Emerald Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Emerald Beach clear sky chart from 2005-11-06 to 2026-01-02.

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	10% 5% 2 5% 4 4 5% 4 7% 9% 45%	126665
	Night	10% 5% 2 5% 4 4 4 4 6% 9% 46%	124697
Transparency	Day	21% 40% 11% 13% 10% 5%	130558
	Night	21% 40% 10% 13% 12% 5%	128877
Seeing	Day	10% 5% 17% 26% 28% 14%	16112
	Night	11% 5% 18% 27% 28% 10%	26061

By Month

Percentage Cloud Cover SE (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	13% 4 1 4 3 4 4 3 5% 7% 52%	4180
	11th to 20th	Day	13% 6% 2 5% 4 3 4 4 5% 7% 47%	4520
	21st to end	Day	18% 8% 2 6% 4 4 4 3 5% 7% 37%	4972
February	1st to 10th	Day	15% 9% 2 7% 4 4 4 3 4 7% 42%	2000
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 7% 45%	1948
	21st to end	Day	13% 7% 3 5% 5% 5% 4 4 6% 7% 41%	1650
March	1st to 10th	Day	17% 8% 3 7% 4 3 4 3 5% 6% 41%	4480
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 3 5% 7% 52%	4787
	21st to end	Day	17% 5% 2 6% 4 4 4 3 5% 5% 45%	5709
April	1st to 10th	Day	12% 6% 3 5% 4 4 4 3 6% 7% 48%	2400
	11th to 20th	Day	9% 6% 2 5% 4 5% 4 4 5% 7% 49%	2374
	21st to end	Day	6% 4 1 4 4 2 4 4 6% 7% 58%	2400
May	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 4 6% 9% 40%	5469
	11th to 20th	Day	13% 4 1 5% 3 3 4 4 7% 10% 46%	5861
	21st to end	Day	5% 3 2 4 4 4 5% 4 7% 13% 50%	6433
June	1st to 10th	Day	7% 5% 3 6% 5% 6% 6% 5% 8% 11% 39%	2600
	11th to 20th	Day	5% 3 1 4 4 5% 6% 7% 10% 14% 40%	2600
	21st to end	Day	6% 5% 2 6% 6% 6% 6% 6% 9% 13% 37%	2600
July	1st to 10th	Day	6% 3 2 6% 5% 6% 6% 6% 10% 14% 36%	5900
	11th to 20th	Day	3 3 1 6% 6% 6% 6% 6% 9% 13% 42%	5745
	21st to end	Day	3 3 1 5% 5% 6% 7% 7% 12% 15% 34%	5922
August	1st to 10th	Day	5% 3 1 4 4 4 5% 5% 9% 13% 47%	3905
	11th to 20th	Day	5% 3 1 5% 4 4 5% 5% 8% 12% 48%	3849
	21st to end	Day	6% 4 2 5% 4 5% 6% 6% 9% 12% 41%	4312
September	1st to 10th	Day	9% 6% 2 6% 4 3 6% 5% 9% 10% 42%	2329
	11th to 20th	Day	10% 5% 2 6% 4 4 6% 4 7% 9% 42%	2200
	21st to end	Day	6% 4 1 5% 3 4 4 5% 7% 9% 52%	2200
October	1st to 10th	Day	8% 5% 2 4 3 4 4 3 6% 8% 54%	2200
	11th to 20th	Day	7% 3 2 4 3 2 3 2 4 6% 64%	2200
	21st to end	Day	8% 4 2 5% 4 3 4 2 5% 6% 56%	2240
November	1st to 10th	Day	8% 5% 2 5% 3 3 3 4 5% 6% 57%	1852
	11th to 20th	Day	9% 4 2 4 4 3 3 2 6% 7% 55%	1890
	21st to end	Day	9% 5% 2 6% 4 4 4 4 7% 8% 48%	1890
December	1st to 10th	Day	14% 5% 2 5% 3 3 3 3 5% 8% 49%	3020
	11th to 20th	Day	10% 7% 3 6% 4 4 3 3 5% 6% 49%	3463
	21st to end	Day	14% 8% 3 7% 4 3 4 3 4 5% 46%	4565
January	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 6% 49%	5783
	11th to 20th	Night	18% 7% 2 6% 3 3 3 3 5% 6% 43%	5440
	21st to end	Night	16% 7% 2 5% 4 5% 4 4 6% 8% 38%	5984
February	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 4 5% 46%	2400
	11th to 20th	Night	15% 8% 3 6% 3 3 3 3 5% 6% 45%	2338
