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 2025-04-11.

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%	113522
	Night	10% 7% 3 6% 4 3 4 3 5% 6% 48%	114964
Transparency	Day	37% 5% 12% 26% 17% 3	117175
	Night	36% 5% 11% 26% 19% 4	119453
Seeing	Day	14% 10% 29% 28% 16% 4	16141
	Night	13% 9% 33% 32% 11% 1	26174

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	15% 10% 3 9% 4 4 4 3 4 6% 37%	4077
	11th to 20th	Day	6% 10% 4 9% 7% 7% 5% 3 4 5% 41%	4080
	21st to end	Day	13% 13% 5% 7% 4 4 5% 3 4 5% 38%	4488
February	1st to 10th	Day	15% 11% 4 7% 5% 4 3 2 5% 6% 38%	1800
	11th to 20th	Day	12% 11% 3 7% 4 4 4 3 5% 6% 40%	1754
	21st to end	Day	11% 9% 3 6% 4 4 4 4 6% 6% 45%	1709
March	1st to 10th	Day	12% 8% 3 6% 3 3 3 3 3 5% 51%	4936
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 4 6% 56%	4980
	21st to end	Day	11% 11% 4 8% 5% 5% 5% 4 5% 7% 35%	5462
April	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 5% 6% 45%	2301
	11th to 20th	Day	14% 9% 3 6% 4 5% 4 3 5% 7% 41%	2254
	21st to end	Day	19% 8% 3 7% 5% 5% 4 3 4 6% 37%	2422
May	1st to 10th	Day	15% 9% 3 6% 5% 4 5% 3 6% 6% 39%	4082
	11th to 20th	Day	16% 7% 3 7% 4 4 4 4 5% 7% 39%	4082
	21st to end	Day	12% 6% 3 5% 5% 4 4 4 5% 8% 44%	4529
June	1st to 10th	Day	7% 4 2 5% 4 4 6% 4 7% 10% 48%	2660
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 4 7% 9% 47%	2660
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 9% 52%	2617
July	1st to 10th	Day	10% 7% 2 7% 5% 4 4 5% 6% 9% 41%	4120
	11th to 20th	Day	5% 3 2 5% 3 3 4 4 7% 10% 53%	4120
	21st to end	Day	6% 3 2 5% 5% 5% 6% 5% 8% 10% 45%	4465
August	1st to 10th	Day	5% 4 2 5% 4 4 4 4 6% 9% 53%	4104
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 5% 8% 47%	4041
	21st to end	Day	6% 4 2 5% 3 4 4 3 6% 8% 56%	4281
September	1st to 10th	Day	13% 5% 2 4 3 3 3 3 4 7% 53%	2280
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 5% 7% 49%	2095
	21st to end	Day	9% 5% 2 6% 3 4 4 3 5% 7% 54%	2085
October	1st to 10th	Day	11% 5% 2 5% 3 2 4 3 5% 7% 53%	1900
	11th to 20th	Day	11% 7% 2 4 3 3 2 2 4 6% 57%	1900
	21st to end	Day	14% 7% 3 6% 4 3 3 3 4 6% 48%	2090
November	1st to 10th	Day	10% 6% 1 5% 3 4 4 3 4 6% 54%	1950
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 7% 51%	1745
	21st to end	Day	14% 8% 2 6% 4 3 2 2 4 5% 48%	1600
December	1st to 10th	Day	6% 6% 2 5% 4 4 4 3 4 7% 54%	2610
	11th to 20th	Day	10% 8% 3 8% 4 3 3 3 4 5% 49%	3008
	21st to end	Day	18% 17% 7% 11% 4 3 4 3 4 5% 25%	4235
January	1st to 10th	Night	12% 10% 3 14% 6% 4 4 2 3 5% 36%	5888
	11th to 20th	Night	8% 8% 3 9% 5% 6% 5% 3 4 4 43%	5900
	21st to end	Night	14% 9% 4 10% 4 3 3 3 4 5% 41%	6490
February	1st to 10th	Night	11% 11% 3 7% 6% 4 4 3 5% 6% 39%	2600
	11th to 20th	Night	12% 10% 3 7% 4 4 4 3 4 7% 42%	2533
	21st to end	Night	12% 7% 3 6% 5% 4 4 3 5% 6% 47%	1936
