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 2024-01-13.

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	27% 11% 4 7% 6% 3 4 4 5% 6% 23%	74828
	Night	29% 12% 4 7% 5% 3 4 4 4 5% 23%	74890
Transparency	Day	40% 40% 8% 7% 4 1	74521
	Night	41% 39% 7% 7% 4 1	74715
Seeing	Day	29% 6% 19% 26% 17% 3	14240
	Night	34% 6% 15% 22% 18% 4	22726

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	45% 11% 3 8% 6% 3 3 3 2 2 13%	1329
	11th to 20th	Day	37% 12% 3 7% 5% 3 4 3 3 4 21%	1396
	21st to end	Day	34% 11% 3 7% 5% 3 4 3 4 4 21%	1762
February	1st to 10th	Day	39% 11% 3 7% 5% 3 4 4 4 5% 14%	1620
	11th to 20th	Day	35% 11% 4 7% 5% 3 4 4 4 3 21%	1575
	21st to end	Day	32% 14% 4 7% 6% 4 5% 4 4 5% 15%	1338
March	1st to 10th	Day	35% 12% 4 6% 5% 3 4 3 4 5% 18%	1940
	11th to 20th	Day	36% 11% 4 7% 5% 3 4 3 4 5% 18%	1980
	21st to end	Day	35% 12% 5% 7% 7% 4 5% 5% 4 4 12%	2179
April	1st to 10th	Day	33% 12% 4 7% 6% 3 5% 4 5% 6% 13%	2160
	11th to 20th	Day	31% 11% 4 6% 6% 3 4 4 4 6% 20%	2215
	21st to end	Day	27% 10% 4 8% 6% 4 5% 4 5% 7% 18%	2340
May	1st to 10th	Day	23% 10% 4 7% 6% 3 5% 4 5% 6% 27%	2443
	11th to 20th	Day	25% 11% 4 8% 6% 4 5% 4 5% 8% 20%	2477
	21st to end	Day	29% 13% 4 8% 7% 4 5% 5% 4 6% 16%	2723
June	1st to 10th	Day	30% 12% 4 7% 5% 3 4 4 4 6% 20%	2605
	11th to 20th	Day	28% 13% 5% 7% 7% 3 5% 5% 5% 6% 16%	2700
	21st to end	Day	20% 12% 3 7% 7% 3 5% 5% 5% 7% 28%	2700
July	1st to 10th	Day	19% 14% 4 6% 5% 3 4 4 6% 7% 28%	2700
	11th to 20th	Day	18% 14% 3 6% 5% 3 4 4 5% 8% 30%	2638
	21st to end	Day	15% 13% 4 7% 6% 3 3 4 6% 9% 30%	2726
August	1st to 10th	Day	19% 14% 5% 7% 6% 3 4 5% 5% 9% 25%	2328
	11th to 20th	Day	14% 10% 3 7% 5% 2 5% 5% 5% 10% 35%	2298
	21st to end	Day	17% 11% 3 8% 6% 3 5% 5% 5% 8% 28%	2516
September	1st to 10th	Day	13% 9% 3 6% 5% 3 4 4 6% 9% 39%	2160
	11th to 20th	Day	17% 9% 4 8% 6% 3 4 5% 6% 9% 29%	2093
	21st to end	Day	22% 7% 3 6% 4 3 5% 4 5% 6% 36%	1936
October	1st to 10th	Day	25% 8% 3 6% 5% 3 4 4 4 6% 32%	1800
	11th to 20th	Day	27% 7% 4 7% 5% 3 4 4 4 7% 29%	1800
	21st to end	Day	30% 9% 3 5% 4 3 4 4 4 5% 27%	1968
November	1st to 10th	Day	38% 10% 3 8% 5% 3 5% 4 4 5% 15%	1488
	11th to 20th	Day	37% 9% 3 6% 5% 3 4 4 5% 6% 19%	1520
	21st to end	Day	38% 9% 3 6% 5% 2 4 4 3 4 23%	1520
December	1st to 10th	Day	31% 10% 4 6% 5% 3 4 4 4 5% 24%	1520
	11th to 20th	Day	37% 10% 3 6% 7% 3 4 4 4 5% 15%	1893
	21st to end	Day	33% 16% 4 9% 6% 3 4 3 3 4 14%	2442
January	1st to 10th	Night	43% 11% 3 7% 5% 3 4 4 3 3 14%	2836
	11th to 20th	Night	39% 12% 3 6% 4 3 4 3 4 4 16%	2605
	21st to end	Night	34% 12% 4 7% 5% 3 4 3 3 4 22%	2592
February	1st to 10th	Night	34% 12% 5% 8% 6% 4 3 4 4 4 16%	2340
