Echo Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Echo Park clear sky chart from 2005-11-06 to 2025-03-27.

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	3 6% 2 6% 4 4 5% 4 6% 8% 52%	113166
	Night	3 6% 2 6% 4 4 5% 4 6% 8% 52%	115065
Transparency	Day	25% 8% 14% 24% 19% 11%	112924
	Night	27% 8% 14% 25% 19% 8%	114897
Seeing	Day	7% 12% 28% 31% 17% 4	15921
	Night	6% 5% 22% 43% 21% 3	26224

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	1 5% 3 9% 6% 6% 6% 5% 7% 9% 42%	3886
	11th to 20th	Day	1 6% 2 8% 6% 5% 6% 5% 7% 8% 45%	4100
	21st to end	Day	1 9% 4 10% 5% 4 4 3 5% 6% 49%	4510
February	1st to 10th	Day	2 6% 4 10% 6% 6% 4 5% 7% 10% 39%	1800
	11th to 20th	Day	3 10% 3 7% 5% 4 6% 5% 7% 9% 40%	1755
	21st to end	Day	1 7% 4 10% 6% 5% 5% 4 7% 7% 43%	1621
March	1st to 10th	Day	2 10% 3 8% 6% 5% 5% 4 6% 7% 43%	3554
	11th to 20th	Day	3 9% 3 5% 4 4 4 4 5% 8% 49%	3600
	21st to end	Day	3 13% 4 9% 6% 6% 7% 5% 8% 9% 30%	3892
April	1st to 10th	Day	4 9% 3 7% 5% 5% 4 4 7% 8% 44%	2242
	11th to 20th	Day	4 9% 4 9% 4 6% 5% 3 7% 6% 43%	2251
	21st to end	Day	4 8% 3 8% 5% 5% 6% 4 7% 9% 41%	2408
May	1st to 10th	Day	6% 13% 4 9% 6% 6% 6% 5% 6% 8% 34%	4110
	11th to 20th	Day	3 4 2 5% 5% 5% 6% 6% 9% 9% 47%	4156
	21st to end	Day	5% 6% 2 5% 4 4 4 4 6% 8% 51%	4825
June	1st to 10th	Day	3 3 1 4 4 4 5% 4 6% 10% 56%	2660
	11th to 20th	Day	3 3 1 4 3 4 3 4 7% 8% 59%	2660
	21st to end	Day	2 2 1 3 3 3 3 4 6% 8% 65%	2660
July	1st to 10th	Day	1 2 1 2 2 3 3 3 5% 6% 72%	4430
	11th to 20th	Day	2 3 1 4 4 5% 7% 7% 9% 11% 48%	4174
	21st to end	Day	2 2 1 4 4 4 5% 4 7% 9% 57%	4454
August	1st to 10th	Day	3 2 1 4 4 4 5% 5% 8% 10% 53%	4092
	11th to 20th	Day	2 2 1 3 3 3 4 5% 8% 10% 58%	4028
	21st to end	Day	2 2 1 3 3 4 4 5% 7% 8% 62%	4252
September	1st to 10th	Day	3 2 1 4 3 3 3 3 5% 6% 66%	2280
	11th to 20th	Day	2 3 1 5% 4 3 4 3 5% 7% 64%	2177
	21st to end	Day	5% 3 2 3 2 3 2 2 4 5% 69%	2057
October	1st to 10th	Day	4 4 1 3 2 2 3 3 4 5% 70%	3170
	11th to 20th	Day	4 4 1 3 3 3 3 3 6% 10% 58%	3150
	21st to end	Day	4 5% 2 5% 3 3 5% 4 5% 7% 58%	3438
November	1st to 10th	Day	3 5% 2 6% 4 3 5% 4 6% 8% 54%	1924
	11th to 20th	Day	2 6% 2 6% 4 4 4 3 6% 7% 56%	1600
	21st to end	Day	2 7% 3 6% 4 4 4 5% 7% 8% 49%	1600
December	1st to 10th	Day	2 5% 2 5% 3 3 4 3 4 6% 62%	2620
	11th to 20th	Day	2 5% 2 5% 4 5% 5% 4 6% 11% 49%	3026
	21st to end	Day	3 10% 4 9% 6% 5% 6% 5% 6% 8% 38%	4004
January	1st to 10th	Night	1 6% 3 8% 5% 5% 7% 5% 7% 9% 43%	6120
	11th to 20th	Night	1 7% 2 8% 5% 5% 5% 4 7% 9% 46%	5880
	21st to end	Night	1 8% 3 8% 5% 5% 5% 4 4 7% 50%	6468
February	1st to 10th	Night	2 6% 3 8% 6% 4 5% 5% 7% 9% 45%	2600
	11th to 20th	Night	2 8% 3 9% 5% 5% 5% 4 5% 10% 43%	2532
	21st to end	Night	1 8% 4 7% 6% 4 5% 4 6% 7% 47%	2005
March	1st to 10th	Night	2 9% 4 8% 6% 5% 3 4 7% 7% 45%	3540
