Evans Above Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Evans Above Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	20% 9% 3 7% 5% 4 4 3 4 6% 36%	101649
	Night	22% 9% 3 7% 4 4 4 3 4 5% 35%	97413
Transparency	Day	50% 5% 12% 17% 12% 4	101392
	Night	51% 5% 13% 18% 10% 3	97259
Seeing	Day	23% 6% 20% 27% 18% 6%	14695
	Night	26% 4 18% 35% 16% 1	23512

By Month

Percentage Cloud Cover SW (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	43% 14% 3 9% 5% 5% 4 4 3 3 7%	2539
	11th to 20th	Day	39% 13% 4 8% 4 4 2 2 3 3 17%	2540
	21st to end	Day	38% 13% 5% 9% 5% 4 4 3 3 4 13%	3027
February	1st to 10th	Day	33% 12% 4 8% 5% 4 3 4 5% 5% 16%	1710
	11th to 20th	Day	33% 13% 4 9% 5% 5% 3 3 3 4 17%	1665
	21st to end	Day	33% 15% 4 7% 5% 4 3 3 4 5% 19%	1488
March	1st to 10th	Day	22% 15% 4 11% 6% 5% 5% 4 5% 6% 16%	3281
	11th to 20th	Day	22% 10% 3 8% 4 3 3 2 4 5% 35%	3490
	21st to end	Day	26% 14% 4 11% 6% 6% 4 4 5% 6% 15%	3912
April	1st to 10th	Day	28% 14% 5% 10% 6% 5% 4 2 5% 5% 17%	2280
	11th to 20th	Day	24% 12% 4 8% 6% 5% 4 3 4 5% 25%	2249
	21st to end	Day	22% 10% 3 10% 6% 5% 5% 5% 5% 6% 23%	2465
May	1st to 10th	Day	20% 8% 3 7% 5% 4 4 3 4 5% 35%	4376
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 6% 8% 41%	4377
	21st to end	Day	23% 8% 3 9% 6% 6% 6% 4 6% 6% 23%	4813
June	1st to 10th	Day	22% 8% 3 7% 5% 5% 4 3 6% 6% 30%	2660
	11th to 20th	Day	19% 9% 3 7% 5% 6% 6% 4 6% 7% 27%	2660
	21st to end	Day	8% 5% 2 6% 4 4 4 3 4 7% 50%	2753
July	1st to 10th	Day	5% 3 1 3 2 3 3 2 4 5% 69%	4420
	11th to 20th	Day	4 3 1 3 2 2 3 2 3 4 74%	4420
	21st to end	Day	6% 3 1 3 3 2 3 2 4 6% 67%	4790
August	1st to 10th	Day	3 4 2 4 3 2 3 2 5% 6% 67%	4157
	11th to 20th	Day	6% 3 2 6% 4 5% 4 4 7% 8% 50%	4026
	21st to end	Day	10% 6% 2 5% 4 4 4 3 4 6% 52%	4306
September	1st to 10th	Day	7% 4 2 5% 3 3 4 3 4 6% 59%	2280
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 3 5% 7% 42%	2280
	21st to end	Day	16% 6% 2 7% 5% 4 5% 3 5% 6% 44%	2000
October	1st to 10th	Day	22% 8% 2 6% 5% 4 4 3 5% 5% 35%	1900
	11th to 20th	Day	23% 7% 3 9% 5% 5% 4 3 6% 7% 30%	1900
	21st to end	Day	30% 9% 3 7% 4 4 3 2 3 4 28%	2036
November	1st to 10th	Day	32% 13% 5% 10% 6% 4 5% 3 4 5% 15%	1567
	11th to 20th	Day	35% 11% 3 8% 4 5% 4 3 4 5% 20%	1520
	21st to end	Day	31% 12% 4 8% 5% 4 3 3 4 4 22%	1520
December	1st to 10th	Day	30% 14% 3 7% 5% 4 3 3 4 4 23%	1520
	11th to 20th	Day	33% 14% 4 7% 5% 4 5% 4 5% 5% 14%	1928
	21st to end	Day	33% 14% 5% 11% 7% 6% 5% 3 4 4 10%	2794
January	1st to 10th	Night	39% 13% 3 9% 6% 4 4 3 4 4 10%	4406
	11th to 20th	Night	38% 14% 3 7% 4 4 4 2 3 4 16%	4420
	21st to end	Night	38% 13% 4 9% 5% 4 3 2 4 4 15%	4632
February	1st to 10th	Night	31% 12% 3 8% 6% 5% 4 3 4 5% 19%	2470
	11th to 20th	Night	31% 12% 3 7% 5% 5% 3 3 4 4 23%	2402
	21st to end	Night	29% 13% 4 8% 5% 4 5% 4 4 5% 19%	1965
