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 2024-11-10.

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	25% 12% 3 8% 5% 4 4 3 5% 6% 24%	105649
	Night	27% 14% 3 8% 4 4 4 3 4 5% 24%	102095
Transparency	Day	31% 49% 6% 8% 5% 1	105405
	Night	34% 48% 6% 8% 4 1	101985
Seeing	Day	28% 6% 19% 26% 17% 3	15413
	Night	34% 7% 15% 22% 18% 4	23716

By Month

Percentage Cloud Cover NW (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	39% 13% 3 11% 7% 5% 4 3 3 3 9%	2219
	11th to 20th	Day	37% 12% 3 7% 4 4 3 2 2 3 21%	2402
	21st to end	Day	45% 13% 3 9% 4 3 3 2 3 3 12%	3112
February	1st to 10th	Day	38% 11% 3 8% 5% 4 4 3 4 5% 15%	1710
	11th to 20th	Day	35% 12% 4 7% 4 4 3 4 4 3 20%	1665
	21st to end	Day	32% 15% 3 8% 5% 5% 4 3 4 5% 15%	1420
March	1st to 10th	Day	22% 16% 4 9% 6% 6% 4 3 6% 7% 17%	3380
	11th to 20th	Day	25% 11% 3 7% 4 4 3 2 4 6% 31%	3490
	21st to end	Day	27% 14% 4 9% 6% 6% 5% 4 4 4 16%	3838
April	1st to 10th	Day	32% 14% 4 8% 6% 4 5% 4 5% 6% 13%	2280
	11th to 20th	Day	29% 12% 3 7% 5% 4 4 3 4 6% 22%	2340
	21st to end	Day	27% 11% 4 9% 6% 5% 5% 4 5% 7% 18%	2470
May	1st to 10th	Day	22% 10% 3 6% 4 4 4 3 5% 6% 33%	4291
	11th to 20th	Day	16% 15% 5% 9% 5% 5% 5% 4 6% 7% 22%	4377
	21st to end	Day	30% 11% 3 8% 5% 5% 5% 4 5% 7% 17%	4813
June	1st to 10th	Day	30% 13% 3 8% 5% 4 4 4 4 6% 20%	2750
	11th to 20th	Day	27% 14% 4 8% 6% 4 4 4 6% 6% 17%	2850
	21st to end	Day	19% 12% 3 8% 6% 4 4 4 6% 6% 27%	2850
July	1st to 10th	Day	12% 13% 3 6% 3 3 4 3 5% 7% 41%	4740
	11th to 20th	Day	11% 16% 3 7% 4 4 5% 4 6% 9% 31%	4622
	21st to end	Day	19% 16% 3 7% 4 4 4 3 5% 8% 27%	4763
August	1st to 10th	Day	12% 17% 4 10% 5% 5% 5% 4 5% 8% 25%	4092
	11th to 20th	Day	16% 13% 4 9% 6% 5% 5% 5% 6% 8% 24%	4026
	21st to end	Day	16% 10% 3 8% 5% 4 4 3 5% 7% 33%	4411
September	1st to 10th	Day	13% 10% 3 7% 4 3 4 3 6% 9% 38%	2280
	11th to 20th	Day	17% 10% 4 8% 5% 5% 4 4 6% 9% 28%	2209
	21st to end	Day	21% 7% 2 7% 4 4 5% 3 5% 6% 36%	2043
October	1st to 10th	Day	19% 7% 2 5% 3 3 3 3 5% 8% 41%	3180
	11th to 20th	Day	32% 9% 3 9% 4 4 4 2 4 6% 23%	3161
	21st to end	Day	23% 8% 3 8% 5% 6% 5% 4 6% 8% 25%	3410
November	1st to 10th	Day	37% 11% 3 9% 4 5% 4 3 4 5% 15%	1560
	11th to 20th	Day	37% 9% 3 7% 4 3 3 3 5% 6% 19%	1520
	21st to end	Day	38% 10% 3 7% 4 3 4 2 3 4 23%	1520
