Long Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Beach clear sky chart from 2005-11-06 to 2024-04-10.

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	5% 4 2 3 3 2 3 3 4 7% 61%	83795
	Night	6% 6% 2 4 4 2 4 4 5% 7% 56%	85062
Transparency	Day	16% 33% 7% 14% 16% 13%	83521
	Night	20% 33% 7% 13% 15% 13%	84857
Seeing	Day	6% 6% 22% 37% 23% 7%	14877
	Night	7% 3 10% 32% 36% 11%	24858

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 1 3 2 2 3 3 4 7% 66%	2539
	11th to 20th	Day	9% 5% 2 4 4 1 4 4 5% 8% 54%	2912
	21st to end	Day	13% 6% 3 4 3 3 3 3 4 6% 51%	3498
February	1st to 10th	Day	9% 5% 2 4 3 2 4 4 3 5% 60%	1900
	11th to 20th	Day	7% 3 1 3 3 3 3 3 6% 8% 60%	1850
	21st to end	Day	7% 5% 2 4 4 3 4 3 5% 7% 57%	1570
March	1st to 10th	Day	6% 4 2 4 5% 3 5% 6% 8% 9% 48%	3138
	11th to 20th	Day	4 3 2 3 3 2 3 4 6% 9% 59%	3280
	21st to end	Day	9% 5% 2 4 4 3 4 5% 5% 8% 52%	4165
April	1st to 10th	Day	5% 4 2 4 3 2 3 4 4 9% 60%	2270
	11th to 20th	Day	3 3 1 3 4 2 3 3 4 7% 67%	2129
	21st to end	Day	3 4 2 3 3 2 2 3 3 8% 67%	2160
May	1st to 10th	Day	4 4 2 3 4 2 3 4 5% 9% 60%	2200
	11th to 20th	Day	4 6% 3 4 2 2 2 3 3 8% 62%	2301
	21st to end	Day	5% 5% 2 4 3 2 3 3 4 7% 62%	2530
June	1st to 10th	Day	7% 6% 3 4 3 2 2 3 4 8% 58%	2340
	11th to 20th	Day	3 5% 2 3 3 1 2 3 3 7% 68%	2500
	21st to end	Day	3 6% 2 4 3 2 2 3 3 6% 66%	2520
July	1st to 10th	Day	4 5% 2 3 2 2 3 3 4 8% 65%	2520
	11th to 20th	Day	2 5% 1 3 3 2 3 3 4 8% 66%	2466
	21st to end	Day	2 3 2 3 3 2 4 3 6% 7% 66%	2352
August	1st to 10th	Day	2 3 2 3 2 1 2 2 3 7% 72%	2149
	11th to 20th	Day	2 3 1 2 2 1 2 3 3 8% 73%	2122
	21st to end	Day	2 3 1 3 2 2 3 3 4 7% 71%	2376
September	1st to 10th	Day	3 3 1 2 2 2 2 3 4 7% 71%	2160
	11th to 20th	Day	3 4 1 3 3 1 2 3 3 6% 71%	2029
	21st to end	Day	2 3 1 3 2 2 2 3 4 7% 72%	1980
October	1st to 10th	Day	4 3 2 2 3 2 3 3 4 6% 67%	1980
	11th to 20th	Day	4 3 1 3 2 2 3 3 3 6% 69%	1868
	21st to end	Day	2 3 2 3 2 1 2 4 6% 6% 68%	1954
November	1st to 10th	Day	2 3 2 3 3 2 3 4 3 7% 67%	1674
	11th to 20th	Day	4 4 1 2 3 1 3 3 4 6% 68%	1710
	21st to end	Day	6% 2 2 3 4 3 4 3 5% 8% 61%	1710
December	1st to 10th	Day	7% 6% 3 4 3 3 4 4 4 7% 56%	1710
	11th to 20th	Day	13% 6% 2 4 5% 3 4 4 6% 7% 46%	2169
	21st to end	Day	11% 8% 3 6% 5% 3 5% 4 5% 8% 43%	3064
January	1st to 10th	Night	6% 4 2 3 3 2 3 4 4 7% 62%	4406
	11th to 20th	Night	8% 7% 2 4 4 3 4 4 5% 9% 50%	4020
	21st to end	Night	12% 6% 2 4 4 3 4 5% 4 6% 49%	4180
February	1st to 10th	Night	7% 6% 3 5% 4 2 3 3 3 6% 58%	2280
	11th to 20th	Night	9% 5% 2 4 4 2 3 3 4 6% 58%	2218
	21st to end	Night	9% 5% 2 4 4 3 4 5% 4 5% 54%	1884
March	1st to 10th	Night	7% 5% 2 5% 5% 2 5% 5% 7% 11% 47%	3736
	11th to 20th	Night	5% 6% 2 5% 4 3 5% 5% 5% 8% 53%	3695
	21st to end	Night	7% 7% 2 4 4 3 4 4 5% 8% 51%	3488