	21st to end	Night	14% 7% 2 5% 4 4 4 4 5% 5% 45%	1980
March	1st to 10th	Night	20% 9% 3 5% 4 4 3 3 5% 7% 38%	5373
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 6% 7% 52%	5171
	21st to end	Night	13% 6% 2 7% 4 3 3 3 4 7% 48%	5248
April	1st to 10th	Night	10% 7% 3 5% 5% 4 4 3 6% 7% 46%	2000
	11th to 20th	Night	11% 6% 2 5% 3 4 3 4 6% 7% 49%	1975
	21st to end	Night	5% 3 1 4 3 3 4 4 5% 7% 61%	2000
May	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 7% 10% 41%	4408
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 48%	4032
	21st to end	Night	4 3 1 4 4 4 5% 4 7% 13% 51%	4421
June	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 4 9% 11% 41%	1800
	11th to 20th	Night	4 3 1 5% 5% 4 6% 4 10% 12% 47%	1800
	21st to end	Night	5% 5% 2 5% 4 5% 5% 6% 9% 14% 41%	1800
July	1st to 10th	Night	4 3 2 7% 5% 5% 7% 6% 10% 16% 34%	4058
	11th to 20th	Night	2 2 1 4 4 4 6% 6% 9% 15% 49%	4192
	21st to end	Night	3 2 1 4 5% 5% 7% 7% 12% 17% 36%	4929
August	1st to 10th	Night	3 2 1 5% 4 5% 6% 4 8% 13% 49%	3244
	11th to 20th	Night	4 3 1 4 4 4 4 4 8% 12% 51%	3200
	21st to end	Night	5% 4 2 7% 5% 6% 6% 5% 10% 12% 38%	3586
September	1st to 10th	Night	9% 5% 1 6% 6% 5% 5% 6% 7% 12% 38%	2050
	11th to 20th	Night	9% 5% 2 6% 5% 6% 5% 4 6% 8% 43%	2200
	21st to end	Night	7% 5% 1 5% 3 4 4 4 5% 9% 51%	2200
October	1st to 10th	Night	7% 5% 2 6% 4 4 3 4 6% 8% 52%	2200
	11th to 20th	Night	5% 4 1 4 2 3 3 3 5% 6% 63%	2200
	21st to end	Night	9% 5% 2 5% 4 4 4 3 4 6% 54%	2594
November	1st to 10th	Night	8% 5% 1 4 4 3 4 3 5% 7% 56%	2666
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 54%	2730
	21st to end	Night	10% 5% 2 6% 4 4 4 3 6% 8% 49%	2730
December	1st to 10th	Night	13% 5% 2 6% 4 4 3 3 5% 7% 49%	4380
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	4952
	21st to end	Night	16% 8% 2 6% 4 3 4 3 3 5% 45%	6633

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	22% 28% 5% 14% 23% 8%	4181
	11th to 20th	Day	26% 29% 5% 12% 21% 7%	4520
	21st to end	Day	35% 29% 5% 12% 12% 7%	4972
February	1st to 10th	Day	19% 61% 3 5% 8% 4	2000
	11th to 20th	Day	16% 61% 3 9% 9% 2	1958
	21st to end	Day	16% 64% 4 6% 5% 6%	1650
March	1st to 10th	Day	34% 30% 6% 13% 10% 7%	4480
	11th to 20th	Day	22% 31% 6% 10% 17% 13%	4787
	21st to end	Day	32% 30% 8% 13% 11% 7%	5711
April	1st to 10th	Day	15% 62% 4 7% 8% 4	2400
	11th to 20th	Day	13% 63% 4 9% 8% 3	2374
	21st to end	Day	11% 62% 6% 9% 8% 3	2400
May	1st to 10th	Day	29% 34% 13% 15% 7% 2	5504
	11th to 20th	Day	25% 31% 13% 22% 8% 1	5865
	21st to end	Day	18% 32% 16% 24% 9% 1	6447
June	1st to 10th	Day	16% 65% 8% 9% 3	2600
	11th to 20th	Day	15% 64% 9% 7% 5%	2600
	21st to end	Day	15% 64% 10% 7% 4	2600
July	1st to 10th	Day	23% 35% 31% 10% 1	5835
	11th to 20th	Day	21% 34% 33% 11%	5676
	21st to end	Day	23% 38% 26% 12% 1	5752
August	1st to 10th	Day	14% 38% 13% 22% 10% 2	3893
