Anaheim
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anaheim 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 3 4 7% 64%	79641
	Night	6% 5% 2 4 3 2 3 3 4 7% 60%	80493
Transparency	Day	21% 4 9% 18% 25% 23%	79367
	Night	25% 5% 10% 16% 22% 22%	80290
Seeing	Day	6% 7% 24% 37% 19% 6%	14871
	Night	7% 2 11% 35% 36% 9%	24844

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	6% 3 2 3 3 1 3 3 4 7% 65%	2571
	11th to 20th	Day	9% 5% 2 4 3 2 3 4 5% 8% 55%	3000
	21st to end	Day	14% 6% 3 4 4 2 3 3 4 6% 51%	3498
February	1st to 10th	Day	9% 4 1 3 4 2 3 3 4 7% 59%	1900
	11th to 20th	Day	8% 3 1 3 4 2 4 3 5% 8% 60%	1850
	21st to end	Day	8% 5% 2 4 3 3 3 5% 4 8% 56%	1570
March	1st to 10th	Day	7% 4 2 5% 3 3 4 6% 6% 7% 52%	1900
	11th to 20th	Day	7% 4 2 3 4 2 3 4 6% 9% 57%	1941
	21st to end	Day	6% 3 2 3 4 2 4 4 6% 8% 59%	2508
April	1st to 10th	Day	5% 4 2 3 3 2 3 4 5% 9% 60%	2185
	11th to 20th	Day	4 4 2 3 3 2 3 4 4 5% 67%	2129
	21st to end	Day	4 4 2 3 3 2 2 2 4 7% 67%	2160
May	1st to 10th	Day	5% 4 2 4 4 2 3 4 4 9% 60%	2224
	11th to 20th	Day	4 6% 2 4 3 1 3 3 4 7% 64%	2301
	21st to end	Day	5% 6% 2 3 4 1 2 3 4 7% 62%	2530
June	1st to 10th	Day	5% 7% 2 4 3 2 2 3 3 7% 62%	2340
	11th to 20th	Day	3 4 2 3 2 2 2 2 3 6% 70%	2458
	21st to end	Day	2 4 2 3 3 2 3 3 3 5% 71%	2520
July	1st to 10th	Day	3 3 2 3 3 1 2 3 4 6% 70%	2520
	11th to 20th	Day	2 3 1 3 2 1 3 2 4 7% 72%	2430
	21st to end	Day	2 3 2 2 2 1 3 4 4 7% 70%	2384
August	1st to 10th	Day	2 3 1 2 2 2 2 2 3 5% 77%	2149
	11th to 20th	Day	2 2 1 2 2 1 2 2 2 6% 78%	2122
	21st to end	Day	1 2 1 2 2 2 2 3 4 6% 75%	2376
September	1st to 10th	Day	3 2 1 3 2 1 2 2 4 5% 76%	2160
	11th to 20th	Day	2 3 1 2 2 1 2 3 3 5% 76%	2014
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 76%	1980
October	1st to 10th	Day	4 3 1 3 3 2 3 3 4 5% 69%	1980
	11th to 20th	Day	5% 4 1 2 3 1 2 3 3 5% 71%	1890
	21st to end	Day	4 2 1 3 3 2 2 3 4 5% 71%	1932
November	1st to 10th	Day	3 2 2 3 3 2 2 3 5% 7% 69%	1674
	11th to 20th	Day	5% 2 1 2 3 2 3 3 4 6% 70%	1710
	21st to end	Day	5% 3 2 3 4 3 3 4 4 9% 61%	1710
December	1st to 10th	Day	7% 5% 2 4 3 2 3 3 5% 7% 57%	1710
	11th to 20th	Day	12% 6% 2 5% 4 2 4 4 6% 9% 46%	2169
	21st to end	Day	12% 7% 3 5% 6% 3 4 5% 5% 7% 43%	3146
January	1st to 10th	Night	7% 4 2 3 3 2 3 3 4 6% 65%	4346
	11th to 20th	Night	8% 5% 2 4 4 2 4 4 5% 7% 55%	3943
	21st to end	Night	15% 7% 3 4 3 2 3 4 4 5% 50%	4180
February	1st to 10th	Night	8% 5% 2 5% 4 2 3 2 3 5% 61%	2280
	11th to 20th	Night	8% 5% 2 4 3 1 3 3 4 5% 61%	2218
	21st to end	Night	9% 5% 2 4 4 3 4 4 4 5% 56%	1884
March	1st to 10th	Night	7% 6% 2 4 4 3 3 4 6% 8% 52%	2280
	11th to 20th	Night	7% 6% 2 4 4 2 3 4 5% 9% 54%	2234
	21st to end	Night	7% 6% 2 4 3 2 3 3 4 8% 57%	2090
April	1st to 10th	Night	7% 5% 3 5% 3 1 3 3 4 8% 55%	1820
