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 2024-02-20.

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% 7% 3 6% 5% 3 4 4 5% 7% 44%	78493
	Night	11% 7% 3 6% 5% 3 4 4 5% 6% 47%	80733
Transparency	Day	40% 6% 12% 25% 15% 2	78216
	Night	38% 5% 11% 25% 17% 3	80530
Seeing	Day	14% 9% 28% 28% 16% 4	14606
	Night	13% 9% 33% 32% 11% 1	24667

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	14% 10% 4 8% 5% 3 3 4 5% 6% 37%	2847
	11th to 20th	Day	9% 11% 5% 8% 7% 4 7% 3 3 4 38%	2850
	21st to end	Day	14% 15% 6% 7% 5% 2 3 3 4 5% 35%	3135
February	1st to 10th	Day	15% 10% 5% 7% 5% 3 3 3 4 6% 39%	1710
	11th to 20th	Day	12% 9% 4 7% 4 2 5% 4 5% 6% 41%	1655
	21st to end	Day	12% 9% 4 6% 5% 3 4 5% 5% 6% 42%	1532
March	1st to 10th	Day	11% 9% 3 7% 5% 2 4 5% 5% 6% 41%	1980
	11th to 20th	Day	20% 11% 4 6% 4 2 4 4 4 6% 37%	1980
	21st to end	Day	19% 12% 4 7% 5% 3 4 4 5% 5% 31%	2178
April	1st to 10th	Day	14% 7% 3 6% 5% 3 3 4 5% 6% 45%	2070
	11th to 20th	Day	14% 8% 3 5% 5% 4 5% 4 5% 7% 40%	2134
	21st to end	Day	19% 7% 3 6% 6% 4 4 4 4 6% 36%	2294
May	1st to 10th	Day	17% 9% 5% 6% 5% 3 5% 4 5% 6% 36%	2340
	11th to 20th	Day	16% 7% 3 5% 5% 3 4 4 5% 7% 40%	2302
	21st to end	Day	14% 7% 4 6% 7% 3 5% 5% 6% 9% 35%	2556
June	1st to 10th	Day	7% 3 2 4 4 3 5% 5% 7% 10% 49%	2520
	11th to 20th	Day	7% 5% 2 4 5% 3 5% 6% 7% 9% 47%	2520
	21st to end	Day	6% 4 2 4 5% 3 4 5% 6% 10% 53%	2480
July	1st to 10th	Day	9% 5% 2 4 5% 3 4 5% 7% 10% 45%	2340
	11th to 20th	Day	4 3 1 4 4 2 5% 6% 7% 9% 54%	2340
	21st to end	Day	8% 4 2 5% 6% 3 6% 6% 7% 9% 44%	2546
August	1st to 10th	Day	7% 4 2 6% 5% 3 5% 6% 7% 10% 45%	2328
	11th to 20th	Day	8% 4 2 4 5% 3 4 5% 6% 9% 50%	2301
	21st to end	Day	8% 3 2 5% 4 3 5% 5% 5% 8% 52%	2435
September	1st to 10th	Day	13% 5% 2 3 4 2 3 4 5% 8% 52%	2160
	11th to 20th	Day	9% 5% 2 5% 5% 3 4 5% 5% 7% 50%	1985
	21st to end	Day	8% 4 2 5% 3 3 4 4 5% 7% 55%	1976
October	1st to 10th	Day	12% 5% 2 5% 3 2 4 4 5% 8% 51%	1800
	11th to 20th	Day	12% 7% 3 3 4 2 2 3 4 6% 55%	1800
	21st to end	Day	15% 7% 3 5% 5% 2 4 3 4 6% 47%	1980
November	1st to 10th	Day	9% 6% 1 4 4 3 4 3 4 7% 55%	1851
	11th to 20th	Day	13% 7% 2 4 4 2 3 4 4 7% 51%	1658
	21st to end	Day	14% 7% 3 6% 4 3 2 3 4 5% 48%	1520
December	1st to 10th	Day	10% 8% 3 5% 5% 3 4 4 4 8% 46%	1520
	11th to 20th	Day	12% 10% 4 7% 6% 3 3 4 5% 5% 42%	1918
	21st to end	Day	15% 15% 7% 12% 5% 3 4 4 4 6% 25%	2952
January	1st to 10th	Night	9% 9% 3 13% 7% 3 4 3 3 5% 40%	4108
	11th to 20th	Night	10% 9% 3 8% 6% 4 8% 5% 4 5% 38%	4120
	21st to end	Night	16% 12% 5% 10% 5% 2 3 3 4 5% 36%	4532
February	1st to 10th	Night	11% 10% 4 6% 7% 3 4 4 5% 7% 40%	2470
	11th to 20th	Night	12% 9% 4 6% 4 3 4 4 4 7% 43%	2397
	21st to end	Night	13% 7% 3 6% 5% 3 4 4 4 6% 46%	1737
March	1st to 10th	Night	11% 7% 4 4 5% 2 3 5% 4 6% 49%	1980
