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 2024-11-25.

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 7% 5% 4 5% 4 6% 7% 39%	101883
	Night	11% 8% 3 8% 5% 4 4 3 5% 7% 41%	97666
Transparency	Day	42% 7% 14% 24% 12% 1	105489
	Night	41% 6% 13% 24% 13% 2	102202
Seeing	Day	15% 10% 30% 28% 14% 3	16065
	Night	14% 9% 33% 33% 11% 1	25970

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	11% 15% 5% 16% 10% 6% 4 3 4 5% 21%	2218
	11th to 20th	Day	5% 14% 6% 11% 7% 7% 9% 6% 9% 7% 19%	2709
	21st to end	Day	6% 17% 9% 13% 7% 6% 5% 5% 5% 6% 22%	3135
February	1st to 10th	Day	8% 12% 4 9% 7% 7% 7% 5% 6% 6% 28%	1710
	11th to 20th	Day	7% 13% 4 10% 7% 7% 6% 4 5% 6% 30%	1664
	21st to end	Day	10% 11% 4 11% 8% 6% 4 4 6% 8% 29%	1490
March	1st to 10th	Day	11% 11% 4 11% 6% 5% 5% 3 5% 6% 35%	3393
	11th to 20th	Day	10% 11% 3 8% 4 4 5% 3 4 7% 41%	3480
	21st to end	Day	25% 13% 5% 10% 6% 4 4 3 4 6% 20%	3814
April	1st to 10th	Day	18% 9% 2 7% 4 4 3 4 6% 7% 36%	2211
	11th to 20th	Day	20% 11% 3 7% 4 5% 4 3 4 6% 33%	2386
	21st to end	Day	23% 10% 2 6% 4 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 4 6% 8% 38%	4082
	11th to 20th	Day	14% 6% 3 6% 4 4 3 4 4 7% 46%	4332
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 7% 8% 38%	4824
June	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 6% 7% 46%	2717
	11th to 20th	Day	14% 7% 2 6% 5% 3 5% 3 6% 7% 41%	2850
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 6% 10% 46%	2850
July	1st to 10th	Day	9% 5% 2 5% 4 5% 6% 5% 8% 10% 40%	4750
	11th to 20th	Day	5% 3 1 4 3 3 4 4 5% 8% 59%	4609
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 8% 9% 51%	4469
August	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 44%	4104
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	4041
	21st to end	Day	8% 4 2 5% 4 4 5% 3 6% 8% 50%	4478
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 5% 8% 51%	2280
	11th to 20th	Day	10% 6% 3 5% 4 4 4 3 6% 7% 49%	2111
	21st to end	Day	15% 5% 1 4 3 3 3 3 6% 6% 51%	2085
October	1st to 10th	Day	15% 7% 2 5% 4 3 3 3 5% 6% 46%	1900
	11th to 20th	Day	14% 8% 3 5% 3 4 4 3 5% 7% 45%	1900
	21st to end	Day	18% 9% 3 6% 4 3 3 3 4 6% 43%	2057
November	1st to 10th	Day	13% 9% 4 8% 4 3 3 3 5% 7% 40%	1674
	11th to 20th	Day	10% 12% 3 11% 8% 5% 4 3 4 6% 34%	1600
	21st to end	Day	12% 12% 4 8% 6% 4 4 3 6% 7% 35%	1552
December	1st to 10th	Day	9% 12% 3 13% 9% 7% 5% 3 6% 5% 29%	1520
	11th to 20th	Day	10% 12% 5% 11% 7% 6% 4 4 5% 8% 29%	1918
	21st to end	Day	19% 12% 5% 18% 4 3 4 3 4 5% 22%	2500
January	1st to 10th	Night	8% 14% 6% 16% 11% 5% 4 3 5% 5% 24%	4737
	11th to 20th	Night	4 10% 5% 16% 9% 8% 10% 6% 8% 5% 20%	4238
	21st to end	Night	8% 16% 10% 12% 5% 5% 5% 3 5% 5% 26%	4532