March	1st to 10th	Night	13% 9% 3 5% 3 3 3 3 4 4 51%	4919
	11th to 20th	Night	8% 7% 1 4 3 3 3 3 6% 7% 56%	4980
	21st to end	Night	13% 8% 4 7% 4 4 4 4 6% 7% 39%	5467
April	1st to 10th	Night	10% 7% 3 6% 4 4 3 3 5% 6% 49%	2097
	11th to 20th	Night	13% 8% 3 6% 4 3 3 3 5% 5% 48%	1881
	21st to end	Night	17% 7% 3 6% 4 4 3 3 5% 6% 43%	1753
May	1st to 10th	Night	15% 7% 3 6% 5% 4 4 4 7% 7% 40%	2823
	11th to 20th	Night	15% 7% 2 5% 4 3 4 3 6% 7% 44%	2823
	21st to end	Night	11% 5% 1 5% 4 3 3 3 5% 7% 53%	3032
June	1st to 10th	Night	5% 3 1 4 4 5% 4 5% 6% 9% 55%	1520
	11th to 20th	Night	5% 3 2 5% 4 5% 4 4 7% 11% 51%	1520
	21st to end	Night	4 3 1 4 3 2 3 4 6% 8% 61%	1555
July	1st to 10th	Night	10% 7% 3 7% 3 4 4 3 6% 7% 47%	2850
	11th to 20th	Night	2 3 1 4 3 3 4 3 6% 10% 60%	2850
	21st to end	Night	5% 3 2 4 4 4 5% 5% 8% 12% 48%	3098
August	1st to 10th	Night	2 2 1 3 3 3 6% 4 6% 10% 60%	2836
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 6% 52%	2798
	21st to end	Night	3 3 2 5% 4 4 4 3 5% 7% 60%	3377
September	1st to 10th	Night	9% 5% 2 4 4 3 3 3 5% 4 58%	1900
	11th to 20th	Night	9% 4 1 4 4 3 4 4 6% 7% 54%	2081
	21st to end	Night	6% 4 2 5% 4 4 4 3 4 6% 58%	2090
October	1st to 10th	Night	10% 5% 1 4 3 4 3 3 4 5% 58%	2266
	11th to 20th	Night	12% 5% 2 4 3 2 3 2 3 5% 58%	2280
	21st to end	Night	14% 7% 2 5% 3 2 3 2 4 4 51%	2508
November	1st to 10th	Night	10% 4 1 4 3 3 3 2 4 5% 61%	2345
	11th to 20th	Night	10% 7% 1 4 3 3 3 3 5% 7% 54%	2651
	21st to end	Night	14% 7% 2 4 3 3 3 3 3 5% 53%	2800
December	1st to 10th	Night	7% 6% 2 5% 4 3 4 3 4 6% 57%	4580
	11th to 20th	Night	11% 8% 3 8% 4 3 4 3 5% 6% 45%	5199
	21st to end	Night	18% 17% 5% 10% 4 4 3 3 3 4 30%	6738

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	49% 4 10% 24% 12% 1	4078
	11th to 20th	Day	47% 2 10% 22% 15% 4	4080
	21st to end	Day	50% 3 10% 15% 18% 3	4488
February	1st to 10th	Day	49% 4 12% 22% 10% 3	1800
	11th to 20th	Day	45% 5% 11% 22% 14% 3	1763
	21st to end	Day	39% 5% 10% 25% 17% 4	1709
March	1st to 10th	Day	37% 4 8% 21% 22% 8%	4936
	11th to 20th	Day	30% 4 10% 22% 28% 7%	4980
	21st to end	Day	47% 5% 15% 26% 6% 1	5464
April	1st to 10th	Day	40% 5% 12% 24% 17% 2	2301
	11th to 20th	Day	43% 5% 12% 22% 16% 1	2254
	21st to end	Day	49% 6% 11% 23% 11% 1	2422
May	1st to 10th	Day	45% 8% 10% 22% 13% 2	4120
	11th to 20th	Day	42% 8% 13% 22% 14%	4086
	21st to end	Day	37% 8% 11% 30% 12% 2	4542
June	1st to 10th	Day	29% 9% 16% 29% 15% 2	2660
	11th to 20th	Day	31% 8% 15% 29% 16% 2	2660
	21st to end	Day	28% 7% 15% 29% 17% 4	2617
July	1st to 10th	Day	39% 7% 13% 20% 18% 3	4056
	11th to 20th	Day	24% 7% 13% 36% 18% 2	4051
	21st to end	Day	28% 8% 17% 32% 13% 2	4325
August	1st to 10th	Day	27% 7% 14% 29% 22% 2	4090
	11th to 20th	Day	36% 6% 17% 25% 15% 1	4080
	21st to end	Day	25% 6% 14% 35% 15% 5%	4280
