Vasquez Rocks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vasquez Rocks clear sky chart from 2005-11-06 to 2025-11-18.

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 1 3 2 2 2 2 3 5% 74%	135254
	Night	3 4 1 3 2 2 3 2 4 5% 71%	132611
Transparency	Day	13% 3 6% 15% 29% 34%	130340
	Night	14% 4 7% 15% 28% 32%	128497
Seeing	Day	7% 12% 31% 32% 14% 5%	16959
	Night	6% 6% 18% 37% 28% 5%	26751

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 3 2 2 2 2 3 5% 71%	3639
	11th to 20th	Day	5% 3 1 3 2 2 2 2 4 6% 69%	3985
	21st to end	Day	6% 6% 2 6% 3 3 3 3 5% 9% 54%	4938
February	1st to 10th	Day	7% 6% 1 4 3 2 3 3 4 5% 61%	2000
	11th to 20th	Day	6% 5% 1 4 3 3 3 2 5% 8% 61%	1950
	21st to end	Day	6% 7% 1 5% 4 3 3 3 4 4 59%	1650
March	1st to 10th	Day	9% 6% 2 6% 4 3 3 4 5% 6% 52%	4518
	11th to 20th	Day	4 6% 2 5% 4 4 4 3 5% 6% 57%	4704
	21st to end	Day	5% 5% 2 5% 3 4 4 4 6% 8% 54%	5969
April	1st to 10th	Day	4 5% 2 3 3 2 2 3 4 7% 65%	2400
	11th to 20th	Day	3 4 1 3 2 2 2 3 4 5% 70%	2369
	21st to end	Day	2 3 2 3 2 2 2 3 5% 8% 70%	2400
May	1st to 10th	Day	2 2 1 3 2 2 2 2 3 5% 76%	5588
	11th to 20th	Day	1 2 1 2 2 2 2 2 5% 5% 76%	5841
	21st to end	Day	1 1 1 2 1 1 1 2 3 5% 81%	6423
June	1st to 10th	Day	1 2 1 2 2 2 2 2 3 6% 77%	2678
	11th to 20th	Day	1 2 1 1 1 1 3 5% 85%	2800
	21st to end	Day	1 1 1 1 1 1 1 2 2 3 87%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 2 1 1 1 1 2 3 87%	6320
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	6025
August	1st to 10th	Day	1 1 1 1 2 2 2 4 85%	5346
	11th to 20th	Day	1 1 1 2 94%	5364
	21st to end	Day	1 1 1 1 1 1 2 3 89%	5984
September	1st to 10th	Day	2 1 1 1 1 2 2 1 2 3 84%	2400
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 2 86%	2265
	21st to end	Day	1 1 2 2 2 2 2 2 3 83%	2200
October	1st to 10th	Day	1 1 1 1 1 1 2 1 3 3 84%	3600
	11th to 20th	Day	1 1 1 1 2 2 2 3 4 82%	3331
	21st to end	Day	2 2 1 3 2 2 3 3 4 5% 72%	3494
November	1st to 10th	Day	2 2 1 2 2 2 3 2 4 4 75%	1854
	11th to 20th	Day	3 4 2 3 3 3 3 3 4 6% 67%	1863
	21st to end	Day	4 4 2 5% 3 4 3 3 6% 6% 60%	1800
December	1st to 10th	Day	3 2 1 4 3 3 4 3 5% 6% 64%	2950
	11th to 20th	Day	5% 5% 2 5% 4 4 6% 4 6% 7% 54%	3409
	21st to end	Day	6% 6% 2 7% 4 4 4 3 5% 8% 51%	4078
January	1st to 10th	Night	4 4 2 4 2 2 2 2 3 5% 69%	6306
	11th to 20th	Night	3 4 2 4 2 2 2 2 4 6% 70%	5985
	21st to end	Night	6% 8% 2 5% 3 3 3 3 5% 5% 55%	6054
February	1st to 10th	Night	6% 7% 2 5% 4 3 3 3 4 5% 59%	2400
	11th to 20th	Night	5% 7% 1 4 3 2 3 3 5% 6% 62%	2338
	21st to end	Night	5% 6% 3 5% 4 3 3 3 4 5% 59%	1980
March	1st to 10th	Night	5% 13% 3 5% 3 3 3 3 4 6% 50%	5376
	11th to 20th	Night	4 6% 2 5% 4 4 3 3 5% 6% 58%	5277
