EverStaR Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the EverStaR Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	11% 7% 3 6% 4 4 4 3 5% 7% 46%	143113
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 48%	139108
Transparency	Day	37% 5% 12% 26% 17% 3	146725
	Night	36% 4 11% 26% 19% 4	143576
Seeing	Day	14% 10% 30% 28% 15% 3	18135
	Night	13% 9% 33% 32% 11% 1	27895

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% 11% 3 8% 4 4 3 3 4 6% 41%	5289
	11th to 20th	Day	5% 8% 4 9% 7% 6% 5% 3 4 6% 43%	5310
	21st to end	Day	12% 13% 5% 7% 4 4 4 2 3 4 41%	5812
February	1st to 10th	Day	14% 11% 4 7% 5% 4 3 2 4 6% 39%	1890
	11th to 20th	Day	12% 11% 3 7% 4 4 4 3 5% 6% 41%	1844
	21st to end	Day	10% 8% 3 6% 4 4 3 4 5% 6% 46%	1792
March	1st to 10th	Day	12% 9% 3 6% 3 3 3 2 3 5% 51%	5046
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 4 6% 56%	5090
	21st to end	Day	11% 11% 4 8% 5% 5% 5% 4 5% 7% 36%	5583
April	1st to 10th	Day	15% 8% 3 6% 4 4 3 3 5% 6% 44%	2416
	11th to 20th	Day	14% 8% 3 6% 4 5% 4 3 5% 7% 41%	2494
	21st to end	Day	18% 9% 3 8% 5% 5% 4 3 4 6% 36%	2677
May	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 5% 6% 44%	7617
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	7627
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 7% 37%	8486
June	1st to 10th	Day	7% 4 2 5% 4 4 6% 4 7% 9% 47%	2940
	11th to 20th	Day	7% 6% 2 5% 4 4 5% 4 7% 9% 47%	2940
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 9% 50%	2892
July	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	7680
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 6% 9% 53%	7680
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 40%	8337
August	1st to 10th	Day	5% 4 2 6% 4 4 4 4 6% 9% 52%	4364
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 48%	4224
	21st to end	Day	6% 4 2 5% 3 4 4 3 6% 8% 55%	4416
September	1st to 10th	Day	12% 5% 2 4 3 3 4 3 5% 7% 53%	2400
	11th to 20th	Day	8% 5% 2 6% 4 4 4 4 5% 8% 48%	2205
	21st to end	Day	9% 5% 2 6% 3 4 4 3 5% 7% 54%	2194
October	1st to 10th	Day	11% 5% 2 5% 3 2 4 3 5% 7% 53%	2000
	11th to 20th	Day	11% 7% 2 4 3 3 2 2 4 5% 56%	2000
	21st to end	Day	15% 7% 3 5% 4 3 3 3 4 6% 48%	2200
November	1st to 10th	Day	9% 6% 1 5% 3 4 3 3 4 6% 55%	2049
	11th to 20th	Day	13% 6% 1 5% 3 3 3 3 4 7% 51%	1832
	21st to end	Day	15% 9% 3 6% 4 3 2 2 4 5% 47%	1680
December	1st to 10th	Day	6% 6% 2 6% 4 4 4 3 4 7% 54%	2690
	11th to 20th	Day	10% 7% 3 8% 4 3 3 3 4 5% 49%	3088
	21st to end	Day	18% 16% 7% 11% 4 3 4 3 4 5% 25%	4329
January	1st to 10th	Night	12% 11% 3 13% 5% 4 3 2 3 5% 39%	7634
	11th to 20th	Night	7% 8% 3 8% 5% 5% 5% 3 4 5% 49%	7680
	21st to end	Night	13% 10% 4 9% 4 4 4 3 4 5% 40%	8402
February	1st to 10th	Night	11% 11% 3 7% 6% 4 4 3 5% 6% 40%	2730
	11th to 20th	Night	12% 10% 3 7% 4 4 4 3 4 7% 42%	2663
