George Landis Arboretum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the George Landis Arboretum 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	15% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	101448
	Night	16% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	97632
Transparency	Day	48% 8% 12% 21% 10% 1	104942
	Night	49% 8% 12% 20% 10% 1	102227
Seeing	Day	23% 19% 28% 18% 9% 3	14796
	Night	21% 18% 27% 24% 8% 1	23865

By Month

Percentage Cloud Cover NE (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% 13% 5% 12% 7% 6% 6% 4 6% 4 23%	2517
	11th to 20th	Day	13% 16% 7% 12% 8% 6% 5% 4 5% 5% 20%	2520
	21st to end	Day	18% 17% 5% 12% 7% 5% 5% 4 4 5% 18%	2905
February	1st to 10th	Day	14% 13% 4 10% 8% 7% 6% 5% 5% 6% 22%	1710
	11th to 20th	Day	10% 12% 5% 12% 8% 7% 6% 4 4 5% 26%	1794
	21st to end	Day	16% 13% 5% 12% 7% 5% 4 3 3 6% 27%	1570
March	1st to 10th	Day	22% 13% 4 10% 5% 4 4 3 4 5% 26%	3116
	11th to 20th	Day	13% 13% 5% 11% 6% 4 4 4 5% 7% 28%	3346
	21st to end	Day	18% 11% 4 9% 5% 4 4 3 4 5% 34%	4124
April	1st to 10th	Day	17% 12% 4 9% 6% 3 4 3 5% 5% 33%	2280
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 3 6% 4 36%	2254
	21st to end	Day	20% 9% 3 8% 6% 4 5% 3 5% 6% 32%	2342
May	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 5% 7% 29%	4252
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 5% 6% 7% 32%	4398
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	4837
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 9% 32%	2660
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 5% 7% 9% 32%	2660
	21st to end	Day	13% 7% 3 7% 5% 5% 6% 5% 6% 10% 32%	2660
July	1st to 10th	Day	9% 6% 3 7% 6% 5% 6% 6% 8% 10% 34%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 6% 8% 10% 37%	4440
	21st to end	Day	12% 7% 3 8% 6% 6% 5% 4 6% 8% 35%	4814
August	1st to 10th	Day	16% 6% 2 7% 5% 5% 6% 5% 6% 8% 33%	4361
	11th to 20th	Day	11% 8% 3 8% 6% 6% 6% 5% 7% 9% 30%	3765
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 7% 10% 38%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 6% 7% 42%	2280
	11th to 20th	Day	12% 5% 2 6% 3 4 4 4 5% 8% 47%	2214
	21st to end	Day	13% 7% 3 6% 4 4 5% 4 7% 8% 39%	2090
October	1st to 10th	Day	18% 9% 2 7% 5% 5% 6% 4 6% 5% 33%	1952
	11th to 20th	Day	15% 7% 3 8% 5% 4 4 4 6% 7% 37%	1900
	21st to end	Day	21% 10% 3 8% 5% 4 5% 4 5% 8% 28%	1912
November	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 5% 8% 40%	1717
	11th to 20th	Day	15% 10% 3 8% 7% 4 4 3 5% 8% 33%	1710
	21st to end	Day	16% 12% 3 8% 6% 5% 4 4 6% 6% 30%	1530
December	1st to 10th	Day	17% 17% 4 10% 7% 5% 5% 4 5% 5% 20%	1520
	11th to 20th	Day	19% 13% 4 9% 6% 5% 4 4 4 6% 26%	1906
	21st to end	Day	21% 16% 8% 8% 6% 5% 4 3 4 6% 18%	2772
January	1st to 10th	Night	15% 13% 5% 12% 6% 6% 5% 4 5% 6% 24%	4429
	11th to 20th	Night	12% 14% 5% 13% 9% 7% 6% 4 6% 6% 20%	4440
	21st to end	Night	19% 16% 5% 12% 7% 5% 5% 4 5% 5% 18%	4747
