Suburban Lights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Suburban Lights Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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% 4 7% 6% 3 5% 5% 6% 7% 36%	78191
	Night	14% 9% 4 7% 5% 3 4 4 5% 7% 37%	80820
Transparency	Day	47% 6% 12% 22% 12% 1	77891
	Night	47% 5% 11% 22% 13% 1	80640
Seeing	Day	16% 10% 29% 26% 14% 5%	14809
	Night	17% 10% 31% 30% 11% 1	24859

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	12% 12% 8% 13% 8% 4 5% 4 4 6% 26%	2527
	11th to 20th	Day	10% 12% 5% 12% 8% 3 5% 9% 7% 9% 21%	2530
	21st to end	Day	17% 16% 8% 12% 6% 3 4 3 4 5% 21%	2893
February	1st to 10th	Day	11% 12% 7% 8% 6% 3 4 6% 4 6% 32%	1701
	11th to 20th	Day	14% 10% 4 6% 6% 4 5% 4 5% 6% 35%	1691
	21st to end	Day	13% 11% 5% 10% 8% 3 5% 5% 5% 5% 31%	1480
March	1st to 10th	Day	14% 9% 5% 7% 5% 3 5% 6% 6% 6% 36%	1800
	11th to 20th	Day	13% 7% 4 6% 5% 3 5% 5% 5% 7% 40%	1902
	21st to end	Day	18% 12% 4 6% 6% 3 5% 4 4 8% 30%	2350
April	1st to 10th	Day	17% 11% 5% 7% 5% 4 4 4 6% 6% 30%	2160
	11th to 20th	Day	17% 9% 4 6% 6% 3 5% 5% 5% 7% 33%	2134
	21st to end	Day	19% 10% 3 7% 6% 3 4 4 5% 6% 33%	2227
May	1st to 10th	Day	17% 8% 3 6% 6% 4 6% 5% 7% 8% 30%	2412
	11th to 20th	Day	18% 7% 3 7% 5% 3 5% 4 5% 7% 36%	2479
	21st to end	Day	15% 7% 2 5% 5% 3 5% 5% 6% 7% 39%	2725
June	1st to 10th	Day	11% 4 2 6% 4 3 5% 4 6% 9% 45%	2520
	11th to 20th	Day	12% 6% 2 5% 5% 3 5% 4 6% 9% 43%	2520
	21st to end	Day	11% 5% 3 5% 5% 3 5% 5% 7% 10% 41%	2520
July	1st to 10th	Day	8% 4 2 3 4 3 5% 5% 7% 10% 47%	2520
	11th to 20th	Day	7% 4 2 4 5% 4 6% 6% 8% 9% 45%	2520
	21st to end	Day	7% 4 2 4 5% 3 5% 5% 7% 11% 46%	2743
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 5% 7% 12% 43%	2486
	11th to 20th	Day	11% 5% 2 6% 5% 3 4 6% 6% 8% 44%	2172
	21st to end	Day	10% 5% 2 5% 5% 3 5% 5% 6% 7% 47%	2376
September	1st to 10th	Day	13% 5% 3 5% 5% 3 4 5% 5% 8% 43%	2160
	11th to 20th	Day	13% 5% 2 4 4 2 4 4 4 7% 50%	2098
	21st to end	Day	12% 7% 2 6% 4 3 4 4 6% 7% 44%	1980
October	1st to 10th	Day	14% 6% 3 6% 4 3 4 4 5% 6% 46%	1846
	11th to 20th	Day	20% 8% 3 7% 5% 3 4 4 5% 8% 33%	1800
	21st to end	Day	18% 10% 4 5% 5% 3 4 3 4 5% 38%	1805
November	1st to 10th	Day	12% 7% 4 5% 5% 3 4 4 5% 7% 45%	1672
	11th to 20th	Day	14% 11% 4 8% 7% 4 4 4 6% 7% 32%	1701
	21st to end	Day	15% 12% 5% 6% 7% 3 3 3 4 5% 37%	1520
December	1st to 10th	Day	13% 13% 5% 8% 7% 3 5% 5% 4 7% 29%	1520
	11th to 20th	Day	12% 13% 5% 9% 7% 3 4 5% 5% 7% 28%	1918
	21st to end	Day	20% 19% 9% 11% 7% 3 4 4 4 4 15%	2783
January	1st to 10th	Night	12% 12% 8% 10% 7% 3 4 4 4 5% 32%	4428
	11th to 20th	Night	12% 13% 6% 13% 7% 3 4 6% 6% 7% 21%	4440
	21st to end	Night	16% 17% 9% 10% 6% 3 4 4 4 4 23%	4760
February	1st to 10th	Night	11% 13% 5% 8% 7% 4 4 5% 5% 6% 33%	2464
	11th to 20th	Night	12% 10% 3 7% 6% 4 4 4 5% 7% 38%	2155
