Point Richmond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Point Richmond clear sky chart from 2005-11-06 to 2024-04-25.

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% 6% 2 4 4 2 4 4 5% 8% 53%	83552
	Night	11% 7% 3 6% 5% 3 4 4 5% 7% 48%	85659
Transparency	Day	30% 5% 10% 20% 21% 14%	83272
	Night	36% 6% 10% 18% 18% 12%	85461
Seeing	Day	9% 10% 27% 34% 16% 3	14633
	Night	11% 5% 19% 36% 25% 4	24087

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	16% 7% 3 5% 6% 3 5% 5% 4 7% 39%	2708
	11th to 20th	Day	19% 8% 4 7% 5% 4 4 3 5% 6% 34%	2860
	21st to end	Day	20% 10% 3 6% 6% 3 4 5% 5% 7% 31%	3146
February	1st to 10th	Day	17% 6% 1 4 4 3 4 4 5% 6% 46%	1710
	11th to 20th	Day	13% 7% 2 5% 4 3 5% 4 6% 8% 42%	1731
	21st to end	Day	12% 6% 3 5% 4 3 4 3 5% 7% 48%	1570
March	1st to 10th	Day	14% 10% 3 8% 7% 4 5% 5% 6% 6% 33%	3405
	11th to 20th	Day	10% 4 2 4 4 2 3 4 4 7% 56%	3490
	21st to end	Day	13% 6% 2 5% 5% 3 6% 5% 6% 10% 38%	3872
April	1st to 10th	Day	12% 5% 3 5% 4 2 4 5% 5% 8% 46%	2280
	11th to 20th	Day	8% 5% 2 4 4 2 3 4 4 8% 56%	2249
	21st to end	Day	4 3 2 3 3 2 4 3 5% 10% 59%	2210
May	1st to 10th	Day	4 5% 2 4 3 2 3 4 4 6% 62%	2255
	11th to 20th	Day	5% 3 2 4 3 2 4 3 4 9% 62%	2343
	21st to end	Day	4 6% 2 4 4 2 4 4 5% 8% 58%	2723
June	1st to 10th	Day	5% 5% 2 3 3 2 3 4 5% 9% 58%	2520
	11th to 20th	Day	1 3 2 3 2 1 3 3 4 8% 70%	2520
	21st to end	Day	2 3 2 4 3 2 3 3 3 8% 68%	2520
July	1st to 10th	Day	1 5% 2 3 3 2 2 3 4 10% 65%	2520
	11th to 20th	Day	1 4 2 4 4 2 3 3 4 10% 61%	2350
	21st to end	Day	1 4 2 3 3 2 3 3 5% 10% 64%	2546
August	1st to 10th	Day	2 6% 3 5% 3 2 3 3 4 10% 59%	2328
	11th to 20th	Day	1 4 2 4 4 2 3 4 4 8% 65%	2205
	21st to end	Day	1 6% 2 5% 4 2 3 3 4 9% 62%	2376
September	1st to 10th	Day	1 3 2 3 3 2 2 2 4 7% 71%	2160
	11th to 20th	Day	3 5% 2 5% 3 2 3 3 4 9% 61%	2160
	21st to end	Day	3 3 1 2 2 2 2 2 3 7% 73%	1900
October	1st to 10th	Day	4 4 2 3 3 2 3 4 4 6% 66%	1800
	11th to 20th	Day	6% 5% 2 4 4 2 3 4 3 6% 61%	1800
	21st to end	Day	8% 6% 2 4 3 1 2 3 4 7% 60%	1980
November	1st to 10th	Day	8% 4 2 4 4 2 3 4 5% 8% 55%	1833
	11th to 20th	Day	10% 7% 3 6% 5% 3 3 3 5% 7% 47%	1710
	21st to end	Day	10% 5% 2 3 4 2 3 4 6% 6% 53%	1530
December	1st to 10th	Day	14% 7% 3 5% 3 3 4 5% 4 7% 45%	1520
	11th to 20th	Day	27% 9% 3 6% 5% 2 3 4 4 5% 32%	1928
	21st to end	Day	20% 9% 3 5% 5% 3 4 5% 5% 8% 33%	2794
January	1st to 10th	Night	14% 7% 2 5% 5% 3 4 4 5% 6% 45%	4237
	11th to 20th	Night	19% 8% 3 7% 6% 3 5% 4 5% 6% 34%	4110
	21st to end	Night	21% 11% 3 6% 6% 3 4 4 4 6% 32%	4521
February	1st to 10th	Night	16% 6% 2 4 4 3 4 4 4 6% 49%	2470
	11th to 20th	Night	11% 6% 3 6% 4 3 4 5% 5% 8% 46%	2336
	21st to end	Night	12% 5% 1 4 4 2 4 4 5% 6% 52%	1884
March	1st to 10th	Night	15% 10% 4 6% 5% 3 4 4 4 6% 38%	3466
