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 2024-01-13.

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	14% 8% 3 6% 6% 3 5% 5% 5% 7% 37%	74801
	Night	15% 9% 4 6% 5% 3 4 4 5% 7% 39%	74964
Transparency	Day	45% 7% 13% 21% 12% 2	74502
	Night	44% 6% 12% 22% 14% 2	74784
Seeing	Day	16% 10% 27% 26% 15% 6%	14622
	Night	18% 9% 30% 30% 12% 1	24598

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% 12% 5% 9% 7% 4 6% 4 5% 6% 28%	1517
	11th to 20th	Day	14% 15% 7% 12% 7% 4 6% 4 5% 6% 22%	1461
	21st to end	Day	15% 16% 7% 11% 7% 3 3 4 5% 5% 23%	1678
February	1st to 10th	Day	18% 13% 5% 8% 6% 3 6% 4 4 5% 27%	1631
	11th to 20th	Day	16% 10% 5% 7% 7% 4 5% 4 5% 6% 33%	1748
	21st to end	Day	15% 14% 7% 10% 5% 2 4 3 4 6% 29%	1480
March	1st to 10th	Day	16% 12% 5% 7% 6% 3 4 4 4 6% 33%	1800
	11th to 20th	Day	15% 9% 4 7% 6% 3 5% 5% 6% 8% 32%	1872
	21st to end	Day	20% 11% 5% 7% 7% 4 5% 4 5% 6% 25%	2371
April	1st to 10th	Day	17% 10% 4 6% 6% 4 5% 4 5% 7% 32%	2160
	11th to 20th	Day	16% 11% 2 5% 6% 3 4 4 5% 8% 36%	2134
	21st to end	Day	21% 8% 3 6% 6% 3 5% 4 5% 6% 33%	2215
May	1st to 10th	Day	17% 7% 3 7% 7% 4 4 5% 6% 8% 31%	2340
	11th to 20th	Day	19% 9% 3 6% 6% 3 4 5% 4 8% 35%	2447
	21st to end	Day	15% 6% 3 6% 5% 3 4 6% 7% 8% 37%	2725
June	1st to 10th	Day	10% 4 2 5% 6% 3 5% 4 6% 9% 46%	2520
	11th to 20th	Day	9% 5% 2 4 6% 4 5% 5% 6% 8% 46%	2520
	21st to end	Day	12% 5% 2 6% 7% 3 6% 5% 7% 8% 39%	2520
July	1st to 10th	Day	8% 4 2 5% 4 3 5% 6% 7% 9% 46%	2520
	11th to 20th	Day	10% 4 2 3 4 4 5% 5% 7% 10% 47%	2520
	21st to end	Day	6% 5% 2 5% 6% 3 6% 5% 7% 10% 44%	2743
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 6% 7% 10% 44%	2438
	11th to 20th	Day	9% 5% 2 5% 6% 4 5% 5% 6% 9% 45%	2125
	21st to end	Day	9% 4 2 4 5% 2 5% 6% 6% 10% 48%	2376
September	1st to 10th	Day	12% 5% 2 5% 5% 4 4 5% 5% 7% 47%	2160
	11th to 20th	Day	12% 4 1 3 4 3 3 4 5% 8% 53%	2070
	21st to end	Day	8% 6% 3 6% 5% 3 4 5% 6% 8% 47%	1980
October	1st to 10th	Day	13% 7% 2 5% 4 2 4 4 4 8% 46%	1895
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 5% 7% 37%	1800
	21st to end	Day	20% 9% 3 6% 4 3 4 4 5% 6% 37%	1809
November	1st to 10th	Day	12% 8% 2 4 4 3 4 4 5% 8% 46%	1672
	11th to 20th	Day	17% 10% 4 8% 6% 2 4 4 5% 6% 34%	1710
	21st to end	Day	20% 9% 4 8% 6% 2 4 4 3 4 36%	1623
December	1st to 10th	Day	15% 11% 5% 8% 6% 4 4 4 4 7% 32%	1520
	11th to 20th	Day	14% 13% 5% 7% 6% 3 6% 4 5% 5% 30%	1918
	21st to end	Day	24% 18% 9% 11% 6% 3 3 3 4 4 14%	2783
January	1st to 10th	Night	14% 12% 4 8% 6% 3 4 4 4 6% 34%	2648
	11th to 20th	Night	16% 14% 6% 10% 6% 3 4 3 4 6% 28%	2561
	21st to end	Night	15% 13% 7% 10% 6% 3 4 4 5% 6% 26%	2675
February	1st to 10th	Night	17% 13% 5% 8% 6% 4 4 4 4 5% 31%	2327
	11th to 20th	Night	15% 9% 4 7% 5% 4 5% 5% 5% 6% 37%	2098
	21st to end	Night	19% 11% 3 8% 5% 2 3 3 4 5% 35%	1776