	11th to 20th	Night	5% 6% 2 3 2 2 2 3 4 7% 64%	1779
	21st to end	Night	5% 6% 2 4 4 2 3 3 5% 7% 59%	1800
May	1st to 10th	Night	5% 7% 2 4 4 2 2 2 5% 9% 57%	1733
	11th to 20th	Night	4 8% 3 4 3 2 3 3 4 9% 56%	1594
	21st to end	Night	5% 7% 2 4 3 1 2 3 4 8% 61%	1746
June	1st to 10th	Night	4 8% 3 7% 5% 2 3 4 5% 7% 53%	1620
	11th to 20th	Night	3 6% 2 4 3 2 2 3 4 7% 63%	1494
	21st to end	Night	2 7% 3 5% 4 2 4 4 5% 7% 57%	1440
July	1st to 10th	Night	2 5% 2 4 4 2 3 3 5% 8% 62%	1440
	11th to 20th	Night	2 3 2 4 4 2 3 4 6% 9% 62%	1525
	21st to end	Night	3 4 2 5% 4 2 4 4 5% 9% 59%	1930
August	1st to 10th	Night	3 4 1 3 3 1 2 3 5% 7% 68%	1790
	11th to 20th	Night	1 5% 2 3 3 1 2 3 4 6% 69%	1780
	21st to end	Night	2 3 1 3 3 2 3 3 5% 9% 66%	1980
September	1st to 10th	Night	4 4 2 3 3 2 2 2 4 6% 66%	1800
	11th to 20th	Night	2 3 1 2 2 2 2 2 4 5% 75%	1944
	21st to end	Night	2 3 2 3 2 2 2 2 3 5% 74%	1980
October	1st to 10th	Night	3 3 2 3 3 2 3 3 4 6% 69%	1980
	11th to 20th	Night	5% 5% 1 3 3 2 2 2 3 6% 69%	2065
	21st to end	Night	3 4 1 3 3 2 2 3 3 6% 70%	2421
November	1st to 10th	Night	4 3 2 3 3 2 3 3 4 6% 69%	2405
	11th to 20th	Night	3 3 2 3 3 2 3 3 4 6% 69%	2470
	21st to end	Night	5% 4 2 4 4 2 3 4 5% 7% 59%	2470
December	1st to 10th	Night	8% 4 2 5% 4 2 3 3 5% 7% 57%	2470
	11th to 20th	Night	13% 7% 3 4 5% 2 4 4 4 7% 48%	3041
	21st to end	Night	12% 6% 3 5% 5% 3 4 5% 5% 7% 45%	4521

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	20% 3 7% 24% 28% 18%	2571
	11th to 20th	Day	28% 6% 14% 19% 16% 16%	3000
	21st to end	Day	34% 4 7% 17% 22% 16%	3498
February	1st to 10th	Day	26% 4 7% 13% 24% 25%	1900
	11th to 20th	Day	23% 5% 7% 17% 25% 23%	1860
	21st to end	Day	27% 6% 10% 18% 22% 18%	1570
March	1st to 10th	Day	29% 6% 9% 19% 17% 20%	1900
	11th to 20th	Day	24% 6% 13% 21% 21% 15%	1941
	21st to end	Day	23% 6% 13% 24% 20% 14%	2508
April	1st to 10th	Day	23% 6% 12% 26% 21% 12%	2185
	11th to 20th	Day	20% 5% 8% 22% 27% 18%	2132
	21st to end	Day	18% 4 11% 24% 30% 13%	2160
May	1st to 10th	Day	23% 6% 12% 19% 27% 13%	2224
	11th to 20th	Day	22% 6% 8% 24% 29% 12%	2304
	21st to end	Day	23% 5% 11% 28% 26% 7%	2530
June	1st to 10th	Day	24% 5% 10% 19% 29% 13%	2340
	11th to 20th	Day	17% 3 8% 12% 33% 26%	2458
	21st to end	Day	17% 2 8% 10% 26% 38%	2520
July	1st to 10th	Day	15% 3 8% 10% 23% 41%	2451
	11th to 20th	Day	14% 4 11% 17% 30% 25%	2356
	21st to end	Day	14% 4 12% 22% 32% 16%	2252
August	1st to 10th	Day	12% 2 5% 14% 32% 35%	2135
	11th to 20th	Day	10% 1 6% 15% 34% 33%	2122
	21st to end	Day	12% 2 7% 12% 34% 33%	2376
September	1st to 10th	Day	12% 2 8% 10% 33% 35%	2160
	11th to 20th	Day	12% 2 8% 12% 33% 34%	2014
	21st to end	Day	11% 2 7% 17% 33% 31%	1980
October	1st to 10th	Day	19% 3 6% 21% 22% 29%	1980
