Serena
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Serena clear sky chart from 2005-11-06 to 2026-01-02.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	127330
	Night	14% 10% 4 8% 4 4 4 3 5% 6% 38%	124263
Transparency	Day	44% 6% 12% 23% 13% 2	130850
	Night	45% 5% 11% 22% 15% 2	128817
Seeing	Day	16% 10% 28% 25% 15% 5%	17355
	Night	18% 9% 30% 30% 12% 1	27249

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% 12% 6% 14% 7% 6% 5% 4 6% 6% 25%	3625
	11th to 20th	Day	10% 11% 5% 12% 7% 6% 5% 5% 7% 5% 28%	3620
	21st to end	Day	15% 15% 7% 10% 5% 4 3 3 5% 6% 27%	4230
February	1st to 10th	Day	16% 14% 4 10% 5% 6% 4 3 5% 5% 27%	1812
	11th to 20th	Day	15% 10% 4 8% 6% 5% 4 3 5% 6% 34%	1948
	21st to end	Day	14% 13% 6% 10% 4 4 3 3 5% 7% 31%	1650
March	1st to 10th	Day	18% 12% 3 6% 4 3 3 2 3 5% 41%	4480
	11th to 20th	Day	9% 7% 3 7% 4 4 5% 4 6% 8% 43%	4704
	21st to end	Day	20% 12% 5% 11% 6% 5% 4 3 5% 5% 22%	5962
April	1st to 10th	Day	18% 13% 3 7% 5% 5% 4 3 5% 7% 31%	2400
	11th to 20th	Day	16% 11% 2 7% 5% 4 4 4 5% 7% 36%	2374
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	2462
May	1st to 10th	Day	16% 8% 2 7% 5% 5% 5% 4 6% 8% 34%	5862
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 7% 41%	6245
	21st to end	Day	13% 6% 3 7% 4 4 4 5% 7% 9% 38%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 3 7% 8% 47%	2800
	11th to 20th	Day	9% 6% 2 5% 5% 5% 4 4 7% 8% 45%	2800
	21st to end	Day	11% 6% 2 6% 6% 5% 5% 4 7% 8% 41%	2800
July	1st to 10th	Day	8% 7% 3 7% 4 5% 6% 5% 8% 10% 37%	6360
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 4 7% 11% 42%	6360
	21st to end	Day	10% 7% 2 7% 5% 5% 6% 5% 7% 10% 37%	6924
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 7% 9% 45%	4419
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 8% 11% 42%	3849
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 10% 48%	4312
September	1st to 10th	Day	11% 5% 1 5% 4 4 4 3 6% 7% 50%	2400
	11th to 20th	Day	11% 4 1 4 3 3 4 3 5% 8% 53%	2300
	21st to end	Day	9% 6% 3 6% 4 4 4 4 6% 8% 47%	2200
October	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 4 7% 48%	2105
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 5% 7% 40%	2000
	21st to end	Day	18% 9% 3 7% 4 4 4 4 5% 6% 38%	2009
November	1st to 10th	Day	11% 9% 2 5% 4 4 3 3 5% 7% 46%	1852
	11th to 20th	Day	16% 12% 3 9% 5% 3 4 3 5% 6% 33%	1890
	21st to end	Day	19% 11% 4 9% 5% 4 3 3 3 4 34%	1793
December	1st to 10th	Day	8% 9% 4 8% 5% 4 3 3 4 7% 44%	2690
	11th to 20th	Day	12% 15% 6% 11% 6% 6% 6% 4 6% 5% 24%	3088
	21st to end	Day	26% 20% 7% 12% 6% 4 4 2 3 3 12%	4070
January	1st to 10th	Night	13% 13% 6% 12% 5% 5% 3 3 3 5% 31%	6363
	11th to 20th	Night	12% 15% 6% 13% 7% 5% 5% 4 6% 4 22%	6360
	21st to end	Night	17% 14% 6% 8% 5% 4 3 3 4 4 32%	6745
February	1st to 10th	Night	16% 13% 4 8% 5% 5% 3 3 5% 5% 33%	2586
	11th to 20th	Night	13% 11% 4 8% 5% 4 4 3 5% 6% 37%	2338