March	1st to 10th	Night	23% 15% 4 8% 5% 5% 6% 4 5% 5% 19%	3591
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 4 4 6% 37%	3490
	21st to end	Night	28% 14% 5% 10% 6% 5% 5% 3 4 4 17%	3741
April	1st to 10th	Night	26% 13% 4 9% 6% 4 4 3 4 5% 22%	1900
	11th to 20th	Night	21% 11% 3 7% 5% 5% 4 3 5% 6% 30%	1879
	21st to end	Night	26% 10% 3 8% 4 4 3 3 4 6% 29%	1711
May	1st to 10th	Night	21% 9% 3 7% 4 3 3 3 4 4 39%	2583
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 5% 7% 56%	2516
	21st to end	Night	14% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	2762
June	1st to 10th	Night	19% 6% 3 8% 5% 5% 4 3 3 6% 38%	1520
	11th to 20th	Night	16% 9% 2 8% 5% 4 3 3 4 6% 40%	1520
	21st to end	Night	6% 5% 2 6% 3 3 3 2 3 6% 60%	1379
July	1st to 10th	Night	3 2 1 3 2 2 2 1 3 3 80%	2540
	11th to 20th	Night	3 2 1 4 2 2 2 1 2 3 77%	2540
	21st to end	Night	4 2 1 2 1 1 2 2 2 4 79%	2761
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 5% 76%	2777
	11th to 20th	Night	7% 4 1 5% 4 3 4 3 4 7% 59%	2812
	21st to end	Night	11% 4 2 4 3 3 3 3 3 5% 60%	3367
September	1st to 10th	Night	7% 3 1 4 2 3 3 2 4 5% 66%	1900
	11th to 20th	Night	12% 5% 2 7% 5% 4 4 3 5% 5% 48%	1900
	21st to end	Night	12% 4 2 6% 3 4 4 4 4 7% 51%	2176
October	1st to 10th	Night	17% 6% 2 6% 3 4 3 3 4 5% 46%	2280
	11th to 20th	Night	20% 6% 3 7% 4 3 4 3 4 7% 38%	2280
	21st to end	Night	26% 8% 3 7% 4 3 4 2 4 5% 34%	2561
November	1st to 10th	Night	32% 10% 3 7% 5% 5% 4 3 4 6% 21%	2514
	11th to 20th	Night	36% 9% 3 7% 5% 3 3 3 3 5% 22%	2660
	21st to end	Night	29% 8% 3 8% 5% 5% 4 4 3 4 27%	2660
December	1st to 10th	Night	31% 11% 3 6% 4 4 4 3 5% 5% 24%	2660
	11th to 20th	Night	32% 12% 4 8% 5% 4 4 3 4 6% 18%	3276
	21st to end	Night	32% 14% 4 10% 6% 5% 5% 3 4 4 14%	4862

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	82% 5% 7% 4 2	2539
	11th to 20th	Day	74% 3 6% 11% 4 2	2540
	21st to end	Day	76% 6% 7% 7% 4	3027
February	1st to 10th	Day	70% 5% 9% 11% 4	1710
	11th to 20th	Day	73% 5% 7% 10% 4 1	1674
	21st to end	Day	70% 5% 10% 10% 5% 1	1488
March	1st to 10th	Day	67% 6% 13% 11% 3	3281
	11th to 20th	Day	53% 5% 7% 27% 7%	3490
	21st to end	Day	69% 6% 13% 8% 3	3912
April	1st to 10th	Day	68% 6% 12% 12% 2	2280
	11th to 20th	Day	62% 5% 10% 14% 8% 2	2252
	21st to end	Day	60% 6% 12% 13% 7% 1	2465
May	1st to 10th	Day	49% 5% 14% 19% 12%	4376
	11th to 20th	Day	36% 7% 23% 25% 8% 1	4380
	21st to end	Day	59% 10% 17% 13% 2	4814
June	1st to 10th	Day	53% 5% 17% 17% 7%	2660
	11th to 20th	Day	54% 7% 18% 15% 6%	2660
	21st to end	Day	34% 5% 19% 27% 10% 4	2753
July	1st to 10th	Day	18% 4 9% 18% 22% 28%	4351
	11th to 20th	Day	16% 2 7% 21% 40% 14%	4345
	21st to end	Day	19% 4 12% 28% 33% 5%	4639
August	1st to 10th	Day	19% 3 9% 30% 28% 11%	4141
	11th to 20th	Day	31% 5% 20% 28% 12% 4	4065
