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 2024-11-28.

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 2 2 2 2 3 5% 65%	105395
	Night	13% 4 1 3 2 2 3 2 4 5% 60%	102853
Transparency	Day	23% 3 7% 18% 24% 25%	105149
	Night	27% 4 8% 17% 21% 23%	102689
Seeing	Day	11% 6% 19% 29% 27% 8%	15204
	Night	13% 3 13% 35% 31% 5%	24467

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	30% 7% 2 4 3 3 3 2 4 5% 37%	2539
	11th to 20th	Day	28% 9% 3 6% 4 4 2 2 2 5% 34%	2770
	21st to end	Day	30% 7% 2 5% 3 3 3 2 4 7% 33%	3146
February	1st to 10th	Day	22% 5% 2 4 3 3 4 3 4 6% 46%	1710
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 5% 6% 47%	1750
	21st to end	Day	20% 5% 1 3 2 4 3 3 5% 7% 47%	1570
March	1st to 10th	Day	26% 11% 3 7% 4 3 3 3 4 5% 31%	3277
	11th to 20th	Day	16% 5% 1 3 3 2 2 2 3 6% 56%	3490
	21st to end	Day	21% 9% 2 5% 3 3 4 3 5% 7% 36%	3945
April	1st to 10th	Day	15% 5% 2 5% 4 3 3 3 5% 7% 47%	2280
	11th to 20th	Day	13% 5% 1 4 3 3 2 3 5% 6% 55%	2249
	21st to end	Day	7% 4 1 3 3 3 3 3 5% 7% 61%	2280
May	1st to 10th	Day	7% 3 1 2 1 1 3 2 4 6% 70%	3976
	11th to 20th	Day	3 2 1 2 2 1 2 2 3 4 79%	4377
	21st to end	Day	3 2 1 2 2 1 2 2 3 6% 75%	4813
June	1st to 10th	Day	5% 4 1 3 2 3 3 3 5% 6% 64%	2660
	11th to 20th	Day	1 2 1 2 2 2 2 2 3 5% 79%	2660
	21st to end	Day	2 1 1 1 1 1 1 2 3 85%	2660
July	1st to 10th	Day	1 1 1 1 1 1 93%	4420
	11th to 20th	Day	2 1 1 1 1 1 1 2 3 86%	4420
	21st to end	Day	1 1 1 1 1 1 2 2 89%	4472
August	1st to 10th	Day	2 1 1 2 1 2 2 2 4 5% 77%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 2 90%	3844
	21st to end	Day	1 1 1 1 1 1 1 2 90%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	2280
	11th to 20th	Day	3 2 1 3 2 2 2 2 3 4 78%	2280
	21st to end	Day	4 2 2 1 1 2 1 3 5% 80%	2035
October	1st to 10th	Day	3 2 1 3 2 2 2 2 3 5% 76%	3180
	11th to 20th	Day	7% 2 1 2 1 2 2 2 4 6% 69%	3161
	21st to end	Day	7% 3 1 3 3 3 5% 4 5% 7% 59%	3448
November	1st to 10th	Day	14% 4 1 3 2 3 3 4 4 8% 54%	1809
	11th to 20th	Day	16% 3 2 4 3 3 4 3 5% 7% 50%	1800
	21st to end	Day	15% 5% 1 4 3 3 3 3 5% 6% 53%	1581
December	1st to 10th	Day	19% 4 2 3 3 3 3 3 4 6% 49%	1520
	11th to 20th	Day	33% 6% 2 6% 3 3 3 3 3 6% 31%	1928
	21st to end	Day	20% 7% 2 6% 4 4 5% 4 5% 7% 36%	2794
January	1st to 10th	Night	20% 8% 3 5% 3 3 3 3 4 7% 40%	4406
	11th to 20th	Night	27% 6% 2 5% 3 4 4 3 4 5% 36%	4194
	21st to end	Night	30% 8% 3 6% 4 3 3 3 4 6% 32%	4521
February	1st to 10th	Night	20% 5% 2 3 3 3 2 3 4 6% 49%	2470
	11th to 20th	Night	17% 5% 2 5% 3 3 4 3 5% 6% 48%	2316
	21st to end	Night	19% 5% 2 3 3 3 3 3 4 5% 49%	1884
