Pacheco State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pacheco State Park clear sky chart from 2005-11-06 to 2024-11-04.

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	4 3 1 3 3 3 3 3 4 6% 67%	104979
	Night	6% 3 1 4 3 3 3 3 5% 7% 62%	102793
Transparency	Day	18% 6% 8% 17% 24% 27%	104734
	Night	20% 8% 10% 17% 22% 24%	102628
Seeing	Day	7% 9% 27% 32% 19% 6%	15404
	Night	7% 5% 17% 37% 27% 7%	24805

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	9% 8% 2 7% 5% 4 5% 5% 6% 9% 40%	2635
	11th to 20th	Day	10% 7% 3 9% 7% 6% 6% 4 5% 7% 35%	2860
	21st to end	Day	18% 8% 3 6% 5% 5% 5% 5% 6% 8% 32%	3146
February	1st to 10th	Day	13% 6% 2 6% 4 3 3 4 5% 6% 48%	1710
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 4 5% 8% 50%	1822
	21st to end	Day	11% 5% 2 6% 4 4 4 3 5% 6% 49%	1570
March	1st to 10th	Day	6% 7% 3 9% 6% 6% 8% 6% 9% 8% 31%	3283
	11th to 20th	Day	6% 4 2 4 3 3 4 2 5% 8% 58%	3490
	21st to end	Day	9% 6% 2 6% 5% 6% 7% 6% 7% 8% 38%	3961
April	1st to 10th	Day	8% 6% 2 5% 4 4 4 3 5% 8% 51%	2280
	11th to 20th	Day	6% 4 2 4 3 4 4 3 6% 7% 59%	2249
	21st to end	Day	4 2 1 3 3 3 3 3 4 7% 66%	2280
May	1st to 10th	Day	3 2 1 2 2 3 3 2 4 6% 72%	3800
	11th to 20th	Day	2 1 1 1 2 2 2 3 7% 80%	4199
	21st to end	Day	1 1 1 1 2 2 2 4 7% 78%	4813
June	1st to 10th	Day	2 2 1 3 1 2 2 3 5% 9% 71%	2660
	11th to 20th	Day	1 1 1 1 2 2 3 7% 82%	2660
	21st to end	Day	1 1 1 1 2 1 1 3 4 84%	2660
July	1st to 10th	Day	1 1 1 1 2 3 92%	4420
	11th to 20th	Day	1 1 1 1 1 2 1 3 4 83%	4234
	21st to end	Day	1 1 1 1 1 2 4 90%	4455
August	1st to 10th	Day	1 1 1 1 2 2 2 4 7% 80%	4072
	11th to 20th	Day	1 1 1 2 4 90%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 4 86%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	2280
	11th to 20th	Day	1 1 1 1 2 3 2 5% 6% 79%	2280
	21st to end	Day	1 1 1 2 1 1 2 2 4 5% 82%	2054
October	1st to 10th	Day	1 1 1 2 2 2 2 2 4 5% 78%	3180
	11th to 20th	Day	2 1 2 2 1 2 2 4 5% 78%	3161
	21st to end	Day	2 2 1 3 3 3 5% 3 5% 7% 66%	3448
November	1st to 10th	Day	6% 4 2 3 3 4 4 3 5% 8% 58%	1803
	11th to 20th	Day	6% 5% 1 4 3 3 5% 3 6% 7% 58%	1710
	21st to end	Day	8% 4 2 4 3 3 3 3 6% 7% 57%	1658
December	1st to 10th	Day	10% 6% 2 7% 4 4 5% 4 6% 7% 46%	1520
	11th to 20th	Day	20% 11% 4 7% 5% 3 4 3 6% 6% 33%	1928
	21st to end	Day	10% 9% 3 8% 5% 5% 5% 5% 5% 7% 37%	2794
January	1st to 10th	Night	10% 7% 2 6% 5% 4 4 4 5% 6% 48%	4309
	11th to 20th	Night	14% 8% 3 8% 5% 5% 6% 4 5% 7% 35%	4110
	21st to end	Night	15% 7% 3 7% 6% 5% 5% 4 6% 7% 35%	4521
February	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 4 6% 51%	2470
	11th to 20th	Night	7% 4 1 4 4 4 5% 3 6% 9% 52%	2244
	21st to end	Night	9% 4 2 4 4 3 4 3 4 8% 56%	1884
March	1st to 10th	Night	9% 5% 2 10% 7% 5% 6% 5% 6% 7% 38%	3586
