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 2024-11-06.

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% 8% 3 7% 5% 4 4 4 6% 7% 38%	101465
	Night	13% 9% 3 7% 5% 4 4 3 5% 6% 39%	97681
Transparency	Day	44% 6% 12% 25% 13% 1	104991
	Night	45% 5% 11% 23% 14% 2	102295
Seeing	Day	16% 10% 29% 26% 14% 5%	15913
	Night	17% 10% 31% 30% 11% 1	25759

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% 13% 7% 14% 7% 6% 4 3 4 5% 26%	2527
	11th to 20th	Day	10% 12% 4 14% 6% 5% 5% 7% 7% 9% 21%	2530
	21st to end	Day	17% 17% 8% 12% 5% 4 3 3 4 5% 21%	2893
February	1st to 10th	Day	11% 13% 6% 9% 6% 4 4 5% 5% 6% 32%	1710
	11th to 20th	Day	13% 11% 3 7% 5% 5% 5% 4 5% 7% 35%	1787
	21st to end	Day	12% 11% 4 10% 7% 3 5% 4 6% 5% 32%	1570
March	1st to 10th	Day	13% 7% 2 6% 4 3 4 3 5% 6% 45%	3120
	11th to 20th	Day	11% 5% 2 8% 5% 5% 5% 4 5% 6% 43%	3346
	21st to end	Day	21% 13% 3 10% 5% 4 4 3 4 6% 28%	4125
April	1st to 10th	Day	17% 13% 4 8% 5% 4 4 4 6% 6% 30%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 4 6% 6% 34%	2254
	21st to end	Day	19% 10% 3 8% 5% 4 3 4 5% 6% 34%	2351
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 4 4 6% 7% 37%	4224
	11th to 20th	Day	13% 6% 2 7% 4 4 4 3 5% 7% 44%	4399
	21st to end	Day	13% 8% 2 6% 4 4 5% 4 7% 8% 39%	4824
June	1st to 10th	Day	11% 4 2 6% 4 5% 5% 4 6% 9% 44%	2660
	11th to 20th	Day	11% 7% 2 6% 5% 4 4 4 7% 8% 42%	2660
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 7% 10% 40%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 10% 35%	4440
	11th to 20th	Day	5% 4 1 5% 4 5% 5% 5% 7% 9% 50%	4440
	21st to end	Day	8% 6% 2 7% 5% 4 5% 4 7% 9% 42%	4813
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	4374
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 48%	3802
	21st to end	Day	10% 6% 3 6% 4 4 5% 4 7% 9% 44%	4180
September	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 5% 8% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 4 8% 50%	2214
	21st to end	Day	12% 7% 2 7% 3 4 4 3 6% 7% 45%	2090
October	1st to 10th	Day	13% 6% 3 6% 4 3 4 3 5% 5% 48%	1948
	11th to 20th	Day	19% 8% 3 7% 5% 4 4 4 5% 7% 34%	1900
	21st to end	Day	17% 10% 4 6% 4 4 3 2 4 6% 39%	1905
November	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 5% 7% 44%	1717
	11th to 20th	Day	13% 12% 3 8% 6% 5% 3 3 5% 7% 32%	1701
	21st to end	Day	15% 13% 4 7% 6% 3 3 3 4 5% 37%	1520
December	1st to 10th	Day	13% 14% 4 8% 6% 4 5% 4 5% 7% 29%	1520
	11th to 20th	Day	12% 14% 5% 11% 6% 4 4 4 6% 7% 28%	1918
	21st to end	Day	20% 20% 8% 13% 5% 4 4 3 4 4 15%	2783
January	1st to 10th	Night	11% 13% 8% 11% 6% 4 4 3 4 5% 32%	4428
	11th to 20th	Night	12% 14% 6% 15% 6% 5% 4 4 6% 7% 21%	4440
	21st to end	Night	16% 18% 8% 11% 5% 4 4 3 4 4 23%	4760
February	1st to 10th	Night	10% 14% 4 9% 6% 6% 4 4 5% 5% 34%	2470
	11th to 20th	Night	12% 10% 3 8% 5% 5% 4 3 5% 6% 39%	2279
	21st to end	Night	16% 12% 4 8% 4 4 3 3 5% 6% 36%	1884
March	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 5% 5% 42%	3733
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 4 5% 9% 45%	3644
	21st to end	Night	23% 12% 4 10% 4 4 4 2 4 5% 30%	3505
April	1st to 10th	Night	17% 10% 3 6% 5% 4 5% 3 5% 6% 37%	1900
	11th to 20th	Night	19% 8% 3 6% 4 4 3 4 5% 6% 38%	1875
	21st to end	Night	17% 8% 2 6% 4 4 4 4 5% 7% 38%	1827
May	1st to 10th	Night	17% 8% 2 6% 5% 4 5% 4 6% 7% 36%	2672