March	1st to 10th	Night	28% 11% 3 6% 4 3 3 3 4 5% 32%	3595
	11th to 20th	Night	20% 4 1 3 2 2 2 2 3 5% 56%	3490
	21st to end	Night	23% 9% 2 6% 3 4 4 3 5% 6% 35%	3706
April	1st to 10th	Night	12% 7% 2 4 4 3 4 4 5% 7% 49%	1900
	11th to 20th	Night	12% 4 1 4 3 2 3 3 5% 7% 56%	1879
	21st to end	Night	8% 3 1 2 3 2 3 2 4 7% 65%	1900
May	1st to 10th	Night	5% 3 1 3 2 2 3 2 4 6% 68%	2981
	11th to 20th	Night	3 1 1 1 2 2 2 3 4 5% 76%	2516
	21st to end	Night	4 2 1 2 2 2 2 2 3 4 77%	2762
June	1st to 10th	Night	5% 3 1 3 3 3 4 3 5% 7% 63%	1520
	11th to 20th	Night	2 1 1 2 2 2 2 4 6% 77%	1520
	21st to end	Night	2 1 1 2 2 2 2 2 3 3 81%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 93%	2540
	11th to 20th	Night	1 1 2 2 2 2 2 2 2 84%	2540
	21st to end	Night	1 1 1 1 1 2 2 3 3 86%	3073
August	1st to 10th	Night	3 3 1 3 2 2 2 2 4 4 75%	2848
	11th to 20th	Night	1 1 1 1 1 2 2 91%	2999
	21st to end	Night	3 1 1 1 1 1 1 2 88%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	3 2 2 2 2 2 2 3 5% 77%	1900
	21st to end	Night	2 1 1 1 1 1 2 2 3 4 81%	2140
October	1st to 10th	Night	3 2 1 3 2 2 2 2 2 3 79%	3800
	11th to 20th	Night	4 2 1 2 1 2 2 2 4 4 76%	3777
	21st to end	Night	9% 2 1 2 2 3 3 3 5% 7% 63%	4121
November	1st to 10th	Night	15% 4 1 3 2 2 3 3 5% 7% 54%	2488
	11th to 20th	Night	14% 4 1 3 3 3 3 4 6% 7% 54%	2600
	21st to end	Night	16% 5% 1 4 3 4 3 2 3 6% 54%	2751
December	1st to 10th	Night	22% 4 1 4 2 2 2 3 4 6% 49%	2660
	11th to 20th	Night	34% 5% 2 3 3 3 3 3 5% 6% 33%	3276
	21st to end	Night	24% 6% 2 6% 4 4 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	51% 4 7% 27% 8% 3	2539
	11th to 20th	Day	56% 4 7% 15% 10% 9%	2770
	21st to end	Day	52% 5% 10% 15% 12% 5%	3146
February	1st to 10th	Day	39% 3 10% 20% 19% 9%	1710
	11th to 20th	Day	38% 5% 9% 19% 22% 7%	1759
	21st to end	Day	37% 3 10% 25% 18% 7%	1570
March	1st to 10th	Day	54% 7% 8% 15% 13% 4	3277
	11th to 20th	Day	32% 3 8% 26% 19% 12%	3490
	21st to end	Day	45% 7% 12% 22% 12% 3	3945
April	1st to 10th	Day	36% 5% 10% 24% 20% 5%	2280
	11th to 20th	Day	30% 4 12% 23% 24% 8%	2252
	21st to end	Day	21% 5% 12% 30% 25% 7%	2280
May	1st to 10th	Day	16% 3 9% 27% 25% 20%	3976
	11th to 20th	Day	11% 2 6% 24% 39% 18%	4380
	21st to end	Day	12% 3 11% 34% 29% 10%	4814
June	1st to 10th	Day	19% 5% 10% 25% 26% 15%	2660
	11th to 20th	Day	10% 3 7% 20% 32% 28%	2660
	21st to end	Day	7% 2 4 13% 35% 40%	2660
July	1st to 10th	Day	3 1 2 5% 16% 74%	4351
	11th to 20th	Day	6% 1 2 7% 17% 66%	4345
	21st to end	Day	4 1 2 5% 27% 61%	4331
August	1st to 10th	Day	10% 2 3 7% 26% 53%	4076
	11th to 20th	Day	4 1 2 7% 41% 45%	3883