	21st to end	Night	18% 11% 3 9% 4 3 3 2 4 5% 37%	1980
March	1st to 10th	Night	17% 11% 4 5% 3 4 4 3 4 5% 41%	5373
	11th to 20th	Night	11% 7% 2 6% 4 4 4 4 5% 6% 47%	5284
	21st to end	Night	19% 11% 5% 10% 5% 5% 5% 3 5% 5% 27%	4966
April	1st to 10th	Night	16% 11% 3 6% 4 3 4 3 5% 6% 39%	2000
	11th to 20th	Night	18% 8% 3 6% 5% 3 3 3 5% 6% 41%	1975
	21st to end	Night	18% 7% 3 7% 4 4 4 3 6% 7% 36%	1936
May	1st to 10th	Night	18% 8% 3 7% 5% 4 4 3 5% 7% 35%	4033
	11th to 20th	Night	12% 6% 2 5% 3 4 6% 4 7% 9% 42%	3651
	21st to end	Night	13% 8% 2 7% 4 4 4 3 6% 8% 39%	3942
June	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 51%	1600
	11th to 20th	Night	8% 4 3 6% 5% 4 5% 4 7% 9% 46%	1600
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 7% 7% 44%	1600
July	1st to 10th	Night	9% 7% 2 7% 4 5% 5% 4 7% 9% 41%	3618
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 6% 8% 50%	3617
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 5% 6% 9% 41%	3947
August	1st to 10th	Night	4 4 2 6% 4 4 5% 5% 7% 10% 48%	2733
	11th to 20th	Night	7% 5% 2 5% 3 4 5% 4 6% 9% 50%	3200
	21st to end	Night	7% 4 2 5% 3 3 4 3 6% 9% 53%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 2 3 3 4 7% 56%	2000
	11th to 20th	Night	8% 4 2 5% 3 3 4 3 6% 7% 55%	2080
	21st to end	Night	10% 5% 2 5% 4 4 4 3 6% 8% 47%	2200
October	1st to 10th	Night	10% 5% 2 6% 4 3 3 3 5% 6% 53%	2290
	11th to 20th	Night	17% 6% 2 6% 3 3 3 3 4 6% 47%	2400
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 6% 39%	2830
November	1st to 10th	Night	13% 7% 3 5% 2 3 3 4 5% 6% 49%	2666
	11th to 20th	Night	15% 9% 3 7% 4 4 4 4 5% 6% 38%	2730
	21st to end	Night	17% 11% 4 8% 4 4 4 3 4 5% 37%	2825
December	1st to 10th	Night	12% 9% 3 7% 5% 4 4 3 5% 6% 42%	4720
	11th to 20th	Night	17% 14% 5% 9% 5% 4 3 3 4 5% 32%	5339
	21st to end	Night	24% 19% 6% 10% 6% 4 4 3 4 5% 16%	7150

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	60% 5% 12% 16% 7%	3626
	11th to 20th	Day	55% 6% 9% 11% 15% 4	3620
	21st to end	Day	58% 5% 12% 17% 7%	4230
February	1st to 10th	Day	58% 5% 12% 16% 7% 2	1812
	11th to 20th	Day	52% 6% 10% 22% 9% 2	1958
	21st to end	Day	54% 5% 10% 21% 8% 2	1650
March	1st to 10th	Day	47% 4 9% 24% 13% 3	4480
	11th to 20th	Day	38% 5% 11% 33% 12% 1	4704
	21st to end	Day	61% 7% 11% 14% 6% 1	5964
April	1st to 10th	Day	51% 6% 11% 21% 10%	2400
	11th to 20th	Day	47% 6% 11% 21% 11% 3	2374
	21st to end	Day	50% 7% 12% 18% 11% 2	2462
May	1st to 10th	Day	45% 7% 11% 21% 14% 1	5897
	11th to 20th	Day	41% 6% 11% 26% 14% 2	6249
	21st to end	Day	40% 6% 12% 24% 14% 4	6949
June	1st to 10th	Day	34% 7% 12% 27% 17% 2	2800
	11th to 20th	Day	35% 7% 12% 23% 20% 3	2800
	21st to end	Day	39% 8% 14% 22% 15% 2	2800
July	1st to 10th	Day	40% 6% 12% 26% 14% 1	6291
	11th to 20th	Day	36% 5% 15% 29% 14% 1	6285
	21st to end	Day	40% 6% 19% 20% 13% 2	6728
August	1st to 10th	Day	32% 7% 17% 30% 12% 1	4404
