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 2025-09-19.

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	6% 5% 2 5% 3 3 3 3 4 7% 58%	134844
	Night	9% 7% 3 7% 4 3 3 3 4 6% 51%	131690
Transparency	Day	25% 5% 8% 19% 25% 18%	129753
	Night	33% 7% 9% 17% 20% 14%	127769
Seeing	Day	9% 10% 28% 34% 15% 3	16536
	Night	10% 5% 19% 37% 24% 4	25818

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	13% 6% 2 5% 4 3 4 4 5% 8% 45%	3892
	11th to 20th	Day	13% 7% 3 6% 4 4 3 2 4 5% 50%	4100
	21st to end	Day	15% 10% 3 6% 5% 3 3 3 4 6% 41%	4510
February	1st to 10th	Day	18% 7% 2 5% 4 4 4 3 5% 6% 45%	1800
	11th to 20th	Day	13% 7% 2 6% 4 5% 4 4 6% 8% 41%	1825
	21st to end	Day	12% 7% 3 5% 3 4 4 2 6% 7% 48%	1650
March	1st to 10th	Day	12% 9% 3 8% 5% 5% 4 4 6% 7% 38%	4902
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 8% 51%	5000
	21st to end	Day	12% 7% 2 5% 4 5% 6% 4 7% 10% 38%	5546
April	1st to 10th	Day	12% 6% 2 6% 3 4 4 4 5% 8% 46%	2400
	11th to 20th	Day	7% 6% 2 5% 4 4 3 3 5% 7% 56%	2369
	21st to end	Day	4 4 2 4 3 2 4 3 5% 10% 59%	2400
May	1st to 10th	Day	3 3 1 2 1 2 1 2 3 5% 76%	5691
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 8% 73%	5961
	21st to end	Day	2 3 1 3 2 2 2 2 3 7% 76%	6902
June	1st to 10th	Day	5% 5% 2 4 3 3 3 3 5% 9% 59%	2800
	11th to 20th	Day	1 3 2 3 2 2 2 2 5% 8% 71%	2800
	21st to end	Day	2 3 1 4 3 2 2 2 3 8% 69%	2800
July	1st to 10th	Day	3 2 4 2 2 2 2 3 7% 73%	6319
	11th to 20th	Day	1 5% 3 6% 3 2 2 2 4 9% 64%	5890
	21st to end	Day	1 9% 2 5% 2 2 3 2 4 10% 59%	6402
August	1st to 10th	Day	1 3 3 6% 2 2 3 3 4 7% 65%	5777
	11th to 20th	Day	4 1 4 2 2 2 2 3 6% 74%	5560
	21st to end	Day	1 4 2 5% 3 3 3 2 4 8% 65%	5984
September	1st to 10th	Day	1 4 1 4 2 2 2 2 4 7% 70%	2400
	11th to 20th	Day	4 6% 2 5% 2 3 3 3 4 9% 60%	2377
	21st to end	Day	3 3 1 3 2 2 2 2 3 7% 72%	2005
October	1st to 10th	Day	2 3 1 3 2 2 2 3 4 7% 70%	3180
	11th to 20th	Day	4 7% 2 5% 3 2 3 2 3 5% 63%	3161
	21st to end	Day	6% 5% 1 4 3 3 3 3 5% 8% 57%	3448
November	1st to 10th	Day	7% 5% 2 5% 3 3 3 3 5% 8% 57%	1931
	11th to 20th	Day	11% 8% 3 6% 5% 3 3 3 5% 7% 46%	1800
	21st to end	Day	11% 6% 1 4 3 3 3 4 6% 6% 52%	1610
December	1st to 10th	Day	8% 5% 2 4 2 3 4 3 6% 10% 53%	2620
	11th to 20th	Day	23% 7% 3 7% 4 3 4 4 6% 8% 30%	3028
	21st to end	Day	23% 11% 2 6% 4 4 4 4 5% 7% 29%	4004
January	1st to 10th	Night	10% 6% 3 5% 4 4 4 4 5% 8% 49%	6059
	11th to 20th	Night	13% 7% 3 7% 4 3 3 3 4 5% 48%	5880
	21st to end	Night	15% 9% 3 6% 4 3 3 3 4 6% 44%	6468
February	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 5% 48%	2600
	11th to 20th	Night	12% 7% 3 7% 3 3 4 4 5% 8% 45%	2462
	21st to end	Night	11% 5% 1 5% 4 3 4 3 5% 6% 52%	1980
March	1st to 10th	Night	14% 9% 3 7% 4 4 4 3 4 7% 41%	4989
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 6% 52%	5000
