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 2024-01-15.

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	3 3 2 3 4 3 4 5% 6% 8% 60%	74689
	Night	3 3 2 4 4 3 4 5% 5% 7% 60%	75099
Transparency	Day	20% 6% 9% 21% 27% 17%	74414
	Night	21% 6% 10% 20% 28% 16%	74895
Seeing	Day	7% 16% 26% 29% 18% 4	13913
	Night	5% 10% 26% 39% 19% 2	24176

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 2 2 4 4 3 5% 5% 6% 8% 61%	1708
	11th to 20th	Day	3 4 2 3 3 2 4 3 5% 5% 66%	1656
	21st to end	Day	3 4 2 4 3 3 3 4 6% 6% 62%	1782
February	1st to 10th	Day	2 5% 2 4 4 3 4 3 6% 6% 61%	1634
	11th to 20th	Day	2 4 2 5% 4 2 4 3 5% 9% 58%	1749
	21st to end	Day	1 4 2 4 4 3 4 4 5% 7% 63%	1480
March	1st to 10th	Day	2 4 2 4 5% 3 5% 5% 6% 7% 57%	1912
	11th to 20th	Day	3 5% 2 4 5% 2 5% 4 4 7% 59%	1980
	21st to end	Day	2 3 2 4 4 2 4 4 7% 8% 60%	2236
April	1st to 10th	Day	2 3 1 2 4 2 4 4 5% 8% 66%	2160
	11th to 20th	Day	3 4 2 3 4 3 4 3 5% 6% 63%	2131
	21st to end	Day	2 3 1 3 3 2 4 3 5% 6% 66%	2160
May	1st to 10th	Day	2 2 2 3 3 2 4 4 5% 8% 66%	2160
	11th to 20th	Day	4 3 2 4 5% 3 5% 5% 5% 7% 58%	2190
	21st to end	Day	3 2 1 3 3 2 3 4 5% 7% 67%	2711
June	1st to 10th	Day	2 1 1 3 3 2 4 5% 7% 9% 62%	2520
	11th to 20th	Day	2 2 1 2 3 3 3 4 5% 6% 71%	2520
	21st to end	Day	4 3 1 3 4 3 5% 5% 6% 8% 58%	2520
July	1st to 10th	Day	4 3 1 5% 5% 4 6% 8% 6% 9% 47%	2435
	11th to 20th	Day	3 3 1 4 5% 4 6% 7% 9% 11% 48%	2340
	21st to end	Day	5% 3 2 5% 7% 5% 7% 8% 8% 10% 38%	2545
August	1st to 10th	Day	3 3 2 4 6% 4 6% 7% 8% 10% 46%	2275
	11th to 20th	Day	4 4 2 5% 5% 3 6% 6% 8% 11% 46%	2123
	21st to end	Day	4 3 2 4 5% 3 6% 6% 8% 9% 50%	2376
September	1st to 10th	Day	5% 4 2 4 4 3 6% 5% 7% 9% 51%	2160
	11th to 20th	Day	5% 3 1 3 4 2 4 5% 7% 7% 59%	2160
	21st to end	Day	2 3 1 3 2 2 3 4 4 6% 69%	1950
October	1st to 10th	Day	6% 3 2 4 5% 3 4 4 4 6% 60%	1800
	11th to 20th	Day	2 3 1 2 3 2 2 2 3 4 76%	1800
	21st to end	Day	3 2 1 2 3 2 3 3 3 5% 73%	1980
November	1st to 10th	Day	2 1 1 2 3 2 2 3 4 7% 72%	1836
	11th to 20th	Day	2 2 2 3 3 2 3 3 5% 7% 70%	1710
	21st to end	Day	2 4 2 3 4 3 4 3 4 6% 66%	1710
December	1st to 10th	Day	2 3 1 3 4 2 3 3 5% 8% 66%	1554
	11th to 20th	Day	2 4 3 4 5% 3 5% 6% 5% 8% 55%	1926
	21st to end	Day	2 4 2 4 4 2 3 3 5% 8% 64%	2800
January	1st to 10th	Night	2 3 2 4 4 2 3 3 5% 8% 65%	2466
	11th to 20th	Night	3 3 2 4 4 2 4 5% 4 5% 65%	2398
	21st to end	Night	3 4 2 3 3 2 4 5% 5% 8% 62%	2574
February	1st to 10th	Night	1 4 2 4 4 2 4 3 5% 6% 67%	2324
	11th to 20th	Night	3 5% 2 5% 3 3 5% 4 5% 8% 57%	2098
	21st to end	Night	2 3 2 3 4 3 4 4 4 6% 66%	1776
March	1st to 10th	Night	3 4 2 4 5% 3 3 5% 5% 8% 59%	2044
	11th to 20th	Night	4 4 2 4 5% 2 5% 4 5% 6% 61%	1980
	21st to end	Night	3 4 1 3 4 2 4 5% 5% 6% 62%	2120
