San Pedro Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Pedro Creek clear sky chart from 2005-11-06 to 2026-03-03.

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	2 3 1 4 3 4 4 4 6% 8% 61%	139327
	Night	2 3 1 4 4 4 4 4 6% 8% 60%	139329
Transparency	Day	17% 6% 10% 21% 28% 18%	134333
	Night	19% 6% 9% 20% 29% 17%	135328
Seeing	Day	7% 15% 26% 29% 18% 4	16742
	Night	5% 10% 27% 39% 18% 2	27023

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	1 4 2 6% 3 3 4 4 7% 8% 57%	5318
	11th to 20th	Day	1 2 2 3 2 2 3 2 3 4 75%	5340
	21st to end	Day	2 5% 2 6% 3 4 4 3 6% 6% 60%	5844
February	1st to 10th	Day	2 5% 2 5% 3 4 4 3 6% 6% 61%	1906
	11th to 20th	Day	2 4 2 5% 4 3 4 3 6% 9% 59%	2049
	21st to end	Day	1 4 1 4 3 4 4 2 5% 6% 65%	1730
March	1st to 10th	Day	1 6% 1 4 3 3 4 3 5% 6% 65%	4813
	11th to 20th	Day	1 4 2 5% 5% 4 5% 4 6% 8% 55%	5000
	21st to end	Day	1 2 1 4 4 4 4 4 6% 8% 62%	5634
April	1st to 10th	Day	2 3 1 3 4 3 4 3 5% 7% 65%	2400
	11th to 20th	Day	3 4 2 4 3 3 4 3 5% 7% 63%	2371
	21st to end	Day	2 3 1 3 3 3 3 3 5% 7% 68%	2400
May	1st to 10th	Day	2 2 1 4 3 4 5% 5% 6% 7% 60%	5440
	11th to 20th	Day	2 2 1 3 2 3 4 4 5% 7% 67%	5574
	21st to end	Day	1 1 1 2 2 2 3 3 5% 8% 72%	6898
June	1st to 10th	Day	2 2 1 3 3 3 5% 4 7% 9% 62%	2800
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 6% 71%	2800
	21st to end	Day	4 3 1 4 4 4 5% 4 6% 8% 57%	2800
July	1st to 10th	Day	2 2 1 4 4 5% 5% 5% 7% 8% 59%	6114
	11th to 20th	Day	1 1 1 3 4 5% 7% 7% 11% 13% 47%	5880
	21st to end	Day	3 4 2 6% 5% 7% 7% 6% 9% 12% 39%	6401
August	1st to 10th	Day	1 2 1 3 3 5% 6% 6% 9% 12% 52%	5651
	11th to 20th	Day	2 2 1 4 4 4 6% 5% 8% 11% 53%	5366
	21st to end	Day	2 2 1 5% 5% 6% 7% 6% 9% 11% 46%	5984
September	1st to 10th	Day	5% 4 2 4 4 5% 5% 4 7% 9% 53%	2400
	11th to 20th	Day	5% 3 1 4 4 3 4 5% 6% 7% 59%	2400
	21st to end	Day	2 3 1 3 2 2 3 3 4 6% 69%	2165
October	1st to 10th	Day	3 2 1 3 2 2 3 2 3 4 74%	3270
	11th to 20th	Day	2 2 1 4 3 3 4 3 5% 7% 66%	3250
	21st to end	Day	2 1 1 2 1 2 2 2 3 6% 78%	3548
November	1st to 10th	Day	2 2 1 3 2 3 2 3 4 7% 72%	2033
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 6% 70%	1890
	21st to end	Day	2 4 2 3 3 3 3 2 5% 6% 67%	1890
December	1st to 10th	Day	1 2 1 2 2 2 2 2 3 6% 78%	2749
	11th to 20th	Day	1 2 2 4 4 4 4 3 4 7% 66%	3106
	21st to end	Day	1 3 1 3 2 3 3 3 5% 7% 69%	4113
January	1st to 10th	Night	1 5% 3 6% 4 5% 5% 4 7% 7% 52%	7627
	11th to 20th	Night	1 2 1 3 2 3 3 2 3 5% 75%	7650
	21st to end	Night	2 4 2 5% 3 4 4 3 6% 8% 60%	8370
February	1st to 10th	Night	1 4 2 4 3 3 3 3 5% 5% 66%	2711
	11th to 20th	Night	3 5% 1 5% 3 4 4 4 5% 8% 57%	2458
	21st to end	Night	1 3 1 4 3 4 4 3 4 5% 66%	2076
March	1st to 10th	Night	1 3 1 4 3 3 4 4 5% 6% 65%	5101
	11th to 20th	Night	3 4 2 7% 4 4 4 4 5% 6% 56%	5000