	21st to end	Night	14% 9% 2 6% 4 3 4 3 4 7% 44%	5429
April	1st to 10th	Night	8% 8% 2 6% 4 4 3 3 5% 8% 50%	2000
	11th to 20th	Night	8% 7% 2 5% 4 3 3 3 4 7% 55%	1979
	21st to end	Night	4 4 2 4 3 3 3 3 6% 7% 60%	2000
May	1st to 10th	Night	3 4 2 4 2 2 2 2 3 4 72%	4294
	11th to 20th	Night	2 4 3 7% 4 4 3 3 4 6% 61%	3946
	21st to end	Night	2 3 1 4 2 3 2 2 3 5% 74%	3972
June	1st to 10th	Night	4 8% 2 6% 5% 3 4 3 6% 10% 49%	1600
	11th to 20th	Night	1 4 2 6% 3 3 2 3 5% 8% 64%	1600
	21st to end	Night	2 6% 2 7% 4 3 3 2 4 9% 58%	1600
July	1st to 10th	Night	8% 4 11% 3 2 2 2 3 6% 59%	3640
	11th to 20th	Night	1 17% 7% 12% 4 3 3 2 4 6% 41%	4086
	21st to end	Night	2 23% 4 10% 5% 4 3 2 4 8% 35%	4472
August	1st to 10th	Night	2 6% 5% 14% 6% 5% 4 3 5% 7% 43%	4035
	11th to 20th	Night	9% 2 7% 4 4 3 3 4 6% 59%	4298
	21st to end	Night	2 6% 4 10% 5% 4 3 3 4 7% 52%	5015
September	1st to 10th	Night	2 5% 3 6% 3 2 3 3 5% 7% 61%	2000
	11th to 20th	Night	4 8% 3 7% 4 3 4 3 5% 8% 52%	1980
	21st to end	Night	2 6% 2 6% 3 2 3 2 4 7% 62%	2170
October	1st to 10th	Night	3 3 1 3 3 3 3 3 4 6% 68%	3800
	11th to 20th	Night	5% 9% 3 5% 3 3 3 2 4 6% 59%	3777
	21st to end	Night	7% 4 1 6% 4 3 4 3 5% 6% 58%	4121
November	1st to 10th	Night	7% 6% 2 5% 3 3 3 2 5% 7% 56%	2365
	11th to 20th	Night	9% 7% 2 5% 3 3 4 3 5% 7% 52%	2600
	21st to end	Night	10% 5% 1 5% 4 3 3 3 5% 7% 55%	2785
December	1st to 10th	Night	9% 4 2 4 3 3 4 3 5% 6% 57%	4560
	11th to 20th	Night	22% 10% 3 6% 4 4 4 3 7% 7% 30%	5176
	21st to end	Night	23% 8% 2 7% 5% 5% 5% 3 5% 5% 31%	6952

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	37% 7% 17% 20% 15% 5%	3892
	11th to 20th	Day	38% 4 8% 14% 21% 15%	4100
	21st to end	Day	46% 5% 7% 12% 13% 17%	4510
February	1st to 10th	Day	41% 5% 9% 18% 20% 8%	1800
	11th to 20th	Day	40% 6% 11% 18% 20% 6%	1834
	21st to end	Day	37% 5% 8% 24% 18% 7%	1650
March	1st to 10th	Day	45% 7% 8% 18% 19% 2	4902
	11th to 20th	Day	35% 5% 16% 27% 10% 8%	5000
	21st to end	Day	40% 10% 16% 23% 10% 1	5546
April	1st to 10th	Day	38% 6% 13% 21% 19% 4	2400
	11th to 20th	Day	30% 5% 15% 23% 21% 7%	2372
	21st to end	Day	24% 5% 13% 30% 24% 4	2400
May	1st to 10th	Day	13% 3 8% 28% 31% 17%	5691
	11th to 20th	Day	12% 4 6% 33% 36% 9%	5964
	21st to end	Day	12% 7% 7% 29% 41% 4	6904
June	1st to 10th	Day	23% 6% 10% 27% 26% 8%	2800
	11th to 20th	Day	12% 4 9% 21% 36% 18%	2800
	21st to end	Day	15% 4 4 14% 32% 30%	2800
July	1st to 10th	Day	9% 3 2 7% 23% 55%	6251
	11th to 20th	Day	12% 3 3 7% 17% 58%	5820
	21st to end	Day	17% 5% 3 17% 27% 32%	6217
August	1st to 10th	Day	18% 5% 4 10% 30% 33%	4206
	11th to 20th	Day	11% 4 3 10% 41% 31%	4019
	21st to end	Day	15% 3 3 15% 36% 28%	4311
September	1st to 10th	Day	15% 2 3 12% 30% 38%	2400
	11th to 20th	Day	23% 4 6% 22% 30% 14%	2377
