Sacramento
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sacramento clear sky chart from 2005-11-06 to 2024-03-23.

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	9% 4 2 4 3 2 3 3 4 6% 60%	78830
	Night	11% 4 2 4 3 2 3 3 4 6% 58%	81076
Transparency	Day	26% 4 9% 19% 23% 19%	78545
	Night	27% 5% 9% 19% 22% 17%	80882
Seeing	Day	8% 5% 16% 27% 29% 15%	14337
	Night	9% 3 17% 41% 26% 3	23791

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	23% 10% 3 7% 5% 3 4 4 5% 6% 30%	2539
	11th to 20th	Day	21% 13% 5% 8% 6% 3 4 3 3 4 30%	2842
	21st to end	Day	23% 11% 4 7% 6% 3 4 4 4 7% 27%	3146
February	1st to 10th	Day	18% 5% 3 5% 5% 2 3 4 4 6% 45%	1710
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 4 9% 46%	1770
	21st to end	Day	14% 5% 2 5% 4 2 4 4 4 8% 48%	1570
March	1st to 10th	Day	14% 7% 4 5% 5% 4 5% 5% 5% 8% 38%	1988
	11th to 20th	Day	16% 6% 3 5% 4 2 4 4 6% 7% 43%	2090
	21st to end	Day	13% 4 2 5% 5% 3 4 5% 5% 7% 47%	2267
April	1st to 10th	Day	13% 6% 3 4 4 2 4 5% 5% 7% 47%	2160
	11th to 20th	Day	9% 3 2 3 4 2 3 4 5% 7% 57%	2129
	21st to end	Day	5% 3 2 2 2 2 4 3 5% 7% 64%	2160
May	1st to 10th	Day	4 3 1 4 3 2 3 3 3 6% 68%	2213
	11th to 20th	Day	4 3 1 3 3 2 3 3 4 7% 67%	2449
	21st to end	Day	4 3 1 3 4 2 3 3 5% 7% 66%	2723
June	1st to 10th	Day	4 3 1 3 2 2 3 3 5% 7% 68%	2520
	11th to 20th	Day	1 1 1 2 1 2 2 4 5% 82%	2520
	21st to end	Day	2 1 2 1 1 1 2 3 5% 83%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 4 87%	2520
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 4 86%	2484
	21st to end	Day	1 1 1 1 1 1 2 3 5% 84%	2546
August	1st to 10th	Day	1 1 1 1 2 1 1 2 3 4 82%	2328
	11th to 20th	Day	1 1 1 1 1 2 2 3 5% 83%	2170
	21st to end	Day	1 1 1 1 1 1 1 2 4 87%	2376
September	1st to 10th	Day	1 1 1 1 1 1 1 2 4 87%	2160
	11th to 20th	Day	2 2 1 2 2 1 2 3 4 5% 75%	2160
	21st to end	Day	3 2 1 2 1 1 2 2 2 5% 78%	1931
October	1st to 10th	Day	2 2 1 2 3 2 3 3 4 5% 74%	1800
	11th to 20th	Day	6% 2 1 3 2 1 3 3 4 6% 69%	1800
	21st to end	Day	6% 3 2 4 3 2 3 3 4 5% 65%	1980
November	1st to 10th	Day	9% 4 1 3 4 2 4 4 4 8% 56%	1742
	11th to 20th	Day	11% 6% 3 5% 5% 2 4 4 5% 6% 48%	1710
	21st to end	Day	12% 5% 3 4 3 2 3 3 6% 8% 51%	1565
December	1st to 10th	Day	14% 6% 3 7% 6% 2 4 4 4 7% 42%	1520
	11th to 20th	Day	29% 9% 3 7% 6% 3 3 3 4 5% 27%	1928
	21st to end	Day	17% 7% 3 7% 7% 5% 5% 6% 6% 8% 29%	2794
January	1st to 10th	Night	14% 7% 3 8% 6% 4 4 4 4 8% 38%	4406
	11th to 20th	Night	22% 7% 3 7% 6% 3 4 4 5% 5% 33%	4110
	21st to end	Night	22% 8% 3 7% 5% 3 5% 4 4 7% 33%	4521
February	1st to 10th	Night	17% 6% 2 4 3 3 3 4 4 5% 50%	2470
	11th to 20th	Night	13% 4 2 4 3 3 4 5% 5% 8% 49%	2296
	21st to end	Night	14% 3 2 3 3 2 4 4 4 6% 54%	1884
March	1st to 10th	Night	16% 5% 3 6% 4 2 4 4 4 7% 43%	2189