February	1st to 10th	Night	14% 13% 5% 11% 7% 5% 5% 5% 5% 7% 23%	2470
	11th to 20th	Night	11% 11% 5% 12% 7% 5% 6% 5% 6% 7% 25%	2270
	21st to end	Night	16% 12% 4 10% 6% 5% 4 4 5% 7% 26%	1884
March	1st to 10th	Night	20% 10% 4 9% 5% 6% 5% 3 5% 6% 26%	3724
	11th to 20th	Night	14% 13% 5% 8% 6% 5% 5% 4 5% 5% 30%	3610
	21st to end	Night	13% 14% 4 11% 7% 5% 4 3 4 4 32%	3507
April	1st to 10th	Night	18% 10% 4 8% 6% 5% 4 4 4 7% 30%	1900
	11th to 20th	Night	19% 10% 2 7% 5% 4 5% 3 4 6% 34%	1875
	21st to end	Night	19% 9% 2 6% 4 4 4 4 5% 6% 36%	1837
May	1st to 10th	Night	25% 9% 3 8% 4 4 5% 3 5% 6% 29%	2718
	11th to 20th	Night	16% 11% 3 7% 5% 5% 5% 4 5% 6% 32%	2495
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 5% 6% 8% 36%	2738
June	1st to 10th	Night	16% 7% 2 7% 4 4 4 4 6% 8% 39%	1520
	11th to 20th	Night	15% 7% 2 5% 4 3 4 4 6% 10% 40%	1520
	21st to end	Night	12% 4 2 6% 6% 5% 4 4 6% 9% 41%	1520
July	1st to 10th	Night	9% 6% 2 9% 7% 5% 5% 4 6% 8% 38%	2520
	11th to 20th	Night	12% 7% 2 6% 3 5% 4 4 6% 9% 41%	2520
	21st to end	Night	12% 7% 3 7% 5% 5% 4 4 6% 7% 39%	2739
August	1st to 10th	Night	18% 8% 2 7% 5% 4 4 3 5% 7% 36%	2564
	11th to 20th	Night	14% 8% 2 8% 5% 4 4 4 5% 7% 37%	3030
	21st to end	Night	12% 6% 2 6% 4 3 4 4 5% 9% 43%	3476
September	1st to 10th	Night	13% 5% 2 7% 3 4 4 3 6% 6% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 3 2 5% 7% 52%	1966
	21st to end	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	2090
October	1st to 10th	Night	19% 8% 3 8% 4 4 4 4 5% 6% 35%	2226
	11th to 20th	Night	15% 8% 2 7% 4 4 4 3 5% 7% 39%	2280
	21st to end	Night	21% 10% 3 6% 5% 4 4 4 5% 8% 30%	2684
November	1st to 10th	Night	14% 8% 4 8% 5% 4 4 4 5% 6% 39%	2483
	11th to 20th	Night	16% 9% 3 9% 5% 5% 4 3 6% 7% 32%	2470
	21st to end	Night	14% 12% 4 8% 5% 5% 5% 4 5% 7% 31%	2648
December	1st to 10th	Night	16% 14% 5% 10% 5% 5% 5% 5% 6% 7% 23%	2660
	11th to 20th	Night	19% 11% 4 11% 5% 6% 5% 4 5% 6% 24%	3288
	21st to end	Night	24% 14% 8% 7% 5% 4 4 4 5% 6% 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	55% 12% 10% 16% 6% 1	2518
	11th to 20th	Day	61% 9% 9% 13% 5% 1	2520
	21st to end	Day	65% 8% 9% 12% 5% 1	2905
February	1st to 10th	Day	61% 8% 10% 15% 6% 1	1710
	11th to 20th	Day	58% 7% 8% 17% 9% 1	1803
	21st to end	Day	59% 6% 9% 15% 11% 1	1570
March	1st to 10th	Day	59% 6% 11% 14% 9% 1	3119
	11th to 20th	Day	51% 10% 13% 15% 8% 2	3346
	21st to end	Day	53% 5% 6% 17% 17% 2	4124
April	1st to 10th	Day	53% 5% 7% 22% 11% 2	2280
	11th to 20th	Day	49% 6% 10% 20% 13% 2	2254
	21st to end	Day	52% 6% 9% 18% 12% 3	2342
May	1st to 10th	Day	55% 6% 10% 17% 11% 2	4266
	11th to 20th	Day	49% 8% 13% 21% 8% 1	4402
	21st to end	Day	39% 9% 11% 28% 12% 1	4837
June	1st to 10th	Day	46% 9% 13% 20% 11% 1	2660
	11th to 20th	Day	45% 9% 13% 21% 11% 1	2660
	21st to end	Day	46% 8% 13% 21% 10% 1	2660
July	1st to 10th	Day	41% 9% 14% 24% 11%	4370
	11th to 20th	Day	37% 10% 14% 27% 11%	4365
