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 2024-12-02.

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% 60%	104998
	Night	3 4 2 5% 4 4 4 4 6% 7% 58%	103380
Transparency	Day	18% 6% 10% 21% 27% 17%	104760
	Night	20% 6% 10% 21% 26% 17%	103207
Seeing	Day	7% 16% 26% 29% 18% 4	15127
	Night	5% 10% 26% 39% 19% 2	25306

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 3 7% 4 3 4 5% 6% 7% 58%	2858
	11th to 20th	Day	1 4 2 3 3 3 4 3 5% 6% 67%	2860
	21st to end	Day	3 6% 3 6% 4 4 4 4 6% 8% 51%	3146
February	1st to 10th	Day	2 5% 2 5% 3 4 4 3 6% 6% 60%	1724
	11th to 20th	Day	2 5% 2 5% 4 3 4 3 5% 8% 59%	1849
	21st to end	Day	1 4 2 5% 4 4 4 3 6% 6% 63%	1570
March	1st to 10th	Day	1 5% 1 3 3 3 4 3 5% 6% 65%	3339
	11th to 20th	Day	2 6% 3 7% 7% 4 6% 4 6% 7% 49%	3490
	21st to end	Day	1 3 1 5% 4 4 4 4 6% 7% 59%	3934
April	1st to 10th	Day	2 3 1 2 4 3 4 3 5% 7% 66%	2280
	11th to 20th	Day	3 4 2 4 3 3 4 3 5% 6% 64%	2251
	21st to end	Day	2 4 1 3 3 3 3 3 5% 7% 67%	2280
May	1st to 10th	Day	1 1 1 2 2 3 3 3 5% 7% 72%	3800
	11th to 20th	Day	3 3 1 3 3 4 5% 4 6% 8% 59%	3882
	21st to end	Day	2 1 1 2 2 2 2 2 3 6% 77%	4812
June	1st to 10th	Day	1 2 1 3 3 3 4 4 7% 9% 62%	2660
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 6% 71%	2660
	21st to end	Day	4 4 1 4 4 4 5% 4 6% 8% 56%	2660
July	1st to 10th	Day	2 2 1 4 4 5% 5% 5% 6% 8% 57%	4275
	11th to 20th	Day	2 2 1 4 4 5% 7% 7% 10% 12% 48%	4110
	21st to end	Day	4 3 2 5% 5% 7% 7% 7% 10% 11% 39%	4454
August	1st to 10th	Day	2 2 1 4 4 6% 7% 6% 10% 11% 46%	4000
	11th to 20th	Day	2 2 1 3 3 3 6% 5% 8% 11% 56%	3726
	21st to end	Day	2 3 1 5% 5% 7% 7% 6% 9% 10% 44%	4180
September	1st to 10th	Day	5% 4 2 4 3 5% 5% 4 7% 9% 53%	2280
	11th to 20th	Day	5% 3 1 4 4 3 4 4 6% 7% 59%	2280
	21st to end	Day	2 3 1 3 2 2 3 3 4 6% 70%	2057
October	1st to 10th	Day	3 2 1 3 2 2 3 2 3 5% 74%	3170
	11th to 20th	Day	1 2 1 4 3 3 4 3 5% 7% 66%	3150
	21st to end	Day	2 1 1 2 1 2 2 2 3 6% 79%	3438
November	1st to 10th	Day	2 2 1 3 2 3 2 3 4 7% 71%	1934
	11th to 20th	Day	2 2 1 3 3 2 3 3 5% 6% 71%	1800
	21st to end	Day	2 4 2 3 3 3 4 3 5% 6% 66%	1800
December	1st to 10th	Day	2 4 1 3 3 3 2 3 5% 8% 66%	1563
	11th to 20th	Day	2 4 2 6% 4 4 5% 5% 5% 8% 55%	1926
	21st to end	Day	2 5% 1 4 3 3 2 3 5% 8% 64%	2800
January	1st to 10th	Night	1 4 4 7% 5% 5% 4 3 6% 7% 55%	4119
	11th to 20th	Night	1 3 1 4 4 4 4 3 4 6% 66%	4110
	21st to end	Night	2 5% 2 6% 4 5% 4 4 7% 9% 52%	4521
February	1st to 10th	Night	1 5% 2 4 4 3 4 3 5% 6% 65%	2453
	11th to 20th	Night	3 6% 1 5% 3 4 4 3 5% 8% 58%	2218
	21st to end	Night	2 3 2 4 4 4 4 3 5% 6% 64%	1884
March	1st to 10th	Night	2 4 2 4 4 4 3 3 5% 5% 65%	3528
