Echo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Echo clear sky chart from 2005-11-06 to 2024-01-14.

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	13% 8% 3 7% 6% 3 5% 5% 5% 7% 39%	74856
	Night	11% 8% 3 7% 6% 3 5% 4 5% 7% 41%	74903
Transparency	Day	43% 7% 14% 23% 11% 1	74556
	Night	42% 7% 14% 23% 13% 2	74723
Seeing	Day	16% 10% 30% 28% 14% 3	14817
	Night	15% 9% 32% 33% 11% 1	24850

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	10% 9% 5% 10% 8% 5% 6% 5% 6% 8% 28%	1328
	11th to 20th	Day	9% 15% 7% 8% 9% 5% 6% 6% 5% 6% 24%	1568
	21st to end	Day	8% 14% 6% 11% 10% 5% 7% 7% 6% 6% 20%	1782
February	1st to 10th	Day	9% 11% 4 9% 8% 5% 9% 6% 6% 6% 28%	1620
	11th to 20th	Day	8% 12% 5% 9% 9% 5% 6% 6% 5% 6% 29%	1574
	21st to end	Day	11% 10% 5% 10% 9% 4 5% 5% 5% 8% 27%	1404
March	1st to 10th	Day	14% 11% 6% 10% 7% 3 5% 4 4 6% 30%	1948
	11th to 20th	Day	13% 12% 4 7% 6% 4 5% 4 5% 6% 33%	1980
	21st to end	Day	19% 11% 4 8% 7% 3 5% 5% 5% 7% 26%	2178
April	1st to 10th	Day	18% 9% 3 6% 5% 3 4 5% 6% 8% 35%	2094
	11th to 20th	Day	20% 11% 4 7% 5% 3 5% 4 4 6% 33%	2258
	21st to end	Day	23% 9% 2 5% 5% 3 4 4 4 6% 33%	2340
May	1st to 10th	Day	19% 8% 3 7% 6% 3 4 5% 4 6% 35%	2340
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 4 4 8% 38%	2440
	21st to end	Day	15% 6% 3 6% 6% 3 5% 5% 6% 7% 39%	2725
June	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 8% 46%	2574
	11th to 20th	Day	14% 6% 3 6% 5% 2 5% 4 5% 7% 42%	2700
	21st to end	Day	7% 5% 2 5% 5% 3 5% 5% 6% 10% 47%	2700
July	1st to 10th	Day	7% 3 1 3 4 3 4 5% 7% 10% 52%	2700
	11th to 20th	Day	7% 4 1 3 4 2 4 5% 6% 9% 55%	2624
	21st to end	Day	5% 3 1 4 4 3 5% 5% 7% 9% 53%	2550
August	1st to 10th	Day	9% 4 2 6% 6% 4 6% 6% 7% 8% 43%	2328
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 6% 6% 9% 45%	2301
	21st to end	Day	8% 3 2 3 5% 3 4 4 5% 8% 55%	2548
September	1st to 10th	Day	11% 4 2 4 4 3 4 4 5% 8% 50%	2160
	11th to 20th	Day	10% 6% 3 5% 4 3 4 4 6% 8% 48%	2000
	21st to end	Day	16% 5% 2 4 3 3 3 4 6% 6% 49%	1976
October	1st to 10th	Day	16% 7% 2 5% 6% 2 4 4 5% 6% 44%	1800
	11th to 20th	Day	15% 8% 3 5% 4 3 3 4 5% 7% 44%	1800
	21st to end	Day	18% 8% 3 6% 4 2 3 4 4 5% 43%	1949
November	1st to 10th	Day	12% 8% 4 7% 5% 2 3 4 6% 6% 42%	1589
	11th to 20th	Day	10% 10% 4 10% 9% 4 5% 4 4 6% 34%	1520
	21st to end	Day	12% 11% 4 7% 6% 3 5% 4 6% 8% 36%	1520
December	1st to 10th	Day	9% 11% 4 11% 10% 5% 6% 4 6% 5% 29%	1520
	11th to 20th	Day	10% 12% 6% 9% 8% 4 5% 5% 5% 8% 29%	1918
	21st to end	Day	19% 11% 6% 17% 5% 3 3 4 4 5% 22%	2500
January	1st to 10th	Night	7% 8% 5% 10% 8% 4 5% 6% 6% 7% 33%	2837
	11th to 20th	Night	7% 12% 6% 12% 9% 5% 6% 6% 5% 6% 26%	2454
	21st to end	Night	12% 12% 6% 11% 6% 4 6% 5% 5% 7% 26%	2574
February	1st to 10th	Night	7% 12% 5% 8% 6% 5% 6% 5% 5% 6% 34%	2340
	11th to 20th	Night	7% 9% 4 8% 6% 4 6% 6% 6% 6% 37%	2273