March	1st to 10th	Night	16% 12% 4 6% 4 4 4 4 5% 4 38%	2160
	11th to 20th	Night	14% 7% 4 5% 6% 3 4 5% 5% 6% 41%	2102
	21st to end	Night	21% 11% 4 6% 5% 3 5% 4 5% 6% 30%	1984
April	1st to 10th	Night	16% 9% 4 6% 5% 3 4 4 4 7% 39%	1800
	11th to 20th	Night	19% 7% 3 5% 5% 3 2 3 5% 6% 42%	1775
	21st to end	Night	18% 7% 3 6% 5% 3 4 5% 6% 7% 35%	1743
May	1st to 10th	Night	17% 7% 3 6% 6% 3 5% 4 6% 9% 35%	1620
	11th to 20th	Night	16% 5% 2 5% 5% 2 6% 5% 6% 8% 40%	1445
	21st to end	Night	13% 5% 2 6% 5% 3 4 5% 6% 11% 39%	1551
June	1st to 10th	Night	10% 4 2 5% 5% 2 3 5% 5% 7% 51%	1440
	11th to 20th	Night	9% 4 3 5% 5% 3 5% 5% 7% 9% 46%	1440
	21st to end	Night	10% 5% 2 5% 6% 3 5% 6% 7% 7% 44%	1440
July	1st to 10th	Night	6% 5% 2 5% 5% 3 5% 4 7% 10% 50%	1440
	11th to 20th	Night	7% 3 2 4 4 3 4 4 5% 7% 57%	1440
	21st to end	Night	3 3 2 5% 5% 2 6% 6% 6% 11% 50%	1575
August	1st to 10th	Night	4 4 3 5% 4 3 5% 6% 6% 9% 50%	1496
	11th to 20th	Night	8% 4 2 3 4 3 5% 5% 5% 9% 52%	1776
	21st to end	Night	8% 3 2 4 4 2 4 4 6% 8% 55%	1980
September	1st to 10th	Night	11% 6% 2 4 3 2 3 3 4 7% 54%	1800
	11th to 20th	Night	9% 4 2 4 4 2 4 4 5% 7% 54%	1872
	21st to end	Night	9% 5% 2 5% 5% 3 4 4 6% 8% 48%	1980
October	1st to 10th	Night	11% 5% 2 4 5% 2 4 4 5% 7% 51%	2060
	11th to 20th	Night	18% 6% 2 5% 4 2 3 4 4 6% 46%	2160
	21st to end	Night	21% 8% 3 5% 5% 2 4 3 5% 6% 38%	2546
November	1st to 10th	Night	12% 6% 3 5% 3 3 3 4 5% 6% 50%	2406
	11th to 20th	Night	15% 9% 4 6% 5% 3 5% 4 5% 6% 38%	2470
	21st to end	Night	18% 9% 4 6% 5% 3 4 3 4 6% 39%	2555
December	1st to 10th	Night	17% 10% 4 7% 7% 3 5% 4 4 6% 34%	2660
	11th to 20th	Night	15% 12% 5% 8% 6% 3 4 3 4 5% 34%	3279
	21st to end	Night	24% 17% 7% 9% 7% 3 4 4 4 5% 16%	4884

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	57% 7% 12% 14% 10%	1518
	11th to 20th	Day	63% 6% 11% 14% 5% 1	1461
	21st to end	Day	62% 6% 10% 13% 8% 1	1678
February	1st to 10th	Day	60% 5% 12% 15% 6% 2	1631
	11th to 20th	Day	53% 6% 11% 21% 8% 2	1758
	21st to end	Day	58% 5% 9% 19% 7% 1	1480
March	1st to 10th	Day	53% 5% 13% 22% 7% 1	1800
	11th to 20th	Day	49% 6% 14% 20% 10% 1	1872
	21st to end	Day	59% 7% 11% 19% 4 1	2371
April	1st to 10th	Day	50% 6% 12% 21% 10%	2160
	11th to 20th	Day	47% 6% 11% 21% 11% 3	2134
	21st to end	Day	50% 7% 12% 17% 11% 2	2215
May	1st to 10th	Day	50% 8% 13% 21% 8%	2340
	11th to 20th	Day	49% 7% 11% 22% 11%	2451
	21st to end	Day	43% 8% 12% 18% 16% 2	2725
June	1st to 10th	Day	34% 7% 13% 27% 17% 2	2520
	11th to 20th	Day	34% 8% 12% 22% 21% 3	2520
	21st to end	Day	41% 9% 14% 22% 13% 2	2520
July	1st to 10th	Day	32% 9% 14% 27% 15% 3	2451
	11th to 20th	Day	31% 8% 17% 27% 15% 2	2445
	21st to end	Day	31% 10% 18% 24% 15% 2	2591
August	1st to 10th	Day	32% 10% 17% 28% 12% 2	2423
	11th to 20th	Day	34% 8% 15% 26% 16% 1	2125