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 5% 6% 43%	2506
	21st to end	Night	11% 8% 3 7% 5% 4 4 4 5% 7% 42%	2743
June	1st to 10th	Night	8% 4 2 5% 5% 5% 4 4 6% 10% 46%	1520
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 6% 8% 47%	1520
	21st to end	Night	9% 6% 2 5% 4 4 3 4 4 8% 50%	1520
July	1st to 10th	Night	15% 7% 2 5% 4 4 4 4 6% 8% 42%	2530
	11th to 20th	Night	4 3 2 4 5% 4 4 4 6% 8% 56%	2530
	21st to end	Night	6% 5% 2 5% 4 5% 5% 4 7% 8% 48%	2750
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 8% 49%	2562
	11th to 20th	Night	9% 7% 2 5% 4 4 4 3 5% 8% 49%	3027
	21st to end	Night	10% 4 2 5% 4 4 4 3 6% 9% 49%	3476
September	1st to 10th	Night	9% 4 2 5% 4 3 3 3 5% 7% 55%	1900
	11th to 20th	Night	12% 3 2 5% 4 4 5% 3 5% 7% 52%	1947
	21st to end	Night	11% 5% 1 5% 4 4 5% 3 5% 7% 50%	2090
October	1st to 10th	Night	12% 6% 2 6% 3 3 3 2 6% 7% 50%	2230
	11th to 20th	Night	16% 8% 2 7% 4 4 3 2 4 7% 44%	2280
	21st to end	Night	18% 9% 3 6% 4 4 4 4 6% 7% 36%	2693
November	1st to 10th	Night	13% 8% 3 6% 4 4 3 3 5% 6% 45%	2483
	11th to 20th	Night	14% 11% 4 8% 5% 5% 5% 4 5% 6% 34%	2474
	21st to end	Night	17% 10% 3 6% 4 4 4 4 5% 5% 38%	2660
December	1st to 10th	Night	14% 12% 4 9% 5% 4 4 4 5% 6% 32%	2660
	11th to 20th	Night	15% 14% 5% 10% 5% 4 5% 4 4 5% 28%	3279
	21st to end	Night	21% 18% 5% 10% 5% 4 4 3 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% 10% 1	1710
	11th to 20th	Day	49% 5% 11% 23% 10% 2	1796
	21st to end	Day	53% 5% 10% 18% 11% 2	1570
March	1st to 10th	Day	40% 5% 11% 29% 13% 2	3120
	11th to 20th	Day	40% 5% 10% 30% 13% 1	3346
	21st to end	Day	58% 5% 12% 17% 6% 2	4125
April	1st to 10th	Day	53% 5% 11% 20% 11%	2280
	11th to 20th	Day	49% 6% 9% 21% 12% 2	2254
	21st to end	Day	51% 6% 10% 20% 12% 1	2351
May	1st to 10th	Day	44% 6% 10% 23% 16% 1	4262
	11th to 20th	Day	39% 7% 9% 30% 15%	4403
	21st to end	Day	41% 7% 10% 23% 16% 3	4837
June	1st to 10th	Day	36% 7% 14% 26% 16% 2	2660
	11th to 20th	Day	37% 7% 12% 24% 18% 1	2660
	21st to end	Day	39% 7% 15% 24% 14% 2	2660
July	1st to 10th	Day	43% 7% 13% 27% 9% 2	4371
	11th to 20th	Day	27% 7% 16% 32% 17% 1	4365
	21st to end	Day	37% 8% 15% 20% 19% 2	4662
August	1st to 10th	Day	37% 7% 14% 29% 11% 1	4359
	11th to 20th	Day	34% 6% 14% 34% 13% 1	3839
	21st to end	Day	35% 6% 14% 28% 16% 1	4179
September	1st to 10th	Day	37% 6% 11% 26% 18% 1	2280
	11th to 20th	Day	33% 5% 12% 32% 17% 2	2214
	21st to end	Day	39% 5% 10% 31% 14% 1	2090
October	1st to 10th	Day	24% 3 6% 40% 25% 1	3234
	11th to 20th	Day	35% 3 10% 28% 22% 1	3140
	21st to end	Day	42% 4 10% 30% 13% 2	3117
November	1st to 10th	Day	41% 4 15% 24% 14% 2	1717
	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	2470
	11th to 20th	Night	46% 5% 11% 23% 14% 1	2280
	21st to end	Night	50% 5% 10% 20% 12% 3	1884
March	1st to 10th	Night	45% 4 12% 25% 9% 5%	3733
	11th to 20th	Night	35% 6% 11% 28% 17% 2	3644
	21st to end	Night	59% 4 7% 17% 11% 1	3505
April	1st to 10th	Night	48% 6% 9% 21% 15% 1	1900
	11th to 20th	Night	47% 5% 7% 20% 18% 3	1875
	21st to end	Night	44% 6% 12% 24% 12% 2	1827
May	1st to 10th	Night	45% 6% 12% 17% 18% 2	2699
	11th to 20th	Night	40% 7% 10% 27% 15% 1	2507
	21st to end	Night	40% 5% 11% 19% 19% 5%	2751
June	1st to 10th	Night	33% 6% 13% 28% 19% 1	1520
	11th to 20th	Night	34% 6% 9% 26% 23% 2	1520
	21st to end	Night	34% 6% 16% 23% 19% 3	1520
