Eagle Bluff Environmental Learning Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Bluff Environmental Learning Center clear sky chart from 2005-11-06 to 2026-04-02.

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% 3 8% 5% 4 4 4 6% 7% 38%	131858
	Night	12% 9% 4 9% 5% 4 4 4 5% 6% 38%	130287
Transparency	Day	45% 5% 12% 25% 12% 1	135398
	Night	46% 5% 12% 23% 13% 1	134825
Seeing	Day	18% 13% 31% 24% 11% 3	17799
	Night	17% 11% 32% 29% 10% 1	27835

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	8% 12% 6% 19% 8% 7% 5% 3 4 5% 22%	4691
	11th to 20th	Day	5% 12% 7% 12% 7% 5% 7% 9% 9% 5% 21%	4710
	21st to end	Day	8% 12% 7% 11% 5% 4 6% 3 6% 6% 32%	5792
February	1st to 10th	Day	8% 13% 5% 13% 6% 5% 4 5% 5% 7% 29%	1890
	11th to 20th	Day	11% 11% 4 9% 6% 5% 4 5% 6% 6% 33%	1844
	21st to end	Day	14% 10% 4 10% 5% 6% 3 3 4 7% 34%	1706
March	1st to 10th	Day	14% 8% 2 5% 3 3 3 3 5% 6% 48%	4786
	11th to 20th	Day	11% 7% 3 6% 4 3 4 3 5% 8% 44%	5090
	21st to end	Day	23% 12% 4 9% 5% 4 3 3 4 5% 28%	5763
April	1st to 10th	Day	18% 13% 3 8% 5% 4 3 4 5% 6% 31%	2412
	11th to 20th	Day	20% 12% 4 7% 4 4 4 3 4 6% 32%	2374
	21st to end	Day	20% 12% 3 7% 5% 5% 4 3 5% 6% 30%	2490
May	1st to 10th	Day	14% 7% 2 7% 4 4 3 3 5% 7% 44%	6183
	11th to 20th	Day	14% 6% 3 7% 4 4 4 3 6% 7% 42%	6319
	21st to end	Day	19% 7% 2 6% 4 4 4 4 5% 7% 38%	6935
June	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 45%	2800
	11th to 20th	Day	14% 7% 3 7% 4 5% 5% 4 6% 8% 39%	2800
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 7% 39%	2800
July	1st to 10th	Day	8% 6% 2 6% 4 5% 6% 5% 7% 9% 41%	6360
	11th to 20th	Day	8% 4 2 5% 4 3 5% 4 5% 9% 52%	6360
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	6924
August	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4234
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	4171
	21st to end	Day	9% 4 2 5% 5% 5% 5% 4 6% 9% 46%	4323
September	1st to 10th	Day	12% 6% 2 5% 3 3 4 4 6% 7% 47%	2400
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	2400
	21st to end	Day	13% 7% 2 7% 4 4 3 3 5% 8% 44%	2106
October	1st to 10th	Day	16% 6% 2 5% 3 3 4 3 5% 5% 47%	2000
	11th to 20th	Day	16% 10% 3 7% 3 3 3 4 6% 6% 40%	2000
	21st to end	Day	16% 13% 3 7% 4 4 4 2 4 6% 38%	2136
November	1st to 10th	Day	12% 8% 4 7% 4 4 4 3 6% 6% 41%	1851
	11th to 20th	Day	14% 13% 5% 10% 6% 4 3 3 5% 5% 31%	1680
	21st to end	Day	12% 14% 4 7% 5% 3 3 3 5% 7% 38%	1680
December	1st to 10th	Day	8% 8% 4 12% 9% 6% 6% 4 6% 6% 32%	2690
	11th to 20th	Day	13% 15% 5% 12% 9% 6% 4 4 6% 5% 22%	3088
	21st to end	Day	19% 20% 9% 16% 5% 4 3 3 3 3 15%	4070
January	1st to 10th	Night	9% 12% 5% 15% 7% 7% 5% 3 4 5% 27%	8232
	11th to 20th	Night	7% 13% 5% 13% 8% 7% 7% 8% 8% 4 20%	8280
	21st to end	Night	8% 12% 5% 10% 6% 5% 6% 4 7% 7% 32%	8420
February	1st to 10th	Night	8% 13% 5% 11% 6% 5% 4 4 5% 6% 32%	2730
	11th to 20th	Night	9% 10% 4 10% 6% 5% 6% 3 4 7% 38%	2663
