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 2026-09-14.

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	17% 8% 3 7% 4 4 4 3 5% 6% 39%	158703
	Night	20% 8% 3 7% 5% 4 4 3 4 5% 37%	149720
Transparency	Day	46% 5% 13% 20% 13% 4	153461
	Night	49% 5% 13% 20% 11% 3	145963
Seeing	Day	22% 6% 20% 28% 18% 6%	17040
	Night	26% 4 19% 35% 16% 1	25801

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	40% 15% 4 10% 6% 5% 4 3 3 4 7%	4722
	11th to 20th	Day	23% 9% 2 9% 6% 5% 4 3 5% 5% 28%	4740
	21st to end	Day	28% 8% 4 7% 4 4 4 3 5% 5% 28%	5640
February	1st to 10th	Day	32% 12% 4 8% 5% 5% 4 4 5% 5% 16%	1890
	11th to 20th	Day	32% 14% 5% 9% 6% 5% 3 2 3 4 17%	1845
	21st to end	Day	33% 14% 4 7% 6% 4 3 3 4 5% 19%	1640
March	1st to 10th	Day	20% 13% 4 10% 6% 6% 7% 5% 6% 6% 19%	4830
	11th to 20th	Day	26% 14% 4 9% 5% 4 4 3 4 4 24%	5110
	21st to end	Day	25% 13% 4 11% 7% 6% 5% 4 6% 7% 13%	5736
April	1st to 10th	Day	26% 13% 4 10% 6% 5% 5% 3 5% 6% 18%	2520
	11th to 20th	Day	23% 12% 3 8% 6% 5% 4 3 5% 5% 26%	2489
	21st to end	Day	21% 10% 3 9% 6% 5% 5% 5% 5% 6% 25%	2725
May	1st to 10th	Day	12% 6% 2 6% 5% 4 4 3 5% 7% 45%	8112
	11th to 20th	Day	14% 6% 3 10% 6% 6% 5% 4 6% 9% 31%	8160
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 4 6% 8% 36%	8992
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 3 6% 6% 33%	2940
	11th to 20th	Day	17% 9% 3 7% 5% 6% 5% 4 6% 7% 30%	2940
	21st to end	Day	9% 5% 3 7% 4 5% 4 4 5% 7% 48%	3044
July	1st to 10th	Day	4 3 1 3 2 3 3 2 4 6% 69%	8219
	11th to 20th	Day	4 3 1 3 2 2 2 2 3 4 76%	8220
	21st to end	Day	4 3 1 3 2 2 2 2 4 6% 70%	8922
August	1st to 10th	Day	3 3 1 4 3 3 3 2 4 6% 69%	7665
	11th to 20th	Day	7% 3 2 5% 3 4 4 4 6% 8% 55%	7563
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 8% 52%	7976
September	1st to 10th	Day	7% 4 2 5% 4 3 4 3 5% 6% 56%	2520
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 3 5% 7% 43%	2437
	21st to end	Day	16% 6% 2 7% 4 4 4 3 4 6% 44%	2105
October	1st to 10th	Day	17% 7% 2 5% 4 3 4 3 5% 6% 44%	3280
	11th to 20th	Day	20% 8% 3 9% 5% 5% 5% 4 6% 7% 28%	3261
	21st to end	Day	27% 9% 3 8% 5% 5% 5% 3 5% 6% 23%	3465
November	1st to 10th	Day	32% 13% 5% 10% 5% 4 4 3 4 5% 15%	1735
	11th to 20th	Day	34% 12% 3 8% 4 5% 4 4 4 4 19%	1680
	21st to end	Day	31% 12% 4 8% 6% 4 3 3 4 4 20%	1680
December	1st to 10th	Day	25% 9% 2 7% 5% 6% 4 4 5% 6% 26%	2700
	11th to 20th	Day	33% 14% 5% 9% 6% 5% 5% 3 5% 5% 11%	3108
	21st to end	Day	34% 14% 5% 12% 7% 5% 5% 3 4 4 9%	4092
January	1st to 10th	Night	36% 14% 4 10% 6% 5% 5% 3 4 4 10%	8172
	11th to 20th	Night	22% 9% 3 7% 6% 7% 6% 3 4 5% 29%	8220
	21st to end	Night	26% 10% 3 8% 4 4 4 4 5% 6% 27%	8560
February	1st to 10th	Night	29% 12% 3 8% 7% 5% 5% 4 4 5% 18%	2730
	11th to 20th	Night	31% 12% 3 7% 5% 5% 3 3 4 4 23%	2662
	21st to end	Night	29% 13% 4 8% 5% 4 4 4 4 6% 19%	2165