	11th to 20th	Night	6% 4 1 5% 4 4 3 3 5% 7% 58%	3490
	21st to end	Night	8% 5% 2 5% 6% 5% 6% 5% 7% 9% 42%	3690
April	1st to 10th	Night	7% 5% 2 4 3 4 5% 5% 6% 7% 54%	1900
	11th to 20th	Night	4 4 2 4 4 3 3 3 6% 7% 61%	1879
	21st to end	Night	3 2 2 2 3 3 3 6% 11% 65%	1900
May	1st to 10th	Night	1 2 1 2 2 2 2 2 4 8% 74%	3180
	11th to 20th	Night	1 1 1 1 1 2 2 4 8% 78%	2690
	21st to end	Night	1 1 1 1 1 2 2 4 7% 79%	2762
June	1st to 10th	Night	1 2 1 2 2 3 3 2 5% 11% 68%	1520
	11th to 20th	Night	1 1 1 1 2 2 3 9% 79%	1520
	21st to end	Night	1 1 1 2 1 4 7% 83%	1520
July	1st to 10th	Night	1 1 1 2 5% 89%	2540
	11th to 20th	Night	1 1 1 1 2 2 1 3 6% 83%	2727
	21st to end	Night	1 1 1 1 2 2 3 6% 83%	3109
August	1st to 10th	Night	1 1 1 1 1 2 2 4 9% 78%	2866
	11th to 20th	Night	1 1 1 1 2 3 6% 85%	3126
	21st to end	Night	1 1 1 1 2 3 6% 84%	3498
September	1st to 10th	Night	1 1 1 1 1 2 2 3 7% 82%	1900
	11th to 20th	Night	2 1 1 2 1 1 3 2 4 9% 76%	1900
	21st to end	Night	2 1 2 2 2 2 2 2 6% 79%	2123
October	1st to 10th	Night	2 1 1 2 2 2 2 4 6% 78%	3800
	11th to 20th	Night	1 1 2 2 3 5% 3 5% 7% 70%	3777
	21st to end	Night	3 2 1 2 2 3 3 3 5% 6% 70%	4121
November	1st to 10th	Night	5% 3 1 2 3 2 4 3 5% 8% 63%	2346
	11th to 20th	Night	6% 3 2 4 3 3 3 3 6% 10% 57%	2470
	21st to end	Night	5% 4 2 4 4 3 3 4 5% 7% 59%	2517
December	1st to 10th	Night	10% 5% 2 7% 3 4 4 3 5% 7% 50%	2660
	11th to 20th	Night	16% 9% 3 8% 5% 4 4 5% 6% 7% 34%	3276
	21st to end	Night	14% 7% 2 6% 5% 6% 5% 5% 6% 7% 37%	4862

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	37% 13% 13% 26% 8% 3	2635
	11th to 20th	Day	45% 11% 12% 15% 13% 5%	2860
	21st to end	Day	45% 11% 12% 16% 13% 3	3146
February	1st to 10th	Day	35% 7% 9% 21% 18% 10%	1710
	11th to 20th	Day	31% 9% 12% 20% 22% 7%	1832
	21st to end	Day	34% 9% 10% 22% 20% 6%	1570
March	1st to 10th	Day	40% 17% 14% 12% 14% 3	3283
	11th to 20th	Day	24% 8% 11% 29% 17% 11%	3490
	21st to end	Day	34% 16% 18% 19% 11% 3	3961
April	1st to 10th	Day	31% 8% 12% 23% 19% 7%	2280
	11th to 20th	Day	24% 7% 13% 25% 23% 7%	2252
	21st to end	Day	18% 8% 12% 28% 28% 6%	2280
May	1st to 10th	Day	12% 6% 11% 27% 28% 16%	3800
	11th to 20th	Day	7% 4 7% 24% 43% 16%	4202
	21st to end	Day	8% 6% 13% 26% 39% 8%	4814
June	1st to 10th	Day	12% 8% 12% 22% 29% 17%	2660
	11th to 20th	Day	5% 3 8% 20% 36% 29%	2660
	21st to end	Day	7% 2 3 10% 29% 49%	2660
July	1st to 10th	Day	2 1 2 5% 12% 78%	4351
	11th to 20th	Day	7% 2 3 6% 13% 69%	4161
	21st to end	Day	3 1 2 5% 24% 65%	4315
August	1st to 10th	Day	7% 2 3 7% 24% 57%	4057
	11th to 20th	Day	2 1 2 6% 29% 60%	3760
	21st to end	Day	4 2 2 9% 28% 54%	4179
September	1st to 10th	Day	4 3 2 8% 28% 54%	2280
	11th to 20th	Day	5% 5% 7% 20% 38% 25%	2280
	21st to end	Day	7% 3 4 19% 40% 27%	2054
