Atascadero
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atascadero clear sky chart from 2005-11-06 to 2024-04-03.

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 4 6% 64%	79032
	Night	6% 5% 2 4 4 2 3 4 4 6% 61%	81132
Transparency	Day	22% 4 7% 19% 27% 21%	78752
	Night	24% 4 8% 18% 25% 21%	80934
Seeing	Day	5% 7% 19% 34% 27% 8%	14699
	Night	6% 3 13% 36% 35% 7%	24385

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	7% 4 2 5% 6% 4 4 6% 6% 7% 49%	2703
	11th to 20th	Day	9% 7% 2 6% 5% 3 5% 4 7% 8% 44%	2860
	21st to end	Day	10% 9% 3 6% 5% 3 5% 6% 6% 9% 37%	3146
February	1st to 10th	Day	12% 6% 3 3 3 2 3 4 4 5% 54%	1770
	11th to 20th	Day	8% 6% 3 5% 4 3 3 4 5% 8% 52%	1850
	21st to end	Day	9% 5% 4 5% 4 3 4 4 5% 6% 51%	1570
March	1st to 10th	Day	8% 8% 2 6% 7% 3 4 6% 6% 8% 42%	1959
	11th to 20th	Day	8% 5% 3 5% 5% 4 5% 5% 6% 7% 47%	2090
	21st to end	Day	7% 6% 2 4 5% 2 4 5% 4 7% 53%	2399
April	1st to 10th	Day	8% 6% 2 3 4 2 4 5% 4 8% 54%	2185
	11th to 20th	Day	5% 4 2 4 4 2 4 4 5% 7% 60%	2129
	21st to end	Day	5% 3 2 3 3 2 3 4 4 7% 65%	2160
May	1st to 10th	Day	3 3 2 3 3 2 2 3 4 6% 69%	2160
	11th to 20th	Day	2 2 1 2 2 2 4 3 4 6% 71%	2213
	21st to end	Day	3 3 2 3 2 1 3 3 4 7% 70%	2723
June	1st to 10th	Day	2 3 1 2 2 2 3 3 4 7% 71%	2520
	11th to 20th	Day	1 2 2 1 1 2 2 2 4 84%	2520
	21st to end	Day	1 2 2 1 2 2 2 4 84%	2520
July	1st to 10th	Day	1 1 1 2 1 1 2 3 5% 83%	2520
	11th to 20th	Day	2 1 1 2 2 2 3 3 3 5% 78%	2359
	21st to end	Day	1 1 1 1 2 1 3 3 4 7% 76%	2546
August	1st to 10th	Day	1 1 1 2 2 1 2 3 4 6% 78%	2235
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 4 84%	2122
	21st to end	Day	1 1 1 2 2 1 2 2 3 4 81%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 2 5% 84%	2160
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 4 82%	2160
	21st to end	Day	1 2 1 2 2 1 3 3 4 5% 76%	1976
October	1st to 10th	Day	3 2 1 2 3 2 3 3 4 6% 72%	1800
	11th to 20th	Day	3 3 1 3 3 2 2 3 4 5% 71%	1800
	21st to end	Day	2 2 1 4 3 2 2 3 4 6% 70%	1980
November	1st to 10th	Day	5% 3 2 3 4 1 3 3 4 6% 66%	1783
	11th to 20th	Day	5% 4 1 3 3 2 4 4 5% 6% 63%	1710
	21st to end	Day	6% 4 2 4 4 2 3 4 4 6% 61%	1710
December	1st to 10th	Day	6% 5% 3 6% 6% 3 5% 3 5% 7% 51%	1596
	11th to 20th	Day	17% 9% 3 6% 5% 3 4 4 5% 7% 37%	1928
	21st to end	Day	13% 8% 3 5% 5% 3 5% 5% 5% 8% 40%	2794
January	1st to 10th	Night	7% 7% 3 5% 5% 2 4 3 4 6% 54%	4242
	11th to 20th	Night	8% 8% 3 6% 5% 3 4 4 6% 7% 45%	4110
	21st to end	Night	14% 9% 3 5% 5% 3 4 5% 4 7% 41%	4521
February	1st to 10th	Night	10% 5% 2 4 5% 3 4 3 4 5% 56%	2409
	11th to 20th	Night	7% 5% 2 3 3 2 4 4 5% 6% 58%	2218
	21st to end	Night	8% 6% 3 5% 3 3 3 4 3 6% 56%	1884
March	1st to 10th	Night	8% 8% 3 6% 4 3 4 5% 4 7% 48%	2218