	21st to end	Day	14% 2 6% 21% 33% 23%	2005
October	1st to 10th	Day	16% 3 5% 11% 28% 38%	3180
	11th to 20th	Day	22% 4 6% 23% 28% 18%	3161
	21st to end	Day	25% 4 7% 23% 27% 14%	3448
November	1st to 10th	Day	27% 5% 10% 27% 19% 12%	1931
	11th to 20th	Day	37% 4 10% 22% 20% 6%	1800
	21st to end	Day	32% 4 10% 19% 24% 11%	1610
December	1st to 10th	Day	27% 5% 6% 28% 28% 6%	2620
	11th to 20th	Day	52% 5% 9% 15% 16% 3	3028
	21st to end	Day	55% 5% 12% 17% 9% 2	4004
January	1st to 10th	Night	34% 7% 21% 21% 14% 4	6059
	11th to 20th	Night	40% 5% 9% 14% 20% 13%	5880
	21st to end	Night	44% 5% 8% 10% 18% 16%	6468
February	1st to 10th	Night	39% 4 9% 18% 20% 11%	2600
	11th to 20th	Night	39% 6% 10% 18% 19% 8%	2464
	21st to end	Night	33% 5% 11% 27% 18% 6%	1980
March	1st to 10th	Night	45% 9% 9% 17% 17% 3	4989
	11th to 20th	Night	36% 7% 11% 23% 15% 8%	5000
	21st to end	Night	42% 8% 13% 23% 11% 2	5429
April	1st to 10th	Night	35% 6% 12% 22% 20% 5%	2000
	11th to 20th	Night	32% 5% 12% 25% 18% 8%	1979
	21st to end	Night	25% 7% 11% 30% 22% 6%	2000
May	1st to 10th	Night	18% 4 7% 26% 29% 16%	4291
	11th to 20th	Night	23% 11% 9% 24% 24% 9%	3947
	21st to end	Night	16% 13% 7% 23% 38% 4	3972
June	1st to 10th	Night	29% 9% 10% 20% 26% 7%	1600
	11th to 20th	Night	19% 4 7% 18% 34% 17%	1600
	21st to end	Night	22% 9% 4 12% 27% 27%	1600
July	1st to 10th	Night	18% 8% 2 5% 23% 44%	3600
	11th to 20th	Night	35% 6% 4 5% 12% 37%	4033
	21st to end	Night	46% 7% 3 6% 16% 22%	4345
August	1st to 10th	Night	35% 16% 4 7% 22% 16%	2929
	11th to 20th	Night	21% 8% 6% 6% 33% 26%	3110
	21st to end	Night	27% 7% 7% 8% 28% 22%	3608
September	1st to 10th	Night	21% 5% 6% 7% 27% 35%	2000
	11th to 20th	Night	30% 8% 6% 18% 24% 15%	1980
	21st to end	Night	19% 4 5% 20% 29% 23%	2170
October	1st to 10th	Night	17% 4 5% 10% 20% 45%	3800
	11th to 20th	Night	29% 8% 5% 18% 18% 22%	3777
	21st to end	Night	26% 5% 5% 21% 24% 19%	4121
November	1st to 10th	Night	30% 5% 10% 25% 18% 13%	2365
	11th to 20th	Night	32% 5% 11% 25% 19% 8%	2600
	21st to end	Night	30% 5% 10% 20% 22% 13%	2785
December	1st to 10th	Night	29% 4 6% 21% 29% 11%	4560
	11th to 20th	Night	53% 4 8% 15% 16% 3	5176
	21st to end	Night	55% 6% 13% 15% 9% 3	6952

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	24% 9% 29% 22% 14% 2	310
	11th to 20th	Day	18% 11% 23% 33% 13% 2	400
	21st to end	Day	14% 9% 28% 32% 16% 2	440
February	1st to 10th	Day	23% 11% 19% 29% 17% 2	400
	11th to 20th	Day	18% 17% 25% 25% 13% 1	430
	21st to end	Day	12% 15% 27% 30% 14% 2	414
March	1st to 10th	Day	20% 16% 31% 20% 10% 3	500
	11th to 20th	Day	18% 17% 26% 20% 14% 4	500
	21st to end	Day	14% 18% 32% 25% 10% 1	550
April	1st to 10th	Day	17% 14% 32% 25% 10% 3	500
	11th to 20th	Day	13% 16% 32% 25% 9% 4	492
	21st to end	Day	6% 19% 30% 29% 11% 5%	500
May	1st to 10th	Day	9% 16% 33% 31% 11% 1	503