	11th to 20th	Night	16% 8% 3 6% 4 3 3 4 4 6% 42%	1980
	21st to end	Night	21% 8% 4 7% 5% 2 4 4 5% 6% 34%	2178
April	1st to 10th	Night	10% 6% 3 5% 5% 2 4 4 5% 7% 50%	1888
	11th to 20th	Night	14% 7% 3 5% 4 2 4 3 5% 6% 48%	1775
	21st to end	Night	16% 6% 3 5% 5% 3 3 4 5% 6% 44%	1661
May	1st to 10th	Night	15% 7% 3 5% 5% 3 5% 5% 6% 7% 40%	1620
	11th to 20th	Night	14% 6% 2 4 4 3 4 3 5% 7% 49%	1593
	21st to end	Night	9% 5% 3 5% 5% 3 4 5% 6% 9% 45%	1714
June	1st to 10th	Night	5% 3 1 3 3 3 5% 6% 6% 10% 56%	1440
	11th to 20th	Night	5% 3 2 4 4 4 3 5% 7% 11% 51%	1440
	21st to end	Night	4 3 1 3 3 2 3 4 5% 9% 62%	1473
July	1st to 10th	Night	7% 3 2 4 3 2 5% 5% 8% 10% 51%	1620
	11th to 20th	Night	2 2 1 3 4 2 4 5% 6% 9% 61%	1620
	21st to end	Night	6% 3 2 4 4 3 5% 5% 7% 10% 50%	1772
August	1st to 10th	Night	4 2 2 3 4 3 6% 5% 7% 11% 54%	1611
	11th to 20th	Night	6% 4 1 4 4 2 4 4 6% 7% 58%	1600
	21st to end	Night	5% 4 2 4 4 2 4 3 5% 6% 61%	1920
September	1st to 10th	Night	10% 5% 2 4 4 3 3 4 5% 5% 57%	1800
	11th to 20th	Night	10% 4 2 3 4 2 4 5% 6% 7% 54%	1971
	21st to end	Night	6% 4 2 4 5% 2 4 4 4 6% 59%	1980
October	1st to 10th	Night	11% 5% 1 4 3 2 4 4 4 6% 56%	2146
	11th to 20th	Night	13% 5% 2 4 3 2 3 3 3 6% 56%	2160
	21st to end	Night	15% 7% 3 5% 3 2 3 3 4 5% 51%	2376
November	1st to 10th	Night	9% 4 1 4 4 2 3 2 4 5% 61%	2224
	11th to 20th	Night	10% 6% 2 4 4 2 3 3 5% 7% 54%	2518
	21st to end	Night	14% 6% 3 4 3 2 3 4 3 5% 52%	2660
December	1st to 10th	Night	11% 8% 3 5% 5% 2 4 4 5% 6% 46%	2660
	11th to 20th	Night	11% 8% 3 7% 5% 3 4 3 4 7% 45%	3279
	21st to end	Night	17% 17% 6% 9% 5% 3 3 3 3 4 30%	4710

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	48% 4 11% 24% 13% 1	2848
	11th to 20th	Day	51% 3 12% 22% 11% 1	2850
	21st to end	Day	53% 4 11% 17% 15% 1	3135
February	1st to 10th	Day	49% 4 12% 22% 10% 3	1710
	11th to 20th	Day	44% 6% 12% 23% 14% 2	1664
	21st to end	Day	42% 5% 11% 24% 14% 3	1532
March	1st to 10th	Day	43% 6% 11% 22% 14% 4	1980
	11th to 20th	Day	50% 5% 9% 22% 12% 2	1980
	21st to end	Day	55% 5% 13% 18% 8% 1	2178
April	1st to 10th	Day	40% 5% 12% 24% 17% 2	2070
	11th to 20th	Day	44% 6% 12% 22% 15% 1	2134
	21st to end	Day	49% 5% 11% 23% 11% 1	2294
May	1st to 10th	Day	49% 7% 11% 20% 13% 1	2340
	11th to 20th	Day	44% 7% 13% 23% 13%	2306
	21st to end	Day	45% 10% 13% 20% 9% 2	2556
June	1st to 10th	Day	28% 9% 17% 30% 15% 2	2520
	11th to 20th	Day	31% 8% 14% 28% 17% 2	2520
	21st to end	Day	27% 7% 15% 30% 17% 3	2480
July	1st to 10th	Day	33% 9% 15% 24% 16% 3	2276
	11th to 20th	Day	23% 8% 18% 28% 19% 4	2271
	21st to end	Day	32% 8% 15% 30% 15% 1	2405
August	1st to 10th	Day	31% 10% 18% 27% 13% 1	2314
	11th to 20th	Day	30% 7% 13% 32% 16% 2	2301
	21st to end	Day	29% 8% 11% 26% 19% 6%	2435
September	1st to 10th	Day	32% 6% 12% 26% 18% 6%	2160