March	1st to 10th	Night	21% 13% 4 8% 6% 6% 6% 5% 6% 6% 20%	5282
	11th to 20th	Night	24% 12% 3 9% 6% 4 4 4 4 4 26%	5110
	21st to end	Night	28% 13% 4 10% 6% 6% 5% 3 5% 5% 14%	5481
April	1st to 10th	Night	25% 12% 4 8% 7% 4 4 4 5% 5% 23%	2100
	11th to 20th	Night	20% 11% 3 7% 5% 5% 4 4 5% 6% 31%	2079
	21st to end	Night	24% 9% 3 7% 4 3 3 3 4 6% 32%	1891
May	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 7% 49%	4808
	11th to 20th	Night	13% 7% 3 8% 4 4 4 3 5% 7% 43%	4700
	21st to end	Night	11% 7% 2 6% 4 4 4 4 6% 9% 42%	5181
June	1st to 10th	Night	18% 6% 3 8% 5% 5% 4 3 3 5% 40%	1680
	11th to 20th	Night	14% 8% 2 7% 4 4 3 3 4 7% 44%	1680
	21st to end	Night	7% 5% 2 6% 3 3 3 2 3 6% 59%	1524
July	1st to 10th	Night	2 2 1 2 2 1 2 2 4 5% 78%	4740
	11th to 20th	Night	3 2 1 3 2 2 2 1 3 3 78%	4740
	21st to end	Night	3 2 1 3 2 2 2 2 3 5% 75%	5153
August	1st to 10th	Night	3 2 1 3 2 2 2 2 4 6% 73%	5148
	11th to 20th	Night	8% 4 1 4 3 3 4 3 5% 7% 59%	5292
	21st to end	Night	8% 4 1 5% 3 3 3 3 4 6% 60%	6260
September	1st to 10th	Night	8% 3 1 4 2 3 3 2 5% 5% 63%	2100
	11th to 20th	Night	12% 5% 2 7% 5% 4 4 3 4 5% 49%	2030
	21st to end	Night	11% 4 2 6% 3 4 4 4 4 7% 51%	2291
October	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 5% 7% 48%	3920
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 6% 9% 35%	3897
	21st to end	Night	24% 10% 3 8% 5% 5% 5% 3 5% 6% 26%	4342
November	1st to 10th	Night	31% 10% 3 7% 5% 5% 4 3 4 6% 19%	2780
	11th to 20th	Night	36% 10% 3 7% 5% 3 4 3 3 4 20%	2940
	21st to end	Night	29% 8% 3 8% 6% 5% 5% 4 3 4 25%	2940
December	1st to 10th	Night	22% 8% 3 6% 6% 8% 6% 5% 6% 6% 24%	4700
	11th to 20th	Night	37% 13% 5% 10% 5% 4 4 3 3 4 12%	5316
	21st to end	Night	34% 13% 4 10% 5% 5% 5% 3 4 4 12%	7106

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% 4 6% 5% 3	4723
	11th to 20th	Day	57% 5% 7% 13% 14% 5%	4740
	21st to end	Day	59% 5% 5% 14% 15% 2	5640
February	1st to 10th	Day	70% 6% 9% 11% 4	1890
	11th to 20th	Day	72% 5% 7% 10% 5% 1	1854
	21st to end	Day	69% 5% 9% 10% 6% 1	1640
March	1st to 10th	Day	63% 6% 14% 13% 4	4830
	11th to 20th	Day	63% 5% 6% 20% 5%	5110
	21st to end	Day	70% 7% 13% 8% 3	5736
April	1st to 10th	Day	67% 5% 12% 14% 2	2520
	11th to 20th	Day	60% 5% 11% 15% 8% 2	2492
	21st to end	Day	58% 6% 12% 14% 8% 1	2725
May	1st to 10th	Day	38% 4 14% 29% 15%	8112
	11th to 20th	Day	45% 7% 20% 22% 6%	8163
	21st to end	Day	45% 7% 22% 21% 6%	8994
June	1st to 10th	Day	50% 5% 17% 18% 9% 1	2940
	11th to 20th	Day	51% 7% 17% 17% 8%	2940
	21st to end	Day	36% 5% 18% 27% 10% 4	3044
July	1st to 10th	Day	18% 3 14% 30% 19% 16%	8151
	11th to 20th	Day	15% 2 7% 22% 39% 15%	8145
	21st to end	Day	17% 3 18% 35% 25% 3	8723
August	1st to 10th	Day	16% 3 8% 29% 28% 16%	6069
	11th to 20th	Day	26% 4 19% 37% 11% 3	5962