July	1st to 10th	Night	40% 6% 15% 22% 13% 3	2490
	11th to 20th	Night	25% 6% 15% 33% 18% 2	2482
	21st to end	Night	31% 9% 15% 22% 21% 3	2662
August	1st to 10th	Night	32% 6% 15% 26% 19% 2	2553
	11th to 20th	Night	33% 5% 13% 32% 15% 1	3056
	21st to end	Night	32% 6% 13% 27% 19% 3	3476
September	1st to 10th	Night	29% 6% 11% 28% 24% 2	1900
	11th to 20th	Night	32% 6% 10% 32% 18% 2	1947
	21st to end	Night	34% 4 11% 29% 20% 1	2090
October	1st to 10th	Night	25% 4 6% 37% 27% 1	3724
	11th to 20th	Night	33% 3 10% 29% 22% 2	3779
	21st to end	Night	43% 4 9% 27% 15% 1	4431
November	1st to 10th	Night	41% 4 10% 26% 17% 2	2483
	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	14% 13% 41% 26% 4 1	270
	11th to 20th	Day	19% 18% 34% 22% 7%	270
	21st to end	Day	19% 16% 44% 19% 2	225
March	1st to 10th	Day	16% 16% 42% 21% 4	270
	11th to 20th	Day	19% 17% 33% 21% 7% 3	270
	21st to end	Day	28% 11% 29% 23% 7% 2	479
April	1st to 10th	Day	24% 14% 35% 22% 4	460
	11th to 20th	Day	25% 16% 27% 19% 10% 3	452
	21st to end	Day	25% 13% 28% 23% 11% 2	460
May	1st to 10th	Day	20% 11% 31% 25% 11% 1	540
	11th to 20th	Day	21% 10% 29% 26% 12% 2	675
	21st to end	Day	17% 10% 27% 25% 16% 6%	734
June	1st to 10th	Day	9% 9% 29% 33% 17% 4	680
	11th to 20th	Day	14% 8% 29% 29% 15% 5%	680
	21st to end	Day	13% 8% 29% 29% 17% 4	680
July	1st to 10th	Day	8% 5% 18% 31% 25% 12%	671
	11th to 20th	Day	8% 5% 26% 30% 22% 9%	668
	21st to end	Day	6% 3 24% 36% 24% 7%	739
August	1st to 10th	Day	8% 3 22% 33% 24% 10%	676
	11th to 20th	Day	13% 5% 17% 27% 24% 14%	528
	21st to end	Day	10% 7% 20% 30% 24% 10%	539
September	1st to 10th	Day	14% 8% 23% 27% 20% 8%	490
	11th to 20th	Day	12% 4 21% 28% 26% 9%	490
	21st to end	Day	14% 12% 27% 25% 16% 6%	490
October	1st to 10th	Day	17% 11% 27% 26% 16% 3	348
	11th to 20th	Day	23% 15% 34% 18% 8% 1	300
	21st to end	Day	25% 16% 33% 20% 5% 2	330
November	1st to 10th	Day	16% 14% 37% 24% 6% 2	285
	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	950
	11th to 20th	Night	16% 15% 37% 28% 5%	804
	21st to end	Night	23% 14% 38% 22% 3 1	628
March	1st to 10th	Night	21% 10% 35% 25% 8% 1	760
	11th to 20th	Night	17% 11% 35% 29% 8%	669
	21st to end	Night	23% 10% 29% 30% 7% 1	627
April	1st to 10th	Night	21% 14% 36% 25% 4	570
	11th to 20th	Night	23% 12% 29% 28% 7%	563
	21st to end	Night	21% 10% 32% 29% 8% 1	570
May	1st to 10th	Night	21% 9% 33% 28% 8% 1	570
	11th to 20th	Night	19% 7% 31% 32% 11%	561
	21st to end	Night	15% 5% 27% 38% 16% 1	617
June	1st to 10th	Night	8% 4 30% 42% 14% 1	570
	11th to 20th	Night	15% 4 29% 39% 12%	570
	21st to end	Night	10% 6% 27% 41% 16%	570
July	1st to 10th	Night	9% 2 15% 39% 32% 3	555
	11th to 20th	Night	6% 5% 22% 42% 24% 2	552
	21st to end	Night	6% 2 19% 49% 22% 2	624
August	1st to 10th	Night	6% 2 18% 47% 26% 1	567
	11th to 20th	Night	9% 3 16% 42% 25% 5%	564
	21st to end	Night	11% 2 16% 45% 23% 2	627
September	1st to 10th	Night	11% 5% 22% 34% 24% 4	570
	11th to 20th	Night	12% 3 21% 36% 24% 3	617
	21st to end	Night	12% 8% 26% 33% 19% 2	760
October	1st to 10th	Night	14% 7% 29% 33% 16% 1	760
	11th to 20th	Night	19% 12% 31% 28% 9%	760
	21st to end	Night	23% 11% 31% 28% 7% 1	836
November	1st to 10th	Night	16% 10% 37% 26% 9% 1	764
	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

Page generated at 2024-11-03 12:19:01. Version ac07

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