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 2026-01-17.

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	12% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	127808
	Night	11% 8% 3 9% 5% 5% 5% 4 5% 7% 40%	124095
Transparency	Day	42% 6% 14% 24% 12% 1	131375
	Night	43% 6% 13% 24% 13% 2	128606
Seeing	Day	16% 10% 30% 28% 14% 3	17618
	Night	14% 9% 33% 33% 10% 1	27598

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	8% 13% 5% 17% 11% 8% 6% 3 5% 6% 19%	3248
	11th to 20th	Day	5% 11% 6% 10% 7% 7% 10% 8% 10% 8% 18%	3950
	21st to end	Day	4 13% 8% 12% 6% 6% 5% 4 5% 6% 31%	4488
February	1st to 10th	Day	8% 12% 4 10% 7% 7% 7% 5% 6% 6% 27%	1800
	11th to 20th	Day	7% 12% 4 10% 7% 6% 6% 4 6% 6% 31%	1754
	21st to end	Day	10% 11% 4 11% 7% 5% 4 4 6% 8% 30%	1566
March	1st to 10th	Day	11% 8% 3 8% 4 4 5% 3 5% 7% 42%	4867
	11th to 20th	Day	9% 9% 3 7% 4 4 5% 3 5% 8% 43%	4980
	21st to end	Day	23% 12% 4 10% 6% 4 4 4 5% 7% 22%	5462
April	1st to 10th	Day	18% 10% 2 7% 4 4 3 4 6% 7% 36%	2328
	11th to 20th	Day	19% 11% 3 7% 4 5% 4 4 4 6% 32%	2513
	21st to end	Day	23% 10% 2 6% 4 4 4 3 5% 6% 33%	2600
May	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 5% 6% 49%	5862
	11th to 20th	Day	19% 8% 2 5% 3 3 3 3 4 6% 44%	6224
	21st to end	Day	16% 7% 2 7% 4 5% 5% 4 7% 7% 36%	6935
June	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 7% 46%	2860
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 3 6% 7% 40%	3000
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 10% 46%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 8% 10% 45%	6800
	11th to 20th	Day	8% 4 2 4 3 3 4 3 5% 8% 56%	6594
	21st to end	Day	6% 5% 2 5% 4 5% 5% 4 7% 10% 47%	6426
August	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 43%	4234
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	4171
	21st to end	Day	8% 4 2 5% 4 4 5% 3 6% 8% 50%	4619
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 6% 8% 51%	2400
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 6% 7% 47%	2222
	21st to end	Day	14% 5% 1 4 3 3 3 3 6% 6% 52%	2195
October	1st to 10th	Day	15% 7% 2 5% 4 3 3 3 5% 6% 46%	2000
	11th to 20th	Day	14% 8% 3 5% 4 4 3 3 5% 7% 44%	2000
	21st to end	Day	18% 9% 3 6% 4 3 3 3 4 6% 42%	2165
November	1st to 10th	Day	12% 9% 4 8% 4 3 3 3 5% 7% 40%	1759
	11th to 20th	Day	9% 11% 3 11% 7% 5% 4 3 4 6% 35%	1680
	21st to end	Day	12% 12% 4 9% 6% 4 3 3 6% 7% 34%	1680
December	1st to 10th	Day	6% 10% 4 14% 10% 8% 5% 4 5% 7% 27%	2690
	11th to 20th	Day	9% 14% 6% 12% 9% 7% 6% 4 5% 7% 22%	3088
	21st to end	Day	16% 13% 5% 21% 5% 4 5% 3 4 5% 19%	3648
January	1st to 10th	Night	6% 11% 5% 16% 11% 8% 6% 3 5% 6% 22%	6937
	11th to 20th	Night	4 9% 4 13% 8% 8% 11% 7% 8% 6% 21%	6140
	21st to end	Night	6% 13% 8% 10% 5% 5% 5% 3 5% 5% 35%	6490
February	1st to 10th	Night	7% 13% 4 9% 5% 6% 6% 4 6% 6% 34%	2600
	11th to 20th	Night	6% 10% 4 9% 6% 6% 6% 5% 6% 6% 37%	2533