	21st to end	Night	16% 12% 4 7% 5% 3 4 3 5% 6% 35%	1776
March	1st to 10th	Night	17% 8% 3 6% 5% 3 4 4 6% 6% 36%	2160
	11th to 20th	Night	12% 7% 3 5% 6% 3 5% 5% 5% 9% 40%	2074
	21st to end	Night	19% 10% 3 6% 5% 3 5% 4 5% 6% 32%	2005
April	1st to 10th	Night	17% 8% 4 6% 5% 3 5% 4 5% 6% 36%	1800
	11th to 20th	Night	20% 8% 3 5% 5% 3 4 4 4 6% 37%	1775
	21st to end	Night	17% 8% 3 5% 5% 3 4 5% 5% 7% 38%	1731
May	1st to 10th	Night	17% 8% 2 6% 6% 3 5% 6% 6% 8% 33%	1544
	11th to 20th	Night	18% 6% 3 5% 5% 3 5% 5% 6% 6% 38%	1416
	21st to end	Night	12% 6% 3 5% 6% 3 4 5% 6% 9% 42%	1551
June	1st to 10th	Night	9% 4 2 5% 5% 4 5% 5% 5% 10% 47%	1440
	11th to 20th	Night	13% 5% 2 5% 4 2 4 4 6% 9% 47%	1440
	21st to end	Night	9% 5% 2 5% 4 3 4 4 4 9% 51%	1440
July	1st to 10th	Night	7% 3 1 3 4 3 3 5% 6% 10% 55%	1440
	11th to 20th	Night	6% 4 3 3 5% 2 4 5% 5% 8% 55%	1440
	21st to end	Night	5% 3 2 3 5% 3 5% 5% 7% 9% 53%	1575
August	1st to 10th	Night	5% 3 2 6% 5% 3 4 6% 8% 9% 48%	1449
	11th to 20th	Night	8% 5% 2 4 4 3 4 4 6% 8% 52%	1727
	21st to end	Night	9% 4 2 4 4 2 4 4 5% 7% 53%	1980
September	1st to 10th	Night	10% 4 2 4 4 2 4 4 5% 8% 53%	1800
	11th to 20th	Night	12% 3 2 4 5% 3 4 4 5% 6% 53%	1844
	21st to end	Night	11% 5% 2 4 5% 3 4 5% 5% 7% 49%	1980
October	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 5% 7% 49%	2112
	11th to 20th	Night	17% 8% 2 6% 5% 3 3 3 4 7% 42%	2160
	21st to end	Night	18% 9% 3 6% 5% 3 4 4 5% 7% 35%	2551
November	1st to 10th	Night	12% 7% 3 6% 5% 3 4 4 5% 6% 46%	2406
	11th to 20th	Night	14% 10% 4 7% 6% 4 5% 5% 5% 6% 35%	2474
	21st to end	Night	17% 9% 4 6% 4 3 4 5% 5% 6% 38%	2660
December	1st to 10th	Night	15% 12% 5% 8% 6% 3 5% 5% 5% 6% 32%	2660
	11th to 20th	Night	15% 13% 6% 9% 6% 3 5% 5% 4 5% 29%	3279
	21st to end	Night	21% 17% 6% 8% 7% 3 4 4 4 5% 20%	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	61% 5% 14% 15% 6%	2528
	11th to 20th	Day	59% 6% 12% 15% 7%	2530
	21st to end	Day	66% 3 10% 15% 5%	2893
February	1st to 10th	Day	53% 4 13% 19% 11% 1	1701
	11th to 20th	Day	50% 5% 11% 21% 10% 2	1700
	21st to end	Day	55% 5% 9% 18% 11% 2	1480
March	1st to 10th	Day	49% 6% 13% 22% 8% 1	1800
	11th to 20th	Day	45% 6% 13% 23% 13% 1	1902
	21st to end	Day	54% 5% 12% 21% 7% 1	2350
April	1st to 10th	Day	53% 5% 11% 20% 10%	2160
	11th to 20th	Day	50% 6% 10% 21% 11% 2	2134
	21st to end	Day	52% 6% 10% 19% 11% 1	2227
May	1st to 10th	Day	50% 6% 14% 22% 8% 1	2412
	11th to 20th	Day	48% 7% 11% 21% 12%	2483
	21st to end	Day	44% 7% 11% 22% 14% 2	2725
June	1st to 10th	Day	36% 7% 14% 26% 16% 1	2520
	11th to 20th	Day	37% 7% 12% 24% 18% 1	2520
	21st to end	Day	38% 8% 15% 24% 14% 1	2520
July	1st to 10th	Day	31% 7% 14% 31% 14% 2	2451
	11th to 20th	Day	33% 9% 14% 25% 17% 2	2445
	21st to end	Day	30% 7% 17% 27% 16% 2	2591
August	1st to 10th	Day	33% 9% 16% 30% 12% 1	2471