	21st to end	Night	4 7% 2 4 4 4 4 4 5% 7% 57%	5006
April	1st to 10th	Night	4 6% 1 4 3 3 3 2 4 6% 65%	2000
	11th to 20th	Night	3 5% 1 4 2 2 2 3 4 6% 68%	1979
	21st to end	Night	2 4 1 4 3 3 2 3 4 6% 68%	2000
May	1st to 10th	Night	2 5% 2 4 3 4 4 3 3 4 67%	4404
	11th to 20th	Night	1 2 1 2 2 2 3 3 5% 5% 75%	4074
	21st to end	Night	2 1 2 2 2 2 2 4 5% 78%	4474
June	1st to 10th	Night	3 1 3 2 2 3 2 3 7% 75%	1715
	11th to 20th	Night	1 1 2 1 1 2 1 3 5% 83%	1600
	21st to end	Night	1 1 1 1 1 1 2 4 88%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 93%	3640
	11th to 20th	Night	1 1 1 1 2 1 2 3 89%	3640
	21st to end	Night	1 1 1 1 1 1 2 2 3 86%	4831
August	1st to 10th	Night	1 1 1 2 2 2 2 3 3 83%	4486
	11th to 20th	Night	1 1 1 1 2 94%	4506
	21st to end	Night	1 1 1 1 1 1 1 2 3 87%	5015
September	1st to 10th	Night	2 1 1 1 1 1 2 1 2 4 84%	2000
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 3 84%	2135
	21st to end	Night	1 1 1 2 1 1 2 1 2 4 84%	2200
October	1st to 10th	Night	1 2 2 1 1 1 1 2 2 86%	3600
	11th to 20th	Night	1 2 1 2 1 1 2 1 3 5% 81%	3823
	21st to end	Night	2 3 1 3 2 2 2 1 2 4 78%	4313
November	1st to 10th	Night	2 4 1 3 2 3 2 3 3 6% 72%	2665
	11th to 20th	Night	2 4 2 3 3 2 2 2 5% 5% 69%	2691
	21st to end	Night	4 5% 2 4 3 3 3 4 5% 7% 61%	2600
December	1st to 10th	Night	3 3 1 3 3 3 3 3 4 6% 67%	4240
	11th to 20th	Night	5% 6% 2 5% 4 4 5% 4 6% 7% 53%	4811
	21st to end	Night	5% 5% 2 6% 4 5% 5% 4 7% 10% 47%	6847

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	15% 4 5% 25% 34% 18%	3639
	11th to 20th	Day	16% 4 10% 15% 22% 33%	3985
	21st to end	Day	23% 6% 9% 15% 23% 24%	4938
February	1st to 10th	Day	24% 3 7% 16% 25% 25%	2000
	11th to 20th	Day	22% 4 6% 18% 31% 20%	1960
	21st to end	Day	25% 4 9% 16% 26% 20%	1650
March	1st to 10th	Day	24% 9% 10% 17% 22% 19%	4518
	11th to 20th	Day	21% 8% 11% 27% 23% 11%	4704
	21st to end	Day	18% 7% 15% 29% 23% 7%	5969
April	1st to 10th	Day	20% 4 11% 23% 27% 15%	2400
	11th to 20th	Day	15% 5% 10% 20% 33% 18%	2372
	21st to end	Day	12% 5% 11% 25% 36% 12%	2400
May	1st to 10th	Day	11% 4 9% 19% 34% 24%	5588
	11th to 20th	Day	8% 3 10% 21% 43% 16%	5844
	21st to end	Day	7% 2 8% 21% 45% 18%	6424
June	1st to 10th	Day	11% 3 8% 19% 35% 25%	2678
	11th to 20th	Day	4 2 6% 12% 31% 45%	2800
	21st to end	Day	6% 1 3 6% 27% 56%	2800
July	1st to 10th	Day	3 1 3 14% 78%	6251
	11th to 20th	Day	7% 1 2 7% 18% 66%	6245
	21st to end	Day	4 1 3 9% 31% 52%	5851
August	1st to 10th	Day	6% 1 3 7% 33% 50%	3890
	11th to 20th	Day	3 1 1 6% 28% 61%	3880
	21st to end	Day	4 1 2 4 23% 66%	4311
September	1st to 10th	Day	7% 2 5% 7% 28% 51%	2400
	11th to 20th	Day	5% 1 5% 10% 32% 47%	2265
	21st to end	Day	8% 2 4 10% 35% 42%	2200