	21st to end	Night	9% 10% 3 8% 6% 6% 5% 5% 6% 6% 36%	2080
March	1st to 10th	Night	9% 7% 3 6% 4 4 4 3 5% 6% 50%	4977
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 6% 9% 44%	4980
	21st to end	Night	22% 10% 3 10% 4 4 4 3 4 5% 30%	5467
April	1st to 10th	Night	16% 10% 3 5% 5% 4 4 3 4 7% 40%	2070
	11th to 20th	Night	17% 10% 4 7% 4 3 3 4 3 6% 39%	1833
	21st to end	Night	18% 9% 3 7% 4 4 3 4 4 7% 38%	1800
May	1st to 10th	Night	12% 5% 2 4 3 3 3 3 4 6% 55%	4053
	11th to 20th	Night	14% 8% 1 5% 3 3 4 3 5% 7% 46%	3688
	21st to end	Night	18% 8% 2 7% 4 3 4 3 4 6% 41%	3942
June	1st to 10th	Night	9% 4 1 4 4 4 4 4 5% 7% 54%	1534
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 3 6% 9% 49%	1400
	21st to end	Night	8% 3 2 5% 3 4 4 4 4 6% 57%	1400
July	1st to 10th	Night	7% 4 2 5% 4 3 4 4 7% 9% 51%	3178
	11th to 20th	Night	5% 3 2 5% 4 4 4 3 5% 7% 58%	3369
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 9% 49%	4441
August	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 5% 7% 48%	2926
	11th to 20th	Night	12% 5% 2 4 3 4 3 3 5% 7% 52%	2888
	21st to end	Night	8% 5% 2 5% 3 3 4 3 5% 7% 55%	3288
September	1st to 10th	Night	8% 4 2 5% 3 2 4 3 5% 6% 58%	2000
	11th to 20th	Night	9% 4 2 4 3 3 4 3 5% 8% 55%	2175
	21st to end	Night	11% 5% 1 5% 3 3 4 3 4 6% 55%	2200
October	1st to 10th	Night	14% 6% 2 4 3 3 4 2 4 6% 51%	2384
	11th to 20th	Night	15% 8% 2 6% 3 3 4 3 4 6% 46%	2400
	21st to end	Night	16% 9% 3 7% 4 3 3 3 4 7% 42%	2671
November	1st to 10th	Night	10% 8% 3 6% 5% 5% 4 3 5% 6% 44%	2757
	11th to 20th	Night	11% 10% 4 10% 4 4 4 3 5% 5% 39%	2940
	21st to end	Night	10% 10% 3 9% 5% 4 4 4 5% 7% 38%	2940
December	1st to 10th	Night	6% 8% 4 12% 8% 7% 5% 4 6% 7% 34%	4720
	11th to 20th	Night	10% 12% 5% 13% 7% 6% 5% 4 5% 7% 27%	5339
	21st to end	Night	17% 15% 5% 16% 6% 5% 5% 3 4 5% 19%	7555

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	67% 5% 11% 11% 6%	3249
	11th to 20th	Day	56% 6% 13% 16% 9%	3950
	21st to end	Day	53% 7% 17% 14% 10%	4488
February	1st to 10th	Day	56% 6% 14% 17% 8%	1800
	11th to 20th	Day	53% 7% 13% 19% 8% 1	1763
	21st to end	Day	51% 8% 15% 15% 11% 1	1566
March	1st to 10th	Day	40% 7% 15% 26% 11% 1	4867
	11th to 20th	Day	39% 5% 13% 30% 12% 2	4980
	21st to end	Day	61% 6% 10% 18% 5%	5464
April	1st to 10th	Day	46% 6% 13% 23% 11% 1	2328
	11th to 20th	Day	51% 5% 11% 19% 12% 1	2513
	21st to end	Day	51% 7% 12% 21% 9% 1	2600
May	1st to 10th	Day	33% 6% 12% 27% 21% 1	5900
	11th to 20th	Day	41% 6% 9% 20% 15% 9%	6228
	21st to end	Day	43% 8% 11% 27% 10% 1	6949
June	1st to 10th	Day	34% 8% 15% 28% 13% 1	2860
	11th to 20th	Day	42% 7% 12% 22% 14% 2	3000
	21st to end	Day	33% 8% 17% 27% 14% 2	3000
July	1st to 10th	Day	31% 9% 19% 29% 12%	6726
	11th to 20th	Day	26% 6% 15% 36% 16% 2	6513
	21st to end	Day	31% 7% 17% 29% 15% 1	6243
August	1st to 10th	Day	38% 6% 12% 29% 12% 2	4220