	11th to 20th	Night	32% 14% 4 7% 6% 3 3 3 4 5% 21%	2272
	21st to end	Night	32% 13% 4 8% 6% 3 4 3 4 5% 18%	1916
March	1st to 10th	Night	34% 13% 3 6% 5% 3 3 4 4 6% 18%	2016
	11th to 20th	Night	34% 12% 4 6% 5% 3 4 3 4 5% 19%	1979
	21st to end	Night	35% 13% 4 7% 6% 3 5% 5% 4 4 14%	2176
April	1st to 10th	Night	31% 15% 5% 9% 6% 2 4 3 4 5% 16%	1800
	11th to 20th	Night	27% 13% 5% 7% 6% 3 5% 4 5% 6% 20%	1691
	21st to end	Night	28% 14% 5% 6% 6% 3 4 5% 5% 6% 17%	1620
May	1st to 10th	Night	25% 14% 3 6% 5% 2 3 3 4 6% 27%	1517
	11th to 20th	Night	29% 12% 4 6% 6% 3 5% 5% 5% 6% 20%	1416
	21st to end	Night	27% 17% 4 6% 5% 3 4 5% 5% 7% 17%	1552
June	1st to 10th	Night	27% 13% 5% 6% 4 3 5% 4 4 7% 22%	1350
	11th to 20th	Night	27% 17% 5% 8% 5% 3 4 4 5% 5% 17%	1260
	21st to end	Night	22% 15% 2 7% 3 2 4 4 4 4 33%	1260
July	1st to 10th	Night	19% 14% 3 6% 4 2 3 4 4 7% 34%	1260
	11th to 20th	Night	16% 14% 3 6% 4 2 3 3 4 7% 37%	1322
	21st to end	Night	15% 17% 4 5% 4 2 3 4 4 6% 37%	1587
August	1st to 10th	Night	22% 16% 4 6% 5% 2 2 4 4 8% 27%	1611
	11th to 20th	Night	15% 11% 3 4 4 2 3 3 3 7% 44%	1602
	21st to end	Night	19% 10% 3 5% 4 2 4 4 5% 8% 36%	1840
September	1st to 10th	Night	14% 10% 3 5% 4 2 3 3 4 7% 46%	1800
	11th to 20th	Night	18% 12% 4 7% 6% 3 3 4 4 6% 32%	1864
	21st to end	Night	23% 10% 2 5% 3 2 3 4 3 6% 38%	2024
October	1st to 10th	Night	21% 9% 4 6% 6% 2 4 4 4 6% 34%	2160
	11th to 20th	Night	26% 8% 3 6% 4 3 3 3 4 7% 32%	2160
	21st to end	Night	29% 9% 4 5% 4 3 4 3 4 5% 30%	2384
November	1st to 10th	Night	37% 8% 3 6% 6% 4 5% 3 5% 6% 18%	2590
	11th to 20th	Night	35% 9% 4 6% 6% 3 4 5% 3 5% 20%	2660
	21st to end	Night	30% 10% 3 7% 6% 3 4 3 4 5% 24%	2660
December	1st to 10th	Night	30% 12% 3 7% 5% 2 4 4 5% 5% 23%	2660
	11th to 20th	Night	34% 12% 4 7% 6% 3 4 4 3 4 18%	3294
	21st to end	Night	37% 16% 4 9% 6% 3 4 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	54% 40% 2 3 1	1329
	11th to 20th	Day	42% 41% 6% 3 4 4	1396
	21st to end	Day	43% 39% 4 7% 6% 1	1762
February	1st to 10th	Day	46% 38% 7% 6% 3	1620
	11th to 20th	Day	42% 41% 6% 6% 4 1	1584
	21st to end	Day	48% 39% 6% 4 3	1338
March	1st to 10th	Day	46% 39% 8% 6% 2	1940
	11th to 20th	Day	47% 38% 6% 7% 1	1980
	21st to end	Day	50% 40% 6% 3 1	2179
April	1st to 10th	Day	46% 39% 9% 5% 1	2160
	11th to 20th	Day	42% 38% 8% 6% 5% 1	2215
	21st to end	Day	43% 41% 8% 5% 3	2340
May	1st to 10th	Day	39% 40% 9% 8% 3	2443
	11th to 20th	Day	37% 42% 10% 7% 3 1	2480
	21st to end	Day	46% 41% 7% 6%	2724
June	1st to 10th	Day	45% 40% 8% 4 3	2605
	11th to 20th	Day	47% 40% 8% 4	2700
	21st to end	Day	34% 42% 10% 9% 5% 2	2700
July	1st to 10th	Day	31% 43% 9% 10% 6% 1	2626