	21st to end	Day	5% 1 2 10% 40% 42%	4179
September	1st to 10th	Day	5% 1 2 7% 27% 58%	2280
	11th to 20th	Day	13% 2 5% 20% 38% 22%	2280
	21st to end	Day	10% 2 5% 19% 31% 33%	2035
October	1st to 10th	Day	12% 2 5% 11% 25% 45%	3180
	11th to 20th	Day	16% 4 4 21% 32% 22%	3161
	21st to end	Day	22% 4 6% 22% 29% 17%	3448
November	1st to 10th	Day	28% 4 8% 25% 20% 14%	1809
	11th to 20th	Day	35% 4 11% 23% 19% 9%	1800
	21st to end	Day	32% 5% 9% 20% 22% 12%	1581
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	44% 6% 15% 23% 9% 4	4406
	11th to 20th	Night	50% 6% 11% 11% 13% 9%	4194
	21st to end	Night	55% 4 10% 12% 12% 6%	4521
February	1st to 10th	Night	37% 4 8% 20% 19% 12%	2470
	11th to 20th	Night	36% 4 9% 20% 22% 9%	2318
	21st to end	Night	37% 4 8% 23% 20% 9%	1884
March	1st to 10th	Night	52% 7% 10% 13% 13% 5%	3595
	11th to 20th	Night	32% 3 6% 24% 21% 13%	3490
	21st to end	Night	47% 7% 10% 21% 11% 4	3706
April	1st to 10th	Night	33% 6% 12% 21% 20% 8%	1900
	11th to 20th	Night	27% 5% 12% 25% 19% 12%	1879
	21st to end	Night	20% 4 13% 28% 25% 8%	1900
May	1st to 10th	Night	17% 4 12% 18% 28% 20%	2981
	11th to 20th	Night	11% 3 7% 22% 36% 20%	2516
	21st to end	Night	12% 3 10% 35% 28% 12%	2762
June	1st to 10th	Night	18% 6% 12% 25% 26% 12%	1520
	11th to 20th	Night	8% 4 8% 18% 31% 30%	1520
	21st to end	Night	10% 2 3 12% 29% 43%	1520
July	1st to 10th	Night	3 1 1 6% 15% 74%	2500
	11th to 20th	Night	8% 1 3 7% 14% 68%	2492
	21st to end	Night	5% 1 2 6% 25% 60%	2977
August	1st to 10th	Night	14% 1 2 7% 24% 52%	2839
	11th to 20th	Night	4 1 2 8% 35% 50%	3026
	21st to end	Night	7% 1 2 11% 33% 47%	3498
September	1st to 10th	Night	6% 1 2 6% 27% 57%	1900
	11th to 20th	Night	12% 2 5% 17% 39% 25%	1900
	21st to end	Night	9% 2 4 16% 30% 39%	2140
October	1st to 10th	Night	13% 2 4 10% 17% 54%	3800
	11th to 20th	Night	13% 3 5% 24% 30% 24%	3777
	21st to end	Night	21% 3 5% 20% 31% 21%	4121
November	1st to 10th	Night	30% 4 9% 23% 18% 16%	2488
	11th to 20th	Night	28% 5% 13% 25% 19% 11%	2600
	21st to end	Night	33% 4 6% 21% 23% 13%	2751
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	26% 7% 16% 30% 15% 6%	319
	21st to end	Day	21% 7% 20% 25% 21% 6%	407
February	1st to 10th	Day	22% 8% 17% 27% 22% 4	370
	11th to 20th	Day	22% 10% 25% 24% 16% 3	405
	21st to end	Day	19% 10% 23% 32% 12% 4	382
March	1st to 10th	Day	29% 11% 28% 18% 11% 2	460
	11th to 20th	Day	25% 10% 23% 20% 16% 5%	460
	21st to end	Day	19% 13% 26% 26% 14%	506
April	1st to 10th	Day	17% 10% 28% 24% 17% 4	460
	11th to 20th	Day	16% 12% 25% 24% 18% 6%	452