	21st to end	Night	13% 9% 3 10% 6% 5% 4 3 5% 6% 36%	2098
March	1st to 10th	Night	12% 8% 3 8% 4 3 4 3 4 6% 45%	5316
	11th to 20th	Night	9% 8% 3 7% 5% 5% 4 4 5% 7% 43%	5090
	21st to end	Night	24% 12% 3 10% 4 3 3 3 3 5% 28%	5406
April	1st to 10th	Night	16% 11% 4 7% 3 4 4 3 4 6% 38%	2010
	11th to 20th	Night	19% 10% 2 7% 4 3 4 4 5% 6% 36%	1975
	21st to end	Night	19% 9% 3 7% 4 4 4 3 4 6% 36%	1906
May	1st to 10th	Night	14% 7% 2 6% 4 4 3 3 5% 5% 47%	3732
	11th to 20th	Night	12% 6% 3 5% 3 3 4 3 5% 6% 50%	3596
	21st to end	Night	15% 9% 3 7% 4 4 4 4 5% 6% 40%	3942
June	1st to 10th	Night	9% 5% 1 5% 4 4 5% 3 7% 9% 47%	1600
	11th to 20th	Night	12% 6% 2 6% 4 6% 5% 4 5% 8% 42%	1600
	21st to end	Night	9% 7% 2 4 4 3 3 4 6% 9% 50%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 7% 9% 48%	3618
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 5% 8% 53%	3617
	21st to end	Night	7% 4 2 6% 4 4 4 3 6% 9% 50%	3947
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 49%	2921
	11th to 20th	Night	12% 4 2 4 3 3 4 3 5% 7% 53%	2888
	21st to end	Night	9% 6% 2 6% 4 4 4 3 4 7% 51%	3573
September	1st to 10th	Night	10% 5% 1 4 3 3 4 4 5% 5% 56%	2000
	11th to 20th	Night	11% 4 2 5% 3 3 4 3 5% 6% 53%	2000
	21st to end	Night	11% 6% 1 4 4 4 3 3 4 6% 53%	2270
October	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 5% 6% 51%	2400
	11th to 20th	Night	14% 7% 2 6% 4 4 3 3 6% 7% 44%	2400
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 39%	2702
November	1st to 10th	Night	12% 9% 3 6% 4 4 4 3 5% 6% 45%	2666
	11th to 20th	Night	12% 13% 5% 9% 5% 4 4 3 4 6% 35%	2940
	21st to end	Night	13% 12% 4 10% 5% 3 3 3 4 5% 37%	2940
December	1st to 10th	Night	7% 8% 4 12% 7% 7% 5% 3 6% 7% 33%	4720
	11th to 20th	Night	12% 16% 6% 13% 6% 4 5% 4 5% 5% 24%	5339
	21st to end	Night	20% 17% 8% 15% 6% 4 3 3 4 4 17%	7150

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	65% 4 10% 14% 6%	4692
	11th to 20th	Day	58% 5% 8% 16% 13%	4710
	21st to end	Day	52% 4 11% 23% 9%	5792
February	1st to 10th	Day	54% 5% 12% 17% 11% 1	1890
	11th to 20th	Day	50% 5% 10% 25% 8% 1	1853
	21st to end	Day	52% 4 12% 21% 10% 2	1706
March	1st to 10th	Day	39% 4 14% 27% 13% 4	4786
	11th to 20th	Day	38% 4 13% 31% 12% 2	5090
	21st to end	Day	59% 4 10% 16% 9% 1	5765
April	1st to 10th	Day	54% 5% 10% 20% 10% 1	2412
	11th to 20th	Day	54% 4 10% 19% 11% 2	2374
	21st to end	Day	54% 5% 10% 19% 11% 1	2490
May	1st to 10th	Day	40% 5% 8% 26% 20% 1	6222
	11th to 20th	Day	40% 7% 10% 27% 14% 2	6323
	21st to end	Day	44% 6% 9% 28% 12% 1	6949
June	1st to 10th	Day	36% 7% 11% 30% 14% 2	2800
	11th to 20th	Day	43% 7% 12% 22% 16% 1	2800
	21st to end	Day	41% 8% 13% 23% 13% 2	2800
July	1st to 10th	Day	35% 8% 17% 31% 8% 1	6291
	11th to 20th	Day	30% 6% 14% 33% 17% 1	6285
	21st to end	Day	38% 8% 13% 25% 16% 1	6728
August	1st to 10th	Day	39% 7% 12% 27% 13% 2	4220