	11th to 20th	Day	33% 41% 9% 11% 6%	2557
	21st to end	Day	31% 40% 11% 11% 6% 1	2574
August	1st to 10th	Day	35% 42% 10% 8% 5%	2312
	11th to 20th	Day	28% 40% 9% 14% 7% 3	2298
	21st to end	Day	31% 41% 12% 12% 4	2516
September	1st to 10th	Day	24% 39% 12% 12% 9% 4	2160
	11th to 20th	Day	32% 42% 8% 11% 6% 2	2093
	21st to end	Day	33% 42% 10% 8% 5% 3	1936
October	1st to 10th	Day	34% 40% 8% 11% 6% 1	1800
	11th to 20th	Day	35% 39% 10% 10% 5% 1	1800
	21st to end	Day	36% 41% 8% 8% 8%	1968
November	1st to 10th	Day	46% 43% 4 5% 2	1488
	11th to 20th	Day	42% 41% 7% 5% 3 1	1520
	21st to end	Day	43% 41% 4 7% 4	1520
December	1st to 10th	Day	39% 42% 6% 8% 5% 1	1520
	11th to 20th	Day	49% 34% 8% 6% 3	1896
	21st to end	Day	57% 29% 8% 5% 1	2442
January	1st to 10th	Night	50% 42% 4 3 1	2836
	11th to 20th	Night	43% 42% 5% 4 2 3	2605
	21st to end	Night	42% 38% 5% 7% 8% 1	2592
February	1st to 10th	Night	47% 38% 5% 7% 2 1	2340
	11th to 20th	Night	41% 39% 7% 7% 5% 1	2274
	21st to end	Night	49% 38% 5% 4 3	1916
March	1st to 10th	Night	47% 38% 6% 7% 1	2016
	11th to 20th	Night	45% 39% 7% 6% 3	1980
	21st to end	Night	51% 38% 6% 4 1	2176
April	1st to 10th	Night	46% 38% 8% 6% 2	1800
	11th to 20th	Night	42% 38% 9% 6% 3 2	1691
	21st to end	Night	45% 40% 6% 5% 3 1	1620
May	1st to 10th	Night	41% 39% 8% 9% 3	1517
	11th to 20th	Night	39% 41% 8% 6% 5% 1	1416
	21st to end	Night	45% 41% 8% 5% 1	1552
June	1st to 10th	Night	43% 38% 7% 9% 2	1350
	11th to 20th	Night	47% 39% 10% 3	1260
	21st to end	Night	34% 39% 11% 9% 5% 2	1260
July	1st to 10th	Night	31% 41% 9% 10% 7% 2	1225
	11th to 20th	Night	33% 38% 9% 13% 6% 1	1280
	21st to end	Night	33% 40% 6% 11% 7% 3	1499
August	1st to 10th	Night	36% 41% 9% 7% 6% 1	1602
	11th to 20th	Night	27% 38% 9% 16% 7% 4	1602
	21st to end	Night	32% 39% 10% 12% 7% 1	1840
September	1st to 10th	Night	22% 38% 8% 16% 11% 5%	1800
	11th to 20th	Night	32% 40% 9% 9% 8% 2	1864
	21st to end	Night	32% 39% 7% 10% 9% 3	2024
October	1st to 10th	Night	35% 39% 8% 9% 7% 1	2160
	11th to 20th	Night	32% 39% 10% 12% 6% 1	2160
	21st to end	Night	37% 40% 7% 8% 8% 1	2384
November	1st to 10th	Night	42% 44% 6% 5% 3	2590
	11th to 20th	Night	44% 41% 7% 5% 2 1	2660
	21st to end	Night	41% 41% 6% 6% 5%	2660
December	1st to 10th	Night	40% 42% 5% 7% 5%	2660
	11th to 20th	Night	46% 36% 6% 7% 5%	3290
	21st to end	Night	55% 32% 7% 4 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	41% 18% 21% 13% 6% 2	180
	11th to 20th	Day	43% 10% 23% 13% 9% 2	164
	21st to end	Day	39% 6% 16% 21% 15% 2	354
February	1st to 10th	Day	46% 9% 14% 19% 11%	340
	11th to 20th	Day	42% 7% 23% 18% 10% 1	335
	21st to end	Day	30% 11% 28% 20% 10% 1	284
March	1st to 10th	Day	36% 11% 20% 18% 14%	420
