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 2024-01-16.

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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 37%	74766
	Night	13% 9% 4 7% 6% 3 4 4 5% 7% 39%	75068
Transparency	Day	47% 6% 12% 23% 11% 1	74467
	Night	45% 5% 12% 23% 13% 2	74888
Seeing	Day	17% 12% 31% 24% 12% 3	14782
	Night	17% 11% 32% 29% 10% 1	24796

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	10% 10% 6% 9% 8% 4 7% 5% 5% 6% 28%	1517
	11th to 20th	Day	10% 14% 7% 13% 9% 3 5% 5% 5% 5% 22%	1485
	21st to end	Day	12% 13% 7% 13% 9% 4 5% 4 5% 6% 22%	1776
February	1st to 10th	Day	9% 12% 5% 11% 7% 4 5% 6% 5% 7% 28%	1620
	11th to 20th	Day	12% 10% 4 9% 7% 4 5% 6% 6% 6% 31%	1574
	21st to end	Day	15% 9% 5% 8% 7% 4 4 4 4 6% 32%	1459
March	1st to 10th	Day	13% 12% 5% 8% 5% 3 5% 4 5% 6% 33%	1876
	11th to 20th	Day	14% 10% 5% 7% 4 3 4 5% 4 7% 37%	1980
	21st to end	Day	19% 11% 5% 7% 6% 4 4 4 5% 7% 28%	2243
April	1st to 10th	Day	18% 12% 4 7% 6% 3 4 4 5% 6% 32%	2160
	11th to 20th	Day	20% 12% 4 6% 5% 3 4 4 3 6% 32%	2134
	21st to end	Day	21% 11% 3 7% 6% 3 4 4 5% 6% 30%	2240
May	1st to 10th	Day	18% 9% 3 7% 7% 4 5% 6% 6% 8% 29%	2466
	11th to 20th	Day	18% 7% 4 6% 6% 3 5% 5% 5% 6% 34%	2479
	21st to end	Day	17% 7% 2 5% 6% 3 4 5% 4 8% 38%	2725
June	1st to 10th	Day	12% 5% 2 5% 5% 3 4 5% 5% 8% 46%	2520
	11th to 20th	Day	13% 5% 3 6% 5% 3 5% 6% 5% 8% 41%	2520
	21st to end	Day	12% 6% 3 5% 7% 4 5% 5% 7% 7% 40%	2520
July	1st to 10th	Day	7% 5% 2 4 5% 4 6% 6% 7% 9% 48%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 6% 5% 6% 10% 47%	2520
	21st to end	Day	7% 4 2 4 5% 3 4 6% 7% 11% 46%	2743
August	1st to 10th	Day	7% 5% 3 6% 5% 3 5% 6% 7% 10% 43%	2328
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 9% 42%	2301
	21st to end	Day	10% 4 2 5% 6% 3 4 4 6% 8% 48%	2387
September	1st to 10th	Day	14% 6% 2 4 4 2 4 5% 5% 7% 46%	2160
	11th to 20th	Day	12% 5% 2 5% 5% 3 4 4 6% 8% 47%	2160
	21st to end	Day	14% 7% 3 6% 5% 3 3 4 5% 7% 42%	1897
October	1st to 10th	Day	17% 7% 2 5% 3 3 4 5% 5% 5% 43%	1800
	11th to 20th	Day	16% 11% 3 6% 4 2 3 4 6% 7% 39%	1800
	21st to end	Day	17% 13% 4 6% 4 2 4 3 4 5% 38%	1923
November	1st to 10th	Day	12% 8% 4 6% 5% 3 4 4 5% 7% 42%	1672
	11th to 20th	Day	15% 11% 5% 9% 8% 3 4 4 4 6% 30%	1520
	21st to end	Day	12% 12% 4 5% 6% 2 4 3 4 7% 40%	1520
December	1st to 10th	Day	13% 10% 5% 9% 8% 4 6% 4 5% 5% 29%	1520
	11th to 20th	Day	12% 12% 6% 8% 7% 4 5% 6% 6% 6% 28%	1918
	21st to end	Day	20% 17% 9% 13% 6% 3 3 3 3 4 18%	2783
January	1st to 10th	Night	10% 8% 5% 10% 8% 5% 6% 5% 4 6% 32%	2648
	11th to 20th	Night	12% 11% 5% 11% 7% 5% 5% 5% 5% 7% 26%	2603
	21st to end	Night	13% 14% 6% 11% 7% 4 5% 5% 6% 6% 24%	2578
February	1st to 10th	Night	8% 13% 6% 10% 7% 4 5% 5% 5% 6% 32%	2340
	11th to 20th	Night	9% 9% 4 8% 7% 4 6% 4 4 7% 38%	2273