September	1st to 10th	Day	31% 5% 12% 25% 20% 7%	2280
	11th to 20th	Day	32% 7% 10% 25% 22% 2	2095
	21st to end	Day	30% 5% 10% 28% 24% 3	2085
October	1st to 10th	Day	19% 3 7% 23% 40% 8%	3160
	11th to 20th	Day	20% 2 5% 26% 38% 9%	3140
	21st to end	Day	32% 3 11% 24% 26% 3	3428
November	1st to 10th	Day	32% 4 12% 28% 19% 5%	1950
	11th to 20th	Day	35% 4 10% 27% 21% 4	1745
	21st to end	Day	40% 4 9% 27% 19% 1	1600
December	1st to 10th	Day	30% 4 11% 37% 17% 1	2610
	11th to 20th	Day	38% 4 12% 32% 14% 1	3005
	21st to end	Day	62% 4 10% 16% 6% 1	4235
January	1st to 10th	Night	52% 4 12% 20% 11% 1	5888
	11th to 20th	Night	45% 3 9% 23% 16% 4	5900
	21st to end	Night	47% 3 10% 19% 17% 5%	6490
February	1st to 10th	Night	45% 5% 11% 22% 14% 3	2600
	11th to 20th	Night	43% 4 12% 22% 17% 3	2534
	21st to end	Night	39% 4 9% 22% 20% 7%	1936
March	1st to 10th	Night	37% 4 8% 22% 25% 4	4919
	11th to 20th	Night	27% 3 7% 22% 33% 8%	4980
	21st to end	Night	43% 6% 15% 24% 9% 2	5467
April	1st to 10th	Night	35% 6% 10% 24% 21% 4	2097
	11th to 20th	Night	38% 4 9% 28% 18% 4	1881
	21st to end	Night	42% 6% 12% 24% 15% 1	1753
May	1st to 10th	Night	42% 8% 15% 19% 15% 1	2850
	11th to 20th	Night	39% 7% 12% 27% 14% 1	2824
	21st to end	Night	30% 6% 12% 30% 21% 1	3040
June	1st to 10th	Night	23% 9% 17% 32% 16% 3	1520
	11th to 20th	Night	25% 8% 14% 32% 19% 2	1520
	21st to end	Night	19% 6% 14% 34% 22% 4	1555
July	1st to 10th	Night	35% 5% 12% 24% 19% 4	2805
	11th to 20th	Night	19% 6% 14% 37% 22% 3	2796
	21st to end	Night	26% 7% 20% 31% 15% 1	2999
August	1st to 10th	Night	18% 7% 19% 28% 22% 6%	2826
	11th to 20th	Night	34% 5% 12% 29% 19% 2	2825
	21st to end	Night	24% 4 12% 38% 17% 4	3377
September	1st to 10th	Night	29% 5% 9% 27% 21% 9%	1900
	11th to 20th	Night	28% 6% 11% 26% 25% 4	2081
	21st to end	Night	27% 5% 8% 26% 29% 5%	2090
October	1st to 10th	Night	18% 3 6% 20% 46% 8%	3786
	11th to 20th	Night	21% 3 5% 26% 31% 14%	3779
	21st to end	Night	33% 3 7% 29% 25% 3	4120
November	1st to 10th	Night	28% 3 11% 28% 24% 6%	2345
	11th to 20th	Night	31% 4 10% 26% 24% 5%	2651
	21st to end	Night	36% 3 10% 29% 19% 3	2800
December	1st to 10th	Night	29% 4 13% 34% 18% 1	4580
	11th to 20th	Night	39% 4 12% 27% 16% 2	5201
	21st to end	Night	59% 4 9% 20% 7% 1	6738

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% 37% 22% 5%	300
	11th to 20th	Day	22% 18% 39% 18% 3	300
	21st to end	Day	15% 12% 45% 25% 2	330
February	1st to 10th	Day	23% 19% 39% 16% 2 1	300
	11th to 20th	Day	22% 19% 40% 15% 5%	300
	21st to end	Day	14% 22% 46% 14% 3	249
March	1st to 10th	Day	17% 16% 46% 18% 3	300
	11th to 20th	Day	25% 16% 31% 24% 3 1	300
	21st to end	Day	27% 23% 32% 15% 2 1	330
April	1st to 10th	Day	23% 15% 36% 19% 6%	401
	11th to 20th	Day	17% 17% 38% 22% 5% 1	452
	21st to end	Day	22% 16% 33% 20% 8%	602