	11th to 20th	Day	34% 7% 23% 22% 10% 3	420
	21st to end	Day	35% 10% 23% 19% 12% 2	462
April	1st to 10th	Day	36% 11% 18% 22% 10% 2	420
	11th to 20th	Day	34% 6% 25% 20% 9% 5%	412
	21st to end	Day	32% 3 27% 23% 13% 1	420
May	1st to 10th	Day	24% 5% 25% 27% 15% 3	423
	11th to 20th	Day	34% 7% 17% 26% 15% 2	448
	21st to end	Day	31% 6% 16% 31% 13% 3	485
June	1st to 10th	Day	32% 3 19% 30% 15% 2	535
	11th to 20th	Day	27% 4 26% 31% 11% 1	630
	21st to end	Day	20% 4 19% 35% 20% 3	630
July	1st to 10th	Day	24% 4 15% 33% 21% 2	621
	11th to 20th	Day	19% 3 18% 34% 24% 3	556
	21st to end	Day	17% 2 14% 37% 25% 5%	487
August	1st to 10th	Day	19% 3 14% 34% 25% 5%	447
	11th to 20th	Day	17% 2 10% 28% 35% 8%	437
	21st to end	Day	19% 2 20% 34% 22% 3	495
September	1st to 10th	Day	17% 5% 18% 34% 24% 2	450
	11th to 20th	Day	20% 3 18% 29% 25% 5%	450
	21st to end	Day	23% 4 17% 26% 25% 5%	450
October	1st to 10th	Day	27% 5% 16% 25% 23% 4	450
	11th to 20th	Day	29% 6% 18% 22% 19% 5%	450
	21st to end	Day	30% 10% 21% 21% 14% 5%	487
November	1st to 10th	Day	36% 10% 27% 16% 9% 3	180
	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	45% 7% 14% 17% 16% 2	754
	21st to end	Night	39% 7% 14% 23% 14% 3	792
February	1st to 10th	Night	39% 8% 18% 22% 11% 2	720
	11th to 20th	Night	37% 9% 16% 23% 13% 1	704
	21st to end	Night	36% 9% 21% 23% 10% 1	592
March	1st to 10th	Night	38% 8% 16% 21% 15% 2	720
	11th to 20th	Night	38% 8% 16% 23% 13% 2	720
	21st to end	Night	40% 8% 16% 19% 14% 3	792
April	1st to 10th	Night	37% 8% 17% 22% 14% 2	720
	11th to 20th	Night	32% 5% 20% 27% 13% 3	623
	21st to end	Night	34% 5% 16% 24% 17% 3	540
May	1st to 10th	Night	31% 3 17% 26% 19% 4	437
	11th to 20th	Night	34% 5% 9% 22% 27% 3	354
	21st to end	Night	35% 6% 14% 20% 20% 5%	389
June	1st to 10th	Night	32% 3 11% 26% 24% 3	360
	11th to 20th	Night	33% 5% 16% 29% 15% 3	360
	21st to end	Night	31% 3 10% 23% 28% 5%	360
July	1st to 10th	Night	28% 2 8% 21% 34% 7%	350
	11th to 20th	Night	26% 2 11% 27% 29% 6%	348
	21st to end	Night	23% 3 11% 23% 33% 6%	405
August	1st to 10th	Night	35% 2 8% 16% 28% 11%	537
	11th to 20th	Night	22% 2 6% 20% 37% 13%	534
	21st to end	Night	27% 2 12% 26% 28% 6%	652
September	1st to 10th	Night	19% 2 11% 26% 35% 6%	720
	11th to 20th	Night	22% 3 12% 23% 30% 11%	720
	21st to end	Night	26% 3 13% 29% 26% 3	720
October	1st to 10th	Night	24% 4 14% 23% 29% 5%	720
	11th to 20th	Night	28% 5% 12% 27% 23% 6%	720
	21st to end	Night	33% 5% 18% 24% 17% 2	792
November	1st to 10th	Night	39% 8% 17% 23% 12% 1	740
	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 2024-01-09 22:25:01. Version ac07

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