Picture Canyon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Picture Canyon clear sky chart from 2005-11-06 to 2024-01-13.

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	5% 4 2 3 3 2 3 4 5% 7% 61%	74848
	Night	5% 4 2 4 3 2 4 4 5% 7% 60%	74907
Transparency	Day	22% 5% 10% 23% 26% 14%	74558
	Night	24% 5% 11% 22% 26% 13%	74720
Seeing	Day	7% 7% 27% 33% 20% 6%	14275
	Night	7% 6% 34% 39% 13% 1	24387

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	3 4 2 4 4 1 3 3 4 6% 66%	1518
	11th to 20th	Day	5% 4 2 4 3 2 3 3 3 5% 65%	1459
	21st to end	Day	2 4 2 4 3 2 3 4 5% 6% 65%	1850
February	1st to 10th	Day	4 6% 3 5% 4 3 3 4 4 6% 59%	1800
	11th to 20th	Day	4 5% 3 5% 5% 3 3 4 4 6% 58%	1749
	21st to end	Day	3 5% 2 3 3 2 3 4 5% 6% 64%	1480
March	1st to 10th	Day	4 4 2 5% 4 2 4 3 6% 7% 60%	1800
	11th to 20th	Day	7% 4 2 3 3 2 3 4 4 7% 63%	1841
	21st to end	Day	6% 5% 2 3 2 3 3 3 5% 7% 61%	2363
April	1st to 10th	Day	5% 4 1 3 3 2 3 4 4 7% 66%	2160
	11th to 20th	Day	7% 5% 1 3 3 3 4 5% 5% 6% 57%	2131
	21st to end	Day	8% 5% 2 3 3 2 4 4 5% 8% 57%	2160
May	1st to 10th	Day	8% 4 1 3 3 3 3 4 5% 7% 58%	2337
	11th to 20th	Day	9% 4 2 4 3 2 3 4 5% 7% 56%	2302
	21st to end	Day	5% 3 2 3 4 2 4 5% 5% 9% 57%	2550
June	1st to 10th	Day	4 3 1 3 3 3 4 6% 7% 11% 56%	2520
	11th to 20th	Day	3 3 1 2 2 2 3 4 6% 9% 64%	2520
	21st to end	Day	4 4 1 4 4 2 4 5% 6% 9% 57%	2520
July	1st to 10th	Day	5% 3 1 3 5% 3 5% 6% 7% 9% 54%	2520
	11th to 20th	Day	3 2 1 3 4 2 4 5% 7% 10% 60%	2520
	21st to end	Day	6% 3 2 4 4 3 4 5% 7% 11% 51%	2657
August	1st to 10th	Day	4 2 1 3 4 3 5% 6% 7% 11% 54%	2170
	11th to 20th	Day	7% 3 1 4 4 4 4 6% 7% 9% 51%	2123
	21st to end	Day	4 2 1 3 3 3 4 5% 6% 9% 59%	2376
September	1st to 10th	Day	8% 3 1 3 3 2 3 4 5% 8% 59%	2160
	11th to 20th	Day	7% 4 1 4 3 2 3 3 5% 6% 64%	2025
	21st to end	Day	5% 3 1 3 3 2 3 3 4 6% 68%	1980
October	1st to 10th	Day	9% 4 1 3 3 2 3 3 4 6% 62%	1980
	11th to 20th	Day	5% 3 1 2 2 1 2 2 2 3 75%	1846
	21st to end	Day	7% 3 1 2 3 1 2 2 3 4 70%	1836
November	1st to 10th	Day	2 4 1 3 2 1 1 2 4 5% 75%	1673
	11th to 20th	Day	3 3 1 3 2 1 2 2 4 6% 71%	1710
	21st to end	Day	5% 6% 2 4 3 1 3 2 4 5% 65%	1710
December	1st to 10th	Day	2 5% 2 4 3 2 4 4 5% 6% 63%	1710
	11th to 20th	Day	5% 4 2 3 3 1 3 4 4 7% 64%	1998
	21st to end	Day	4 5% 2 4 3 2 3 3 6% 6% 61%	2794
January	1st to 10th	Night	3 4 2 4 4 2 4 4 5% 6% 62%	2647
	11th to 20th	Night	5% 5% 2 3 3 2 3 3 4 6% 65%	2561
	21st to end	Night	3 5% 3 4 3 2 3 3 4 7% 62%	2516
February	1st to 10th	Night	4 5% 3 4 4 2 3 3 4 5% 61%	2160
	11th to 20th	Night	4 5% 3 5% 5% 3 4 5% 6% 8% 51%	2098
	21st to end	Night	5% 4 2 3 3 2 3 3 5% 6% 65%	1776
March	1st to 10th	Night	4 5% 2 4 3 2 4 4 5% 7% 61%	2160
	11th to 20th	Night	7% 4 2 4 3 2 3 4 4 7% 59%	2117