	21st to end	Night	12% 7% 3 6% 4 4 4 3 5% 6% 47%	2030
March	1st to 10th	Night	13% 9% 3 5% 3 3 3 3 4 4 50%	5029
	11th to 20th	Night	8% 7% 1 4 3 3 3 3 6% 7% 56%	5090
	21st to end	Night	13% 8% 4 7% 4 4 4 4 6% 7% 39%	5588
April	1st to 10th	Night	11% 7% 3 6% 4 4 3 3 5% 6% 48%	2202
	11th to 20th	Night	13% 7% 3 6% 3 3 3 3 4 5% 48%	2075
	21st to end	Night	17% 7% 3 7% 4 4 3 3 5% 6% 42%	1937
May	1st to 10th	Night	14% 7% 2 6% 4 4 3 3 5% 7% 45%	5266
	11th to 20th	Night	12% 6% 2 5% 4 3 4 2 5% 7% 50%	5265
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 45%	5679
June	1st to 10th	Night	6% 3 1 4 4 4 4 5% 6% 9% 54%	1680
	11th to 20th	Night	5% 4 2 5% 4 5% 4 4 7% 10% 51%	1680
	21st to end	Night	5% 3 1 4 3 2 3 4 6% 9% 59%	1719
July	1st to 10th	Night	6% 5% 2 5% 3 4 4 4 7% 10% 51%	5308
	11th to 20th	Night	4 4 2 4 3 3 4 4 6% 9% 57%	5307
	21st to end	Night	7% 5% 2 5% 4 5% 5% 5% 7% 12% 42%	5770
August	1st to 10th	Night	2 2 1 3 3 3 6% 4 6% 10% 60%	3016
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 7% 52%	2924
	21st to end	Night	4 3 2 5% 4 4 4 3 5% 7% 60%	3484
September	1st to 10th	Night	9% 5% 2 5% 4 3 3 3 5% 5% 57%	2000
	11th to 20th	Night	9% 4 2 4 4 3 4 4 6% 7% 54%	2191
	21st to end	Night	6% 4 2 5% 4 4 4 3 5% 6% 58%	2200
October	1st to 10th	Night	10% 5% 1 4 3 4 3 3 4 6% 58%	2385
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 4 6% 57%	2400
	21st to end	Night	15% 7% 2 5% 3 2 3 2 4 4 51%	2640
November	1st to 10th	Night	10% 4 1 4 3 3 3 2 4 5% 61%	2465
	11th to 20th	Night	10% 7% 1 4 3 3 3 3 5% 7% 54%	2784
	21st to end	Night	14% 7% 2 5% 3 3 3 3 3 5% 51%	2940
December	1st to 10th	Night	6% 6% 2 5% 4 3 4 3 5% 6% 56%	4720
	11th to 20th	Night	11% 8% 3 7% 4 3 4 3 5% 7% 46%	5339
	21st to end	Night	17% 16% 5% 10% 4 4 3 3 3 4 31%	6886

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	47% 3 10% 27% 12% 2	5290
	11th to 20th	Day	43% 2 11% 24% 15% 5%	5310
	21st to end	Day	49% 3 11% 18% 17% 3	5812
February	1st to 10th	Day	47% 4 13% 23% 11% 3	1890
	11th to 20th	Day	44% 5% 11% 22% 14% 3	1853
	21st to end	Day	38% 4 11% 25% 18% 4	1792
March	1st to 10th	Day	37% 4 8% 21% 22% 8%	5046
	11th to 20th	Day	30% 4 10% 22% 28% 7%	5090
	21st to end	Day	47% 5% 15% 26% 6% 1	5585
April	1st to 10th	Day	41% 5% 12% 23% 17% 2	2416
	11th to 20th	Day	43% 6% 12% 21% 17% 1	2494
	21st to end	Day	50% 6% 11% 23% 10% 1	2677
May	1st to 10th	Day	41% 6% 9% 27% 16% 1	7655
	11th to 20th	Day	36% 6% 11% 24% 21% 2	7631
	21st to end	Day	45% 6% 9% 26% 12% 1	8500
June	1st to 10th	Day	30% 9% 16% 27% 15% 2	2940
	11th to 20th	Day	31% 8% 14% 28% 16% 2	2940
	21st to end	Day	29% 7% 15% 29% 16% 4	2892
July	1st to 10th	Day	34% 6% 14% 26% 18% 1	7616
	11th to 20th	Day	27% 6% 15% 29% 18% 5%	7611
	21st to end	Day	36% 7% 15% 33% 8% 1	8155
August	1st to 10th	Day	27% 7% 14% 28% 21% 2	4350
	11th to 20th	Day	35% 6% 17% 26% 15% 1	4263