	21st to end	Day	7% 11% 23% 31% 23% 6%	460
May	1st to 10th	Day	8% 12% 28% 29% 19% 5%	463
	11th to 20th	Day	7% 9% 22% 27% 27% 7%	488
	21st to end	Day	4 7% 21% 27% 30% 11%	529
June	1st to 10th	Day	5% 7% 20% 27% 30% 10%	490
	11th to 20th	Day	4 6% 21% 37% 24% 8%	490
	21st to end	Day	1 4 17% 37% 32% 9%	490
July	1st to 10th	Day	2 2 12% 38% 39% 7%	486
	11th to 20th	Day	1 11% 37% 41% 9%	484
	21st to end	Day	1 1 9% 37% 42% 11%	531
August	1st to 10th	Day	1 2 13% 34% 36% 14%	487
	11th to 20th	Day	1 1 17% 30% 36% 15%	477
	21st to end	Day	1 2 11% 33% 40% 13%	539
September	1st to 10th	Day	1 3 10% 40% 34% 13%	490
	11th to 20th	Day	4 4 20% 27% 34% 10%	490
	21st to end	Day	2 5% 21% 29% 32% 10%	490
October	1st to 10th	Day	3 7% 21% 24% 32% 12%	490
	11th to 20th	Day	7% 6% 17% 25% 34% 11%	490
	21st to end	Day	12% 6% 19% 29% 24% 10%	539
November	1st to 10th	Day	17% 3 17% 26% 28% 10%	345
	11th to 20th	Day	14% 4 15% 32% 23% 12%	300
	21st to end	Day	15% 5% 22% 30% 21% 7%	197
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% 3 14% 35% 22% 5%	760
	21st to end	Night	21% 2 15% 33% 23% 5%	836
February	1st to 10th	Night	21% 4 14% 36% 23% 4	760
	11th to 20th	Night	17% 5% 15% 34% 25% 4	744
	21st to end	Night	20% 5% 16% 37% 18% 3	628
March	1st to 10th	Night	26% 7% 16% 30% 18% 4	760
	11th to 20th	Night	21% 5% 14% 30% 26% 4	760
	21st to end	Night	20% 6% 20% 32% 20% 2	836
April	1st to 10th	Night	13% 6% 19% 38% 22% 2	760
	11th to 20th	Night	13% 5% 18% 36% 23% 6%	751
	21st to end	Night	8% 5% 17% 36% 29% 4	760
May	1st to 10th	Night	8% 4 22% 36% 26% 4	652
	11th to 20th	Night	5% 3 17% 40% 32% 3	374
	21st to end	Night	6% 3 14% 35% 40% 2	411
June	1st to 10th	Night	6% 2 15% 37% 35% 4	380
	11th to 20th	Night	1 2 19% 40% 34% 3	380
	21st to end	Night	3 1 13% 40% 38% 4	380
July	1st to 10th	Night	1 7% 43% 45% 4	370
	11th to 20th	Night	1 1 8% 43% 44% 3	368
	21st to end	Night	4 34% 56% 6%	601
August	1st to 10th	Night	3 1 5% 37% 50% 5%	567
	11th to 20th	Night	1 6% 38% 48% 7%	673
	21st to end	Night	1 1 4 34% 54% 5%	836
September	1st to 10th	Night	2 1 8% 34% 50% 6%	760
	11th to 20th	Night	5% 1 9% 34% 42% 10%	760
	21st to end	Night	3 2 12% 36% 36% 11%	760
October	1st to 10th	Night	6% 2 11% 40% 32% 8%	760
	11th to 20th	Night	7% 3 13% 33% 39% 7%	760
	21st to end	Night	9% 3 13% 34% 30% 12%	836
November	1st to 10th	Night	16% 3 12% 29% 32% 8%	780
	11th to 20th	Night	15% 2 14% 35% 29% 5%	800
	21st to end	Night	15% 2 13% 35% 29% 6%	788
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 2024-11-24 21:22:19. Version ac07

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