	11th to 20th	Night	7% 5% 2 5% 4 3 5% 6% 6% 7% 51%	2090
	21st to end	Night	8% 5% 3 4 4 3 4 3 5% 7% 57%	2199
April	1st to 10th	Night	6% 4 2 3 4 2 4 4 4 7% 60%	1820
	11th to 20th	Night	5% 4 2 3 4 2 2 3 4 5% 67%	1779
	21st to end	Night	3 3 2 4 4 1 3 3 4 7% 65%	1800
May	1st to 10th	Night	2 3 1 3 3 2 3 3 4 8% 67%	1800
	11th to 20th	Night	2 3 1 3 3 2 3 3 3 8% 68%	1675
	21st to end	Night	2 3 2 5% 4 2 4 3 4 6% 66%	1552
June	1st to 10th	Night	3 2 1 3 3 2 4 4 5% 7% 68%	1440
	11th to 20th	Night	3 2 2 2 2 2 3 3 5% 77%	1440
	21st to end	Night	1 1 1 1 2 2 2 2 2 3 83%	1440
July	1st to 10th	Night	1 2 3 3 3 3 4 5% 77%	1440
	11th to 20th	Night	1 1 2 3 1 2 3 4 4 79%	1595
	21st to end	Night	1 1 1 2 2 2 3 4 4 5% 73%	1773
August	1st to 10th	Night	1 1 1 2 3 2 3 3 2 4 78%	1702
	11th to 20th	Night	1 1 2 2 1 2 2 3 5% 80%	1780
	21st to end	Night	1 2 3 2 3 2 3 4 79%	1980
September	1st to 10th	Night	1 2 1 2 2 1 1 2 2 4 82%	1800
	11th to 20th	Night	1 2 1 3 2 2 2 2 3 4 79%	1800
	21st to end	Night	2 1 1 2 1 2 2 3 4 82%	1980
October	1st to 10th	Night	3 2 1 3 3 2 2 3 3 6% 73%	2160
	11th to 20th	Night	2 3 2 4 3 3 3 3 4 4 69%	2160
	21st to end	Night	3 4 2 4 3 1 3 2 3 5% 70%	2376
November	1st to 10th	Night	4 3 2 3 3 2 3 3 4 6% 68%	2292
	11th to 20th	Night	3 4 1 3 3 2 4 4 5% 6% 65%	2470
	21st to end	Night	4 4 2 3 3 2 4 4 5% 7% 60%	2470
December	1st to 10th	Night	8% 6% 2 5% 4 2 4 4 4 7% 54%	2579
	11th to 20th	Night	14% 11% 4 5% 6% 3 4 5% 5% 6% 38%	3276
	21st to end	Night	11% 8% 3 7% 6% 3 5% 5% 5% 7% 39%	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	29% 5% 12% 33% 16% 4	2703
	11th to 20th	Day	38% 5% 11% 20% 16% 10%	2860
	21st to end	Day	42% 6% 11% 19% 15% 8%	3146
February	1st to 10th	Day	32% 3 7% 19% 22% 17%	1770
	11th to 20th	Day	32% 4 7% 23% 25% 10%	1860
	21st to end	Day	34% 4 10% 21% 24% 7%	1570
March	1st to 10th	Day	39% 6% 10% 17% 19% 9%	1959
	11th to 20th	Day	35% 4 11% 21% 20% 9%	2090
	21st to end	Day	29% 6% 12% 27% 18% 7%	2399
April	1st to 10th	Day	29% 5% 12% 25% 21% 9%	2185
	11th to 20th	Day	24% 4 11% 27% 26% 8%	2132
	21st to end	Day	20% 5% 10% 27% 30% 8%	2160
May	1st to 10th	Day	18% 3 9% 24% 34% 11%	2160
	11th to 20th	Day	15% 4 7% 28% 36% 11%	2216
	21st to end	Day	18% 3 9% 31% 33% 6%	2724
June	1st to 10th	Day	15% 4 9% 23% 32% 17%	2520
	11th to 20th	Day	8% 2 5% 14% 42% 28%	2520
	21st to end	Day	8% 2 3 11% 36% 41%	2520
July	1st to 10th	Day	6% 1 3 8% 31% 50%	2451
	11th to 20th	Day	9% 3 5% 9% 32% 41%	2288
	21st to end	Day	10% 3 5% 12% 31% 39%	2405
August	1st to 10th	Day	11% 3 2 10% 28% 47%	2219
	11th to 20th	Day	7% 1 3 12% 37% 41%	2122
	21st to end	Day	9% 2 3 10% 37% 41%	2376
September	1st to 10th	Day	7% 2 3 10% 31% 47%	2160
	11th to 20th	Day	9% 2 3 17% 40% 29%	2160
	21st to end	Day	11% 2 3 18% 38% 28%	1976