December	1st to 10th	Day	31% 11% 3 7% 5% 4 4 3 3 5% 24%	1520
	11th to 20th	Day	37% 11% 3 7% 6% 4 4 4 4 5% 15%	1893
	21st to end	Day	33% 17% 4 10% 5% 4 4 2 3 4 14%	2442
January	1st to 10th	Night	36% 15% 4 11% 6% 5% 4 3 3 3 10%	4726
	11th to 20th	Night	34% 14% 3 8% 4 4 3 3 4 5% 18%	4479
	21st to end	Night	47% 13% 3 7% 3 3 3 2 2 3 13%	4552
February	1st to 10th	Night	34% 13% 4 9% 5% 5% 3 3 4 5% 15%	2470
	11th to 20th	Night	32% 15% 4 8% 5% 3 3 2 4 4 20%	2402
	21st to end	Night	31% 14% 3 9% 5% 4 4 3 4 5% 17%	2032
March	1st to 10th	Night	27% 15% 4 8% 5% 5% 5% 5% 6% 6% 14%	3490
	11th to 20th	Night	22% 13% 3 6% 4 4 3 3 5% 6% 31%	3489
	21st to end	Night	29% 20% 3 9% 5% 4 4 3 4 4 15%	3814
April	1st to 10th	Night	30% 16% 4 10% 5% 4 3 3 5% 5% 16%	1900
	11th to 20th	Night	26% 14% 4 9% 5% 4 4 3 5% 5% 22%	1786
	21st to end	Night	28% 15% 4 8% 5% 4 4 4 5% 6% 17%	1710
May	1st to 10th	Night	28% 10% 2 5% 3 2 2 2 4 5% 36%	2673
	11th to 20th	Night	18% 21% 3 7% 6% 5% 4 4 4 5% 23%	2516
	21st to end	Night	22% 17% 4 9% 6% 5% 6% 4 5% 6% 19%	2762
June	1st to 10th	Night	27% 14% 4 6% 4 4 4 3 4 7% 22%	1425
	11th to 20th	Night	26% 17% 4 8% 5% 5% 4 3 5% 5% 18%	1330
	21st to end	Night	21% 16% 2 7% 3 3 4 3 4 4 32%	1330
July	1st to 10th	Night	12% 17% 2 4 2 2 2 2 2 5% 48%	2220
	11th to 20th	Night	11% 23% 4 8% 3 3 4 3 4 5% 32%	2338
	21st to end	Night	20% 22% 3 4 2 2 3 2 3 4 35%	2786
August	1st to 10th	Night	14% 31% 4 8% 3 2 2 3 3 6% 24%	2848
	11th to 20th	Night	18% 16% 3 7% 4 3 3 3 5% 6% 31%	2812
	21st to end	Night	21% 9% 3 6% 3 3 3 2 4 6% 40%	3260
September	1st to 10th	Night	14% 11% 3 5% 3 3 2 3 4 7% 44%	1900
	11th to 20th	Night	18% 13% 4 8% 5% 4 4 4 4 6% 32%	1968
	21st to end	Night	21% 10% 2 6% 3 3 3 3 3 6% 38%	2137
October	1st to 10th	Night	17% 7% 3 6% 4 3 4 4 5% 9% 39%	3800
	11th to 20th	Night	28% 11% 3 8% 4 4 4 3 4 6% 25%	3777
	21st to end	Night	26% 9% 3 7% 5% 5% 5% 4 5% 6% 25%	4153
November	1st to 10th	Night	36% 9% 3 7% 5% 5% 4 3 5% 5% 18%	2722
	11th to 20th	Night	35% 10% 3 7% 5% 4 4 4 3 4 20%	2660
	21st to end	Night	30% 11% 3 8% 5% 4 4 2 4 5% 24%	2660
December	1st to 10th	Night	30% 12% 3 8% 4 3 3 3 5% 5% 23%	2660
	11th to 20th	Night	34% 13% 4 8% 5% 4 3 3 3 4 18%	3294
	21st to end	Night	36% 16% 4 10% 5% 4 3 3 3 4 12%	5214