	11th to 20th	Night	17% 4 2 3 4 3 3 4 4 7% 49%	2090
	21st to end	Night	14% 4 2 4 4 3 4 4 4 7% 52%	2133
April	1st to 10th	Night	10% 4 3 5% 4 2 4 4 5% 6% 54%	1800
	11th to 20th	Night	8% 3 1 3 3 2 4 3 5% 7% 60%	1779
	21st to end	Night	5% 2 1 2 3 2 3 3 5% 8% 67%	1800
May	1st to 10th	Night	4 2 1 2 2 2 3 3 4 7% 68%	1744
	11th to 20th	Night	3 2 1 1 2 2 3 3 4 7% 71%	1444
	21st to end	Night	4 2 1 2 2 2 3 3 4 8% 70%	1552
June	1st to 10th	Night	4 3 1 2 3 2 2 3 4 6% 71%	1440
	11th to 20th	Night	1 1 1 2 1 2 2 3 4 83%	1440
	21st to end	Night	2 1 1 1 1 1 2 1 2 3 85%	1440
July	1st to 10th	Night	1 1 1 1 2 2 2 89%	1440
	11th to 20th	Night	1 1 1 1 1 1 1 1 1 3 87%	1471
	21st to end	Night	1 1 2 1 2 2 4 5% 80%	1773
August	1st to 10th	Night	2 2 1 2 3 1 1 2 3 4 79%	1611
	11th to 20th	Night	1 1 2 1 2 3 3 5% 82%	1728
	21st to end	Night	1 1 1 1 1 2 2 2 4 85%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 87%	1800
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 4 77%	1800
	21st to end	Night	1 1 1 2 2 1 2 2 3 5% 81%	2024
October	1st to 10th	Night	4 2 1 2 3 2 2 2 3 5% 74%	2160
	11th to 20th	Night	4 2 1 3 3 1 2 3 4 7% 70%	2160
	21st to end	Night	5% 2 1 3 3 2 2 3 4 6% 70%	2376
November	1st to 10th	Night	9% 4 2 3 3 2 3 4 5% 8% 58%	2335
	11th to 20th	Night	9% 4 2 4 3 2 3 4 5% 7% 57%	2470
	21st to end	Night	11% 4 2 4 3 2 3 3 4 5% 59%	2612
December	1st to 10th	Night	16% 5% 3 4 4 2 3 3 4 7% 49%	2660
	11th to 20th	Night	25% 7% 3 5% 4 3 3 4 6% 7% 33%	3276
	21st to end	Night	19% 6% 3 7% 7% 4 5% 5% 5% 6% 32%	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	52% 7% 14% 19% 7% 1	2539
	11th to 20th	Day	57% 5% 10% 12% 11% 5%	2842
	21st to end	Day	55% 8% 11% 14% 9% 3	3146
February	1st to 10th	Day	41% 4 10% 21% 16% 7%	1710
	11th to 20th	Day	36% 6% 12% 21% 18% 7%	1779
	21st to end	Day	37% 5% 9% 24% 19% 6%	1570
March	1st to 10th	Day	45% 6% 11% 20% 14% 4	1988
	11th to 20th	Day	40% 4 10% 23% 16% 6%	2090
	21st to end	Day	36% 7% 13% 20% 18% 5%	2267
April	1st to 10th	Day	35% 6% 12% 22% 17% 8%	2160
	11th to 20th	Day	27% 6% 12% 24% 22% 9%	2132
	21st to end	Day	19% 5% 14% 28% 27% 8%	2160
May	1st to 10th	Day	19% 3 10% 26% 30% 13%	2213
	11th to 20th	Day	17% 4 9% 28% 29% 12%	2452
	21st to end	Day	18% 6% 15% 28% 25% 9%	2724
June	1st to 10th	Day	18% 4 10% 27% 28% 14%	2520
	11th to 20th	Day	8% 3 8% 23% 33% 27%	2520
	21st to end	Day	8% 2 4 13% 38% 37%	2520
July	1st to 10th	Day	5% 1 3 10% 27% 54%	2451
	11th to 20th	Day	6% 1 3 14% 26% 50%	2409
	21st to end	Day	6% 1 3 11% 25% 54%	2405
August	1st to 10th	Day	9% 2 4 11% 32% 42%	2312
	11th to 20th	Day	6% 2 3 14% 34% 43%	2170
	21st to end	Day	6% 1 2 12% 36% 43%	2376
September	1st to 10th	Day	6% 1 3 9% 30% 52%	2160
	11th to 20th	Day	12% 3 7% 21% 39% 19%	2160
	21st to end	Day	11% 2 5% 19% 34% 28%	1931