February	1st to 10th	Night	7% 13% 4 9% 5% 6% 6% 4 5% 6% 34%	2470
	11th to 20th	Night	7% 10% 3 9% 5% 6% 6% 5% 6% 6% 37%	2403
	21st to end	Night	9% 10% 3 8% 6% 6% 5% 5% 6% 6% 36%	1979
March	1st to 10th	Night	7% 8% 3 7% 5% 4 4 3 6% 6% 47%	3463
	11th to 20th	Night	9% 8% 3 7% 5% 5% 4 4 6% 7% 43%	3480
	21st to end	Night	26% 11% 3 11% 4 3 3 2 4 6% 27%	3817
April	1st to 10th	Night	16% 10% 3 5% 5% 4 3 3 4 7% 40%	1967
	11th to 20th	Night	17% 10% 4 7% 4 3 3 3 3 6% 38%	1740
	21st to end	Night	18% 9% 3 6% 4 4 3 4 5% 7% 39%	1710
May	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2823
	11th to 20th	Night	11% 6% 1 5% 4 4 5% 4 6% 9% 46%	2570
	21st to end	Night	16% 7% 2 6% 4 3 4 3 5% 7% 44%	2743
June	1st to 10th	Night	9% 3 1 4 4 4 4 4 5% 7% 54%	1458
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 3 6% 9% 50%	1330
	21st to end	Night	8% 2 1 5% 3 4 4 3 4 6% 59%	1330
July	1st to 10th	Night	9% 5% 2 6% 3 4 4 4 7% 9% 46%	2220
	11th to 20th	Night	2 2 1 4 4 3 4 2 5% 7% 67%	2360
	21st to end	Night	5% 3 1 5% 3 4 4 4 7% 10% 55%	3090
August	1st to 10th	Night	12% 6% 2 6% 3 3 3 3 5% 7% 49%	2836
	11th to 20th	Night	13% 5% 2 4 3 4 3 3 5% 7% 52%	2798
	21st to end	Night	8% 5% 2 6% 3 3 4 3 5% 7% 54%	3187
September	1st to 10th	Night	8% 4 2 5% 3 2 4 3 5% 6% 58%	1900
	11th to 20th	Night	9% 4 2 4 3 3 4 3 4 8% 56%	2066
	21st to end	Night	11% 5% 1 5% 3 3 4 3 4 6% 54%	2090
October	1st to 10th	Night	15% 6% 2 5% 3 3 4 3 5% 6% 50%	2265
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 4 6% 47%	2280
	21st to end	Night	16% 9% 3 7% 3 3 4 3 4 7% 42%	2537
November	1st to 10th	Night	10% 8% 3 6% 5% 5% 4 3 5% 6% 45%	2622
	11th to 20th	Night	11% 10% 4 10% 4 4 4 3 5% 5% 40%	2800
	21st to end	Night	10% 9% 3 9% 5% 4 4 4 5% 7% 39%	2723
December	1st to 10th	Night	9% 10% 4 10% 7% 5% 5% 4 5% 7% 34%	2660
	11th to 20th	Night	10% 12% 5% 11% 6% 5% 5% 4 6% 7% 29%	3279
	21st to end	Night	19% 12% 5% 14% 6% 4 4 4 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	66% 6% 11% 14% 4	2219
	11th to 20th	Day	57% 7% 12% 19% 5%	2709
	21st to end	Day	60% 8% 14% 15% 4	3135
February	1st to 10th	Day	55% 6% 14% 17% 7%	1710
	11th to 20th	Day	53% 7% 13% 19% 7% 1	1673
	21st to end	Day	52% 8% 14% 15% 11% 1	1490
March	1st to 10th	Day	47% 9% 12% 24% 8% 1	3393
	11th to 20th	Day	42% 6% 12% 26% 11% 2	3480
	21st to end	Day	65% 6% 9% 15% 5%	3814
April	1st to 10th	Day	46% 6% 13% 23% 10% 1	2211
	11th to 20th	Day	51% 5% 11% 19% 12% 1	2386
	21st to end	Day	51% 7% 12% 21% 9% 1	2470
May	1st to 10th	Day	40% 8% 14% 23% 15%	4120
	11th to 20th	Day	37% 7% 11% 26% 15% 3	4336
	21st to end	Day	40% 10% 13% 25% 11% 1	4837
June	1st to 10th	Day	34% 8% 15% 28% 13% 1	2717
	11th to 20th	Day	41% 7% 13% 23% 15% 2	2850