	11th to 20th	Day	13% 39% 17% 20% 11% 1	3885
	21st to end	Day	18% 42% 23% 11% 7%	4311
September	1st to 10th	Day	16% 60% 10% 7% 4 3	2329
	11th to 20th	Day	14% 58% 8% 11% 8% 2	2200
	21st to end	Day	14% 58% 6% 13% 8% 2	2200
October	1st to 10th	Day	23% 36% 5% 7% 10% 19%	3590
	11th to 20th	Day	7% 35% 3 14% 15% 27%	3568
	21st to end	Day	10% 36% 3 9% 30% 12%	3593
November	1st to 10th	Day	19% 53% 5% 8% 8% 6%	1852
	11th to 20th	Day	16% 54% 4 8% 13% 5%	1890
	21st to end	Day	15% 55% 5% 10% 10% 5%	1890
December	1st to 10th	Day	25% 35% 7% 12% 16% 5%	3020
	11th to 20th	Day	21% 32% 3 16% 18% 8%	3460
	21st to end	Day	32% 27% 5% 11% 23% 2	4565
January	1st to 10th	Night	26% 27% 5% 11% 21% 9%	5783
	11th to 20th	Night	35% 27% 3 9% 23% 3	5440
	21st to end	Night	32% 29% 8% 15% 11% 6%	5984
February	1st to 10th	Night	16% 62% 2 7% 9% 4	2400
	11th to 20th	Night	16% 61% 4 7% 9% 4	2339
	21st to end	Night	16% 63% 4 5% 7% 5%	1980
March	1st to 10th	Night	37% 30% 5% 11% 12% 5%	5373
	11th to 20th	Night	22% 31% 8% 10% 15% 14%	5171
	21st to end	Night	27% 30% 7% 16% 10% 9%	5248
April	1st to 10th	Night	16% 62% 4 5% 7% 6%	2000
	11th to 20th	Night	13% 62% 3 8% 9% 5%	1975
	21st to end	Night	9% 63% 6% 12% 8% 3	2000
May	1st to 10th	Night	27% 34% 17% 13% 7% 2	4438
	11th to 20th	Night	24% 31% 14% 21% 9% 1	4033
	21st to end	Night	16% 32% 15% 28% 8% 1	4429
June	1st to 10th	Night	13% 65% 9% 10% 2 1	1800
	11th to 20th	Night	11% 66% 11% 8% 5% 1	1800
	21st to end	Night	12% 64% 14% 7% 4	1800
July	1st to 10th	Night	24% 34% 31% 10% 1	4015
	11th to 20th	Night	14% 36% 40% 10% 1	4141
	21st to end	Night	20% 40% 22% 17% 1	4785
August	1st to 10th	Night	15% 40% 16% 17% 11% 1	3232
	11th to 20th	Night	11% 40% 18% 24% 7%	3230
	21st to end	Night	20% 42% 19% 12% 7% 1	3586
September	1st to 10th	Night	14% 60% 10% 8% 5% 2	2050
	11th to 20th	Night	13% 59% 8% 10% 9% 2	2200
	21st to end	Night	12% 59% 6% 13% 8% 2	2200
October	1st to 10th	Night	25% 36% 6% 7% 11% 16%	3590
	11th to 20th	Night	5% 35% 2 13% 19% 25%	3571
	21st to end	Night	10% 35% 3 8% 34% 10%	4191
November	1st to 10th	Night	17% 53% 5% 8% 10% 6%	2666
	11th to 20th	Night	17% 55% 2 8% 13% 5%	2730
	21st to end	Night	14% 55% 5% 9% 10% 6%	2730
December	1st to 10th	Night	25% 34% 6% 11% 15% 8%	4380
	11th to 20th	Night	20% 31% 5% 19% 15% 9%	4954
	21st to end	Night	32% 27% 4 13% 21% 3	6633

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	15% 11% 36% 29% 9% 1	303
	11th to 20th	Day	9% 11% 33% 33% 13% 1	300
	21st to end	Day	22% 13% 37% 22% 6%	330
February	1st to 10th	Day	17% 12% 33% 26% 12%	300
	11th to 20th	Day	16% 10% 37% 29% 8%	300
	21st to end	Day	8% 11% 41% 32% 7% 1	249
March	1st to 10th	Day	12% 11% 38% 33% 6%	300
	11th to 20th	Day	12% 10% 32% 32% 12% 1	411
	21st to end	Day	13% 9% 29% 34% 13% 1	550
April	1st to 10th	Day	14% 8% 29% 33% 13% 2	500