October	1st to 10th	Day	14% 3 8% 18% 31% 27%	1800
	11th to 20th	Day	17% 5% 9% 20% 24% 25%	1800
	21st to end	Day	21% 3 9% 21% 27% 19%	1980
November	1st to 10th	Day	27% 5% 10% 25% 22% 10%	1742
	11th to 20th	Day	36% 5% 11% 23% 19% 6%	1710
	21st to end	Day	31% 7% 11% 23% 19% 9%	1565
December	1st to 10th	Day	41% 7% 11% 19% 16% 6%	1520
	11th to 20th	Day	59% 5% 9% 11% 13% 3	1928
	21st to end	Day	47% 12% 16% 15% 9% 2	2794
January	1st to 10th	Night	41% 10% 16% 22% 8% 3	4406
	11th to 20th	Night	50% 9% 12% 12% 11% 7%	4110
	21st to end	Night	51% 7% 12% 15% 11% 5%	4521
February	1st to 10th	Night	37% 5% 8% 22% 20% 9%	2470
	11th to 20th	Night	33% 5% 10% 23% 22% 7%	2298
	21st to end	Night	30% 6% 10% 26% 22% 7%	1884
March	1st to 10th	Night	40% 7% 14% 17% 16% 6%	2189
	11th to 20th	Night	36% 5% 8% 24% 20% 8%	2090
	21st to end	Night	33% 6% 12% 22% 20% 7%	2133
April	1st to 10th	Night	31% 6% 14% 19% 22% 9%	1800
	11th to 20th	Night	25% 4 11% 27% 21% 11%	1779
	21st to end	Night	17% 5% 13% 29% 28% 8%	1800
May	1st to 10th	Night	15% 4 12% 23% 32% 13%	1744
	11th to 20th	Night	14% 4 11% 32% 26% 13%	1444
	21st to end	Night	14% 4 15% 33% 25% 10%	1552
June	1st to 10th	Night	16% 4 12% 25% 30% 14%	1440
	11th to 20th	Night	7% 2 8% 22% 32% 28%	1440
	21st to end	Night	8% 2 3 11% 34% 41%	1440
July	1st to 10th	Night	5% 1 2 10% 28% 53%	1400
	11th to 20th	Night	7% 2 10% 25% 55%	1423
	21st to end	Night	7% 2 2 11% 25% 53%	1674
August	1st to 10th	Night	11% 2 2 13% 29% 42%	1602
	11th to 20th	Night	7% 2 4 10% 31% 47%	1728
	21st to end	Night	7% 1 2 10% 32% 47%	1980
September	1st to 10th	Night	5% 1 3 7% 31% 52%	1800
	11th to 20th	Night	12% 2 5% 19% 38% 24%	1800
	21st to end	Night	9% 2 5% 19% 31% 34%	2024
October	1st to 10th	Night	14% 4 7% 17% 28% 30%	2160
	11th to 20th	Night	14% 4 7% 17% 28% 29%	2160
	21st to end	Night	17% 4 7% 22% 28% 23%	2376
November	1st to 10th	Night	24% 5% 10% 24% 21% 15%	2335
	11th to 20th	Night	26% 4 11% 27% 23% 9%	2470
	21st to end	Night	28% 6% 8% 22% 26% 11%	2612
December	1st to 10th	Night	35% 7% 10% 20% 18% 9%	2660
	11th to 20th	Night	49% 7% 10% 14% 16% 4	3276
	21st to end	Night	47% 10% 12% 16% 10% 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	39% 6% 11% 22% 19% 4	180
	11th to 20th	Day	19% 6% 18% 24% 22% 12%	365
	21st to end	Day	16% 5% 19% 22% 21% 17%	407
February	1st to 10th	Day	18% 8% 16% 18% 23% 16%	370
	11th to 20th	Day	16% 10% 22% 21% 20% 11%	416
	21st to end	Day	13% 12% 20% 29% 20% 7%	382
March	1st to 10th	Day	16% 11% 23% 28% 17% 6%	460
	11th to 20th	Day	17% 11% 20% 22% 18% 12%	460
	21st to end	Day	15% 10% 24% 24% 20% 7%	471
April	1st to 10th	Day	14% 9% 22% 28% 17% 10%	420
	11th to 20th	Day	10% 8% 26% 28% 15% 13%	412
	21st to end	Day	4 9% 18% 31% 22% 15%	420