	21st to end	Day	32% 8% 17% 27% 14% 2	2850
July	1st to 10th	Day	34% 10% 20% 23% 12% 1	4676
	11th to 20th	Day	22% 7% 16% 35% 18% 3	4528
	21st to end	Day	27% 8% 17% 30% 16% 2	4328
August	1st to 10th	Day	38% 6% 12% 30% 12% 2	4090
	11th to 20th	Day	39% 8% 15% 31% 7% 1	4080
	21st to end	Day	31% 7% 19% 27% 15% 1	4477
September	1st to 10th	Day	31% 6% 13% 33% 16% 1	2280
	11th to 20th	Day	33% 6% 17% 31% 13% 1	2111
	21st to end	Day	35% 5% 12% 31% 16% 2	2085
October	1st to 10th	Day	30% 4 8% 29% 28% 1	3160
	11th to 20th	Day	36% 5% 13% 24% 21% 2	3140
	21st to end	Day	41% 4 17% 26% 12% 1	3373
November	1st to 10th	Day	42% 7% 14% 21% 14% 3	1674
	11th to 20th	Day	51% 5% 13% 20% 10%	1600
	21st to end	Day	47% 7% 17% 19% 9% 1	1552
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	62% 6% 10% 16% 5%	4737
	11th to 20th	Night	60% 6% 13% 15% 6%	4238
	21st to end	Night	57% 6% 14% 15% 7% 1	4532
February	1st to 10th	Night	50% 6% 14% 20% 9% 2	2470
	11th to 20th	Night	44% 8% 15% 21% 11% 2	2404
	21st to end	Night	46% 8% 13% 20% 11% 3	1979
March	1st to 10th	Night	35% 7% 13% 29% 14% 2	3463
	11th to 20th	Night	36% 7% 13% 30% 13% 1	3480
	21st to end	Night	60% 5% 11% 17% 5% 1	3817
April	1st to 10th	Night	44% 6% 12% 26% 11% 1	1967
	11th to 20th	Night	47% 5% 9% 20% 17% 2	1740
	21st to end	Night	45% 7% 10% 23% 13% 2	1710
May	1st to 10th	Night	39% 7% 12% 22% 17% 3	2850
	11th to 20th	Night	31% 9% 12% 23% 21% 4	2571
	21st to end	Night	40% 7% 12% 25% 14% 2	2751
June	1st to 10th	Night	28% 7% 15% 29% 17% 3	1458
	11th to 20th	Night	31% 7% 17% 23% 18% 3	1330
	21st to end	Night	26% 7% 15% 29% 20% 2	1330
July	1st to 10th	Night	32% 7% 20% 23% 15% 2	2185
	11th to 20th	Night	18% 5% 13% 40% 21% 3	2318
	21st to end	Night	22% 8% 18% 31% 18% 2	2992
August	1st to 10th	Night	35% 5% 15% 26% 16% 3	2826
	11th to 20th	Night	32% 6% 16% 32% 12% 1	2825
	21st to end	Night	29% 6% 17% 28% 17% 3	3187
September	1st to 10th	Night	27% 6% 13% 34% 20% 1	1900
	11th to 20th	Night	27% 7% 15% 32% 19% 1	2066
	21st to end	Night	30% 6% 10% 30% 22% 1	2090
October	1st to 10th	Night	23% 3 7% 31% 32% 4	3785
	11th to 20th	Night	30% 4 12% 30% 22% 3	3779
	21st to end	Night	39% 4 13% 29% 14% 1	4173
November	1st to 10th	Night	39% 6% 15% 22% 16% 3	2622
	11th to 20th	Night	46% 6% 12% 22% 13% 1	2800
	21st to end	Night	44% 6% 18% 21% 10% 1	2723
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	16% 12% 34% 30% 7% 1	270
	21st to end	Day	14% 7% 39% 27% 11% 2	297
February	1st to 10th	Day	13% 15% 41% 26% 5%	270
	11th to 20th	Day	15% 16% 39% 23% 6% 1	270
	21st to end	Day	16% 12% 40% 28% 4	225
March	1st to 10th	Day	16% 16% 39% 24% 4 1	270
	11th to 20th	Day	19% 11% 40% 22% 6% 2	270
	21st to end	Day	28% 12% 26% 23% 9% 2	297