	21st to end	Night	15% 9% 4 9% 6% 4 4 4 5% 5% 35%	1795
March	1st to 10th	Night	14% 10% 4 6% 5% 3 4 5% 5% 7% 36%	2098
	11th to 20th	Night	13% 8% 4 7% 6% 4 5% 5% 5% 7% 37%	1980
	21st to end	Night	17% 11% 3 6% 6% 3 4 4 4 8% 33%	2111
April	1st to 10th	Night	16% 10% 5% 6% 4 3 4 4 4 6% 38%	1800
	11th to 20th	Night	20% 10% 3 6% 4 2 4 4 5% 6% 35%	1775
	21st to end	Night	19% 9% 3 6% 5% 3 5% 4 4 6% 36%	1716
May	1st to 10th	Night	17% 8% 4 5% 5% 3 4 4 5% 6% 38%	1494
	11th to 20th	Night	16% 6% 3 4 4 2 5% 4 5% 7% 43%	1416
	21st to end	Night	14% 5% 2 5% 5% 3 5% 5% 5% 8% 43%	1551
June	1st to 10th	Night	9% 4 2 4 5% 2 6% 4 6% 10% 48%	1440
	11th to 20th	Night	11% 6% 2 5% 4 4 5% 5% 5% 8% 44%	1440
	21st to end	Night	8% 5% 2 3 4 3 3 5% 6% 9% 52%	1440
July	1st to 10th	Night	6% 4 2 3 4 2 3 5% 6% 10% 56%	1440
	11th to 20th	Night	5% 3 1 4 5% 3 5% 5% 5% 9% 56%	1440
	21st to end	Night	5% 2 1 3 4 2 4 5% 5% 10% 58%	1575
August	1st to 10th	Night	6% 3 2 4 5% 4 4 4 5% 8% 54%	1606
	11th to 20th	Night	11% 4 2 3 4 2 4 4 5% 8% 53%	1600
	21st to end	Night	9% 4 2 3 4 3 4 4 4 8% 55%	1967
September	1st to 10th	Night	11% 5% 1 4 3 2 4 5% 5% 5% 55%	1800
	11th to 20th	Night	11% 4 2 4 4 2 4 4 5% 6% 54%	1800
	21st to end	Night	12% 6% 1 4 5% 3 4 3 4 7% 52%	2042
October	1st to 10th	Night	14% 7% 2 4 4 2 3 4 6% 6% 49%	2160
	11th to 20th	Night	14% 7% 3 6% 4 3 4 4 6% 7% 42%	2160
	21st to end	Night	16% 9% 3 6% 5% 3 3 5% 5% 6% 39%	2431
November	1st to 10th	Night	12% 7% 3 5% 5% 2 5% 4 5% 5% 47%	2406
	11th to 20th	Night	12% 11% 5% 8% 6% 3 5% 4 4 7% 34%	2660
	21st to end	Night	13% 10% 4 8% 6% 3 4 4 4 5% 39%	2660
December	1st to 10th	Night	12% 11% 5% 9% 7% 3 5% 4 5% 7% 30%	2660
	11th to 20th	Night	12% 11% 5% 11% 7% 3 5% 5% 5% 6% 28%	3279
	21st to end	Night	21% 15% 6% 11% 7% 3 4 3 4 4 21%	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	57% 5% 13% 17% 8%	1518
	11th to 20th	Day	63% 5% 10% 14% 8%	1485
	21st to end	Day	63% 4 13% 13% 7% 1	1776
February	1st to 10th	Day	54% 5% 13% 17% 10% 1	1620
	11th to 20th	Day	52% 5% 11% 22% 8% 1	1583
	21st to end	Day	55% 4 11% 19% 10% 1	1459
March	1st to 10th	Day	53% 5% 13% 20% 9% 1	1876
	11th to 20th	Day	49% 4 12% 22% 12% 1	1980
	21st to end	Day	57% 5% 10% 20% 7% 1	2243
April	1st to 10th	Day	54% 5% 11% 20% 10% 1	2160
	11th to 20th	Day	54% 4 10% 19% 11% 2	2134
	21st to end	Day	55% 5% 10% 18% 11% 1	2240
May	1st to 10th	Day	52% 7% 12% 19% 9% 1	2466
	11th to 20th	Day	49% 7% 11% 21% 11% 1	2483
	21st to end	Day	45% 6% 11% 22% 14% 2	2725
June	1st to 10th	Day	36% 7% 12% 30% 14% 2	2520
	11th to 20th	Day	41% 7% 12% 23% 17% 1	2520
	21st to end	Day	40% 9% 13% 24% 13% 1	2520
July	1st to 10th	Day	32% 8% 16% 30% 13% 2	2451
	11th to 20th	Day	33% 7% 13% 27% 17% 2	2445
	21st to end	Day	31% 8% 15% 29% 15% 2	2591
August	1st to 10th	Day	35% 9% 13% 31% 10% 2	2314
	11th to 20th	Day	38% 7% 13% 28% 13% 1	2301