October	1st to 10th	Day	14% 3 6% 21% 24% 32%	1800
	11th to 20th	Day	16% 3 5% 17% 30% 27%	1800
	21st to end	Day	17% 3 5% 16% 29% 29%	1980
November	1st to 10th	Day	21% 3 7% 18% 30% 21%	1783
	11th to 20th	Day	22% 4 10% 18% 26% 20%	1710
	21st to end	Day	26% 3 6% 17% 25% 22%	1710
December	1st to 10th	Day	32% 4 7% 18% 21% 17%	1596
	11th to 20th	Day	47% 6% 7% 15% 16% 9%	1928
	21st to end	Day	39% 6% 12% 23% 16% 5%	2794
January	1st to 10th	Night	30% 6% 10% 28% 22% 5%	4242
	11th to 20th	Night	36% 7% 8% 25% 13% 10%	4110
	21st to end	Night	42% 5% 10% 17% 16% 10%	4521
February	1st to 10th	Night	32% 3 7% 18% 24% 16%	2409
	11th to 20th	Night	27% 4 8% 23% 26% 13%	2219
	21st to end	Night	32% 5% 8% 22% 25% 8%	1884
March	1st to 10th	Night	37% 5% 11% 21% 17% 8%	2218
	11th to 20th	Night	30% 6% 11% 20% 24% 9%	2090
	21st to end	Night	29% 4 13% 23% 23% 7%	2199
April	1st to 10th	Night	26% 5% 12% 27% 19% 12%	1820
	11th to 20th	Night	21% 3 10% 28% 27% 10%	1779
	21st to end	Night	21% 4 7% 26% 32% 9%	1800
May	1st to 10th	Night	17% 4 11% 24% 29% 15%	1800
	11th to 20th	Night	16% 4 7% 25% 34% 13%	1676
	21st to end	Night	19% 6% 9% 26% 31% 10%	1552
June	1st to 10th	Night	14% 5% 11% 19% 33% 18%	1440
	11th to 20th	Night	11% 4 4 14% 37% 31%	1440
	21st to end	Night	8% 3 2 7% 34% 46%	1440
July	1st to 10th	Night	8% 2 4 7% 26% 54%	1400
	11th to 20th	Night	9% 3 3 9% 27% 49%	1543
	21st to end	Night	11% 3 3 10% 29% 44%	1674
August	1st to 10th	Night	11% 1 2 8% 27% 51%	1693
	11th to 20th	Night	8% 2 2 6% 32% 51%	1780
	21st to end	Night	8% 1 2 9% 30% 49%	1980
September	1st to 10th	Night	10% 2 3 8% 25% 53%	1800
	11th to 20th	Night	11% 2 3 14% 33% 37%	1800
	21st to end	Night	9% 1 3 14% 40% 31%	1980
October	1st to 10th	Night	15% 3 5% 19% 25% 33%	2160
	11th to 20th	Night	18% 3 6% 16% 28% 29%	2160
	21st to end	Night	18% 3 4 15% 29% 31%	2376
November	1st to 10th	Night	18% 3 7% 19% 29% 24%	2292
	11th to 20th	Night	20% 4 10% 19% 25% 22%	2470
	21st to end	Night	25% 4 9% 16% 23% 22%	2470
December	1st to 10th	Night	30% 5% 7% 17% 22% 19%	2579
	11th to 20th	Night	45% 6% 9% 14% 17% 9%	3276
	21st to end	Night	42% 7% 10% 18% 17% 6%	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	18% 9% 27% 33% 11% 2	279
	11th to 20th	Day	11% 9% 24% 38% 15% 2	370
	21st to end	Day	10% 9% 25% 32% 21% 3	407
February	1st to 10th	Day	13% 11% 25% 28% 20% 5%	399
	11th to 20th	Day	10% 12% 25% 32% 18% 3	455
	21st to end	Day	8% 12% 27% 36% 14% 3	382
March	1st to 10th	Day	11% 16% 25% 34% 13%	460
	11th to 20th	Day	11% 11% 30% 30% 17% 2	460
	21st to end	Day	9% 16% 28% 31% 15% 1	506
April	1st to 10th	Day	12% 8% 26% 30% 19% 4	429
	11th to 20th	Day	6% 13% 25% 35% 17% 4	412
	21st to end	Day	4 8% 28% 32% 20% 7%	420