	11th to 20th	Day	9% 13% 33% 31% 13% 1	528
	21st to end	Day	6% 12% 33% 35% 12% 2	573
June	1st to 10th	Day	7% 11% 36% 33% 12% 2	530
	11th to 20th	Day	4 12% 37% 36% 9% 2	530
	21st to end	Day	1 7% 35% 43% 14% 1	530
July	1st to 10th	Day	2 4 33% 47% 12% 1	526
	11th to 20th	Day	1 2 24% 54% 17% 2	524
	21st to end	Day	2 2 31% 48% 15% 2	575
August	1st to 10th	Day	2 5% 31% 46% 13% 3	527
	11th to 20th	Day	2 4 30% 44% 16% 4	517
	21st to end	Day	2 3 24% 48% 20% 4	583
September	1st to 10th	Day	2 5% 24% 44% 18% 7%	530
	11th to 20th	Day	4 11% 27% 36% 15% 7%	523
	21st to end	Day	3 8% 26% 33% 26% 6%	490
October	1st to 10th	Day	4 7% 27% 32% 22% 8%	490
	11th to 20th	Day	6% 9% 22% 29% 27% 7%	490
	21st to end	Day	9% 7% 24% 29% 25% 6%	539
November	1st to 10th	Day	10% 10% 20% 24% 30% 6%	467
	11th to 20th	Day	8% 12% 18% 34% 23% 5%	300
	21st to end	Day	14% 7% 29% 32% 16% 2	205
December	1st to 10th	Day	16% 13% 25% 28% 15% 5%	200
	11th to 20th	Day	18% 13% 27% 29% 14% 1	200
	21st to end	Day	21% 10% 29% 28% 11%	220
January	1st to 10th	Night	19% 5% 16% 32% 23% 5%	800
	11th to 20th	Night	14% 6% 17% 36% 23% 4	800
	21st to end	Night	18% 5% 13% 37% 23% 4	880
February	1st to 10th	Night	19% 6% 15% 37% 21% 3	800
	11th to 20th	Night	14% 9% 18% 34% 21% 4	784
	21st to end	Night	14% 8% 20% 34% 21% 2	660
March	1st to 10th	Night	19% 9% 22% 29% 19% 3	800
	11th to 20th	Night	17% 8% 21% 30% 21% 3	800
	21st to end	Night	16% 8% 27% 32% 17% 1	880
April	1st to 10th	Night	12% 8% 26% 35% 17% 2	800
	11th to 20th	Night	10% 13% 25% 31% 18% 3	791
	21st to end	Night	7% 9% 29% 33% 20% 3	800
May	1st to 10th	Night	6% 5% 28% 40% 19% 2	690
	11th to 20th	Night	6% 3 25% 40% 23% 3	542
	21st to end	Night	5% 7% 30% 39% 17% 2	433
June	1st to 10th	Night	4 4 32% 44% 16% 1	400
	11th to 20th	Night	1 4 27% 52% 15% 1	400
	21st to end	Night	3 3 23% 45% 24% 1	400
July	1st to 10th	Night	3 19% 52% 25% 1	390
	11th to 20th	Night	3 1 14% 53% 25% 4	569
	21st to end	Night	3 2 18% 45% 30% 3	657
August	1st to 10th	Night	6% 3 20% 43% 26% 3	597
	11th to 20th	Night	3 1 21% 46% 26% 4	697
	21st to end	Night	5% 1 14% 47% 29% 4	880
September	1st to 10th	Night	2 1 15% 42% 33% 7%	800
	11th to 20th	Night	6% 2 18% 42% 28% 4	792
	21st to end	Night	4 3 15% 37% 34% 6%	760
October	1st to 10th	Night	6% 2 16% 36% 32% 7%	760
	11th to 20th	Night	8% 5% 14% 32% 34% 7%	760
	21st to end	Night	8% 4 12% 33% 33% 10%	836
November	1st to 10th	Night	8% 5% 15% 31% 34% 7%	780
	11th to 20th	Night	12% 4 15% 36% 28% 6%	800
	21st to end	Night	11% 6% 14% 39% 26% 5%	800
December	1st to 10th	Night	15% 5% 16% 35% 24% 5%	800
	11th to 20th	Night	23% 6% 17% 32% 20% 3	800
	21st to end	Night	21% 8% 22% 30% 18% 1	880

Page generated at 2025-09-15 22:49:14. Version ac07

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