	21st to end	Day	33% 4 12% 25% 18% 8%	4305
September	1st to 10th	Day	26% 4 14% 26% 19% 11%	2280
	11th to 20th	Day	41% 6% 14% 18% 14% 7%	2280
	21st to end	Day	42% 5% 14% 20% 15% 5%	2000
October	1st to 10th	Day	49% 5% 8% 21% 13% 3	1900
	11th to 20th	Day	54% 5% 13% 16% 11% 1	1900
	21st to end	Day	62% 3 8% 14% 12% 1	2036
November	1st to 10th	Day	72% 5% 8% 12% 4	1567
	11th to 20th	Day	67% 5% 11% 9% 6% 2	1520
	21st to end	Day	67% 5% 6% 10% 11% 1	1520
December	1st to 10th	Day	66% 4 9% 12% 8% 1	1520
	11th to 20th	Day	70% 6% 10% 12% 2	1928
	21st to end	Day	79% 4 8% 6% 2	2794
January	1st to 10th	Night	77% 4 9% 6% 3 1	4406
	11th to 20th	Night	72% 3 7% 12% 4 1	4420
	21st to end	Night	75% 4 8% 9% 5% 1	4632
February	1st to 10th	Night	68% 6% 10% 12% 4	2470
	11th to 20th	Night	66% 4 11% 12% 6% 2	2404
	21st to end	Night	66% 5% 11% 11% 6% 1	1965
March	1st to 10th	Night	63% 7% 12% 15% 3	3591
	11th to 20th	Night	47% 7% 13% 26% 8% 1	3490
	21st to end	Night	70% 7% 12% 11% 1	3741
April	1st to 10th	Night	64% 5% 15% 13% 4	1900
	11th to 20th	Night	55% 6% 14% 15% 8% 3	1879
	21st to end	Night	56% 6% 14% 17% 5% 2	1711
May	1st to 10th	Night	46% 5% 14% 24% 10% 1	2583
	11th to 20th	Night	27% 5% 23% 33% 9% 2	2516
	21st to end	Night	45% 11% 28% 12% 3	2762
June	1st to 10th	Night	49% 4 16% 25% 6% 1	1520
	11th to 20th	Night	44% 4 23% 23% 6%	1520
	21st to end	Night	27% 5% 20% 33% 11% 4	1379
July	1st to 10th	Night	13% 2 9% 25% 24% 28%	2500
	11th to 20th	Night	15% 2 8% 22% 39% 15%	2492
	21st to end	Night	12% 2 12% 33% 35% 6%	2674
August	1st to 10th	Night	12% 3 11% 36% 32% 7%	2769
	11th to 20th	Night	25% 4 28% 28% 10% 5%	2839
	21st to end	Night	29% 3 15% 27% 21% 5%	3367
September	1st to 10th	Night	21% 4 15% 30% 20% 10%	1900
	11th to 20th	Night	38% 5% 14% 23% 12% 9%	1900
	21st to end	Night	33% 5% 17% 21% 17% 6%	2176
October	1st to 10th	Night	40% 4 10% 26% 16% 3	2280
	11th to 20th	Night	46% 5% 13% 20% 14% 2	2280
	21st to end	Night	53% 5% 10% 17% 14% 2	2561
November	1st to 10th	Night	64% 6% 8% 16% 6%	2514
	11th to 20th	Night	66% 5% 10% 10% 7% 2	2660
	21st to end	Night	61% 5% 9% 11% 12% 1	2660
December	1st to 10th	Night	62% 6% 10% 13% 9% 1	2660
	11th to 20th	Night	68% 7% 10% 11% 4	3276
	21st to end	Night	73% 7% 9% 8% 2	4862

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	49% 3 16% 13% 15% 4	180
	11th to 20th	Day	44% 4 13% 21% 9% 7%	180
	21st to end	Day	37% 6% 14% 21% 14% 7%	340
February	1st to 10th	Day	43% 5% 16% 18% 14% 4	370
	11th to 20th	Day	41% 5% 21% 22% 10% 2	365
	21st to end	Day	41% 9% 19% 19% 10% 3	343
March	1st to 10th	Day	33% 8% 22% 22% 12% 2	460
	11th to 20th	Day	29% 6% 23% 22% 13% 5%	460
	21st to end	Day	33% 8% 21% 22% 13% 3	506
April	1st to 10th	Day	30% 8% 21% 23% 13% 5%	460
	11th to 20th	Day	28% 11% 27% 20% 10% 4	452
	21st to end	Day	25% 7% 27% 23% 14% 4	460