April	1st to 10th	Night	8% 6% 3 4 3 2 3 3 5% 9% 54%	1900
	11th to 20th	Night	5% 6% 2 4 3 2 3 3 4 6% 63%	1779
	21st to end	Night	5% 8% 4 4 4 2 3 4 5% 6% 56%	1800
May	1st to 10th	Night	7% 7% 2 4 4 3 3 4 5% 8% 53%	1759
	11th to 20th	Night	6% 9% 3 4 3 3 3 2 5% 7% 55%	1594
	21st to end	Night	5% 7% 2 4 3 2 2 2 4 8% 61%	1746
June	1st to 10th	Night	5% 10% 3 5% 4 2 4 4 6% 8% 49%	1620
	11th to 20th	Night	4 6% 3 3 3 2 2 3 5% 8% 59%	1454
	21st to end	Night	4 11% 4 5% 6% 2 4 4 5% 8% 48%	1440
July	1st to 10th	Night	4 6% 2 4 3 2 4 4 5% 9% 56%	1440
	11th to 20th	Night	3 5% 2 4 4 3 4 5% 4 11% 55%	1489
	21st to end	Night	4 6% 3 5% 4 2 4 4 5% 9% 53%	1962
August	1st to 10th	Night	4 5% 2 3 3 2 4 5% 4 8% 60%	1790
	11th to 20th	Night	4 7% 2 4 3 2 3 4 4 9% 58%	1780
	21st to end	Night	2 6% 2 4 4 2 4 5% 5% 7% 60%	1980
September	1st to 10th	Night	4 6% 3 6% 3 2 3 4 4 7% 59%	1800
	11th to 20th	Night	3 4 2 3 4 2 3 4 5% 7% 64%	1930
	21st to end	Night	2 6% 3 3 3 2 2 2 4 7% 67%	1980
October	1st to 10th	Night	3 4 2 4 3 2 4 4 4 6% 66%	1980
	11th to 20th	Night	5% 6% 2 4 3 2 3 2 4 5% 64%	2088
	21st to end	Night	3 4 2 3 2 2 3 3 4 7% 68%	2401
November	1st to 10th	Night	3 5% 2 3 3 2 3 3 4 7% 64%	2405
	11th to 20th	Night	3 5% 1 3 3 2 3 3 4 8% 66%	2470
	21st to end	Night	5% 5% 2 3 4 2 4 4 5% 8% 57%	2470
December	1st to 10th	Night	7% 6% 2 5% 5% 3 4 4 4 6% 55%	2470
	11th to 20th	Night	14% 7% 3 4 5% 2 4 3 5% 7% 45%	3041
	21st to end	Night	13% 6% 2 6% 6% 3 5% 5% 5% 6% 43%	4587

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	11% 24% 5% 23% 23% 13%	2539
	11th to 20th	Day	22% 28% 13% 12% 12% 12%	2912
	21st to end	Day	28% 23% 6% 15% 18% 10%	3498
February	1st to 10th	Day	18% 34% 4 11% 17% 16%	1900
	11th to 20th	Day	17% 36% 7% 14% 16% 10%	1860
	21st to end	Day	19% 35% 7% 14% 14% 12%	1570
March	1st to 10th	Day	18% 27% 10% 24% 12% 10%	3138
	11th to 20th	Day	15% 25% 14% 27% 11% 9%	3280
	21st to end	Day	23% 26% 13% 23% 10% 5%	4165
April	1st to 10th	Day	16% 35% 10% 18% 14% 8%	2270
	11th to 20th	Day	14% 36% 7% 18% 16% 9%	2132
	21st to end	Day	13% 37% 5% 17% 20% 8%	2160
May	1st to 10th	Day	13% 37% 8% 15% 17% 10%	2200
	11th to 20th	Day	16% 37% 5% 16% 20% 6%	2304
	21st to end	Day	13% 38% 6% 19% 19% 5%	2530
June	1st to 10th	Day	19% 38% 7% 13% 17% 6%	2340
	11th to 20th	Day	13% 36% 5% 9% 22% 14%	2500
	21st to end	Day	15% 35% 3 6% 17% 23%	2520
July	1st to 10th	Day	14% 36% 5% 6% 14% 25%	2451
	11th to 20th	Day	12% 37% 4 12% 19% 15%	2391
	21st to end	Day	13% 38% 6% 14% 20% 9%	2221
August	1st to 10th	Day	10% 35% 4 12% 20% 20%	2135
	11th to 20th	Day	12% 34% 4 13% 21% 17%	2122
	21st to end	Day	10% 36% 4 8% 22% 20%	2376
September	1st to 10th	Day	13% 35% 4 6% 20% 22%	2160
	11th to 20th	Day	12% 35% 5% 9% 20% 19%	2029
	21st to end	Day	11% 36% 4 12% 18% 19%	1980