	11th to 20th	Night	12% 5% 2 4 4 2 3 3 3 5% 57%	3490
	21st to end	Night	13% 9% 3 6% 6% 3 4 4 4 6% 42%	3781
April	1st to 10th	Night	8% 6% 4 5% 5% 3 3 4 5% 8% 50%	1900
	11th to 20th	Night	9% 6% 2 4 4 2 3 3 4 7% 56%	1879
	21st to end	Night	4 3 3 4 3 2 3 3 5% 8% 60%	1850
May	1st to 10th	Night	4 6% 3 7% 4 2 4 3 5% 7% 56%	1702
	11th to 20th	Night	4 5% 3 4 5% 3 4 3 4 9% 57%	1550
	21st to end	Night	5% 7% 3 6% 5% 3 4 4 4 7% 53%	1552
June	1st to 10th	Night	4 8% 2 6% 5% 2 4 4 5% 10% 50%	1440
	11th to 20th	Night	1 4 3 5% 4 3 3 4 4 8% 62%	1440
	21st to end	Night	2 7% 2 6% 5% 2 3 3 4 9% 58%	1440
July	1st to 10th	Night	1 8% 4 6% 5% 2 3 3 4 10% 54%	1440
	11th to 20th	Night	2 9% 4 7% 6% 3 5% 4 5% 11% 44%	1606
	21st to end	Night	1 11% 6% 11% 9% 4 6% 4 5% 10% 33%	1773
August	1st to 10th	Night	3 11% 5% 9% 7% 4 5% 4 5% 9% 39%	1611
	11th to 20th	Night	1 7% 4 7% 7% 4 4 7% 8% 10% 39%	1694
	21st to end	Night	2 9% 4 6% 5% 3 4 4 5% 11% 46%	1980
September	1st to 10th	Night	1 4 3 5% 4 2 3 3 5% 7% 63%	1800
	11th to 20th	Night	4 7% 3 6% 6% 3 4 4 4 8% 52%	1800
	21st to end	Night	2 6% 2 5% 3 2 3 3 4 8% 63%	2055
October	1st to 10th	Night	5% 5% 2 4 3 2 3 3 4 6% 63%	2160
	11th to 20th	Night	6% 6% 3 4 4 2 3 4 5% 7% 57%	2160
	21st to end	Night	7% 4 2 5% 5% 2 4 3 4 7% 57%	2376
November	1st to 10th	Night	7% 6% 3 5% 3 2 3 3 4 8% 55%	2243
	11th to 20th	Night	10% 6% 2 5% 4 2 3 4 5% 7% 51%	2470
	21st to end	Night	9% 4 2 4 4 2 3 4 5% 6% 57%	2645
December	1st to 10th	Night	16% 6% 2 6% 4 2 3 4 4 6% 47%	2660
	11th to 20th	Night	29% 9% 3 4 4 2 3 4 5% 6% 32%	3276
	21st to end	Night	18% 6% 2 7% 6% 4 5% 5% 6% 6% 35%	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	44% 7% 14% 25% 8% 3	2708
	11th to 20th	Day	54% 5% 11% 13% 11% 7%	2860
	21st to end	Day	54% 7% 9% 14% 12% 4	3146
February	1st to 10th	Day	40% 5% 9% 18% 20% 8%	1710
	11th to 20th	Day	39% 6% 10% 18% 21% 6%	1740
	21st to end	Day	37% 5% 9% 25% 18% 7%	1570
March	1st to 10th	Day	52% 8% 10% 15% 13% 2	3405
	11th to 20th	Day	31% 5% 13% 28% 13% 11%	3490
	21st to end	Day	41% 10% 15% 21% 11% 2	3872
April	1st to 10th	Day	38% 6% 13% 20% 19% 4	2280
	11th to 20th	Day	30% 5% 16% 23% 21% 6%	2252
	21st to end	Day	24% 5% 13% 29% 25% 4	2210
May	1st to 10th	Day	23% 5% 10% 27% 28% 7%	2255
	11th to 20th	Day	23% 6% 8% 32% 23% 9%	2346
	21st to end	Day	27% 6% 15% 26% 23% 4	2724
June	1st to 10th	Day	25% 6% 10% 26% 25% 8%	2520
	11th to 20th	Day	13% 4 10% 22% 34% 16%	2520
	21st to end	Day	17% 5% 4 15% 32% 28%	2520
July	1st to 10th	Day	15% 4 4 11% 26% 40%	2451
	11th to 20th	Day	16% 5% 7% 14% 23% 36%	2280
	21st to end	Day	14% 3 4 13% 27% 39%	2405
August	1st to 10th	Day	21% 4 6% 13% 30% 26%	2312
	11th to 20th	Day	16% 3 4 13% 33% 31%	2205
	21st to end	Day	18% 2 4 17% 33% 26%	2376
September	1st to 10th	Day	14% 2 3 11% 30% 39%	2160
	11th to 20th	Day	23% 4 6% 22% 29% 15%	2160