	21st to end	Night	1 3 1 3 3 3 3 4 5% 8% 67%	5320
April	1st to 10th	Night	3 3 1 4 4 3 3 3 5% 7% 63%	2000
	11th to 20th	Night	4 3 1 4 4 4 3 3 4 7% 62%	1977
	21st to end	Night	4 3 1 4 3 3 3 3 5% 7% 64%	2000
May	1st to 10th	Night	2 4 1 5% 4 4 5% 5% 7% 7% 55%	4540
	11th to 20th	Night	4 4 1 4 3 3 3 4 6% 6% 62%	4337
	21st to end	Night	2 1 1 3 4 4 4 3 5% 7% 66%	3981
June	1st to 10th	Night	2 2 2 5% 5% 4 4 5% 7% 9% 55%	1600
	11th to 20th	Night	2 3 1 3 2 3 4 3 6% 6% 67%	1600
	21st to end	Night	5% 4 2 5% 5% 5% 6% 6% 6% 8% 49%	1600
July	1st to 10th	Night	2 2 2 5% 5% 7% 6% 5% 7% 7% 52%	3859
	11th to 20th	Night	3 3 2 6% 5% 6% 7% 7% 11% 14% 37%	4100
	21st to end	Night	5% 5% 2 7% 7% 6% 7% 6% 10% 11% 33%	4472
August	1st to 10th	Night	2 3 2 7% 6% 7% 8% 7% 9% 10% 39%	4159
	11th to 20th	Night	3 3 1 6% 5% 6% 7% 7% 10% 13% 40%	4483
	21st to end	Night	3 4 2 8% 7% 7% 8% 7% 10% 12% 32%	4993
September	1st to 10th	Night	5% 4 2 6% 6% 5% 4 5% 8% 8% 47%	2000
	11th to 20th	Night	4 4 2 4 3 3 5% 4 6% 8% 58%	2000
	21st to end	Night	3 3 2 4 2 3 3 3 5% 6% 67%	2231
October	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 75%	3920
	11th to 20th	Night	2 2 1 4 3 4 3 3 6% 7% 65%	3898
	21st to end	Night	2 1 1 1 2 2 2 3 5% 79%	4252
November	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 75%	2461
	11th to 20th	Night	1 2 1 3 3 2 3 3 5% 6% 73%	2730
	21st to end	Night	3 4 2 5% 4 3 4 3 5% 6% 63%	2730
December	1st to 10th	Night	1 2 2 2 2 3 3 4 6% 74%	4644
	11th to 20th	Night	1 2 1 3 3 2 4 3 5% 8% 67%	5321
	21st to end	Night	2 3 2 3 3 3 3 3 4 6% 67%	7128

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	20% 5% 9% 34% 28% 4	5321
	11th to 20th	Day	11% 5% 8% 24% 36% 17%	5340
	21st to end	Day	20% 5% 7% 16% 37% 15%	5844
February	1st to 10th	Day	21% 3 9% 25% 29% 13%	1906
	11th to 20th	Day	21% 4 8% 25% 31% 11%	2059
	21st to end	Day	19% 3 5% 20% 31% 22%	1730
March	1st to 10th	Day	16% 4 4 13% 37% 26%	4813
	11th to 20th	Day	19% 9% 8% 18% 31% 15%	5000
	21st to end	Day	15% 5% 7% 26% 38% 10%	5634
April	1st to 10th	Day	16% 5% 7% 18% 35% 20%	2400
	11th to 20th	Day	19% 4 6% 17% 31% 23%	2374
	21st to end	Day	15% 4 6% 20% 36% 19%	2400
May	1st to 10th	Day	17% 7% 10% 19% 27% 20%	5440
	11th to 20th	Day	14% 6% 7% 14% 32% 28%	5577
	21st to end	Day	9% 5% 8% 14% 19% 45%	6899
June	1st to 10th	Day	15% 6% 9% 20% 26% 24%	2800
	11th to 20th	Day	13% 4 5% 12% 23% 43%	2800
	21st to end	Day	22% 5% 9% 20% 21% 23%	2800
July	1st to 10th	Day	18% 9% 12% 14% 21% 26%	6050
	11th to 20th	Day	19% 10% 23% 28% 14% 7%	5811
	21st to end	Day	29% 11% 19% 24% 13% 4	6217
August	1st to 10th	Day	22% 11% 20% 23% 15% 8%	4113
	11th to 20th	Day	18% 8% 12% 26% 22% 13%	3882
	21st to end	Day	27% 10% 18% 23% 18% 3	4311
September	1st to 10th	Day	25% 7% 12% 19% 25% 12%	2400
	11th to 20th	Day	22% 7% 8% 18% 26% 19%	2400