	11th to 20th	Day	18% 2 6% 16% 25% 33%	1890
	21st to end	Day	17% 4 7% 12% 19% 41%	1932
November	1st to 10th	Day	16% 3 9% 17% 22% 32%	1674
	11th to 20th	Day	18% 4 8% 16% 18% 37%	1710
	21st to end	Day	22% 4 10% 13% 22% 30%	1710
December	1st to 10th	Day	27% 5% 8% 17% 18% 25%	1710
	11th to 20th	Day	35% 6% 11% 14% 19% 16%	2168
	21st to end	Day	40% 6% 11% 18% 14% 12%	3146
January	1st to 10th	Night	22% 4 7% 14% 31% 20%	4346
	11th to 20th	Night	29% 6% 13% 21% 14% 17%	3943
	21st to end	Night	35% 5% 9% 15% 19% 18%	4180
February	1st to 10th	Night	28% 4 8% 13% 21% 27%	2280
	11th to 20th	Night	26% 4 9% 16% 21% 24%	2219
	21st to end	Night	33% 5% 7% 15% 20% 21%	1884
March	1st to 10th	Night	30% 6% 10% 19% 18% 17%	2280
	11th to 20th	Night	29% 6% 12% 17% 21% 16%	2234
	21st to end	Night	26% 6% 12% 23% 20% 12%	2090
April	1st to 10th	Night	28% 7% 12% 22% 18% 13%	1820
	11th to 20th	Night	23% 6% 9% 21% 23% 18%	1779
	21st to end	Night	24% 6% 17% 20% 22% 11%	1800
May	1st to 10th	Night	26% 8% 15% 20% 19% 13%	1733
	11th to 20th	Night	28% 7% 14% 21% 19% 11%	1595
	21st to end	Night	25% 6% 14% 25% 22% 8%	1746
June	1st to 10th	Night	30% 7% 15% 16% 21% 11%	1620
	11th to 20th	Night	20% 5% 13% 13% 28% 19%	1494
	21st to end	Night	26% 3 13% 11% 20% 27%	1440
July	1st to 10th	Night	19% 2 14% 12% 20% 33%	1400
	11th to 20th	Night	19% 3 14% 19% 24% 22%	1477
	21st to end	Night	22% 5% 14% 22% 23% 13%	1823
August	1st to 10th	Night	17% 2 11% 13% 30% 26%	1780
	11th to 20th	Night	18% 2 10% 12% 31% 27%	1780
	21st to end	Night	15% 3 12% 13% 28% 29%	1980
September	1st to 10th	Night	21% 2 10% 10% 28% 30%	1800
	11th to 20th	Night	14% 3 10% 10% 28% 35%	1944
	21st to end	Night	15% 3 8% 13% 32% 29%	1980
October	1st to 10th	Night	19% 4 7% 18% 23% 29%	1980
	11th to 20th	Night	20% 3 8% 14% 23% 31%	2065
	21st to end	Night	18% 4 6% 11% 20% 42%	2421
November	1st to 10th	Night	18% 3 10% 15% 20% 34%	2405
	11th to 20th	Night	18% 3 8% 15% 17% 38%	2470
	21st to end	Night	25% 5% 7% 16% 17% 29%	2470
December	1st to 10th	Night	27% 5% 9% 13% 18% 27%	2470
	11th to 20th	Night	37% 5% 8% 14% 20% 16%	3041
	21st to end	Night	36% 8% 12% 18% 14% 12%	4521

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	12% 8% 22% 34% 21% 3	189
	11th to 20th	Day	12% 10% 25% 34% 16% 4	386
	21st to end	Day	9% 11% 31% 30% 16% 2	506
February	1st to 10th	Day	12% 10% 28% 30% 15% 5%	460
	11th to 20th	Day	10% 11% 32% 33% 11% 3	455
	21st to end	Day	10% 15% 29% 35% 10% 1	382
March	1st to 10th	Day	11% 15% 35% 28% 10% 2	460
	11th to 20th	Day	12% 11% 34% 29% 13% 2	460
	21st to end	Day	10% 16% 36% 28% 9% 2	506
April	1st to 10th	Day	8% 10% 34% 28% 17% 3	429
	11th to 20th	Day	6% 14% 40% 30% 7% 4	412
	21st to end	Day	5% 13% 30% 33% 13% 5%	420
May	1st to 10th	Day	6% 14% 33% 30% 13% 5%	423
