Pine Valley Creek trailhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pine Valley Creek trailhead clear sky chart from 2005-11-06 to 2025-06-10.

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 4 1 3 2 3 3 3 4 5% 69%	123926
	Night	3 6% 1 4 2 3 3 3 4 5% 66%	123343
Transparency	Day	15% 4 5% 12% 26% 37%	123696
	Night	15% 5% 6% 11% 23% 40%	123162
Seeing	Day	9% 11% 30% 31% 13% 5%	16486
	Night	8% 6% 14% 33% 31% 8%	26859

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	4 6% 2 4 3 2 3 2 3 4 68%	4098
	11th to 20th	Day	4 4 2 4 3 2 3 3 4 5% 67%	4283
	21st to end	Day	7% 10% 2 5% 4 4 4 4 5% 8% 49%	5016
February	1st to 10th	Day	7% 8% 2 4 4 4 3 2 4 5% 58%	2000
	11th to 20th	Day	5% 9% 2 5% 4 3 4 4 5% 7% 52%	1950
	21st to end	Day	6% 12% 2 6% 3 4 3 3 5% 6% 50%	1650
March	1st to 10th	Day	4 9% 2 6% 4 4 5% 4 7% 9% 46%	4518
	11th to 20th	Day	6% 10% 2 5% 3 4 4 4 5% 6% 53%	4841
	21st to end	Day	4 8% 1 4 3 3 3 3 5% 6% 58%	5651
April	1st to 10th	Day	4 7% 2 6% 3 3 3 3 5% 6% 58%	2400
	11th to 20th	Day	2 3 1 4 2 3 3 3 4 5% 69%	2369
	21st to end	Day	3 5% 1 3 3 3 2 2 4 7% 67%	2400
May	1st to 10th	Day	1 4 2 4 2 2 2 2 2 4 75%	5787
	11th to 20th	Day	1 2 2 1 1 2 2 3 5% 82%	5841
	21st to end	Day	1 2 1 2 1 2 2 2 3 4 81%	6423
June	1st to 10th	Day	1 2 2 2 2 2 2 3 5% 79%	2589
	11th to 20th	Day	1 1 1 1 1 1 2 3 87%	2470
	21st to end	Day	2 2 2 1 2 2 1 2 3 83%	2470
July	1st to 10th	Day	1 1 2 1 1 1 1 2 3 86%	4110
	11th to 20th	Day	1 1 1 2 2 3 3 3 6% 8% 70%	4110
	21st to end	Day	1 1 1 2 2 2 3 3 5% 7% 73%	4333
August	1st to 10th	Day	1 1 1 2 2 3 4 3 5% 7% 72%	3783
	11th to 20th	Day	1 1 2 2 2 2 2 3 4 80%	3724
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 82%	4180
September	1st to 10th	Day	3 2 1 3 2 2 4 3 4 5% 71%	2233
	11th to 20th	Day	1 1 1 1 1 1 1 3 3 87%	2090
	21st to end	Day	1 2 1 2 2 2 2 2 3 4 79%	2090
October	1st to 10th	Day	2 2 1 3 3 2 3 2 4 4 75%	3490
	11th to 20th	Day	1 1 1 2 2 2 2 1 2 3 84%	3469
	21st to end	Day	1 2 1 3 2 2 3 3 4 5% 74%	3325
November	1st to 10th	Day	3 5% 1 4 2 2 2 3 3 5% 70%	1764
	11th to 20th	Day	2 4 1 5% 3 3 2 3 4 4 68%	1800
	21st to end	Day	6% 6% 2 5% 3 3 4 4 5% 5% 58%	1800
December	1st to 10th	Day	3 4 1 3 3 4 2 3 4 6% 68%	2950
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 4 6% 6% 52%	3409
	21st to end	Day	4 6% 2 6% 6% 6% 5% 5% 7% 8% 45%	4510
January	1st to 10th	Night	3 5% 1 4 2 3 3 3 4 5% 65%	5867
	11th to 20th	Night	2 6% 1 4 3 3 3 3 5% 6% 65%	5690
	21st to end	Night	8% 12% 2 5% 4 3 4 3 5% 6% 48%	5984
February	1st to 10th	Night	5% 9% 3 5% 3 3 4 3 4 5% 56%	2400
	11th to 20th	Night	5% 10% 2 6% 4 4 4 3 4 5% 53%	2338
	21st to end	Night	4 13% 2 6% 4 4 4 3 5% 5% 49%	1980
March	1st to 10th	Night	4 19% 3 5% 3 3 4 5% 6% 7% 40%	5376