	21st to end	Day	15% 4 7% 21% 33% 20%	2165
October	1st to 10th	Day	14% 4 5% 13% 32% 33%	3270
	11th to 20th	Day	15% 6% 7% 16% 32% 24%	3250
	21st to end	Day	9% 2 5% 18% 41% 25%	3548
November	1st to 10th	Day	12% 3 5% 22% 40% 18%	2033
	11th to 20th	Day	14% 3 7% 24% 40% 13%	1890
	21st to end	Day	18% 4 7% 23% 32% 16%	1890
December	1st to 10th	Day	10% 3 6% 29% 38% 14%	2749
	11th to 20th	Day	17% 4 8% 27% 35% 8%	3104
	21st to end	Day	14% 4 9% 28% 35% 12%	4113
January	1st to 10th	Night	24% 6% 9% 28% 26% 7%	7627
	11th to 20th	Night	10% 4 7% 24% 40% 16%	7650
	21st to end	Night	19% 6% 7% 15% 37% 17%	8370
February	1st to 10th	Night	17% 4 11% 23% 30% 16%	2711
	11th to 20th	Night	22% 5% 9% 24% 27% 13%	2458
	21st to end	Night	17% 4 6% 16% 35% 22%	2076
March	1st to 10th	Night	16% 4 6% 13% 37% 24%	5101
	11th to 20th	Night	21% 8% 8% 16% 32% 16%	5000
	21st to end	Night	12% 4 8% 24% 40% 12%	5320
April	1st to 10th	Night	18% 4 6% 19% 32% 21%	2000
	11th to 20th	Night	20% 4 6% 17% 28% 25%	1977
	21st to end	Night	17% 4 9% 16% 35% 19%	2000
May	1st to 10th	Night	19% 8% 11% 20% 22% 20%	4537
	11th to 20th	Night	17% 8% 9% 14% 28% 25%	4338
	21st to end	Night	13% 6% 8% 13% 15% 45%	3981
June	1st to 10th	Night	21% 7% 13% 16% 19% 24%	1600
	11th to 20th	Night	15% 5% 6% 13% 22% 40%	1600
	21st to end	Night	28% 8% 12% 14% 16% 23%	1600
July	1st to 10th	Night	24% 9% 13% 17% 14% 23%	3815
	11th to 20th	Night	27% 11% 24% 23% 9% 6%	4046
	21st to end	Night	36% 11% 19% 22% 11% 2	4344
August	1st to 10th	Night	35% 13% 16% 17% 12% 6%	3021
	11th to 20th	Night	27% 10% 16% 20% 17% 11%	3243
	21st to end	Night	36% 11% 17% 21% 10% 4	3597
September	1st to 10th	Night	29% 8% 14% 17% 21% 11%	2000
	11th to 20th	Night	23% 6% 10% 18% 22% 21%	2000
	21st to end	Night	19% 4 8% 16% 29% 22%	2231
October	1st to 10th	Night	13% 4 6% 14% 30% 34%	3920
	11th to 20th	Night	15% 5% 8% 17% 27% 27%	3898
	21st to end	Night	10% 2 4 18% 42% 25%	4252
November	1st to 10th	Night	11% 2 5% 21% 42% 19%	2461
	11th to 20th	Night	13% 4 5% 20% 41% 17%	2730
	21st to end	Night	21% 4 5% 19% 32% 18%	2730
December	1st to 10th	Night	11% 4 6% 31% 33% 16%	4644
	11th to 20th	Night	13% 4 7% 23% 39% 13%	5322
	21st to end	Night	16% 4 9% 25% 37% 9%	7128

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	7% 23% 32% 32% 6%	330
	11th to 20th	Day	12% 20% 30% 28% 10% 1	330
	21st to end	Day	4 18% 35% 29% 13% 1	363
February	1st to 10th	Day	7% 25% 33% 25% 10% 1	330
	11th to 20th	Day	14% 25% 37% 20% 4	330
	21st to end	Day	16% 27% 32% 21% 3 1	273
March	1st to 10th	Day	11% 29% 30% 23% 7%	431
	11th to 20th	Day	16% 28% 28% 19% 7% 1	500
	21st to end	Day	13% 35% 31% 15% 6%	550
April	1st to 10th	Day	12% 26% 35% 18% 8% 1	500
	11th to 20th	Day	13% 32% 33% 15% 6%	492
	21st to end	Day	10% 28% 36% 20% 4 1	500