October	1st to 10th	Day	8% 1 4 9% 19% 60%	3600
	11th to 20th	Day	8% 1 3 12% 35% 41%	3331
	21st to end	Day	15% 2 4 8% 31% 40%	3494
November	1st to 10th	Day	14% 2 5% 15% 35% 29%	1854
	11th to 20th	Day	19% 2 6% 14% 25% 34%	1863
	21st to end	Day	23% 3 7% 13% 26% 29%	1800
December	1st to 10th	Day	19% 3 6% 11% 30% 32%	2950
	11th to 20th	Day	27% 4 7% 18% 31% 12%	3408
	21st to end	Day	29% 6% 8% 21% 28% 8%	4078
January	1st to 10th	Night	16% 4 6% 17% 37% 20%	6306
	11th to 20th	Night	15% 5% 7% 17% 23% 32%	5985
	21st to end	Night	24% 6% 9% 13% 24% 23%	6054
February	1st to 10th	Night	25% 4 8% 15% 24% 25%	2400
	11th to 20th	Night	22% 3 8% 16% 28% 22%	2339
	21st to end	Night	23% 6% 9% 17% 25% 21%	1980
March	1st to 10th	Night	23% 10% 10% 18% 21% 17%	5376
	11th to 20th	Night	20% 8% 13% 28% 20% 12%	5277
	21st to end	Night	19% 9% 13% 28% 24% 7%	5006
April	1st to 10th	Night	20% 4 10% 25% 24% 17%	2000
	11th to 20th	Night	15% 5% 9% 24% 28% 20%	1979
	21st to end	Night	12% 4 13% 23% 35% 12%	2000
May	1st to 10th	Night	13% 7% 8% 19% 32% 20%	4401
	11th to 20th	Night	6% 3 7% 25% 43% 16%	4075
	21st to end	Night	5% 2 9% 22% 42% 20%	4474
June	1st to 10th	Night	9% 3 10% 21% 30% 26%	1715
	11th to 20th	Night	4 2 6% 14% 29% 44%	1600
	21st to end	Night	5% 1 4 6% 26% 60%	1600
July	1st to 10th	Night	3 1 3 15% 78%	3600
	11th to 20th	Night	4 1 3 7% 19% 66%	3592
	21st to end	Night	5% 1 2 9% 32% 51%	4693
August	1st to 10th	Night	6% 1 3 5% 35% 49%	3256
	11th to 20th	Night	3 2 6% 27% 62%	3256
	21st to end	Night	4 1 1 4 26% 64%	3608
September	1st to 10th	Night	7% 1 3 8% 26% 55%	2000
	11th to 20th	Night	6% 2 4 8% 34% 46%	2135
	21st to end	Night	6% 1 3 11% 34% 44%	2200
October	1st to 10th	Night	8% 1 3 8% 17% 64%	3600
	11th to 20th	Night	8% 1 3 10% 38% 39%	3823
	21st to end	Night	13% 2 3 7% 30% 45%	4313
November	1st to 10th	Night	13% 3 5% 14% 30% 34%	2665
	11th to 20th	Night	17% 2 7% 12% 28% 34%	2691
	21st to end	Night	21% 3 8% 16% 23% 28%	2600
December	1st to 10th	Night	18% 2 5% 9% 28% 38%	4240
	11th to 20th	Night	23% 8% 10% 16% 27% 16%	4811
	21st to end	Night	26% 7% 12% 24% 24% 8%	6847

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	18% 18% 38% 24% 4	200
	11th to 20th	Day	17% 18% 35% 25% 4 1	350
	21st to end	Day	14% 24% 35% 20% 6% 1	531
February	1st to 10th	Day	15% 20% 36% 21% 7% 1	500
	11th to 20th	Day	15% 21% 36% 21% 6% 1	495
	21st to end	Day	14% 18% 40% 22% 5%	414
March	1st to 10th	Day	18% 23% 34% 20% 6%	500
	11th to 20th	Day	13% 22% 34% 23% 7% 1	500
	21st to end	Day	15% 19% 35% 25% 6%	550
April	1st to 10th	Day	12% 15% 34% 24% 14% 1	500
	11th to 20th	Day	9% 21% 37% 22% 9% 3	492
	21st to end	Day	6% 19% 32% 25% 12% 5%	500
May	1st to 10th	Day	8% 14% 34% 29% 12% 3	503