	21st to end	Day	45% 8% 13% 23% 10%	4661
August	1st to 10th	Day	46% 9% 14% 21% 10% 1	4347
	11th to 20th	Day	45% 10% 16% 24% 5%	3802
	21st to end	Day	37% 9% 13% 31% 9% 1	4180
September	1st to 10th	Day	40% 8% 11% 27% 14% 1	2280
	11th to 20th	Day	35% 7% 11% 27% 18% 1	2214
	21st to end	Day	42% 8% 11% 24% 13% 2	2090
October	1st to 10th	Day	43% 8% 10% 24% 14% 1	3238
	11th to 20th	Day	39% 6% 13% 25% 15% 2	3140
	21st to end	Day	37% 8% 15% 27% 11% 2	3124
November	1st to 10th	Day	42% 7% 13% 24% 13% 1	1717
	11th to 20th	Day	49% 8% 11% 18% 12% 2	1710
	21st to end	Day	52% 7% 15% 17% 7% 1	1530
December	1st to 10th	Day	64% 8% 10% 12% 6% 1	1520
	11th to 20th	Day	57% 8% 14% 14% 5% 1	1906
	21st to end	Day	66% 7% 8% 13% 5%	2772
January	1st to 10th	Night	54% 11% 11% 15% 8% 1	4429
	11th to 20th	Night	57% 12% 9% 14% 7% 1	4440
	21st to end	Night	66% 8% 8% 12% 6% 1	4747
February	1st to 10th	Night	59% 6% 10% 16% 7% 1	2470
	11th to 20th	Night	55% 9% 11% 16% 8% 1	2272
	21st to end	Night	56% 7% 11% 16% 8% 2	1884
March	1st to 10th	Night	56% 7% 10% 17% 9% 1	3734
	11th to 20th	Night	53% 8% 11% 21% 6% 1	3611
	21st to end	Night	55% 6% 6% 16% 14% 2	3507
April	1st to 10th	Night	53% 7% 10% 19% 10% 2	1900
	11th to 20th	Night	50% 6% 9% 20% 14% 1	1875
	21st to end	Night	48% 7% 10% 18% 15% 3	1837
May	1st to 10th	Night	55% 7% 10% 15% 11% 2	2724
	11th to 20th	Night	50% 7% 13% 20% 8% 1	2496
	21st to end	Night	42% 10% 13% 20% 14% 1	2739
June	1st to 10th	Night	43% 6% 12% 25% 12% 2	1520
	11th to 20th	Night	39% 7% 16% 25% 13% 1	1520
	21st to end	Night	38% 8% 15% 26% 13%	1520
July	1st to 10th	Night	41% 7% 15% 21% 14% 1	2480
	11th to 20th	Night	37% 8% 15% 26% 13%	2472
	21st to end	Night	41% 8% 11% 28% 11% 1	2651
August	1st to 10th	Night	46% 8% 13% 25% 8%	2554
	11th to 20th	Night	43% 9% 17% 24% 9%	3059
	21st to end	Night	35% 7% 14% 33% 10%	3476
September	1st to 10th	Night	37% 7% 11% 29% 14% 1	1900
	11th to 20th	Night	33% 5% 12% 28% 21% 1	1966
	21st to end	Night	40% 7% 11% 25% 15% 2	2090
October	1st to 10th	Night	47% 7% 12% 23% 10% 1	3720
	11th to 20th	Night	35% 7% 13% 25% 18% 2	3779
	21st to end	Night	41% 7% 14% 28% 10% 1	4422
November	1st to 10th	Night	43% 7% 11% 21% 15% 2	2483
	11th to 20th	Night	50% 8% 10% 19% 11% 2	2470
	21st to end	Night	49% 9% 14% 20% 6% 1	2648
December	1st to 10th	Night	58% 10% 12% 15% 6%	2660
	11th to 20th	Night	57% 10% 11% 14% 8% 1	3288
	21st to end	Night	63% 9% 10% 13% 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	31% 24% 28% 13% 3 1	180
	11th to 20th	Day	33% 30% 27% 7% 2 1	180
	21st to end	Day	24% 28% 37% 7% 4	237
February	1st to 10th	Day	31% 33% 29% 7% 1	270
	11th to 20th	Day	29% 36% 24% 10% 1	402
	21st to end	Day	30% 25% 31% 12% 2	382
March	1st to 10th	Day	29% 26% 31% 11% 3	460
	11th to 20th	Day	32% 25% 28% 10% 4 1	460
	21st to end	Day	33% 26% 22% 13% 5% 1	506
April	1st to 10th	Day	31% 27% 22% 13% 7% 1	460