	21st to end	Day	15% 2 6% 22% 32% 23%	1900
October	1st to 10th	Day	20% 3 7% 17% 31% 23%	1800
	11th to 20th	Day	24% 4 9% 19% 22% 22%	1800
	21st to end	Day	25% 4 9% 21% 23% 18%	1980
November	1st to 10th	Day	28% 5% 10% 27% 19% 12%	1833
	11th to 20th	Day	37% 4 10% 22% 20% 6%	1710
	21st to end	Day	31% 4 11% 19% 24% 11%	1530
December	1st to 10th	Day	38% 6% 10% 20% 17% 8%	1520
	11th to 20th	Day	55% 5% 9% 12% 15% 4	1928
	21st to end	Day	48% 6% 13% 20% 10% 3	2794
January	1st to 10th	Night	40% 6% 20% 22% 9% 3	4237
	11th to 20th	Night	53% 6% 12% 12% 9% 8%	4110
	21st to end	Night	55% 6% 10% 12% 11% 6%	4521
February	1st to 10th	Night	38% 4 9% 19% 19% 10%	2470
	11th to 20th	Night	38% 6% 10% 17% 20% 8%	2338
	21st to end	Night	33% 5% 11% 28% 18% 5%	1884
March	1st to 10th	Night	48% 11% 11% 14% 14% 3	3466
	11th to 20th	Night	32% 8% 9% 23% 18% 11%	3490
	21st to end	Night	44% 9% 14% 20% 11% 3	3781
April	1st to 10th	Night	36% 6% 13% 21% 20% 5%	1900
	11th to 20th	Night	30% 5% 12% 25% 19% 8%	1879
	21st to end	Night	24% 6% 12% 29% 23% 6%	1850
May	1st to 10th	Night	29% 4 8% 25% 24% 11%	1702
	11th to 20th	Night	29% 9% 9% 22% 23% 7%	1551
	21st to end	Night	33% 8% 12% 21% 22% 4	1552
June	1st to 10th	Night	30% 8% 10% 19% 26% 8%	1440
	11th to 20th	Night	21% 4 8% 19% 32% 16%	1440
	21st to end	Night	23% 9% 5% 12% 26% 25%	1440
July	1st to 10th	Night	23% 8% 4 6% 25% 34%	1400
	11th to 20th	Night	25% 6% 9% 11% 18% 30%	1553
	21st to end	Night	39% 5% 7% 7% 15% 27%	1674
August	1st to 10th	Night	39% 5% 7% 9% 20% 19%	1602
	11th to 20th	Night	31% 5% 6% 9% 22% 26%	1694
	21st to end	Night	32% 5% 6% 10% 24% 23%	1980
September	1st to 10th	Night	21% 4 6% 6% 27% 36%	1800
	11th to 20th	Night	30% 8% 6% 18% 23% 15%	1800
	21st to end	Night	19% 4 5% 20% 29% 23%	2055
October	1st to 10th	Night	23% 5% 7% 17% 24% 24%	2160
	11th to 20th	Night	28% 5% 6% 18% 19% 24%	2160
	21st to end	Night	27% 5% 7% 20% 21% 20%	2376
November	1st to 10th	Night	30% 5% 10% 25% 17% 13%	2243
	11th to 20th	Night	33% 5% 11% 25% 19% 8%	2470
	21st to end	Night	29% 5% 10% 21% 23% 13%	2645
December	1st to 10th	Night	39% 5% 10% 17% 17% 11%	2660
	11th to 20th	Night	53% 5% 9% 14% 15% 4	3276
	21st to end	Night	48% 7% 15% 16% 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	25% 9% 30% 20% 14% 2	284
	11th to 20th	Day	19% 11% 22% 34% 13% 2	370
	21st to end	Day	14% 9% 27% 31% 16% 2	407
February	1st to 10th	Day	20% 12% 19% 30% 18% 2	370
	11th to 20th	Day	19% 16% 25% 24% 13% 2	396
	21st to end	Day	12% 15% 26% 29% 15% 2	382
March	1st to 10th	Day	21% 17% 30% 20% 10% 3	460
	11th to 20th	Day	17% 17% 27% 21% 15% 4	460
	21st to end	Day	13% 19% 32% 26% 9% 1	506
April	1st to 10th	Day	17% 14% 32% 24% 10% 3	460
	11th to 20th	Day	13% 17% 31% 24% 9% 5%	452
	21st to end	Day	6% 19% 29% 29% 11% 5%	437