	21st to end	Night	5% 4 2 3 3 3 4 4 6% 6% 59%	1990
April	1st to 10th	Night	5% 4 1 3 3 3 3 4 4 8% 62%	1800
	11th to 20th	Night	8% 4 1 3 4 3 5% 4 5% 8% 55%	1777
	21st to end	Night	12% 4 1 3 4 2 4 4 5% 7% 56%	1800
May	1st to 10th	Night	7% 4 2 3 3 2 5% 4 5% 8% 56%	1620
	11th to 20th	Night	10% 4 2 4 4 2 4 5% 6% 8% 52%	1593
	21st to end	Night	8% 3 2 4 4 2 4 6% 5% 9% 52%	1722
June	1st to 10th	Night	4 3 1 4 3 3 4 5% 7% 11% 54%	1440
	11th to 20th	Night	2 2 1 2 3 2 3 5% 6% 11% 62%	1440
	21st to end	Night	5% 3 1 4 4 3 5% 7% 7% 10% 51%	1440
July	1st to 10th	Night	4 3 2 4 3 2 6% 6% 8% 10% 52%	1440
	11th to 20th	Night	3 3 1 4 5% 3 4 5% 8% 12% 53%	1440
	21st to end	Night	7% 4 3 6% 6% 4 6% 6% 7% 11% 41%	1659
August	1st to 10th	Night	5% 3 2 4 6% 4 6% 7% 8% 11% 44%	1764
	11th to 20th	Night	8% 3 1 3 3 3 5% 6% 7% 11% 49%	1778
	21st to end	Night	4 3 2 4 4 3 5% 5% 6% 10% 54%	1980
September	1st to 10th	Night	7% 4 1 3 3 3 3 4 5% 8% 60%	1800
	11th to 20th	Night	7% 4 1 3 4 2 3 4 5% 7% 61%	1934
	21st to end	Night	5% 3 1 3 3 2 3 4 4 6% 66%	1980
October	1st to 10th	Night	10% 4 1 3 3 3 3 4 6% 5% 60%	1980
	11th to 20th	Night	5% 2 1 2 2 1 2 2 3 4 75%	2110
	21st to end	Night	6% 4 1 2 2 1 3 4 4 5% 68%	2502
November	1st to 10th	Night	4 3 1 3 2 1 2 3 4 5% 72%	2405
	11th to 20th	Night	2 3 1 3 2 1 3 3 4 4 74%	2470
	21st to end	Night	4 5% 2 3 3 2 3 3 5% 5% 64%	2470
December	1st to 10th	Night	3 4 2 4 3 1 3 3 4 7% 63%	2470
	11th to 20th	Night	4 4 2 3 4 2 3 3 4 7% 63%	3195
	21st to end	Night	4 4 3 4 5% 3 4 5% 5% 5% 59%	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	21% 3 9% 27% 32% 10%	1519
	11th to 20th	Day	22% 3 8% 24% 32% 11%	1459
	21st to end	Day	21% 3 8% 27% 30% 11%	1850
February	1st to 10th	Day	27% 3 11% 23% 23% 13%	1800
	11th to 20th	Day	29% 3 7% 23% 25% 13%	1759
	21st to end	Day	22% 3 7% 20% 29% 20%	1480
March	1st to 10th	Day	24% 4 10% 20% 24% 18%	1800
	11th to 20th	Day	23% 3 9% 24% 30% 12%	1841
	21st to end	Day	24% 4 10% 25% 26% 11%	2363
April	1st to 10th	Day	20% 4 8% 23% 27% 18%	2160
	11th to 20th	Day	27% 5% 10% 22% 22% 15%	2134
	21st to end	Day	26% 4 12% 23% 26% 8%	2160
May	1st to 10th	Day	25% 6% 10% 23% 23% 12%	2337
	11th to 20th	Day	27% 6% 14% 26% 21% 6%	2306
	21st to end	Day	24% 7% 14% 22% 21% 12%	2550
June	1st to 10th	Day	20% 8% 16% 26% 20% 10%	2520
	11th to 20th	Day	16% 6% 11% 21% 25% 21%	2520
	21st to end	Day	23% 6% 11% 24% 21% 15%	2520
July	1st to 10th	Day	25% 8% 12% 19% 24% 11%	2451
	11th to 20th	Day	18% 6% 13% 25% 28% 10%	2445
	21st to end	Day	26% 9% 16% 30% 16% 3	2509
August	1st to 10th	Day	21% 10% 19% 27% 15% 8%	2156
	11th to 20th	Day	27% 8% 12% 23% 21% 10%	2123
	21st to end	Day	21% 7% 11% 25% 25% 11%	2376
September	1st to 10th	Day	24% 6% 10% 22% 22% 16%	2160
	11th to 20th	Day	22% 5% 7% 20% 27% 19%	2025