April	1st to 10th	Night	3 2 2 3 4 2 3 4 5% 7% 64%	1800
	11th to 20th	Night	4 3 2 3 4 3 4 4 3 7% 62%	1777
	21st to end	Night	4 3 1 3 4 2 4 4 5% 7% 64%	1800
May	1st to 10th	Night	3 3 1 3 3 2 4 4 6% 6% 64%	1800
	11th to 20th	Night	5% 4 2 4 4 3 5% 5% 6% 7% 54%	1701
	21st to end	Night	3 2 2 3 5% 2 4 3 4 6% 66%	1561
June	1st to 10th	Night	2 2 3 4 5% 3 4 6% 7% 9% 56%	1440
	11th to 20th	Night	2 2 1 3 2 2 3 4 5% 7% 68%	1440
	21st to end	Night	5% 4 2 4 4 4 6% 6% 6% 7% 52%	1440
July	1st to 10th	Night	4 3 2 6% 7% 5% 7% 7% 8% 8% 43%	1519
	11th to 20th	Night	4 5% 2 5% 6% 4 6% 8% 10% 11% 41%	1620
	21st to end	Night	5% 4 3 7% 8% 5% 6% 7% 11% 12% 32%	1773
August	1st to 10th	Night	4 3 2 4 6% 4 7% 9% 9% 12% 40%	1662
	11th to 20th	Night	6% 4 2 5% 6% 4 7% 8% 8% 10% 39%	1778
	21st to end	Night	3 2 2 4 5% 4 6% 6% 8% 12% 47%	1980
September	1st to 10th	Night	5% 3 2 5% 6% 4 4 7% 8% 9% 46%	1800
	11th to 20th	Night	5% 4 2 3 5% 2 4 5% 6% 8% 57%	1800
	21st to end	Night	3 3 2 3 3 2 3 3 4 6% 67%	2006
October	1st to 10th	Night	5% 3 1 4 4 2 3 4 5% 6% 62%	2160
	11th to 20th	Night	2 2 1 2 2 2 2 3 4 4 76%	2160
	21st to end	Night	4 2 1 2 2 2 3 3 4 5% 72%	2376
November	1st to 10th	Night	1 2 1 2 2 2 2 3 4 6% 75%	2220
	11th to 20th	Night	1 1 1 2 4 2 2 4 4 6% 73%	2470
	21st to end	Night	3 3 3 4 4 3 4 4 5% 6% 63%	2470
December	1st to 10th	Night	2 3 1 3 3 2 4 5% 5% 7% 65%	2622
	11th to 20th	Night	2 3 2 4 5% 2 5% 5% 6% 9% 56%	3271
	21st to end	Night	3 5% 2 4 4 3 3 4 4 6% 61%	4873

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	17% 5% 11% 31% 31% 6%	1709
	11th to 20th	Day	19% 4 8% 27% 34% 7%	1656
	21st to end	Day	22% 4 8% 25% 30% 12%	1782
February	1st to 10th	Day	22% 3 10% 27% 26% 12%	1634
	11th to 20th	Day	23% 4 8% 25% 29% 12%	1759
	21st to end	Day	20% 3 5% 20% 31% 21%	1480
March	1st to 10th	Day	22% 4 7% 21% 30% 17%	1912
	11th to 20th	Day	22% 5% 7% 19% 32% 15%	1980
	21st to end	Day	19% 5% 9% 21% 32% 15%	2236
April	1st to 10th	Day	15% 4 7% 19% 35% 20%	2160
	11th to 20th	Day	20% 4 5% 17% 31% 21%	2134
	21st to end	Day	17% 4 7% 20% 34% 18%	2160
May	1st to 10th	Day	15% 5% 7% 18% 32% 24%	2160
	11th to 20th	Day	25% 6% 10% 17% 25% 17%	2193
	21st to end	Day	16% 5% 8% 17% 25% 28%	2711
June	1st to 10th	Day	14% 6% 9% 20% 26% 24%	2520
	11th to 20th	Day	13% 4 6% 12% 23% 42%	2520
	21st to end	Day	22% 5% 9% 20% 21% 23%	2520
July	1st to 10th	Day	27% 10% 14% 15% 18% 15%	2370
	11th to 20th	Day	24% 9% 18% 23% 15% 10%	2271
	21st to end	Day	32% 14% 20% 24% 9% 2	2404
August	1st to 10th	Day	27% 13% 18% 20% 14% 9%	2260
	11th to 20th	Day	28% 11% 14% 21% 19% 7%	2123
	21st to end	Day	24% 10% 14% 24% 22% 6%	2376
September	1st to 10th	Day	26% 7% 12% 19% 23% 12%	2160
	11th to 20th	Day	23% 7% 9% 17% 25% 19%	2160