	21st to end	Day	30% 8% 13% 26% 20% 3	2376
September	1st to 10th	Day	35% 8% 14% 22% 17% 5%	2160
	11th to 20th	Day	30% 5% 14% 28% 20% 4	2070
	21st to end	Day	34% 8% 10% 26% 20% 2	1980
October	1st to 10th	Day	37% 5% 13% 24% 19% 2	1895
	11th to 20th	Day	46% 5% 11% 22% 14% 2	1800
	21st to end	Day	48% 6% 11% 23% 10% 3	1809
November	1st to 10th	Day	36% 6% 15% 24% 17% 2	1672
	11th to 20th	Day	51% 4 12% 22% 11% 1	1710
	21st to end	Day	52% 5% 11% 23% 9%	1623
December	1st to 10th	Day	53% 5% 14% 19% 8% 1	1520
	11th to 20th	Day	54% 7% 12% 19% 8% 1	1915
	21st to end	Day	75% 5% 8% 9% 3	2783
January	1st to 10th	Night	51% 5% 12% 19% 12% 1	2648
	11th to 20th	Night	58% 6% 14% 13% 8%	2561
	21st to end	Night	57% 6% 13% 15% 9% 1	2675
February	1st to 10th	Night	56% 5% 11% 17% 9% 2	2327
	11th to 20th	Night	48% 6% 11% 23% 11% 1	2099
	21st to end	Night	52% 5% 11% 18% 11% 3	1776
March	1st to 10th	Night	50% 6% 13% 21% 10% 1	2160
	11th to 20th	Night	43% 6% 12% 20% 15% 3	2102
	21st to end	Night	55% 7% 11% 17% 9% 1	1984
April	1st to 10th	Night	46% 5% 12% 21% 13% 3	1800
	11th to 20th	Night	44% 4 9% 23% 15% 5%	1775
	21st to end	Night	46% 7% 12% 22% 10% 3	1743
May	1st to 10th	Night	45% 7% 14% 23% 11%	1620
	11th to 20th	Night	41% 8% 12% 23% 15% 1	1446
	21st to end	Night	40% 8% 13% 20% 17% 3	1552
June	1st to 10th	Night	32% 7% 13% 25% 20% 4	1440
	11th to 20th	Night	33% 7% 12% 24% 22% 3	1440
	21st to end	Night	36% 10% 14% 21% 15% 3	1440
July	1st to 10th	Night	30% 8% 14% 27% 17% 4	1400
	11th to 20th	Night	27% 6% 15% 28% 22% 3	1392
	21st to end	Night	25% 9% 16% 27% 19% 4	1487
August	1st to 10th	Night	27% 8% 19% 28% 16% 2	1487
	11th to 20th	Night	27% 9% 16% 26% 21% 2	1776
	21st to end	Night	27% 7% 12% 28% 21% 5%	1980
September	1st to 10th	Night	31% 5% 12% 25% 22% 4	1800
	11th to 20th	Night	28% 6% 10% 29% 23% 3	1872
	21st to end	Night	33% 7% 12% 27% 18% 3	1980
October	1st to 10th	Night	33% 7% 9% 25% 22% 3	2060
	11th to 20th	Night	40% 4 9% 24% 20% 2	2160
	21st to end	Night	47% 5% 10% 23% 13% 1	2546
November	1st to 10th	Night	35% 6% 10% 27% 17% 4	2406
	11th to 20th	Night	46% 6% 12% 21% 13% 2	2470
	21st to end	Night	47% 4 12% 24% 12% 1	2555
December	1st to 10th	Night	52% 5% 12% 21% 8% 1	2660
	11th to 20th	Night	53% 5% 12% 20% 9% 1	3281
	21st to end	Night	70% 6% 9% 11% 4	4884

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% 12% 31% 25% 10%	270
	11th to 20th	Day	23% 16% 34% 19% 6% 1	248
	21st to end	Day	23% 16% 29% 24% 7%	264
February	1st to 10th	Day	24% 16% 38% 19% 2	240
	11th to 20th	Day	23% 15% 38% 20% 4	240
	21st to end	Day	25% 16% 41% 16% 3	198
March	1st to 10th	Day	23% 23% 33% 19% 3	240
	11th to 20th	Day	27% 13% 35% 18% 7%	240
	21st to end	Day	29% 13% 33% 16% 7% 2	457
April	1st to 10th	Day	22% 14% 34% 23% 6% 1	420
	11th to 20th	Day	19% 17% 30% 21% 11% 3	412