	11th to 20th	Day	32% 7% 10% 25% 23% 3	1985
	21st to end	Day	29% 5% 10% 29% 24% 3	1976
October	1st to 10th	Day	33% 5% 12% 28% 20% 3	1800
	11th to 20th	Day	33% 3 8% 27% 24% 5%	1800
	21st to end	Day	39% 4 11% 22% 19% 5%	1980
November	1st to 10th	Day	31% 4 12% 29% 19% 5%	1851
	11th to 20th	Day	35% 4 10% 27% 21% 3	1658
	21st to end	Day	40% 4 9% 26% 20% 1	1520
December	1st to 10th	Day	37% 5% 13% 30% 13% 1	1520
	11th to 20th	Day	44% 5% 12% 25% 11% 2	1915
	21st to end	Day	60% 5% 10% 16% 7% 2	2952
January	1st to 10th	Night	47% 4 14% 21% 12% 1	4108
	11th to 20th	Night	50% 4 11% 22% 13% 1	4120
	21st to end	Night	52% 4 12% 20% 11% 1	4532
February	1st to 10th	Night	45% 5% 11% 21% 14% 3	2470
	11th to 20th	Night	42% 4 12% 23% 17% 3	2398
	21st to end	Night	41% 4 9% 22% 18% 6%	1737
March	1st to 10th	Night	36% 4 10% 25% 20% 5%	1980
	11th to 20th	Night	44% 5% 11% 22% 15% 4	1980
	21st to end	Night	51% 5% 12% 20% 10% 2	2178
April	1st to 10th	Night	34% 6% 10% 25% 21% 4	1888
	11th to 20th	Night	39% 4 9% 28% 17% 3	1775
	21st to end	Night	41% 6% 12% 25% 15% 1	1661
May	1st to 10th	Night	43% 6% 13% 21% 16% 1	1620
	11th to 20th	Night	36% 6% 14% 25% 17% 1	1594
	21st to end	Night	34% 8% 17% 27% 11% 2	1715
June	1st to 10th	Night	22% 9% 17% 33% 16% 3	1440
	11th to 20th	Night	26% 8% 14% 31% 19% 2	1440
	21st to end	Night	19% 6% 14% 34% 22% 4	1473
July	1st to 10th	Night	25% 7% 16% 31% 16% 4	1575
	11th to 20th	Night	18% 7% 15% 34% 22% 4	1566
	21st to end	Night	26% 8% 13% 31% 20% 1	1673
August	1st to 10th	Night	22% 10% 17% 33% 15% 3	1601
	11th to 20th	Night	25% 6% 12% 34% 22% 2	1600
	21st to end	Night	24% 5% 10% 29% 25% 7%	1920
September	1st to 10th	Night	30% 6% 10% 28% 19% 8%	1800
	11th to 20th	Night	28% 7% 11% 26% 25% 4	1971
	21st to end	Night	26% 5% 8% 27% 29% 5%	1980
October	1st to 10th	Night	30% 5% 9% 26% 25% 6%	2146
	11th to 20th	Night	31% 4 7% 28% 22% 8%	2160
	21st to end	Night	37% 4 8% 22% 25% 4	2376
November	1st to 10th	Night	27% 3 12% 27% 24% 6%	2224
	11th to 20th	Night	30% 4 10% 27% 24% 4	2518
	21st to end	Night	36% 3 10% 29% 19% 3	2660
December	1st to 10th	Night	38% 6% 12% 27% 16% 1	2660
	11th to 20th	Night	39% 4 11% 27% 17% 1	3281
	21st to end	Night	60% 4 7% 18% 9% 2	4710

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% 35% 24% 5%	270
	11th to 20th	Day	24% 18% 37% 19% 3	270
	21st to end	Day	15% 13% 45% 25% 3	297
February	1st to 10th	Day	24% 18% 38% 17% 3 1	270
	11th to 20th	Day	19% 18% 42% 16% 5%	267
	21st to end	Day	18% 23% 41% 15% 4	198
March	1st to 10th	Day	15% 17% 49% 18% 3	240
	11th to 20th	Day	28% 15% 29% 24% 3 1	240
	21st to end	Day	30% 22% 31% 14% 2 1	264
April	1st to 10th	Day	19% 15% 38% 20% 7%	330
	11th to 20th	Day	17% 18% 37% 22% 6%	412
	21st to end	Day	22% 16% 33% 20% 9% 1	554