	21st to end	Day	33% 7% 13% 27% 18% 2	2387
September	1st to 10th	Day	38% 6% 13% 26% 17% 1	2160
	11th to 20th	Day	35% 8% 13% 32% 12% 1	2160
	21st to end	Day	42% 5% 11% 30% 12% 1	1897
October	1st to 10th	Day	42% 5% 11% 27% 14% 1	1800
	11th to 20th	Day	45% 5% 13% 23% 13% 1	1800
	21st to end	Day	50% 4 12% 22% 12% 1	1923
November	1st to 10th	Day	42% 6% 14% 22% 15% 2	1672
	11th to 20th	Day	56% 5% 11% 19% 9% 1	1520
	21st to end	Day	46% 5% 18% 23% 8% 1	1520
December	1st to 10th	Day	56% 5% 14% 15% 8% 1	1520
	11th to 20th	Day	55% 5% 17% 15% 7% 1	1915
	21st to end	Day	72% 4 7% 13% 3	2783
January	1st to 10th	Night	53% 4 11% 20% 10% 1	2648
	11th to 20th	Night	57% 6% 13% 15% 9%	2603
	21st to end	Night	60% 5% 11% 15% 9% 1	2578
February	1st to 10th	Night	54% 3 11% 20% 10% 2	2340
	11th to 20th	Night	49% 4 12% 22% 11% 2	2274
	21st to end	Night	52% 4 10% 21% 11% 2	1795
March	1st to 10th	Night	49% 5% 13% 22% 9% 1	2098
	11th to 20th	Night	47% 4 12% 23% 13% 2	1980
	21st to end	Night	52% 5% 12% 21% 9% 2	2111
April	1st to 10th	Night	48% 5% 9% 21% 15% 2	1800
	11th to 20th	Night	49% 5% 10% 19% 15% 3	1775
	21st to end	Night	50% 5% 9% 21% 14% 2	1716
May	1st to 10th	Night	47% 5% 11% 22% 14% 1	1494
	11th to 20th	Night	40% 5% 14% 24% 14% 2	1417
	21st to end	Night	39% 7% 11% 25% 16% 2	1552
June	1st to 10th	Night	32% 8% 13% 29% 17% 2	1440
	11th to 20th	Night	36% 7% 12% 23% 19% 3	1440
	21st to end	Night	29% 6% 17% 29% 15% 4	1440
July	1st to 10th	Night	26% 6% 14% 35% 19% 2	1400
	11th to 20th	Night	25% 7% 16% 31% 18% 3	1392
	21st to end	Night	22% 6% 17% 33% 18% 5%	1487
August	1st to 10th	Night	28% 6% 15% 32% 17% 3	1597
	11th to 20th	Night	30% 7% 14% 29% 18% 2	1600
	21st to end	Night	30% 5% 13% 29% 17% 5%	1967
September	1st to 10th	Night	30% 7% 9% 31% 22% 1	1800
	11th to 20th	Night	31% 5% 14% 32% 17% 1	1800
	21st to end	Night	34% 5% 12% 29% 19% 1	2042
October	1st to 10th	Night	35% 6% 9% 30% 17% 2	2160
	11th to 20th	Night	41% 5% 13% 22% 18% 1	2160
	21st to end	Night	47% 5% 11% 22% 14% 1	2431
November	1st to 10th	Night	39% 5% 12% 25% 17% 2	2406
	11th to 20th	Night	51% 5% 12% 19% 11% 1	2660
	21st to end	Night	50% 3 14% 24% 8% 1	2660
December	1st to 10th	Night	54% 4 14% 19% 8% 1	2660
	11th to 20th	Night	55% 6% 13% 18% 7% 1	3281
	21st to end	Night	67% 4 9% 14% 6%	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	14% 20% 36% 20% 9% 2	270
	11th to 20th	Day	22% 17% 37% 18% 5% 1	257
	21st to end	Day	19% 15% 40% 21% 5%	264
February	1st to 10th	Day	16% 22% 43% 14% 5%	240
	11th to 20th	Day	23% 25% 33% 16% 3 2	240
	21st to end	Day	24% 19% 41% 15% 1	198
March	1st to 10th	Day	18% 21% 40% 15% 5%	240
	11th to 20th	Day	21% 15% 40% 15% 7% 1	240
	21st to end	Day	27% 17% 29% 18% 7% 1	329
April	1st to 10th	Day	27% 16% 35% 15% 6%	420
	11th to 20th	Day	25% 19% 26% 20% 9% 1	412