	11th to 20th	Day	38% 6% 12% 32% 11% 1	4210
	21st to end	Day	33% 7% 15% 30% 14% 1	4322
September	1st to 10th	Day	36% 6% 14% 27% 17% 1	2400
	11th to 20th	Day	36% 8% 14% 30% 11% 1	2400
	21st to end	Day	40% 5% 10% 31% 13% 1	2106
October	1st to 10th	Day	26% 4 7% 40% 23% 1	3260
	11th to 20th	Day	37% 4 13% 25% 20% 2	3240
	21st to end	Day	42% 4 11% 31% 12%	3426
November	1st to 10th	Day	42% 6% 13% 22% 14% 2	1851
	11th to 20th	Day	55% 4 10% 20% 9% 1	1680
	21st to end	Day	48% 5% 17% 22% 7% 1	1680
December	1st to 10th	Day	52% 6% 15% 18% 8% 1	2690
	11th to 20th	Day	64% 4 12% 14% 6% 1	3085
	21st to end	Day	76% 3 7% 12% 3	4070
January	1st to 10th	Night	59% 4 13% 18% 5%	8233
	11th to 20th	Night	62% 4 9% 13% 12%	8280
	21st to end	Night	50% 5% 12% 22% 12%	8420
February	1st to 10th	Night	53% 3 13% 19% 11% 1	2730
	11th to 20th	Night	48% 4 12% 24% 10% 2	2664
	21st to end	Night	50% 4 12% 22% 12% 2	2098
March	1st to 10th	Night	41% 4 10% 28% 12% 4	5316
	11th to 20th	Night	39% 5% 10% 27% 16% 2	5090
	21st to end	Night	60% 4 10% 16% 9% 1	5406
April	1st to 10th	Night	48% 5% 9% 21% 15% 2	2010
	11th to 20th	Night	47% 5% 10% 20% 15% 3	1975
	21st to end	Night	49% 5% 8% 21% 14% 2	1906
May	1st to 10th	Night	39% 5% 8% 23% 23% 1	3758
	11th to 20th	Night	34% 6% 11% 24% 19% 7%	3597
	21st to end	Night	43% 7% 8% 29% 12% 1	3950
June	1st to 10th	Night	32% 8% 13% 29% 16% 2	1600
	11th to 20th	Night	38% 7% 13% 21% 18% 2	1600
	21st to end	Night	32% 6% 16% 28% 16% 4	1600
July	1st to 10th	Night	31% 7% 18% 30% 13% 1	3580
	11th to 20th	Night	29% 6% 15% 35% 14% 2	3572
	21st to end	Night	30% 7% 17% 26% 17% 2	3832
August	1st to 10th	Night	34% 5% 12% 29% 17% 2	2912
	11th to 20th	Night	31% 6% 15% 31% 16% 1	2915
	21st to end	Night	34% 5% 14% 28% 16% 3	3573
September	1st to 10th	Night	29% 7% 9% 32% 21% 1	2000
	11th to 20th	Night	32% 5% 15% 31% 16% 1	2000
	21st to end	Night	32% 5% 11% 29% 21% 1	2270
October	1st to 10th	Night	24% 4 6% 35% 28% 3	3920
	11th to 20th	Night	29% 5% 12% 27% 25% 2	3899
	21st to end	Night	45% 4 10% 25% 15% 1	4362
November	1st to 10th	Night	40% 4 12% 26% 16% 2	2666
	11th to 20th	Night	51% 5% 11% 20% 11% 2	2940
	21st to end	Night	52% 3 14% 23% 8% 1	2940
December	1st to 10th	Night	49% 5% 18% 21% 6%	4720
	11th to 20th	Night	62% 5% 11% 15% 7% 1	5341
	21st to end	Night	73% 4 7% 11% 5%	7150

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	14% 19% 37% 19% 8% 2	330
	11th to 20th	Day	19% 21% 38% 17% 4 1	330
	21st to end	Day	18% 17% 39% 20% 5%	363
February	1st to 10th	Day	18% 19% 42% 14% 5% 1	330
	11th to 20th	Day	21% 23% 35% 18% 2 1	330
	21st to end	Day	21% 21% 42% 15% 1	273
March	1st to 10th	Day	20% 18% 40% 16% 5%	330
	11th to 20th	Day	25% 17% 38% 15% 5% 1	330
	21st to end	Day	28% 18% 31% 17% 6% 1	440
April	1st to 10th	Day	29% 16% 35% 15% 5%	504
	11th to 20th	Day	27% 20% 25% 19% 8% 1	492
	21st to end	Day	25% 17% 31% 19% 6% 2	590