	21st to end	Day	23% 14% 30% 22% 9% 1	420
May	1st to 10th	Day	21% 13% 29% 25% 9% 3	423
	11th to 20th	Day	21% 10% 29% 26% 11% 4	593
	21st to end	Day	15% 8% 30% 22% 16% 10%	679
June	1st to 10th	Day	9% 7% 27% 30% 20% 6%	630
	11th to 20th	Day	12% 5% 28% 30% 20% 5%	630
	21st to end	Day	13% 7% 31% 29% 15% 5%	630
July	1st to 10th	Day	11% 2 15% 29% 24% 18%	621
	11th to 20th	Day	10% 5% 21% 32% 22% 11%	618
	21st to end	Day	7% 2 21% 36% 26% 8%	684
August	1st to 10th	Day	7% 3 15% 35% 27% 13%	602
	11th to 20th	Day	10% 5% 14% 28% 27% 15%	439
	21st to end	Day	7% 4 18% 31% 27% 13%	495
September	1st to 10th	Day	14% 6% 18% 29% 27% 6%	450
	11th to 20th	Day	10% 4 18% 30% 26% 12%	450
	21st to end	Day	11% 11% 24% 24% 23% 7%	450
October	1st to 10th	Day	15% 7% 28% 27% 17% 5%	365
	11th to 20th	Day	21% 19% 31% 21% 7% 1	270
	21st to end	Day	30% 15% 29% 21% 4 1	297
November	1st to 10th	Day	13% 13% 38% 23% 8% 4	270
	11th to 20th	Day	23% 16% 32% 20% 6% 1	270
	21st to end	Day	26% 9% 36% 23% 6%	270
December	1st to 10th	Day	17% 18% 39% 18% 7% 1	270
	11th to 20th	Day	16% 13% 40% 25% 6%	270
	21st to end	Day	26% 20% 36% 16% 2	297
January	1st to 10th	Night	21% 13% 36% 23% 6%	950
	11th to 20th	Night	22% 13% 36% 23% 5%	915
	21st to end	Night	21% 13% 35% 27% 4	990
February	1st to 10th	Night	25% 10% 37% 23% 4	887
	11th to 20th	Night	20% 12% 37% 27% 4	703
	21st to end	Night	25% 12% 36% 22% 4 1	592
March	1st to 10th	Night	21% 15% 34% 24% 6%	720
	11th to 20th	Night	19% 9% 36% 29% 6% 1	662
	21st to end	Night	25% 11% 34% 23% 6% 1	594
April	1st to 10th	Night	19% 14% 34% 26% 6%	540
	11th to 20th	Night	22% 11% 32% 28% 7%	533
	21st to end	Night	22% 10% 33% 28% 7% 1	540
May	1st to 10th	Night	18% 9% 35% 30% 7% 1	540
	11th to 20th	Night	18% 5% 30% 35% 10% 1	531
	21st to end	Night	14% 6% 26% 36% 19%	584
June	1st to 10th	Night	11% 4 26% 43% 17% 1	540
	11th to 20th	Night	11% 4 26% 44% 15% 1	540
	21st to end	Night	10% 4 28% 38% 19% 1	540
July	1st to 10th	Night	8% 2 14% 39% 32% 4	525
	11th to 20th	Night	8% 2 18% 40% 28% 3	522
	21st to end	Night	4 2 15% 47% 29% 2	591
August	1st to 10th	Night	6% 1 12% 45% 31% 4	537
	11th to 20th	Night	7% 3 11% 41% 34% 4	534
	21st to end	Night	9% 1 16% 40% 31% 3	594
September	1st to 10th	Night	14% 2 18% 34% 28% 3	540
	11th to 20th	Night	9% 3 18% 37% 28% 4	612
	21st to end	Night	11% 6% 25% 35% 21% 3	720
October	1st to 10th	Night	13% 6% 26% 35% 19% 1	720
	11th to 20th	Night	20% 12% 31% 27% 10%	720
	21st to end	Night	25% 11% 32% 24% 8%	792
November	1st to 10th	Night	16% 9% 39% 25% 11% 1	740
	11th to 20th	Night	20% 14% 33% 26% 7%	760
	21st to end	Night	23% 10% 34% 26% 7%	845
December	1st to 10th	Night	22% 11% 37% 24% 6%	950
	11th to 20th	Night	23% 10% 33% 29% 5%	950
	21st to end	Night	27% 16% 33% 22% 3	1045

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