20th	Day	1 11% 37% 41% 9%	444
	21st to end	Day	1 1 9% 36% 43% 10%	487
August	1st to 10th	Day	1 2 13% 34% 36% 14%	447
	11th to 20th	Day	1 1 15% 30% 37% 16%	437
	21st to end	Day	1 1 10% 35% 41% 12%	495
September	1st to 10th	Day	2 2 9% 40% 34% 13%	450
	11th to 20th	Day	4 4 18% 28% 35% 10%	450
	21st to end	Day	2 5% 22% 29% 32% 10%	450
October	1st to 10th	Day	4 8% 22% 25% 31% 11%	450
	11th to 20th	Day	6% 6% 15% 26% 34% 12%	450
	21st to end	Day	12% 5% 18% 28% 26% 11%	495
November	1st to 10th	Day	18% 2 16% 26% 28% 11%	313
	11th to 20th	Day	13% 4 12% 33% 25% 13%	270
	21st to end	Day	13% 3 22% 31% 22% 8%	183
December	1st to 10th	Day	25% 6% 17% 24% 18% 10%	180
	11th to 20th	Day	27% 3 19% 21% 21% 9%	180
	21st to end	Day	23% 6% 22% 24% 22% 3	198
January	1st to 10th	Night	25% 3 13% 29% 23% 6%	760
	11th to 20th	Night	20% 4 15% 34% 22% 5%	736
	21st to end	Night	21% 2 15% 33% 24% 5%	792
February	1st to 10th	Night	20% 3 12% 37% 24% 4	720
	11th to 20th	Night	15% 5% 15% 35% 25% 5%	704
	21st to end	Night	21% 5% 17% 36% 18% 3	592
March	1st to 10th	Night	24% 6% 16% 30% 19% 4	720
	11th to 20th	Night	22% 5% 14% 31% 25% 4	720
	21st to end	Night	19% 6% 20% 32% 21% 2	792
April	1st to 10th	Night	13% 6% 19% 38% 22% 2	720
	11th to 20th	Night	12% 5% 19% 36% 22% 6%	711
	21st to end	Night	9% 5% 18% 35% 29% 5%	720
May	1st to 10th	Night	9% 3 20% 37% 28% 4	619
	11th to 20th	Night	5% 3 18% 39% 32% 3	354
	21st to end	Night	6% 4 13% 35% 40% 2	389
June	1st to 10th	Night	6% 3 15% 36% 36% 4	360
	11th to 20th	Night	1 2 18% 39% 36% 3	360
	21st to end	Night	3 1 12% 39% 41% 5%	360
July	1st to 10th	Night	1 7% 42% 46% 4	350
	11th to 20th	Night	1 1 7% 43% 46% 3	348
	21st to end	Night	1 3 34% 56% 6%	569
August	1st to 10th	Night	3 1 4 35% 52% 5%	537
	11th to 20th	Night	5% 37% 50% 8%	637
	21st to end	Night	1 1 4 33% 56% 6%	792
September	1st to 10th	Night	2 1 7% 32% 52% 6%	720
	11th to 20th	Night	5% 8% 33% 44% 10%	720
	21st to end	Night	3 2 12% 35% 37% 11%	720
October	1st to 10th	Night	7% 2 11% 39% 32% 9%	720
	11th to 20th	Night	7% 3 11% 33% 39% 7%	720
	21st to end	Night	9% 3 12% 33% 31% 12%	792
November	1st to 10th	Night	16% 3 11% 29% 33% 8%	740
	11th to 20th	Night	15% 1 12% 36% 31% 5%	760
	21st to end	Night	13% 2 13% 36% 30% 6%	760
December	1st to 10th	Night	23% 3 12% 33% 23% 7%	760
	11th to 20th	Night	29% 2 13% 31% 22% 4	760
	21st to end	Night	26% 2 16% 33% 21% 2	836

Page generated at 2024-01-11 10:31:58. Version ac07

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