October	1st to 10th	Day	16% 36% 6% 14% 15% 14%	1980
	11th to 20th	Day	13% 36% 5% 11% 16% 20%	1868
	21st to end	Day	12% 38% 4 9% 13% 23%	1954
November	1st to 10th	Day	15% 41% 4 13% 12% 15%	1674
	11th to 20th	Day	11% 38% 4 11% 12% 23%	1710
	21st to end	Day	14% 39% 6% 7% 15% 18%	1710
December	1st to 10th	Day	16% 40% 5% 11% 13% 15%	1710
	11th to 20th	Day	29% 34% 7% 11% 12% 8%	2168
	21st to end	Day	34% 29% 10% 14% 9% 5%	3064
January	1st to 10th	Night	16% 25% 6% 13% 26% 15%	4406
	11th to 20th	Night	22% 28% 11% 16% 10% 13%	4020
	21st to end	Night	28% 25% 7% 13% 16% 11%	4180
February	1st to 10th	Night	20% 34% 5% 10% 14% 18%	2280
	11th to 20th	Night	19% 36% 6% 13% 14% 12%	2219
	21st to end	Night	22% 35% 5% 11% 13% 14%	1884
March	1st to 10th	Night	21% 26% 9% 21% 15% 7%	3736
	11th to 20th	Night	19% 27% 12% 23% 10% 9%	3695
	21st to end	Night	22% 27% 12% 19% 15% 5%	3488
April	1st to 10th	Night	19% 35% 7% 18% 12% 8%	1900
	11th to 20th	Night	17% 36% 7% 17% 13% 10%	1779
	21st to end	Night	24% 37% 6% 12% 15% 6%	1800
May	1st to 10th	Night	21% 37% 7% 13% 14% 8%	1759
	11th to 20th	Night	25% 37% 4 14% 14% 7%	1595
	21st to end	Night	15% 38% 7% 18% 17% 5%	1746
June	1st to 10th	Night	26% 38% 8% 9% 13% 5%	1620
	11th to 20th	Night	20% 36% 7% 9% 20% 9%	1454
	21st to end	Night	23% 36% 5% 5% 15% 16%	1440
July	1st to 10th	Night	15% 37% 6% 6% 14% 21%	1400
	11th to 20th	Night	16% 37% 5% 10% 18% 14%	1441
	21st to end	Night	18% 38% 9% 15% 13% 8%	1853
August	1st to 10th	Night	17% 35% 5% 10% 18% 14%	1780
	11th to 20th	Night	18% 35% 5% 10% 19% 14%	1780
	21st to end	Night	16% 36% 6% 7% 16% 19%	1980
September	1st to 10th	Night	15% 36% 6% 4 17% 21%	1800
	11th to 20th	Night	14% 36% 5% 8% 18% 20%	1930
	21st to end	Night	16% 35% 4 9% 18% 18%	1980
October	1st to 10th	Night	16% 36% 5% 11% 16% 16%	1980
	11th to 20th	Night	17% 36% 4 8% 15% 20%	2088
	21st to end	Night	13% 36% 4 7% 15% 25%	2401
November	1st to 10th	Night	16% 41% 4 10% 11% 17%	2405
	11th to 20th	Night	12% 38% 4 9% 14% 23%	2470
	21st to end	Night	17% 40% 5% 9% 11% 19%	2470
December	1st to 10th	Night	18% 40% 4 8% 12% 17%	2470
	11th to 20th	Night	30% 33% 6% 10% 14% 7%	3041
	21st to end	Night	31% 30% 10% 15% 9% 6%	4587

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% 4 16% 42% 20% 5%	180
	11th to 20th	Day	11% 5% 24% 36% 19% 4	377
	21st to end	Day	10% 7% 27% 35% 18% 3	506
February	1st to 10th	Day	11% 7% 28% 29% 19% 6%	460
	11th to 20th	Day	8% 10% 30% 30% 18% 3	455
	21st to end	Day	8% 12% 29% 36% 13% 2	382
March	1st to 10th	Day	12% 11% 32% 30% 13% 2	460
	11th to 20th	Day	9% 11% 28% 33% 15% 3	460
	21st to end	Day	8% 15% 31% 33% 12% 2	506
April	1st to 10th	Day	7% 11% 30% 30% 17% 5%	457
	11th to 20th	Day	3 14% 35% 33% 10% 4	412
	21st to end	Day	4 10% 30% 35% 15% 5%	420