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	48% 42% 5% 2 3 1	2219
	11th to 20th	Day	47% 38% 4 9% 2	2426
	21st to end	Day	53% 41% 3 2 1	3112
February	1st to 10th	Day	27% 66% 3 3 1	1710
	11th to 20th	Day	29% 65% 2 3 1	1674
	21st to end	Day	25% 66% 3 2 4	1420
March	1st to 10th	Day	33% 47% 11% 6% 2	3380
	11th to 20th	Day	28% 43% 7% 15% 7%	3490
	21st to end	Day	37% 47% 9% 6% 1	3838
April	1st to 10th	Day	26% 67% 4 3	2280
	11th to 20th	Day	23% 67% 3 4 2	2340
	21st to end	Day	23% 67% 4 5% 1	2470
May	1st to 10th	Day	26% 44% 13% 9% 8%	4291
	11th to 20th	Day	28% 50% 11% 8% 3	4380
	21st to end	Day	37% 49% 11% 3 1	4814
June	1st to 10th	Day	21% 66% 6% 4 2	2750
	11th to 20th	Day	21% 67% 4 7% 2	2850
	21st to end	Day	22% 66% 5% 5% 2	2850
July	1st to 10th	Day	23% 37% 2 6% 17% 14%	4666
	11th to 20th	Day	27% 39% 6% 14% 14%	4541
	21st to end	Day	37% 37% 6% 18% 2	4612
August	1st to 10th	Day	32% 41% 5% 14% 8% 1	4076
	11th to 20th	Day	39% 41% 9% 7% 3 1	4065
	21st to end	Day	30% 38% 8% 12% 12%	4410
September	1st to 10th	Day	21% 61% 6% 7% 4 1	2280
	11th to 20th	Day	21% 61% 4 5% 6% 1	2209
	21st to end	Day	17% 62% 7% 9% 5%	2043
October	1st to 10th	Day	24% 38% 8% 25% 6%	3180
	11th to 20th	Day	43% 39% 4 9% 5%	3161
	21st to end	Day	36% 39% 9% 9% 7% 1	3410
November	1st to 10th	Day	32% 57% 3 6% 1	1560
	11th to 20th	Day	25% 62% 4 4 3 2	1520
	21st to end	Day	25% 60% 1 4 9% 2	1520
December	1st to 10th	Day	27% 61% 3 4 5% 1	1520
	11th to 20th	Day	36% 50% 7% 4 3	1896
	21st to end	Day	46% 40% 8% 4 2	2442
January	1st to 10th	Night	50% 41% 3 3 2 1	4726
	11th to 20th	Night	44% 40% 5% 9% 2	4517
	21st to end	Night	53% 41% 2 3 1	4552
February	1st to 10th	Night	27% 66% 3 3 1	2470
	11th to 20th	Night	29% 64% 2 3 2	2404
	21st to end	Night	22% 66% 4 4 2	2032
March	1st to 10th	Night	33% 48% 10% 7% 1	3490
	11th to 20th	Night	25% 44% 8% 17% 6% 1	3490
	21st to end	Night	43% 44% 6% 6% 1	3814
April	1st to 10th	Night	26% 66% 4 3 1	1900
	11th to 20th	Night	23% 66% 4 5% 3	1786
	21st to end	Night	23% 65% 4 5% 2	1710
May	1st to 10th	Night	26% 43% 11% 14% 6%	2673
	11th to 20th	Night	36% 44% 9% 5% 6%	2516
	21st to end	Night	36% 49% 11% 3 1	2762
June	1st to 10th	Night	21% 67% 6% 6% 1	1425
	11th to 20th	Night	21% 65% 4 8% 1	1330
	21st to end	Night	23% 65% 6% 5% 1	1330
July	1st to 10th	Night	24% 35% 3 6% 17% 15%	2185
	11th to 20th	Night	35% 35% 5% 13% 11%	2296
	21st to end	Night	36% 35% 4 20% 4 1	2698
August	1st to 10th	Night	42% 37% 4 11% 4 1	2839
	11th to 20th	Night	38% 39% 11% 8% 3 2	2839
	21st to end	Night	30% 37% 8% 13% 11% 1	3260
September	1st to 10th	Night	19% 61% 4 10% 4 2	1900
	11th to 20th	Night	23% 61% 4 5% 5% 2	1968
	21st to end	Night	18% 60% 4 10% 7% 1	2137
October	1st to 10th	Night	23% 38% 10% 25% 4	3800
	11th to 20th	Night	43% 37% 6% 10% 4	3777
	21st to end	Night	38% 38% 6% 9% 7% 1	4153
November	1st to 10th	Night	32% 57% 5% 5% 2	2722
	11th to 20th	Night	27% 61% 3 4 3 2	2660
	21st to end	Night	25% 60% 2 2 9% 2	2660
December	1st to 10th	Night	28% 60% 3 4 4 1	2660
	11th to 20th	Night	35% 52% 5% 5% 3	3290
	21st to end	Night	44% 44% 6% 5% 1	5214