	11th to 20th	Night	2 8% 3 6% 5% 5% 4 4 6% 8% 50%	3600
	21st to end	Night	4 13% 4 11% 6% 6% 6% 4 6% 7% 33%	3899
April	1st to 10th	Night	5% 9% 3 6% 5% 5% 5% 4 6% 7% 45%	1938
	11th to 20th	Night	6% 9% 3 8% 4 5% 5% 4 7% 8% 40%	1877
	21st to end	Night	6% 7% 3 6% 6% 6% 5% 5% 7% 8% 42%	1768
May	1st to 10th	Night	7% 9% 3 7% 5% 5% 5% 4 6% 7% 41%	2860
	11th to 20th	Night	4 5% 2 8% 4 5% 6% 5% 6% 8% 47%	2747
	21st to end	Night	7% 6% 2 3 4 4 5% 5% 6% 7% 51%	2762
June	1st to 10th	Night	3 4 2 4 4 5% 5% 5% 7% 10% 52%	1520
	11th to 20th	Night	5% 4 1 5% 4 4 4 4 5% 7% 57%	1520
	21st to end	Night	2 2 1 4 3 4 5% 4 6% 7% 62%	1520
July	1st to 10th	Night	2 2 1 3 4 3 3 3 5% 6% 66%	2540
	11th to 20th	Night	2 3 1 5% 5% 5% 6% 5% 8% 10% 48%	2791
	21st to end	Night	1 2 1 4 4 4 5% 5% 7% 10% 58%	3109
August	1st to 10th	Night	2 3 1 5% 4 4 4 4 7% 9% 57%	2847
	11th to 20th	Night	2 3 1 4 4 5% 6% 6% 7% 8% 53%	2811
	21st to end	Night	2 3 1 4 4 5% 5% 4 5% 8% 61%	3415
September	1st to 10th	Night	3 4 1 4 2 3 3 3 4 6% 66%	1900
	11th to 20th	Night	4 3 1 6% 4 4 4 4 5% 6% 59%	2000
	21st to end	Night	3 2 1 4 3 3 3 3 4 7% 68%	2122
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 73%	3800
	11th to 20th	Night	4 3 1 4 3 3 4 3 5% 8% 60%	3778
	21st to end	Night	4 5% 2 5% 3 3 4 3 5% 8% 58%	4120
November	1st to 10th	Night	4 5% 2 6% 4 4 4 4 6% 7% 54%	2351
	11th to 20th	Night	2 5% 2 5% 5% 4 3 4 7% 8% 56%	2800
	21st to end	Night	3 6% 3 6% 4 4 4 4 6% 9% 51%	2800
December	1st to 10th	Night	2 7% 2 5% 3 3 3 2 4 6% 63%	4570
	11th to 20th	Night	2 6% 3 6% 4 4 5% 4 7% 10% 49%	5181
	21st to end	Night	2 8% 4 10% 6% 6% 5% 4 6% 8% 42%	6974

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	31% 13% 23% 23% 9% 1	3887
	11th to 20th	Day	26% 12% 18% 27% 14% 2	4100
	21st to end	Day	33% 10% 17% 22% 17% 1	4510
February	1st to 10th	Day	35% 12% 20% 22% 10% 1	1800
	11th to 20th	Day	36% 9% 18% 26% 10% 1	1764
	21st to end	Day	36% 7% 18% 24% 12% 2	1621
March	1st to 10th	Day	32% 12% 17% 25% 12% 2	3554
	11th to 20th	Day	29% 9% 20% 30% 10% 1	3600
	21st to end	Day	39% 15% 17% 20% 7% 1	3892
April	1st to 10th	Day	33% 9% 15% 21% 17% 5%	2242
	11th to 20th	Day	35% 9% 14% 22% 17% 3	2254
	21st to end	Day	33% 9% 15% 25% 16% 2	2408
May	1st to 10th	Day	36% 14% 14% 16% 18% 3	4110
	11th to 20th	Day	21% 11% 16% 30% 18% 4	4159
	21st to end	Day	25% 7% 12% 27% 26% 3	4825
June	1st to 10th	Day	20% 7% 11% 23% 26% 11%	2660
	11th to 20th	Day	19% 6% 8% 15% 29% 23%	2660
	21st to end	Day	14% 4 7% 15% 30% 30%	2660
July	1st to 10th	Day	12% 3 6% 10% 16% 52%	4361
	11th to 20th	Day	21% 6% 8% 15% 26% 24%	4103
	21st to end	Day	19% 5% 9% 16% 19% 32%	4314
August	1st to 10th	Day	21% 7% 10% 26% 18% 19%	4078
	11th to 20th	Day	17% 7% 11% 23% 25% 17%	4067
	21st to end	Day	16% 6% 10% 20% 24% 23%	4251