May	1st to 10th	Day	19% 14% 37% 20% 9% 1	603
	11th to 20th	Day	20% 9% 30% 26% 13% 2	625
	21st to end	Day	17% 9% 28% 25% 17% 4	679
June	1st to 10th	Day	6% 4 20% 35% 28% 7%	630
	11th to 20th	Day	8% 3 26% 37% 21% 5%	630
	21st to end	Day	6% 6% 33% 36% 18% 2	630
July	1st to 10th	Day	10% 3 13% 31% 32% 12%	621
	11th to 20th	Day	3 3 18% 40% 29% 8%	618
	21st to end	Day	8% 2 16% 38% 29% 7%	684
August	1st to 10th	Day	8% 2 16% 39% 31% 5%	626
	11th to 20th	Day	9% 3 15% 40% 27% 7%	615
	21st to end	Day	9% 2 14% 29% 36% 10%	554
September	1st to 10th	Day	15% 1 17% 34% 27% 6%	450
	11th to 20th	Day	5% 3 21% 39% 27% 6%	275
	21st to end	Day	10% 7% 26% 37% 16% 4	270
October	1st to 10th	Day	15% 6% 30% 25% 17% 7%	270
	11th to 20th	Day	11% 17% 43% 19% 8% 1	270
	21st to end	Day	23% 14% 35% 21% 6% 1	297
November	1st to 10th	Day	16% 10% 36% 29% 7% 3	270
	11th to 20th	Day	15% 15% 35% 25% 9% 1	270
	21st to end	Day	21% 11% 39% 20% 8%	270
December	1st to 10th	Day	9% 16% 41% 27% 5% 3	270
	11th to 20th	Day	20% 14% 37% 21% 7% 1	270
	21st to end	Day	19% 24% 38% 18% 1	297
January	1st to 10th	Night	13% 13% 39% 29% 6%	950
	11th to 20th	Night	15% 13% 41% 26% 4 1	950
	21st to end	Night	14% 12% 42% 28% 3	1045
February	1st to 10th	Night	17% 13% 43% 25% 3	950
	11th to 20th	Night	17% 14% 39% 28% 3	927
	21st to end	Night	19% 13% 43% 20% 4 1	553
March	1st to 10th	Night	14% 14% 44% 22% 5%	540
	11th to 20th	Night	20% 11% 36% 28% 5%	540
	21st to end	Night	26% 11% 38% 21% 4	594
April	1st to 10th	Night	13% 13% 41% 27% 5%	540
	11th to 20th	Night	20% 12% 34% 29% 5%	533
	21st to end	Night	18% 9% 39% 26% 6% 1	540
May	1st to 10th	Night	18% 8% 35% 31% 8% 1	540
	11th to 20th	Night	16% 5% 32% 35% 12%	531
	21st to end	Night	10% 5% 31% 34% 16% 3	584
June	1st to 10th	Night	5% 3 22% 45% 22% 2	540
	11th to 20th	Night	5% 4 26% 46% 18% 1	540
	21st to end	Night	5% 3 32% 46% 14% 1	540
July	1st to 10th	Night	7% 2 12% 46% 30% 3	525
	11th to 20th	Night	3 1 16% 48% 30% 2	522
	21st to end	Night	7% 1 14% 49% 28% 1	591
August	1st to 10th	Night	4 1 15% 48% 30% 1	537
	11th to 20th	Night	7% 3 12% 46% 30% 3	534
	21st to end	Night	6% 1 15% 41% 35% 3	594
September	1st to 10th	Night	11% 4 19% 42% 22% 3	540
	11th to 20th	Night	9% 4 19% 40% 24% 4	540
	21st to end	Night	7% 5% 24% 44% 17% 2	540
October	1st to 10th	Night	13% 5% 28% 34% 18% 2	706
	11th to 20th	Night	15% 9% 40% 29% 7% 1	720
	21st to end	Night	20% 10% 35% 27% 8%	792
November	1st to 10th	Night	11% 9% 37% 32% 10% 1	744
	11th to 20th	Night	12% 14% 38% 28% 8%	950
	21st to end	Night	18% 12% 35% 31% 5%	950
December	1st to 10th	Night	15% 11% 39% 27% 6% 1	950
	11th to 20th	Night	18% 10% 41% 27% 5%	950
	21st to end	Night	19% 16% 38% 24% 4	1045

Page generated at 2024-02-17 05:28:36. Version ac07

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