	11th to 20th	Night	4 13% 4 6% 3 4 6% 4 5% 6% 47%	5145
	21st to end	Night	2 13% 2 4 3 4 5% 5% 6% 6% 49%	5319
April	1st to 10th	Night	4 8% 2 5% 4 3 3 3 5% 7% 56%	2000
	11th to 20th	Night	3 5% 1 5% 2 3 3 3 5% 6% 65%	1979
	21st to end	Night	1 5% 2 4 4 4 3 3 5% 6% 64%	2000
May	1st to 10th	Night	1 4 1 2 2 2 3 3 4 5% 73%	4195
	11th to 20th	Night	1 1 2 2 2 3 4 6% 6% 73%	4074
	21st to end	Night	1 1 2 1 2 2 3 5% 6% 75%	4474
June	1st to 10th	Night	1 2 1 3 2 1 2 2 3 6% 78%	1795
	11th to 20th	Night	1 1 1 2 1 1 1 2 4 86%	1710
	21st to end	Night	2 1 1 2 1 1 1 2 3 3 82%	1710
July	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	2860
	11th to 20th	Night	1 1 2 1 1 2 2 3 5% 82%	2860
	21st to end	Night	1 2 2 2 2 2 2 3 5% 79%	3228
August	1st to 10th	Night	1 1 1 2 2 2 4 6% 80%	3166
	11th to 20th	Night	1 1 1 1 1 2 3 5% 84%	3126
	21st to end	Night	1 1 1 1 1 1 1 2 3 90%	3498
September	1st to 10th	Night	1 1 1 2 2 2 2 1 3 5% 80%	1947
	11th to 20th	Night	1 1 2 1 1 1 1 2 3 85%	2090
	21st to end	Night	1 1 2 2 1 2 2 3 4 82%	2090
October	1st to 10th	Night	2 2 1 3 1 2 2 1 2 4 80%	3490
	11th to 20th	Night	1 1 1 2 1 1 3 3 4 3 81%	3469
	21st to end	Night	1 3 1 4 3 2 3 3 4 5% 71%	4229
November	1st to 10th	Night	3 5% 1 4 3 2 2 2 3 5% 68%	2535
	11th to 20th	Night	3 4 1 4 3 3 3 3 4 4 68%	2600
	21st to end	Night	4 8% 2 5% 4 3 4 4 5% 5% 55%	2600
December	1st to 10th	Night	4 5% 1 4 3 3 3 3 4 4 67%	4240
	11th to 20th	Night	5% 7% 2 5% 4 5% 5% 5% 6% 8% 49%	4811
	21st to end	Night	3 8% 2 6% 3 3 4 4 6% 10% 49%	6468

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% 4 11% 33% 29%	4099
	11th to 20th	Day	17% 5% 5% 16% 19% 38%	4283
	21st to end	Day	28% 7% 6% 10% 23% 25%	5016
February	1st to 10th	Day	26% 4 6% 10% 23% 31%	2000
	11th to 20th	Day	25% 6% 7% 14% 23% 25%	1960
	21st to end	Day	29% 6% 8% 12% 20% 25%	1650
March	1st to 10th	Day	20% 12% 7% 13% 26% 22%	4518
	11th to 20th	Day	25% 6% 9% 18% 27% 14%	4841
	21st to end	Day	19% 9% 8% 22% 31% 12%	5651
April	1st to 10th	Day	22% 3 8% 15% 31% 20%	2400
	11th to 20th	Day	14% 3 7% 14% 29% 33%	2372
	21st to end	Day	15% 4 6% 15% 35% 26%	2400
May	1st to 10th	Day	12% 4 4 12% 35% 33%	5787
	11th to 20th	Day	8% 2 3 10% 38% 40%	5844
	21st to end	Day	8% 2 4 7% 32% 47%	6424
June	1st to 10th	Day	9% 2 3 11% 32% 42%	2589
	11th to 20th	Day	5% 1 4 6% 19% 65%	2470
	21st to end	Day	9% 2 2 6% 14% 68%	2470
July	1st to 10th	Day	7% 1 2 3 11% 76%	4046
	11th to 20th	Day	13% 4 6% 15% 32% 31%	4041
	21st to end	Day	11% 5% 8% 23% 19% 36%	4197
August	1st to 10th	Day	12% 3 8% 20% 28% 29%	3770
	11th to 20th	Day	9% 3 6% 9% 24% 49%	3760
	21st to end	Day	8% 2 3 6% 19% 62%	4179
September	1st to 10th	Day	15% 3 6% 7% 22% 46%	2233
	11th to 20th	Day	5% 1 3 5% 28% 57%	2090
	21st to end	Day	10% 2 5% 7% 26% 50%	2090