May	1st to 10th	Day	5% 6% 26% 29% 20% 13%	423
	11th to 20th	Day	7% 4 21% 28% 25% 15%	448
	21st to end	Day	4 5% 18% 26% 29% 18%	485
June	1st to 10th	Day	4 5% 20% 25% 32% 14%	450
	11th to 20th	Day	2 5% 17% 29% 39% 8%	450
	21st to end	Day	1 13% 34% 38% 14%	450
July	1st to 10th	Day	1 1 9% 37% 40% 12%	446
	11th to 20th	Day	6% 35% 40% 18%	444
	21st to end	Day	9% 33% 40% 17%	487
August	1st to 10th	Day	2 1 12% 35% 37% 14%	447
	11th to 20th	Day	9% 32% 39% 19%	437
	21st to end	Day	1 1 8% 28% 42% 19%	495
September	1st to 10th	Day	1 1 7% 27% 43% 20%	450
	11th to 20th	Day	3 3 13% 28% 33% 20%	450
	21st to end	Day	2 2 15% 26% 32% 22%	450
October	1st to 10th	Day	2 6% 16% 25% 27% 24%	450
	11th to 20th	Day	4 5% 13% 20% 32% 26%	450
	21st to end	Day	8% 6% 14% 22% 30% 20%	495
November	1st to 10th	Day	11% 5% 17% 20% 27% 21%	338
	11th to 20th	Day	10% 6% 13% 23% 33% 15%	270
	21st to end	Day	12% 1 12% 31% 30% 13%	201
December	1st to 10th	Day	19% 8% 15% 20% 24% 14%	180
	11th to 20th	Day	18% 6% 15% 25% 26% 11%	180
	21st to end	Day	20% 8% 20% 27% 19% 6%	198
January	1st to 10th	Night	18% 5% 17% 32% 24% 4	760
	11th to 20th	Night	17% 4 13% 38% 24% 4	760
	21st to end	Night	18% 4 15% 34% 26% 3	836
February	1st to 10th	Night	18% 4 16% 36% 23% 3	760
	11th to 20th	Night	14% 6% 20% 35% 22% 3	744
	21st to end	Night	14% 6% 21% 38% 18% 3	628
March	1st to 10th	Night	16% 7% 21% 33% 20% 2	760
	11th to 20th	Night	17% 6% 17% 34% 24% 2	760
	21st to end	Night	15% 5% 24% 36% 20% 1	800
April	1st to 10th	Night	11% 4 23% 40% 21% 2	720
	11th to 20th	Night	8% 5% 26% 36% 21% 4	711
	21st to end	Night	5% 3 25% 41% 24% 2	720
May	1st to 10th	Night	5% 3 27% 41% 23% 2	664
	11th to 20th	Night	3 1 23% 52% 20% 1	382
	21st to end	Night	4 3 22% 50% 21%	389
June	1st to 10th	Night	5% 2 21% 50% 22%	360
	11th to 20th	Night	1 2 23% 53% 21%	360
	21st to end	Night	1 1 21% 51% 25% 1	360
July	1st to 10th	Night	15% 61% 24%	350
	11th to 20th	Night	2 1 12% 63% 23% 1	379
	21st to end	Night	1 11% 57% 31% 1	591
August	1st to 10th	Night	3 1 16% 54% 25% 1	537
	11th to 20th	Night	1 1 13% 51% 33% 2	660
	21st to end	Night	1 11% 48% 38% 1	792
September	1st to 10th	Night	1 2 9% 46% 41% 2	720
	11th to 20th	Night	2 2 15% 44% 33% 4	720
	21st to end	Night	2 1 15% 40% 37% 6%	720
October	1st to 10th	Night	5% 3 13% 40% 32% 7%	720
	11th to 20th	Night	5% 3 14% 37% 36% 5%	720
	21st to end	Night	5% 3 13% 36% 33% 9%	792
November	1st to 10th	Night	9% 2 17% 33% 34% 6%	740
	11th to 20th	Night	9% 2 15% 41% 29% 4	760
	21st to end	Night	12% 3 15% 40% 26% 4	760
December	1st to 10th	Night	17% 5% 16% 34% 23% 5%	760
	11th to 20th	Night	24% 4 13% 33% 23% 3	760
	21st to end	Night	20% 5% 20% 32% 21% 1	836

Page generated at 2024-03-19 20:31:03. Version ac07

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