	21st to end	Day	20% 3 8% 18% 33% 17%	1980
October	1st to 10th	Day	25% 4 9% 19% 29% 14%	1980
	11th to 20th	Day	16% 3 5% 16% 35% 25%	1846
	21st to end	Day	20% 3 6% 20% 31% 19%	1836
November	1st to 10th	Day	14% 2 7% 22% 32% 22%	1673
	11th to 20th	Day	16% 2 7% 25% 34% 16%	1710
	21st to end	Day	23% 2 7% 15% 29% 23%	1710
December	1st to 10th	Day	22% 4 11% 27% 25% 12%	1710
	11th to 20th	Day	20% 3 9% 21% 35% 13%	1996
	21st to end	Day	22% 5% 10% 22% 24% 16%	2794
January	1st to 10th	Night	23% 4 8% 27% 26% 11%	2647
	11th to 20th	Night	22% 3 7% 25% 29% 14%	2561
	21st to end	Night	24% 3 8% 24% 33% 9%	2516
February	1st to 10th	Night	26% 3 9% 22% 29% 11%	2160
	11th to 20th	Night	30% 5% 9% 22% 23% 11%	2098
	21st to end	Night	21% 3 4 21% 32% 18%	1776
March	1st to 10th	Night	23% 3 8% 20% 30% 16%	2160
	11th to 20th	Night	26% 4 10% 23% 24% 13%	2117
	21st to end	Night	24% 6% 11% 23% 24% 12%	1990
April	1st to 10th	Night	22% 5% 9% 21% 25% 17%	1800
	11th to 20th	Night	27% 5% 12% 22% 21% 13%	1777
	21st to end	Night	28% 5% 14% 23% 20% 10%	1800
May	1st to 10th	Night	27% 7% 11% 23% 21% 11%	1620
	11th to 20th	Night	29% 8% 18% 20% 17% 8%	1594
	21st to end	Night	29% 9% 16% 15% 17% 14%	1723
June	1st to 10th	Night	23% 9% 20% 24% 14% 10%	1440
	11th to 20th	Night	17% 7% 14% 22% 21% 19%	1440
	21st to end	Night	26% 7% 13% 24% 18% 12%	1440
July	1st to 10th	Night	26% 10% 15% 22% 20% 7%	1400
	11th to 20th	Night	21% 8% 15% 26% 22% 8%	1392
	21st to end	Night	36% 10% 17% 23% 12% 2	1567
August	1st to 10th	Night	30% 11% 21% 22% 11% 6%	1754
	11th to 20th	Night	29% 8% 15% 26% 16% 6%	1778
	21st to end	Night	25% 7% 13% 23% 25% 7%	1980
September	1st to 10th	Night	24% 7% 12% 24% 21% 13%	1800
	11th to 20th	Night	24% 5% 12% 18% 23% 18%	1934
	21st to end	Night	21% 4 8% 21% 32% 15%	1980
October	1st to 10th	Night	25% 5% 10% 19% 26% 15%	1980
	11th to 20th	Night	15% 2 7% 17% 34% 25%	2110
	21st to end	Night	20% 3 7% 21% 30% 19%	2502
November	1st to 10th	Night	15% 3 8% 20% 30% 24%	2405
	11th to 20th	Night	15% 3 5% 24% 36% 17%	2470
	21st to end	Night	22% 4 7% 17% 28% 22%	2470
December	1st to 10th	Night	22% 4 10% 27% 27% 11%	2470
	11th to 20th	Night	22% 3 8% 19% 36% 12%	3196
	21st to end	Night	24% 5% 10% 22% 28% 11%	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% 5% 34% 37% 14% 3	270
	11th to 20th	Day	10% 9% 27% 35% 14% 5%	246
	21st to end	Day	4 8% 37% 32% 18% 2	264
February	1st to 10th	Day	5% 8% 49% 27% 10% 2	240
	11th to 20th	Day	6% 8% 48% 26% 9% 3	240
	21st to end	Day	5% 13% 41% 32% 7% 2	198
March	1st to 10th	Day	3 11% 38% 33% 14% 2	240
	11th to 20th	Day	11% 13% 30% 29% 14% 3	240
	21st to end	Day	14% 18% 38% 21% 8% 1	449
April	1st to 10th	Day	7% 14% 42% 24% 10% 3	420
	11th to 20th	Day	11% 20% 35% 24% 8% 2	412