	11th to 20th	Day	39% 8% 15% 30% 7% 1	4210
	21st to end	Day	31% 7% 19% 27% 14% 1	4618
September	1st to 10th	Day	31% 7% 14% 32% 16% 1	2400
	11th to 20th	Day	34% 6% 17% 30% 12% 1	2222
	21st to end	Day	34% 4 11% 31% 17% 2	2195
October	1st to 10th	Day	30% 4 8% 29% 28% 1	3260
	11th to 20th	Day	37% 5% 13% 23% 21% 2	3240
	21st to end	Day	42% 4 16% 26% 12% 1	3481
November	1st to 10th	Day	42% 6% 14% 21% 14% 3	1759
	11th to 20th	Day	50% 5% 14% 21% 10%	1680
	21st to end	Day	49% 6% 15% 20% 9% 1	1680
December	1st to 10th	Day	55% 6% 15% 18% 6%	2690
	11th to 20th	Day	62% 7% 13% 14% 5%	3085
	21st to end	Day	67% 5% 12% 12% 5%	3648
January	1st to 10th	Night	63% 5% 10% 16% 6%	6937
	11th to 20th	Night	59% 5% 12% 13% 10% 1	6140
	21st to end	Night	49% 5% 14% 21% 10%	6490
February	1st to 10th	Night	50% 6% 14% 20% 9% 2	2600
	11th to 20th	Night	44% 8% 15% 22% 11% 2	2534
	21st to end	Night	44% 7% 14% 20% 12% 2	2080
March	1st to 10th	Night	34% 6% 10% 34% 14% 2	4977
	11th to 20th	Night	35% 6% 15% 31% 13%	4980
	21st to end	Night	57% 5% 11% 20% 7% 1	5467
April	1st to 10th	Night	44% 6% 12% 26% 11% 1	2070
	11th to 20th	Night	46% 5% 10% 21% 16% 2	1833
	21st to end	Night	46% 7% 10% 22% 12% 2	1800
May	1st to 10th	Night	29% 6% 12% 28% 23% 3	4080
	11th to 20th	Night	36% 7% 9% 18% 21% 9%	3689
	21st to end	Night	44% 6% 9% 27% 12% 1	3950
June	1st to 10th	Night	28% 7% 15% 30% 17% 3	1534
	11th to 20th	Night	33% 6% 18% 23% 17% 3	1400
	21st to end	Night	28% 7% 15% 28% 20% 2	1400
July	1st to 10th	Night	29% 6% 18% 30% 17% 1	3145
	11th to 20th	Night	26% 5% 13% 38% 16% 2	3330
	21st to end	Night	31% 8% 18% 30% 13% 1	4313
August	1st to 10th	Night	35% 5% 15% 26% 16% 3	2916
	11th to 20th	Night	33% 6% 16% 32% 12% 1	2915
	21st to end	Night	29% 6% 17% 29% 17% 3	3288
September	1st to 10th	Night	27% 6% 13% 34% 19% 1	2000
	11th to 20th	Night	28% 7% 15% 31% 18% 1	2175
	21st to end	Night	30% 6% 10% 30% 22% 2	2200
October	1st to 10th	Night	22% 3 7% 31% 32% 4	3904
	11th to 20th	Night	30% 4 12% 29% 22% 3	3899
	21st to end	Night	40% 4 13% 29% 14% 1	4307
November	1st to 10th	Night	39% 6% 15% 22% 15% 3	2757
	11th to 20th	Night	46% 6% 12% 22% 13% 1	2940
	21st to end	Night	44% 6% 18% 22% 9% 1	2940
December	1st to 10th	Night	49% 5% 18% 20% 7%	4720
	11th to 20th	Night	56% 7% 14% 18% 4	5341
	21st to end	Night	65% 6% 11% 15% 3	7555

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	16% 11% 32% 26% 14% 2	330
	11th to 20th	Day	15% 13% 36% 28% 7% 1	318
	21st to end	Day	13% 8% 41% 25% 10% 2	330
February	1st to 10th	Day	15% 15% 41% 25% 4	300
	11th to 20th	Day	14% 15% 39% 24% 7% 1	300
	21st to end	Day	16% 12% 40% 28% 4	249
March	1st to 10th	Day	15% 15% 40% 25% 4 1	300
	11th to 20th	Day	19% 12% 39% 23% 5% 2	300
	21st to end	Day	27% 13% 27% 23% 9% 2	330
April	1st to 10th	Day	27% 13% 33% 21% 6%	428
	11th to 20th	Day	26% 17% 28% 20% 7% 1	631