April	1st to 10th	Day	28% 14% 31% 21% 6%	391
	11th to 20th	Day	27% 16% 27% 21% 8% 1	584
	21st to end	Day	24% 14% 29% 22% 10% 2	650
May	1st to 10th	Day	20% 13% 33% 24% 9% 1	653
	11th to 20th	Day	20% 12% 29% 23% 13% 3	675
	21st to end	Day	18% 8% 31% 28% 14% 2	734
June	1st to 10th	Day	9% 8% 27% 30% 22% 4	680
	11th to 20th	Day	16% 9% 32% 30% 11% 3	680
	21st to end	Day	11% 7% 30% 32% 17% 2	680
July	1st to 10th	Day	7% 6% 21% 34% 25% 6%	671
	11th to 20th	Day	7% 4 29% 34% 19% 6%	668
	21st to end	Day	6% 4 21% 40% 23% 5%	739
August	1st to 10th	Day	11% 4 20% 38% 24% 4	676
	11th to 20th	Day	12% 4 21% 32% 24% 6%	665
	21st to end	Day	8% 5% 27% 37% 19% 4	720
September	1st to 10th	Day	13% 5% 28% 32% 18% 4	490
	11th to 20th	Day	8% 6% 30% 35% 15% 6%	321
	21st to end	Day	19% 13% 28% 22% 14% 5%	300
October	1st to 10th	Day	15% 13% 31% 24% 13% 4	300
	11th to 20th	Day	15% 18% 34% 21% 10% 1	300
	21st to end	Day	23% 16% 34% 19% 8% 1	330
November	1st to 10th	Day	21% 13% 30% 25% 9% 2	300
	11th to 20th	Day	17% 20% 38% 20% 4	300
	21st to end	Day	19% 20% 28% 27% 5% 1	282
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% 35% 33% 7% 1	950
	21st to end	Night	18% 11% 34% 31% 7%	1045
February	1st to 10th	Night	13% 10% 39% 31% 7%	950
	11th to 20th	Night	12% 12% 40% 28% 7% 1	929
	21st to end	Night	14% 12% 35% 29% 9% 1	723
March	1st to 10th	Night	14% 10% 38% 30% 8%	603
	11th to 20th	Night	19% 10% 36% 28% 7%	570
	21st to end	Night	22% 11% 27% 28% 10% 2	627
April	1st to 10th	Night	20% 13% 38% 24% 5%	570
	11th to 20th	Night	22% 12% 32% 27% 7% 1	563
	21st to end	Night	20% 12% 32% 27% 7% 2	570
May	1st to 10th	Night	19% 9% 34% 30% 8% 1	570
	11th to 20th	Night	16% 9% 33% 30% 12% 1	561
	21st to end	Night	15% 7% 31% 34% 13% 1	617
June	1st to 10th	Night	11% 5% 25% 42% 16%	570
	11th to 20th	Night	10% 3 37% 40% 10%	570
	21st to end	Night	7% 4 26% 49% 13%	570
July	1st to 10th	Night	6% 3 23% 40% 27% 1	555
	11th to 20th	Night	4 2 26% 49% 19% 1	552
	21st to end	Night	4 2 22% 49% 22% 1	624
August	1st to 10th	Night	10% 3 19% 48% 19% 2	567
	11th to 20th	Night	11% 3 17% 42% 23% 3	564
	21st to end	Night	7% 2 24% 44% 20% 2	627
September	1st to 10th	Night	12% 2 25% 42% 18% 2	570
	11th to 20th	Night	11% 4 30% 36% 18% 1	570
	21st to end	Night	11% 7% 36% 30% 13% 1	570
October	1st to 10th	Night	17% 8% 33% 30% 11% 1	745
	11th to 20th	Night	19% 11% 35% 28% 7% 1	760
	21st to end	Night	20% 12% 32% 30% 7%	865
November	1st to 10th	Night	14% 11% 32% 32% 10%	975
	11th to 20th	Night	15% 12% 39% 25% 8% 1	1000
	21st to end	Night	15% 13% 35% 30% 6%	973
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

Page generated at 2024-11-22 07:02:30. Version ac07

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