September	1st to 10th	Day	17% 3 9% 18% 26% 26%	2280
	11th to 20th	Day	18% 5% 10% 23% 27% 17%	2177
	21st to end	Day	19% 2 5% 23% 36% 14%	2057
October	1st to 10th	Day	16% 3 7% 19% 31% 24%	3170
	11th to 20th	Day	20% 4 10% 33% 29% 4	3150
	21st to end	Day	24% 5% 12% 36% 20% 3	3438
November	1st to 10th	Day	27% 6% 15% 32% 19% 2	1924
	11th to 20th	Day	26% 6% 19% 32% 15% 1	1600
	21st to end	Day	29% 9% 19% 27% 17%	1600
December	1st to 10th	Day	23% 7% 14% 45% 11%	2620
	11th to 20th	Day	27% 11% 28% 28% 7%	3024
	21st to end	Day	40% 10% 18% 20% 9% 2	4004
January	1st to 10th	Night	29% 11% 21% 26% 11% 2	6120
	11th to 20th	Night	29% 11% 16% 29% 14% 1	5880
	21st to end	Night	31% 10% 17% 21% 20% 1	6468
February	1st to 10th	Night	33% 9% 20% 25% 11% 1	2600
	11th to 20th	Night	36% 8% 17% 23% 15% 2	2533
	21st to end	Night	34% 6% 19% 24% 14% 3	2005
March	1st to 10th	Night	32% 8% 15% 27% 17% 1	3540
	11th to 20th	Night	28% 9% 19% 31% 11% 2	3600
	21st to end	Night	43% 11% 16% 20% 8% 1	3899
April	1st to 10th	Night	35% 7% 14% 20% 18% 6%	1938
	11th to 20th	Night	37% 7% 15% 20% 18% 3	1877
	21st to end	Night	34% 9% 13% 25% 17% 2	1768
May	1st to 10th	Night	35% 9% 12% 17% 21% 6%	2860
	11th to 20th	Night	24% 11% 15% 27% 17% 7%	2748
	21st to end	Night	25% 7% 12% 25% 28% 2	2762
June	1st to 10th	Night	24% 8% 11% 20% 23% 13%	1520
	11th to 20th	Night	25% 4 8% 14% 25% 23%	1520
	21st to end	Night	18% 5% 7% 13% 26% 31%	1520
July	1st to 10th	Night	17% 4 6% 11% 17% 45%	2500
	11th to 20th	Night	25% 6% 7% 18% 24% 21%	2740
	21st to end	Night	17% 6% 9% 17% 23% 28%	3011
August	1st to 10th	Night	21% 4 11% 25% 20% 20%	2838
	11th to 20th	Night	25% 7% 12% 18% 23% 15%	2838
	21st to end	Night	21% 4 10% 17% 26% 22%	3415
September	1st to 10th	Night	20% 3 7% 18% 26% 26%	1900
	11th to 20th	Night	23% 6% 8% 21% 21% 20%	2000
	21st to end	Night	18% 3 7% 18% 38% 16%	2122
October	1st to 10th	Night	15% 3 7% 16% 38% 21%	3800
	11th to 20th	Night	21% 4 8% 30% 29% 7%	3778
	21st to end	Night	24% 5% 11% 35% 21% 3	4120
November	1st to 10th	Night	28% 6% 13% 28% 23% 3	2351
	11th to 20th	Night	22% 7% 16% 35% 19% 1	2800
	21st to end	Night	29% 7% 14% 32% 17% 2	2800
December	1st to 10th	Night	22% 6% 15% 42% 14% 1	4570
	11th to 20th	Night	27% 9% 24% 33% 7%	5182
	21st to end	Night	36% 11% 17% 23% 12% 1	6974

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	5% 13% 31% 34% 15% 2	300
	11th to 20th	Day	5% 8% 32% 39% 15% 2	300
	21st to end	Day	5% 11% 25% 42% 16% 1	330
February	1st to 10th	Day	8% 12% 41% 33% 6%	300
	11th to 20th	Day	6% 11% 37% 37% 7% 2	300
	21st to end	Day	5% 14% 35% 36% 10% 1	295
March	1st to 10th	Day	9% 14% 36% 27% 13% 1	500
	11th to 20th	Day	9% 16% 31% 32% 11% 2	500
	21st to end	Day	11% 21% 36% 24% 6% 1	531
April	1st to 10th	Day	9% 20% 35% 22% 12% 2	460
	11th to 20th	Day	11% 26% 35% 19% 8% 1	452