	21st to end	Day	30% 4 15% 31% 15% 6%	6255
September	1st to 10th	Day	29% 4 14% 25% 18% 10%	2520
	11th to 20th	Day	41% 6% 13% 18% 15% 7%	2437
	21st to end	Day	41% 5% 14% 20% 16% 4	2105
October	1st to 10th	Day	40% 3 8% 28% 18% 2	3280
	11th to 20th	Day	54% 5% 13% 16% 11% 1	3261
	21st to end	Day	61% 4 8% 18% 9% 1	3465
November	1st to 10th	Day	72% 4 8% 12% 4	1735
	11th to 20th	Day	68% 5% 11% 9% 5% 2	1680
	21st to end	Day	68% 5% 7% 10% 10% 1	1680
December	1st to 10th	Day	55% 6% 9% 17% 12% 1	2700
	11th to 20th	Day	76% 5% 9% 10% 1	3108
	21st to end	Day	79% 4 8% 6% 2	4092
January	1st to 10th	Night	78% 5% 7% 6% 3	8172
	11th to 20th	Night	55% 7% 7% 14% 15% 3	8220
	21st to end	Night	58% 6% 6% 13% 16% 1	8560
February	1st to 10th	Night	68% 6% 10% 12% 4	2730
	11th to 20th	Night	65% 4 11% 12% 6% 2	2664
	21st to end	Night	65% 5% 11% 12% 6% 1	2165
March	1st to 10th	Night	61% 7% 12% 14% 5%	5282
	11th to 20th	Night	59% 7% 10% 19% 6% 1	5110
	21st to end	Night	70% 6% 12% 10% 1	5481
April	1st to 10th	Night	63% 5% 15% 14% 3	2100
	11th to 20th	Night	54% 6% 14% 16% 8% 2	2079
	21st to end	Night	54% 6% 14% 18% 6% 2	1891
May	1st to 10th	Night	34% 3 14% 35% 14% 1	4806
	11th to 20th	Night	39% 6% 21% 27% 6% 1	4700
	21st to end	Night	37% 8% 27% 25% 4	5182
June	1st to 10th	Night	46% 4 16% 25% 8% 1	1680
	11th to 20th	Night	40% 4 21% 26% 8%	1680
	21st to end	Night	28% 4 19% 32% 12% 4	1524
July	1st to 10th	Night	11% 2 17% 36% 18% 16%	4700
	11th to 20th	Night	14% 2 9% 22% 42% 11%	4692
	21st to end	Night	14% 3 19% 37% 24% 3	5040
August	1st to 10th	Night	9% 2 8% 35% 34% 12%	4069
	11th to 20th	Night	22% 3 26% 35% 10% 4	4169
	21st to end	Night	25% 3 20% 33% 16% 4	4905
September	1st to 10th	Night	23% 4 16% 29% 18% 10%	2100
	11th to 20th	Night	38% 5% 13% 22% 13% 8%	2030
	21st to end	Night	33% 5% 18% 21% 18% 6%	2291
October	1st to 10th	Night	34% 4 11% 32% 17% 2	3920
	11th to 20th	Night	46% 4 18% 19% 11% 1	3897
	21st to end	Night	57% 6% 9% 18% 9% 1	4342
November	1st to 10th	Night	66% 6% 8% 15% 6%	2780
	11th to 20th	Night	68% 5% 10% 10% 6% 1	2940
	21st to end	Night	63% 5% 9% 11% 11% 1	2940
December	1st to 10th	Night	52% 14% 9% 16% 9%	4700
	11th to 20th	Night	76% 5% 8% 8% 3	5316
	21st to end	Night	75% 6% 9% 8% 2	7106

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	48% 5% 15% 16% 13% 3	220
	11th to 20th	Day	37% 4 14% 25% 13% 8%	220
	21st to end	Day	35% 6% 15% 22% 15% 8%	400
February	1st to 10th	Day	41% 6% 17% 19% 13% 4	430
	11th to 20th	Day	39% 5% 24% 21% 10% 2	425
	21st to end	Day	41% 9% 18% 21% 10% 2	399
March	1st to 10th	Day	33% 8% 22% 23% 12% 2	540
	11th to 20th	Day	32% 7% 23% 21% 12% 5%	540
	21st to end	Day	32% 8% 23% 22% 13% 2	594
April	1st to 10th	Day	28% 8% 19% 25% 13% 6%	540
	11th to 20th	Day	25% 11% 27% 20% 12% 5%	532
	21st to end	Day	24% 6% 25% 25% 16% 4	540