	11th to 20th	Night	4 6% 3 9% 4 4 5% 3 5% 6% 50%	3490
	21st to end	Night	2 4 1 4 3 4 4 4 5% 7% 62%	3715
April	1st to 10th	Night	3 3 1 4 4 3 3 3 5% 7% 64%	1900
	11th to 20th	Night	4 3 1 4 4 4 3 3 4 7% 62%	1877
	21st to end	Night	4 3 2 4 3 3 3 3 6% 7% 63%	1900
May	1st to 10th	Night	2 3 1 3 3 3 3 4 6% 6% 66%	3170
	11th to 20th	Night	5% 5% 2 5% 4 4 4 4 7% 7% 52%	3019
	21st to end	Night	3 2 1 3 3 2 3 2 4 5% 72%	2771
June	1st to 10th	Night	2 2 2 4 5% 4 4 5% 7% 9% 55%	1520
	11th to 20th	Night	2 3 1 3 2 3 4 3 6% 6% 67%	1520
	21st to end	Night	5% 4 2 5% 5% 5% 6% 6% 6% 7% 49%	1520
July	1st to 10th	Night	2 2 1 5% 5% 7% 7% 5% 8% 7% 50%	2689
	11th to 20th	Night	4 4 2 6% 5% 6% 6% 6% 10% 12% 39%	2860
	21st to end	Night	6% 5% 3 7% 6% 5% 6% 6% 9% 11% 36%	3109
August	1st to 10th	Night	2 4 3 8% 7% 7% 8% 8% 9% 12% 32%	2937
	11th to 20th	Night	3 3 1 5% 5% 6% 7% 6% 9% 11% 43%	3113
	21st to end	Night	3 4 2 7% 7% 8% 9% 7% 10% 11% 31%	3487
September	1st to 10th	Night	5% 4 2 6% 5% 5% 5% 5% 8% 8% 48%	1900
	11th to 20th	Night	5% 4 2 4 3 3 4 4 6% 8% 57%	1900
	21st to end	Night	3 3 2 4 2 3 3 3 4 6% 67%	2119
October	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 76%	3800
	11th to 20th	Night	2 2 1 4 3 4 3 3 6% 7% 66%	3778
	21st to end	Night	2 1 1 1 2 2 2 3 5% 79%	4120
November	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 74%	2341
	11th to 20th	Night	1 2 1 3 3 2 3 3 5% 5% 74%	2600
	21st to end	Night	3 4 2 5% 4 3 4 3 5% 6% 63%	2600
December	1st to 10th	Night	2 4 1 4 3 3 4 4 5% 7% 65%	2648
	11th to 20th	Night	2 4 1 5% 4 4 5% 4 6% 9% 56%	3271
	21st to end	Night	2 5% 2 5% 4 3 4 3 5% 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	19% 5% 9% 34% 29% 4	2859
	11th to 20th	Day	14% 7% 11% 36% 27% 4	2860
	21st to end	Day	25% 8% 9% 24% 27% 7%	3146
February	1st to 10th	Day	22% 3 10% 27% 26% 12%	1724
	11th to 20th	Day	22% 4 8% 24% 30% 12%	1859
	21st to end	Day	20% 3 5% 20% 31% 21%	1570
March	1st to 10th	Day	16% 4 5% 18% 37% 20%	3339
	11th to 20th	Day	23% 11% 10% 22% 25% 9%	3490
	21st to end	Day	17% 6% 8% 21% 36% 12%	3934
April	1st to 10th	Day	16% 5% 7% 18% 35% 20%	2280
	11th to 20th	Day	19% 4 5% 17% 31% 23%	2254
	21st to end	Day	16% 4 7% 20% 35% 17%	2280
May	1st to 10th	Day	9% 5% 7% 17% 34% 28%	3800
	11th to 20th	Day	18% 7% 9% 18% 31% 16%	3885
	21st to end	Day	9% 4 5% 12% 22% 48%	4812
June	1st to 10th	Day	15% 6% 9% 20% 26% 24%	2660
	11th to 20th	Day	13% 4 6% 11% 23% 43%	2660
	21st to end	Day	23% 5% 9% 20% 21% 22%	2660
July	1st to 10th	Day	19% 9% 13% 14% 19% 25%	4210
	11th to 20th	Day	21% 9% 20% 28% 16% 6%	4041
	21st to end	Day	27% 11% 18% 29% 12% 2	4314
August	1st to 10th	Day	23% 12% 21% 23% 15% 7%	3986
	11th to 20th	Day	18% 8% 12% 25% 22% 13%	3762