	21st to end	Day	15% 5% 7% 21% 33% 19%	1950
October	1st to 10th	Day	23% 6% 7% 19% 25% 20%	1800
	11th to 20th	Day	15% 3 3 13% 35% 32%	1800
	21st to end	Day	15% 3 7% 21% 37% 18%	1980
November	1st to 10th	Day	12% 3 6% 23% 38% 19%	1836
	11th to 20th	Day	14% 4 7% 24% 40% 12%	1710
	21st to end	Day	19% 4 6% 22% 33% 16%	1710
December	1st to 10th	Day	17% 4 10% 33% 24% 11%	1554
	11th to 20th	Day	23% 7% 13% 22% 27% 9%	1924
	21st to end	Day	18% 4 10% 21% 31% 16%	2800
January	1st to 10th	Night	17% 4 11% 28% 32% 8%	2466
	11th to 20th	Night	19% 5% 7% 27% 31% 11%	2398
	21st to end	Night	18% 5% 11% 23% 34% 9%	2574
February	1st to 10th	Night	18% 4 12% 25% 29% 13%	2324
	11th to 20th	Night	23% 5% 8% 24% 26% 14%	2098
	21st to end	Night	18% 4 6% 17% 34% 21%	1776
March	1st to 10th	Night	21% 5% 7% 23% 29% 16%	2044
	11th to 20th	Night	22% 5% 8% 19% 32% 14%	1980
	21st to end	Night	20% 5% 8% 17% 35% 14%	2120
April	1st to 10th	Night	18% 3 6% 19% 33% 21%	1800
	11th to 20th	Night	20% 4 6% 18% 28% 23%	1777
	21st to end	Night	18% 4 9% 16% 35% 17%	1800
May	1st to 10th	Night	18% 5% 8% 15% 31% 23%	1800
	11th to 20th	Night	26% 7% 10% 18% 21% 18%	1702
	21st to end	Night	18% 5% 9% 16% 25% 28%	1561
June	1st to 10th	Night	21% 8% 14% 16% 19% 23%	1440
	11th to 20th	Night	15% 4 6% 13% 21% 40%	1440
	21st to end	Night	26% 8% 12% 14% 17% 24%	1440
July	1st to 10th	Night	33% 10% 13% 18% 12% 14%	1475
	11th to 20th	Night	27% 13% 20% 19% 13% 8%	1566
	21st to end	Night	35% 14% 24% 20% 6% 1	1674
August	1st to 10th	Night	28% 15% 19% 19% 11% 8%	1653
	11th to 20th	Night	32% 12% 17% 18% 13% 8%	1778
	21st to end	Night	25% 11% 15% 26% 16% 7%	1980
September	1st to 10th	Night	29% 8% 15% 17% 20% 11%	1800
	11th to 20th	Night	24% 7% 10% 18% 20% 22%	1800
	21st to end	Night	20% 4 8% 17% 29% 22%	2006
October	1st to 10th	Night	22% 6% 9% 18% 21% 23%	2160
	11th to 20th	Night	13% 3 4 13% 34% 33%	2160
	21st to end	Night	15% 3 7% 17% 38% 20%	2376
November	1st to 10th	Night	11% 3 5% 22% 40% 19%	2220
	11th to 20th	Night	12% 4 6% 21% 41% 16%	2470
	21st to end	Night	22% 4 5% 19% 33% 17%	2470
December	1st to 10th	Night	17% 5% 9% 28% 30% 9%	2622
	11th to 20th	Night	21% 6% 10% 24% 29% 9%	3272
	21st to end	Night	20% 6% 9% 21% 32% 13%	4873

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	6% 21% 31% 34% 7%	270
	11th to 20th	Day	12% 21% 29% 29% 9%	252
	21st to end	Day	3 20% 35% 31% 9% 2	264
February	1st to 10th	Day	4 27% 33% 25% 11%	240
	11th to 20th	Day	13% 27% 37% 19% 5%	240
	21st to end	Day	14% 33% 31% 20% 3	198
March	1st to 10th	Day	9% 30% 31% 22% 8%	352
	11th to 20th	Day	15% 28% 28% 20% 9% 1	420
	21st to end	Day	13% 38% 29% 14% 6%	462
April	1st to 10th	Day	10% 27% 36% 18% 8% 1	420
	11th to 20th	Day	14% 33% 31% 15% 7%	412
	21st to end	Day	10% 29% 36% 20% 4 1	420