	11th to 20th	Day	28% 26% 25% 12% 6% 2	452
	21st to end	Day	32% 20% 28% 13% 5% 2	460
May	1st to 10th	Day	33% 20% 26% 13% 5% 3	463
	11th to 20th	Day	20% 20% 30% 21% 7% 2	487
	21st to end	Day	19% 13% 30% 24% 11% 3	529
June	1st to 10th	Day	19% 17% 33% 21% 9% 2	490
	11th to 20th	Day	19% 16% 30% 23% 12% 1	490
	21st to end	Day	18% 18% 30% 23% 10% 1	490
July	1st to 10th	Day	12% 10% 32% 27% 16% 4	485
	11th to 20th	Day	13% 7% 32% 31% 14% 3	484
	21st to end	Day	12% 10% 38% 27% 9% 3	532
August	1st to 10th	Day	11% 11% 30% 26% 17% 5%	486
	11th to 20th	Day	16% 8% 30% 25% 13% 7%	479
	21st to end	Day	13% 15% 27% 24% 16% 5%	539
September	1st to 10th	Day	16% 12% 26% 23% 16% 8%	490
	11th to 20th	Day	13% 9% 27% 21% 18% 11%	490
	21st to end	Day	18% 11% 29% 23% 13% 6%	490
October	1st to 10th	Day	24% 14% 26% 18% 14% 3	490
	11th to 20th	Day	25% 16% 27% 21% 10% 1	490
	21st to end	Day	27% 20% 29% 18% 7%	444
November	1st to 10th	Day	26% 18% 23% 19% 13% 2	381
	11th to 20th	Day	26% 26% 24% 17% 5% 1	370
	21st to end	Day	29% 25% 26% 17% 2 1	190
December	1st to 10th	Day	29% 26% 27% 13% 4	180
	11th to 20th	Day	33% 28% 28% 10% 2	180
	21st to end	Day	27% 27% 32% 10% 4 1	198
January	1st to 10th	Night	23% 28% 32% 15% 2	760
	11th to 20th	Night	26% 25% 29% 17% 3	760
	21st to end	Night	18% 28% 33% 18% 2	836
February	1st to 10th	Night	23% 25% 33% 17% 2	760
	11th to 20th	Night	23% 28% 31% 15% 1	743
	21st to end	Night	29% 25% 28% 17% 2	628
March	1st to 10th	Night	25% 25% 33% 15% 3	760
	11th to 20th	Night	26% 25% 30% 16% 3	760
	21st to end	Night	24% 23% 28% 19% 5%	836
April	1st to 10th	Night	27% 22% 28% 19% 3	760
	11th to 20th	Night	25% 22% 27% 19% 7%	751
	21st to end	Night	24% 21% 26% 22% 6%	697
May	1st to 10th	Night	28% 14% 28% 21% 8% 1	506
	11th to 20th	Night	21% 12% 30% 30% 7% 1	374
	21st to end	Night	16% 10% 29% 31% 13% 1	411
June	1st to 10th	Night	18% 9% 28% 33% 11% 1	380
	11th to 20th	Night	16% 12% 22% 37% 13%	380
	21st to end	Night	14% 8% 27% 36% 14% 1	380
July	1st to 10th	Night	10% 6% 25% 39% 18% 1	370
	11th to 20th	Night	14% 4 25% 40% 16% 1	368
	21st to end	Night	11% 6% 24% 44% 15% 1	416
August	1st to 10th	Night	12% 4 29% 34% 21%	410
	11th to 20th	Night	16% 5% 22% 36% 18% 4	707
	21st to end	Night	15% 9% 21% 33% 20% 1	836
September	1st to 10th	Night	15% 7% 25% 32% 19% 1	760
	11th to 20th	Night	14% 8% 23% 29% 20% 6%	760
	21st to end	Night	17% 9% 25% 31% 16% 2	760
October	1st to 10th	Night	21% 13% 24% 26% 14% 2	760
	11th to 20th	Night	21% 15% 27% 28% 9%	760
	21st to end	Night	28% 16% 28% 23% 5%	836
November	1st to 10th	Night	20% 18% 25% 28% 7%	764
	11th to 20th	Night	23% 22% 26% 21% 7% 1	760
	21st to end	Night	22% 23% 28% 22% 6%	760
December	1st to 10th	Night	25% 26% 30% 15% 4	760
	11th to 20th	Night	26% 25% 27% 19% 3	760
	21st to end	Night	29% 27% 26% 16% 2	836

Page generated at 2024-11-03 13:19:00. Version ac07

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