	21st to end	Day	24% 13% 30% 21% 9% 2	700
May	1st to 10th	Day	19% 13% 31% 24% 11% 2	703
	11th to 20th	Day	22% 11% 27% 23% 13% 3	725
	21st to end	Day	17% 7% 30% 29% 14% 2	789
June	1st to 10th	Day	10% 8% 27% 30% 22% 4	730
	11th to 20th	Day	17% 9% 32% 29% 11% 3	730
	21st to end	Day	12% 8% 32% 31% 16% 2	730
July	1st to 10th	Day	7% 5% 22% 34% 25% 6%	721
	11th to 20th	Day	8% 5% 30% 34% 19% 5%	718
	21st to end	Day	7% 4 23% 39% 22% 5%	794
August	1st to 10th	Day	10% 4 21% 37% 24% 4	726
	11th to 20th	Day	12% 5% 21% 32% 23% 7%	715
	21st to end	Day	8% 5% 26% 36% 20% 5%	773
September	1st to 10th	Day	13% 6% 28% 31% 19% 4	530
	11th to 20th	Day	9% 6% 31% 35% 14% 5%	352
	21st to end	Day	18% 12% 26% 24% 15% 5%	330
October	1st to 10th	Day	14% 13% 30% 26% 13% 4	330
	11th to 20th	Day	17% 18% 35% 19% 9% 1	330
	21st to end	Day	24% 15% 34% 20% 7% 1	363
November	1st to 10th	Day	21% 14% 32% 24% 8% 2	330
	11th to 20th	Day	16% 20% 39% 20% 5%	330
	21st to end	Day	19% 18% 30% 25% 6% 1	330
December	1st to 10th	Day	13% 9% 42% 26% 10%	330
	11th to 20th	Day	14% 17% 38% 26% 6%	330
	21st to end	Day	26% 11% 35% 24% 4 1	363
January	1st to 10th	Night	9% 11% 38% 31% 9% 2	1050
	11th to 20th	Night	13% 12% 35% 32% 7% 1	1031
	21st to end	Night	17% 11% 35% 31% 6%	1100
February	1st to 10th	Night	14% 11% 39% 30% 6%	1000
	11th to 20th	Night	12% 12% 40% 28% 7% 1	979
	21st to end	Night	13% 13% 35% 29% 8% 1	760
March	1st to 10th	Night	14% 10% 38% 30% 7%	634
	11th to 20th	Night	19% 10% 37% 28% 7%	600
	21st to end	Night	23% 11% 28% 28% 10% 2	660
April	1st to 10th	Night	20% 13% 37% 25% 5%	600
	11th to 20th	Night	21% 13% 32% 27% 7% 1	593
	21st to end	Night	21% 12% 31% 27% 7% 2	600
May	1st to 10th	Night	18% 9% 33% 31% 9% 1	600
	11th to 20th	Night	17% 8% 33% 30% 12% 1	591
	21st to end	Night	15% 7% 30% 35% 13% 1	650
June	1st to 10th	Night	11% 6% 25% 42% 16%	600
	11th to 20th	Night	11% 4 36% 39% 10%	600
	21st to end	Night	9% 4 27% 48% 13%	600
July	1st to 10th	Night	6% 3 23% 41% 26% 1	585
	11th to 20th	Night	5% 2 26% 48% 18% 1	582
	21st to end	Night	4 2 23% 48% 22% 1	657
August	1st to 10th	Night	10% 3 19% 48% 19% 2	597
	11th to 20th	Night	11% 3 18% 41% 23% 4	594
	21st to end	Night	7% 3 24% 44% 21% 2	660
September	1st to 10th	Night	12% 3 25% 42% 18% 2	600
	11th to 20th	Night	11% 4 29% 37% 19% 1	600
	21st to end	Night	11% 7% 35% 30% 15% 2	600
October	1st to 10th	Night	16% 9% 33% 30% 11% 1	784
	11th to 20th	Night	20% 11% 35% 28% 7% 1	800
	21st to end	Night	20% 12% 31% 30% 7%	911
November	1st to 10th	Night	14% 11% 34% 32% 9%	1025
	11th to 20th	Night	15% 12% 39% 25% 8% 1	1050
	21st to end	Night	15% 13% 36% 30% 6%	1050
December	1st to 10th	Night	13% 10% 40% 29% 7%	1050
	11th to 20th	Night	20% 11% 34% 28% 6% 1	1050
	21st to end	Night	23% 11% 34% 26% 5% 1	1155

Page generated at 2026-01-14 00:14:29. Version ac07

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