	11th to 20th	Day	38% 6% 14% 27% 13% 1	2172
	21st to end	Day	34% 6% 12% 27% 19% 2	2376
September	1st to 10th	Day	38% 7% 11% 25% 17% 2	2160
	11th to 20th	Day	33% 5% 12% 32% 16% 1	2098
	21st to end	Day	40% 5% 10% 32% 13% 1	1980
October	1st to 10th	Day	39% 5% 10% 29% 15% 1	1846
	11th to 20th	Day	50% 4 12% 22% 11% 1	1800
	21st to end	Day	49% 4 10% 23% 12% 1	1805
November	1st to 10th	Day	40% 5% 15% 24% 14% 2	1672
	11th to 20th	Day	52% 5% 12% 21% 9% 1	1701
	21st to end	Day	51% 4 15% 22% 7% 1	1520
December	1st to 10th	Day	55% 5% 14% 17% 7% 1	1520
	11th to 20th	Day	56% 4 15% 15% 7% 3	1915
	21st to end	Day	74% 4 8% 9% 5%	2783
January	1st to 10th	Night	55% 4 9% 22% 9% 1	4428
	11th to 20th	Night	62% 4 10% 14% 9%	4440
	21st to end	Night	66% 4 9% 15% 5%	4760
February	1st to 10th	Night	52% 5% 11% 19% 12% 2	2464
	11th to 20th	Night	48% 5% 11% 21% 14% 1	2156
	21st to end	Night	51% 5% 10% 20% 12% 3	1776
March	1st to 10th	Night	48% 5% 14% 21% 9% 3	2160
	11th to 20th	Night	40% 6% 13% 22% 16% 2	2074
	21st to end	Night	54% 4 9% 20% 11% 2	2005
April	1st to 10th	Night	48% 7% 9% 20% 15% 1	1800
	11th to 20th	Night	48% 5% 7% 20% 17% 3	1775
	21st to end	Night	45% 6% 12% 24% 12% 2	1731
May	1st to 10th	Night	47% 7% 13% 20% 13% 1	1544
	11th to 20th	Night	45% 6% 12% 22% 13% 1	1417
	21st to end	Night	39% 6% 13% 25% 15% 2	1552
June	1st to 10th	Night	33% 6% 13% 28% 20% 1	1440
	11th to 20th	Night	34% 6% 9% 26% 23% 2	1440
	21st to end	Night	32% 6% 17% 24% 19% 3	1440
July	1st to 10th	Night	25% 8% 14% 31% 19% 3	1400
	11th to 20th	Night	28% 7% 11% 29% 21% 3	1392
	21st to end	Night	26% 8% 15% 29% 17% 5%	1487
August	1st to 10th	Night	29% 9% 15% 28% 16% 3	1440
	11th to 20th	Night	31% 6% 14% 31% 18% 1	1727
	21st to end	Night	30% 6% 11% 28% 21% 4	1980
September	1st to 10th	Night	30% 7% 11% 27% 23% 2	1800
	11th to 20th	Night	32% 5% 11% 32% 18% 2	1844
	21st to end	Night	35% 5% 11% 30% 19% 1	1980
October	1st to 10th	Night	36% 5% 9% 29% 20% 1	2112
	11th to 20th	Night	43% 4 11% 23% 17% 1	2160
	21st to end	Night	48% 5% 11% 23% 12% 1	2551
November	1st to 10th	Night	39% 5% 10% 27% 17% 2	2406
	11th to 20th	Night	50% 5% 12% 20% 12% 1	2474
	21st to end	Night	48% 4 14% 22% 10% 1	2660
December	1st to 10th	Night	54% 5% 12% 20% 8% 1	2660
	11th to 20th	Night	58% 5% 11% 17% 8% 1	3281
	21st to end	Night	67% 5% 9% 15% 5%	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	17% 11% 35% 24% 10% 2	270
	11th to 20th	Day	16% 13% 39% 25% 7% 1	270
	21st to end	Day	23% 9% 34% 27% 5% 1	297
February	1st to 10th	Day	13% 14% 42% 25% 4 1	267
	11th to 20th	Day	21% 18% 31% 23% 7%	240
	21st to end	Day	20% 16% 42% 19% 2 1	198
March	1st to 10th	Day	15% 17% 41% 22% 5%	240
	11th to 20th	Day	18% 16% 32% 23% 8% 4	240
	21st to end	Day	28% 11% 29% 22% 7% 2	436
April	1st to 10th	Day	23% 15% 35% 23% 5%	420
	11th to 20th	Day	24% 17% 27% 19% 10% 3	412