	21st to end	Day	26% 16% 29% 20% 7% 2	500
May	1st to 10th	Day	22% 15% 34% 22% 6% 2	603
	11th to 20th	Day	23% 12% 28% 24% 10% 3	625
	21st to end	Day	20% 11% 28% 24% 13% 3	679
June	1st to 10th	Day	11% 7% 31% 30% 18% 3	630
	11th to 20th	Day	14% 9% 34% 29% 10% 3	630
	21st to end	Day	13% 10% 32% 27% 14% 5%	630
July	1st to 10th	Day	9% 4 21% 33% 24% 9%	621
	11th to 20th	Day	9% 7% 29% 31% 18% 6%	618
	21st to end	Day	8% 4 29% 36% 17% 6%	684
August	1st to 10th	Day	8% 3 25% 33% 23% 8%	626
	11th to 20th	Day	14% 4 22% 28% 22% 8%	615
	21st to end	Day	14% 6% 24% 30% 20% 7%	506
September	1st to 10th	Day	17% 8% 23% 30% 16% 5%	450
	11th to 20th	Day	14% 5% 29% 30% 17% 5%	450
	21st to end	Day	17% 16% 31% 23% 12% 2	321
October	1st to 10th	Day	19% 13% 26% 28% 11% 2	270
	11th to 20th	Day	24% 23% 31% 14% 8%	270
	21st to end	Day	28% 17% 34% 14% 5% 2	297
November	1st to 10th	Day	16% 17% 36% 23% 6% 1	270
	11th to 20th	Day	22% 22% 34% 17% 4	270
	21st to end	Day	23% 16% 41% 16% 4	270
December	1st to 10th	Day	14% 17% 42% 19% 7% 1	270
	11th to 20th	Day	18% 17% 42% 17% 6%	270
	21st to end	Day	30% 17% 39% 13% 1	297
January	1st to 10th	Night	14% 18% 37% 24% 7% 1	950
	11th to 20th	Night	20% 13% 38% 24% 5% 1	930
	21st to end	Night	22% 14% 34% 24% 6%	990
February	1st to 10th	Night	15% 16% 39% 24% 4 1	900
	11th to 20th	Night	14% 18% 41% 21% 5% 1	879
	21st to end	Night	20% 15% 35% 25% 5%	611
March	1st to 10th	Night	20% 14% 36% 23% 7% 1	658
	11th to 20th	Night	18% 13% 35% 27% 7% 1	540
	21st to end	Night	21% 12% 31% 25% 9% 1	594
April	1st to 10th	Night	21% 14% 36% 25% 4	540
	11th to 20th	Night	25% 10% 33% 24% 7% 1	533
	21st to end	Night	22% 10% 35% 25% 7% 1	540
May	1st to 10th	Night	21% 9% 32% 30% 6% 1	540
	11th to 20th	Night	20% 7% 32% 32% 8% 1	531
	21st to end	Night	18% 6% 27% 34% 14% 1	584
June	1st to 10th	Night	12% 4 27% 44% 12% 1	540
	11th to 20th	Night	14% 4 31% 40% 11%	540
	21st to end	Night	12% 4 27% 40% 16% 1	540
July	1st to 10th	Night	9% 1 20% 38% 30% 2	525
	11th to 20th	Night	6% 4 27% 38% 23% 2	522
	21st to end	Night	6% 1 18% 52% 20% 3	591
August	1st to 10th	Night	6% 1 20% 46% 24% 2	537
	11th to 20th	Night	11% 4 17% 36% 27% 5%	534
	21st to end	Night	12% 2 24% 36% 23% 3	594
September	1st to 10th	Night	13% 4 23% 37% 17% 5%	540
	11th to 20th	Night	13% 4 27% 37% 16% 4	540
	21st to end	Night	12% 10% 30% 32% 14% 1	656
October	1st to 10th	Night	16% 8% 30% 29% 16% 1	720
	11th to 20th	Night	19% 14% 31% 28% 8%	720
	21st to end	Night	22% 11% 31% 28% 7%	792
November	1st to 10th	Night	18% 12% 36% 27% 7% 1	740
	11th to 20th	Night	19% 17% 39% 20% 5%	950
	21st to end	Night	19% 15% 37% 22% 7%	950
December	1st to 10th	Night	19% 12% 40% 22% 6% 1	950
	11th to 20th	Night	21% 13% 37% 23% 6% 1	950
	21st to end	Night	26% 15% 33% 22% 4	1045

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