May	1st to 10th	Day	9% 17% 30% 31% 11% 1	423
	11th to 20th	Day	9% 15% 33% 31% 12% 1	448
	21st to end	Day	7% 12% 32% 34% 12% 2	485
June	1st to 10th	Day	8% 12% 33% 32% 13% 3	450
	11th to 20th	Day	4 13% 35% 37% 10% 2	450
	21st to end	Day	1 6% 34% 43% 14% 1	450
July	1st to 10th	Day	2 4 32% 48% 13%	446
	11th to 20th	Day	2 23% 55% 18% 2	444
	21st to end	Day	1 1 30% 48% 16% 3	487
August	1st to 10th	Day	2 5% 30% 48% 13% 3	447
	11th to 20th	Day	2 3 28% 46% 17% 5%	437
	21st to end	Day	2 2 24% 49% 20% 3	495
September	1st to 10th	Day	2 4 21% 46% 20% 7%	450
	11th to 20th	Day	4 9% 26% 39% 16% 7%	450
	21st to end	Day	3 8% 25% 33% 26% 6%	450
October	1st to 10th	Day	4 7% 27% 32% 21% 8%	450
	11th to 20th	Day	6% 9% 21% 29% 27% 8%	450
	21st to end	Day	9% 7% 23% 28% 26% 6%	495
November	1st to 10th	Day	11% 9% 19% 24% 32% 5%	429
	11th to 20th	Day	7% 10% 17% 35% 26% 5%	270
	21st to end	Day	12% 8% 26% 34% 18% 2	185
December	1st to 10th	Day	17% 14% 22% 27% 16% 5%	180
	11th to 20th	Day	17% 13% 26% 29% 14% 1	180
	21st to end	Day	19% 10% 30% 28% 12% 1	198
January	1st to 10th	Night	19% 5% 16% 31% 24% 5%	760
	11th to 20th	Night	15% 6% 16% 36% 23% 4	760
	21st to end	Night	19% 5% 13% 36% 23% 3	836
February	1st to 10th	Night	18% 6% 15% 37% 22% 3	760
	11th to 20th	Night	14% 9% 19% 33% 22% 4	744
	21st to end	Night	14% 9% 20% 33% 21% 2	628
March	1st to 10th	Night	19% 9% 22% 29% 19% 3	760
	11th to 20th	Night	16% 8% 20% 31% 22% 3	760
	21st to end	Night	15% 8% 27% 32% 16% 1	836
April	1st to 10th	Night	12% 8% 26% 35% 17% 3	760
	11th to 20th	Night	10% 13% 25% 30% 19% 3	751
	21st to end	Night	6% 9% 30% 32% 20% 3	740
May	1st to 10th	Night	7% 5% 26% 39% 21% 2	622
	11th to 20th	Night	6% 2 24% 39% 25% 3	488
	21st to end	Night	6% 8% 29% 37% 18% 3	389
June	1st to 10th	Night	4 4 29% 44% 18% 1	360
	11th to 20th	Night	1 4 24% 53% 16% 1	360
	21st to end	Night	4 3 23% 44% 26% 1	360
July	1st to 10th	Night	3 18% 51% 27% 1	350
	11th to 20th	Night	3 1 13% 51% 28% 5%	509
	21st to end	Night	3 2 16% 44% 32% 3	591
August	1st to 10th	Night	6% 2 19% 42% 28% 4	537
	11th to 20th	Night	3 1 19% 45% 28% 4	626
	21st to end	Night	5% 1 14% 47% 30% 4	792
September	1st to 10th	Night	2 1 14% 41% 35% 8%	720
	11th to 20th	Night	6% 2 17% 41% 30% 4	720
	21st to end	Night	4 3 15% 37% 34% 7%	720
October	1st to 10th	Night	7% 3 16% 36% 31% 7%	720
	11th to 20th	Night	8% 5% 14% 33% 34% 7%	720
	21st to end	Night	8% 4 12% 32% 34% 10%	792
November	1st to 10th	Night	8% 5% 14% 31% 34% 8%	740
	11th to 20th	Night	12% 3 14% 35% 30% 6%	760
	21st to end	Night	10% 6% 13% 39% 27% 5%	760
December	1st to 10th	Night	16% 6% 16% 34% 24% 5%	760
	11th to 20th	Night	23% 6% 16% 32% 20% 3	760
	21st to end	Night	20% 8% 22% 30% 19% 1	836

Page generated at 2024-04-22 06:25:46. Version ac07

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