October	1st to 10th	Day	9% 3 6% 11% 24% 47%	3180
	11th to 20th	Day	10% 4 5% 21% 38% 22%	3161
	21st to end	Day	15% 4 7% 20% 36% 18%	3448
November	1st to 10th	Day	23% 7% 13% 19% 24% 14%	1803
	11th to 20th	Day	24% 7% 11% 25% 25% 7%	1710
	21st to end	Day	26% 7% 12% 18% 28% 11%	1658
December	1st to 10th	Day	34% 8% 12% 18% 17% 11%	1520
	11th to 20th	Day	49% 9% 9% 15% 13% 5%	1928
	21st to end	Day	41% 11% 14% 20% 11% 3	2794
January	1st to 10th	Night	32% 13% 16% 25% 13% 3	4309
	11th to 20th	Night	43% 12% 13% 15% 10% 7%	4110
	21st to end	Night	43% 13% 11% 15% 13% 5%	4521
February	1st to 10th	Night	32% 7% 9% 20% 21% 11%	2470
	11th to 20th	Night	26% 9% 13% 20% 23% 9%	2245
	21st to end	Night	27% 9% 12% 27% 18% 7%	1884
March	1st to 10th	Night	38% 18% 14% 13% 15% 3	3586
	11th to 20th	Night	25% 9% 12% 23% 20% 11%	3490
	21st to end	Night	29% 17% 19% 19% 11% 4	3690
April	1st to 10th	Night	27% 10% 15% 22% 18% 8%	1900
	11th to 20th	Night	21% 9% 14% 27% 21% 8%	1879
	21st to end	Night	13% 10% 15% 27% 27% 7%	1900
May	1st to 10th	Night	9% 10% 13% 22% 29% 18%	3180
	11th to 20th	Night	7% 5% 15% 17% 34% 22%	2690
	21st to end	Night	6% 6% 18% 21% 39% 10%	2762
June	1st to 10th	Night	13% 8% 11% 20% 31% 17%	1520
	11th to 20th	Night	5% 5% 7% 17% 33% 32%	1520
	21st to end	Night	4 3 6% 10% 28% 49%	1520
July	1st to 10th	Night	2 2 3 5% 11% 78%	2500
	11th to 20th	Night	5% 2 3 7% 13% 70%	2678
	21st to end	Night	4 2 3 6% 22% 64%	3011
August	1st to 10th	Night	6% 3 4 8% 22% 56%	2857
	11th to 20th	Night	3 2 2 6% 26% 61%	3156
	21st to end	Night	4 2 4 10% 25% 54%	3498
September	1st to 10th	Night	4 4 4 7% 22% 59%	1900
	11th to 20th	Night	7% 6% 6% 17% 33% 30%	1900
	21st to end	Night	8% 4 6% 14% 36% 32%	2123
October	1st to 10th	Night	9% 4 5% 10% 18% 54%	3800
	11th to 20th	Night	9% 4 6% 24% 33% 24%	3777
	21st to end	Night	13% 4 6% 20% 35% 22%	4121
November	1st to 10th	Night	18% 8% 11% 21% 24% 18%	2346
	11th to 20th	Night	23% 7% 12% 20% 30% 9%	2470
	21st to end	Night	24% 7% 10% 18% 27% 14%	2517
December	1st to 10th	Night	31% 8% 11% 20% 18% 12%	2660
	11th to 20th	Night	44% 12% 11% 14% 15% 4	3276
	21st to end	Night	40% 14% 14% 17% 11% 4	4862

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	24% 10% 26% 23% 14% 3	237
	11th to 20th	Day	14% 8% 23% 32% 20% 4	370
	21st to end	Day	13% 9% 23% 31% 21% 4	407
February	1st to 10th	Day	19% 12% 18% 29% 16% 5%	370
	11th to 20th	Day	13% 14% 25% 30% 15% 1	442
	21st to end	Day	13% 13% 27% 31% 15% 2	382
March	1st to 10th	Day	19% 14% 26% 27% 12% 2	460
	11th to 20th	Day	17% 13% 25% 23% 17% 5%	460
	21st to end	Day	16% 14% 30% 27% 10% 2	506
April	1st to 10th	Day	13% 17% 30% 20% 15% 5%	460
	11th to 20th	Day	11% 18% 30% 26% 11% 5%	452
	21st to end	Day	5% 18% 35% 22% 12% 8%	460