May	1st to 10th	Day	5% 27% 41% 21% 5% 1	423
	11th to 20th	Day	7% 20% 33% 27% 10% 3	448
	21st to end	Day	5% 17% 29% 33% 15% 1	666
June	1st to 10th	Day	2 8% 25% 39% 24% 2	630
	11th to 20th	Day	3 9% 24% 37% 24% 3	630
	21st to end	Day	7% 6% 21% 34% 27% 5%	630
July	1st to 10th	Day	3 4 18% 36% 30% 9%	540
	11th to 20th	Day	5% 1 9% 33% 36% 17%	444
	21st to end	Day	3 1 8% 29% 39% 19%	487
August	1st to 10th	Day	3 3 13% 33% 37% 11%	447
	11th to 20th	Day	5% 3 19% 37% 28% 9%	437
	21st to end	Day	5% 3 14% 36% 32% 10%	495
September	1st to 10th	Day	5% 5% 19% 35% 28% 9%	450
	11th to 20th	Day	4 5% 25% 37% 24% 5%	450
	21st to end	Day	4 10% 26% 32% 20% 8%	302
October	1st to 10th	Day	7% 15% 25% 25% 21% 7%	270
	11th to 20th	Day	8% 12% 26% 30% 19% 5%	270
	21st to end	Day	12% 14% 24% 28% 19% 3	297
November	1st to 10th	Day	6% 21% 30% 29% 14% 1	270
	11th to 20th	Day	4 13% 30% 35% 16% 1	270
	21st to end	Day	8% 23% 29% 27% 12% 1	270
December	1st to 10th	Day	9% 19% 31% 31% 9%	270
	11th to 20th	Day	9% 22% 30% 31% 8%	270
	21st to end	Day	12% 27% 28% 30% 4	297
January	1st to 10th	Night	4 11% 31% 39% 15% 1	769
	11th to 20th	Night	4 12% 31% 38% 15% 1	738
	21st to end	Night	5% 12% 31% 37% 14% 1	792
February	1st to 10th	Night	3 13% 33% 40% 10% 1	720
	11th to 20th	Night	6% 13% 39% 33% 8% 1	704
	21st to end	Night	5% 16% 41% 33% 4	592
March	1st to 10th	Night	6% 17% 34% 33% 10% 1	720
	11th to 20th	Night	6% 14% 30% 36% 13%	720
	21st to end	Night	5% 16% 34% 37% 8%	734
April	1st to 10th	Night	5% 19% 39% 31% 6%	540
	11th to 20th	Night	7% 21% 31% 32% 9%	533
	21st to end	Night	5% 19% 35% 33% 7% 1	540
May	1st to 10th	Night	5% 11% 35% 40% 10%	540
	11th to 20th	Night	6% 10% 27% 40% 14% 2	531
	21st to end	Night	3 10% 31% 42% 13%	584
June	1st to 10th	Night	3 7% 24% 46% 20% 1	540
	11th to 20th	Night	2 5% 29% 46% 17% 1	540
	21st to end	Night	4 4 18% 46% 26% 2	540
July	1st to 10th	Night	3 3 14% 42% 36% 3	525
	11th to 20th	Night	4 1 10% 33% 47% 6%	522
	21st to end	Night	5% 2 8% 29% 49% 8%	591
August	1st to 10th	Night	4 2 7% 30% 48% 8%	537
	11th to 20th	Night	5% 3 10% 41% 38% 3	534
	21st to end	Night	3 1 10% 40% 42% 5%	594
September	1st to 10th	Night	5% 4 11% 43% 34% 3	540
	11th to 20th	Night	6% 5% 11% 43% 33% 3	540
	21st to end	Night	4 4 20% 43% 27% 2	599
October	1st to 10th	Night	4 7% 22% 44% 21% 2	720
	11th to 20th	Night	3 9% 22% 45% 19% 2	720
	21st to end	Night	5% 9% 23% 37% 22% 4	792
November	1st to 10th	Night	3 7% 23% 44% 22% 2	740
	11th to 20th	Night	2 9% 26% 42% 18% 2	950
	21st to end	Night	5% 15% 25% 35% 18% 3	950
December	1st to 10th	Night	5% 12% 27% 43% 12% 1	950
	11th to 20th	Night	7% 12% 29% 39% 12% 1	950
	21st to end	Night	6% 16% 31% 39% 8%	1045

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