October	1st to 10th	Day	10% 3 4 7% 16% 59%	3490
	11th to 20th	Day	7% 2 3 7% 31% 51%	3469
	21st to end	Day	12% 3 3 6% 31% 47%	3325
November	1st to 10th	Day	16% 3 5% 11% 24% 41%	1764
	11th to 20th	Day	16% 3 6% 10% 25% 40%	1800
	21st to end	Day	24% 3 7% 11% 21% 33%	1800
December	1st to 10th	Day	18% 2 3 9% 27% 41%	2950
	11th to 20th	Day	26% 6% 7% 13% 28% 20%	3408
	21st to end	Day	27% 10% 9% 17% 22% 16%	4510
January	1st to 10th	Night	16% 6% 4 14% 27% 32%	5867
	11th to 20th	Night	14% 8% 6% 14% 18% 40%	5690
	21st to end	Night	29% 8% 5% 9% 20% 28%	5984
February	1st to 10th	Night	25% 5% 7% 10% 20% 33%	2400
	11th to 20th	Night	30% 5% 6% 10% 22% 27%	2339
	21st to end	Night	29% 7% 7% 10% 20% 28%	1980
March	1st to 10th	Night	20% 20% 7% 10% 20% 23%	5376
	11th to 20th	Night	28% 8% 7% 16% 30% 12%	5145
	21st to end	Night	18% 13% 8% 15% 24% 22%	5319
April	1st to 10th	Night	21% 6% 9% 13% 28% 24%	2000
	11th to 20th	Night	16% 4 8% 11% 25% 35%	1979
	21st to end	Night	14% 5% 10% 11% 29% 31%	2000
May	1st to 10th	Night	11% 4 7% 7% 33% 39%	4192
	11th to 20th	Night	7% 2 5% 9% 31% 45%	4075
	21st to end	Night	9% 2 7% 8% 22% 52%	4474
June	1st to 10th	Night	8% 2 5% 9% 27% 49%	1795
	11th to 20th	Night	4 2 3 8% 13% 71%	1710
	21st to end	Night	8% 1 2 5% 13% 70%	1710
July	1st to 10th	Night	3 1 2 3 9% 81%	2815
	11th to 20th	Night	6% 2 4 13% 30% 44%	2806
	21st to end	Night	8% 3 5% 23% 23% 38%	3127
August	1st to 10th	Night	7% 2 6% 23% 30% 33%	3156
	11th to 20th	Night	5% 2 6% 11% 21% 55%	3156
	21st to end	Night	5% 1 2 4 16% 72%	3498
September	1st to 10th	Night	10% 3 4 10% 24% 51%	1947
	11th to 20th	Night	6% 2 4 4 24% 61%	2090
	21st to end	Night	8% 1 5% 7% 28% 52%	2090
October	1st to 10th	Night	11% 2 4 6% 16% 62%	3490
	11th to 20th	Night	5% 3 4 6% 22% 60%	3469
	21st to end	Night	12% 3 4 6% 25% 49%	4229
November	1st to 10th	Night	16% 4 4 7% 26% 42%	2535
	11th to 20th	Night	17% 3 5% 10% 24% 42%	2600
	21st to end	Night	26% 4 8% 11% 21% 31%	2600
December	1st to 10th	Night	19% 3 4 8% 24% 42%	4240
	11th to 20th	Night	26% 6% 6% 11% 26% 24%	4811
	21st to end	Night	21% 9% 8% 20% 22% 21%	6468

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	23% 11% 26% 29% 9% 1	300
	11th to 20th	Day	19% 10% 27% 32% 11% 1	379
	21st to end	Day	19% 17% 31% 25% 6% 2	550
February	1st to 10th	Day	17% 16% 38% 19% 8% 2	500
	11th to 20th	Day	17% 19% 34% 22% 7%	495
	21st to end	Day	20% 21% 33% 18% 7%	414
March	1st to 10th	Day	21% 20% 35% 18% 6% 1	500
	11th to 20th	Day	19% 16% 35% 20% 8% 1	500
	21st to end	Day	18% 21% 35% 19% 6% 1	550
April	1st to 10th	Day	15% 18% 32% 21% 12% 3	500
	11th to 20th	Day	10% 21% 38% 19% 10% 3	492
	21st to end	Day	12% 16% 32% 23% 13% 5%	500
May	1st to 10th	Day	11% 17% 32% 24% 12% 4	503