	11th to 20th	Day	12% 9% 27% 29% 20% 3	492
	21st to end	Day	6% 3 25% 35% 25% 6%	500
May	1st to 10th	Day	7% 5% 22% 35% 26% 5%	503
	11th to 20th	Day	8% 3 12% 38% 28% 11%	527
	21st to end	Day	6% 1 8% 35% 35% 15%	573
June	1st to 10th	Day	9% 2 9% 29% 36% 14%	530
	11th to 20th	Day	7% 2 8% 22% 38% 24%	530
	21st to end	Day	8% 1 5% 19% 38% 28%	530
July	1st to 10th	Day	7% 2 4 12% 41% 35%	525
	11th to 20th	Day	6% 1 3 9% 39% 42%	524
	21st to end	Day	5% 4 13% 41% 36%	576
August	1st to 10th	Day	7% 1 2 12% 38% 40%	526
	11th to 20th	Day	8% 2 2 10% 39% 40%	519
	21st to end	Day	7% 2 6% 17% 40% 28%	583
September	1st to 10th	Day	12% 2 4 16% 40% 25%	530
	11th to 20th	Day	12% 2 6% 20% 41% 18%	530
	21st to end	Day	8% 1 9% 25% 38% 19%	530
October	1st to 10th	Day	10% 2 16% 36% 28% 8%	530
	11th to 20th	Day	6% 3 15% 29% 35% 11%	530
	21st to end	Day	9% 6% 16% 32% 31% 6%	468
November	1st to 10th	Day	11% 4 15% 32% 33% 5%	330
	11th to 20th	Day	13% 5% 21% 32% 24% 5%	330
	21st to end	Day	11% 5% 24% 38% 18% 4	330
December	1st to 10th	Day	19% 8% 26% 31% 14% 2	330
	11th to 20th	Day	15% 9% 26% 34% 13% 2	330
	21st to end	Day	19% 6% 26% 30% 15% 3	363
January	1st to 10th	Night	14% 12% 34% 30% 9% 1	805
	11th to 20th	Night	15% 12% 27% 33% 13% 1	800
	21st to end	Night	18% 10% 35% 30% 7%	880
February	1st to 10th	Night	15% 10% 29% 33% 12% 1	800
	11th to 20th	Night	17% 13% 30% 27% 13%	783
	21st to end	Night	16% 10% 31% 34% 10%	660
March	1st to 10th	Night	15% 7% 30% 35% 13% 1	800
	11th to 20th	Night	11% 7% 28% 33% 18% 3	800
	21st to end	Night	11% 7% 25% 36% 20% 1	790
April	1st to 10th	Night	14% 7% 25% 34% 19% 2	600
	11th to 20th	Night	12% 5% 24% 32% 25% 3	593
	21st to end	Night	7% 3 16% 35% 33% 6%	600
May	1st to 10th	Night	8% 3 15% 33% 33% 8%	600
	11th to 20th	Night	7% 2 12% 33% 36% 10%	591
	21st to end	Night	6% 1 8% 24% 48% 13%	650
June	1st to 10th	Night	8% 1 6% 25% 46% 13%	600
	11th to 20th	Night	3 2 5% 20% 48% 23%	600
	21st to end	Night	7% 1 3 15% 49% 25%	600
July	1st to 10th	Night	6% 1 2 11% 46% 34%	585
	11th to 20th	Night	4 1 1 7% 40% 46%	582
	21st to end	Night	4 2 11% 47% 35%	657
August	1st to 10th	Night	4 2 11% 42% 42%	597
	11th to 20th	Night	8% 3 9% 44% 37%	594
	21st to end	Night	7% 2 6% 17% 43% 24%	660
September	1st to 10th	Night	10% 2 4 19% 42% 24%	650
	11th to 20th	Night	11% 2 8% 20% 46% 13%	800
	21st to end	Night	10% 2 9% 26% 42% 12%	800
October	1st to 10th	Night	8% 2 16% 36% 31% 6%	800
	11th to 20th	Night	6% 4 17% 33% 32% 9%	800
	21st to end	Night	11% 5% 17% 35% 28% 3	880
November	1st to 10th	Night	10% 5% 19% 39% 24% 4	820
	11th to 20th	Night	13% 6% 24% 33% 22% 2	840
	21st to end	Night	11% 6% 29% 32% 20% 2	840
December	1st to 10th	Night	14% 7% 28% 29% 18% 3	840
	11th to 20th	Night	15% 7% 29% 28% 19% 1	840
	21st to end	Night	20% 9% 27% 28% 14% 2	924

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