	21st to end	Night	11% 10% 4 8% 7% 5% 6% 5% 5% 6% 35%	1866
March	1st to 10th	Night	11% 9% 4 8% 7% 4 5% 4 5% 6% 37%	2012
	11th to 20th	Night	13% 11% 4 7% 6% 3 4 4 5% 5% 39%	1980
	21st to end	Night	17% 9% 4 7% 6% 3 4 5% 5% 8% 33%	2178
April	1st to 10th	Night	16% 9% 3 5% 5% 3 4 4 4 7% 41%	1864
	11th to 20th	Night	18% 10% 4 6% 5% 2 3 4 3 5% 38%	1648
	21st to end	Night	17% 8% 3 6% 4 2 4 5% 4 7% 38%	1620
May	1st to 10th	Night	16% 6% 3 5% 4 3 4 4 6% 7% 42%	1620
	11th to 20th	Night	14% 6% 2 4 4 2 5% 4 6% 9% 43%	1452
	21st to end	Night	12% 5% 3 6% 5% 3 6% 4 6% 7% 44%	1551
June	1st to 10th	Night	9% 3 2 4 4 3 5% 5% 4 8% 54%	1382
	11th to 20th	Night	7% 4 2 5% 5% 2 4 5% 5% 9% 52%	1260
	21st to end	Night	6% 2 2 5% 3 3 4 4 4 7% 60%	1260
July	1st to 10th	Night	4 3 1 4 3 2 3 4 6% 10% 60%	1260
	11th to 20th	Night	3 1 1 2 4 2 4 3 6% 7% 66%	1335
	21st to end	Night	4 3 1 4 4 2 3 4 6% 10% 59%	1764
August	1st to 10th	Night	8% 3 1 5% 5% 3 3 5% 5% 9% 51%	1611
	11th to 20th	Night	9% 4 2 4 3 2 3 5% 4 8% 58%	1600
	21st to end	Night	5% 3 2 4 3 2 3 3 4 6% 64%	1808
September	1st to 10th	Night	9% 4 2 5% 4 2 4 4 5% 6% 57%	1800
	11th to 20th	Night	9% 4 2 4 4 2 4 4 4 8% 55%	1957
	21st to end	Night	11% 5% 2 4 4 3 5% 4 4 6% 53%	1980
October	1st to 10th	Night	15% 7% 2 4 4 2 4 3 5% 6% 48%	2145
	11th to 20th	Night	15% 8% 2 5% 4 2 4 4 4 6% 46%	2160
	21st to end	Night	16% 8% 3 6% 4 3 3 4 4 7% 42%	2403
November	1st to 10th	Night	10% 8% 3 5% 6% 4 4 4 4 7% 45%	2487
	11th to 20th	Night	11% 10% 4 9% 5% 4 4 4 5% 5% 39%	2660
	21st to end	Night	10% 9% 3 7% 6% 3 5% 5% 5% 8% 40%	2660
December	1st to 10th	Night	9% 10% 5% 9% 8% 4 5% 4 5% 7% 34%	2660
	11th to 20th	Night	11% 11% 5% 10% 7% 4 5% 6% 6% 8% 29%	3279
	21st to end	Night	20% 12% 6% 12% 7% 3 5% 5% 4 5% 22%	5163

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	53% 7% 17% 17% 6%	1329
	11th to 20th	Day	59% 7% 12% 14% 8% 1	1568
	21st to end	Day	62% 7% 15% 11% 5%	1782
February	1st to 10th	Day	54% 6% 14% 17% 7%	1620
	11th to 20th	Day	54% 7% 13% 17% 8% 1	1583
	21st to end	Day	54% 8% 13% 13% 11% 1	1404
March	1st to 10th	Day	55% 6% 14% 18% 6% 1	1948
	11th to 20th	Day	51% 6% 14% 22% 6%	1980
	21st to end	Day	57% 7% 12% 19% 5%	2178
April	1st to 10th	Day	47% 6% 13% 23% 9% 1	2094
	11th to 20th	Day	52% 5% 11% 19% 11% 1	2258
	21st to end	Day	51% 6% 12% 21% 8% 1	2340
May	1st to 10th	Day	49% 7% 12% 20% 11%	2340
	11th to 20th	Day	44% 8% 13% 21% 12% 1	2444
	21st to end	Day	42% 9% 13% 23% 11% 2	2725
June	1st to 10th	Day	35% 8% 16% 28% 12% 1	2574
	11th to 20th	Day	40% 8% 13% 23% 15% 2	2700
	21st to end	Day	31% 9% 18% 27% 14% 2	2700
July	1st to 10th	Day	25% 9% 17% 32% 16% 1	2626
	11th to 20th	Day	24% 8% 16% 29% 19% 4	2543
	21st to end	Day	24% 8% 18% 31% 17% 2	2408
August	1st to 10th	Day	36% 9% 16% 25% 11% 3	2314
	11th to 20th	Day	34% 9% 15% 30% 11% 1	2301