	21st to end	Day	26% 6% 14% 35% 15% 5%	4415
September	1st to 10th	Day	32% 5% 12% 25% 19% 6%	2400
	11th to 20th	Day	33% 7% 10% 26% 21% 2	2205
	21st to end	Day	30% 5% 9% 29% 25% 3	2194
October	1st to 10th	Day	19% 3 7% 23% 40% 8%	3260
	11th to 20th	Day	20% 2 5% 26% 37% 9%	3240
	21st to end	Day	33% 3 11% 24% 26% 3	3538
November	1st to 10th	Day	31% 4 12% 30% 18% 5%	2049
	11th to 20th	Day	35% 4 10% 28% 20% 4	1832
	21st to end	Day	41% 4 9% 27% 18% 1	1680
December	1st to 10th	Day	31% 4 12% 36% 17% 1	2690
	11th to 20th	Day	37% 4 12% 32% 14% 1	3085
	21st to end	Day	62% 4 10% 17% 6% 1	4329
January	1st to 10th	Night	50% 3 12% 22% 12% 1	7635
	11th to 20th	Night	39% 3 9% 26% 19% 4	7680
	21st to end	Night	48% 3 11% 19% 15% 4	8402
February	1st to 10th	Night	45% 5% 11% 22% 14% 3	2730
	11th to 20th	Night	43% 4 12% 23% 16% 3	2664
	21st to end	Night	39% 4 8% 22% 21% 7%	2030
March	1st to 10th	Night	37% 4 8% 22% 25% 5%	5029
	11th to 20th	Night	28% 3 7% 22% 32% 8%	5090
	21st to end	Night	42% 6% 15% 24% 10% 2	5588
April	1st to 10th	Night	36% 6% 10% 23% 22% 4	2202
	11th to 20th	Night	38% 4 9% 27% 18% 4	2075
	21st to end	Night	42% 6% 12% 24% 14% 1	1937
May	1st to 10th	Night	39% 5% 11% 26% 18% 2	5293
	11th to 20th	Night	35% 5% 11% 24% 20% 5%	5266
	21st to end	Night	40% 6% 10% 26% 18% 1	5690
June	1st to 10th	Night	25% 9% 17% 31% 16% 3	1680
	11th to 20th	Night	26% 7% 14% 31% 20% 2	1680
	21st to end	Night	21% 6% 15% 33% 22% 4	1719
July	1st to 10th	Night	28% 5% 15% 27% 22% 2	5265
	11th to 20th	Night	24% 6% 15% 29% 19% 6%	5256
	21st to end	Night	32% 6% 16% 36% 9%	5641
August	1st to 10th	Night	18% 7% 18% 29% 22% 6%	3006
	11th to 20th	Night	33% 5% 12% 30% 19% 2	2951
	21st to end	Night	24% 4 12% 38% 17% 5%	3484
September	1st to 10th	Night	30% 5% 10% 27% 20% 8%	2000
	11th to 20th	Night	28% 6% 11% 26% 24% 4	2191
	21st to end	Night	27% 5% 8% 26% 30% 5%	2200
October	1st to 10th	Night	18% 3 6% 20% 46% 8%	3905
	11th to 20th	Night	22% 3 5% 26% 30% 14%	3899
	21st to end	Night	34% 3 7% 29% 24% 3	4252
November	1st to 10th	Night	28% 3 11% 29% 23% 6%	2465
	11th to 20th	Night	30% 4 11% 27% 24% 5%	2784
	21st to end	Night	37% 3 10% 29% 19% 3	2940
December	1st to 10th	Night	30% 4 13% 34% 18% 1	4720
	11th to 20th	Night	39% 4 12% 27% 17% 2	5341
	21st to end	Night	59% 4 9% 20% 7% 1	6886

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	22% 14% 38% 22% 5%	330
	11th to 20th	Day	20% 20% 40% 17% 3	330
	21st to end	Day	15% 13% 46% 24% 2	363
February	1st to 10th	Day	21% 20% 40% 16% 3 1	330
	11th to 20th	Day	22% 18% 40% 15% 5%	330
	21st to end	Day	14% 22% 45% 16% 3	273
March	1st to 10th	Day	19% 16% 45% 17% 3	330
	11th to 20th	Day	26% 15% 32% 23% 3 1	330
	21st to end	Day	27% 23% 33% 14% 3 1	363
April	1st to 10th	Day	25% 16% 36% 18% 6%	436
	11th to 20th	Day	18% 19% 38% 20% 5% 1	532
	21st to end	Day	22% 17% 34% 19% 7%	697