	11th to 20th	Day	6% 8% 32% 38% 12% 4	448
	21st to end	Day	8% 10% 32% 32% 14% 3	485
June	1st to 10th	Day	4 4 26% 39% 20% 5%	450
	11th to 20th	Day	3 6% 23% 41% 20% 8%	450
	21st to end	Day	2 3 21% 44% 22% 9%	450
July	1st to 10th	Day	4 1 9% 49% 28% 9%	446
	11th to 20th	Day	1 7% 45% 29% 17%	444
	21st to end	Day	2 1 9% 46% 28% 15%	487
August	1st to 10th	Day	2 1 14% 46% 26% 11%	447
	11th to 20th	Day	2 1 8% 51% 25% 13%	437
	21st to end	Day	2 1 12% 47% 28% 11%	495
September	1st to 10th	Day	3 2 20% 47% 18% 11%	450
	11th to 20th	Day	2 3 23% 46% 18% 8%	450
	21st to end	Day	2 6% 22% 40% 22% 8%	450
October	1st to 10th	Day	4 8% 24% 38% 21% 5%	450
	11th to 20th	Day	6% 5% 27% 38% 20% 5%	450
	21st to end	Day	3 7% 23% 34% 24% 8%	447
November	1st to 10th	Day	6% 5% 18% 33% 31% 7%	270
	11th to 20th	Day	4 4 20% 36% 27% 9%	270
	21st to end	Day	6% 5% 24% 33% 24% 9%	270
December	1st to 10th	Day	9% 7% 16% 38% 26% 4	270
	11th to 20th	Day	5% 6% 19% 39% 24% 7%	270
	21st to end	Day	13% 11% 22% 36% 15% 3	297
January	1st to 10th	Night	10% 4 13% 42% 23% 8%	760
	11th to 20th	Night	8% 3 15% 40% 29% 6%	760
	21st to end	Night	13% 4 17% 35% 27% 4	836
February	1st to 10th	Night	10% 4 16% 37% 27% 7%	760
	11th to 20th	Night	9% 3 15% 41% 26% 6%	744
	21st to end	Night	11% 6% 17% 41% 22% 4	628
March	1st to 10th	Night	8% 4 18% 43% 24% 4	760
	11th to 20th	Night	10% 3 15% 38% 26% 8%	760
	21st to end	Night	8% 4 16% 40% 28% 4	836
April	1st to 10th	Night	9% 3 13% 42% 28% 5%	728
	11th to 20th	Night	6% 4 17% 39% 28% 6%	711
	21st to end	Night	7% 3 13% 38% 32% 7%	720
May	1st to 10th	Night	6% 4 16% 38% 33% 4	653
	11th to 20th	Night	6% 2 14% 35% 37% 6%	531
	21st to end	Night	5% 3 17% 40% 31% 5%	584
June	1st to 10th	Night	5% 2 14% 38% 37% 4	540
	11th to 20th	Night	3 3 7% 33% 48% 7%	414
	21st to end	Night	4 1 6% 27% 53% 9%	360
July	1st to 10th	Night	5% 3 12% 67% 14%	350
	11th to 20th	Night	2 1 19% 61% 16%	433
	21st to end	Night	3 1 2 23% 51% 20%	748
August	1st to 10th	Night	4 1 3 25% 50% 16%	716
	11th to 20th	Night	4 1 3 19% 53% 21%	712
	21st to end	Night	3 2 20% 53% 22%	792
September	1st to 10th	Night	4 1 4 23% 49% 18%	720
	11th to 20th	Night	3 1 5% 28% 51% 12%	720
	21st to end	Night	3 1 5% 31% 46% 14%	720
October	1st to 10th	Night	3 1 8% 38% 44% 7%	720
	11th to 20th	Night	5% 2 9% 34% 39% 11%	720
	21st to end	Night	4 3 10% 35% 37% 13%	792
November	1st to 10th	Night	5% 2 9% 37% 36% 12%	740
	11th to 20th	Night	3 1 8% 41% 35% 12%	760
	21st to end	Night	6% 3 13% 42% 30% 7%	760
December	1st to 10th	Night	8% 4 12% 42% 28% 6%	760
	11th to 20th	Night	14% 3 15% 37% 26% 5%	760
	21st to end	Night	10% 4 17% 39% 23% 6%	836

Page generated at 2024-03-31 03:08:56. Version ac07

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