	21st to end	Day	28% 10% 17% 23% 19% 3	4179
September	1st to 10th	Day	25% 7% 12% 19% 25% 12%	2280
	11th to 20th	Day	22% 7% 8% 17% 26% 19%	2280
	21st to end	Day	15% 4 6% 21% 33% 20%	2057
October	1st to 10th	Day	14% 4 4 13% 31% 33%	3170
	11th to 20th	Day	15% 5% 7% 17% 32% 24%	3150
	21st to end	Day	9% 2 5% 17% 41% 26%	3438
November	1st to 10th	Day	13% 3 6% 22% 39% 18%	1934
	11th to 20th	Day	13% 4 7% 23% 40% 14%	1800
	21st to end	Day	18% 4 7% 21% 33% 17%	1800
December	1st to 10th	Day	17% 4 10% 33% 24% 12%	1563
	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	21% 6% 12% 27% 26% 8%	4119
	11th to 20th	Night	15% 6% 9% 36% 27% 7%	4110
	21st to end	Night	23% 8% 11% 23% 28% 6%	4521
February	1st to 10th	Night	18% 4 12% 24% 29% 13%	2453
	11th to 20th	Night	22% 4 8% 24% 27% 14%	2218
	21st to end	Night	18% 4 6% 16% 34% 21%	1884
March	1st to 10th	Night	17% 4 5% 17% 39% 18%	3528
	11th to 20th	Night	27% 10% 9% 19% 24% 10%	3490
	21st to end	Night	16% 5% 8% 24% 34% 12%	3715
April	1st to 10th	Night	18% 4 6% 19% 32% 22%	1900
	11th to 20th	Night	20% 4 6% 17% 28% 25%	1877
	21st to end	Night	18% 4 9% 17% 35% 17%	1900
May	1st to 10th	Night	12% 7% 9% 16% 29% 28%	3170
	11th to 20th	Night	22% 11% 12% 19% 20% 16%	3020
	21st to end	Night	12% 5% 5% 11% 18% 48%	2771
June	1st to 10th	Night	21% 8% 13% 16% 19% 24%	1520
	11th to 20th	Night	15% 4 6% 13% 22% 40%	1520
	21st to end	Night	28% 8% 12% 13% 16% 23%	1520
July	1st to 10th	Night	26% 8% 13% 18% 11% 25%	2645
	11th to 20th	Night	28% 10% 18% 29% 10% 5%	2806
	21st to end	Night	34% 11% 18% 27% 9% 1	3011
August	1st to 10th	Night	35% 13% 17% 18% 12% 6%	2928
	11th to 20th	Night	26% 10% 16% 19% 17% 11%	3143
	21st to end	Night	36% 11% 17% 21% 10% 4	3487
September	1st to 10th	Night	28% 8% 14% 17% 21% 11%	1900
	11th to 20th	Night	23% 6% 10% 17% 21% 22%	1900
	21st to end	Night	19% 4 8% 16% 30% 22%	2119
October	1st to 10th	Night	13% 4 6% 14% 30% 34%	3800
	11th to 20th	Night	15% 5% 8% 17% 27% 28%	3778
	21st to end	Night	10% 2 4 18% 41% 25%	4120
November	1st to 10th	Night	11% 3 5% 22% 40% 19%	2341
	11th to 20th	Night	12% 4 6% 20% 41% 18%	2600
	21st to end	Night	22% 4 5% 19% 32% 18%	2600
December	1st to 10th	Night	17% 5% 9% 28% 30% 10%	2648
	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	13% 21% 29% 29% 9%	270
	21st to end	Day	3 18% 33% 31% 13% 2	297
February	1st to 10th	Day	8% 26% 32% 24% 10%	270
	11th to 20th	Day	11% 26% 38% 20% 4	270
	21st to end	Day	17% 31% 30% 20% 3	225
March	1st to 10th	Day	10% 30% 30% 23% 7%	389
	11th to 20th	Day	15% 27% 28% 20% 8% 1	460
	21st to end	Day	14% 36% 30% 14% 6%	506
April	1st to 10th	Day	11% 27% 35% 18% 7% 1	460