May	1st to 10th	Day	21% 14% 31% 24% 8% 2	703
	11th to 20th	Day	23% 11% 27% 25% 11% 3	725
	21st to end	Day	20% 11% 29% 24% 12% 3	789
June	1st to 10th	Day	12% 9% 31% 29% 17% 3	730
	11th to 20th	Day	15% 10% 34% 28% 9% 3	730
	21st to end	Day	15% 11% 32% 25% 13% 5%	730
July	1st to 10th	Day	9% 5% 22% 32% 23% 9%	721
	11th to 20th	Day	9% 7% 29% 31% 17% 7%	718
	21st to end	Day	7% 5% 29% 36% 17% 6%	794
August	1st to 10th	Day	9% 5% 25% 32% 22% 8%	726
	11th to 20th	Day	14% 5% 23% 29% 22% 8%	715
	21st to end	Day	13% 7% 25% 30% 19% 7%	594
September	1st to 10th	Day	15% 9% 24% 29% 17% 5%	530
	11th to 20th	Day	13% 5% 28% 33% 17% 4	530
	21st to end	Day	15% 15% 30% 24% 14% 3	386
October	1st to 10th	Day	16% 13% 28% 28% 12% 2	330
	11th to 20th	Day	25% 22% 32% 14% 7%	330
	21st to end	Day	27% 17% 33% 16% 5% 2	363
November	1st to 10th	Day	18% 20% 35% 20% 5% 1	330
	11th to 20th	Day	24% 23% 32% 16% 4	330
	21st to end	Day	24% 18% 39% 15% 4	330
December	1st to 10th	Day	15% 19% 42% 17% 7% 1	330
	11th to 20th	Day	21% 18% 40% 17% 5%	330
	21st to end	Day	29% 16% 39% 13% 2 1	363
January	1st to 10th	Night	14% 17% 37% 25% 6% 1	1050
	11th to 20th	Night	20% 14% 38% 23% 5% 1	1050
	21st to end	Night	20% 14% 35% 25% 5%	1155
February	1st to 10th	Night	15% 16% 38% 25% 5% 1	1050
	11th to 20th	Night	14% 18% 40% 22% 5% 1	1029
	21st to end	Night	19% 15% 36% 25% 4	714
March	1st to 10th	Night	20% 14% 36% 23% 6% 1	767
	11th to 20th	Night	18% 14% 35% 25% 6% 1	630
	21st to end	Night	22% 12% 32% 25% 8% 1	693
April	1st to 10th	Night	21% 15% 34% 25% 4	603
	11th to 20th	Night	24% 11% 34% 24% 6% 1	593
	21st to end	Night	23% 10% 34% 26% 7% 1	600
May	1st to 10th	Night	21% 9% 31% 31% 7% 1	600
	11th to 20th	Night	19% 8% 31% 31% 9% 1	591
	21st to end	Night	18% 7% 26% 35% 13% 1	650
June	1st to 10th	Night	12% 4 29% 42% 13% 1	600
	11th to 20th	Night	15% 5% 31% 40% 10%	600
	21st to end	Night	13% 5% 28% 38% 16% 1	600
July	1st to 10th	Night	8% 2 19% 40% 29% 2	585
	11th to 20th	Night	6% 4 27% 38% 23% 2	582
	21st to end	Night	6% 2 18% 51% 21% 3	657
August	1st to 10th	Night	7% 2 20% 46% 24% 2	597
	11th to 20th	Night	12% 4 16% 38% 26% 4	594
	21st to end	Night	12% 2 23% 37% 24% 3	660
September	1st to 10th	Night	13% 4 24% 37% 17% 5%	600
	11th to 20th	Night	12% 4 26% 37% 17% 4	600
	21st to end	Night	11% 9% 28% 34% 17% 1	730
October	1st to 10th	Night	16% 8% 30% 31% 15% 1	800
	11th to 20th	Night	19% 14% 32% 28% 7%	800
	21st to end	Night	22% 11% 32% 28% 7%	880
November	1st to 10th	Night	18% 13% 35% 27% 7% 1	820
	11th to 20th	Night	19% 17% 37% 21% 5%	1050
	21st to end	Night	20% 16% 36% 22% 6%	1050
December	1st to 10th	Night	19% 13% 40% 23% 6% 1	1050
	11th to 20th	Night	21% 14% 36% 22% 6% 1	1050
	21st to end	Night	26% 15% 32% 23% 4	1155

Page generated at 2026-03-30 01:18:39. Version ac07

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