May	1st to 10th	Day	8% 14% 33% 27% 14% 4	463
	11th to 20th	Day	4 15% 36% 29% 13% 3	488
	21st to end	Day	5% 13% 31% 34% 13% 4	529
June	1st to 10th	Day	3 11% 38% 30% 11% 7%	490
	11th to 20th	Day	2 12% 35% 31% 17% 4	490
	21st to end	Day	2 6% 34% 35% 18% 4	490
July	1st to 10th	Day	2 30% 43% 19% 5%	486
	11th to 20th	Day	1 1 27% 43% 23% 5%	484
	21st to end	Day	1 2 26% 41% 20% 10%	531
August	1st to 10th	Day	2 5% 31% 39% 16% 6%	487
	11th to 20th	Day	1 6% 27% 37% 20% 9%	477
	21st to end	Day	1 3 22% 41% 23% 11%	539
September	1st to 10th	Day	2 5% 22% 35% 22% 14%	490
	11th to 20th	Day	3 9% 28% 32% 19% 9%	490
	21st to end	Day	2 6% 19% 35% 28% 10%	490
October	1st to 10th	Day	3 8% 21% 29% 27% 11%	490
	11th to 20th	Day	4 7% 20% 29% 29% 11%	490
	21st to end	Day	6% 6% 20% 28% 31% 9%	539
November	1st to 10th	Day	8% 6% 18% 27% 34% 7%	381
	11th to 20th	Day	5% 5% 15% 38% 30% 7%	270
	21st to end	Day	9% 4 22% 35% 29% 2	246
December	1st to 10th	Day	16% 6% 23% 29% 23% 4	180
	11th to 20th	Day	16% 9% 23% 25% 22% 5%	180
	21st to end	Day	17% 9% 26% 26% 19% 3	198
January	1st to 10th	Night	15% 3 11% 36% 25% 9%	760
	11th to 20th	Night	12% 4 11% 38% 27% 8%	760
	21st to end	Night	14% 4 11% 37% 27% 7%	836
February	1st to 10th	Night	16% 4 12% 36% 25% 8%	760
	11th to 20th	Night	10% 6% 16% 37% 24% 7%	744
	21st to end	Night	12% 7% 15% 43% 19% 4	628
March	1st to 10th	Night	14% 9% 17% 35% 21% 5%	760
	11th to 20th	Night	11% 6% 20% 35% 23% 6%	760
	21st to end	Night	10% 10% 22% 35% 19% 4	836
April	1st to 10th	Night	11% 8% 20% 36% 23% 4	760
	11th to 20th	Night	7% 12% 26% 30% 20% 6%	751
	21st to end	Night	5% 9% 29% 29% 22% 6%	760
May	1st to 10th	Night	3 6% 29% 37% 20% 5%	760
	11th to 20th	Night	3 6% 25% 42% 21% 3	483
	21st to end	Night	3 7% 27% 38% 23% 2	411
June	1st to 10th	Night	3 4 28% 39% 23% 3	380
	11th to 20th	Night	1 6% 27% 41% 24% 2	380
	21st to end	Night	1 3 21% 42% 30% 4	380
July	1st to 10th	Night	1 2 21% 41% 33% 3	370
	11th to 20th	Night	1 1 13% 45% 33% 8%	476
	21st to end	Night	1 1 17% 37% 36% 8%	624
August	1st to 10th	Night	1 1 17% 42% 32% 6%	572
	11th to 20th	Night	2 22% 39% 28% 9%	752
	21st to end	Night	1 2 13% 38% 37% 9%	836
September	1st to 10th	Night	1 1 16% 34% 38% 10%	760
	11th to 20th	Night	2 3 20% 37% 30% 8%	760
	21st to end	Night	3 3 12% 36% 34% 11%	760
October	1st to 10th	Night	4 3 13% 38% 33% 10%	760
	11th to 20th	Night	4 3 13% 34% 33% 12%	760
	21st to end	Night	4 2 14% 32% 28% 19%	836
November	1st to 10th	Night	5% 3 13% 34% 32% 12%	754
	11th to 20th	Night	9% 2 9% 37% 34% 9%	760
	21st to end	Night	7% 4 13% 36% 32% 9%	760
December	1st to 10th	Night	13% 4 9% 39% 27% 8%	760
	11th to 20th	Night	16% 4 11% 39% 26% 5%	760
	21st to end	Night	16% 7% 15% 35% 23% 4	836

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