May	1st to 10th	Day	7% 25% 39% 22% 6% 1	503
	11th to 20th	Day	9% 21% 32% 27% 9% 2	528
	21st to end	Day	5% 17% 30% 32% 15% 1	775
June	1st to 10th	Day	3 8% 26% 39% 23% 2	730
	11th to 20th	Day	3 8% 24% 38% 24% 3	730
	21st to end	Day	7% 5% 23% 34% 26% 5%	730
July	1st to 10th	Day	3 4 19% 37% 29% 9%	630
	11th to 20th	Day	4 1 9% 32% 37% 17%	524
	21st to end	Day	4 2 8% 32% 38% 17%	575
August	1st to 10th	Day	3 2 13% 34% 36% 11%	527
	11th to 20th	Day	4 3 17% 36% 30% 11%	517
	21st to end	Day	4 3 14% 36% 33% 9%	583
September	1st to 10th	Day	4 5% 19% 34% 29% 8%	530
	11th to 20th	Day	3 5% 26% 36% 24% 5%	530
	21st to end	Day	4 9% 25% 34% 21% 7%	365
October	1st to 10th	Day	6% 14% 25% 25% 23% 7%	330
	11th to 20th	Day	8% 15% 27% 28% 17% 5%	330
	21st to end	Day	11% 14% 25% 29% 18% 4	363
November	1st to 10th	Day	6% 19% 29% 29% 14% 2	330
	11th to 20th	Day	4 13% 32% 35% 15% 2	330
	21st to end	Day	7% 22% 31% 27% 12% 1	330
December	1st to 10th	Day	9% 19% 30% 32% 10% 1	330
	11th to 20th	Day	8% 21% 28% 31% 11% 1	330
	21st to end	Day	11% 26% 29% 28% 5% 1	363
January	1st to 10th	Night	4 11% 31% 40% 14% 1	849
	11th to 20th	Night	3 12% 32% 38% 14% 1	840
	21st to end	Night	5% 11% 32% 37% 14% 1	924
February	1st to 10th	Night	4 13% 34% 40% 9% 1	840
	11th to 20th	Night	6% 14% 41% 31% 7%	824
	21st to end	Night	5% 16% 42% 32% 4	692
March	1st to 10th	Night	6% 17% 34% 33% 10%	808
	11th to 20th	Night	8% 14% 32% 34% 12%	800
	21st to end	Night	5% 16% 35% 36% 7%	814
April	1st to 10th	Night	7% 18% 38% 31% 6%	600
	11th to 20th	Night	7% 21% 34% 30% 8%	593
	21st to end	Night	5% 19% 36% 33% 6% 1	600
May	1st to 10th	Night	6% 12% 33% 40% 9%	600
	11th to 20th	Night	6% 11% 29% 38% 14% 1	591
	21st to end	Night	3 11% 32% 41% 12%	650
June	1st to 10th	Night	3 7% 25% 46% 19% 1	600
	11th to 20th	Night	2 4 30% 46% 17% 1	600
	21st to end	Night	4 4 19% 46% 25% 2	600
July	1st to 10th	Night	3 3 16% 42% 33% 3	585
	11th to 20th	Night	4 1 10% 34% 46% 5%	582
	21st to end	Night	4 3 9% 31% 46% 7%	657
August	1st to 10th	Night	4 2 8% 32% 46% 8%	597
	11th to 20th	Night	5% 3 10% 41% 38% 3	594
	21st to end	Night	3 1 10% 40% 40% 5%	660
September	1st to 10th	Night	5% 4 13% 45% 32% 3	600
	11th to 20th	Night	5% 4 13% 44% 31% 3	600
	21st to end	Night	4 4 20% 45% 26% 1	667
October	1st to 10th	Night	3 7% 22% 45% 21% 2	800
	11th to 20th	Night	3 10% 23% 43% 19% 2	800
	21st to end	Night	5% 8% 24% 39% 21% 4	880
November	1st to 10th	Night	3 6% 26% 42% 21% 1	821
	11th to 20th	Night	2 9% 27% 42% 18% 2	1050
	21st to end	Night	5% 15% 27% 35% 16% 2	1050
December	1st to 10th	Night	5% 12% 28% 42% 12% 1	1050
	11th to 20th	Night	6% 11% 30% 40% 12% 1	1050
	21st to end	Night	5% 15% 32% 39% 8%	1155

Page generated at 2026-02-27 23:40:25. Version ac07

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