	11th to 20th	Day	13% 32% 33% 15% 6%	452
	21st to end	Day	10% 29% 36% 21% 4 1	460
May	1st to 10th	Day	7% 27% 40% 21% 5% 1	463
	11th to 20th	Day	7% 21% 32% 28% 10% 3	488
	21st to end	Day	5% 17% 29% 33% 14% 1	721
June	1st to 10th	Day	3 8% 24% 39% 24% 2	680
	11th to 20th	Day	4 9% 25% 37% 23% 3	680
	21st to end	Day	7% 6% 22% 34% 26% 5%	680
July	1st to 10th	Day	3 4 19% 37% 29% 9%	585
	11th to 20th	Day	4 1 9% 32% 37% 17%	484
	21st to end	Day	3 2 8% 31% 38% 18%	531
August	1st to 10th	Day	3 3 12% 33% 38% 12%	487
	11th to 20th	Day	4 2 18% 37% 28% 10%	477
	21st to end	Day	5% 3 14% 37% 32% 9%	539
September	1st to 10th	Day	4 5% 19% 34% 29% 9%	490
	11th to 20th	Day	3 5% 26% 36% 24% 5%	490
	21st to end	Day	4 9% 25% 33% 21% 7%	333
October	1st to 10th	Day	6% 14% 24% 26% 23% 7%	300
	11th to 20th	Day	8% 13% 26% 29% 19% 5%	300
	21st to end	Day	12% 14% 24% 28% 19% 4	330
November	1st to 10th	Day	6% 21% 29% 28% 14% 1	300
	11th to 20th	Day	4 13% 30% 35% 15% 1	300
	21st to end	Day	8% 22% 29% 28% 12% 1	300
December	1st to 10th	Day	9% 19% 30% 32% 10%	273
	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% 37% 15% 1	760
	21st to end	Night	5% 11% 29% 37% 16% 1	836
February	1st to 10th	Night	5% 13% 33% 39% 10% 1	760
	11th to 20th	Night	6% 13% 40% 33% 8% 1	744
	21st to end	Night	5% 16% 42% 32% 4	628
March	1st to 10th	Night	6% 17% 34% 33% 10% 1	760
	11th to 20th	Night	7% 14% 31% 35% 13%	760
	21st to end	Night	5% 16% 34% 37% 8%	774
April	1st to 10th	Night	7% 18% 38% 30% 6%	570
	11th to 20th	Night	7% 21% 32% 31% 9%	563
	21st to end	Night	5% 19% 35% 33% 7% 1	570
May	1st to 10th	Night	5% 12% 34% 39% 9%	570
	11th to 20th	Night	7% 10% 27% 40% 15% 1	561
	21st to end	Night	3 11% 31% 41% 13%	617
June	1st to 10th	Night	3 7% 24% 45% 20% 1	570
	11th to 20th	Night	2 5% 30% 46% 16% 1	570
	21st to end	Night	4 4 18% 45% 26% 2	570
July	1st to 10th	Night	3 3 15% 42% 34% 3	555
	11th to 20th	Night	4 1 10% 34% 46% 6%	552
	21st to end	Night	4 3 8% 30% 47% 7%	624
August	1st to 10th	Night	4 2 8% 31% 47% 8%	567
	11th to 20th	Night	5% 3 10% 41% 38% 3	564
	21st to end	Night	3 1 10% 40% 42% 5%	627
September	1st to 10th	Night	5% 4 12% 44% 33% 3	570
	11th to 20th	Night	5% 4 12% 44% 32% 3	570
	21st to end	Night	4 4 20% 44% 27% 1	633
October	1st to 10th	Night	4 7% 21% 45% 21% 2	760
	11th to 20th	Night	4 9% 22% 44% 20% 2	760
	21st to end	Night	5% 8% 24% 37% 22% 4	836
November	1st to 10th	Night	3 7% 25% 43% 21% 2	781
	11th to 20th	Night	2 9% 27% 42% 18% 2	1000
	21st to end	Night	5% 15% 26% 35% 17% 2	1000
December	1st to 10th	Night	5% 12% 27% 43% 12% 1	960
	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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