	21st to end	Day	25% 12% 28% 23% 11% 2	420
May	1st to 10th	Day	20% 11% 32% 25% 10% 2	495
	11th to 20th	Day	22% 10% 29% 26% 11% 2	625
	21st to end	Day	17% 9% 26% 24% 17% 7%	679
June	1st to 10th	Day	8% 8% 28% 34% 18% 5%	630
	11th to 20th	Day	14% 7% 27% 30% 15% 6%	630
	21st to end	Day	11% 8% 29% 30% 18% 4	630
July	1st to 10th	Day	8% 4 17% 31% 26% 13%	621
	11th to 20th	Day	8% 5% 27% 31% 21% 9%	618
	21st to end	Day	6% 3 25% 36% 24% 6%	684
August	1st to 10th	Day	8% 3 20% 33% 25% 11%	626
	11th to 20th	Day	13% 4 15% 27% 25% 15%	486
	21st to end	Day	11% 7% 20% 30% 22% 11%	495
September	1st to 10th	Day	16% 8% 21% 27% 19% 9%	450
	11th to 20th	Day	13% 5% 22% 28% 24% 9%	450
	21st to end	Day	15% 13% 26% 24% 16% 6%	450
October	1st to 10th	Day	19% 10% 25% 26% 17% 3	316
	11th to 20th	Day	24% 16% 34% 17% 7% 1	270
	21st to end	Day	26% 15% 32% 21% 5% 2	297
November	1st to 10th	Day	13% 15% 38% 24% 7% 3	270
	11th to 20th	Day	16% 19% 34% 22% 9%	270
	21st to end	Day	24% 11% 39% 21% 6%	270
December	1st to 10th	Day	18% 17% 40% 18% 6% 1	270
	11th to 20th	Day	17% 13% 37% 21% 11% 1	270
	21st to end	Day	25% 16% 39% 17% 3	297
January	1st to 10th	Night	16% 16% 36% 23% 8% 1	950
	11th to 20th	Night	19% 13% 36% 26% 5% 1	950
	21st to end	Night	20% 11% 37% 27% 6% 1	1045
February	1st to 10th	Night	17% 11% 40% 25% 6% 1	948
	11th to 20th	Night	17% 15% 36% 27% 5%	760
	21st to end	Night	23% 14% 37% 22% 4 1	592
March	1st to 10th	Night	21% 10% 35% 25% 8% 1	720
	11th to 20th	Night	17% 10% 35% 29% 8%	634
	21st to end	Night	23% 10% 29% 30% 8% 1	594
April	1st to 10th	Night	21% 13% 36% 25% 4	540
	11th to 20th	Night	24% 12% 28% 29% 7%	533
	21st to end	Night	21% 9% 31% 29% 8% 1	540
May	1st to 10th	Night	21% 9% 33% 28% 8% 1	540
	11th to 20th	Night	20% 6% 31% 31% 11%	531
	21st to end	Night	14% 4 27% 38% 16% 1	584
June	1st to 10th	Night	9% 4 29% 43% 15% 1	540
	11th to 20th	Night	16% 4 28% 39% 13%	540
	21st to end	Night	9% 5% 26% 42% 17%	540
July	1st to 10th	Night	8% 2 15% 39% 33% 3	525
	11th to 20th	Night	6% 4 22% 42% 24% 2	522
	21st to end	Night	6% 2 19% 49% 22% 2	591
August	1st to 10th	Night	6% 2 17% 48% 26% 1	537
	11th to 20th	Night	9% 2 15% 42% 26% 5%	534
	21st to end	Night	11% 2 16% 45% 23% 2	594
September	1st to 10th	Night	11% 5% 22% 34% 24% 4	540
	11th to 20th	Night	12% 3 22% 35% 24% 3	584
	21st to end	Night	13% 8% 26% 32% 19% 2	720
October	1st to 10th	Night	15% 7% 28% 32% 17% 1	720
	11th to 20th	Night	20% 12% 30% 28% 9%	720
	21st to end	Night	23% 11% 30% 28% 7% 1	792
November	1st to 10th	Night	16% 10% 37% 26% 10% 1	740
	11th to 20th	Night	20% 14% 38% 22% 6%	764
	21st to end	Night	21% 14% 34% 23% 8%	950
December	1st to 10th	Night	20% 14% 38% 21% 6%	950
	11th to 20th	Night	23% 13% 35% 24% 5% 1	950
	21st to end	Night	28% 14% 33% 22% 3	1045

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