May	1st to 10th	Day	3 11% 31% 36% 13% 5%	423
	11th to 20th	Day	4 8% 29% 40% 15% 5%	448
	21st to end	Day	6% 8% 31% 35% 16% 3	485
June	1st to 10th	Day	7% 4 22% 37% 26% 4	450
	11th to 20th	Day	4 2 23% 39% 24% 7%	450
	21st to end	Day	4 2 17% 43% 27% 8%	450
July	1st to 10th	Day	3 9% 46% 33% 9%	446
	11th to 20th	Day	2 6% 39% 36% 16%	444
	21st to end	Day	1 9% 42% 32% 15%	487
August	1st to 10th	Day	2 1 11% 44% 31% 11%	447
	11th to 20th	Day	3 1 8% 44% 34% 11%	437
	21st to end	Day	3 2 11% 40% 35% 9%	495
September	1st to 10th	Day	3 2 16% 45% 24% 10%	450
	11th to 20th	Day	4 2 20% 44% 24% 7%	450
	21st to end	Day	2 5% 20% 39% 25% 9%	450
October	1st to 10th	Day	3 5% 24% 38% 24% 6%	450
	11th to 20th	Day	5% 3 24% 39% 22% 7%	450
	21st to end	Day	4 6% 19% 36% 27% 9%	469
November	1st to 10th	Day	5% 5% 14% 33% 32% 11%	270
	11th to 20th	Day	5% 3 16% 36% 31% 10%	270
	21st to end	Day	3 4 18% 37% 28% 9%	270
December	1st to 10th	Day	8% 3 17% 38% 28% 6%	270
	11th to 20th	Day	6% 5% 14% 37% 28% 10%	270
	21st to end	Day	11% 8% 23% 32% 23% 3	271
January	1st to 10th	Night	10% 3 12% 40% 29% 6%	760
	11th to 20th	Night	7% 3 14% 39% 31% 6%	760
	21st to end	Night	11% 3 17% 39% 27% 5%	836
February	1st to 10th	Night	10% 4 14% 36% 30% 6%	760
	11th to 20th	Night	9% 4 15% 38% 28% 5%	744
	21st to end	Night	11% 5% 14% 43% 23% 4	628
March	1st to 10th	Night	9% 5% 16% 43% 23% 4	760
	11th to 20th	Night	10% 3 13% 39% 27% 8%	760
	21st to end	Night	8% 5% 16% 39% 29% 4	836
April	1st to 10th	Night	9% 6% 12% 39% 29% 5%	760
	11th to 20th	Night	7% 5% 14% 36% 32% 6%	711
	21st to end	Night	7% 4 12% 34% 34% 8%	720
May	1st to 10th	Night	9% 3 13% 35% 34% 7%	679
	11th to 20th	Night	7% 3 15% 32% 36% 8%	531
	21st to end	Night	6% 2 14% 36% 34% 7%	584
June	1st to 10th	Night	6% 4 10% 36% 37% 6%	540
	11th to 20th	Night	5% 3 4 21% 51% 16%	374
	21st to end	Night	8% 3 5% 23% 48% 14%	360
July	1st to 10th	Night	5% 1 3 8% 59% 25%	350
	11th to 20th	Night	4 1 2 12% 49% 33%	397
	21st to end	Night	6% 1 2 18% 47% 27%	780
August	1st to 10th	Night	4 1 3 22% 48% 22%	716
	11th to 20th	Night	8% 1 2 13% 47% 28%	712
	21st to end	Night	5% 1 2 15% 50% 27%	792
September	1st to 10th	Night	6% 1 5% 20% 46% 22%	720
	11th to 20th	Night	5% 1 3 25% 52% 14%	720
	21st to end	Night	5% 1 6% 23% 50% 15%	720
October	1st to 10th	Night	5% 1 7% 32% 46% 9%	720
	11th to 20th	Night	7% 2 7% 30% 42% 11%	720
	21st to end	Night	4 3 8% 33% 38% 14%	792
November	1st to 10th	Night	4 3 10% 32% 39% 12%	740
	11th to 20th	Night	4 1 6% 38% 37% 13%	760
	21st to end	Night	6% 3 12% 41% 32% 6%	760
December	1st to 10th	Night	9% 2 12% 41% 31% 6%	760
	11th to 20th	Night	15% 3 11% 39% 27% 5%	760
	21st to end	Night	10% 4 17% 39% 24% 6%	836

Page generated at 2024-04-07 06:28:13. Version ac07

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