May	1st to 10th	Day	18% 14% 38% 20% 9% 1	653
	11th to 20th	Day	19% 9% 29% 27% 13% 2	675
	21st to end	Day	17% 9% 28% 26% 16% 4	734
June	1st to 10th	Day	6% 4 21% 35% 27% 7%	680
	11th to 20th	Day	8% 4 28% 36% 20% 5%	680
	21st to end	Day	6% 6% 34% 35% 17% 2	680
July	1st to 10th	Day	10% 3 16% 31% 30% 11%	671
	11th to 20th	Day	4 3 19% 39% 28% 7%	668
	21st to end	Day	8% 2 17% 37% 29% 8%	739
August	1st to 10th	Day	7% 2 17% 39% 30% 5%	676
	11th to 20th	Day	9% 3 16% 40% 25% 6%	665
	21st to end	Day	8% 2 15% 30% 35% 10%	601
September	1st to 10th	Day	14% 1 16% 34% 29% 6%	490
	11th to 20th	Day	5% 3 21% 38% 27% 6%	305
	21st to end	Day	11% 7% 26% 36% 15% 4	300
October	1st to 10th	Day	13% 5% 30% 26% 19% 7%	300
	11th to 20th	Day	10% 17% 41% 22% 9% 1	300
	21st to end	Day	20% 15% 38% 20% 6% 1	330
November	1st to 10th	Day	17% 11% 37% 27% 6% 2	300
	11th to 20th	Day	18% 16% 33% 25% 8% 1	300
	21st to end	Day	21% 13% 38% 20% 8%	300
December	1st to 10th	Day	8% 16% 42% 26% 5% 2	300
	11th to 20th	Day	19% 14% 39% 21% 6% 1	300
	21st to end	Day	20% 24% 37% 18% 1	330
January	1st to 10th	Night	13% 14% 39% 28% 6%	1000
	11th to 20th	Night	14% 13% 42% 26% 4 1	1000
	21st to end	Night	14% 12% 43% 27% 3	1100
February	1st to 10th	Night	17% 13% 43% 24% 3	1000
	11th to 20th	Night	17% 15% 39% 27% 3	979
	21st to end	Night	17% 12% 46% 20% 4	616
March	1st to 10th	Night	15% 13% 45% 23% 5%	600
	11th to 20th	Night	20% 11% 37% 28% 5%	600
	21st to end	Night	24% 12% 38% 22% 4	660
April	1st to 10th	Night	14% 14% 41% 26% 5%	600
	11th to 20th	Night	19% 13% 34% 29% 5%	565
	21st to end	Night	18% 10% 39% 26% 6% 1	570
May	1st to 10th	Night	17% 8% 36% 31% 7% 1	570
	11th to 20th	Night	15% 6% 30% 36% 13%	561
	21st to end	Night	11% 6% 31% 34% 16% 2	617
June	1st to 10th	Night	5% 4 22% 46% 21% 2	570
	11th to 20th	Night	5% 4 28% 46% 18% 1	570
	21st to end	Night	5% 3 33% 46% 13% 1	570
July	1st to 10th	Night	7% 2 14% 45% 29% 3	555
	11th to 20th	Night	3 1 18% 47% 29% 2	552
	21st to end	Night	7% 2 14% 47% 29% 1	624
August	1st to 10th	Night	4 1 16% 48% 30% 1	567
	11th to 20th	Night	8% 3 13% 46% 28% 2	564
	21st to end	Night	6% 1 15% 42% 33% 3	627
September	1st to 10th	Night	10% 3 19% 42% 23% 3	570
	11th to 20th	Night	9% 3 20% 40% 24% 3	570
	21st to end	Night	8% 5% 23% 45% 17% 2	570
October	1st to 10th	Night	12% 5% 28% 35% 19% 2	746
	11th to 20th	Night	15% 8% 40% 30% 7% 1	760
	21st to end	Night	20% 10% 36% 27% 7%	836
November	1st to 10th	Night	12% 10% 35% 33% 10% 1	785
	11th to 20th	Night	13% 15% 38% 28% 7%	1000
	21st to end	Night	17% 12% 36% 30% 5%	1000
December	1st to 10th	Night	15% 12% 39% 28% 6% 1	1000
	11th to 20th	Night	18% 10% 41% 26% 5%	1000
	21st to end	Night	19% 15% 37% 25% 4	1100

Page generated at 2025-04-08 08:17:25. Version ac07

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