	11th to 20th	Day	8% 13% 37% 26% 12% 5%	528
	21st to end	Day	7% 16% 33% 28% 10% 7%	573
June	1st to 10th	Day	3 10% 30% 33% 15% 9%	527
	11th to 20th	Day	2 7% 34% 32% 15% 9%	490
	21st to end	Day	3 3 31% 34% 18% 11%	490
July	1st to 10th	Day	2 20% 47% 21% 11%	486
	11th to 20th	Day	1 18% 45% 21% 15%	484
	21st to end	Day	1 1 13% 48% 21% 15%	531
August	1st to 10th	Day	2 1 23% 41% 18% 14%	487
	11th to 20th	Day	2 2 19% 42% 20% 15%	477
	21st to end	Day	1 2 18% 50% 18% 12%	539
September	1st to 10th	Day	4 3 28% 41% 17% 8%	490
	11th to 20th	Day	3 5% 37% 37% 14% 4	490
	21st to end	Day	3 11% 27% 38% 17% 5%	490
October	1st to 10th	Day	6% 9% 32% 35% 15% 2	490
	11th to 20th	Day	4 11% 36% 34% 14% 1	490
	21st to end	Day	8% 9% 27% 32% 18% 5%	411
November	1st to 10th	Day	13% 10% 25% 37% 13% 3	300
	11th to 20th	Day	7% 11% 31% 33% 16% 2	300
	21st to end	Day	14% 14% 31% 27% 12% 3	300
December	1st to 10th	Day	11% 10% 32% 33% 13% 2	300
	11th to 20th	Day	8% 10% 33% 31% 16% 1	300
	21st to end	Day	22% 15% 30% 21% 11% 2	330
January	1st to 10th	Night	13% 7% 22% 33% 19% 7%	800
	11th to 20th	Night	9% 9% 21% 36% 20% 5%	800
	21st to end	Night	18% 10% 19% 33% 18% 3	880
February	1st to 10th	Night	13% 9% 22% 31% 19% 6%	800
	11th to 20th	Night	12% 11% 22% 34% 16% 4	784
	21st to end	Night	16% 12% 21% 33% 15% 3	660
March	1st to 10th	Night	15% 12% 22% 34% 15% 3	800
	11th to 20th	Night	14% 7% 17% 35% 21% 7%	800
	21st to end	Night	11% 9% 18% 38% 20% 4	880
April	1st to 10th	Night	11% 10% 17% 38% 20% 5%	800
	11th to 20th	Night	8% 9% 19% 38% 21% 5%	791
	21st to end	Night	8% 8% 15% 33% 28% 7%	800
May	1st to 10th	Night	6% 7% 15% 38% 30% 4	643
	11th to 20th	Night	3 6% 13% 38% 33% 7%	591
	21st to end	Night	4 6% 15% 39% 32% 4	650
June	1st to 10th	Night	2 3 10% 41% 37% 7%	599
	11th to 20th	Night	1 1 9% 44% 40% 5%	570
	21st to end	Night	1 2 5% 35% 49% 8%	570
July	1st to 10th	Night	2 24% 61% 13%	555
	11th to 20th	Night	1 1 21% 66% 11%	552
	21st to end	Night	2 2 1 16% 62% 17%	694
August	1st to 10th	Night	1 1 25% 56% 17%	756
	11th to 20th	Night	2 1 2 14% 59% 23%	752
	21st to end	Night	2 1 17% 57% 22%	836
September	1st to 10th	Night	2 1 3 26% 52% 15%	760
	11th to 20th	Night	2 2 6% 35% 44% 11%	760
	21st to end	Night	1 2 9% 38% 38% 12%	760
October	1st to 10th	Night	5% 6% 9% 43% 32% 6%	760
	11th to 20th	Night	3 6% 14% 38% 29% 10%	760
	21st to end	Night	4 4 16% 36% 27% 13%	836
November	1st to 10th	Night	8% 6% 16% 41% 22% 8%	780
	11th to 20th	Night	6% 6% 19% 36% 23% 11%	800
	21st to end	Night	12% 8% 20% 33% 21% 6%	800
December	1st to 10th	Night	12% 8% 20% 33% 21% 6%	800
	11th to 20th	Night	15% 7% 22% 33% 20% 4	800
	21st to end	Night	14% 10% 21% 31% 18% 5%	880

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