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	40% 19% 21% 13% 6% 2	180
	11th to 20th	Day	43% 9% 23% 14% 8% 2	180
	21st to end	Day	41% 6% 17% 20% 13% 2	386
February	1st to 10th	Day	44% 10% 15% 19% 11% 1	370
	11th to 20th	Day	42% 8% 22% 18% 10% 1	365
	21st to end	Day	30% 12% 27% 21% 9% 1	312
March	1st to 10th	Day	34% 12% 20% 20% 13%	460
	11th to 20th	Day	32% 7% 23% 22% 12% 4	460
	21st to end	Day	34% 11% 22% 20% 11% 2	506
April	1st to 10th	Day	35% 11% 18% 24% 10% 2	460
	11th to 20th	Day	32% 7% 26% 22% 9% 5%	452
	21st to end	Day	32% 4 27% 23% 13% 1	460
May	1st to 10th	Day	24% 6% 25% 28% 14% 3	463
	11th to 20th	Day	31% 7% 18% 27% 15% 2	488
	21st to end	Day	31% 6% 18% 29% 13% 3	529
June	1st to 10th	Day	32% 3 18% 30% 15% 2	580
	11th to 20th	Day	26% 5% 26% 31% 11% 1	680
	21st to end	Day	20% 4 19% 36% 19% 3	680
July	1st to 10th	Day	23% 4 16% 33% 22% 2	671
	11th to 20th	Day	19% 3 17% 33% 25% 3	602
	21st to end	Day	18% 4 14% 37% 23% 4	531
August	1st to 10th	Day	19% 4 14% 35% 24% 5%	487
	11th to 20th	Day	17% 3 11% 27% 34% 8%	477
	21st to end	Day	18% 3 20% 34% 22% 3	539
September	1st to 10th	Day	18% 5% 17% 33% 24% 3	490
	11th to 20th	Day	20% 4 18% 30% 24% 5%	490
	21st to end	Day	22% 3 19% 27% 23% 5%	490
October	1st to 10th	Day	26% 5% 16% 25% 24% 4	490
	11th to 20th	Day	31% 7% 18% 21% 19% 5%	490
	21st to end	Day	29% 10% 22% 22% 13% 4	529
November	1st to 10th	Day	36% 10% 26% 16% 9% 3	198
	11th to 20th	Day	39% 6% 14% 26% 13% 2	180
	21st to end	Day	37% 12% 17% 17% 13% 4	180
December	1st to 10th	Day	37% 14% 18% 17% 12% 2	180
	11th to 20th	Day	42% 12% 17% 22% 7% 1	180
	21st to end	Day	41% 11% 24% 18% 6% 1	198
January	1st to 10th	Night	46% 13% 18% 14% 7% 2	850
	11th to 20th	Night	44% 7% 14% 18% 15% 2	787
	21st to end	Night	41% 7% 14% 22% 13% 3	836
February	1st to 10th	Night	38% 9% 18% 22% 11% 2	760
	11th to 20th	Night	37% 10% 16% 23% 13% 1	744
	21st to end	Night	37% 10% 21% 22% 10% 1	628
March	1st to 10th	Night	37% 9% 16% 21% 15% 2	760
	11th to 20th	Night	37% 8% 16% 23% 14% 2	760
	21st to end	Night	39% 8% 17% 19% 13% 3	836
April	1st to 10th	Night	36% 8% 17% 22% 15% 2	760
	11th to 20th	Night	31% 5% 20% 29% 12% 3	658
	21st to end	Night	34% 6% 16% 24% 16% 3	570
May	1st to 10th	Night	30% 4 17% 26% 18% 4	461
	11th to 20th	Night	33% 5% 10% 23% 26% 3	374
	21st to end	Night	33% 7% 15% 21% 20% 5%	411
June	1st to 10th	Night	33% 3 11% 27% 24% 3	380
	11th to 20th	Night	32% 5% 17% 29% 14% 3	380
	21st to end	Night	31% 3 10% 23% 28% 5%	380
July	1st to 10th	Night	28% 2 8% 22% 34% 7%	370
	11th to 20th	Night	26% 2 10% 26% 30% 5%	368
	21st to end	Night	24% 3 12% 23% 32% 6%	428
August	1st to 10th	Night	37% 2 8% 16% 27% 10%	567
	11th to 20th	Night	23% 2 6% 20% 36% 14%	564
	21st to end	Night	26% 2 11% 26% 28% 6%	689
September	1st to 10th	Night	20% 2 10% 25% 36% 6%	760
	11th to 20th	Night	23% 3 12% 23% 29% 11%	760
	21st to end	Night	25% 4 13% 29% 25% 3	760
October	1st to 10th	Night	23% 4 14% 24% 29% 5%	760
	11th to 20th	Night	29% 5% 12% 27% 22% 5%	760
	21st to end	Night	33% 5% 19% 24% 17% 2	836
November	1st to 10th	Night	39% 8% 17% 22% 13% 1	778
	11th to 20th	Night	37% 9% 21% 21% 12% 1	760
	21st to end	Night	34% 10% 17% 24% 14% 2	760
December	1st to 10th	Night	33% 10% 18% 24% 13% 2	760
	11th to 20th	Night	42% 9% 19% 19% 10% 1	766
	21st to end	Night	48% 12% 18% 14% 7% 1	935

Page generated at 2024-11-07 03:55:49. Version ac07

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