May	1st to 10th	Day	17% 10% 24% 27% 18% 5%	543
	11th to 20th	Day	25% 9% 21% 23% 16% 6%	568
	21st to end	Day	19% 7% 20% 28% 20% 7%	617
June	1st to 10th	Day	21% 6% 23% 27% 19% 4	570
	11th to 20th	Day	15% 6% 27% 33% 14% 4	570
	21st to end	Day	7% 5% 27% 34% 21% 6%	674
July	1st to 10th	Day	9% 3 20% 35% 24% 8%	566
	11th to 20th	Day	6% 4 23% 37% 24% 6%	564
	21st to end	Day	5% 3 16% 38% 31% 7%	619
August	1st to 10th	Day	7% 2 17% 36% 28% 10%	567
	11th to 20th	Day	5% 2 15% 33% 32% 13%	557
	21st to end	Day	9% 4 20% 34% 23% 9%	627
September	1st to 10th	Day	8% 4 19% 37% 24% 9%	570
	11th to 20th	Day	16% 4 17% 30% 24% 9%	543
	21st to end	Day	17% 4 21% 32% 22% 5%	530
October	1st to 10th	Day	20% 6% 16% 30% 21% 7%	530
	11th to 20th	Day	24% 6% 18% 26% 18% 7%	530
	21st to end	Day	32% 6% 21% 23% 12% 6%	526
November	1st to 10th	Day	33% 5% 21% 23% 14% 4	267
	11th to 20th	Day	35% 6% 22% 19% 13% 6%	220
	21st to end	Day	36% 3 18% 20% 16% 6%	220
December	1st to 10th	Day	40% 2 17% 16% 18% 7%	220
	11th to 20th	Day	45% 7% 20% 18% 8% 2	220
	21st to end	Day	37% 8% 15% 24% 13% 3	242
January	1st to 10th	Night	42% 6% 14% 24% 12% 2	840
	11th to 20th	Night	36% 5% 12% 30% 16% 1	840
	21st to end	Night	32% 3 14% 31% 17% 2	924
February	1st to 10th	Night	34% 5% 17% 30% 14% 1	840
	11th to 20th	Night	36% 4 17% 27% 14% 1	824
	21st to end	Night	37% 4 16% 32% 11%	692
March	1st to 10th	Night	31% 6% 15% 32% 14% 1	840
	11th to 20th	Night	31% 4 18% 34% 12% 1	840
	21st to end	Night	32% 6% 18% 29% 13%	924
April	1st to 10th	Night	29% 6% 17% 30% 17% 1	840
	11th to 20th	Night	26% 5% 23% 33% 12% 2	831
	21st to end	Night	28% 3 21% 33% 14% 1	631
May	1st to 10th	Night	17% 5% 28% 36% 14% 1	453
	11th to 20th	Night	17% 3 23% 43% 12% 1	414
	21st to end	Night	17% 4 23% 38% 17%	455
June	1st to 10th	Night	20% 3 27% 38% 11%	420
	11th to 20th	Night	15% 4 30% 42% 8%	420
	21st to end	Night	8% 3 33% 47% 9%	420
July	1st to 10th	Night	5% 1 29% 52% 11% 1	410
	11th to 20th	Night	6% 4 38% 41% 12%	408
	21st to end	Night	3 1 32% 53% 10% 1	460
August	1st to 10th	Night	5% 2 22% 46% 24% 1	578
	11th to 20th	Night	5% 1 14% 50% 27% 2	624
	21st to end	Night	8% 3 23% 43% 21% 1	837
September	1st to 10th	Night	8% 3 21% 46% 19% 2	840
	11th to 20th	Night	14% 4 15% 36% 28% 4	812
	21st to end	Night	13% 2 20% 43% 21% 2	800
October	1st to 10th	Night	20% 3 17% 35% 21% 3	800
	11th to 20th	Night	23% 3 16% 33% 23% 3	800
	21st to end	Night	29% 3 18% 33% 15% 2	880
November	1st to 10th	Night	35% 3 15% 34% 13% 1	820
	11th to 20th	Night	40% 5% 14% 26% 13% 1	840
	21st to end	Night	31% 3 15% 33% 17% 1	840
December	1st to 10th	Night	34% 4 14% 30% 16% 2	840
	11th to 20th	Night	43% 5% 16% 25% 11% 1	840
	21st to end	Night	42% 5% 18% 25% 10% 1	924

Page generated at 2026-09-11 01:11:54. Version ac07

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