May	1st to 10th	Day	17% 15% 37% 22% 9% 1	753
	11th to 20th	Day	18% 10% 30% 26% 12% 3	775
	21st to end	Day	18% 9% 29% 26% 15% 4	844
June	1st to 10th	Day	6% 6% 24% 33% 25% 6%	780
	11th to 20th	Day	8% 5% 28% 35% 19% 5%	780
	21st to end	Day	7% 7% 35% 34% 16% 2	780
July	1st to 10th	Day	9% 3 17% 32% 29% 10%	771
	11th to 20th	Day	4 3 19% 37% 28% 9%	768
	21st to end	Day	9% 3 17% 37% 28% 7%	849
August	1st to 10th	Day	7% 2 20% 39% 28% 5%	776
	11th to 20th	Day	9% 3 17% 41% 25% 6%	736
	21st to end	Day	9% 2 16% 30% 34% 10%	648
September	1st to 10th	Day	13% 2 17% 35% 27% 6%	530
	11th to 20th	Day	5% 3 20% 40% 26% 6%	335
	21st to end	Day	11% 7% 25% 36% 16% 6%	330
October	1st to 10th	Day	13% 5% 30% 28% 18% 6%	330
	11th to 20th	Day	11% 16% 41% 23% 8% 1	330
	21st to end	Day	23% 14% 37% 20% 5% 1	363
November	1st to 10th	Day	17% 12% 38% 25% 5% 2	330
	11th to 20th	Day	16% 15% 35% 25% 8% 1	330
	21st to end	Day	23% 13% 36% 20% 7%	330
December	1st to 10th	Day	8% 17% 42% 25% 5% 2	330
	11th to 20th	Day	18% 15% 41% 20% 6% 1	330
	21st to end	Day	19% 22% 39% 18% 1	363
January	1st to 10th	Night	13% 14% 40% 27% 5%	1050
	11th to 20th	Night	14% 14% 43% 25% 4 1	1050
	21st to end	Night	14% 13% 43% 27% 3	1155
February	1st to 10th	Night	16% 13% 43% 24% 3	1050
	11th to 20th	Night	17% 15% 39% 26% 2	1029
	21st to end	Night	17% 12% 46% 20% 4	646
March	1st to 10th	Night	16% 13% 44% 22% 5%	630
	11th to 20th	Night	20% 12% 37% 27% 4	630
	21st to end	Night	24% 13% 39% 21% 4	693
April	1st to 10th	Night	14% 14% 42% 25% 5%	630
	11th to 20th	Night	19% 16% 34% 27% 5%	623
	21st to end	Night	18% 11% 40% 25% 6%	630
May	1st to 10th	Night	17% 8% 36% 31% 7%	630
	11th to 20th	Night	14% 8% 30% 34% 13%	621
	21st to end	Night	12% 5% 31% 35% 14% 2	683
June	1st to 10th	Night	6% 4 22% 46% 20% 2	630
	11th to 20th	Night	5% 5% 28% 45% 17% 1	630
	21st to end	Night	5% 3 34% 44% 12% 1	630
July	1st to 10th	Night	7% 2 14% 45% 29% 2	615
	11th to 20th	Night	3 2 17% 46% 30% 2	612
	21st to end	Night	7% 2 14% 48% 27% 1	690
August	1st to 10th	Night	4 1 17% 48% 28% 1	627
	11th to 20th	Night	7% 2 13% 46% 28% 3	606
	21st to end	Night	7% 1 14% 43% 33% 2	660
September	1st to 10th	Night	11% 3 19% 43% 22% 3	600
	11th to 20th	Night	9% 3 20% 41% 24% 3	600
	21st to end	Night	8% 5% 23% 45% 18% 2	600
October	1st to 10th	Night	12% 5% 29% 35% 18% 2	785
	11th to 20th	Night	15% 8% 40% 30% 7% 1	800
	21st to end	Night	20% 10% 36% 26% 7%	880
November	1st to 10th	Night	12% 9% 36% 32% 9% 1	825
	11th to 20th	Night	12% 14% 38% 29% 7%	1050
	21st to end	Night	18% 12% 35% 30% 5%	1050
December	1st to 10th	Night	15% 12% 40% 27% 6% 1	1050
	11th to 20th	Night	18% 11% 42% 26% 4	1050
	21st to end	Night	18% 15% 38% 25% 4	1155

Page generated at 2026-08-12 02:37:14. Version ac07

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