	11th to 20th	Day	34% 6% 13% 32% 15% 1	3885
	21st to end	Day	31% 6% 12% 31% 17% 2	4311
September	1st to 10th	Day	32% 7% 12% 25% 19% 5%	2400
	11th to 20th	Day	29% 5% 13% 28% 22% 3	2300
	21st to end	Day	34% 7% 10% 26% 21% 2	2200
October	1st to 10th	Day	26% 4 7% 29% 33% 2	3430
	11th to 20th	Day	30% 4 12% 25% 28% 2	3240
	21st to end	Day	41% 4 9% 27% 16% 3	3221
November	1st to 10th	Day	37% 6% 14% 26% 16% 2	1852
	11th to 20th	Day	52% 4 11% 21% 11% 1	1890
	21st to end	Day	53% 5% 10% 23% 8%	1793
December	1st to 10th	Day	42% 3 15% 31% 8% 1	2690
	11th to 20th	Day	60% 5% 11% 17% 6% 1	3085
	21st to end	Day	78% 4 7% 7% 4	4070
January	1st to 10th	Night	56% 5% 10% 19% 10%	6363
	11th to 20th	Night	63% 5% 10% 9% 13% 1	6360
	21st to end	Night	57% 4 11% 17% 11% 1	6745
February	1st to 10th	Night	54% 4 11% 18% 11% 1	2586
	11th to 20th	Night	48% 5% 10% 23% 12% 1	2339
	21st to end	Night	50% 5% 11% 19% 12% 3	1980
March	1st to 10th	Night	46% 5% 10% 24% 10% 5%	5373
	11th to 20th	Night	36% 5% 11% 29% 15% 3	5284
	21st to end	Night	58% 6% 9% 19% 7% 1	4966
April	1st to 10th	Night	46% 5% 12% 22% 13% 2	2000
	11th to 20th	Night	44% 4 10% 23% 15% 4	1975
	21st to end	Night	45% 7% 11% 23% 10% 3	1936
May	1st to 10th	Night	47% 7% 12% 16% 14% 3	4060
	11th to 20th	Night	36% 9% 14% 26% 12% 4	3652
	21st to end	Night	41% 7% 11% 23% 15% 3	3950
June	1st to 10th	Night	32% 7% 13% 25% 19% 3	1600
	11th to 20th	Night	33% 7% 12% 25% 21% 3	1600
	21st to end	Night	36% 10% 14% 21% 16% 3	1600
July	1st to 10th	Night	40% 4 13% 25% 16% 3	3580
	11th to 20th	Night	31% 5% 13% 28% 21% 1	3572
	21st to end	Night	38% 7% 15% 22% 16% 3	3832
August	1st to 10th	Night	29% 6% 18% 27% 18% 1	2724
	11th to 20th	Night	30% 6% 16% 28% 18% 1	3230
	21st to end	Night	28% 5% 12% 34% 18% 3	3586
September	1st to 10th	Night	29% 5% 11% 27% 24% 4	2000
	11th to 20th	Night	27% 5% 10% 29% 25% 3	2080
	21st to end	Night	34% 6% 12% 26% 19% 3	2200
October	1st to 10th	Night	22% 4 6% 35% 31% 3	3745
	11th to 20th	Night	32% 4 8% 22% 32% 3	3899
	21st to end	Night	40% 4 9% 24% 20% 4	4568
November	1st to 10th	Night	36% 5% 10% 28% 17% 4	2666
	11th to 20th	Night	46% 5% 12% 22% 13% 2	2730
	21st to end	Night	50% 4 12% 23% 11%	2825
December	1st to 10th	Night	43% 4 13% 28% 11% 1	4720
	11th to 20th	Night	55% 4 12% 18% 10% 1	5341
	21st to end	Night	71% 4 9% 11% 5%	7150

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	21% 12% 31% 25% 10%	303
	11th to 20th	Day	20% 19% 37% 18% 5% 1	300
	21st to end	Day	24% 15% 32% 23% 6%	330
February	1st to 10th	Day	21% 16% 38% 21% 4	300
	11th to 20th	Day	21% 16% 40% 19% 5%	300
	21st to end	Day	22% 15% 43% 17% 3	249
March	1st to 10th	Day	23% 22% 35% 18% 3	300
	11th to 20th	Day	24% 17% 36% 17% 6%	300
	21st to end	Day	28% 15% 34% 16% 6% 2	545
April	1st to 10th	Day	24% 14% 33% 21% 6% 1	500
	11th to 20th	Day	20% 18% 29% 21% 10% 2	492