	11th to 20th	Day	6% 13% 31% 33% 12% 5%	528
	21st to end	Day	6% 12% 34% 29% 14% 5%	573
June	1st to 10th	Day	2 9% 25% 37% 20% 8%	530
	11th to 20th	Day	2 8% 27% 36% 20% 8%	530
	21st to end	Day	2 6% 27% 38% 17% 11%	530
July	1st to 10th	Day	1 2 18% 45% 24% 9%	526
	11th to 20th	Day	2 2 13% 45% 23% 16%	524
	21st to end	Day	2 1 17% 43% 23% 15%	575
August	1st to 10th	Day	1 2 25% 43% 18% 10%	527
	11th to 20th	Day	1 2 17% 46% 21% 12%	517
	21st to end	Day	1 3 23% 42% 21% 10%	583
September	1st to 10th	Day	1 4 25% 42% 21% 7%	530
	11th to 20th	Day	2 8% 30% 39% 18% 4	530
	21st to end	Day	1 10% 30% 35% 19% 4	530
October	1st to 10th	Day	2 9% 35% 34% 15% 3	530
	11th to 20th	Day	4 11% 32% 38% 13% 1	530
	21st to end	Day	4 12% 34% 33% 15% 2	543
November	1st to 10th	Day	7% 11% 33% 33% 13% 3	330
	11th to 20th	Day	9% 16% 36% 28% 7% 3	321
	21st to end	Day	11% 14% 41% 25% 8% 1	300
December	1st to 10th	Day	10% 14% 42% 26% 7%	300
	11th to 20th	Day	8% 16% 38% 30% 7% 1	300
	21st to end	Day	19% 17% 35% 21% 7% 1	237
January	1st to 10th	Night	11% 9% 29% 36% 12% 4	800
	11th to 20th	Night	8% 11% 32% 35% 13% 1	800
	21st to end	Night	14% 13% 28% 33% 11% 2	880
February	1st to 10th	Night	12% 11% 24% 34% 16% 3	800
	11th to 20th	Night	9% 8% 30% 33% 16% 4	784
	21st to end	Night	9% 13% 26% 36% 14% 2	660
March	1st to 10th	Night	10% 12% 26% 38% 13% 1	800
	11th to 20th	Night	10% 6% 22% 36% 21% 6%	800
	21st to end	Night	9% 8% 21% 43% 18% 2	880
April	1st to 10th	Night	7% 7% 20% 41% 23% 3	800
	11th to 20th	Night	5% 7% 22% 41% 23% 2	791
	21st to end	Night	4 6% 22% 39% 25% 5%	800
May	1st to 10th	Night	7% 5% 18% 42% 25% 3	735
	11th to 20th	Night	4 5% 16% 38% 35% 3	591
	21st to end	Night	2 4 18% 42% 30% 3	650
June	1st to 10th	Night	1 3 10% 43% 41% 2	515
	11th to 20th	Night	2 9% 43% 42% 5%	400
	21st to end	Night	1 5% 38% 52% 5%	400
July	1st to 10th	Night	1 31% 62% 7%	390
	11th to 20th	Night	1 22% 69% 8%	388
	21st to end	Night	2 1 2 25% 59% 10%	811
August	1st to 10th	Night	2 3 32% 53% 10%	796
	11th to 20th	Night	1 2 25% 59% 13%	792
	21st to end	Night	1 2 29% 54% 14%	880
September	1st to 10th	Night	2 1 4 30% 50% 13%	800
	11th to 20th	Night	1 1 5% 41% 40% 11%	800
	21st to end	Night	1 2 11% 42% 35% 9%	800
October	1st to 10th	Night	3 2 13% 50% 29% 3	800
	11th to 20th	Night	5% 5% 17% 38% 29% 6%	800
	21st to end	Night	4 6% 21% 38% 22% 9%	880
November	1st to 10th	Night	5% 5% 22% 43% 22% 5%	820
	11th to 20th	Night	6% 5% 28% 38% 18% 5%	828
	21st to end	Night	8% 8% 28% 37% 17% 3	800
December	1st to 10th	Night	9% 9% 29% 37% 14% 3	800
	11th to 20th	Night	10% 9% 28% 38% 13% 1	800
	21st to end	Night	10% 13% 28% 37% 10% 2	880

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