May	1st to 10th	Day	6% 8% 28% 30% 23% 5%	423
	11th to 20th	Day	2 9% 21% 39% 22% 7%	448
	21st to end	Day	4 11% 22% 32% 22% 8%	485
June	1st to 10th	Day	4 5% 18% 34% 28% 13%	450
	11th to 20th	Day	1 4 19% 36% 28% 12%	450
	21st to end	Day	1 2 15% 35% 32% 15%	450
July	1st to 10th	Day	7% 40% 35% 17%	446
	11th to 20th	Day	2 3 34% 41% 19%	444
	21st to end	Day	6% 32% 41% 20%	487
August	1st to 10th	Day	1 13% 38% 33% 13%	447
	11th to 20th	Day	1 1 7% 34% 38% 19%	437
	21st to end	Day	2 1 7% 30% 43% 16%	495
September	1st to 10th	Day	1 2 10% 31% 41% 16%	450
	11th to 20th	Day	2 3 11% 36% 39% 9%	450
	21st to end	Day	1 4 11% 33% 40% 11%	450
October	1st to 10th	Day	2 5% 18% 39% 30% 6%	450
	11th to 20th	Day	3 4 22% 34% 30% 7%	450
	21st to end	Day	3 5% 16% 37% 33% 6%	495
November	1st to 10th	Day	4 5% 21% 33% 30% 7%	379
	11th to 20th	Day	7% 6% 19% 39% 26% 4	270
	21st to end	Day	7% 5% 20% 39% 26% 3	270
December	1st to 10th	Day	9% 10% 23% 39% 15% 4	216
	11th to 20th	Day	8% 8% 24% 32% 23% 5%	180
	21st to end	Day	14% 15% 25% 33% 11% 3	198
January	1st to 10th	Night	12% 6% 19% 39% 20% 4	760
	11th to 20th	Night	10% 2 18% 45% 21% 3	760
	21st to end	Night	13% 3 18% 42% 21% 3	836
February	1st to 10th	Night	12% 5% 14% 40% 25% 4	760
	11th to 20th	Night	8% 4 18% 43% 22% 4	744
	21st to end	Night	10% 5% 19% 45% 18% 3	628
March	1st to 10th	Night	10% 7% 18% 42% 21% 2	760
	11th to 20th	Night	8% 4 19% 38% 26% 5%	760
	21st to end	Night	8% 4 22% 39% 24% 3	836
April	1st to 10th	Night	8% 4 19% 41% 27% 2	728
	11th to 20th	Night	6% 5% 20% 36% 27% 5%	711
	21st to end	Night	4 3 22% 34% 29% 7%	720
May	1st to 10th	Night	4 2 17% 38% 32% 6%	720
	11th to 20th	Night	4 3 13% 38% 37% 6%	613
	21st to end	Night	3 1 18% 38% 33% 6%	389
June	1st to 10th	Night	3 1 9% 39% 44% 4	360
	11th to 20th	Night	1 10% 33% 48% 7%	360
	21st to end	Night	1 3 33% 53% 10%	360
July	1st to 10th	Night	1 1 23% 62% 13%	350
	11th to 20th	Night	1 1 8% 64% 25%	499
	21st to end	Night	2 1 1 10% 60% 27%	591
August	1st to 10th	Night	1 3 25% 54% 17%	628
	11th to 20th	Night	2 22% 60% 15%	712
	21st to end	Night	1 1 19% 63% 16%	792
September	1st to 10th	Night	1 1 3 22% 59% 14%	720
	11th to 20th	Night	2 1 5% 33% 46% 12%	720
	21st to end	Night	2 1 8% 29% 49% 12%	720
October	1st to 10th	Night	4 1 8% 38% 44% 6%	720
	11th to 20th	Night	3 3 9% 39% 41% 6%	720
	21st to end	Night	5% 2 8% 42% 33% 9%	792
November	1st to 10th	Night	5% 3 13% 42% 34% 4	740
	11th to 20th	Night	4 2 13% 47% 29% 5%	760
	21st to end	Night	4 3 18% 45% 27% 3	760
December	1st to 10th	Night	10% 4 16% 45% 23% 3	760
	11th to 20th	Night	14% 3 17% 44% 21% 2	760
	21st to end	Night	11% 5% 25% 41% 17% 2	836

Page generated at 2024-03-31 03:08:55. Version ac07

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