	21st to end	Day	26% 7% 16% 30% 18% 2	2548
September	1st to 10th	Day	32% 7% 13% 31% 17% 1	2160
	11th to 20th	Day	34% 6% 17% 31% 12% 1	2000
	21st to end	Day	36% 5% 12% 32% 14% 1	1976
October	1st to 10th	Day	41% 6% 13% 25% 15% 1	1800
	11th to 20th	Day	39% 6% 12% 27% 14% 2	1800
	21st to end	Day	44% 5% 14% 25% 11% 1	1949
November	1st to 10th	Day	40% 7% 14% 21% 14% 3	1589
	11th to 20th	Day	51% 5% 14% 20% 10%	1520
	21st to end	Day	47% 7% 17% 20% 9% 1	1520
December	1st to 10th	Day	55% 7% 15% 14% 8% 1	1520
	11th to 20th	Day	53% 8% 17% 17% 5%	1915
	21st to end	Day	62% 5% 13% 14% 5% 1	2500
January	1st to 10th	Night	48% 7% 14% 21% 9%	2837
	11th to 20th	Night	58% 6% 15% 14% 6% 1	2454
	21st to end	Night	57% 5% 14% 15% 8% 1	2574
February	1st to 10th	Night	49% 6% 14% 20% 9% 2	2340
	11th to 20th	Night	44% 8% 15% 20% 11% 2	2274
	21st to end	Night	48% 7% 12% 20% 11% 2	1866
March	1st to 10th	Night	46% 8% 16% 22% 8% 1	2012
	11th to 20th	Night	48% 5% 12% 23% 11%	1980
	21st to end	Night	51% 6% 13% 22% 6% 1	2178
April	1st to 10th	Night	43% 6% 13% 26% 11% 1	1864
	11th to 20th	Night	48% 5% 9% 20% 16% 2	1648
	21st to end	Night	45% 7% 11% 23% 12% 2	1620
May	1st to 10th	Night	41% 7% 13% 25% 13% 1	1620
	11th to 20th	Night	37% 8% 14% 22% 17% 3	1453
	21st to end	Night	40% 8% 13% 22% 15% 3	1552
June	1st to 10th	Night	28% 7% 15% 30% 17% 2	1382
	11th to 20th	Night	30% 7% 18% 24% 18% 3	1260
	21st to end	Night	25% 7% 16% 30% 20% 2	1260
July	1st to 10th	Night	21% 6% 15% 35% 20% 3	1225
	11th to 20th	Night	17% 6% 17% 36% 19% 6%	1293
	21st to end	Night	20% 7% 17% 33% 19% 4	1666
August	1st to 10th	Night	29% 7% 17% 28% 15% 4	1601
	11th to 20th	Night	25% 7% 17% 34% 15% 2	1600
	21st to end	Night	23% 6% 13% 31% 23% 4	1808
September	1st to 10th	Night	28% 6% 13% 32% 20% 1	1800
	11th to 20th	Night	28% 7% 14% 32% 19% 1	1957
	21st to end	Night	31% 6% 11% 30% 20% 1	1980
October	1st to 10th	Night	36% 6% 12% 27% 18% 2	2145
	11th to 20th	Night	40% 5% 12% 25% 17% 2	2160
	21st to end	Night	42% 5% 14% 23% 14% 1	2403
November	1st to 10th	Night	39% 6% 15% 22% 16% 3	2487
	11th to 20th	Night	47% 6% 11% 21% 13% 1	2660
	21st to end	Night	42% 7% 18% 22% 10% 1	2660
December	1st to 10th	Night	50% 7% 17% 18% 8%	2660
	11th to 20th	Night	51% 10% 17% 17% 5%	3281
	21st to end	Night	62% 7% 11% 16% 4	5163

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	17% 10% 32% 25% 14% 1	270
	11th to 20th	Day	17% 11% 33% 31% 8% 1	249
	21st to end	Day	16% 8% 41% 27% 8% 1	264
February	1st to 10th	Day	13% 15% 43% 25% 4	240
	11th to 20th	Day	17% 16% 39% 23% 5% 1	240
	21st to end	Day	18% 12% 38% 28% 5%	198
March	1st to 10th	Day	18% 14% 38% 25% 5% 1	240
	11th to 20th	Day	21% 10% 40% 22% 6% 2	240
	21st to end	Day	27% 12% 25% 24% 9% 2	264
April	1st to 10th	Day	27% 14% 31% 22% 6%	354
	11th to 20th	Day	27% 16% 26% 22% 8% 1	536