	21st to end	Day	15% 15% 36% 25% 7% 1	420
May	1st to 10th	Day	9% 9% 35% 30% 15% 3	600
	11th to 20th	Day	12% 7% 29% 32% 16% 5%	625
	21st to end	Day	9% 9% 35% 34% 11% 2	679
June	1st to 10th	Day	5% 5% 24% 33% 23% 9%	630
	11th to 20th	Day	5% 4 27% 39% 20% 6%	630
	21st to end	Day	6% 2 24% 38% 23% 7%	630
July	1st to 10th	Day	4 2 16% 38% 29% 11%	621
	11th to 20th	Day	4 1 9% 38% 36% 12%	618
	21st to end	Day	6% 1 10% 31% 42% 11%	684
August	1st to 10th	Day	4 1 13% 34% 36% 13%	468
	11th to 20th	Day	5% 1 19% 38% 28% 9%	437
	21st to end	Day	5% 14% 42% 27% 13%	495
September	1st to 10th	Day	7% 1 16% 39% 30% 8%	450
	11th to 20th	Day	5% 2 16% 42% 22% 13%	315
	21st to end	Day	7% 6% 20% 27% 28% 13%	270
October	1st to 10th	Day	13% 6% 22% 29% 20% 9%	270
	11th to 20th	Day	4 5% 31% 31% 20% 10%	270
	21st to end	Day	14% 6% 28% 25% 20% 7%	297
November	1st to 10th	Day	7% 7% 31% 29% 20% 5%	270
	11th to 20th	Day	6% 9% 24% 36% 20% 5%	270
	21st to end	Day	11% 14% 27% 26% 15% 7%	270
December	1st to 10th	Day	3 7% 34% 36% 16% 4	270
	11th to 20th	Day	10% 6% 36% 31% 15% 2	270
	21st to end	Day	8% 13% 38% 32% 9%	297
January	1st to 10th	Night	4 7% 36% 41% 11% 1	950
	11th to 20th	Night	7% 7% 34% 38% 12% 2	915
	21st to end	Night	6% 5% 38% 40% 10% 1	806
February	1st to 10th	Night	7% 6% 41% 36% 9%	720
	11th to 20th	Night	6% 9% 50% 28% 7%	704
	21st to end	Night	9% 9% 48% 30% 5%	592
March	1st to 10th	Night	6% 11% 43% 33% 6%	720
	11th to 20th	Night	10% 10% 37% 35% 7% 1	677
	21st to end	Night	7% 13% 50% 24% 5%	594
April	1st to 10th	Night	7% 11% 48% 31% 4	540
	11th to 20th	Night	11% 11% 48% 26% 3	533
	21st to end	Night	14% 10% 40% 29% 6% 1	540
May	1st to 10th	Night	8% 11% 36% 37% 7%	540
	11th to 20th	Night	10% 6% 38% 34% 12% 1	531
	21st to end	Night	9% 8% 45% 31% 7%	584
June	1st to 10th	Night	4 5% 37% 41% 12% 1	540
	11th to 20th	Night	3 5% 46% 38% 8%	540
	21st to end	Night	5% 3 32% 46% 14%	540
July	1st to 10th	Night	5% 1 20% 50% 22% 1	525
	11th to 20th	Night	4 1 16% 54% 24% 2	522
	21st to end	Night	8% 1 15% 45% 29% 2	591
August	1st to 10th	Night	7% 1 13% 46% 31% 2	537
	11th to 20th	Night	10% 1 15% 51% 22% 1	534
	21st to end	Night	5% 1 19% 48% 25% 2	594
September	1st to 10th	Night	7% 1 22% 51% 19% 1	540
	11th to 20th	Night	8% 1 32% 41% 17% 1	540
	21st to end	Night	6% 5% 30% 43% 15% 2	540
October	1st to 10th	Night	12% 5% 31% 41% 12% 1	540
	11th to 20th	Night	5% 5% 33% 40% 14% 3	670
	21st to end	Night	8% 7% 29% 36% 17% 2	918
November	1st to 10th	Night	5% 5% 27% 48% 13% 2	925
	11th to 20th	Night	4 7% 35% 39% 13% 2	950
	21st to end	Night	7% 8% 31% 38% 13% 3	950
December	1st to 10th	Night	5% 7% 36% 41% 11% 1	950
	11th to 20th	Night	7% 7% 37% 38% 10% 1	950
	21st to end	Night	8% 10% 38% 34% 9%	1045

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