	21st to end	Day	9% 25% 26% 24% 14% 2	460
May	1st to 10th	Day	11% 22% 35% 23% 10% 1	463
	11th to 20th	Day	7% 15% 31% 29% 15% 3	534
	21st to end	Day	9% 12% 25% 29% 21% 4	734
June	1st to 10th	Day	5% 8% 26% 31% 25% 5%	680
	11th to 20th	Day	6% 16% 25% 31% 20% 2	680
	21st to end	Day	5% 8% 26% 35% 23% 3	680
July	1st to 10th	Day	4 4 22% 35% 30% 5%	671
	11th to 20th	Day	3 5% 25% 35% 23% 9%	520
	21st to end	Day	4 6% 17% 38% 28% 7%	531
August	1st to 10th	Day	5% 4 28% 34% 21% 7%	487
	11th to 20th	Day	4 6% 24% 36% 21% 8%	477
	21st to end	Day	4 6% 25% 33% 26% 7%	539
September	1st to 10th	Day	4 8% 23% 30% 24% 10%	490
	11th to 20th	Day	4 12% 31% 27% 18% 8%	490
	21st to end	Day	7% 15% 21% 28% 22% 7%	457
October	1st to 10th	Day	7% 12% 23% 26% 21% 11%	300
	11th to 20th	Day	7% 14% 29% 25% 21% 4	300
	21st to end	Day	8% 13% 31% 34% 12% 2	330
November	1st to 10th	Day	9% 19% 26% 27% 15% 4	300
	11th to 20th	Day	6% 13% 32% 34% 12% 3	300
	21st to end	Day	8% 8% 28% 40% 15% 1	300
December	1st to 10th	Day	6% 7% 32% 37% 15% 4	300
	11th to 20th	Day	5% 7% 34% 44% 10%	300
	21st to end	Day	11% 12% 28% 38% 9% 2	330
January	1st to 10th	Night	6% 4 25% 45% 18% 2	910
	11th to 20th	Night	4 5% 27% 49% 14% 2	800
	21st to end	Night	7% 4 26% 48% 13% 2	880
February	1st to 10th	Night	5% 4 32% 48% 10% 1	800
	11th to 20th	Night	5% 5% 32% 46% 12%	784
	21st to end	Night	5% 7% 32% 47% 9% 1	660
March	1st to 10th	Night	7% 7% 27% 44% 15% 1	800
	11th to 20th	Night	6% 7% 25% 45% 16% 1	800
	21st to end	Night	8% 7% 30% 40% 14% 1	862
April	1st to 10th	Night	11% 10% 28% 39% 12%	608
	11th to 20th	Night	11% 11% 27% 38% 12% 1	563
	21st to end	Night	8% 13% 27% 32% 17% 3	570
May	1st to 10th	Night	12% 9% 26% 35% 15% 2	570
	11th to 20th	Night	6% 5% 20% 40% 23% 5%	561
	21st to end	Night	9% 7% 19% 38% 23% 3	617
June	1st to 10th	Night	5% 5% 18% 42% 28% 3	570
	11th to 20th	Night	6% 7% 22% 44% 20% 1	570
	21st to end	Night	2 2 16% 47% 29% 3	570
July	1st to 10th	Night	3 2 13% 39% 41% 2	555
	11th to 20th	Night	2 2 10% 41% 40% 5%	552
	21st to end	Night	2 1 8% 38% 48% 4	624
August	1st to 10th	Night	4 1 7% 46% 39% 2	567
	11th to 20th	Night	3 2 10% 46% 35% 5%	564
	21st to end	Night	4 2 10% 41% 36% 7%	627
September	1st to 10th	Night	5% 2 11% 40% 35% 6%	570
	11th to 20th	Night	5% 3 15% 42% 29% 5%	670
	21st to end	Night	5% 3 19% 35% 30% 8%	760
October	1st to 10th	Night	8% 4 16% 44% 23% 5%	760
	11th to 20th	Night	5% 4 22% 41% 24% 3	760
	21st to end	Night	7% 6% 20% 43% 21% 3	836
November	1st to 10th	Night	7% 6% 20% 41% 24% 2	784
	11th to 20th	Night	4 6% 29% 46% 13% 3	1000
	21st to end	Night	5% 7% 21% 47% 17% 2	1000
December	1st to 10th	Night	7% 5% 23% 50% 15% 1	1000
	11th to 20th	Night	8% 4 28% 46% 12% 1	1000
	21st to end	Night	7% 7% 28% 47% 9% 2	1100

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