	21st to end	Day	22% 15% 31% 22% 9% 1	500
May	1st to 10th	Day	20% 13% 29% 25% 10% 3	503
	11th to 20th	Day	19% 11% 28% 25% 12% 4	690
	21st to end	Day	15% 9% 31% 22% 15% 9%	789
June	1st to 10th	Day	10% 8% 27% 30% 19% 6%	730
	11th to 20th	Day	12% 5% 28% 30% 20% 5%	730
	21st to end	Day	12% 7% 32% 28% 15% 5%	730
July	1st to 10th	Day	11% 3 17% 30% 24% 16%	721
	11th to 20th	Day	10% 4 21% 31% 22% 11%	718
	21st to end	Day	9% 3 20% 35% 26% 8%	794
August	1st to 10th	Day	7% 3 16% 35% 28% 12%	698
	11th to 20th	Day	10% 5% 16% 29% 26% 14%	519
	21st to end	Day	6% 4 17% 30% 30% 13%	583
September	1st to 10th	Day	12% 6% 19% 27% 28% 8%	530
	11th to 20th	Day	9% 3 16% 29% 29% 14%	530
	21st to end	Day	12% 10% 24% 25% 22% 8%	530
October	1st to 10th	Day	13% 7% 26% 29% 19% 6%	435
	11th to 20th	Day	18% 17% 30% 24% 9% 2	330
	21st to end	Day	27% 16% 31% 21% 4 1	363
November	1st to 10th	Day	15% 15% 37% 22% 8% 4	330
	11th to 20th	Day	23% 18% 32% 20% 6% 1	330
	21st to end	Day	27% 11% 35% 22% 5%	330
December	1st to 10th	Day	16% 17% 40% 20% 6% 1	330
	11th to 20th	Day	18% 13% 40% 23% 5%	330
	21st to end	Day	29% 18% 35% 16% 2	363
January	1st to 10th	Night	21% 13% 36% 23% 6%	1006
	11th to 20th	Night	21% 14% 37% 23% 5%	1000
	21st to end	Night	21% 13% 35% 27% 4	1100
February	1st to 10th	Night	24% 11% 37% 23% 4	986
	11th to 20th	Night	19% 13% 37% 27% 4	783
	21st to end	Night	23% 12% 38% 23% 4	660
March	1st to 10th	Night	21% 15% 35% 23% 6%	800
	11th to 20th	Night	19% 10% 36% 28% 6% 1	735
	21st to end	Night	25% 11% 35% 23% 5% 1	660
April	1st to 10th	Night	19% 14% 35% 27% 6%	600
	11th to 20th	Night	22% 13% 32% 27% 6%	593
	21st to end	Night	21% 11% 33% 29% 6% 1	600
May	1st to 10th	Night	18% 9% 35% 31% 7% 1	600
	11th to 20th	Night	17% 6% 30% 35% 11% 1	591
	21st to end	Night	14% 6% 26% 36% 17%	650
June	1st to 10th	Night	10% 5% 26% 43% 16% 1	600
	11th to 20th	Night	11% 4 26% 45% 14% 1	600
	21st to end	Night	10% 4 28% 40% 18% 1	600
July	1st to 10th	Night	9% 2 15% 39% 30% 4	585
	11th to 20th	Night	7% 3 19% 41% 27% 3	582
	21st to end	Night	5% 2 14% 47% 30% 2	657
August	1st to 10th	Night	6% 2 12% 46% 30% 4	597
	11th to 20th	Night	7% 3 11% 43% 32% 4	594
	21st to end	Night	9% 1 15% 42% 31% 3	660
September	1st to 10th	Night	13% 2 18% 34% 30% 3	600
	11th to 20th	Night	9% 3 18% 38% 30% 3	680
	21st to end	Night	12% 6% 24% 35% 21% 2	800
October	1st to 10th	Night	12% 6% 26% 37% 19% 1	800
	11th to 20th	Night	19% 12% 29% 28% 11%	800
	21st to end	Night	23% 12% 32% 25% 8%	880
November	1st to 10th	Night	18% 10% 38% 24% 10%	820
	11th to 20th	Night	20% 14% 33% 25% 7%	840
	21st to end	Night	24% 11% 34% 25% 6%	935
December	1st to 10th	Night	22% 10% 37% 25% 5%	1050
	11th to 20th	Night	24% 11% 34% 28% 4	1050
	21st to end	Night	28% 15% 33% 21% 2	1155

Page generated at 2025-12-30 00:14:10. Version ac07

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