	21st to end	Day	24% 14% 29% 22% 10% 2	600
May	1st to 10th	Day	21% 13% 32% 24% 10% 1	603
	11th to 20th	Day	22% 11% 30% 21% 13% 3	625
	21st to end	Day	18% 7% 30% 29% 14% 2	679
June	1st to 10th	Day	9% 6% 27% 30% 23% 4	630
	11th to 20th	Day	15% 8% 32% 30% 12% 3	630
	21st to end	Day	10% 6% 31% 33% 17% 3	630
July	1st to 10th	Day	7% 5% 21% 34% 26% 6%	621
	11th to 20th	Day	8% 5% 29% 35% 18% 5%	618
	21st to end	Day	7% 4 22% 40% 23% 5%	684
August	1st to 10th	Day	10% 3 19% 38% 26% 4	626
	11th to 20th	Day	12% 4 20% 33% 24% 7%	615
	21st to end	Day	8% 5% 26% 37% 20% 4	667
September	1st to 10th	Day	14% 6% 27% 31% 18% 4	450
	11th to 20th	Day	9% 6% 30% 34% 15% 6%	290
	21st to end	Day	21% 13% 29% 21% 13% 3	270
October	1st to 10th	Day	17% 12% 31% 24% 12% 4	270
	11th to 20th	Day	14% 20% 34% 19% 11% 1	270
	21st to end	Day	23% 17% 34% 18% 8% 1	297
November	1st to 10th	Day	20% 13% 30% 25% 9% 2	270
	11th to 20th	Day	16% 20% 39% 21% 4	270
	21st to end	Day	20% 19% 29% 26% 6% 1	270
December	1st to 10th	Day	11% 9% 43% 26% 11%	270
	11th to 20th	Day	14% 14% 39% 26% 7%	270
	21st to end	Day	27% 11% 34% 23% 4	297
January	1st to 10th	Night	10% 11% 39% 30% 10% 1	950
	11th to 20th	Night	14% 11% 33% 33% 8% 1	918
	21st to end	Night	18% 10% 34% 31% 5%	990
February	1st to 10th	Night	13% 10% 39% 31% 6%	900
	11th to 20th	Night	13% 13% 39% 27% 7% 1	879
	21st to end	Night	14% 13% 34% 29% 9% 1	682
March	1st to 10th	Night	15% 10% 38% 29% 8% 1	572
	11th to 20th	Night	20% 8% 36% 29% 7%	540
	21st to end	Night	21% 11% 27% 29% 11% 2	594
April	1st to 10th	Night	20% 12% 39% 24% 5%	540
	11th to 20th	Night	23% 11% 31% 27% 8% 1	533
	21st to end	Night	20% 11% 32% 27% 8% 2	540
May	1st to 10th	Night	19% 9% 34% 29% 8% 1	540
	11th to 20th	Night	16% 9% 34% 28% 12% 1	531
	21st to end	Night	15% 6% 31% 34% 13% 1	584
June	1st to 10th	Night	11% 5% 24% 43% 17%	540
	11th to 20th	Night	10% 3 36% 40% 11%	540
	21st to end	Night	6% 4 27% 49% 14%	540
July	1st to 10th	Night	5% 2 23% 41% 27% 1	525
	11th to 20th	Night	4 2 27% 49% 18% 1	522
	21st to end	Night	4 2 22% 49% 22% 1	591
August	1st to 10th	Night	9% 2 18% 48% 19% 2	537
	11th to 20th	Night	11% 3 17% 42% 24% 4	534
	21st to end	Night	7% 3 24% 44% 21% 2	594
September	1st to 10th	Night	12% 2 25% 42% 17% 2	540
	11th to 20th	Night	11% 4 29% 36% 18% 1	540
	21st to end	Night	12% 7% 37% 30% 12% 1	540
October	1st to 10th	Night	17% 8% 34% 30% 11% 1	705
	11th to 20th	Night	19% 11% 34% 28% 7% 1	720
	21st to end	Night	20% 12% 31% 30% 7%	819
November	1st to 10th	Night	14% 11% 33% 32% 10%	925
	11th to 20th	Night	15% 11% 39% 25% 9% 1	950
	21st to end	Night	15% 13% 36% 30% 6%	950
December	1st to 10th	Night	14% 10% 39% 29% 7% 1	950
	11th to 20th	Night	20% 9% 34% 29% 7% 1	950
	21st to end	Night	24% 12% 33% 26% 5% 1	1045

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