May	1st to 10th	Day	19% 10% 24% 26% 17% 4	463
	11th to 20th	Day	25% 8% 19% 23% 17% 7%	488
	21st to end	Day	20% 7% 20% 25% 21% 7%	529
June	1st to 10th	Day	22% 5% 21% 28% 19% 4	490
	11th to 20th	Day	17% 7% 26% 33% 13% 3	490
	21st to end	Day	7% 5% 26% 35% 21% 5%	583
July	1st to 10th	Day	9% 4 20% 34% 24% 8%	486
	11th to 20th	Day	6% 5% 21% 37% 24% 7%	484
	21st to end	Day	5% 3 16% 39% 30% 7%	531
August	1st to 10th	Day	7% 2 16% 37% 28% 10%	487
	11th to 20th	Day	4 2 15% 33% 32% 14%	477
	21st to end	Day	9% 4 20% 33% 23% 10%	539
September	1st to 10th	Day	8% 4 20% 37% 23% 9%	490
	11th to 20th	Day	16% 3 17% 30% 24% 10%	490
	21st to end	Day	17% 4 21% 32% 22% 5%	490
October	1st to 10th	Day	21% 6% 16% 29% 21% 7%	490
	11th to 20th	Day	25% 4 18% 27% 19% 7%	490
	21st to end	Day	32% 6% 20% 22% 13% 6%	485
November	1st to 10th	Day	32% 5% 23% 23% 14% 4	219
	11th to 20th	Day	36% 4 23% 16% 14% 7%	180
	21st to end	Day	37% 3 18% 19% 16% 6%	180
December	1st to 10th	Day	40% 2 19% 16% 17% 6%	180
	11th to 20th	Day	44% 6% 19% 19% 9% 3	180
	21st to end	Day	38% 6% 16% 25% 13% 3	198
January	1st to 10th	Night	43% 6% 13% 23% 13% 2	760
	11th to 20th	Night	40% 4 12% 28% 15% 1	760
	21st to end	Night	35% 3 13% 31% 17% 2	836
February	1st to 10th	Night	35% 4 16% 30% 14% 1	760
	11th to 20th	Night	37% 4 17% 27% 15% 1	744
	21st to end	Night	36% 4 16% 32% 11%	628
March	1st to 10th	Night	33% 6% 15% 31% 14% 1	760
	11th to 20th	Night	29% 4 18% 35% 13% 1	760
	21st to end	Night	33% 6% 17% 29% 14%	836
April	1st to 10th	Night	31% 6% 17% 29% 16% 1	760
	11th to 20th	Night	27% 4 23% 33% 12% 2	751
	21st to end	Night	30% 2 20% 33% 14% 1	571
May	1st to 10th	Night	18% 5% 28% 36% 13%	410
	11th to 20th	Night	17% 3 21% 45% 13% 1	374
	21st to end	Night	18% 4 22% 38% 18%	411
June	1st to 10th	Night	22% 2 26% 38% 12%	380
	11th to 20th	Night	17% 4 28% 43% 8% 1	380
	21st to end	Night	7% 2 33% 48% 9%	380
July	1st to 10th	Night	6% 2 27% 53% 12% 1	370
	11th to 20th	Night	6% 3 35% 43% 13%	368
	21st to end	Night	2 1 31% 53% 12% 1	416
August	1st to 10th	Night	4 2 20% 47% 25% 2	522
	11th to 20th	Night	5% 1 12% 51% 29% 3	564
	21st to end	Night	8% 3 23% 43% 22% 2	757
September	1st to 10th	Night	8% 3 21% 46% 20% 2	760
	11th to 20th	Night	14% 3 14% 36% 29% 4	760
	21st to end	Night	13% 2 19% 43% 21% 2	760
October	1st to 10th	Night	21% 3 17% 35% 22% 3	760
	11th to 20th	Night	23% 3 15% 33% 24% 3	760
	21st to end	Night	30% 3 18% 33% 15% 2	836
November	1st to 10th	Night	35% 3 14% 35% 12% 1	742
	11th to 20th	Night	40% 4 15% 26% 14% 1	760
	21st to end	Night	31% 3 15% 34% 16% 1	760
December	1st to 10th	Night	35% 4 14% 31% 14% 2	760
	11th to 20th	Night	42% 4 16% 26% 11% 1	760
	21st to end	Night	42% 5% 18% 25% 10% 1	836

Page generated at 2024-10-29 08:20:49. Version ac07

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